Carlos Lourenço

A golden age for heavy-quarkonium physics dawned a decade ago, initiated by the confluence of exciting advances in quantum chromodynamics (QCD) and an explosion of related experimental activity. The early years of this period were chronicled in the Quarkonium Working Group (QWG) CERN Yellow Report (YR) in 2004, which presented a comprehensive review of the status of the field at that time and provided specific recommendations for further progress. However, the broad spectrum of subsequent breakthroughs, surprises, and continuing puzzles could only be partially anticipated. Since the release of the YR, the BESII program concluded only to give birth to BESIII; the B-factories and CLEO-c flourished; quarkonium production and polarization measurements at HERA and the Tevatron matured; and heavy-ion collisions at RHIC have opened a window on the deconfinement regime. All these experiments leave legacies of quality, precision, and unsolved mysteries for quarkonium physics, and therefore beg for continuing investigations at BESIII, the LHC, RHIC, FAIR, the Super Flavor and/or Tau–Charm factories, JLab, the ILC, and beyond. The list of newly found conventional states expanded to include h c (1P), χ c2(2P), $B_{c}^{+}$ , and η b (1S). In addition, the unexpected and still-fascinating X(3872) has been joined by more than a dozen other charmonium- and bottomonium-like “XYZ” states that appear to lie outside the quark model. Many of these still need experimental confirmation. The plethora of new states unleashed a flood of theoretical investigations into new forms of matter such as quark–gluon hybrids, mesonic molecules, and tetraquarks. Measurements of the spectroscopy, decays, production, and in-medium behavior of $c\bar{c}$ , $b\bar{b}$ , and $b\bar{c}$ bound states have been shown to validate some theoretical approaches to QCD and highlight lack of quantitative success for others. Lattice QCD has grown from a tool with computational possibilities to an industrial-strength effort now dependent more on insight and innovation than pure computational power. New effective field theories for the description of quarkonium in different regimes have been developed and brought to a high degree of sophistication, thus enabling precise and solid theoretical predictions. Many expected decays and transitions have either been measured with precision or for the first time, but the confusing patterns of decays, both above and below open-flavor thresholds, endure and have deepened. The intriguing details of quarkonium suppression in heavy-ion collisions that have emerged from RHIC have elevated the importance of separating hot- and cold-nuclear-matter effects in quark–gluon plasma studies. This review systematically addresses all these matters and concludes by prioritizing directions for ongoing and future efforts.

This report reviews the study of open heavy-flavour and quarkonium production in high-energy hadronic collisions, as tools to investigate fundamental aspects of Quantum Chromodynamics, from the proton and nucleus structure at high energy to deconfinement and the properties of the Quark-Gluon Plasma. Emphasis is given to the lessons learnt from LHC Run 1 results, which are reviewed in a global picture with the results from SPS and RHIC at lower energies, as well as to the questions to be addressed in the future. The report covers heavy flavour and quarkonium production in proton-proton, proton-nucleus and nucleus-nucleus collisions. This includes discussion of the effects of hot and cold strongly interacting matter, quarkonium photo-production in nucleus-nucleus collisions and perspectives on the study of heavy flavour and quarkonium with upgrades of existing experiments and new experiments. The report results from the activity of the SaporeGravis network of the I3 Hadron Physics programme of the European Union 7th Framework Programme.

We report on a precision measurement of low-mass muon pairs in 158 AGeV indium-indium collisions at the CERN SPS. A significant excess of pairs is observed above the yield expected from neutral meson decays. The unprecedented sample size of 360,000 dimuons and the good mass resolution of about 2% allow us to isolate the excess by subtraction of the decay sources. The shape of the resulting mass spectrum is consistent with a dominant contribution from pi+pi- -->rho -->mu+mu- annihilation. The associated space-time averaged spectral function shows a strong broadening, but essentially no shift in mass. This may rule out theoretical models linking hadron masses directly to the chiral condensate.

A bstract The discovery by the ATLAS and CMS experiments of a new boson with mass around 125 GeV and with measured properties compatible with those of a Standard-Model Higgs boson, coupled with the absence of discoveries of phenomena beyond the Standard Model at the TeV scale, has triggered interest in ideas for future Higgs factories. A new circular e + e − collider hosted in a 80 to 100 km tunnel, TLEP, is among the most attractive solutions proposed so far. It has a clean experimental environment, produces high luminosity for top-quark, Higgs boson, W and Z studies, accommodates multiple detectors, and can reach energies up to the $$ \mathrm{t}\overline{\mathrm{t}} $$ threshold and beyond. It will enable measurements of the Higgs boson properties and of Electroweak Symmetry-Breaking (EWSB) parameters with unequalled precision, offering exploration of physics beyond the Standard Model in the multi-TeV range. Moreover, being the natural precursor of the VHE-LHC, a 100 TeV hadron machine in the same tunnel, it builds up a long-term vision for particle physics. Altogether, the combination of TLEP and the VHE-LHC offers, for a great cost effectiveness, the best precision and the best search reach of all options presently on the market. This paper presents a first appraisal of the salient features of the TLEP physics potential, to serve as a baseline for a more extensive design study.

The analysis of the data collected by the NA50 experiment in 1998, reported in this paper, extends and clarifies the pattern of the previously observed J/ψ anomalous suppression. This new measurement, besides providing a deeper understanding of the previous observations, reveals a steady significative decrease in the J/ψ production rate up to the most central Pb-Pb collisions. It clearly rules out the presently available conventional (hadronic) models of J/ψ suppression, which unanimously predict a saturation of the J/ψ rate for central Pb-Pb collisions. On the contrary and together with the sharp onset of the anomalous suppression previously reported, the new observation leads to a global production rate pattern which finds its natural explanation in the framework of the formation of a deconfined state of quarks and gluons.

The ratio of cross-sections for muon pair production through the Drell-Yan process in p − p and p − d reactions has been measured at y ≈ 0, with 450 GeVc incident protons. The asymmetry ADY = δpp − δpnδpp+δpn amounts to −0.09 ± 0.02 ± 0.025. The ratio ud of the nucleon sea structure functions derived from this measurement amounts to 0.51 ± 0.04 ± 0.05 at x = 0.18 and suggests that isospin symmetry is broken in the light quark sea of the nucleon.

We present a new measurement of J/psi production in Pb-Pb collisions at 158 GeV/nucleon, from the data sample collected in year 2000 by the NA50 Collaboration, under improved experimental conditions with respect to previous years. With the target system placed in vacuum, the setup was better adapted to study, in particular, the most peripheral nuclear collisions with unprecedented accuracy. The analysis of this data sample shows that the (J/psi)/Drell-Yan cross-sections ratio measured in the most peripheral Pb-Pb interactions is in good agreement with the nuclear absorption pattern extrapolated from the studies of proton-nucleus collisions. Furthermore, this new measurement confirms our previous observation that the (J/psi)/Drell-Yan cross-sections ratio departs from the normal nuclear absorption pattern for semi-central Pb-Pb collisions and that this ratio persistently decreases up to the most central collisions.

This report presents the capabilities of the CMS experiment to explore the rich heavy-ion physics programme offered by the CERN Large Hadron Collider (LHC). The collisions of lead nuclei at energies , will probe quark and gluon matter at unprecedented values of energy density. The prime goal of this research is to study the fundamental theory of the strong interaction — Quantum Chromodynamics (QCD) — in extreme conditions of temperature, density and parton momentum fraction (low-x).

The Drell-Yan and Jψ cross-sections measured in PbPb collisions are compared with the values extrapolated from the results obtained in proton and light ion induced reactions. While the Drell-Yan production exhibits the normal expected behaviour, the yield of Jψ in PbPb interactions is abnormally low, as it lies 9 standard deviations below the expected value. Moreover, the departure from the expected behaviour increases significantly from peripheral to central collisions.

The study of oxygen-uranium reactions at 200 GeV/nucleon shows a significant transverse energy dependence of the yield of JΨ's relative to muon pairs produced in the mass continuum. This feature, observed for the first time, is in agreement with predictions from quark-gluon plasma formation, although alternative explanations by hadronic effects cannot be ruled out at this stage.

Data from J/psi and psi' production in p-A collisions are used to determine the cross section for absorption of pre-resonance charmonium in nuclear matter. The J/psi suppression in O-Cu, O-U and S-U collisions is fully reproduced by the corresponding nuclear absorption, while Pb-Pb collisions show an additional suppression increasing with centrality. We study the onset of this change in terms of hadronic comover interactions and conclude that so far no conventional hadronic description can consistently account for all data. Deconfinement, starting at a critical point determined by central S-U collisions, is in accord with the observed suppression pattern.

