Physics perspectives of the ALICE experiment at the large hadron collider

The large hadron collider (LHC) under construction at CERN will deliver ion beams up to centre of mass energies of the order of 5.5 TeV per nucleon, in case of lead. If compared to the available facilities for the study of nucleus-nucleus collisions (SpS and RHIC), this represents a huge step forward in terms of both volume and energy density that can be attained in nuclear interactions. ALICE (a large ion collider experiment) is the only detector specifically designed for the physics of nuclear collisions at LHC, even though it can also study high cross-section processes occurring in proton-proton collisions. The main goal of the experiment is to observe and study the phase transition from hadronic matter to deconfined partonic matter (quark gluon plasma —QGP). ALICE is conceived as a general-purpose detector and will address most of the phenomena related to the QGP formation at LHC energies: for this purpose, a large fraction of the hadrons, leptons and photons produced in each interaction will be measured and identified.     

Heavy-ion physics with the ATLAS detector

The CERN LHC collider will operate with lead ions at √s of 5.5 TeV/nucleon. The ATLAS detector, designed to study high-pT physics in the pp mode of the LHC, has the potential to study ultrarelativistic heavy-ion collisions in a full range of observables characterized extremely dense matter and the formation of a quark-gluon plasma. The ATLAS physics program includes global event measurements (particle multiplicities, transverse momentum), suppression of heavy-quarkonia production, jet quenching, and a study of ultraperipheral collisions. (on behalf of the ATLAS Collaboration) The text was submitted by the author in English.     

Large hadron collider physics program: Compact muon solenoid experiment

The LHC physics program at CERN addresses some of the fundamental issues in particle physics and CMS experiment would concentrate on them. The CMS detector is designed for the search of Standard Model Higgs boson in the whole possible mass range. Also it will be sensitive to Higgs bosons in the minimal supersymmetric model and well adapted to searches for SUSY particles, new massive vector bosons, CP-violation in B-system, search for subtructure of quarks and leptons, etc. In the LHC heavy ion collisions the energy density would be well above the threshold for the possible formation of quark-gluon plasma.     

From the LHC to future colliders

Discoveries at the LHC will soon set the physics agenda for future colliders. This report of a CERN Theory Institute includes the summaries of Working Groups that reviewed the physics goals and prospects of LHC running with 10 to 300 fb^?1 of integrated luminosity, of the proposed sLHC luminosity upgrade, of the ILC, of CLIC, of the LHeC and of a muon collider. The four Working Groups considered possible scenarios for the first 10 fb^?1 of data at the LHC in which (i) a state with properties that are compatible with a Higgs boson is discovered, (ii) no such state is discovered either because the Higgs properties are such that it is difficult to detect or because no Higgs boson exists, (iii) a missing-energy signal beyond the Standard Model is discovered as in some supersymmetric models, and (iv) some other exotic signature of new physics is discovered. In the contexts of these scenarios, the Working Groups reviewed the capabilities of the future colliders to study in more detail whatever new physics may be discovered by the LHC. Their reports provide the particle physics community with some tools for reviewing the scientific priorities for future colliders after the LHC produces its first harvest of new physics from multi-TeV collisions.     

Recent results from CERN SPS experiments and the future heavy ion programme

We describe the important results from the recent experiments using lead beams at the CERN SPS. The results of the WA98 experiment, which has substantial Indian participation along with the photon multiplicity detector is described in some detail. Combining the preliminary results from various experiments looking at different signals of phase transition, one finds enough evidences to suggest that phase transition has taken place in nuclear collisions at the SPS. Future programme of heavy ion physics at the LHC is being greared around the ALICE experiment. This will comprise of detector subsystems capable of studying almost all the signals in the same event. The photon multiplicity detector will be an important component of the ALICE experiment, being a totally Indian contribution to ALICE.     

Open charm and beauty at ultrarelativistic heavy ion colliders

Important goals of BNL RHIC and CERN LHC experiments with ion beams include the creation and study of new forms of matter, such as the quark gluon plasma. Heavy quark production and attenuation provide unique tomographic probes of that matter. We predict the suppression pattern of open charm and beauty in Au+Au collisions at RHIC and LHC energies based on the DGLV formalism of radiative energy loss. A cancellation between effects due to the sqrt[s] energy dependence of the high p(T) slope and heavy quark energy loss is predicted to lead to surprising similarity of heavy quark suppression at RHIC and LHC.     

