LHC能区ALICE实验及其PHOS触发选判 王亚平 ( 华中师大 粒子物理研究所 ) 高能物理学会第七届学术年会, 2006/10/27-2006/11/1, 桂林

实验：超高能核-核碰撞 thermal system of partons 0) initial conditions: target/projectile mass collision energy impact parameter 4) Hadron gas freeze-out interacting hadronic matter 1) hard interactions (jets, heavy quarks, J/) 2) pre-equilibrium thermal system of partons 3) quark-gluon plasma Phase transition formation of hadrons 高能物理学会第七届学术年会, 2006/10/27-2006/11/1, 桂林

RHIC隧道 LHC隧道 高能物理学会第七届学术年会, 2006/10/27-2006/11/1, 桂林 BRAHMS PHOBOS PHENIX STAR Heavy ion实验@ BNL/RHIC(4km) Heavy ion实验@BNL/AGS RHIC隧道 STAR 探测器 Heavy ion实验@ CERN/LHC (27km) Heavy ion实验@CERN/SPS (6.7km) ALICE 探测器 LHC隧道 高能物理学会第七届学术年会, 2006/10/27-2006/11/1, 桂林

碰撞的实验初始环境 碰撞能量更高 碰撞核 更重 碰撞末态系统 －温度 更热 －密度 更密 – 体积 更大 – 寿命 更长 – 产生粒子更多 < 0.2 ~0.5 ~1 τ0 (fm/c) 4 - 10 1.5-4.0 <1 τQGP (fm/c) 2×104 (?)7x103 103 Vf(fm3) 15 - 40 3.5-7.5 2.5 ε(GeV/fm3) 2-6×103 700-1500 430 dNch/dy 5500 200 17 s1/2 (GeV) LHC RHIC SPS Central collisions expect conditions to be significantly different 碰撞的实验初始环境 Significant gain in ε, V, τ » ×10 SPS → LHC » ×3-5 RHIC → LHC 碰撞能量更高 碰撞核　更重 碰撞末态系统 　－温度　　更热 －密度　　更密 　– 体积　　更大 　– 寿命　　更长 　– 产生粒子更多 LHC将于2007年正式投入物理运行 有关课题的理论研究和实验研究 更为必要，更为紧迫 高能物理学会第七届学术年会, 2006/10/27-2006/11/1, 桂林

Initial Conditions pre-RHIC guess LHC √s RHIC SPS AGS Ycm still expect conditions to be significantly different √s [GeV] Ycm RHIC LHC SPS AGS 高能物理学会第七届学术年会, 2006/10/27-2006/11/1, 桂林

ALICE @ LHC RHIC LHC 200 GeV 5500 GeV CERN/LHC运行时将碰撞质心系能量为 =14 TeV的质子流和 =5.5 TeV的铅束流，包括四大实验：ATLAS，CMS，LHCb和ALICE。 ALICE（A Large Ion Collider Experiment），an experiment is optimized to study in detail the behaviour of matter at high densities and temperatures, in view of probing deconfinement and chiral-symmetry restoration。 ------探究QGP态物质 高能物理学会第七届学术年会, 2006/10/27-2006/11/1, 桂林

ALICE Set-up HMPID TOF TRD TPC PMD ITS Muon Arm PHOS Size: 16 x 26 meters Weight: 10,000 tons ALICE Set-up 高能物理学会第七届学术年会, 2006/10/27-2006/11/1, 桂林

Novel aspects: Qualitatively new regime 10-6 10-4 10-2 100 x 108 106 104 102 100 M2 (GeV2) LHC RHIC SPS Probe initial partonic state in a novel Bjorken-x range (10-3-10-5): nuclear shadowing, high-density saturated gluon distribution. Parton dynamics dominate the fireball expansion 高能物理学会第七届学术年会, 2006/10/27-2006/11/1, 桂林

Novel aspects: Qualitatively new regime Hard processes contribute significantly to the total AA cross-section (σhard/σtot = 98%) Bulk properties dominated by hard processes; Very hard probes are abundantly produced. Weakly interacting probes become accessible (g, Z0, W±). LHC RHIC SPS (h++h-)/2 p0 17 GeV 200 GeV 5500 GeV = √s 高能物理学会第七届学术年会, 2006/10/27-2006/11/1, 桂林

ALICE/PHOton Spectrometer PHOton Spectrometer (PHOS), will detect electromagnetic particles in a limited acceptance domain at central rapidity and provide photon identification as well as neutral mesons identification via the 2-photon decay channel. Main physical goals: Testing thermal and dynamical properties of the initial phase of collision, in particular the initial temperature and space-time dimensions of hot zone. measurement of direct single-photon and di-photon spectra measurement of Bose-Einsten correlations of direct photons Investigating jet quenching as a probe of deconfinement, studied via high pT π0 spectrum, and identifying jets through gamma-jet and jet-jet correlations measurements. signals of chiral-symmetry restoration. 高能物理学会第七届学术年会, 2006/10/27-2006/11/1, 桂林

