M. De Palma

The four LEP collaborations, ALEPH, DELPHI, L3 and OPAL, have searched for the neutral Higgs bosons which are predicted by the Minimal Supersymmetric standard model (MSSM). The data of the four collaborations are statistically combined and examined for their consistency with the background hypothesis and with a possible Higgs boson signal. The combined LEP data show no significant excess of events which would indicate the production of Higgs bosons. The search results are used to set upper bounds on the cross-sections of various Higgs-like event topologies. The results are interpreted within the MSSM in a number of “benchmark” models, including CP-conserving and CP-violating scenarios. These interpretations lead in all cases to large exclusions in the MSSM parameter space. Absolute limits are set on the parameter cosβ and, in some scenarios, on the masses of neutral Higgs bosons.

The RD48 (ROSE) collaboration has succeeded to develop radiation hard silicon detectors, capable to withstand the harsh hadron fluences in the tracking areas of LHC experiments. In order to reach this objective, a defect engineering technique was employed resulting in the development of Oxygen enriched FZ silicon (DOFZ), ensuring the necessary O-enrichment of about 2×1017 O/cm3 in the normal detector processing. Systematic investigations have been carried out on various standard and oxygenated silicon diodes with neutron, proton and pion irradiation up to a fluence of 5×1014 cm−2 (1 MeV neutron equivalent). Major focus is on the changes of the effective doping concentration (depletion voltage). Other aspects (reverse current, charge collection) are covered too and the appreciable benefits obtained with DOFZ silicon in radiation tolerance for charged hadrons are outlined. The results are reliably described by the “Hamburg model”: its application to LHC experimental conditions is shown, demonstrating the superiority of the defect engineered silicon. Microscopic aspects of damage effects are also discussed, including differences due to charged and neutral hadron irradiation.

The performance of the ALEPH detector at the LEP e+e− collider is reviewed. The accuracy of the tracking detectors to measure the impact parameter and momentum of charged tracks is specified. Calorimeters are used to measure photons and neutral hadrons, and the accuracy obtained in energy and angle is given. An essential property of the detector is its ability to identify particles; the performance in identification of electrons, muons, neutrinos (from missing energy), charged hadrons, π0's and V0's is described.

The full LEP-1 data set collected with the ALEPH detector at the Z pole during 1991–1995 is analysed in order to measure the τ decay branching fractions. The analysis follows the global method used in the published study based on 1991–1993 data, but several improvements are introduced, especially concerning the treatment of photons and π0's. Extensive systematic studies are performed, in order to match the large statistics of the data sample corresponding to over 300 000 measured and identified τ decays. Branching fractions are obtained for the two leptonic channels and 11 hadronic channels defined by their respective numbers of charged particles and π0's. Using previously published ALEPH results on final states with charged and neutral kaons, corrections are applied to the hadronic channels to derive branching ratios for exclusive final states without kaons. Thus the analyses of the full LEP-1 ALEPH data are combined to yield a complete description of τ decays, encompassing 22 non-strange and 11 strange hadronic modes. Some physics implications of the results are given, in particular related to universality in the leptonic charged weak current, isospin invariance in a1 decays, and the separation of vector and axial-vector components of the total hadronic rate. Finally, spectral functions are determined for the dominant hadronic modes and updates are given for several analyses. These include: tests of isospin invariance between the weak charged and electromagnetic hadronic currents, fits of the ρ resonance lineshape, and a QCD analysis of the non-strange hadronic decays using spectral moments, yielding the value αs(mτ2)=0.340±0.005exp±0.014th. The evolution to the Z mass scale yields αs(MZ2)=0.1209±0.0018. This value agrees well with the direct determination from the Z width and provides the most accurate test to date of asymptotic freedom in the QCD gauge theory.

The flavour changing neutral current decay b→sγ has been detected in hadronic Z decays collected by ALEPH at LEP. The signal is isolated in lifetime-tagged bb̄ events by the presence of a hard photon associated with a system of high momentum and high rapidity hadrons. The background processes are normalised from the data themselves. The inclusive branching ratio is measured to be(3.11±0.80stat±0.72syst)×10−4,consistent with the Standard Model expectation via penguin processes.

The cross-section for e+e− → hadrons in the vicinity of the Z boson peak has been measured with the ALEPH detector at the CERN Large Electron Positron collider, LEP. Measurements of the Z mass, Mz = (91.174±0.070) GeV, the Z width Γz=(2.68±0.15) GeV, and of the peak hadronic cross-section, σhadpeak=(29.3±1.2) nb, are presented. With the constraints of the standard electroweak model, the number of light neutrino species is found to be Nv=3.27±0.30. this results rules out of the possibility of a fourth type of light neutrino at 98% CL.

Previously published and as yet unpublished QCD results obtained with the ALEPH detector at LEP1 are presented. The unprecedented statistics allows detailed studies of both perturbative and non-perturbative aspects of strong interactions to be carried out using hadronic Z and tau decays. The studies presented include precise determinations of the strong coupling constant, tests of its flavour independence, tests of the SU(3) gauge structure of QCD, study of coherence effects, and measurements of single-particle inclusive distributions and two-particle correlations for many identified baryons and mesons.

First results from ultrarelativistic 16O+Pb collisions at 200 GeV/nucleon are presented. The transverse energy ET in average central collisions is ≈ 75 GeV for the interval 2.2⩽y⩽3.8. A 16-fold convolution of the inelastic p+Au transverse energy spectrum, also measured at 200 GeV, reproduces the mean ET of 16O+Pb. The amount of nuclear stopping power appears to be high.

Interactions of 200-GeV/c protons and antiprotons on hydrogen, argon, and xenon targets were studied with a streamer-chamber vertex spectrometer at the CERN SPS. Results on multiplicities, rapidity distributions, and correlations are presented and compared with predictions of current models.

Abstract The next generation of water Cherenkov neutrino telescopes in the Mediterranean Sea are under construction offshore France (KM3NeT/ORCA) and Sicily (KM3NeT/ARCA). The KM3NeT/ORCA detector features an energy detection threshold which allows to collect atmospheric neutrinos to study flavour oscillation. This paper reports the KM3NeT/ORCA sensitivity to this phenomenon. The event reconstruction, selection and classification are described. The sensitivity to determine the neutrino mass ordering was evaluated and found to be 4.4 $$\sigma $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>σ</mml:mi> </mml:math> if the true ordering is normal and 2.3 $$\sigma $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>σ</mml:mi> </mml:math> if inverted, after 3 years of data taking. The precision to measure $$\varDelta m^2_{32}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>Δ</mml:mi> <mml:msubsup> <mml:mi>m</mml:mi> <mml:mn>32</mml:mn> <mml:mn>2</mml:mn> </mml:msubsup> </mml:mrow> </mml:math> and $$\theta _{23}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>θ</mml:mi> <mml:mn>23</mml:mn> </mml:msub> </mml:math> were also estimated and found to be $$85 . 10^{-6}~{\mathrm{eV}^{2}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mn>85</mml:mn> <mml:mo>.</mml:mo> <mml:msup> <mml:mn>10</mml:mn> <mml:mrow> <mml:mo>-</mml:mo> <mml:mn>6</mml:mn> </mml:mrow> </mml:msup> <mml:mspace /> <mml:msup> <mml:mrow> <mml:mi>eV</mml:mi> </mml:mrow> <mml:mn>2</mml:mn> </mml:msup> </mml:mrow> </mml:math> and $$(^{+1.9}_{-3.1})^{\circ }$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mrow> <mml:msubsup> <mml:mo>(</mml:mo> <mml:mrow> <mml:mo>-</mml:mo> <mml:mn>3.1</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>1.9</mml:mn> </mml:mrow> </mml:msubsup> <mml:mo>)</mml:mo> </mml:mrow> <mml:mo>∘</mml:mo> </mml:msup> </mml:math> for normal neutrino mass ordering and, $$75 . 10^{-6}~{\mathrm{eV}^{2}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mn>75</mml:mn> <mml:mo>.</mml:mo> <mml:msup> <mml:mn>10</mml:mn> <mml:mrow> <mml:mo>-</mml:mo> <mml:mn>6</mml:mn> </mml:mrow> </mml:msup> <mml:mspace /> <mml:msup> <mml:mrow> <mml:mi>eV</mml:mi> </mml:mrow> <mml:mn>2</mml:mn> </mml:msup> </mml:mrow> </mml:math> and $$(^{+2.0}_{-7.0})^{\circ }$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mrow> <mml:msubsup> <mml:mo>(</mml:mo> <mml:mrow> <mml:mo>-</mml:mo> <mml:mn>7.0</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>2.0</mml:mn> </mml:mrow> </mml:msubsup> <mml:mo>)</mml:mo> </mml:mrow> <mml:mo>∘</mml:mo> </mml:msup> </mml:math> for inverted ordering. Finally, a unitarity test of the leptonic mixing matrix by measuring the rate of tau neutrinos is described. Three years of data taking were found to be sufficient to exclude "Equation missing"<!-- image only, no MathML or LaTex --> event rate variations larger than 20% at $$3\sigma $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mn>3</mml:mn> <mml:mi>σ</mml:mi> </mml:mrow> </mml:math> level.