Charmonium production in proton-proton collisions and in collisions of lead nuclei at CERN and comparison with Brookhaven data

A review of experimental data on charmoniumproduction that were obtained in fixed-target experiments at the SPS synchrotron and in proton-proton collisions and in collisions of lead nuclei in beams of the Large Hadron Collider (LHC) at CERN (Switzerland) is presented. A comparison with data obtained at the Brookhaven National Laboratory (USA) from experiments at the Relativistic Heavy Ion Collider (RHIC) is performed. Measurement of the suppression of J/ψ-meson production as a possible signal of the production of quark-gluon plasmawas proposed back in 1986 by T. Matsui and H. Satz. An anomalous suppression of J/ψ-meson production was discovered by the NA50 Collaboration at SPS (CERN) in central collisions of lead nuclei at the c.m. collision energy of 158 GeV per nucleon. Data obtained at the c.m. energy of 200 GeV per nucleon in the PHENIX experiment at RHIC indicate that, depending on multiplicity, the suppression of J/ψ-meson production at this energy approximately corresponds to the suppression of J/ψ-meson production in collisions of lead nuclei at the SPS accelerator. Theoretical models that take into account the regeneration of J/ψ mesons describe better RHIC experimental data. The measurement of charmonium production in proton-proton collisions and in collisions of lead nuclei in LHC beams revealed the importance of taking into account the regeneration process. At the LHC energies, it is also necessary to take into account the contribution of B-meson decays. Future measurements of charmonium production at the LHC to a higher statistical precision and over an extended energy region would be of importance for obtaining deeper insight into the mechanism of charmonium production and for studying the properties of matter at high energy density and temperature.     

At the national physical laboratory

The experimental discovery of the W and 2 bosons at CERN in 1983 confirmed the detailed predictions of the electroweak theory, which unifies the electromagnetic and weak nuclear forces. After a brief introduction to the most important ideas in this force unification, this account describes the antiproton-proton collider project at CERN. This provided the energetic collisions which enabled the W and 2 bosons, which are around one hundred times heavier than a proton, to be produced for the first time.

These heavy particles are produced only very rarely in such collisions and as they decay within 10^?-²⁴s, their discovery relied on sophisticated detectors and analysis techniques. This article describes how the evidence for these new particles was extracted from the study of millions of antiproton-proton collisions and includes a first hand account of the exciting experimental runs which led to the discovery of the W^?, W⁺ and Z⁰ bosons in 1983.     

Direct photons in ATLAS@LHC

The ATLAS detector at the LHC is capable of efficiently separating photons and neutral hadrons based on their shower shapes over a wide range in η, ϕ and E _T , either in addition to or instead of isolation cuts. This provides ATLAS with a unique strength for direct photon and γ-jet physics (“tomography”) as well as access to the unique capability to measure non-isolated photons from fragmentation or from the medium. We present a first look at the ATLAS direct photon measurement capabilities in p+p and Pb+Pb collisions at LHC energies over the region |η| < 2.4.     

超高能诱发核反应的国际合作实验研究进展

综述超高能诱发核反应的国际合作实验进展及相关的重离子物理研究现状.内容包括:1.有关夸克物质(夸克胶子等离子体QGP)的理论预言.2.超高能重离子碰撞的实验:(1)BNL/AGS能区的固定靶实验回顾;(2)CERN/SPS能区的固定靶实验回顾;(3)BNL/RHIC能区的对撞实验现状;(4)CERN/LHC能区的对撞实验现状.     

Silicon detector technology development in India for the participation in international experiments

A specific research and development program has been carried out by BARC in India to develop the technology for large area silicon strip detectors for application in nuclear and high energy physics experiments. These strip detectors will be used as pre-shower detector in the CMS experiment at LHC, CERN for π ⁰/λ rejection. The fabrication technology to produce silicon strip detectors with very good uniformity over a large area of ∼40 cm², low leakage currents of the order of 10 nA/cm² per strip and high breakdown voltage of >500 V has been developed by BARC. The production of detectors is already under way to deliver 1000 detector modules for the CMS and 90% production is completed. In this paper, research and development work carried out to develop the detector fabrication technology is briefly described. The performance of the silicon strip detectors produced in India is presented. The present status of the detector technology is discussed.      

Performance studies of a full-length prototype for the CASTOR forward calorimeter at the CMS experiment

The Time-Of-Flight detector (TOF) of the ALICE experiment at the CERN LHC is based on Multi-gap Resistive Plate Chambers (MRPCs). The TOF detector consists of 152928 readout channels covering a total area of 141 m². In this paper the results of the calibration with cosmic-ray data collected during 2009 are presented.     

Status and plans of the ion program of NA61 at the CERN SPS

The NA61/SHINE at the CERN SPS is a new experiment to study hadron production in p+p, p+A, h+A and A+A interactions. The main goal of the NA61 ion program is to explore the phase diagram (T ? ?? _B ) of strongly interacting matter. In particular, we plan to study the properties of the onset of deconfinement and to search for the signatures of the critical point. A two-dimensional scan of the phase diagram will be performed by varying the energy (13A?C158A GeV) and system size (p+p, Be+Be, Ar+Ca, Xe+La) of collisions. This paper summarizes the status and plans of the NA61/SHINE ion program. In particular the detector upgrades, data taking schedule and the first results on spectra and correlations are discussed.     

Dark matter production at the LHC from black hole remnants

We study dark matter production at CERN LHC from black hole remnants (BHR). We find that the typical mass of these BHR at the LHC is ∼5–10 TeV which is heavier than other dark matter candidates, such as axion, axino, neutralino, etc. We propose the detection of this dark matter via single jet production in the process pp → jet + BHR (dark matter) at CERN LHC. We find that for zero impact parameter partonic collisions, the monojet cross section is not negligible in comparison to the standard model background and is much higher than the other dark matter scenarios studied so far. We also find that dσ/dp _T of jet production in this process increases as p _T increases, whereas in all other dark matter scenarios the dσ/dp _T decreases at CERN LHC. This may provide a useful signature for dark matter detection at the LHC. However, we find that when the impact parameter dependent effect of inelasticity is included, the monojet cross section from the above process becomes much smaller than the standard model background and may not be detectable at the LHC.     