The NA60 experiment at the CERN SPS has studied low-mass muon pairs in 158AGeV In–In collisions. The mass and pT spectra associated with peripheral collisions can quantitatively be described by the known neutral meson decays. The high data quality has allowed to remeasure the electromagnetic transition form factors of the Dalitz decays η→μ+μ−γ and ω→μ+μ−π0. Using the usual pole approximation F=(1−M2/Λ2)−1 for the form factors, we find Λ−2 (in GeV−2) to be 1.95±0.17(stat.)±0.05(syst.) for the η and 2.24±0.06(stat.)±0.02(syst.) for the ω. While the values agree with previous results from the Lepton-G experiment, the errors are greatly improved, confirming now on the level of 10σ the strong enhancement of the ω form factor beyond the expectation from vector meson dominance. An improved value of the branching ratio BR(ω→μ+μ−π0)=[1.73±0.25(stat.)±0.14(syst.)]×10−4 has been obtained as a byproduct.

We highlight issues which are often underestimated in the experimental analyses on quarkonium polarization: the relation between the parameters of the angular distributions and the angular momentum composition of the quarkonium, the importance of the choice of the reference frame, the interplay between observed decay and production kinematics, and the consequent influence of the experimental acceptance on the comparison between experimental measurements and theoretical calculations. Given the puzzles raised by the available experimental results, new measurements must provide more detailed information, such that physical conclusions can be derived without relying on model-dependent assumptions. We describe a frame-invariant formalism which minimizes the dependence of the measurements on the experimental acceptance, facilitates the comparison with theoretical calculations, and probes systematic effects due to experimental biases. This formalism is a direct and generic consequence of the rotational invariance of the dilepton decay distribution and is independent of any assumptions specific to particular models of quarkonium production. The use of this improved approach, which exploits the intrinsic multidimensionality of the problem, will significantly contribute to a faster progress in our understanding of quarkonium production, especially if adopted as a common analysis framework by the LHC experiments, which will soon perform analyses of quarkonium polarization in proton-proton collisions.

Polarization measurements are usually considered as the most difficult challenge for the QCD description of quarkonium production. In fact, global data fits for the determination of the non-perturbative parameters of bound-state formation traditionally exclude polarization observables and use them as a posteriori verifications of the predictions, with perplexing results. With a change of perspective, we move polarization data to the centre of the study, advocating that they actually provide the strongest fundamental indications about the production mechanisms, even before we explicitly consider perturbative calculations. Considering ψ(2S) and ϒ(3S) measurements from LHC experiments and state-of-the-art next-to-leading order cross sections for the short-distance production of heavy quark–antiquark pairs of relevant colour and angular momentum configurations, we perform a search for a kinematic domain where quarkonium polarizations can be correctly reproduced together with the respective cross sections, by systematically scanning the phase space and accurately treating the experimental uncertainties. This strategy provides a straightforward solution to the "quarkonium polarization puzzle" and reassuring signs that the factorization of short- and long-distance effects works, at least in the high-transverse-momentum region, least affected by limitations in the current fixed-order calculations. The results expose unexpected hierarchies in the phenomenological long-distance parameters that open new paths towards the understanding of bound-state formation in QCD.

Cross sections for Jψ,ψ′ and Drell-Yan production in Pb+Pb collisions at 158×A GeV/c are presented and compared with results obtained by the NA38 and NA51 collaborations. The Pb+Pb data have been collected by the NA50 collaboration using the NA38 dimuon spectrometer. The Drell-Yan mechanism is found to scale as (Aprojectile · Btarget) in p+Btarget and Aprojectile+Btarget collisions including Pb+Pb collisions. Regarding Jψ, an anomalous suppression is observed in Pb+Pb collisions with respect to the suppression observed in p+Btarget, O+Btarget and S+U collisions. The cross section ratios ψ′(Jψ) are similar in Pb+Pb and S+U collisions.

The NA60 experiment studies muon pair production at the CERN Super Proton Synchrotron. In this Letter we report on a precision measurement of J/ψ in In-In collisions. We have studied the J/ψ centrality distribution, and we have compared it with the one expected if absorption in cold nuclear matter were the only active suppression mechanism. For collisions involving more than ∼80 participant nucleons, we find that an extra suppression is present. This result is in qualitative agreement with previous Pb-Pb measurements by the NA50 experiment, but no theoretical explanation is presently able to coherently describe both results.Received 30 March 2007DOI:https://doi.org/10.1103/PhysRevLett.99.132302©2007 American Physical Society

The NA60 experiment at the CERN SPS has measured muon pairs with unprecedented precision in 158 A GeV In–In collisions. A strong excess of pairs above the known sources is observed in the whole mass region 0.2<M<2.6 GeV. The mass spectrum for M<1 GeV is consistent with a dominant contribution from π + π −→ρ→μ + μ − annihilation. The associated ρ spectral function shows a strong broadening, but essentially no shift in mass. For M>1 GeV, the excess is found to be prompt, not due to enhanced charm production, with pronounced differences to Drell–Yan pairs. The slope parameter T eff associated with the transverse momentum spectra rises with mass up to the ρ, followed by a sudden decline above. The rise for M<1 GeV is consistent with radial flow of a hadronic emission source. The seeming absence of significant flow for M>1 GeV and its relation to parton–hadron duality is discussed in detail, suggesting a dominantly partonic emission source in this region. A comparison of the data to the present status of theoretical modeling is also contained. The accumulated empirical evidence, including also a Planck-like shape of the mass spectra at low p T and the lack of polarization, is consistent with a global interpretation of the excess dimuons as thermal radiation. We conclude with first results on ω in-medium effects.

We report a new measurement of J/psi, psi' and Drell-Yan cross-sections, in the kinematical domain $-0.425<y_{\rm cm}<0.575$ and $-0.5<\cos\theta_{\rm CS}<0.5$, performed at the CERN-SPS using 400 GeV/c incident protons on Be, Al, Cu, Ag, W and Pb targets. The dependence of the charmonia production cross-sections on the size of the target nucleus allows to quantify the so-called normal nuclear absorption. In the framework of the Glauber model, this new measurement is combined with results previously obtained with the same apparatus, under different experimental conditions, and leads to a precise determination of the J/psi and psi' absorption cross-sections in the surrounding nuclear matter.

Charmonium states are expected to be considerably suppressed in the case of quark-gluon plasma formation in high-energy heavy-ion collisions. However, a robust identification of suppression patterns as signatures of a deconfined QCD medium requires a detailed understanding of the ``normal nuclear absorption'' already present in proton-nucleus collisions, where the charmonium production cross sections increase less than linearly with the number of target nucleons. We analyse the J/ψ production cross sections measured in proton-nucleus collisions in fixed target experiments, with proton beam energies from 200 to 920 GeV, and in d-Au collisions at RHIC, at (sNN)1/2 = 200 GeV, in the framework of the Glauber formalism, using several sets of parton distributions with and without nuclear modifications. The results reveal a significant dependence of the ``absorption cross section'' on the kinematics of the J/ψ and on the collision energy. Extrapolating the observed patterns we derive the level of absorption expected at Elab = 158 GeV, the energy at which the heavy-ion data sets were collected at the CERN SPS.

The yield of muon pairs in the invariant mass region 1<M<2.5 GeV/c 2 produced in heavy-ion collisions significantly exceeds the sum of the two expected contributions, Drell-Yan dimuons and muon pairs from the decays of D meson pairs. These sources properly account for the dimuons produced in proton-nucleus collisions. In this paper, we show that dimuons are also produced in excess in 158 A GeV In-In collisions. We furthermore observe, by tagging the dimuon vertices, that this excess is not due to enhanced D meson production, but made of prompt muon pairs, as expected from a source of thermal dimuons specific to high-energy nucleus-nucleus collisions. The yield of this excess increases significantly from peripheral to central collisions, both with respect to the Drell-Yan yield and to the number of nucleons participating in the collisions. Furthermore, the transverse mass distributions of the excess dimuons are well described by an exponential function, with inverse slope values around 190 MeV. The values are independent of mass and significantly lower than those found at masses below 1 GeV/c 2, rising there up to 250 MeV due to radial flow. This suggests the emission source of thermal dimuons above 1 GeV/c 2 to be of largely partonic origin, when radial flow has not yet built up.

The NA60 experiment at the CERN SPS has studied low-mass dimuon production in 158A GeV In-In collisions. An excess of pairs above the known meson decays has been reported before. We now present precision results on the associated transverse momentum spectra. The slope parameter Teff extracted from the spectra rises with dimuon mass up to the ρ, followed by a sudden decline above. While the initial rise is consistent with the expectations for radial flow of a hadronic decay source, the decline signals a transition to an emission source with much smaller flow. This may well represent the first direct evidence for thermal radiation of partonic origin in nuclear collisions.Received 26 June 2007DOI:https://doi.org/10.1103/PhysRevLett.100.022302©2008 American Physical Society

First results are reported on Jψ and Drell-Yan cross-sections in PbPb reactions at 158 GeV/c per nucleon. The ratio of cross-sections σJ/ψ/σDY is studied as a function of the impact parameter of the collision estimated from the measured transverse energy.

