ALICE-USA Electromagnetic Calorimeter

1. Quantity Value ALICE-USA Electromagnetic Calorimeter Tower Size Sampling Ratio 5mm Pb/5mm Scintillator ~6.5~6.524.5 cm3 Sampling Fraction 13/1 ΔηΔφ=0.01420.0146 Depth ~25 rad. lengths No. of Towers 13248 No. of Modules 48 No. of Super-modules 12 Super-module Weight ~ 9 U.S. Tons Total coverage -0.7<η<0.7, Δφ=115º Invariant mass spectrum of electron pairs in the central region including all background sources. D and B decays dominate in the vicinity of the J/y., but the peak can still be seen. Some Physical parameter describing the proposed Electromagnetic Calorimeter for ALICE. End view of the EMCAL in a common support structure with the HMPID. A continuous arch of super-modules spanning ~120 degrees in azimuth is indicated. The EMCAL is positioned to provide almost complete back-to-back coverage with the PHOS calorimeter. Jet fragmentation functions of PYTHIA jets reconstructed with the ALICE tracking system for jets of pT=50 to 600 GeV/c (black curves). The soft non-jet background found within the jet cone is indicated in red. The pT spectrum of direct J/y’s compared to J/y’s from B decay assuming no suppression. Response of the calorimeter to central HIJING events with (dN/dy)charged =8000. A mean tower energy of ~200MeV at 40% occupancy is observed. The lower right hand panel shows that this energy deposition is made up of 50% charged hadrons, 40% electromagnetic energy and ~10% long lived neutral hadrons. PYTHIA calculations of p0 spectra at SPS, RHIC, and LHC energies showing the dramatic growth of the cross section at high pT Response of the first two scintillator layers to 5 GeV/c hadrons and electrons. The spectra seen here are approximately independent of electron energy. Inclusive direct photon yield per ALICE year for minimum bias Pb+Pb collisions at sNN = 5.5 TeV into the PHOS (red), EMCal (blue) and sum (black) acceptance. Calculations are based on PYTHIA scaled as A2 assuming a 30 day ALICE run with 100% efficiency. Similarly scaled yields for the sum acceptance from the direct photon measurements of CDF are plotted for comparison. (Note the suppressed scale.) The ALICE EMCAL super-module (dimensions in mm). Four modules (one of which is highlighted) are installed in a single super-module. The left hand panel shows reconstructed PT=50 GeV/c jets from PYTHIA pp collisions at s=5.5 TeV. The gaussian s is just over ~15%. In the right hand panel, the jet resolution determined in this way is plotted from PT=50 GeV/c to 200 GeV/c and is observed to be approximately constant at ~15%. Estimated inclusive jet events per 10 GeV pT bin per ALICE year (30 days) at 75% efficiency for minimum bias Pb+Pb collisions at sNN = 5.5 TeV. Calculations are based on PYTHIA using a k factor of 1 and CTEQ2M parton distributions without nuclear or medium modifications. The horizontal axis is the single jet ET. The proposed calorimeter acceptance is labeled EMCAL. Lead – Scintillator – Lead sandwich showing the fiber routing layer, the readout grooves, and the tower-to-tower isolation grooves. Primary parton spatial resolution from reconstructed jets. We find s(h)/R~s(f)/R ~10% where R=0.2 is the jet cone radius. Simulated calorimeter response to mono-energetic photons from 25 GeV (upper left) through 200 GeV (lower left) for a total active depth of 21 radiation lengths (top figures) and 25 radiation lengths (bottom figures). Note the asymmetric low energy tails for the 21 radiation length deep calorimeter, and how they are much more symmetric for the 25 radiation length deep calorimeter. Single electron yield from W and Z0 decays into the PHOS (red) or EMCal (blue) acceptance per ALICE year for minimum bias Pb+Pb collisions at sNN = 5.5 TeV as predicted by PYTHIA scaled by A2. Electrons from Drell Yan pairs are also included. General layout of the EMCAL optical system showing the scintillating megatiles, fiber routing layer, fiber decoding, and APD matrix. An analysis of jet reconstruction for PT>75 GeV/c with the ALICE EMCAL and tracking system in central Pb+Pb collisions. left panel comparison of the true and ghost jet rates. The right hand panel shows the distribution of reconstructed jet energies minus primary parton energies. The observed resolution is s ~18%. Predicted rates of g+jet events as a function of the invariant mass of the g-jet pair per ALICE year for minimum bias Pb+Pb collisions at sNN=5.5 TeV into the PHOS (red), EMCAL (blue) and sum (black) acceptance. Calculations are based on PYTHIA scaled as A2 assuming a 30 day ALICE run with 100% efficiency. Results are shown for quark (solid) and gluon (dashed) jets. Electron pair invariant mass yield from Drell Yan and Z0 decays into the PHOS (blue) or EMCal (red) acceptance per ALICE year for minimum bias Pb+Pb collisions at sNN = 5.5 TeV as predicted by PYTHIA and scaled by A2. Lego plots of 100 GeV/c and 200 GeV/c jets in ALICE. The energy deposited in pseudo cells is plotted versus h and f. The pseudo cell energy is deduced from the calorimeter tower