Experimental limits on the production of fractionally charged particles in proton-nucleus and neutrino-nucleus collisions

A search for fractionally chargedQ=1/3 (2/3) particles of different properties of interaction produced in (anti)neutrino-nucleus and in protonnucleus collisions was performed using the scintillator system of the CHARM neutrino detector at the CERN SPS. No events of the cases considered were found. In (anti)neutrino beams production was found to be less than a few times 10^?5 per interaction of a beam particle. In a proton beam an upper limit on the production cross section of ～10^?40 cm² was obtained.     

Investigating the microscopic properties of strongly interacting matter with HADES

In the energy domain of 1?C2 GeV kinetic energy per nucleon, HADES has measured rare and penetrating probes in elementary and heavy ion collisions. Our results demonstrate that electron pair emission in C+C collisions can essentially be explained as a superposition of independent N+N collisions. HADES results on e⁺e^? production in Ar+KCl collisions, however, show a strong enhancement of the dilepton yield relative to a reference spectrum obtained from elementary nucleon-nucleon reactions, signal the onset of medium effects beyond the superposition of individual N+N collisions. Intriguing results where also obtained from the reconstruction of hadrons with open and hidden strangeness. Analyses of the experimentally obtained hadronic yields measured in Ar+KCl allows to extract the chemical freeze-out conditions in the T -??B phase diagram of strongly interacting matter. While the measured abundance of all reconstructed particles are well described assuming thermalization, the also reconstructed double strange baryon ??^? appears about ten times more abundant than expected. This result will be discussed in the context of the exploration of the nuclear matter phase diagram in the region of finite density. Further investigations to search for significant medium effects, will be followed over the coming years with an upgraded HADES detector.     

Probing small parton densities in ultraperipheral A A and pA collisions at the CERN large Hadron Collider

We calculate photoproduction rates for several hard processes in ultraperipheral proton-lead and lead-lead collisions at the CERN Large Hadron Collider (LHC) with square root of sNN = 8.8 and 5.5 TeV, respectively, which could be triggered in the large LHC detectors. We use ATLAS as an example. The lead ion is treated as a source of (coherently produced) photons with energies and intensities greater than those of equivalent ep collisions at the DESY collider HERA. We find very large rates for both inclusive and diffractive production that will extend the HERA x range by nearly an order of magnitude for similar virtualities. We demonstrate that it is possible to reach the kinematic regime where nonlinear effects are larger than at HERA.     

Possibility of recording rare muonic decays of <Emphasis Type="Italic">B</Emphasis> mesons at the ATLAS detector in the case of LHC operation in the initial-luminosity mode

The possibility of recording the rare muonic decays B _d,s ⁰ → μ ⁺ μ ^? at the ATLAS detector (LHC, CERN) is studied. The question of what results can be expected within the first three years of LHC operation in the initial-luminosity mode is examined. The most important noncombinatorial background processes are listed for rare muonic decays of B mesons.     

Charmonium production in fixed-target experiments with SPS and LHC beams at CERN

The possibility of measuring cross sections for the production of J/ψ mesons in fixed-target experiments with the proton and ion beams of the Large Hadron Collider (LHC) at CERN (Switzerland) is considered. At the present time, measurements of charmonium production in proton-proton collisions at an energy of 7 TeV have begun at LHC. Previously, the production of J/ψ and ψ′ mesons was studied in the NA38, NA50, and NA60 fixed-target experiments with beams of the CERN synchrotron (SPS) and in the PHENIX experiment at the Relativistic Heavy Ion Collider (RHIC, Brookhaven National Laboratory, USA). A normal nuclear absorption of J/ψ mesons in proton-nucleus collisions and an enhanced, anomalous, suppression of the production of charmonium states in central collisions of relativistic nuclei were observed. At the present time, there are no theoretical models that could describe the entire body of experimental data. Measurements over a broad interval of proton and ion energies are required. Measurements of charmonium production using LHC beams with fixed targets in the energy range between the SPS and RHIC energies-a beam of 7-TeV protons (√s = 114.6 GeV) and a beam of 2.75-TeV/nucleon lead ions (√s = 71.8 GeV)-will provide an additional possibility for studying the charmonium-production mechanism. Estimates of the geometric acceptance, luminosity, and counting rate for the production of J/ψ mesons are presented.     

Kaon interferometry in heavy-ion collisions at the CERN SPS

K⁺K⁺ and K^–K^– correlations from S+Pb collisions at 200 GeV/c per nucleon and K⁺K⁺ correlations from p+Pb collisions at 450 GeV/c per nucleon, are presented as measured by the focusing spectrometer of the NA44 experiment at CERN. Multidimensional fits are performed in order to characterize the kaon-emission volume, which is found to be smaller than the pion-emission volume.