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Register a new userContribution of the HMPID detector to the high-pT physics at LHC
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The LHC will deliver unexplored energy regimes for proton-proton and heavy-ion collisions. As shown by the RHIC experiments, particle identification over a large momentum range is essential to disentangle physics processes, especially in the intermediate p$_T$ (1 $<p_{T}<5$ GeV/c) region. The novel design of the High-Momentum Particle Identification Detector (HMPID), based on large surface CsI photocathodes, is able to identify $pi^{pm}$, $K^{pm}$, $p$ and $bar{p}$ in the momentum region where bulk medium properties and hard scatterings interplay. Furthermore, measurement of resonance particles such as the $phi to K^+K^-$ could provide information on the system evolution. The HMPID layout and segmentation are optimized to study particle correlations at high momenta describing the early phase and the dynamical evolution of the collision. At LHC, the increased hard cross section will significantly be enhanced compared to RHIC. Jet reconstruction via Deterministic Annealing can address jet quenching and detailed measurements of jet properties. In this paper, we present these selected topics from the possible HMPID contributions to the physics goals of LHC.
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ALICE has been specifically optimized to study heavy-ion collisions at the LHC, up to a charged particle density of 8000 per unit of rapidity in central heavy-ion collisions at $sqrt{s_{NN}}$ = 5.5 TeV. The High Momentum Particle Identification Detector (HMPID) has a proximity focusing geometry with a liquid $rm C_{6}F_{14}$ Cherenkov radiator coupled to Multi-Wire Pad Chambers (MWPC) equipped with CsI photocathodes, over a total active area of 11 $rm m^2$. It has been designed to identify charged pions and kaons in the range 1 $leq p leq$ 3 GeV/$c$ and protons in the range 2 $leq p leq$ 5 GeV/$c$. The as-built detector and all relevant subsystems (gas, liquid $rm C_{6}F_{14}$, cooling and control) are described. Installation issues and first commissioning results are also presented.
The ALICE experiment studies nucleus-nucleus collisions at the LHC in order to investigate the properties of QCD matter at extreme energy densities. The measurement of open charm and open beauty production allows one to probe the mechanisms of heavy-quark propagation, energy loss and hadronization in the hot and dense medium formed in high-energy nucleus-nucleus collisions. In particular, in-medium energy loss is predicted to be different for massless partons (light quarks and gluons) and heavy quarks at moderate momentum. The ALICE apparatus allows us to measure open heavy-flavour particles in several decay channels and with a wide phase-space coverage. We present the results on the nuclear modification factors for heavy-flavour particle production in Pb-Pb collisions at sqrtsNN=2.76 TeV. Using proton-proton and lead-lead collision samples at sqrts=2.76 and 7 TeV and at sqrtsNN=2.76 TeV, respectively, nuclear modification factors R_AA(pT) were measured for D mesons at central rapidity (via displaced decay vertex reconstruction), and for electrons and muons from heavy-flavour decays, at central and forward rapidity, respectively. A large suppression is observed, by a factor 2.5-4 in central Pb--Pb collisions with respect to the pp reference, in the high-pT region, indicating a strong in-medium energy loss of heavy quarks.
The High-Luminosity Large Hadron Collider is expected to deliver up to 3000 fb$^{-1}$ of proton-proton collisions at 14 TeV center-of-mass energy. We present prospects for selected heavy-ion, Standard Model and Higgs sector measurements with the CMS detector at the HL-LHC, and discuss potential sensitivity to several beyond-Standard Model new physics scenarios.
We discuss the physics of large impact parameter interactions at the LHC: ultraperipheral collisions (UPCs). The dominant processes in UPCs are photon-nucleon (nucleus) interactions. The current LHC detector configurations can explore small $x$ hard phenomena with nuclei and nucleons at photon-nucleon center-of-mass energies above 1 TeV, extending the $x$ range of HERA by a factor of ten. In particular, it will be possible to probe diffractive and inclusive parton densities in nuclei using several processes. The interaction of small dipoles with protons and nuclei can be investigated in elastic and quasi-elastic $J/psi$ and $Upsilon$ production as well as in high $t$ $rho^0$ production accompanied by a rapidity gap. Several of these phenomena provide clean signatures of the onset of the new high gluon density QCD regime. The LHC is in the kinematic range where nonlinear effects are several times larger than at HERA. Two-photon processes in UPCs are also studied. In addition, while UPCs play a role in limiting the maximum beam luminosity, they can also be used a luminosity monitor by measuring mutual electromagnetic dissociation of the beam nuclei. We also review similar studies at HERA and RHIC as well as describe the potential use of the LHC detectors for UPC measurements.
Results are presented from the ATLAS collaboration from the 2010 LHC heavy ion run, during which nearly 10 inverse microbarns of luminosity were delivered. Soft physics results include charged particle multiplicities and collective flow. The charged particle multiplicity, which tracks initial state entropy production, increases by a factor of two relative to the top RHIC energy, with a centrality dependence very similar to that already measured at RHIC. Measurements of elliptic flow out to large transverse momentum also show similar results to what was measured at RHIC, but no significant pseudorapidity dependence. Extensions of these measurements to higher harmonics have also been made, and can be used to explain structures in the two-particle correlation functions that had long been attributed to jet-medium interactions. New hard probe measurements include single muons, jets and high $p_T$ hadrons. Single muons at high momentum are used to extract the yield of $W^{pm}$ bosons and are found to be consistent within statistical uncertainties with binary collision scaling. Conversely, jets are found to be suppressed in central events by a factor of two relative to peripheral events, with no significant dependence on the jet energy. Fragmentation functions are also found to be the same in central and peripheral events. Finally, charged hadrons have been measured out to 30 GeV, and their centrality dependence relative to peripheral events is similar to that found for jets.
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