.The production of \({\rm J}/\psi\) and \(\psi^\prime\) charmonium states in proton-nucleus interactions has been investigated by the NA50 experiment, at the CERN SPS. High statistics data sets were collected with collisions induced by 450 GeV protons incident on Be, Al, Cu, Ag and W targets. The \({\rm J}/\psi\) and \(\psi^\prime\) production cross-sections have been determined for each p-A system and their dependences on the nucleus size have been studied, leading to the so-called normal nuclear absorption. Comparing the two patterns we see that the nuclear absorption is stronger for the \(\psi^\prime\) than for the \({\rm J}/\psi\). Given the high statistics of the data samples, the \(x_{\rm F}\) (or rapidity) differential cross-sections of the \({\rm J}/\psi\) and \(\psi^\prime\) states have also been studied, for each of the target nuclei.

This report is the result of the collaboration and research effort of the Quarkonium Working Group over the last three years. It provides a comprehensive overview of the state of the art in heavy-quarkonium theory and experiment, covering quarkonium spectroscopy, decay, and production, the determination of QCD parameters from quarkonium observables, quarkonia in media, and the effects on quarkonia of physics beyond the Standard Model. An introduction to common theoretical and experimental tools is included. Future opportunities for research in quarkonium physics are also discussed.

The NA60 experiment has measured muon pair production in In–In collisions at 158 AGeV at the CERN SPS. This paper presents a high statistics measurement of φ→μ μ meson production. Differential spectra, yields, mass and width are measured as a function of centrality and compared to previous measurements in other colliding systems at the same energy. The width of the rapidity distribution is found to be constant as a function of centrality, compatible with previous results. The decay muon polar angle distribution is measured in several reference frames. No evidence of polarization is found as a function of transverse momentum and centrality. The analysis of the p T spectra shows that the φ has a small radial flow, implying a weak coupling to the medium. The T eff parameter measured in In–In collisions suggests that the high value observed in Pb–Pb in the kaon channel is difficult to reconcile with radial flow alone. The absolute yield is compared to results in Pb–Pb collisions: though significantly smaller than measured by NA50 in the muon channel, it is found to exceed the NA49 and CERES data in the kaon channel at any centrality. The mass and width are found to be compatible with the PDG values at any centrality and at any p T : no evidence for in-medium modifications is observed.

The covariance properties of angular momentum eigenstates imply the existence of a rotation-invariant relation among the parameters of the difermion decay distribution of inclusively observed vector mesons. This relation is a generalization of the Lam-Tung identity, a result specific to Drell-Yan production in perturbative QCD, here shown to be equivalent to the dynamical condition that the dilepton is always produced transversely polarized with respect to quantization axes belonging to the production plane.

The NA60 experiment studied low-mass muon pair production in proton-nucleus (p-A) collisions using a 400~GeV proton beam at the CERN SPS. The low-mass dimuon spectrum is well described by the superposition of the two-body and Dalitz decays of the light neutral mesons $\eta$, $\rho$, $\omega$, $\eta'$ and $\phi$, and no evidence of in-medium effects is found. A new high-precision measurement of the electromagnetic transition form factors of the $\eta$ and $\omega$ was performed, profiting from a 10~times larger data sample than the peripheral In-In sample previously collected by NA60. Using the pole-parameterisation $|F(M)|^2 = (1 -M^2/\mathrm{\Lambda}^2)^{-2}$ we find $\mathrm{\Lambda}_\eta^{-2} = 1.934\ \pm\ 0.067$~(stat.) $\pm\ 0.050$~(syst.)~(GeV/$c^2$)$^{-2}$ and $\mathrm{\Lambda}_\omega^{-2} = 2.223\ \pm\ 0.026$~(stat.) $\pm\ 0.037$~(syst.)~(GeV/$c^2$)$^{-2}$. An improved value of the branching ratio of the Dalitz decay $\omega \to \mu^+\mu^-\pi^0$ is also obtained, with $BR(\omega \to \mu^+\mu^-\pi^0) = [1.41~\pm~0.09~\mathrm{(stat.)}$ $\pm~0.15~\mathrm{(syst.)}] \times 10^{-4}$. Further results refer to the $\rho$ line shape and a new limit on $\rho/\omega$ interference in hadron interactions.

Muon pairs produced in Pb–Pb interactions at 158 GeV/c per nucleon are used to study the transverse momentum distributions of the J/ψ, ψ′ and dimuons in the mass continuum. In particular, the dependence of these distributions on the centrality of the Pb–Pb collision is investigated in detail.

The dimuon production in 200 GeV/nucleon oxygen-uranium interactions is studied by the NA 38 Collaboration. The production ofJ/ψ, correlated with the transverse energyET, is investigated and compared to the continuum, as a function of the dimuon massM and transverse momentumPT. A value of 0.64±0.06 is found for the ratio (ψ/Continuum at highET)/(ψ/Continuum at lowET), from which theJ/ψ relative suppression can be extracted. This suppression is enhanced at lowPT.

Significant progress in understanding quarkonium production requires improved polarization measurements, fully considering the intrinsic multidimensionality of the problem. We propose a frame-invariant formalism which minimizes the dependence of the measured result on the experimental acceptance, facilitates the comparison with theoretical calculations, and provides a much needed control over systematic effects due to detector limitations and analysis biases. This formalism is a direct and generic consequence of the rotational invariance of the dilepton decay distribution and is independent of any assumptions specific to particular models of quarkonium production.

The NA60 experiment has studied J/ψ production in p–A collisions at 158 and 400 GeV, at the CERN SPS. Nuclear effects on the J/ψ yield have been estimated from the A-dependence of the production cross section ratios σJ/ψA/σJ/ψBe (A = Al, Cu, In, W, Pb, U). We observe a significant nuclear suppression of the J/ψ yield per nucleon–nucleon collision, with a larger effect at lower incident energy, and we compare this result with previous observations by other fixed-target experiments. An attempt to disentangle the different contributions to the observed suppression has been carried out by studying the dependence of nuclear effects on x2, the fraction of the nucleon momentum carried by the interacting parton in the target nucleus.

A detailed study of J/ψ, ψ′ and Drell-Yan production in S-U collisions has been performed by experiment NA38 at the CERN SPS. This paper presents production cross sections and their centrality dependence, based on the largest sample of S-U events collected by the experiment.

The production of the J/ψ and ψ′ charmonia states has been studied, through their dimuon decay, in proton, Oxygen and Sulphur induced reactions, by the NA38 experiment at the CERN SPS. The proton data was collected with beams of 200 and 450 GeV, while the ion beams had an energy of 200 GeV per incident nucleon. The J/ψ production cross-section per nucleon-nucleon collision exhibits a remarkably continuous pattern, as a function of the product of the mass numbers of the interacting nuclei, from pp up to S-U reactions. The same pattern is observed within S-U collisions, as a function of the collision centrality. While in p-A interactions both charmonia states exhibit the same A-dependence, in S-U collisions the ψ′ production is very strongly suppressed.

psi' production is studied in Pb-Pb collisions at 158 GeV/c per nucleon incident momentum. Absolute cross-sections are measured and production rates are investigated as a function of the centrality of the collision. The results are compared with those obtained for lighter colliding systems and also for the J/psi meson produced under identical conditions.

The study of the Jψ transverse momentum distribution in oxygen-uranium reactions at 200 GeV/nucleon shows that 〈PT〉 and 〈PT2〉 increase with the transverse energy of the reaction. Muon pairs in the mass continuum do not exhibit the same behaviour. The comparison of the Jψproduction rates in central and peripheral collisions shows a significant diminution for low PT central events.

Muon-pair production has been measured in pCu, pU, OCu, OU and SU collisions at 200 GeV per nucleon. The cross sections are compatible with the atomic number dependence (Aproj.Atarg.)α where α=0.91±0.04 for the J/ψ resonance and α=1.01±0.04 for muon pairs produced in the mass continuum between 1.7 and 2.7 GeV/c2.

The interpretation of the J/ψ suppression patterns observed in nuclear collisions, at CERN and RHIC, as a signature of the formation of a deconfined phase of QCD matter, requires knowing which fractions of the measured J/ψ yields, in elementary collisions, are due to decays of heavier charmonium states. From a detailed analysis of the available mid-rapidity charmonium hadro-production cross sections, or their ratios, we determine that the J/ψ feed-down contributions from ψ' and χc decays are, respectively, (8.1±0.3)% and (25±5)%. These proton-proton values are derived from global averages of the proton-nucleus measurements, assuming that the charmonium states are exponentially absorbed with the length of matter they traverse in the nuclear targets.

