D. Contardo

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.

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.

This Technical Proposal presents the upgrades foreseen to prepare the CMS experiment for the High Luminosity LHC. In this second phase of the LHC physics program, the accelerator will provide to CMS an additional integrated luminosity of about 2500 fb-1 over 10 years of operation, starting in 2025. This will substantially enlarge the mass reach in the search for new particles and will also greatly extend the potential to study the properties of the Higgs boson discovered at the LHC in 2012. In order to meet the experimental challenges of unprecedented p-p luminosity, the CMS collaboration will need to address the aging of the present detector and to improve the ability of the apparatus to isolate and precisely measure the products of the most interesting collisions. This document describes the conceptual designs and the expected performance of the upgrades, along with the plans to develop the appropriate experimental techniques. The infrastructure upgrades and the logistics of the installation in the experimental area are also discussed. Finally, the initial cost estimates of the upgrades are presented.

Data for the Δ excitation by the (3He,t) reaction at 2.0 GeV on various nuclei are presented together with results on 12C at 1.5 and 2.3 GeV. The Δ peak position and width are found to be target mass independent. Comparison with the p(3He,t) Δ++ reaction, however, shows a shift of the position in energy of the Δ peak. Implications of these results are discussed.

The European Particle Physics Strategy Update (EPPSU) process takes a bottom-up approach, whereby the community is first invited to submit proposals (also called inputs) for projects that it would like to see realised in the near-term, mid-term and longer-term future. National inputs as well as inputs from National Laboratories are also an important element of the process. All these inputs are then reviewed by the Physics Preparatory Group (PPG), whose role is to organize a Symposium around the submitted ideas and to prepare a community discussion on the importance and merits of the various proposals. The results of these discussions are then concisely summarised in this Briefing Book, prepared by the Conveners, assisted by Scientific Secretaries, and with further contributions provided by the Contributors listed on the title page. This constitutes the basis for the considerations of the European Strategy Group (ESG), consisting of scientific delegates from CERN Member States, Associate Member States, directors of major European laboratories, representatives of various European organizations as well as invitees from outside the European Community. The ESG has the mission to formulate the European Strategy Update for the consideration and approval of the CERN Council.

The CMS detector at the CERN LHC features a silicon pixel detector as its innermost subdetector. The original CMS pixel detector has been replaced with an upgraded pixel system (CMS Phase-1 pixel detector) in the extended year-end technical stop of the LHC in 2016/2017. The upgraded CMS pixel detector is designed to cope with the higher instantaneous luminosities that have been achieved by the LHC after the upgrades to the accelerator during the first long shutdown in 2013–2014. Compared to the original pixel detector, the upgraded detector has a better tracking performance and lower mass with four barrel layers and three endcap disks on each side to provide hit coverage up to an absolute value of pseudorapidity of 2.5. This paper describes the design and construction of the CMS Phase-1 pixel detector as well as its performance from commissioning to early operation in collision data-taking.

We have succeeded in measuring at 0\ifmmode^\circ\else\textdegree\fi{} and small angles the energy spectra for the (d,2p${[\mathrm{}}^{1}$${S}_{0}$]) reaction (with the two protons in the singlet S state) at 650 MeV and 2 GeV. It is demonstrated that the reaction is a one-step process that can be used to study isospin-spin excitations. The \ensuremath{\Delta} excitation is very clearly observed. A shift down in energy of the \ensuremath{\Delta} peak from the proton to the $^{12}\mathrm{C}$ target is observed. The experiments are performed with a tensor polarized beam and the tensor analyzing power for the p(${d}_{\mathrm{pol}}$,${\mathrm{}}^{2}$He)n reaction at 2 GeV is given.

In a search for quark-gluon plasma formation, the production of J/ψ and muon pairs in the mass continuum region is studied in oxygen-uranium and sulphur-uranium interactions. The yield of J/ψ relative to the continuum is measured to be a decreasing function of the neutral transverse energy produced in the collision, i.e. of the energy density. A comparison is made with proton-uranium reactions.

The (3He, t) reaction has been studied at intermediate energies, 600 MeV–2.3 GeV. The reaction is a single-step direct reaction, and the angular distributions are well described by DWIA calculations. At these energies the σρ component of the interaction dominates. The ratio of the isovector strengths ¦Jσρ/ρ¦ derived from the data on 13C appears to remain roughly constant in the energy range 300–700 MeV per nucleon. The triton spectra exhibit a prominent quasi-free peak. The data at momentum transfers q ⪢ 1.7 fm−1 show a shift of the peak towards smaller energy loss than observed in (e, e') experiments at corresponding four-momentum transfers. The shift becomes progressively larger with increasing q and is about 45 MeV at q = 2.5 fm−1. The shift may be caused by particle-hole correlations in the spin-longitudinal channel.

Excitation of the Δ resonance is observed for the first time with heavy ions. It is very strong in the two mirror charge-exchange reactions (20Ne, 20F) and (20Ne, 20Na) at 950 MeV per nucleon. With similar incident energies per nucleon, the Δ is weakly excited with a 14N beam and nearly absent with a 12C beam. The role of the ejectile bound states is discussed.