A search has been performed for the Standard Model Higgs boson in the data sample collected with the ALEPH detector at LEP, at centre-of-mass energies up to 209GeV. An excess of 3sigma beyond the background expectation is found, consistent with the production of the Higgs boson with a mass near 114GeV/c2. Much of this excess is seen in the four-jet analyses, where three high purity events are selected.

The fragmentation of b quarks into B mesons is studied with four million hadronic Z decays collected by the ALEPH experiment during the years 1991–1995. A semi-exclusive reconstruction of B→ℓνD(★) decays is performed, by combining lepton candidates with fully reconstructed D(★) mesons while the neutrino energy is estimated from the missing energy of the event. The mean value of xBwd, the energy of the weakly-decaying B meson normalised to the beam energy, is found to be 〈xBwd〉=0.716±0.006(stat)±0.006(syst), using a model-independent method; the corresponding value for the energy of the leading B meson is 〈xBL〉=0.736±0.006(stat)±0.006(syst). The reconstructed spectra are compared with different fragmentation models.

More extensive and precise results are reported on the parameters of Z decay. On the basis of 20 000 Z decays collected with the ALEPH detector at LEP we find Mz=91.182±0.026 (exp.) ±0.030 (beam) GeV, Γz=2.541±0.056 GeV and σhad0=41.4±0.8 nb. The partial widths for the hadronic and leptonic channels are Γhad=1804±44 MeV, Γe+e−=82.1±3.4 MeV, Γμ+μ−=87.9±6.0 MeV and Γτ+τ−=86.1±5.6 MeV, in good agreement with the standard model. On the basis of the average leptonic width Γℓ+ℓ−=83.9±2.2 MeV, the effective weak mixing angle is found to be sin2θw(Mz)=0.231±0.008. Usin g the partial widths calculated in the standard model, the number of light neutrino families is Nν=3.01±0.15 (exp.)±0.05 (theor.).

From an analysis of inclusive leptons in data collected by the ALEPH detector at LEP, we measure the fractions of bb and cc events in hadronic Z decays. The bb fraction times semileptonic branching ratio is measured to be Br(b→e)·Γbb/Γhad= 0.0224 ± 0.0016 ± 0.0010. Assuming a b semileptonic branching ratio of 0.102 ± 0.010 gives Γbb/Γhad= 0.220 ± 0.016 ± 0.024, in good agreement with the standard model prediction of 0.217. The cc fraction times semileptonic branching ratio is measured to be Br(c→e)·Γcc/Γhad= 0.0133 ± 0.0040−0.0031+0.0038. Assuming a c semileptonic branching ratio of 0.090 ± 0.013 gives Γcc/Γhad= 0.148 ± 0.044−0.038+0.045, in agreement with the standard model prediction of 0.171.

The polarization of Λ baryons from Z decays is studied with the Aleph apparatus. Evidence of longitudinal polarization of s quarks from Z decay is observed for the first time. The measured longitudinal Λ polarization is PLΛ = −0.32 ± 0.07 for z =ppbeam> 0.3. This agrees with the prediction of −0.39 ± 0.08 from the standard model and the constituent quark model, where the error is due to uncertainties in the mechanism for Λ production. The observed Λ polarization is diluted with respect to the primary s quark polarization by Λ baryons without a primary s quark. Measurements of the Λ forward-backward asymmetry and of the correlation between back-to-back ΛΛ pairs are used to check this dilution. In addition the transverse Λ polarization is measured. An indication of transverse polarization, more than two standard deviations away from zero, is found along the normal to the plane defined by the thrust axis and the Λ direction.

This report summarises the final results obtained by the RD48 collaboration. The emphasis is on the more practical aspects directly relevant for LHC applications. The report is based on the comprehensive survey given in the 1999 status report (RD48 3rd Status Report, CERN/LHCC 2000-009, December 1999), a recent conference report (Lindström et al. (RD48), and some latest experimental results. Additional data have been reported in the last ROSE workshop (5th ROSE workshop, CERN, CERN/LEB 2000-005). A compilation of all RD48 internal reports and a full publication list can be found on the RD48 homepage (http://cern.ch/RD48/). The success of the oxygen enrichment of FZ-silicon as a highly powerful defect engineering technique and its optimisation with various commercial manufacturers are reported. The focus is on the changes of the effective doping concentration (depletion voltage). The RD48 model for the dependence of radiation effects on fluence, temperature and operational time is verified; projections to operational scenarios for main LHC experiments demonstrate vital benefits. Progress in the microscopic understanding of damage effects as well as the application of defect kinetics models and device modelling for the prediction of the macroscopic behaviour has also been achieved but will not be covered in detail.

A search for charginos nearly mass degenerate with the lightest neutralino is performed with the data collected by the ALEPH detector at LEP, at centre-of-mass energies between 189 and 209 GeV, corresponding to an integrated luminosity of 628 pb−1. The analysis is based on the detection of isolated and energetic initial state radiation photons, produced in association with chargino pairs whose decay products have little visible energy. The number of candidate events observed is in agreement with that expected from Standard Model background sources. These results are combined with those of other direct searches for charginos, and a lower limit of 88 GeV/c2 at 95% confidence level is derived for the chargino mass in the case of heavy sfermions, irrespective of the chargino-neutralino mass difference.

The results on spectra of negative particles produced in16O+Au andp-Au collisions at 200 GeV/nucleon and16O+Au at 60 GeV/nucleon are presented. The correlations of average rapidity and average transverse momentum with event multiplicity are studied. Spectral shapes are similar for central16O+Au andp-Au collisions. The transverse momentum and rapidity distributions for central16O+Au andp-Au collisions differ strongly from corresponding distributions forp+p interactions. The FRITIOF model fails to describe the shapes of the transverse momentum distributions. The simple thermodynamical model of a single fireball does not fit the midrapidity transverse momentum distributions, and the rapidity distributions.

Inclusive π±, K± and $$(p,\bar p)$$ differential cross-sections in hadronic decays of the Z have been measured as a function ofz=P hadron/P beam, the scaled momentum. The results are based on approximately 520 000 events measured by the ALEPH detector at LEP during 1992. Charged particles are identified by their rate of ionization energy loss in the ALEPH Time Projection Chamber. The position, ξ*, of the peak in the ln(1/z) distribution is determined, and the evolution of the peak position with centre-of-mass energy is compared with the prediction of QCD.

We have performed a search for supersymmetric particles using acoplanar pairs of oppositely-charged particles in decays of the Z0. In 0.53 pb−1 of integrated luminosity near the Z0 peak, we observe two events where approximately four are expected from background, allowing limits to be extended on combined photino and slepton masses, and also on combined photino and chargino masses.

Recent results from the NA35 Collaboration are presented for the reactions of 60 and 200 GeV/nucleon p and 16O, and 200 GeV/nucleon 32S with various targets ranging from S to Au. Midrapidity transverse energy distributions and forward energy flow, p⊥ spectra and rapidity distributions of hadrons are presented. Two-pion interferometry results are discussed. Neutral strange particle yields and p⊥ distributions are presented. Conclusions are drawn from the experimental results.

Large transverse energy cross sections of 300 GeV/c pions and protons on hydrogen have been measured with a segmented calorimeter covering the central rapidity region −0.88 < y < 0.67 and 2π in azimuth. The selected events show large multiplicities and no jet-like event structure. Processes more complicated than the scattering of two constituents appear to dominate these inelastic collisions.