Magnitude and "sign" of the measured J / psi polarization crucially depends on the reference frame used in the data analysis: a full understanding of the polarization phenomenon requires measurements reported in two "orthogonal" frames, such as the Collins-Soper and helicity frames. Moreover, the azimuthal anisotropy can be, in certain frames, as significant as the polar one. The seemingly contradictory results reported by the experiments E866, HERA-B, and CDF can be consistently described assuming that the most suitable axis for the measurement is along the direction of the relative motion of the colliding partons, and that directly produced J / psi's are longitudinally polarized at low momentum and transversely polarized at high momentum. We make specific predictions that can be tested on existing CDF data and by LHC measurements, which should show a full transverse polarization for direct J / psi's of p_{T} > 25 GeV / c.

J/ψ and ψ′ production cross-sections are measured in pp and pd collisions at 450 GeV/c at the CERN-SPS. The Drell-Yan cross section for muon pairs in the mass range [4.3–8.0] GeV/c2 is also determined in the same experiment.

The present knowledge on hard processes in the context of heavy ion collisions is reviewed, with particular emphasis on J/psi production. The p-A data on charmonia production from Fermilab experiments is shown to be in excelent agreement with the p-A data collected at CERN. The simultaneous analysis of all existing p-A data reaches a precision which allows us to rule out some preconceived ideas, setting a good frame against which the data collected with ion beams at CERN can be compared.

The charge collection efficiency (CCE) of heavily irradiated silicon diode detectors was investigated at temperatures between 77 and 200 K. The CCE was found to depend on the radiation dose, bias voltage value and history, temperature, and bias current generated by light. The detector irradiated to the highest fluence 2×1015 n/cm2 yields a MIP signal of at least 15000 e− both at 250 V forward bias voltage, and at 250 V reverse bias voltage in the presence of a light-generated current. The “Lazarus effect” was thus shown to extend to fluences at least ten times higher than was previously studied.

Charmonium production in p–A collisions is a unique tool for the study of the interaction of bound cc states in nuclear matter. It can provide details on the basic features of the resonance formation mechanism and, in particular, on its non-perturbative aspects. In this Letter, we present an experimental study of charmonia and Drell–Yan production in proton–nucleus collisions at 450 GeV/c. The results are analyzed in the framework of the Glauber model and lead to the values of the nuclear absorption cross-section σabspA for J/ψ and ψ′. Then, we compare the J/ψ absorption in proton–nucleus and sulphur–uranium interactions, using NA38 data. We obtain that, for the J/ψ, σabspA and σabsSU are compatible, showing that no sizeable additional suppression mechanism is present in S–U collisions, and confirming that the anomalous J/ψ suppression only sets in for Pb–Pb interactions.

The production of vector mesons φ, ρ and ω has been measured in Pb–Pb collisions at 158 GeV/c per nucleon incident momentum at the CERN/SPS. The muon spectrometer of experiment NA50 detects φ, ρ and ω mesons via their μ+μ− decay channel in the collision center of mass rapidity range 0⩽yCM⩽1. The results reported here show that the relative production of the φ compared to the (ρ+ω) and the φ multiplicity per participant nucleon (Npart) increase with the centrality of the collision. On the other hand, the (ρ+ω) multiplicity per participant does not exhibit any Npart dependence within our errors. The inverse slope parameter as deduced from an exponential fit to the φ transverse mass distribution is 228±10 MeV. Our results are compared with those obtained by experiment NA49 and with theoretical calculations.

The transverse energy ET distributions of nucleus-nucleus collisions are studied in the framework of a simple geometrical model. The distributions for inclusive production of Jψ and muon pairs in the mass continuum are analyzed. The shape of the ET distribution of the continuum agreed with the model. The previously oberved decrease of the ratio (Jψ)/continuum with increasing ET is due to the behavior of the Jψ.

We present a brief overview of the most relevant current issues related to quarkonium production in high energy proton-proton and proton-nucleus collisions along with some perspectives. After reviewing recent experimental and theoretical results on quarkonium production in pp and pA collisions, we discuss the emerging field of polarisation studies. Thereafter, we report on issues related to heavy-quark production, both in pp and pA collisions, complemented by AA collisions. To put the work in a broader perspective, we emphasize the need for new observables to investigate quarkonium production mechanisms and reiterate the qualities that make quarkonia a unique tool for many investigations in particle and nuclear physics.

The angular distributions of the decay products in the successive decays chi_c (chi_b) to J/psi (Upsilon) gamma and J/psi (Upsilon) to l+l- are calculated as a function of the angular momentum composition of the decaying chi meson and of the multipole structure of the photon radiation, using a formalism independent of production mechanisms and polarization frames. The polarizations of the chi states produced in high energy collisions can be derived from the dilepton decay distributions of the daughter J/psi or Upsilon mesons, with a reduced dependence on the details of the photon reconstruction or simulation. Moreover, this method eliminates the dependence of the polarization measurement on the actual details of the multipole structure of the radiative transition. Problematic points in previous calculations of the chi_c decay angular distributions are identified and clarified.

<h2>Summary</h2><h3>Background</h3> Emergence of drug resistance demands novel antimalarial drugs with new mechanisms of action. We aimed to identify effective and well tolerated doses of ganaplacide plus lumefantrine solid dispersion formulation (SDF) in patients with uncomplicated <i>Plasmodium falciparum</i> malaria. <h3>Methods</h3> This open-label, multicentre, parallel-group, randomised, controlled, phase 2 trial was conducted at 13 research clinics and general hospitals in ten African and Asian countries. Patients had microscopically-confirmed uncomplicated <i>P falciparum</i> malaria (>1000 and <150 000 parasites per μL). Part A identified the optimal dose regimens in adults and adolescents (aged ≥12 years) and in part B, the selected doses were assessed in children (≥2 years and <12 years). In part A, patients were randomly assigned to one of seven groups (once a day ganaplacide 400 mg plus lumefantrine-SDF 960 mg for 1, 2, or 3 days; ganaplacide 800 mg plus lumefantrine-SDF 960 mg as a single dose; once a day ganaplacide 200 mg plus lumefantrine-SDF 480 mg for 3 days; once a day ganaplacide 400 mg plus lumefantrine-SDF 480 mg for 3 days; or twice a day artemether plus lumefantrine for 3 days [control]), with stratification by country (2:2:2:2:2:2:1) using randomisation blocks of 13. In part B, patients were randomly assigned to one of four groups (once a day ganaplacide 400 mg plus lumefantrine-SDF 960 mg for 1, 2, or 3 days, or twice a day artemether plus lumefantrine for 3 days) with stratification by country and age (2 to <6 years and 6 to <12 years; 2:2:2:1) using randomisation blocks of seven. The primary efficacy endpoint was PCR-corrected adequate clinical and parasitological response at day 29, analysed in the per protocol set. The null hypothesis was that the response was 80% or lower, rejected when the lower limit of two-sided 95% CI was higher than 80%. This study is registered with EudraCT (2020–003284–25) and ClinicalTrials.gov (NCT03167242). <h3>Findings</h3> Between Aug 2, 2017, and May 17, 2021, 1220 patients were screened and of those, 12 were included in the run-in cohort, 337 in part A, and 175 in part B. In part A, 337 adult or adolescent patients were randomly assigned, 326 completed the study, and 305 were included in the per protocol set. The lower limit of the 95% CI for PCR-corrected adequate clinical and parasitological response on day 29 was more than 80% for all treatment regimens in part A (46 of 50 patients [92%, 95% CI 81–98] with 1 day, 47 of 48 [98%, 89–100] with 2 days, and 42 of 43 [98%, 88–100] with 3 days of ganaplacide 400 mg plus lumefantrine-SDF 960 mg; 45 of 48 [94%, 83–99] with ganaplacide 800 mg plus lumefantrine-SDF 960 mg for 1 day; 47 of 47 [100%, 93–100] with ganaplacide 200 mg plus lumefantrine-SDF 480 mg for 3 days; 44 of 44 [100%, 92–100] with ganaplacide 400 mg plus lumefantrine-SDF 480 mg for 3 days; and 25 of 25 [100%, 86–100] with artemether plus lumefantrine). In part B, 351 children were screened, 175 randomly assigned (ganaplacide 400 mg plus lumefantrine-SDF 960 mg once a day for 1, 2, or 3 days), and 171 completed the study. Only the 3-day regimen met the prespecified primary endpoint in paediatric patients (38 of 40 patients [95%, 95% CI 83–99] <i>vs</i> 21 of 22 [96%, 77–100] with artemether plus lumefantrine). The most common adverse events were headache (in seven [14%] of 51 to 15 [28%] of 54 in the ganaplacide plus lumefantrine-SDF groups and five [19%] of 27 in the artemether plus lumefantrine group) in part A, and malaria (in 12 [27%] of 45 to 23 [44%] of 52 in the ganaplacide plus lumefantrine-SDF groups and 12 [50%] of 24 in the artemether plus lumefantrine group) in part B. No patients died during the study. <h3>Interpretation</h3> Ganaplacide plus lumefantrine-SDF was effective and well tolerated in patients, especially adults and adolescents, with uncomplicated <i>P falciparum</i> malaria. Ganaplacide 400 mg plus lumefantrine-SDF 960 mg once daily for 3 days was identified as the optimal treatment regimen for adults, adolescents, and children. This combination is being evaluated further in a phase 2 trial (NCT04546633). <h3>Funding</h3> Novartis and Medicines for Malaria Venture.