Data are presented for the p(3He,t)Δ++ reaction at 2.0, 2.3 and 1.5 GeV. The reaction specifically excites the Δ++ with very little yield outside the resonance. The data are analysed as one pion exchange and the hadronic form factor for the 3He−1 system is extracted and compared with the magnetic form factor from electron scattering.

The result of a search at the LHC for heavy stable charged particles produced in pp collisions at $ \sqrt {s} = 7\;{\text{TeV}} $ is described. The data sample was collected with the CMS detector and corresponds to an integrated luminosity of 3.1 pb−1. Momentum and ionization-energy-loss measurements in the inner tracker detector are used to identify tracks compatible with heavy slow-moving particles. Additionally, tracks passing muon identification requirements are also analyzed for the same signature. In each case, no candidate passes the selection, with an expected background of less than 0.1 events. A lower limit at the 95% confidence level on the mass of a stable gluino is set at 398GeV/c 2, using a conventional model of nuclear interactions that allows charged hadrons containing this particle to reach the muon detectors. A lower limit of 311 GeV/c 2 is also set for a stable gluino in a conservative scenario of complete charge suppression, where any hadron containing this particle becomes neutral before reaching the muon detectors.

Hadronic event shapes have been measured in proton-proton collisions at sqrt(s)=7 TeV, with a data sample collected with the CMS detector at the LHC. The sample corresponds to an integrated luminosity of 3.2 inverse picobarns. Event-shape distributions, corrected for detector response, are compared with five models of QCD multijet production.

A measurement of the top-antitop production cross section in proton-proton collisions at a centre-of-mass energy of 7 TeV has been performed at the LHC with the CMS detector. The analysis uses a data sample corresponding to an integrated luminosity of 36 inverse picobarns and is based on the reconstruction of the final state with one isolated, high transverse-momentum electron or muon and three or more hadronic jets. The kinematic properties of the events are used to separate the top-antitop signal from W+jets and QCD multijet background events. The measured cross section is 173 + 39 - 32 (stat. + syst.) pb, consistent with standard model expectations.

The charge asymmetry in the production of top quark and antiquark pairs is measured in proton-proton collisions at a center-of-mass energy of 8 TeV. The data, corresponding to an integrated luminosity of 19.6 inverse femtobarns, were collected by the CMS experiment at the LHC. Events with a single isolated electron or muon, and four or more jets, at least one of which is likely to have originated from hadronization of a bottom quark, are selected. A template technique is used to measure the asymmetry in the distribution of differences in the top quark and antiquark absolute rapidities. The measured asymmetry is A[c,y] = [0.33 +/- 0.26 (stat) +/- 0.33 (syst)]%, which is the most precise result to date. The results are compared to calculations based on the standard model and on several beyond-the-standard-model scenarios.

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.

Ψ′ and J/Ψ yields are compared in p-W, p-U and S-U interactions at 200 GeV/nucleon. Their ratio decreases from proton-t to sulphur-induced reactions. It also decreases in sulphur-induced reactions from peripheral to central collisions. This result could indicate that the Ψ′ and J/Ψ suppression mechanisms have different origins in p- and S-induced reactions.

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.

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 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.

Spin structure and cross section data for Δ production in the (n, p-like reaction (d, 2p[1S0]) on p, d and 12C targets are presented. At laboratory kinetic energies 2 GeV and 1.6 GeV, and forward scattering angles, we find dominance of spin transverse over spin longitudinal cross section for free Δ production. On the nucleus 12C we find significant enhancement of the transverse dominance, and a large downwards shift in the peak position of the laboratory energy transfer associated with the production of the Δ.

The upgrade of the LHC to the High-Luminosity LHC (HL-LHC) is expected to increase the LHC design luminosity by an order of magnitude. This will require silicon tracking detectors with a significantly higher radiation hardness. The CMS Tracker Collaboration has conducted an irradiation and measurement campaign to identify suitable silicon sensor materials and strip designs for the future outer tracker at the CMS experiment. Based on these results, the collaboration has chosen to use n-in-p type silicon sensors and focus further investigations on the optimization of that sensor type. This paper describes the main measurement results and conclusions that motivated this decision.

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.

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.

Data for the (3He, t) reaction at 900 MeV and 2 GeV on the targets 26Mg, 40Ca, 48Ca, 54Fe, 90Zr and 208Pb are presented. A multipole decomposition for the data at 900 MeV has been made and the different distributions have been analysed. From the L = 0 cross section the Gamow-Teller strength distributions are extracted and compared with (p, n) data. The L = 1 and 2 distributions are analysed in a schematic model which describes the general systematics fairly well. The spectra at 2 GeV and Θ = 4° show for all targets a well-developed quasi-elastic peak. The A-dependence of the cross section is analysed in a simple model.