Abstract The KM3NeT research infrastructure is under construction in the Mediterranean Sea. It consists of two water Cherenkov neutrino detectors, ARCA and ORCA, aimed at neutrino astrophysics and oscillation research, respectively. Instrumenting a large volume of sea water with $$\sim {6200}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mo>∼</mml:mo> <mml:mn>6200</mml:mn> </mml:mrow> </mml:math> optical modules comprising a total of $$\sim {200{,}000}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mo>∼</mml:mo> <mml:mrow> <mml:mn>200</mml:mn> <mml:mo>,</mml:mo> <mml:mn>000</mml:mn> </mml:mrow> </mml:mrow> </mml:math> photomultiplier tubes, KM3NeT will achieve sensitivity to $$\sim {10} \ \mathrm{MeV}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mo>∼</mml:mo> <mml:mn>10</mml:mn> <mml:mspace /> <mml:mi>MeV</mml:mi> </mml:mrow> </mml:math> neutrinos from Galactic and near-Galactic core-collapse supernovae through the observation of coincident hits in photomultipliers above the background. In this paper, the sensitivity of KM3NeT to a supernova explosion is estimated from detailed analyses of background data from the first KM3NeT detection units and simulations of the neutrino signal. The KM3NeT observational horizon (for a $$5\,\sigma $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mn>5</mml:mn> <mml:mspace /> <mml:mi>σ</mml:mi> </mml:mrow> </mml:math> discovery) covers essentially the Milky-Way and for the most optimistic model, extends to the Small Magellanic Cloud ( $$\sim {60} \ \mathrm{kpc}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mo>∼</mml:mo> <mml:mn>60</mml:mn> <mml:mspace /> <mml:mi>kpc</mml:mi> </mml:mrow> </mml:math> ). Detailed studies of the time profile of the neutrino signal allow assessment of the KM3NeT capability to determine the arrival time of the neutrino burst with a few milliseconds precision for sources up to 5–8 kpc away, and detecting the peculiar signature of the standing accretion shock instability if the core-collapse supernova explosion happens closer than 3–5 kpc, depending on the progenitor mass. KM3NeT’s capability to measure the neutrino flux spectral parameters is also presented.

The final results of the ALEPH search for the Standard Model Higgs boson at LEP, with data collected in the year 2000 at centre-of-mass energies up to 209 GeV, are presented. The changes with respect to the preceding publication are described and a complete study of systematic effects is reported. The findings of this final analysis confirm the preliminary results published in November 2000 shortly after the closing down of the LEP collider: a significant excess of events is observed, consistent with the production of a $115 \Gcs$ Standard Model Higgs boson. The final results of the searches for the neutral Higgs bosons of the MSSM are also reported, in terms of limits on $\mh$, $\mA$ and $\tanb$. Limits are also set on $\mh$ in the case of invisible decays.

A search for selectron, smuon and stau pair production is performed with the data collected by the ALEPH detector at LEP at centre-of-mass energies up to 209 GeV. The numbers of candidate events are consistent with the background predicted by the Standard Model. Final mass limits from ALEPH are reported.

We have performed a search for gluinos (g) and scalar quarks (q) in a data sample of 84 pb(-1) of pp collisions at square root[s] = 1.8 TeV, recorded by the Collider Detector at Fermilab. We investigate the final state of large missing transverse energy and three or more jets, a characteristic signature in R-parity-conserving supersymmetric models. The analysis has been performed "blind," in that the inspection of the signal region is made only after the predictions from standard model backgrounds have been calculated. Comparing the data with predictions of constrained supersymmetric models, we exclude gluino masses below 195 GeV/c2 (95% C.L.), independent of the squark mass. For the case m(q) approximately m(g), gluino masses below 300 GeV/c2 are excluded.

A data sample corresponding to 1.23 million hadronic Z decays collected by the ALEPH detector at LEP has been searched for signals of the production of a non-minimal CP-even Higgs boson h in the reaction e+e−→hZ∗. The h decay modes considered were: those of the minimal standard model Higgs boson, with modified branching ratios; decays into a pair of CP-odd Higgs bosons A; and decays into invisible final states. Only one event was found, a very acoplanar e+e− pair which could originate from the standard model background process e+e−→e+e−vv̄. Upper limits for the cross-section of the reaction e+e−→hZ∗ have been derived as a function of mh, the mass of the Higgs boson h. In the case of invisible decays, the 95% CL lower limit on mh is 65 GeV/c2 for a production cross-section equal to that of a minimal standard model Higgs boson. When combined with previous ALEPH results on the reaction e+e− → hA, these cross-section upper limits exclude a domain in the (mhmA) plane of the MSSM such that if invisible h and A decays can be neglected, 95% CL lower limits of 44 and 21 GeV/c2 result for mh and mA, respectively, independent of the other parameters of the model.

From a sample of 152,000 τ decays collected by the ALEPH detector at LEP an upper limit of 24 MeV at 95% CL on the τ neutrino mass has been determined. The limit is obtained using a two dimensional likelihood fit of the visible energy and the invariant mass distribution of 25 τ → 5π(π0)ντ events.

The charged particle multiplicity distribution of hadronic Z decays was measured on the peak of the Z resonance using the ALEPH detector at LEP. Using a model independent unfolding procedure the distribution was found to have a mean 〈n〉=20.85±0.24 and a dispersion D=6.34±0.12. Comparison with lower energy data supports the KNO scaling hypothesis in the energy range s=29−91.25 GeV. At s=91.25 GeV the shape of the multiplicity distribution is well described by a log-normal distribution, as predicted from a cascading model for multi-particle production. The same model also successfully describes the energy dependence of the mean and width of the multiplicity distribution. A next-to-leading order QCD prediction in the framework of the modified leading-log approximation and local parton-hadron duality is found to fit the energy dependence of the mean but not the width of the charged multiplicity distribution, indicating that the width of the multiplicity distribution is a sensitive probe for higher order QCD or non-perturbative effects.

A search for the neutral Higgs boson in the mass range above 11 GeV (above the H0→bb threshold), using the process Z0→H0e+e−, Z0→H0μ+μ− and Z0→H0vv, is performed on data collected by the ALEPH detector corresponding to about 25 000 events of Z0→ hadrons. Combining all these processes, the mass range excluded is 11 GeV at 95% CL. Together with a previously published result from ALEPH, the mass range excluded is 32 MeV to 24 GeV at 95% CL. This result also extends the excluded mass region for neutral Higgs bosons from supersymmetry.

A data sample corresponding to about 100 000 hadronic Z decays collected by ALEPH at LEP has been used to search for the standard Higgs boson produced in the reaction e+e− → H0Z0∗. No indication for any signal was found, and a 95% CL lower limit on the Higgs boson mass has been set at 41.6 GeV.

The polarization of τ leptons produced in the reaction e+e−→τ+τ− at the Z resonance has been measured using the τ decay modes eνeντ, μνμντ, πντ, ϱντ, and a1ντ. The mean value obtained is Pτ = −0.152±0.045, indicating that parity is violated in the neutral current process e+e− → τ+τ−. The result corresponds to a ratio of a neutral current vector and axial vector coupling constants of the τ lepton gVτ(M2Z)gAτ(M2Z)= 0.076±0.023 and a value of the electroweak mixing parameter sin2θw(M2Z) = 0.2302 ± 0.0058.

The light scalar Higgs boson h and the pseudoscalar Higgs boson A of the minimal supersymmetric standard model have been searched for in the processes e+e−→hff and e+e−→hA using data collected by ALEPH at the LEP e+e− collider, with center of mass energies at and near the Z peak. Using a variety of signatures adapted to various mass ranges for h and A, we have excluded a large domain in the parameter space. For large values of ν2ν1, the ratio of the vacuum expectation values of the two Higgs fields, the whole range from 0 to 38.8 GeV is excluded for Mh and MA at 95% CL.

A search for the production and non-standard decay of a Higgs boson, h, into four taus through intermediate pseudoscalars, a, is conducted on 683 pb−1 of data collected by the ALEPH experiment at centre-of-mass energies from 183 to 209 GeV. No excess of events above background is observed, and exclusion limits are placed on the combined production cross section times branching ratio, $ {\xi^2} = \frac{{\sigma \left( {{\text{e}^{+} }{\text{e}^{-} } \to {\text{Zh}}} \right)}}{{{\sigma_{\text{SM}}}\left( {{\text{e}^{+} }{\text{e}^{-} } \to {\text{Zh}}} \right)}} \times B\left( {h \to {\text{aa}}} \right) \times B{\left( {{\text{a}} \to {\tau^{+} }{\tau^{-} }} \right)^2} $ . For m h < 107 GeV/c 2 and 4 < m a < 10 GeV/c 2, ξ 2 > 1 is excluded at the 95% confidence level.

KM3NeT is a research infrastructure located in the Mediterranean Sea, that will consist of two deep-sea Cherenkov neutrino detectors. With one detector (ARCA), the KM3NeT Collaboration aims at identifying and studying TeV-PeV astrophysical neutrino sources. With the other detector (ORCA), the neutrino mass ordering will be determined by studying GeV-scale atmospheric neutrino oscillations. The first KM3NeT detection units were deployed at the Italian and French sites between 2015 and 2017. In this paper, a description of the detector is presented, together with a summary of the procedures used to calibrate the detector in-situ. Finally, the measurement of the atmospheric muon flux between 2232-3386 m seawater depth is obtained.