Absolute J/ψ and ψ′ production cross sections have been measured at the CERN SPS, with 450 GeV/c protons incident on a set of C, Al, Cu and W targets. Complementing these values with the results obtained by experiment NA51, which used the same beam and detector with H and D targets, we establish a coherent picture of charmonia production in proton-induced reactions at SPS energies. In particular, we show that the scaling of the J/ψ cross section with the mass number of the target, A, is well described as Aα, with αψ=0.919±0.015. The ratio between the J/ψ and ψ′ yields, in our kinematical window, is found to be independent of A, with αψ′−αψ=0.014±0.011.

The observation of an anomalous J/ψ suppression in Pb–Pb collisions by the NA50 Collaboration can be considered as the most striking indication for the deconfinement of quarks and gluons at SPS energies. In this Letter, we determine the J/ψ suppression pattern as a function of the forward hadronic energy EZDC measured in a Zero Degree Calorimeter (ZDC). The direct connection between EZDC and the geometry of the collision allows us to calculate, within a Glauber approach, the precise relation between the number of participant nucleons Npart and EZDC. Then, we check if the experimental data can be better explained by a sudden or a smooth onset of the anomalous J/ψ suppression as a function of the number of participants.

A kinetic equation approach is applied to model anomalous J/ψ suppression at RHIC and SPS by absorption in a hadron resonance gas which successfully describes statistical hadron production in both experiments. The puzzling rapidity dependence of the PHENIX data is reproduced as a geometric effect due to a longer absorption path for J/ψ production at forward rapidity.

The charged particle multiplicity distribution dNch/dη has been measured by the NA50 experiment in Pb–Pb collisions at the CERN SPS. Measurements were done at incident energies of 40 and 158 GeV per nucleon over a broad impact parameter range. The multiplicity distributions are studied as a function of centrality using the number of participating nucleons (Npart), or the number of binary nucleon–nucleon collisions (Ncoll). Their values at midrapidity exhibit a power law scaling behaviour given by Npart1.00 and Ncoll0.75 at 158 GeV. Compatible results are found for the scaling behaviour at 40 GeV. The width of the dNch/dη distributions is larger at 158 than at 40 GeV/nucleon and decreases slightly with centrality at both energies. Our results are compared to similar studies performed by other experiments both at the CERN SPS and at RHIC.

The NA60 experiment at the CERN SPS has studied low-mass muon pairs in 158 A GeV In–In collisions. A strong excess of pairs is observed above the yield expected from neutral meson decays. The unprecedented sample size close to 400000 events and the good mass resolution of about 2% made it possible to isolate the excess by subtraction of the decay sources. The shape of the resulting mass spectrum shows some non-trivial centrality dependence, but is largely consistent with a dominant contribution from π+π-→ϱ→μ+μ- annihilation. The associated ϱ spectral function exhibits considerable broadening, but essentially no shift in mass. The pT-differential mass spectra show the excess to be much stronger at low pT than at high pT. The results are compared to theoretical model predictions; they tend to rule out models linking hadron masses directly to the chiral condensate.

The coefficients determining the dilepton decay angular distribution of vector particles obey certain positivity constraints and a rotation-invariant identity. These relations are a direct consequence of the covariance properties of angular momentum eigenstates and are independent of the production mechanism. The Lam-Tung relation can be derived as a particular case, simply recognizing that the Drell-Yan dilepton is always produced transversely polarized with respect to one or more quantization axes. The dilepton angular distribution continues to be characterized by a frame-independent identity also when the Lam-Tung relation is violated. Moreover, the violation can be easily characterized by measuring a one-dimensional distribution depending on one shape coefficient.

In this paper we present a study on the production of the Jψ and ψ′ resonances, decaying into muon pairs, in S-U collisions, at 200 GeV per incident nucleon. We find that the ratio between ψ′ and tJψ yields decreases as ET, the neutral transverse energy produced in the collision, increases. There is also a clear decrease of this ratio when going from p-W to S-U interactions. Assuming the high mass continuum to be Drell-Yan we discuss the possible understanding of the intermediate dimuon mass region as a superposition of Drell-Yan (extrapolated down in mass) and muon pairs from the semileptonic decays of charmed mesons. The p-W data is found to be explained by this procedure. However, the S-U data seems to be incompatible with a linear extrapolation from the proton-nucleus results.

While non-relativistic QCD (NRQCD) foresees a variety of elementary quarkonium production mechanisms naturally leading to state-dependent kinematic patterns, the LHC cross sections and polarization measurements reveal a remarkably simple production scenario, independent of the quantum numbers and masses of the quarkonia. Surprisingly, NRQCD is able to accommodate the observed universal scenario, through a series of conspiring cancellations smoothing out its otherwise variegated hierarchy of mechanisms. This seemingly unnatural solution implies that the $\chi_{c1}$ and $\chi_{c2}$ polarizations, not yet measured, are strong and opposite, representing the only potential exception to a remarkably simple picture of quarkonium production. The observation of a large difference between $\chi_{c2}$ and $\chi_{c1}$ polarizations, which cannot be indirectly extracted from existing measurements because they mutually cancel each other in their contribution to the observed J/$\psi$ production, would be a smoking gun signal finally proving the multifaceted but mysteriously elusive structure of NRQCD. On the other hand, the measurement of two similar, small polarizations will urge improved P-wave calculations, if not a substantial revision of the NRQCD hierarchies.

Measurements of open charm hadro-production from CERN and Fermilab experiments are reviewed, with particular emphasis on the absolute cross sections and on their A and √s dependences. Differentialp T andx F cross sections calculated with thePythia event generator are found to be in reasonable agreement with recent data. The calculations are scaled to nucleus-nucleus collisions and the expected lepton pair yield is deduced. The charm contribution to the low mass dilepton continuum observed by the CERES experiment is found to be negligible. In particular, it is shown that the observed low mass dilepton excess in S-Au collisions cannot be explained by charm enhancement.

The NA50 experiment measures, at CERN SPS, the dimuon production in PbPb collisions at 158 GeV/c incident momentum. In this paper an analysis of the intermediate mass region (1.5⩽Mμμ⩽2.5 GeV/c2) is presented. Known dimuon sources in this interval of the spectrum are the e.m. annihilation of qq pairs (i.e. Drell-Yan) and the semileptonic decay of charmed hadrons. The contribution of these processes is calculated by means of a fit to the measured invariant mass distribution (for Drell-Yan) and of a linear extrapolation of p-A experimental results obtained by NA38 (for charm). It will be shown that known sources do not account for all of the dimuon yield measured by NA50, i.e. an excess is observed. The size of the excess measured in PbPb is larger than the one seen by NA38 in SU collisions. The centrality dependence of this effect, both in SU and PbPb, is also discussed.

The NA50 collaboration has measured J/ψ, ψ′ and Drell Yan pair production in PbPb interactions at 158 GeV/c per nucleon at the CERN SPS. Final results from the 1995 run and preliminary ones from the higher statistics 1996 run are presented. A anomalous J/ψ suppression (relative to the Drell-Yan process) has been observed with respect to the suppression pattern established in experiments NA38 and NA51 with proton, oxygen and sulfur beams. The 1996 data allow a detailed study of the suppression pattern in the PbPb sample itself, showing a discontinuity around an ET value (the neutral transverse electromagnetic energy) of 50 GeV. The ψ′ is also suppressed relative to Drell-Yan, with a pattern very similar to the one observed in SU collisions. Finally, the pT distributions of dimuons are presented. The average pT2 of the J/ψ in PbPb collisions does not increase any more with ET above 100 GeV.

Muon pairs produced in PbPb interactions at 158 GeV/c per nucleon and in p-A interactions at 400 GeV/c, together with older S-U results obtained at 200 GeV/c are used to study the transverse momentum and transverse mass distributions of the J/Ψ.

Muon pairs produced in PbPb interactions at 158 GeV/c per nucleon and in p-A interactions at 400 GeV/c, together with older S-U results obtained at 200 GeV/c are used to study the transverse momentum and transverse mass distributions of the J/Ψ.

J/ψ suppression has been studied by the NA60 experiment in Indium-Indium collisions. A new analysis technique, based only on the J/ψ sample, allows to accurately study the centrality dependence of J/ψ production. The observed pattern indicates that a suppression is already present in In-In collisions, setting in at ∼ 90 participant nucleons. A comparison with the available theoretical models is also presented.