Low mass muon pair production at high PT and low XF studied in pU, OU and SU 200 GeV per nucleon react ions. When energy density or projectile mass are increased, φ production is enhanced as compared with the yield of muon pairs in the mass continuum (1.7<Mμμ< 2.4 GeV/c2), whereas the production of ω and ϱ, experimentally unresolved, remains approximately constant. This φ enhancement is in agreement with predictions based on quark-gluon plasma formation and, together with the previously reported J/Ψ suppression, puts severe constraints on a purely hadronic description of nucleus-nucleus collisions.

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.

The mean squared transverse momentum of J/ψ's measured in pCu, pU, OCu, OU and SU collisions at 200 GeV/ nucleon is analyzed in terms of initial state interactions. Taking this effect into account, the mechanism which suppresses the J/ψ production in ion-induced collisions would only have a weak PT dependence.

We describe the “drift chamber” detection setup of SPES4, the 4 GeV/c spectrometer at Laboratoire National Saturne. The particle identification is performed by combining magnetic rigidity selection with energy loss and time of flight measurements. This allows to separate analysed isotopes from Z = 1 to at least Z = 10 up to a rigidity of 4 GeV/c. A charge resolution of ΔZrms = 0.1 and a time resolution of Δtrms = 120 ps for 18Ne at about 3 GeV/c per Z are easily obtained. Two sets of multiwire drift chambers are used to measure and reconstruct the particle trajectories at the output of the system. A position resolution better than Δxrms = 160 μm can be achieved in the focal plane. This corresponds to a momentum resolution of Δδrms = 0.22 × 10−4. The performances of SPES4 (Δδrms = 2.2 × 10−4) can then be wholly exploited.

The degradation of signal in silicon sensors is studied under conditions expected at the CERN High-Luminosity LHC. 200 μm thick n-type silicon sensors are irradiated with protons of different energies to fluences of up to 3 · 1015 neq/cm2. Pulsed red laser light with a wavelength of 672 nm is used to generate electron-hole pairs in the sensors. The induced signals are used to determine the charge collection efficiencies separately for electrons and holes drifting through the sensor. The effective trapping rates are extracted by comparing the results to simulation. The electric field is simulated using Synopsys device simulation assuming two effective defects. The generation and drift of charge carriers are simulated in an independent simulation based on PixelAV. The effective trapping rates are determined from the measured charge collection efficiencies and the simulated and measured time-resolved current pulses are compared. The effective trapping rates determined for both electrons and holes are about 50% smaller than those obtained using standard extrapolations of studies at low fluences and suggest an improved tracker performance over initial expectations.

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.

Results on the Δ excitation by heavy ion charge exchange are presented. 900 MeV per nucleon 12C, 16O, 20Ne and 1100 MeV per nucleon 12C have been used. The Δ excitation strength depends on the projectile — ejectile nature and on the incident energy. The role of the target mass is also discussed. The peak for the Δ in nuclei is energy shifted from the free Δ peak.

The dimuon production in 200 GeV/nucleon O-U, O-Cu, S-U and p-U reactions is studied in function of transverse energy ET produced by the collision. The J/ψ production relative to continuum events is suppressed for heavy ion induced reactions when ET increases. This suppression is enhanced at low transverse momentum. The π and K meson distributions extracted from the data, have, for each reaction, a similar average transverse momentum which increases only slightly with the transverse energy.

During summer 2006 a fraction of the CMS silicon strip tracker was operated in a comprehensive slice test called the Magnet Test and Cosmic Challenge (MTCC). At the MTCC, cosmic rays detected in the muon chambers were used to trigger the readout of all CMS sub-detectors in the general data acquisition system and in the presence of the 4 T magnetic field produced by the CMS superconducting solenoid. This document describes the operation of the Tracker hardware and software prior, during and after data taking. The performance of the detector as resulting from the MTCC data analysis is also presented.

A new CMS tracker detector will be installed for operation at the High Luminosity LHC (HL-LHC). This detector comprises modules with two closely spaced parallel sensor plates and front-end ASICs capable of transmitting tracking information to the CMS Level-1 (L1) trigger at the 40 MHz beam crossing rate. The inclusion of tracking information in the L1 trigger decision will be essential for selecting events of interest efficiently at the HL-LHC. The CMS Binary Chip (CBC) has been designed to read out and correlate hits from pairs of tracker sensors, forming so-called track stubs. For the first time, a prototype irradiated module and a full-sized module, both equipped with the version 2 of the CBC, have been operated in test beam facilities. The efficiency of the stub finding logic of the modules for various angles of incidence has been studied. The ability of the modules to reject tracks with transverse momentum less than 2 GeV has been demonstrated. For modules built with irradiated sensors, no significant drop in the stub finding performance has been observed. Results from the beam tests are described in this paper.