Two samples of exclusive semileptonic decays, 579 B0 →D∗+ℓ−νℓ events and 261 B0 → D+ℓ−νℓ events, are selected from approximately 3.9 million hadronic Z decays collected by the ALEPH detector at LEP. From the reconstructed differential decay rate of each sample, the product of the hadronic form factor F(ω) at zero recoil of the D(∗)+ meson and the CKM matrix element |Vcb| are measured to be FD∗+(1)|Vcb| = (31.9 ± 1.8stat ± 1.9syst) × 10−3, FD+(1)|Vcb| = (27.8 ± 6.8stat ± 6.5syst) × 10−3. The ratio of the form factors FD+(1) and FD∗+(1) is measured to be FD+(1)FD∗+(1) = 0.87 ± 0.22stat ± 0.21syst. A value of |Vcb| is extracted from the two samples, using theoretical constraints on the slope and curvature of the hadronic form factors and their normalization at zero recoil, with the result |Vcb| = (34.4 ± 1.6stat ± 2.3syst ± 1.4th) × 10−3. The branching fractions are measured from the two integrated spectra to be Br(B0 → D∗+ℓ−νℓ) = (5.53 ± 0.26stat ±0.52syst)%, Br(B0 → D∗+ℓ−νℓ) = (2.35 ± 0.20stat ± 0.44syst)%.

The strong coupling constant is determined from the leptonic branching ratios, the lifetime, and the invariant mass distribution of the hadronic final state of the τ lepton, using data accumulated at LEP with the ALEPH detector. The strong coupling constant measurement, αs(mτ2) = 0.330±0.046, evolved to the Z mass yields αs(MZ2) = 0.188±0.005. The error includes experimental and theoretical uncertainties, the latter evaluated in the framework of the Shifman, Vainshtein and Zakharov (SVZ) approach. The method allows the non-perturbative contribution to the hadronic decay rate to be determined to be 0.3±0.5%.

Using 1.45 million hadronic Z decays collected by the ALEPH experiment at LEP, the b → τ−ν-τX branching ratio is measured to be 2.75 ± 0.30 ± 0.37%. In addition an upper limit of 1.8 × 10−3 at 90% confidence level is placed upon the exclusive branching ratio of B−→ τ−ν-τ. These measurements are consistent with SM expectations, and put the constraint tan βMh±< 0.52 GeV−1 at 90% confidence level on all Type II two Higgs doublet models (such as the MSSM).

Searches for scalar top, scalar bottom and mass-degenerate scalar quarks are performed in the data collected by the ALEPH detector at LEP, at centre-of-mass energies up to 209 GeV, corresponding to an integrated luminosity of 675 pb−1. No evidence for the production of such particles is found in the decay channels t̃→c/uχ, t̃→bℓν̃, b̃→bχ, q̃→qχ or in the stop four-body decay channel t̃→bχff̄′ studied for the first time at LEP. The results of these searches yield improved mass lower limits. In particular, an absolute lower limit of 63 GeV/c2 is obtained for the stop mass, at 95% confidence level, irrespective of the stop lifetime and decay branching ratios.

A search for charged Higgs bosons produced in pairs is performed with data collected at centre-of-mass energies ranging from 189 to 209 GeV by ALEPH at LEP, corresponding to a total luminosity of 629 invpb. The three final states taunutaunu, taunucs and cscs are considered. No evidence for a signal is found and lower limits are set on the mass M_H+ as a function of the branching fraction B(H to taunu). In the framework of a two-Higgs-doublet model, and assuming B(H+ to taunu + B(H+ to cs) = 1 charged Higgs bosons with masses below 79.3 Gev/c2 are excluded at 95% confidence level independently of the branching ratios.

This paper describes a study of Bose-Einstein correlations made using the ALEPH detector at LEP. The correlations are found to enhance the two particle differential cross section for pairs of identical pions by a factor which can be roughly parametrized byR(Q)=1+λ exp(-Q2σ2), whereQ is the difference in the 3-momenta of the two pions in their centre of mass frame, λ=0.51±0.04±0.11 and σ=3.3±0.2±0.8 GeV−1, which corresponds to a source size of 0.65±0.04±0.16 fm. The large systematic errors on these results reflect their strong dependence on the choice of the reference sample used in the analysis. This problem is believed to occur primarily because of uncertainties in the rates of resonance production and a lack of knowledge about the pion-pion strong interaction. No significant correlations are seen amongst like-charged pion-kaon pairs.

An option of increasing the luminosity of the Large Hadron Collider (LHC) at CERN to 1035 cm−2 s−1 has been envisaged to extend the physics reach of the machine. An efficient tracking down to a few centimetres from the interaction point will be required to exploit the physics potential of the upgraded LHC. As a consequence, the semiconductor detectors close to the interaction region will receive severe doses of fast hadron irradiation and the inner tracker detectors will need to survive fast hadron fluences of up to above 1016 cm−2. The CERN-RD50 project “Development of Radiation Hard Semiconductor Devices for Very High Luminosity Colliders” has been established in 2002 to explore detector materials and technologies that will allow to operate devices up to, or beyond, this limit. The strategies followed by RD50 to enhance the radiation tolerance include the development of new or defect engineered detector materials (SiC, GaN, Czochralski and epitaxial silicon, oxygen enriched Float Zone silicon), the improvement of present detector designs and the understanding of the microscopic defects causing the degradation of the irradiated detectors. The latest advancements within the RD50 collaboration on radiation hard semiconductor detectors will be reviewed and discussed in this work.

We present predictions of the distribution of groomed heavy jet mass in electron-positron collisions at the next-to-next-to-leading order accuracy matched with the resummation of large logarithms to next-to-next-to-next-to-leading logarithmic accuracy. Resummation at this accuracy is possible through extraction of necessary two-loop constants and three-loop anomalous dimensions from fixed-order codes.

Using a data sample corresponding to about 1 233 000 hadronic Z decays collected by the ALEPH experiment at LEP, the reaction e+e−→HZ∗ has been used to search for the standard model Higgs boson, in association with missing energy when Z∗→ vv̄, or with a pair of energetic leptons when Z∗→e+e−orμ+μ−. No signal was found and, at the 95% confidence level, mH exceeds 58.4 GeV/c2.

Deuteron and anti-deuteron production in Z decays has been observed in the ALEPH experiment at LEP. The production rate of anti-deuterons is measured to be 5.9+-1.8+-0.5 10^-6 per hadronic Z decay in the anti-deuteron momentum range 0.62 to 1.03 GeV/c. The coalescence parameter B_2, which characterizes the likelihood of anti-deuteron production, is measured to be 0.0033+-0.0013 GeV^2 in Z dedays. These measurements indicate that the production of anti-deuterons is suppressed in e+e- collisions compared to pp and photoproduction collisions.

Triple gauge-boson couplings γWW and ZWW involving single-photon, single-W and W-pair production are determined using data samples collected at LEP with the ALEPH detector at centre-of-mass energies between 183 and 209 GeV. The integrated luminosity used is 700 pb−1 for the single-photon measurement and 683 pb−1 for the W channels. Restricting the measurement to C- and P-conserving terms and applying local SU(2)L×U(1)Y gauge invariance, the measured values of the parameters g1Z, κγ and λγ are: g1Z=1.001±0.027(stat)±0.013(syst),κγ=0.971±0.055(stat)±0.030(syst),λγ=−0.012±0.027(stat)±0.011(syst) for single-parameter fits, where the two other parameters are fixed to their Standard Model values. Results are also presented for the cases where two or all three couplings are allowed to vary. An additional analysis using W-pair events is performed to measure the unconstrained real and imaginary parts of all 14 triple gauge-boson couplings and to perform an indirect search for a techni-ρ resonance. No deviations from the Standard Model expectations are observed and the lower limit on the techni-ρ mass is set to 600 GeV/c2 at 95% confidence level.

An analysis of global event-shape variables has been carried out for the reaction e+e−→Z0→hadrons to measure the strong coupling constant αs. This study is based on 52 720 hadronic events obtained in 1989/90 with the ALEPH detector at the LEP collider at energies near the peak of the Z-resonance. In order to determine αs, second order QCD predictions modified by effects of perturbative higher orders and hadronization were fitted to the experimental distributions of event-shape variables. From a detailed analysis of the theoretical uncertainties we find that this approach is best justified for the differential two-jet rate, from which we obtain αs(MZ2) = 0.121 ± 0.002(stat.)±0.003(sys.)±0.007(theor.) using a renormalization scale ω =12MZ. The dependence of αs(MZ2) on ω is parameterized. For scales mb<ω<MZ the result varies by −0.012+0.007.

