T. Gunji

Energy loss of pions and electrons of 1– in drift chambers operated with Xe,CO2(15%)

Abstract We present measurements of the energy loss of pions and electrons in drift chambers (DC) operated with a Xe,CO 2 (15%) mixture. The measurements are carried out for particle momenta from 1 to 6 GeV /c using prototype DC for the ALICE transition radiation detectors. Microscopic calculations are performed using input parameters calculated with GEANT3. These calculations reproduce well the measured average and most probable values for pions, but a higher Fermi plateau is required in order to reproduce our electron data. The widths of the measured distributions are smaller for data compared to the calculations. The electron/pion identification performance using the energy loss is also presented.

Ion backflow studies for the ALICE TPC upgrade with GEMs

The ALICE (A Large Ion Collider Experiment at CERN) collaboration plans an upgrade of the detector during the second long shutdown of the LHC, during which the interaction rate will be increased to 50 kHz for Pb-Pb collisions. This demands operation of the Time Projection Chamber (TPC) in an ungated continuous mode. A gating grid can not be used to prevent ions drifting back into the drift volume. Gas Electron Multipliers (GEM) offer intrinsic suppression of the ion backflow. To keep distortions due to space-charge at a manageable level an ion yield of 10 to 20 back drifting ions per incoming electron is required. In this manuscript, we describe the concept of ion backflow suppression with our triple GEM prototype. Within a detailed gas study, we show our lowest ion backflow values for several different gas mixtures that have been considered for the TPC upgrade. These values have been compared with detailed simulations using ANSYS and Garfield++. Within the scope of this study, a large impact of space-charges on the ion backflow has been observed. Systematic measurements over a wide range of charge densities, for different field configurations and different drift gaps have been carried out.

RCU2 — The ALICE TPC readout electronics consolidation for Run2

This paper presents the solution for optimization of the ALICE TPC readout for running at full energy in the Run2 period after 2014. For the data taking with heavy ion beams an event readout rate of 400 Hz with a low dead time is envisaged for the ALICE central barrel detectors during these three years. A new component, the Readout Control Unit 2 (RCU2), is being designed to increase the present readout rate by a factor of up to 2.6. The immunity to radiation induced errors will also be significantly improved by the new design.

Development of a time projection chamber using gas electron multipliers (GEM-TPC)

A prototype of time projection chambers using gas electron multipliers (GEM-TPC) has been developed for relativistic heavy ion collision experiments. The performance of the GEM-TPC was investigated using particle beams at KEK with 3 kinds of gases (Ar(90%)-CH/sub 4/(10%), Ar(70%)-C/sub 2/H/sub 6/(30%) and CF/sub 4/). Detection efficiency of 99%, spatial resolution of 80 /spl mu/m in the pad-row direction and double track resolution of 12 mm in the drift direction were achieved. The test results show that the GEM-TPC meets requirements of relativistic heavy ion collision experiments. This paper describes the configuration and performance of the GEM-TPC.

Measurement of basic features of Thick-GEM and Resistive-GEM

Recently, Thick-GEM (TGEM) whose geometry is at the millimeter-scale has been developed to overcome the disadvantages of micro-scale Gas Electron Multiplier (GEM) such as fragility against a discharge, difficulty in obtaining enough gain at low pressure and so on. In addition, TGEM with resistive electrodes (RETGEM) also has been developed to make TGEM more tolerant with a discharge. Active research is carried out worldwide for applications such as liquid Argon detectors, Cerenkov light detectors, sampling elements in calorimeter and low-pressure time projection chamber. TGEM and RETGEM look very promising, but their basic properties have not yet been studied thoroughly. TGEM and RETGEM with different geometries were made and the basic properties such as the voltage dependence of gain, the energy resolution and the gain variation as a function of time at different gain levels were measured. A gain of about 104 was obtained with Ar(90%) + CH4 (10%) gas mixture for both TGEM and RETGEM. The gain variation as a function of time of TGEM at the gain ~ 2000 was within 6% after the correction by pressure and temperature. On the other hand, the gain variation as a function of time of TGEM was large at higher gain and can not be explained by only the correlation between the gain and the value of pressure over temperature. The gain variation as a function of time of RETGEM was within 4% after the correction by pressure and temperature. The achieved energy resolution was ~ 13% (TGEM) and ~ 10% (RETGEM). The energy resolution of RETGEM is comparable to that of micro-scale GEM.