To cope with the challenging environment of the planned high luminosity upgrade of the Large Hadron Collider (HL-LHC), scheduled to start operation in 2029, CMS will replace its entire tracking system. The requirements for the tracker are largely determined by the long operation time of 10 years with an instantaneous peak luminosity of up to 7.5 × 1034 cm−2 s−1 in the ultimate performance scenario. Depending on the radial distance from the interaction point, the silicon sensors will receive a particle fluence corresponding to a non-ionising energy loss of up to Φeq= 3.5 × 1016 cm−2. This paper focuses on planar pixel sensor design and qualification up to a fluence of Φeq = 1.4 × 1016 cm−2.For the development of appropriate planar pixel sensors an R&D program was initiated, which includes n+-p sensors on 150 mm (6”) wafers with an active thickness of 150 µm with pixel sizes of 100×25 µm2 and 50×50 µm2 manufactured by Hamamatsu Photonics K.K. (HPK). Single chip modules with ROC4Sens and RD53A readout chips were made. Irradiation with protons and neutrons, as well was an extensive test beam campaign at DESY were carried out. This paper presents the investigation of various assemblies mainly with ROC4Sens readout chips. It demonstrates that multiple designs fulfil the requirements in terms of breakdown voltage, leakage current and efficiency. The single point resolution for 50×50 µm2 pixels is measured as 4.0 µm for non-irradiated samples, and 6.3 µm after irradiation to Φeq = 7.2 × 1015 cm−2.

Abstract The Large Hadron Collider at CERN will undergo an upgrade in order to increase its luminosity to 7.5 × 10 34 cm -2 s -1 . The increased luminosity during this High-Luminosity running phase, starting around 2029, means a higher rate of proton-proton interactions, hence a larger ionizing dose and particle fluence for the detectors. The current tracking system of the CMS experiment will be fully replaced in order to cope with the new operating conditions. Prototype planar pixel sensors for the CMS Inner Tracker with square 50 μm × 50 μm and rectangular 100 μm × 25 μm pixels read out by the RD53A chip were characterized in the lab and at the DESY-II testbeam facility in order to identify designs that meet the requirements of CMS during the High-Luminosity running phase. A spatial resolution of approximately 3.4 μm (2 μm) is obtained using the modules with 50 μm × 50 μm (100 μm × 25 μm) pixels at the optimal angle of incidence before irradiation. After irradiation to a 1 MeV neutron equivalent fluence of Φ eq = 5.3 × 10 15 cm -2 , a resolution of 9.4 μm is achieved at a bias voltage of 800 V using a module with 50 μm × 50 μm pixel size. All modules retain a hit efficiency in excess of 99% after irradiation to fluences up to 2.1 × 10 16 cm -2 . Further studies of the electrical properties of the modules, especially crosstalk, are also presented in this paper.

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 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 March 2007 the assembly of the Silicon Strip Tracker was completed at the Tracker Integration Facility at CERN. Nearly 15% of the detector was instrumented using cables, fiber optics, power supplies, and electronics intended for the operation at the LHC. A local chiller was used to circulate the coolant for low temperature operation. In order to understand the efficiency and alignment of the strip tracker modules, a cosmic ray trigger was implemented. From March through July 4.5 million triggers were recorded. This period, referred to as the Sector Test, provided practical experience with the operation of the Tracker, especially safety, data acquisition, power, and cooling systems. This paper describes the performance of the strip system during the Sector Test, which consisted of five distinct periods defined by the coolant temperature. Significant emphasis is placed on comparisons between the data and results from Monte Carlo studies.

The results of the CMS tracker alignment analysis are presented using the data from cosmic tracks, optical survey information, and the laser alignment system at the Tracker Integration Facility at CERN. During several months of operation in the spring and summer of 2007, about five million cosmic track events were collected with a partially active CMS Tracker. This allowed us to perform first alignment of the active silicon modules with the cosmic tracks using three different statistical approaches; validate the survey and laser alignment system performance; and test the stability of Tracker structures under various stresses and temperatures ranging from +15 °C to −15 °C. Comparison with simulation shows that the achieved alignment precision in the barrel part of the tracker leads to residual distributions similar to those obtained with a random misalignment of 50 (80) μm RMS in the outer (inner) part of the barrel.

During the high-luminosity phase of the LHC (HL-LHC), planned to start in 2027, the accelerator is expected to deliver an instantaneous peak luminosity of up to 7.5×1034 cm−2 s−1. A total integrated luminosity of 0300 or even 0400 fb−1 is foreseen to be delivered to the general purpose detectors ATLAS and CMS over a decade, thereby increasing the discovery potential of the LHC experiments significantly. The CMS detector will undergo a major upgrade for the HL-LHC, with entirely new tracking detectors consisting of an Outer Tracker and Inner Tracker. However, the new tracking system will be exposed to a significantly higher radiation than the current tracker, requiring new radiation-hard sensors. CMS initiated an extensive irradiation and measurement campaign starting in 2009 to systematically compare the properties of different silicon materials and design choices for the Outer Tracker sensors. Several test structures and sensors were designed and implemented on 18 different combinations of wafer materials, thicknesses, and production technologies. The devices were electrically characterized before and after irradiation with neutrons, and with protons of different energies, with fluences corresponding to those expected at different radii of the CMS Outer Tracker after 0300 fb−1. The tests performed include studies with β sources, lasers, and beam scans. This paper compares the performance of different options for the HL-LHC silicon sensors with a focus on silicon bulk material and thickness.