The NA60 experiment at the CERN Super Proton Synchrotron has studied dimuon production in 158A GeV In-In collisions. The strong excess of pairs above the known sources found in the complete mass region 0.2<M<2.6 GeV has previously been interpreted as thermal radiation. We now present first results on the associated angular distributions. Using the Collins-Soper reference frame, the structure function parameters lambda, mu, and nu are measured to be zero, and the projected distributions in polar and azimuth angles are found to be uniform. The absence of any polarization is consistent with the interpretation of the excess dimuons as thermal radiation from a randomized system.

A global analysis of ATLAS and CMS measurements reveals that, at mid-rapidity, the directly-produced $\chi_{c1}$, $\chi_{c2}$ and J/$\psi$ mesons have differential cross sections of seemingly identical shapes, when presented as a function of the mass-rescaled transverse momentum, $p_{\rm T}/M$. This identity of kinematic behaviours among S- and P-wave quarkonia is certainly not a natural expectation of non-relativistic QCD (NRQCD), where each quarkonium state is supposed to reflect a specific family of elementary production processes, of significantly different $p_{\rm T}$-differential cross sections. Remarkably, accurate kinematic cancellations among the variegated NRQCD terms (colour singlets and octets) of its factorization expansion can lead to a surprisingly good description of the data. This peculiar tuning of the NRQCD mixtures leads to a clear prediction regarding the $\chi_{c1}$ and $\chi_{c2}$ polarizations, the only observables not yet measured: they should be almost maximally different from one another, and from the J/$\psi$ polarization, a striking exception in the global panorama of quarkonium production. Measurements of the difference between the $\chi_{c1}$, $\chi_{c2}$ and J/$\psi$ polarizations, complementing the observed identity of momentum dependences, represent a decisive probe of NRQCD.

The charged particle distributions dNch/dη have been measured by the NA50 experiment in Pb–Pb collisions at the CERN SPS. Measurements have been done at incident energies of 158 and 40 GeV per nucleon over a broad impact parameter range. Results obtained with two independent centrality estimators, namely the neutral transverse energy ET and the forward energy EZDC, are reported.

The NA60 experiment has studied low-mass muon pairs in 158 AGeV Indium-Indium collisions at the CERN SPS. A strong excess of pairs is observed above the expectation from neutral meson decays. The unprecedented sample size of 360 000 events and the good mass resolution of about 2% allow to isolate the excess by subtraction of the known sources. The shape of the resulting mass spectrum is consistent with a dominant contribution from π+π−→ρ→μ+μ− annihilation. The associated ρ spectral function shows a strong broadening, but essentially no shift in mass.

The NA60 experiment at the CERN SPS has studied low-mass muon pairs in 158 AGeV In–In collisions. A strong excess of pairs is observed above the yield expected from neutral meson decays. The unprecedented sample size of close to 400K events and the good mass resolution of about 2% have made it possible to isolate the excess by subtraction of the decay sources (keeping the ρ). The shape of the resulting mass spectrum exhibits considerable broadening, but essentially no shift in mass. The acceptance-corrected transverse-momentum spectra have a shape atypical for radial flow and show a significant mass dependence, pointing to different sources in different mass regions.

Muon pair production is studied in p-W and SU collisions at 200 GeV per nucleon, as a function of transverse momentum PTμμ. The inclusive ϱ+ω and Φ differential cross-sections dσdPT are measured in the dimuon decay channel, for PT ≥ 0.6 GeV/c, in the central rapidity region, 3.0≤ y ≤ 4.0. Assuming the power law A-dependence σ = σ0(Abeam·Atarget)α, the study of the integrated cross-sections for p-W and SU collisions leads to αϱ+ω = 1.00±0.02±0.07 and αΦ = 1.23±0.03±0.05, showing clear evidence of Φ enhancement in SU interactions as compared to p-W collisions.

This open-access book addresses general characteristics of the angular distributions and emphasizes discussion of use-cases and methodological pitfall

A study of secondary Drell-Yan production in nuclear collisions is presented for SPS energies. In addition to the lepton pairs produced in the initial collisions of the projectile and target nucleons, we consider the potentially high dilepton yield from hard valence antiquarks in produced mesons and antibaryons. We calculate the secondary Drell-Yan contributions taking the collision spectrum of hadrons from the microscopic model URQMD. The contributions from meson-baryon interactions, small in hadron-nucleus interactions, are found to be substantial in nucleus-nucleus collisions at low dilepton masses. Preresonance collisions of partons may further increase the yields.

This article gives a brief overview of some recent advances in our understanding of the physics of dense strongly interacting matter, from measurements done at the CERN SPS. The presently available results are very interesting, and are likely to reflect the production of a new state of matter in central Pb-Pb collisions, at the highest SPS energies. However, important questions require further work. Particular emphasis is given to developments made since the Quark Matter 1999 conference, and to issues that justify the continuation of the SPS heavy ion physics program beyond year 2000.

In my (“not a summary”) talk at the Hard Probes 2006 conference, I gave “a personal and surely biased view on only a few of the many open questions on quarkonium and electromagnetic probes”. Some of the points reported in that talk are exposed in this paper, having in mind the most important of all the open questions: do we have, today, from experimental data on electromagnetic probes and quarkonium production, convincing evidence that shows, beyond reasonable doubt, the existence of “new physics” in high-energy heavy-ion collisions?

Abstract The transverse mass differential cross-sections for the ϱ + ω and Φ resonances is obtained, in the central rapidity region, in p - W and S  U interactions at 200 GeV/nucleon. The measured ϱ + ω and Φ temperatures are ∼ 15% higher in S  U as compared to p - W collisions. The ratio of cross-sections times branching ratios into the dimuon channel B Φ σ Φ (B ϱ σ ϱ + B ω σ ω ) is studied as a function of the energy density reached in the collision and of the dimuon transverse momentum. The measured ratio is 2 to 3 times larger in S  U than in p - W collisions and an enhancement is observed in S  U interactions with increasing energy density.

The NA38 experiment measures muon pair production in 200 GeV per nucleon nucleus-nucleus interactions at the CERN SPS. Dimuon production is studied as a function of the neutral transverse energy produced in the collisions, which reflects the energy density reached in the interaction. The J/ψ yield relative to muon pairs in the mass continuum decreases with increasing energy density. The atomic number dependence of the cross sections has been studied using the parametrization σ ∞ (Aproj.Atarg.)α which leads to α = 0.91 ± 0.04 for the J/ψ, and α = 1.01 ± 0.04 for muon pairs in the mass range [1.7, 2.7] GeV/c2. The study of dimuon transverse momentum distributions shows an enhancement of the J/ψ suppression for low PT values. The average values 〈PT〉 and 〈PT2〉 increase with increasing transverse energy in case of the J/ψ, and are rather flat for muon pairs in the mass continuum. Such a behaviour is expected in case of quark-gluon plasma formation. However, a model based on parton multiple scattering in the initial state leads to a variation of 〈PT2〉 as a function of the mean thickness of nuclear matter encountered by the partons, which seems also to account for the observed effect. In addition, low mass dimuons are studied. An enhancement of the φ/(ϱ + ω) ratio is observed with increasing energy density.

We present a study of the modeling of the electric field distribution, which is controlled by injection and trapping of nonequilibrium carriers, in Si detectors irradiated by high neutron fluences. An analytical calculation of the electric field distribution in detectors irradiated by neutrons up to fluences of 1 /spl middot/ 10/sup 14/ to 5 /spl middot/ 10/sup 15/ cm/sup -2/ shows the possibility of reducing the full depletion voltage at low temperatures via hole injection. For this calculation, we use the detector operating parameters and equivalent neutron fluences expected for Large Hadron Collider experiments. The results of the calculation are in good qualitative agreement with published experimental data, lending strong support for the model and for an earlier proposal of electric field manipulation by free carrier injection.

We present preliminary results on the production of intermediate mass dimuons in 158 A⋅GeV In-In collisions at the CERN SPS. NA38 and NA50 observed a strong excess in this region in S-U and Pb-Pb interactions with respect to the dimuon production rate expected from p-A data. Thanks to the use of a pixel vertex telescope, NA60 can separate the prompt dimuons from the pairs resulting from open charm decays and show that the excess dimuons are of prompt origin.

The di-fermion angular distribution observed in decays of inclusively produced vector particles is characterized by two frame-independent observables, reflecting the average spin alignment of the produced particle and the magnitude of parity violation in the decay. The existence of these observables derives from the rotational properties of angular momentum eigenstates and is a completely general result, valid for any $J=1$ state and independent of the production process. Rotation-invariant formulations of polarization and of the decay parity asymmetry can provide more significant measurements than the commonly used frame-dependent definitions, also improving the quality of the comparisons between the measurements and the theoretical calculations.