Position reconstruction in drift chambers operated with Xe, CO2 (15%)

Abstract We present measurements of position and angular resolution of drift chambers operated with a Xe, CO 2 (15%) mixture. The results are compared to Monte Carlo simulations and important systematic effects—in particular the dispersive nature of the absorption of transition radiation and non-linearities—are discussed. The measurements were carried out with prototype drift chambers of the ALICE Transition Radiation Detector, but our findings can be generalized to other drift chambers with similar geometry, where the electron drift is perpendicular to the wire planes.

Space charge in drift chambers operated with the Xe,CO2(15%) mixture

Using prototype modules of the ALICE Transition Radiation Detector (TRD) we investigate space-charge effects and the dependence of the pion rejection performance on the incident angle of the ionizing particle. The average pulse height distributions in the drift chambers operated with the Xe; CO2ð15%Þ mixture provide quantitative information on the gas gain reduction due to space charge accumulating during the drift of the primary ionization. Our results demonstrate that the pion rejection performance of a TRD is better for tracks which are not at normal incidence to the anode wires. We present detailed simulations of detector signals, which reproduce the measurements and lend strong support to our interpretation of the measurements in terms of space-charge effects. r 2004 Elsevier B.V. All rights reserved. PACS: 29.40.Cs

Centrality Dependence of J/psi Production in Au+Au and Cu+Cu Collisions by the PHENIX Experiment at RHIC

J/{psi} production has been measured in Au+Au and Cu+Cu at {radical}(s{sub NN})=200 GeV by the PHENIX experiment at the relativistic heavy ion collider (RHIC) during 2004 and 2005, respectively, at mid-rapidity (|{eta}|{le} 0.35) via J/{psi} {yields} e{sup +}e{sup -} decay and at forward rapidity (1.2 {le}|{eta}|{le} 2.2) via J/{psi} {yields} {mu}{sup +}{mu}{sup -} decay. The nuclear modification factor (RAA) of J/{psi} is presented as a function of the collision centrality for Au+Au collisions (final results) and Cu+Cu collisions (preliminary results) in both rapidity windows. These results are compared to SPS results at lower energy and to various theoretical calculations.

Future upgrade and physics perspectives of the ALICE TPC

Abstract The ALICE experiment at the Large Hadron Collider (LHC) proposes major detector upgrades to fully exploit the increase of the luminosity of the LHC in RUN 3 and to extend the physics reach for rare probes at low transverse momentum. The Time Projection Chamber (TPC) is one of the main tracking and PID devices in the central barrel of ALICE. The maximum trigger rate of the TPC is currently limited to about 3.5 kHz by the operation of a gating grid system. In order to make full use of the luminosity in RUN 3, the TPC is foreseen to be operated in an ungated mode with continuous readout. The existing MWPC readout will be replaced by a Micro-Pattern Gaseous Detector (MPGD) based readout, which provides intrinsic ion capture capability without gating. Extensive detector R&D employing Gas Electron Multiplier (GEM) and Micro-Mesh Gaseous detector (Micromegas) technologies, and simulation studies to advance the techniques for the corrections of space-charge distortions have been performed since 2012. In this paper, the expected detector performance and the status of the R&D program to achieve this ambitious goal are described.

Simulation study for Forward Calorimater in LHC-ALICE experiment

We propose Forward Calorimeter (FOCAL) as an upgrade plan of ALICE detector at LHC. FOCAL will contribute to small-re physics in pb+Pb collisions and Quark Gluon Plasma (QGP) physics in Pb+Pb collisions. Our conceptual desgin of FOCAL consists of SiW sandwith-type calorimeter and Si Strip layers to measure prompt γ and π° → γ + γ up to 200 GeV energy, which corresponds to < 20 (10) GeV/c transverse momentum at η = 3 (4).