The behaviour of the microstrip gas chamber has been studied in strong magnetic fields (up to 2.3 T). An almost complete compensation of the effect due to the E × B factor, which is otherwise responsible for a degradation of the spatial resolution, has been obtained by applying a small tilt to the chamber equal to the Lorentz angle. Different. gas mixtures have been studied: an improvement in the resolution has been achieved using gas mixtures with higher cluster density (DME-CO2, DME-CF4).

One of the proposed solutions for a transverse momentum (pT) based trigger at SLHC for the CMS experiment is based on the concept known as the "cluster width" approach, in which clusters produced by low pT tracks are rejected based on the width of the cluster shape, made either on a single strip sensor or a doublet of strip sensors by a suitable electronics logic at the level of the front-end. This information can then be used in many ways to provide first level trigger primitives. These kinds of modules are inexpensive, and coupled high-speed opto-electronic components this concept provides the simplest solution to the first level trigger for SLHC trackers. We will present the simulation studies aimed to optimize the concept, as well as the basic building blocks of the module and their connectivity. Finally we will provide the experimental validation of it by using data collected by the CMS Tracker during the Cosmic runs in 2008 and 2009 as well as the first collision data from the LHC.

A new pixel detector for the CMS experiment was built in order to cope with the instantaneous luminosities anticipated for the Phase~I Upgrade of the LHC. The new CMS pixel detector provides four-hit tracking with a reduced material budget as well as new cooling and powering schemes. A new front-end readout chip mitigates buffering and bandwidth limitations, and allows operation at low comparator thresholds. In this paper, comprehensive test beam studies are presented, which have been conducted to verify the design and to quantify the performance of the new detector assemblies in terms of tracking efficiency and spatial resolution. Under optimal conditions, the tracking efficiency is $99.95\pm0.05\,\%$, while the intrinsic spatial resolutions are $4.80\pm0.25\,\mu \mathrm{m}$ and $7.99\pm0.21\,\mu \mathrm{m}$ along the $100\,\mu \mathrm{m}$ and $150\,\mu \mathrm{m}$ pixel pitch, respectively. The findings are compared to a detailed Monte Carlo simulation of the pixel detector and good agreement is found.

A search is performed for the production of a massive W′ boson decaying to a top and a bottom quark. The data analysed correspond to an integrated luminosity of 19.7 fb−1 collected with the CMS detector at the LHC in proton-proton collisions at $$ \sqrt{s}=8 $$ TeV. The hadronic decay products of the top quark with high Lorentz boost from the W′ boson decay are detected as a single top flavoured jet. The use of jet substructure algorithms allows the top quark jet to be distinguished from standard model QCD background. Limits on the production cross section of a right-handed W′ boson are obtained, together with constraints on the left-handed and right-handed couplings of the W′ boson to quarks. The production of a right-handed W′ boson with a mass below 2.02 TeV decaying to a hadronic final state is excluded at 95% confidence level. This mass limit increases to 2.15 TeV when both hadronic and leptonic decays are considered, and is the most stringent lower mass limit to date in the tb decay mode.

The design of the Small Gap Chamber combines features of the MicroStrip Gas Chamber [1] and of the MicroGap Chamber [2]. It is a detector for a single coordinate read-out with the single metal layer pattern of a MSGC and the anode-cathode separation of a MGC. A polyimide layer, suitably patterned on top of the metal, ensures an insulation at the edge of the electrodes and defines the conductive areas in front of the gas. We report on the performance measured in a test beam at CERN and with an X-ray tube in the laboratory.

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.

The NA50 segmented target and vertex recognition system is described. The segmented target consists of 7 sub-targets of 1–2 mm thickness. The vertex recognition system used to determine the sub-target where an interaction has occured is based upon quartz elements which produce Čerenkov light when traversed by charged particles from the interaction. The geometrical arrangement of the quartz elements has been optimized for vertex recognition in 208PbPb collisions at 158 GeV/nucleon. A simple algorithm provides a vertex recognition efficiency of better than 85% for dimuon trigger events collected with a 1 mm sub-target set-up. A method for recognizing interactions of projectile fragments (nuclei and/or groups of nucleons) is presented. The segmented target allows a large target thickness which together with a high beam intensity (≈ 107 ions/s) enables high statistics measurements.

Inelastic nuclear collisions of hadrons incident on silicon sensors can generate secondary highly ionising particles (HIPs) and deposit as much energy within the sensor bulk as several hundred minimum ionising particles. The large signals generated by these ‘HIP events’ can momentarily saturate the APV25 front-end readout chip for the silicon strip tracker (SST) sub-detector of the compact muon solenoid (CMS) experiment, resulting in deadtime in the detector readout system. This paper presents studies of this phenomenon through simulation, laboratory measurements and dedicated beam tests. A proposed change to a front-end component to reduce the APV25 sensitivity to HIP events is also examined. The results are used to infer the expected effect on the performance of the CMS SST at the future large hadron collider. The induced inefficiencies are at the percent level and will have a negligible effect on the physics performance of the SST.