Cross sections, angular distributions and forward-backward asymmetries are presented, of two-fermion events produced in e+e- collisions at centre-of-mass energies from 189 to 209 GeV at LEP, measured with the ALEPH detector. Results for e+e-, μ+μ-, τ+τ-, qq̄, bb̄ and cc̄ production are in agreement with the standard model predictions. Constraints are set on scenarios of new physics such as four-fermion contact interactions, leptoquarks, Z′ bosons, TeV-scale quantum gravity and R-parity violating squarks and sneutrinos.

Cross sections for inclusive direct photon production in π−p, π+p, and pp collisions at 300 GeV/c are measured at transverse momenta pT up to 7 GeV/c (xT=0.6). For π−p→γX also the rapidity distribution is presented. The cross-section ratio σ(π−p→γX)/σ(π+p→γX) is found to be 1 at pT=4 GeV/c and rises with increasing pT. This observation signals the occurrence of valence-quark–antiquark annihilation. The results are in good agreement with QCD predictions.Received 19 December 1986DOI:https://doi.org/10.1103/PhysRevD.36.8©1987 American Physical Society

Inelastic cross sections at 60 and 200 GeV/nucleon are determined in a streamer chamber for 16O on several nuclear targets. Charged particle multiplicity distributions for inelastic and central collisions are studied and compared with theoretical predictions. The inelastic cross section exhibit a geometrical dependence on nuclear radii. The multiplicity data are governed by the collision geometry. They are consistent with a picture of superposition of independent nucleon-nucleus interactions.

The gSeaGen code is a GENIE-based application developed to efficiently generate high statistics samples of events, induced by neutrino interactions, detectable in a neutrino telescope. The gSeaGen code is able to generate events induced by all neutrino flavours, considering topological differences between track-type and shower-like events. Neutrino interactions are simulated taking into account the density and the composition of the media surrounding the detector. The main features of gSeaGen are presented together with some examples of its application within the KM3NeT project. Program Title: gSeaGen CPC Library link to program files: http://dx.doi.org/10.17632/ymgxvy2br4.1 Licensing provisions: GPLv3 Programming language: C++ External routines/libraries: GENIE [1] and its external dependencies. Linkable to MUSIC [2] and PROPOSAL [3]. Nature of problem: Development of a code to generate detectable events in neutrino telescopes, using modern and maintained neutrino interaction simulation libraries which include the state-of-the-art physics models. The default application is the simulation of neutrino interactions within KM3NeT [4]. Solution method: Neutrino interactions are simulated using GENIE, a modern framework for Monte Carlo event generators. The GENIE framework, used by nearly all modern neutrino experiments, is considered as a reference code within the neutrino community. Additional comments including restrictions and unusual features: The code was tested with GENIE version 2.12.10 and it is linkable with release series 3. Presently valid up to 5 TeV. This limitation is not intrinsic to the code but due to the present GENIE valid energy range. References: [1] C. Andreopoulos at al., Nucl. Instrum. Meth. A614 (2010) 87. [2] P. Antonioli et al., Astropart. Phys. 7 (1997) 357. [3] J. H. Koehne et al., Comput. Phys. Commun. 184 (2013) 2070. [4] S. Adrián-Martínez et al., J. Phys. G: Nucl. Part. Phys. 43 (2016) 084001.

A study of scaling violations in fragmentation functions performed by the ALEPH collaboration at LEP is presented. Data samples enriched in uds, c, b and gluon jets, respectively, together with measurements of the longitudinal and transverse inclusive cross sections are used to extract the fragmentation function for the gluon and for each flavour. The measurements are compared to data from experiments at energies between 22 GeV and 91 GeV and scaling violations consistent with QCD predictions are observed. From this, a measurement of the strong coupling constant αs(Mz) = 0.126 ±0.009 is obtained.

Searches for pair production of squarks, sleptons, charginos, and neutralinos are performed with the data collected by the ALEPH detector at LEP at centre-of-mass energies from 188.6 to 201.6 GeV. No evidence for any such signals is observed in a total integrated luminosity of about 410pb-1. The negative results of the searches are translated into exclusion domains in the space of the relevant MSSM parameters, which improve significantly on the constraints set previously. Under the assumptions of gaugino and sfermion mass unification, these results allow a 95% C.L. lower limit of 37GeV/c2 to be set on the mass of the lightest neutralino for any tan beta and sfermion mass. Additional constraints in the MSSM parameter space are derived from the negative results of ALEPH searches for Higgs bosons. The results are also interpreted in the framework of minimal supergravity.

Using 106 000 hadronic events obtained with the ALEPH detector at LEP at energies close to the Z resonance peak, the strong coupling constant αs is measured by an analysis of energy-energy correlations (EEC) and the global event shape variables thrust, C-parameter and oblateness. It is shown that the theoretical uncertainties can be significantly reduced if the final state particles are first combined in clusters using a minimum scaled invariant mass cut, Ycut, before these variables are computed. The combined result from all shape variables of pre-clustered events is αs(MZ2 = 0.117±0.005 for a renormalization scale μ=12MZ. For μ values between MZ and the b-quark mass, the result changes by −0.009+0.006.

Exotic hadrons made of five quarks (pentaquarks) are searched for in hadronic Z decays collected by the ALEPH detector at LEP. No significant signal is observed. At 95% C.L., upper limits are set on the production rates N of such particles and their charge-conjugate state per Z decay: NΘ(1535)+⋅BR(Θ(1535)+→pKS0)<6.2×10−4,NΞ(1862)−−⋅BR(Ξ(1862)−−→Ξ−π−)<4.5×10−4,NΞ(1862)0⋅BR(Ξ(1862)0→Ξ−π+)<8.9×10−4,NΘc(3100)0⋅BR(Θc(3100)0→D*−p)<6.3×10−4,NΘc(3100)0⋅BR(Θc(3100)0→D−p)<31×10−4.

Limits on Z decay branching ratios into neutralinos are reported. They were obtained from searches for monojets, acoplanar jets, acoplanar lepton pairs, single photons and acoplanar photon pairs as signaturs for the reactions e+e- → χχ′ and e+e- → χχ′, where χ is the lightest neutralino and χ′ any heavier one. The data sample used for these searches corresponds to about 23 000 events of Z decay into multihadrons, collected at LEP by the ALEPH detector for centre of mass energies at and near the Z peak. The results obtained are used to restrict the parameter space of the minimal supersymmetric standard model.

In a sample of 190 000 hadronic Z decays, three signals of charm production are observed: two from the exclusive decays D° →K−π+andD∗+→D°π+→K−π+π+ and one in the transverse-momentum distribution of soft hadrons relative to the nearest jet. The features of these signals are in good agreement with expectations based on the standard model and previous measurements of the branching fractions. The number of D∗±→K±π±π± per hadronic decay of the Z is measured to be (5.11±0.34) × 10−3, and the branching ratio B(D0 → K−π+) is (3.62 ± 0.34 ± 0.44)%. Charm hadronization has been studied. The average fraction of the beam energy carried by the D∗ meson is found to be 〈XE〉c = 0.504−0.017+0.013±0.008, and implications of the measurements on the pseudoscalar-to-vector production ratio of charmed mesons are discussed.

The mass of the W boson is determined from the direct reconstruction of its decays into purely hadronic and semi-leptonic events in e+e- collisions at LEP. The data sample corresponds to an integrated luminosity of 683 inverse picobarns collected with the ALEPH detector at centre-of-mass energies up to 209 GeV. To minimise any effect from colour reconnection a new procedure is adopted in which low energy particles are not considered in the mass determination from the purely hadronic channel. The combined result from all channels is Mw = 80.440+-0.043(stat.)+-0.024(syst.)+-0.009(FSI)+-0.009(LEP) GeV/c**2 where FSI represents the possible effects of final state interactions in the purely hadronic channel. From two-parameter fits to the W mass and width, the W width is found to be Gw = 2.14+-0.09(stat.)+-0.04(syst.)+-0.05(FSI)+-0.01(LEP) GeV

The KM3NeT research infrastructure is currently under construction at two locations in the Mediterranean Sea. The KM3NeT/ORCA water-Cherenkov neutrino detector off the French coast will instrument several megatons of seawater with photosensors. Its main objective is the determination of the neutrino mass ordering. This work aims at demonstrating the general applicability of deep convolutional neural networks to neutrino telescopes, using simulated datasets for the KM3NeT/ORCA detector as an example. To this end, the networks are employed to achieve reconstruction and classification tasks that constitute an alternative to the analysis pipeline presented for KM3NeT/ORCA in the KM3NeT Letter of Intent. They are used to infer event reconstruction estimates for the energy, the direction, and the interaction point of incident neutrinos. The spatial distribution of Cherenkov light generated by charged particles induced in neutrino interactions is classified as shower- or track-like, and the main background processes associated with the detection of atmospheric neutrinos are recognized. Performance comparisons to machine-learning classification and maximum-likelihood reconstruction algorithms previously developed for KM3NeT/ORCA are provided. It is shown that this application of deep convolutional neural networks to simulated datasets for a large-volume neutrino telescope yields competitive reconstruction results and performance improvements with respect to classical approaches.