Abstract This paper presents results on the measurement of the cluster shapes, resolution and charge collection efficiency of a double-sided silicon microstrip detector after irradiation with 24 GeV protons to a fluence of 3.5×10 14  p/cm 2 and operated at cryogenic temperatures. An empirical model is presented which describes the expected cluster shapes as a function of depletion depth, and is shown to agree with the data. It is observed that the clusters on the p-side broaden if the detector is under-depleted, leading to a degradation of resolution and efficiency. The model is used to make predictions for detector types envisaged for the LHC experiments. The results also show that at cryogenic temperature the charge collection efficiency varies depending on the operating conditions of the detector and can reach values of 100% at unexpectedly low bias voltage. By analysing the cluster shapes it is shown that these variations are due to changes in depletion depth. This phenomenon, known as the “Lazarus effect”, can be related to similar recent observations on diode behaviour.

The NA60 experiment at the CERN SPS has studied ϕ meson production in In–In collisions at 158 A GeV via both the K+K− and the μ+μ− decay channels. The yields and inverse slope parameters of the mT spectra observed in the two channels are compatible within errors, different from the large discrepancies seen in Pb–Pb collisions between the hadronic (NA49) and dimuon (NA50) decay channels. Possible physics implications are discussed.

Dimensional analysis reveals general kinematic scaling rules for the momentum, mass, and energy dependence of Drell–Yan and quarkonium cross sections. Their application to mid-rapidity LHC data provides strong experimental evidence supporting the validity of the factorization ansatz, a cornerstone of non-relativistic QCD, still lacking theoretical demonstration. Moreover, data-driven patterns emerge for the factorizable long-distance bound-state formation effects, including a remarkable correlation between the S-wave quarkonium cross sections and their binding energies. Assuming that this scaling can be extended to the P-wave case, we obtain precise predictions for the not yet measured feed-down fractions, thereby providing a complete picture of the charmonium and bottomonium feed-down structure. This is crucial information for quantitative interpretations of quarkonium production data, including studies of the suppression patterns measured in nucleus-nucleus collisions.

We have studied the production of J/ψ, ψ′ and prompt muon pairs in the mass continuum from a sample of sulfur-uranium interactions at 200 GeV/c per nucleon. We report, in this letter, results obtained for the transverse momentum distributions and their dependence on the transverse energy released in the collision, used as an estimator of the centrality of the nucleus-nucleus interaction.

In this paper, we report on the performance of heavily irradiated silicon detectors operated at cryogenic temperatures. The results discussed here show that cryogenic operation indeed represents a reliable method to increase the radiation tolerance of standard silicon detectors by more than one order of magnitude. In particular, a 400 μm thick "double-p" silicon detector irradiated up to 1×1015 n/cm2 delivers a mip signal of about 27 000 electrons when operated at 130 K and 500 V bias. The position resolution of an irradiated microstrip detector, and "in situ" irradiation of a pad detector during operation in the cold are also discussed.

NA60 is a fixed target experiment at the CERN SPS, which studies dimuon production in proton- and ion-induced collisions. Downstream of the target system a silicon pixel telescope made with p-on-n silicon sensors measures the charged tracks originating from the interactions. During the 2003 data taking period with indium–indium collisions at 158 GeV per incident nucleon, a significant radiation dose with a very inhomogeneous distribution has been accumulated in the pixel telescope, leading to partially type-inverted silicon sensors. Measurements of the depletion voltage and leakage current performed during this run are shown and compared with simulation results. It is also shown that the operation of partially type-inverted sensors poses no major problem.

The NA60 experiment has measured the production of muon pairs and charged particles in In+In collisions at a beam energy of 158 A GeV. For invariant dimuon masses below the ϕ, the spacetime averaged ρ spectral function was isolated by a novel procedure. It shows a strong broadening but essentially no shift in mass. The production of J/ψ was measured as a function of the collision centrality. As in previous experiments studying Pb+Pb collisions an anomalous suppression is observed, setting in at approximately 90 participant nucleons. Using the charged particles, the reaction plane was reconstructed. The elliptic flow of charged particles increases with pt showing a saturation for pt > 2 GeV/c. For the first time, azimuthal distributions for J/ψ are shown.

The cryogenic silicon Beam Tracker of NA60 is the first detector based on the Lazarus effect used in a high-energy physics experiment. It employs single-sided silicon strip sensors of 50 μm pitch operated at a temperature of 130 K. Two tracking stations determine the transverse coordinates of the interaction point at the target with 20 μm resolution, to improve the determination of the offset of secondary vertices. This impact parameter measurement allows NA60 to distinguish between prompt dimuons and muon pairs from D-meson decays. The detector concept and technical feasibility have been demonstrated in beam time periods between 1999 and 2002.

We present the set of measurements carried out by the NA50 experiment to study J/ψ production in proton- and ion-induced reactions. We also make use of results obtained previously under similar conditions by experiments NA51, NA38 and NA3. All these measurements were performed in fixed target experiments at the CERN SPS. Due to accelerator constraints, momentum was 450, 400 and 200 GeV/c for incident proton beams (corresponding to √s = 29.0, 27.4, 19.4 GeV respectively) whereas, for ion beams, incident momentum was 200 GeV/nucleon for oxygen and sulfur and 158 GeV/nucleon for Pb beams (√s = 19.4 and √s = 17.2 GeV respectively). The p-A data allow us to determine with high accuracy the absorption cross section of the (pre-)resonant cc state with nuclear matter. The J/ψ production cross section normally expected for ion-induced reactions can then be determined and compared to the results obtained from the data collected for oxygen- and sulfur-induced collisions. Finally, we also present the most recent results on J/ψ production in Pb-Pb interactions. They are based on the last data sample collected with an improved experimental set-up and are compared with the expectations inferred from similar measurements on lighter nuclei collisions.

Jψ and ψ′ production cross sections are studied for several proton induced reactions and in SU collisions, in the NA38 experiment, by measuring the resonances' decays in the muon pair channel. Whereas in p-A interactions the ψ′/J/ψ ratio remains constantin going from p-p and p-d collisions to p-W and p-U, with a mean value of 1.76% ± 0.04%, in the SU data it exhibits half of this value and decreases as centrality of the collision increases. Also studied are the differences between the γπ0 ratio yields correlated with the Jψ mass range and other dimuon masses; no significant effect is seen.

We present results on the measurement of the charge collection efficiency of a p+/n/p+ silicon detector irradiated to 1×1015 n/cm2, operated in the temperature range between 80 and 200 K. For comparison, measurements obtained with a standard silicon diode (p+/n/n+), irradiated to the same fluence, are also presented. Both detectors show a dramatic increase of the CCE when operated at temperatures around 130 K. The double-p detector shows a higher CCE regardless of the applied bias and temperature, besides being symmetric with respect to the polarity of the bias voltage. At 130 K and 500 V applied bias the double-p detector shows a CCE of 80%, an unprecedented result for a silicon detector irradiated to such a high dose.

We review the hadro-production data presently available on charm and beauty absolute production cross-sections, collected by experiments at CERN, DESY and Fermilab. After correcting the published values, in particular for the 'time evolution' of the branching ratios, the measurements are compared to LO pQCD calculations performed with Pythia, as a function of the collision energy, using the latest parametrizations of the parton distribution functions. We then estimate, including nuclear effects on the parton densities, the charm and beauty production cross-sections relevant for future measurements at SPS, RHIC and LHC energies, in proton–proton and nucleus–nucleus collisions. We also compare some indirect charm measurements, done using leptonic decays, to the others and we briefly address the importance of beauty production as a feed-down mechanism of J/ψ production.

The J/ψ azimuthal distribution relative to the reaction plane has been measured by the NA50 experiment in Pb-Pb collisions at 158 GeV/nucleon. Various physical mechanisms related to charmonium dissociation in the medium created in the heavy ion collision are expected to introduce an anisotropy in the azimuthal distribution of the observed J/ψ mesons at SPS energies. Hence, the measurement of J/ψ elliptic anisotropy, quantified by the Fourier coefficient v 2 of the J/ψ azimuthal distribution relative to the reaction plane, is an important tool to constrain theoretical models aimed at explaining the anomalous J/ψ suppression observed in Pb-Pb collisions. We present the measured J/ψ yields in different bins of azimuthal angle relative to the reaction plane, as well as the resulting values of the Fourier coefficient v 2 as a function of the collision centrality and of the J/ψ transverse momentum. The reaction plane has been estimated from the azimuthal distribution of the neutral transverse energy detected in an electromagnetic calorimeter. The analysis has been performed on a data sample of about 100 000 events, distributed in five centrality or p T sub-samples. The extracted v 2 values are significantly larger than zero for non-central collisions and are seen to increase with p T.