The high luminosity upgrade of the Large Hadron Collider, foreseen for 2026, necessitates the replacement of the CMS experiment’s silicon tracker. The innermost layer of the new pixel detector will be exposed to severe radiation, corresponding to a 1 MeV neutron equivalent fluence of up to $$\Phi _{eq} = 2 \times 10^{16}$$ cm $$^{-2}$$ , and an ionising dose of $${\approx } 5$$ MGy after an integrated luminosity of 3000 fb $$^{-1}$$ . Thin, planar silicon sensors are good candidates for this application, since the degradation of the signal produced by traversing particles is less severe than for thicker devices. In this paper, the results obtained from the characterisation of 100 and 200 $$\upmu $$ m thick p-bulk pad diodes and strip sensors irradiated up to fluences of $$\Phi _{eq} = 1.3 \times 10^{16}$$ cm $$^{-2}$$ are shown.

In 2017 a new pixel detector was installed in the CMS detector. This so-called Phase-1 pixel detector features four barrel layers in the central region and three disks per end in the forward regions. The upgraded pixel detector requires an upgraded data acquisition (DAQ) system to accept a new data format and larger event sizes. A new DAQ and control system has been developed based on a combination of custom and commercial microTCA parts. Custom mezzanine cards on standard carrier cards provide a front-end driver for readout, and two types of front-end controller for configuration and the distribution of clock and trigger signals. Before the installation of the detector the DAQ system underwent a series of integration tests, including readout of the pilot pixel detector, which was constructed with prototype Phase-1 electronics and operated in CMS from 2015 to 2016, quality assurance of the CMS Phase-1 detector during its assembly, and testing with the CMS Central DAQ. This paper describes the Phase-1 pixel DAQ and control system, along with the integration tests and results. A description of the operational experience and performance in data taking is included.

Production and decay into two muons of ψI and J/ψ mesons is studied in p-U and S-U interactions at 200 GeV/nucleon. The ratio Bmumuσ(ψl)/Bmumuσ(J/ψ is found to be 0.0201 ± 0.0044 ± 0.0020 in p-U and 0.0093 ± 0.0011 ± 0.0013 in S-U. For S-U interactions, this ratio decreases by about 40% with increasing transverse energy. Our p-U result confirms previous measurements which show that the relative production of ψt and Jψ in p-A interactions is independent of A. The results are discussed in the frame of QGP formation and final state absorption.

Abstract Measurements with variants of micro-gap chambers built on silicon wafers are reported: • - we compare the ability of the detectors to sustain high voltage on the cathodes for two fabrication processes; • - we present results on the measurement of the second coordinate with small stereo angle cathodes and for two kinds of insulating layer on the silicon; • - we discuss a first attempt to build a one-dimensional micro-gap chamber with a single metal layer.

Abstract The Large Hadron Collider (LHC) at CERN will undergo major upgrades to increase the instantaneous luminosity up to 5–7.5×10 34 cm -2 s -1 . This High Luminosity upgrade of the LHC (HL-LHC) will deliver a total of 3000–4000 fb -1 of proton-proton collisions at a center-of-mass energy of 13–14 TeV. To cope with these challenging environmental conditions, the strip tracker of the CMS experiment will be upgraded using modules with two closely-spaced silicon sensors to provide information to include tracking in the Level-1 trigger selection. This paper describes the performance, in a test beam experiment, of the first prototype module based on the final version of the CMS Binary Chip front-end ASIC before and after the module was irradiated with neutrons. Results demonstrate that the prototype module satisfies the requirements, providing efficient tracking information, after being irradiated with a total fluence comparable to the one expected through the lifetime of the experiment.

Following endorsement of the update of the European Strategy for Particle Physics by the CERN council in 2020, ECFA was charged to prepare a Detector R&D roadmap and then to develop an organisation to execute it. This paper oultines the main steps that led to form new Detector Research and Development collaborations, it briefly describes the framework to host them at CERN and highlights the scientific programs and the work plan established by the participating institutes.

A four-dimensional method to unfold NA38 experimental distributions is presented. It is based on the Bayes theorem and uses an iterative procedure. Tests of this method on Monte-Carlo simulated distributions are described. Subtraction of the background is discussed. This method is applied to the S-U data collected in 1992 by the NA38 experiment.

The study of muon pairs in the mass region 1.5 < Mμμ < 2.5 GeV/c2 in 450 GeV/c p-A, 200 GeV/nucleon S-U and 158 GeV/nucleon Pb-Pb collisions is presented. In p-A interactions, the dimuon signal mass spectra are well described by a superposition of Drell-Yan and charmed meson semi-leptonic decay contributions, in agreement with previous experiments when considering a linear A dependence. In nucleus-nucleus reactions, taking only into account these two physical ingredients, a dimuon enhancement both with increasing A·B and centrality is observed.

PoS(EPS-HEP2015)018luminosity by 30%, by the end of Phase II, sets the margin of the detector radiation tolerance to the doses accumulated in 4000 fb -1 .