Measurements of the inclusive cross-sections forK 0 and Λ production in hadronic decays of the Z are presented together with measurements of two-particle correlations within pairs of Λ andK 0. The results are compared with predictions from the hadronization models Jetset, based on string fragmentation, and Herwig, based on cluster decays. TheK 0 spectrum is found to be harder than predicted by both models, while the Λ spectrum is softer than predicted. The correlation measurements are all reproduced well by Jetset, while Herwig misses some of the qualitative features and overestimates the size of the $$\Lambda \bar \Lambda $$ correlation. Finally, the possibility of Bose-Einstein correlation in theK 0 K 0 system is discussed.

The results of searches for selectrons, charginos and neutralinos performed with the data collected by the ALEPH detector at LEP at centre-of-mass energies up to 209 GeV are interpreted in the framework of the Minimal Supersymmetric extension of the Standard Model with R-parity conservation. Under the assumptions of gaugino and sfermion mass unification and no sfermion mixing, an absolute lower limit of 73 GeV/c2 is set on the mass of the lighter selectron ẽR at the 95% confidence level. Similarly, limits on the masses of the heavier selectron ẽL and of the sneutrino ν̃e are set at 107 and 84 GeV/c2, respectively. Additional constraints are derived from the results of the searches for Higgs bosons. The results are also interpreted in the framework of minimal supergravity.

The decay B0 -> J/psi K0_S is reconstructed with J/psi -> e+ e- or mu+ mu- and K0_S -> pi+ pi-. From the full ALEPH dataset at LEP1 of about 4 million hadronic Z decays, 23 candidates are selected with an estimated purity of 71%. They are used to measure the CP asymmetry of this decay, given by sin 2beta in the Standard Model, with the result sin 2beta = 0.84 +0.82-1.04 +-0.16. This is combined with existing measurements from other experiments, and increases the confidence level that CP violation has been observed in this channel to 98%.

Single top production via the flavour changing neutral current reactions e+e- -> \bar{t}c, \bar{t}u is searched for within the 214 pb-1 of data collected by ALEPH at centre-of-mass energies between 204 and 209 GeV. No deviation from the Standard Model expectation is observed and upper limits on the single top production cross sections are derived. The combination with data collected at lower centre-of-mass energies yields an upper limit on the branching ratio BR(t -> Zc)+BR(t -> Zu) 14%, for BR(t -> \gamma c)+BR(t -> \gamma u)= 0 and mt=174 GeV/c2.

Quark and gluon jets with the same energy, 24 GeV, are compared in symmetric three-jet configurations from hadronic Z decays observed by the ALEPH detector. Jets are defined using the Durham algorithm. Gluon jets are identified using an anti-tag on b jets, based on a track impact parameter method. The comparison of gluon and mixed flavour quark jets shows that gluon jets have a softer fragmentation function, a larger angular width and a higher particle multiplicity, Evidence is presented which shows that the corresponding differences between gluon and b jets are significantly smaller. In a statistically limited comparison the multiplicity in c jets was found to be comparable with that observed for the jets of mixed quark flavour.

A search for pair-produced charged Higgs bosons in decays of the Z0 has been performed using the ALEPH detector at LEP for the decay channels H+H− → ντντ, H+H− → ντ cs and H+H− → cs cs. Searches for two additional decay channels in which cs is replaced by cb were also performed. With 1.17 pb−1 of integrated luminosity, corresponding to about 25 000 hadronic decays of the Z0, the charged Higgs has been excluded at 95% CL in the mass range 7.6 to 43.0 GeV for BR[H± → ντ] = 100%, 8.3 to 40.6 GeV for BR[H±→ντ] = BR[H±→cs] = 50%, and 14.4 to 35.4 GeV for BR[H±→cs] = 100% . With cs replaced by cb, the charged Higgs has been excluded at 95% CL in the mass range 12.0 to 40.7 GeV for BR[H±→ντ] = BR[H±→cb] = 50%, and 16.2 to 35.7 GeV for BR[H±→cb] = 100%.

B0B0 oscillation is studied using almost a million hadronic Z decays collected by the ALEPH experiment at LEP. Events are selected with two leptons present, on opposite sides of the event and with high transverse momentum. The leptons are expected to be dominantly from b decays; a topological vertexing technique is applied to measure the decay length of the b hadrons, and their momentum is determined using an energy-flow method. The fraction of events in which the leptons have the same charge is studied as a function of the measured decay time, and clear evidence is seen for the time-dependent nature of Bd0Bd0 mixing. The frequency measured for the oscillation corresponds to a mass difference for the Bd0 mass eigenstates Δmd = (3.3−0.4+0.5 ± 0.7) × 10−4 eV/c2. Allowing a second frequency component for the Bs0 a high value for Δms is favoured, leading to the limit Δms > 12 × 10−4 eV/c2 (95% CL), from which (Δm/Γ)s > 2.0 is derived.

From a sample of 150 000 hadronic Z decays collected with the ALEPH detector at LEP, events containing prompt leptons are used to measure the forward-backward asymmetries for the channels Z→bb and Z→cc, giving the results AFBb=0.126±0.028±0.012 and AFBc=0.064±0.039±0.030. These asymmetries correspond to the value of effective electroweak mixing angle at the Z mass sin2θW(mZ2) = 0.2262±0.0053.

A search has been made for a very light Higgs boson in the processes e+e- → e+e-H and e+e- →μ+μ-H using data collected by ALEPH at the LEP e+e- collider at centre of mass energies close to the Z peak. The mass range between 0 and 57 MeV is unambigously excluded at the 95% confidence level. If we combine this with our previously published analysis, the complete range from 0 to 24 GeV is excluded at 95% CL. The search is extended to light Higgs bosons of the minimal supersymmetric standard model, with the result that all possibilities of coupling are excluded for Higgs masses below 3 GeV.

A significant charge asymmetry is observed in the hadronic Z decays with the ALEPH detector at LEP. The asymmetry expressed in terms of the difference in momentum weighted charges in the two event hemispheres is measured to be <Qforward>−<Qbackward>= −0.0084±0.0015 (stat.) ±0.0004 (exp. sys.). In the framework of the standard model this can be interpreted as a measurement of the effective electroweak mixing angle, sin2Ow (Mz2=0.2300±0.0034 (stat.) ±0.0010 (exp. sys.) ±0.0038 (theor. sys.) or of the ratio of the vector to axual- vector coupling costants of the electron, gvegAe=+0.073±0.024.

The production of neutral strange particlesK s o , Λ and % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaacciGaf83MdW% Kbaebaaaa!3780! $$\bar \Lambda $$ has been studied in 60 and 200 GeV per nucleon OAu and pAu collisions with the streamer chamber vertex spectrometer of the NA35 experiment at the CERN-SPS accelerator. Ratios of neutral strange particle production to negatively charged particle production in selected regions of phase space were measured to be the same in OAu and pAu reactions. The rates of strange particle production in central OAu collisions are about a factor of 16 higher than in pAu collisions when compared in the same regions of phase space. If an enhancement of strange particle production in OAu collisions relative to pAu collisions is considered to be a signature for quark-gluon plasma formation, no evidence supporting it is observed. The experimental results are compared to the Lund FRITIOF model.

Interactions of 200-GeV/c protons on hydrogen, neon, argon, and xenon were studied with a streamer-chamber spectrometer. The number of projectile collisions inside the nucleus and the number of secondary collisions in the intranuclear cascade were estimated. The dependence of multiplicity and rapidity distributions on the number of projectile collisions was analyzed. The predictions of the additive quark model were found to be in qualitative agreement with the results of the experiment.

Interactions of 150 GeV pions and 300 GeV pions and protons on hydrogen which result in final states with large transverse energy in the central rapidity region −0.88 < y < 0.67 were studied with a calorimeter trigger. The dependence of the cross section on the azimuthal acceptance of the trigger, on the beam energy and on the incident particle type and the jet properties of the events were investigated. No dominant two-jet structure was found. Nevertheless, the parton spectrum in the colliding hadrons appears to be relevant for large transverse energy reactions.