response and from ITS/TPC/TRD tracking. In the right hand panel, the cell size is chosen equal to the calorimeter tower size. A 100 GeV Jet-Jet Phythia simulated event. Shown is the tracks in the inner tracking detectors, ITS TPC and TRD, along with signals from the PHOS below and EMCAL above. The 16x18 matrix at the end of a module where layer-to-tower fiber mapping, light mixer, APD, preamplifier, and APD bias systems are located. Collaborating US Institutions: Creighton University,Kent State University, Lawrence Berkeley National Laboratory, Michigan State University, Oak Ridge National Laboratory, Ohio Supercomputer Center, Purdue University, The Ohio State University, University of California, Berkeley, University of California, Davis, University of California, Los Angeles, University of Houston, University of Tennessee, University of Washington, Vanderbilt University, Wayne State University High PT Physics in Heavy Ions at the LHC Proposed EMCAL Physics Capabilities when EMCAL is added Heavy ion collisions at LHC energies will allow us to explore regions of energies and particle densities which are significantly larger than those reachable at the SPS and RHIC. Soft interactions are not expected to produce results very different from those seen at the SPS or RHIC, where as the rate of hard or high PT interactions are expected to be significantly enhanced. Consequently, the the production rate for jets, at the LHC, will be large enough to allow them to be effectively used as probes of the hot dense matter. Additionally, it is expected from most theoretical calculations, that the changes induced by the QGP will be significantly enhanced over that expected at RHIC. To maximize the physics potential at a minimum cost, the ALICE-USA group, in consultations with the ALICE collaboration, is proposing to place a thick relatively large partial barrel Pb sintilator sampling electromagnetic calori-meter which will be coarsely segmented placed opposite the much smaller but finer segmented BaSO4 crystal, PHOS, calorimeter. The EMCAL has the acceptance for jets while the PHOS has the fine energy resolution for the recoil photon. In this way the two detectors complement each other. In addition to Jets, a large coverage EMCAL can aid in identifying heavy resonances. Bellow is shown some of these resonances and their anticipated rates at the LHC. In addition are shown the rates for Direct photons (with or without accompanying jets), W’s and Z bosons. The ALICE EMCAL is based on the STAR calorimeter. Consequently the response of the EMCAL can be anticipated. Never the less, many simulations of the EMCAL have been done in order to optimize the design and to make sure that our physics goals can be met. The EMCAL has been fully integrated into the ALICE simulation and analysis framework. This has allowed us to do more complete studies of the EMCAL. Below is shown the predicted rates, as expected to be seen by ALICE, with the EMCAL included. In addition to jets, Heavy flavor states and W and Z boson production will be greatly enhanced. EMCAL Extz Gamma-Jet events come either with a leading quark or gluon in the jet. The direction of this leading quark or gluon can be inferred by summing all of the tracks within a predefined cone around a leading high PT particle. If the leading particle is neutral, π0 for instance, a large coverage electromagnetic calorimeter would be needed to find such a “track”.

2. Calorimeter response to 200 GeV (left) and 50 GeV (right) photons. The top panels show the tower response plotted as a percent of the full energy and the bottom panels show the reconstructed energies after clustering. The EMCal electronics will provide overlapping 4x4 tower sums that will produce the data seen in the lower panels at the trigger level. Calculated momentum resolution in ALICE for charged particles based on simulations with charged particle multiplicities of dN/d = 8000 (red) or dN/d=2000 (blue) with all tracking systems TPC+ITS+TRD (dashed) and without use of the TRD (solid). Note that the red solid and blue dashed curves overlap. An analysis of jet reconstruction for PT > 75 GeV/c with the ALICE EMCal and tracking system in central PbPb collisions. (a) left panel comparison of the true and ghost jet rates (b) Distribution of reconstructed jet energies minus primary parton energies. The observed resolution is s ~18%. Parton kinematics as can be seen at the LHC. For W, Z production x=(M/5.5 TeV) exp(-y). For gluon production at y=0 & x=pT/5.5 TeV, for example, x = 0.002 @ pT=10 GeV/c. Simulated L spectra for min bias Pb+Pb collisions at sNN=5.5 TeV in one ALICE year of integrated running with a jet trigger of pT > 100 GeV/c. The charged hadron spectra, with hadron opposite a 15 or 20 GeV direct photon as predicted at RHIC[1] energies. The solid (dashed) curves show the predicted result without (with) parton energy loss. The soft hadron background due to the underlying event is indicated.[1]X.N.Wang, Z.Huang, and I.Sarcevic, Phys. Rev. Lett. 77 (1996) 231.