Abstract During the beam test of a tracker prototype for the Compact Muon Solenoid detector proposed for the LHC, the time response of the Microstrip Gas Chambers was studied using different gases and chamber gaps. The subsequent efficiency to identify the bunch crossing at LHC is discussed for several algorithms used in the off-line signal processing of the data.

Abstract A system of detector modules consisting of a large size Gas Electron Multiplier (GEM), coupled to Micro Strip Gas Counters (MSGC), has been exposed to a pion beam at the Paul Scherrer Institute Cyclotron facility. As part of a CMS tracker milestone, the aim of this test was to investigate the robustness of such detectors when exposed to experimental conditions close to what is expected at the Large Hadron Collider (LHC) of CERN. Eighteen detector modules have been operated at voltage settings corresponding to 98% detection efficiency for Minimum Ionizing Particles during a period of 5 weeks. Sparking rates and strip losses have been monitored throughout the exposure. An operation margin of at least a factor of three with respect to the required gas gain has been demonstrated.

Abstract A central tracking detector based on micro strip gas chambers (MSGC) for the compact muon solenoid (CMS) at LHC is part of a hybrid inner tracking system to be operated in a 4 Tesla magnetic field. Expected performance in terms of momentum resolution, rate capability and long term survivability will be discussed. Considerable efforts in simulation studies have been made, to optimize the tracking system for pattern recognition and track finding efficiencies. A preliminary engineering study on mechanical stability and heat load shows that the detector structures can be made sufficiently stiff to maintain systematic alignment precision within the intrinsic spatial measurement accuracy of the detector.

Two Small Gap Chambers developed for the CMS experiment at LHC were tested in a high-intensity hadron beam at PSI. We discuss the outstanding question of the occurrence of streamers and their effect on the chamber strips.

The capability of Small Gap Chambers to withstand a high flux of hadrons was studied at the Paul Scherrer Institut. We report the observed radiation hardness according to the level of signal required from the chambers.

A prototype of the barrel Tracking Detector of the Compact Muon Solenoid (CMS) experiment proposed for LHC was built and tested in a beam and in a magnetic field of up to 3 T. It contained six microstrip gas chambers, 25 cm long, and three double-sided silicon microstrip detectors, 12.5 cm long. We report some preliminary results on the performance of the chambers.

The production of J/ψ at 200 GeV/N, in proton, oxygen, and sulfur collisions with copper and uranium targets has been studied by the NA38 collaboration. When the energy density reached in the collisions increases a suppression of the muon pairs coming from the J/ψ disintegration, relative to those from the continuum, is observed. This relative suppression is stronger when the J/ψ transverse momentum is smaller.[Journal translation]

Excitation of the Δ resonance has been observed for the first time in a heavy ion reaction. The strength of the Δ signal depends on the projectile nuclear structure. In the same incident energy range, about 900 MeV per nucleon, we observe — a strong Δ excitation in 27Aℓ(20Ne, 20F) and 27Aℓ(20Ne, 20Na), — a weak Δ in 12C(14N, 14C) and — nearly no Δ excitation in (12C, 12B) and (12C, 12N) whatever the target is among a sample of nuclei from 12C to 89Y.

In order to check the system aspects of the forward–backward MSGC tracker designed for the future CMS experiment at LHC, 38 trapezoidal MSGC counters assembled in six multi-substrates detector modules were built and exposed to a muon beam at the CERN SPS. Results on the gain uniformity along the wedge-shaped strip pattern and across the detector modules are shown together with measurements of the detection efficiency and the spatial resolution.

A small series production of detector modules made of MicroStrip Gas Counters (MSGC) and a Gas Electron Multiplier (GEM) foil has been exposed to a high-intensity hadron beam. We report about the reproductibility and stability of the detector responses and about the occurrence and consequences of discharges in the detector. The interdependence of the four voltage differences used in the detector has been studied by simulation and with X-ray measurements. Rate dependence of the signal amplitude is observed. The behaviour of the MSGC+GEM is compared to that of a state-of-the-art MSGC. Influence of various parameters on the detector response is investigated.

Large size small gap chambers (SGC) equipped with gas electron multiplier (GEM) were exposed to a low-energy hadron beam to characterize their hardness to highly ionizing radiations. During the test, rate and effect of discharges induced by highly ionizing particles were studied as a function of the cathode and GEM voltages. We propose an optimization of the voltages to safely operate the detectors at the largest signal-to-noise ratio. In a second test, the ageing properties of the chambers were measured up to a 5mC/cm integrated charge, induced by an X-ray beam. We conclude from the two measurements on the good reliability and possible improvements of the SG plus GEM Chambers for long term use in a harsh radiation environment.

A micro-strip gas counter equipped with an RC-CR (τ = 30 ns) VLSI preamplifier (the RD20 chip) has been tested with minimum ionizing particles. The measured pulse shape and the signal to noise ratio are presented. The time resolution of the detector has been studied as a function of the charge collected at the input of the preamplifier with an ArDME gas mixture. Three methods for the bunch crossing identification at LHC are discussed.