From approximately 3 million hadronic decays of Z bosons recorded with the aleph detector at lep, a sample of 410 ± 32 B0→ D∗+ℓ−νℓ candidates is selected, where ℓ is either an electron or a muon. The differential decay rate dΓ (B0→ D∗+ℓ−νℓ)dω from this sample is fitted, yielding a value for the product of the CKM matrix element |Vcb| and the normalisation of the decay form factor at the point of zero recoil of the D∗+ meson F(ω = 1)|Vcb| = (31.4 ± 2.3stat ± 2.5syst) × 10−3. A value for |Vcb| is extracted using theoretical calculations of the form factor normalisation, with the result |Vcb| = (34.5 ± 2.5stat ± 2.7syst ± 1.5theory) × 10−3. From the integrated s the measured branching fraction is Br(B0→ D∗+ℓ−νℓ) = (5.18 ± 0.30stat± 0.62syst)%.

Using a sample of about 1.46 million hadronic Z decays collected between 1991 and 1993 with the ALEPH detector at LEP, the energy distribution of the B0 and B± mesons produced at the Z resonance is measured by reconstructing semileptonic decays B → ℓνℓD(X) or B→ ℓνℓD∗+(X). The charmed mesons are reconstructed through the decay modes D0 → K−π+, D0 → K−π+π−π+, D+ → K−π+π+ and D∗+→ D0π+. The neutrino energy is estimated from the missing energy in the lepton hemisphere. Accounting for B∗ and B∗∗ production, the shape of the scaled energy distribution xE(b) for mesons containing a b quark is compared to the predictions of different fragmentation models. The mean value of xE(b) is found to be 〈xE(b)〉 = 0.715 ± 0.007(stat) ± 0.013(syst).

The Λb polarization in hadronic Z decays is measured in semileptonic decays from the average energies of the charged lepton and the neutrino. In a data sample of approximately 3 million hadronic Z decays collected by the ALEPH detector at LEP between 1991 and 1994, 462 ± 31 Λb candidates are selected using (Λπ+)-lepton correlations. From this event sample, the Λb polarization is measured to be PΛb = −0.23−0.20+0.24(stat.)−0.07+0.08(syst.).

Using the 18.8 pb−1 of data accumulated at LEP in 1990 and 1991 with the ALEPH detector, a direct test of neutral current CP-invariance is performed by a search for CP-odd correlations in Z decays to τ pairs where both τ decay modes are identified. No evidence for CP-violation is observed. The weak dipole moment of the τ has been measured to be dτ(mZ) = (1.3 ± 1.4 ± 0.1) × 10−17 e·cm which results in an upper limit on the weak dipole moment of |dτ(mZ)| ⩽ 3.7 × 10−17 e·cm with 95% confidence level.

The reaction e+e− → HZ∗ is used to search for the standard model Higgs boson in the Hνν and the Hℓ+ℓ− channels. The data sample corresponds to about 4.5 million hadronic Z decays collected by the ALEPH experiment at LEP from 1989 to 1995 at centre-of-mass energies at and around the Z peak. Three candidate events are found in the Hμ+μ− channel, in agreement with the expected background from the electroweak process e+e− ℓ+ℓ−qq. This search results in a 95% C.L. lower limit on the Higgs boson mass of 63.9 GeV/c2.

Data taken with the ALEPH detector at LEP1 have been used to search for gamma gamma production of the glueball candidates f0(1500) and fJ(1710) via their decay to pi+pi-. No signal is observed and upper limits to the product of gamma gamma width and pi+pi- branching ratio of the f0(1500) and the fJ(1710) have been measured to be Gamma_(gamma gamma -&gt; f0(1500)). BR(f0(1500)-&gt;pi+pi-) &lt; 0.31 keV and Gamma_(gamma gamma -&gt; fJ(1710)). BR(fJ(1710)-&gt;pi+pi-) &lt; 0.55 keV at 95% confidence level.

The lifetimes of the B0 and B− mesons have been measured with the ALEPH detector at LEP. Semileptonic decays of B0 and B− mesons were partially reconstructed by identifying events containing a lepton with an associated D∗+orD0 meson. The proper time of the B meson was estimated from the measured decay length and the momentum and mass of the D-lepton system. A fit to the proper time of 77 D∗+ℓ− and 77 D0ℓ− candidates, combined with a constraint on the lifetime ratio (τ−τ0) arising from the relative rates of observed D∗+ℓ− and D0ℓ− events, yielded the following lifetimes: τ0=1.52−0.18+0.20(stat.)−0.13+0.07(syst.)ps, τ−= 1.47−0.19+0.22(stat.)−0.14+0.15(syst.)ps,τ−τ0= 0.96−0.15+0.19(stat.)−0.12+0.18(syst.).

A search for the pseudoscalar meson ηb is performed in two-photon interactions at LEP 2 with an integrated luminosity of 699 pb−1 collected at e+e− centre-of-mass energies from 181 GeV to 209 GeV. One candidate event is found in the six-charged-particle final state and none in the four-charged-particle final state, in agreement with the total expected background of about one event. Upper limits of Γγγ(ηb)×BR(ηb→4charged particles)<48 eV, Γγγ(ηb)×BR(ηb→6charged particles)<132 eV are obtained at 95% confidence level, which correspond to upper limits of 9.0% and 25% on these branching ratios.

Using a missing energy tag, evidence is presented for the decay b → τ−ντX, and its branching ratio is measured to be (4.08 ± 0.76 ± 0.62)%.

The envisaged upgrade of the Large Hadron Collider (LHC) at CERN towards the Super-LHC (SLHC) with a 10 times increased luminosity of 1035 cm−2 s−1 will present severe challenges for the tracking detectors of the SLHC experiments. Unprecedented high radiation levels and track densities and a reduced bunch crossing time in the order of 10 ns as well as the need for cost effective detectors have called for an intensive R&D program. The CERN RD50 collaboration "Development of Radiation Hard Semiconductor Devices for Very High Luminosity Colliders" is working on the development of semiconductor sensors matching the requirements of the SLHC. Sensors based on defect engineered silicon like Czochralski, epitaxial and oxygen enriched silicon have been developed. With 3D, Semi-3D and thin detectors new detector concepts have been evaluated and a study on the use of standard and oxygen enriched p-type silicon detectors revealed a promising approach for radiation tolerant cost effective devices. These and other most recent advancements of the RD50 collaboration are presented.

In 160 000 hadronic Z decays recorded with the ALEPH detector at LEP, the yields of Λℓ− and Λℓ+ combinations have been measured. The observed excess of Λℓ− over Λℓ+ of 53±13 is interpreted as evidence for b baryons and their semileptonic decay. Assuming that three body decay processes such as Λb→Λc+ℓ−v dominate the semileptonic decay of b baryons, this ex cess corresponds to a product branching ratio BR(b→Λb)·BR(Λb→Λc+ℓ−v)·BR(Λc+→ΛX) = (0.95±0.22 (stat.)±0.21(syst.))%, where Λb and Λc+ denote the bottom and charm baryons respectively.

From a data sample of 450 000 hadronic events recorded with the ALEPH detector at LEP, 92±10 events are observed containing a J/ψ meson decaying to μ+μ− or e+e−. From these data the measured inclusive branching fraction for a b flavoured hadron to decay to a J/ψ is BR(b→ J/ψX) = (1.21±0.13 (stat.)±0.08 (syst.))%, and the average b hadron lifetime in the events tagged with a J/ψ is τb = 1.35+0.19−0.17±0.05 ps. Five events are observed consistent with the exclusive decay B± → J/ψK± and from these events the exclusive branching fraction is measured to be BR(B± → J/ψK±) = (0.22±0.10±0.02)%. Upper limits for other exclusive branching ratios are given.

The proposed luminosity upgrade of the Large Hadron Collider (S-LHC) at CERN will demand the innermost layers of the vertex detectors to sustain fluences of about 1016 hadrons/cm2. Due to the high multiplicity of tracks, the required spatial resolution and the extremely harsh radiation field new detector concepts and semiconductor materials have to be explored for a possible solution of this challenge. The CERN RD50 collaboration “Development of Radiation Hard Semiconductor Devices for Very High Luminosity Colliders” has started in 2002 an R&D program for the development of detector technologies that will fulfill the requirements of the S-LHC. Different strategies are followed by RD50 to improve the radiation tolerance. These include the development of defect engineered silicon like Czochralski, epitaxial and oxygen-enriched silicon and of other semiconductor materials like SiC and GaN as well as extensive studies of the microscopic defects responsible for the degradation of irradiated sensors. Further, with 3D, Semi-3D and thin devices new detector concepts have been evaluated. These and other recent advancements of the RD50 collaboration are presented and discussed.