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Abstract While the prompt $$\mathrm{J}/\psi $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>J</mml:mi><mml:mo>/</mml:mo><mml:mi>ψ</mml:mi></mml:mrow></mml:math> cross section and polarization have been measured with good precision as a function of transverse momentum, $$p_\mathrm{T}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>p</mml:mi><mml:mi>T</mml:mi></mml:msub></mml:math> , those of the directly produced $$\mathrm{J}/\psi $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>J</mml:mi><mml:mo>/</mml:mo><mml:mi>ψ</mml:mi></mml:mrow></mml:math> are practically unknown, given that the cross sections and polarizations of the $$\chi _{{c}1} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>χ</mml:mi><mml:mrow><mml:mi>c</mml:mi><mml:mn>1</mml:mn></mml:mrow></mml:msub></mml:math> and $$\chi _{{c}2} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>χ</mml:mi><mml:mrow><mml:mi>c</mml:mi><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:math> mesons, large indirect contributors to $$\mathrm{J}/\psi $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>J</mml:mi><mml:mo>/</mml:mo><mml:mi>ψ</mml:mi></mml:mrow></mml:math> production, are only known with rather poor accuracy. The lack of precise measurements of the $$\chi _{{c}J} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>χ</mml:mi><mml:mrow><mml:mi>cJ</mml:mi></mml:mrow></mml:msub></mml:math> polarizations induces large uncertainties in the level of their feed-down contributions to the prompt $$\mathrm{J}/\psi $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>J</mml:mi><mml:mo>/</mml:mo><mml:mi>ψ</mml:mi></mml:mrow></mml:math> yield, because of the polarization-dependent acceptance corrections. The experimental panorama of charmonium production can be significantly improved through a consistent and model-independent global analysis of existing measurements of $$\mathrm{J}/\psi $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>J</mml:mi><mml:mo>/</mml:mo><mml:mi>ψ</mml:mi></mml:mrow></mml:math> , $$\psi \mathrm{(2S)}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>ψ</mml:mi><mml:mrow><mml:mo>(</mml:mo><mml:mn>2</mml:mn><mml:mi>S</mml:mi><mml:mo>)</mml:mo></mml:mrow></mml:mrow></mml:math> and $$\chi _{c}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>χ</mml:mi><mml:mi>c</mml:mi></mml:msub></mml:math> cross sections and polarizations, faithfully respecting all the correlations and uncertainties. In particular, it is seen that the $$\chi _{{c}J} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>χ</mml:mi><mml:mrow><mml:mi>cJ</mml:mi></mml:mrow></mml:msub></mml:math> polarizations and feed-down fractions to $$\mathrm{J}/\psi $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>J</mml:mi><mml:mo>/</mml:mo><mml:mi>ψ</mml:mi></mml:mrow></mml:math> production have a negligible dependence on the $$\mathrm{J}/\psi $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>J</mml:mi><mml:mo>/</mml:mo><mml:mi>ψ</mml:mi></mml:mrow></mml:math> $$p_\mathrm{T}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>p</mml:mi><mml:mi>T</mml:mi></mml:msub></mml:math> , with average values $$\lambda _\vartheta ^{\chi _{{c}1}} = 0.55 \pm 0.23$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msubsup><mml:mi>λ</mml:mi><mml:mi>ϑ</mml:mi><mml:msub><mml:mi>χ</mml:mi><mml:mrow><mml:mi>c</mml:mi><mml:mn>1</mml:mn></mml:mrow></mml:msub></mml:msubsup><mml:mo>=</mml:mo><mml:mn>0.55</mml:mn><mml:mo>±</mml:mo><mml:mn>0.23</mml:mn></mml:mrow></mml:math> , $$\lambda _\vartheta ^{\chi _{{c}2}} = -0.39 \pm 0.22$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msubsup><mml:mi>λ</mml:mi><mml:mi>ϑ</mml:mi><mml:msub><mml:mi>χ</mml:mi><mml:mrow><mml:mi>c</mml:mi><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:msubsup><mml:mo>=</mml:mo><mml:mo>-</mml:mo><mml:mn>0.39</mml:mn><mml:mo>±</mml:mo><mml:mn>0.22</mml:mn></mml:mrow></mml:math> , $$R^{\chi _{{c}1}} = (18.8 \pm 1.4)\%$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msup><mml:mi>R</mml:mi><mml:msub><mml:mi>χ</mml:mi><mml:mrow><mml:mi>c</mml:mi><mml:mn>1</mml:mn></mml:mrow></mml:msub></mml:msup><mml:mo>=</mml:mo><mml:mrow><mml:mo>(</mml:mo><mml:mn>18.8</mml:mn><mml:mo>±</mml:mo><mml:mn>1.4</mml:mn><mml:mo>)</mml:mo></mml:mrow><mml:mo>%</mml:mo></mml:mrow></mml:math> and $$R^{\chi _{{c}2}} = (6.5 \pm 0.5)\%$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msup><mml:mi>R</mml:mi><mml:msub><mml:mi>χ</mml:mi><mml:mrow><mml:mi>c</mml:mi><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:msup><mml:mo>=</mml:mo><mml:mrow><mml:mo>(</mml:mo><mml:mn>6.5</mml:mn><mml:mo>±</mml:mo><mml:mn>0.5</mml:mn><mml:mo>)</mml:mo></mml:mrow><mml:mo>%</mml:mo></mml:mrow></mml:math> . The analysis also shows that $$(67.2 \pm 1.9)$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mo>(</mml:mo><mml:mn>67.2</mml:mn><mml:mo>±</mml:mo><mml:mn>1.9</mml:mn><mml:mo>)</mml:mo></mml:mrow></mml:math> % of the prompt $$\mathrm{J}/\psi $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>J</mml:mi><mml:mo>/</mml:mo><mml:mi>ψ</mml:mi></mml:mrow></mml:math> yield is due to directly-produced mesons, of polarization constrained to remarkably small values, $$\lambda _\vartheta ^{\mathrm{J}/\psi } = 0.04 \pm 0.06$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msubsup><mml:mi>λ</mml:mi><mml:mi>ϑ</mml:mi><mml:mrow><mml:mi>J</mml:mi><mml:mo>/</mml:mo><mml:mi>ψ</mml:mi></mml:mrow></mml:msubsup><mml:mo>=</mml:mo><mml:mn>0.04</mml:mn><mml:mo>±</mml:mo><mml:mn>0.06</mml:mn></mml:mrow></mml:math> .

Measurements made at the LHC have shown that the production of the ${\rm J}/\psi$, $\psi$(2S), $\Upsilon$(1S) and $\Upsilon$(2S) quarkonia is suppressed in Pb-Pb collisions, with respect to the extrapolation of the pp production yields. The $\psi$(2S) and $\Upsilon$(2S) states are more strongly suppressed than the ground states and the level of the suppression changes with the centrality of the collision. We show that the measured patterns can be reproduced by a simple model, where all quarkonia are treated in a unified way, starting from the recent realisation that, in pp collisions, the probability of quarkonium formation has a universal dependence on the binding-energy of the bound state. The hot-medium suppression effect is parametrized by a penalty factor in the binding energy, identical for all (S- and P-wave) charmonium and bottomonium states, including those that indirectly contribute to the measured results through feed-down decays. This single parameter, computed through a global fit of all available suppression patterns, fully determines the hierarchy of nuclear effects, for all states and centrality bins. The resulting faithful description of the data provides convincing evidence in favour of the conjecture of sequential quarkonium suppression induced by QGP formation.

Of the J/$\psi$ mesons (inclusively) produced in pp collisions, a big fraction results from B decays, increasing with transverse momentum and exceeding 50\% for $p_{\rm T} > 20$ GeV. These events must be subtracted in measurements of the polarization of prompt J/$\psi$ mesons. While several studies have addressed the $\psi$(2S) and $\chi_c$ impact on the determination of the polarization of the directly-produced J/$\psi$ mesons, the theoretical and experimental knowledge of the non-prompt polarization is very poor. Furthermore, non-prompt J/$\psi$ polarization measurements can provide interesting information on quarkonium hadroproduction, complementing the studies of prompt production. We review the method of measuring the polarization of non-prompt J/$\psi$ mesons (produced in decays of unreconstructed B mesons and detected in the dilepton channel), in conditions typical of LHC experiments studying J/$\psi$ production. Realistic model-independent scenarios are validated with data from experiments studying $e^+e^- \to \Upsilon$(4S) interactions, converted to the high-momentum regime using B differential cross sections measured at the LHC. The non-prompt J/$\psi$ polarization measurements are seen to remain dependent on the event selection criteria, even after correcting for the dilepton acceptance and efficiencies. This implies that reproducible definitions of all relevant analysis choices must be reported with the polarization result, for rigorous comparisons with other measurements and/or theoretical calculations. We also discuss how the non-prompt J/$\psi$ polarization significantly depends on the relative importance of two complementary $\mathrm{B}\to {\rm J}/\psi$ decay topologies, two-body (reasonably dominated by singlet production) and multi-body (including octet contributions), providing, hence, valuable information for studies of the charmonium formation mechanisms.