MicroStrip Gas Chambers (MSGC's) have been proposed for equipping the outer region of the tracker of the Compact Muon Solenoid (CMS) experiment at the Large Hadron Collider (LHC). The MSGC's have undergone extensive development and tests during the last few years and their performance is well established. An important issue that has to be addressed to date is whether MSGC's can maintain their characteristics after a long exposure to an intense flux of particles, similar to LHC. We report results from the most recent beam test addressing this topic.

The inelastic hadronic cross section in proton-lead collisions at a centre-of-mass energy per nucleon pair of 5.02 TeV is measured with the CMS detector at the LHC. The data sample, corresponding to an integrated luminosity of 12.6 +/- 0.4 inverse nanobarns, has been collected with an unbiased trigger for inclusive particle production. The cross section is obtained from the measured number of proton-lead collisions with hadronic activity produced in the pseudorapidity ranges 3<abs(eta)<5 and/or -5<abs(eta)<-3, corrected for photon-induced contributions, experimental acceptance, and other instrumental effects. The inelastic cross section is measured to be sigma[inel,pPb]=2061 +/- 3 (stat) +/- 34 (syst) +/- 72 (lum) mb. Various Monte Carlo generators, commonly used in heavy ion and cosmic ray physics, are found to reproduce the data within uncertainties. The value of sigma[inel,pPb] is compatible with that expected from the proton-proton cross section at 5.02 TeV scaled up within a simple Glauber approach to account for multiple scatterings in the lead nucleus, indicating that further net nuclear corrections are small.

The FEAFS chip has been designed for the upgrades of the CMS Silicon Strip Tracker, which is planned in view of the LHC high luminosity upgrade. Its primary function is to provide a 40 MHz selective readout of particle hits that will be used for the generation of the 100 kHz hardware trigger of the experiment within a latency of 6.4 μs. To achieve this goal, the chip identifies clusters of limited number of activated strips and correlated in position, in a given window, in two closely superimposed sensors connected to the same chip. Finally, trigger and DAQ data are transmitted off detector via a common link. The FEAFS chip has been developed in IBM 0.13 μm technology. This paper presents the design of the chip and test results.

In November and December 2009, the LHC delivered the first proton–proton collisions with beams of 450 GeV and then of 1.18 TeV, an unprecedented energy. On the 30th of March 2010, LHC operation moved forward to the physics era with collisions at a 7 TeV center of mass energy and, by the time of the IPRD10 conference, an integrated luminosity of 20nb−1 was accumulated. This paper relates how the CMS data reconstruction and Monte-Carlo simulations were validated in only few months. It presents the first physics results.

A high-speed serial link has been developed for data acquisition for s-LHC experiment upgrade at CERN or between tiers in 3D-IC application. To reduce the required bandwidth of the channel for a given bit rate and the maximum on-chip clock frequency a current multi level signaling was used. The circuit specifications concerning the number of analog levels used (Pulse Amplitude Modulation 16-bit) were inspired by the 10GBASE-T standard in current mode. The circuit frequency is 250 MHz for a 1Gbit/s data transmission. The analog and digital voltage supply is 1,6 V. This data link is implemented in IBM 130 nm 8RF CMOS process.

Deux ans apres son demarrage, le plus grand collisionneur de particules du monde apporte de nouveaux elements de reponse a des questions fondamentales encore non resolues, telles que quelle est l'origine de la masse des particules ? . Nous exposons ici les conclusions les plus marquantes d'une premiere moisson de resultats obtenus par les experiences ATLAS et CMS.

The FEAFS chip has been designed for a super-LHC CMS Silicon Strip Tracker front-end electronics. Its primary function is to find clusters of activated strips for the level 1 trigger. A filtering is done to remove clusters associated with low transverse momentum particles using either a cut on their width and/or a correlation between their positions on two modules. The processing results are sent on a shared link with the readout data to lower the power consumption. The FEAFS chip has been developed in IBM 0.13μm technology. This paper presents the foreseen processing and the design of the chip. Some simulation results are reported.

A measurement of the ttbar production cross section at sqrt(s)=13 TeV is presented using proton-proton collisions, corresponding to an integrated luminosity of 2.3 inverse femtobarns, collected with the CMS detector at the LHC. Final states with one isolated charged lepton (electron or muon) and at least one jet are selected and categorized according to the accompanying jet multiplicity. From a likelihood fit to the invariant mass distribution of the isolated lepton and a jet identified as coming from the hadronization of a bottom quark, the cross section is measured to be sigma(ttbar)= 835 +/- 3 (stat) +/- 23 (syst) +/- 23 (lum) pb, in agreement with the standard model prediction. Using the expected dependence of the cross section on the pole mass of the top quark (m[t]), the value of m[t] is found to be 172.7+2.4-2.7 GeV.

Abstract We present a simulation of the signal delivered by minimum ionising particles crossing an MSGC. The parameters, adjusted to the experimental data, are reported for different gas mixtures. The simulation is then applied to the study of the bunch crossing identification at LHC. We present the performance of different pulse shapings and processing algorithms in the LHC environment.