We have measured $〈{p}_{\ensuremath{\perp}}〉$ as a function of multiplicity for the reaction proton (antiproton) on proton, neon, argon, and xenon. For all reactions, $〈{p}_{\ensuremath{\perp}}〉$ is independent of multiplicity. We observed that the pion-emission volume is the same for both hydrogen and xenon targets and has a radius about 1.5 fm. Our analysis shows no indication of a deconfinement phase transition in nuclear matter.

In current particle physics experiments, silicon strip detectors are widely used as part of the inner tracking layers. A foreseeable large-scale application for such detectors consists of the luminosity upgrade of the Large Hadron Collider (LHC), the super-LHC or sLHC, where silicon detectors with extreme radiation hardness are required. The mission statement of the CERN RD50 Collaboration is the development of radiation-hard semiconductor devices for very high luminosity colliders. As a consequence, the aim of the R&D programme presented in this article is to develop silicon particle detectors able to operate at sLHC conditions. Research has progressed in different areas, such as defect characterisation, defect engineering and full detector systems. Recent results from these areas will be presented. This includes in particular an improved understanding of the macroscopic changes of the effective doping concentration based on identification of the individual microscopic defects, results from irradiation with a mix of different particle types as expected for the sLHC, and the observation of charge multiplication effects in heavily irradiated detectors at very high bias voltages.

The KM3NeT infrastructure consists of two deep-sea neutrino telescopes being deployed in the Mediterranean Sea. The telescopes will detect extraterrestrial and atmospheric neutrinos by means of the incident photons induced by the passage of relativistic charged particles through the seawater as a consequence of a neutrino interaction. The telescopes are configured in a three-dimensional grid of digital optical modules, each hosting 31 photomultipliers. The photomultiplier signals produced by the incident Cherenkov photons are converted into digital information consisting of the integrated pulse duration and the time at which it surpasses a chosen threshold. The digitization is done by means of time to digital converters (TDCs) embedded in the field programmable gate array of the central logic board. Subsequently, a state machine formats the acquired data for its transmission to shore. We present the architecture and performance of the front-end firmware consisting of the TDCs and the state machine.

The production of final states involving one or more energetic photons from e+e− collisions is studied in a sample of 58.5pb−1 of data recorded at a centre-of-mass energy of 183 GeV by the ALEPH detector at LEP. The e+e−→νν̄γ(γ) and e+e−→γγ(γ) cross sections are measured. The data are in good agreement with predictions based on the Standard Model and are used to set upper limits on the cross sections for anomalous photon production in the context of two supersymmetric models and for various extensions to QED. In particular, in the context of a super-light gravitino model a cross section upper limit of 0.38 pb is placed on the process e+e−→G̃G̃γ, allowing a lower limit to be set on the mass of the gravitino. Limits are also set on the mass of the lightest neutralino in Gauge Mediated Supersymmetry Breaking models. In the case of equal ee∗γ and eeγ couplings a 95% C.L. lower limit on Me∗ of 250GeV/c2 is obtained.

ALEPH's published measurement of Rb = Γ(Z → bb)Γ(Z → hadrons) using a lifetime tag is updated using the full LEP 1 data sample. Considerable effort has been devoted to understanding systematic effects. Charm background is better controlled by combining the lifetime tag with a tag based on the bc hadron mass difference. Furthermore, the algorithm used to reconstruct the event primary vertex is designed so as to reduce correlations between the two hemispheres of an event. The value of Rb is measured to be 0.2167 ± 0.0011(stat) ± 0.0013(syst).

In June 1996, the LEP centre-of-mass energy was raised to 161 GeV. Pair production of W bosons in e+e− collisions was observed for the first time by the LEP experiments. An integrated luminosity of 11 pb−1 was recorded in the ALEPH detector, in which WW candidate events were observed. In 6 events both Ws decay leptonically. In 16 events, one W decays leptonically, the other into hadrons. In the channel where both Ws decay into hadrons, a signal was separated from the large background by means of several multi-variate analyses. The W pair cross-section is measured to be σWW = 4.23 ± 0.73 (stat.) ± 0.19 (syst.) pb. From this cross-section, the W mass is derived within the framework of the Standard Model: mW = 80.14 ± 0.34 (stat.) ± 0.09 (syst.) ± 0.03 (LEP energy) GeV/c2

In 450 000 hadronic Z decays recorded with the ALEPH detector at LEP, the yields of Ds−ℓ+ and Λc+ℓ− combinations have been measured. 16.0 ± 4.3 Ds−ℓ+ combinations were observed in the Ds− → ππ− channel and 17.0 ± 4.5 combinations were observed in the Ds−→K∗0K− channel. 21.0 ± 5.0 Λc+ℓ− combinations were observed, with the Λc+ reconstructed in the decay mode Λc+ → pK−π+. These events provide evidence for the decays Bs→Ds−Xℓ+νandΛb→ Λc+Xℓ−ν. Assuming that the Bs and Λb semileptonic decays are dominantly three-body, these observed yields, after background subtraction, translate into the following product branching ratios: Br(b→Bs)Br(Bs→Ds−Xℓ+ν) = 0.040±0.011−0.012+0.010, Br(b→ Λb)Br(Λb→ Λc+Xℓ−ν) = 0.030±0.007±0.009.

Precise values of theZ resonance cross sections and lepton pair forward-backward asymmetries are measured from a sample of 1.3 millionZ decays into hadrons and charged leptons taken with the ALEPH detector at LEP. A silicon-tungsten luminosity calorimeter was installed in ALEPH in 1992, permitting the determination of the absolute luminosity to a systematic precision of 0.15% (experimental) and 0.25% (theoretical). This is combined with a better understanding of the hadronic event selection and an improved tau pair selection. Including the ALEPH results of the past three years one obtains σ 0 =(41.60±0.16) nb, andR l =20.69±0.09. The corresponding number of light neutrino species isN v =2.983±0.034. The lepton pair forward-backward asymmetry is used to derive the ratio of vector to axial-vector couplings of leptons:g 2 (M 2 )/g 2 (M 2 )=0.0058 ±0.0011. An application of these results to constrain one model with extraZ bosons is presented.

We study electron-positron annihilations into six jets at the parton level in perturbative Quantum Chromo-Dynamics (QCD), via the elementary processes ϵ+ϵ− → qq−gggg, ϵ+ϵ− → qq−q′q−′ gg and ϵ+ϵ− → qq−q′q−′q″q−″, for massive quarks q, q′ and q″ and massless gluons g. Several numerical results of phenomenological relevance are given, at three different collider energies and for a representative selection of jet clustering algorithms. We also present helicity amplitudes and colour factors needed for the tree-level calculation.

In a sample of about 1.1 million hadronic Z decays recorded with the ALEPH detector during the 1990–1992 running of LEP, two unambiguous BS meson candidates were observed. From these events the mass of the BS meson has been measured to be 5.3686 ± 0.0056 (stat.) ± 0.0015 (syst.) GeV.

We report on the properties of theZ resonance from 62 500Z decays into fermion pairs collected with the ALEPH detector at LEP, the Large Electron-Positron storage ring at CERN. We findM Z=(91.193±0.016exp±0.030LEP) GeV, Γ Z =(2497±31) MeV, σ had 0 =(41.86±0.66)nb, and for the partial widths Γinv=(489±24) MeV, Γhad(1754±27) MeV, Γ ee =(85.0±1.6)MeV, Γ μμ =(80.0±2.5) MeV, and Γττ=(81.3±2.5) MeV, all in good agreement with the Standard Model. Assuming lepton universality and using a lepton sample without distinction of the final state we measure Γu=(84.3±1.3) MeV. The forward-backward asymmetry in leptonic decays is used to determine the vector and axial-vector weak coupling constants of leptors,g v 2 (M 2 )=(0.12±0.12)×10−2 andg A 2 (M 2 )=0.2528±0.0040. The number of light neutrino species isN ν=2.91±0.13; the electroweak mixing angle is sin2θW(M Z 2 )=0.2291±0.0040.

A search for events with a photon pair arising from the decay of a Higgs boson produced in association with a fermion pair, is performed in 893 pb−1 of data recorded by the ALEPH detector at LEP at centre-of-mass energies up to 209 GeV. No excess of such events is found over the expected background. An upper limit is derived on the product of the e+e−→HZ cross section and the H→γγ branching fraction as a function of the Higgs boson mass. A fermiophobic Higgs boson produced with the Standard Model cross section is excluded at 95% confidence level for all masses below 105.4 GeV/c2.

From more than 175 000 hadronic Z decays observed with the ALEPH detector at LEP, we select 823 events with pairs of leptons in the final state. From these we measure χ, the probability thata b hadron which is observed to decay originated as a b hadron. We find χ=0.132−0.026+0.027.