Physical goals Direct photons once produced don’t interact with the fireball → carry information about early stage of a collision Thermal photon spectra: pT  ~ 5GeV dominantly from early, hot QGP phase  initial temperature of a QGP fireball Thermal photon HBT correlations  space-time dimension of the fireball and direct photon yield at low pT Hard process (pQCD) photon spectra: pT > ~ 5GeV Test of Ncoll scaling of hard processes γ– tagged jets Spectra of identified π0 in a broad transverse momentum range Determination of the decay photon background Study of the jet quenching Spectra of identified η-mesons 高能物理学会第七届学术年会, 2006/10/27-2006/11/1, 桂林

Technical data: 17920 lead-tungstate crystals(PWO) -distance to IP 4600mm -coverage in pseudorapidity -0.12;+0.12 -coverage in azimuthal angle 100o -crystal size 22x22x180 mm3 -depth in radiation length 20 -modularity 5 modules -total area 8m2 -total crystal weight 12.5 t -operating temperature -25 oC -photon readout APD PHOS (PHOton Spectrometer) is a high resolution electromagnetic calorimeter consisting of 17920 detection channels based on lead-tungstate crystals(PWO). 高能物理学会第七届学术年会, 2006/10/27-2006/11/1, 桂林

Assembly of PHOS module Strip unit of 16 detectors FEE card in cooling cassette ALICE-PHOS前端电子学系统主板FEE ( 武汉组完成 ) PbW04 crystal 高能物理学会第七届学术年会, 2006/10/27-2006/11/1, 桂林

Energy and spatial resolution of PHOS 从图中我们可以观察到在1 GeV/c时的位置分辨率依赖于角度的不同而从3.2 mm变化到3.9 mm，同样的在10 GeV/c时会从1.2 mm变化 到2.6 mm 能量分辨率从1 GeV/c时的4%变化到100 GeV/c时的1% 高能物理学会第七届学术年会, 2006/10/27-2006/11/1, 桂林

Trigger system of ALICE ALICE触发系统要解决的问题是如何充分利用各个子探测器在不同的碰撞模式下有效的进行触发判选。ALICE子探测器数据读出时间的不同要求ALICE触发系统有三个并行级别的触发，这样的设计使得ALCIE触发系统可以从较快的探测器中读出数据。ALICE触发系统的这三个级别的触发选判信号：零级触发（Level 0，简称L0），一级触发（Level 1，简称L1）和二级触发（Level 2，简称L2）: L0：固定延时，碰撞发生后1.2 μs产生，用来选通ALICE一些子探测器的前端电子学（FEE）部分。 L1：固定延时，碰撞发生后6.5 μs产生，选通L0触发之后余下的所有探测器，也被数据获取系统（DAQ）做为允许数据从探测器的前端电子学开始读出的触发信号。 L2：最终一级的触发信号，碰撞发生后88 μs后产生，主要目的是保证TPC探测器中不发生堆叠效应，同时参与测量的探测器的数据开始从各自的前端电子学部分读出并送到DAQ和HLT（High Level Trigger）系统。 高能物理学会第七届学术年会, 2006/10/27-2006/11/1, 桂林

Trigger signals: L0, L1, L2 L0信号的产生主要基于T0和V0计数器，同时也依赖PHOS、EMCAL、前向TRD和μ子触发的输入。 L1是否触发是通过以下探测器的信息来判选的：（1）来自μ子探测器系统的信息；（2）来自中央探测器，如PHOS、FMD和ZDC的信息。 L2信号的产生基于TPC探测器的漂移时间。L2有可变的等待时间，其上限是TPC的漂移时间。 在ALICE触发系统中，有24个L0输入，20个L1输入和6个L2输入。 作为ALICE子探测器的PHOS（ Photon Spectrometer ）产生L0和L1触发信号，参与ALICE触发系统的工作。 高能物理学会第七届学术年会, 2006/10/27-2006/11/1, 桂林

Trigger decision criterion of PHOS 7 FEE cards TRU card 64 crystals ( 20 degree sector) TRU region 3584 Xtals 8 TRU domains 16 28 56 crystals One TRU region Fast OR cables from FEE to TRU 1 trigger region ( 1 TRU) = 448 crystals 1 Fast OR for 2*2 crystal signals Fast OR generated per FEE 112 Fast OR inputs to each TRU PHOS module PHOS的触发逻辑在FPGA逻辑器件中得到执行，包括产生对应于高亮度下质子-质子碰撞中无偏碰撞事件的L0触发和对应于铅-铅碰撞中大横动量的光子事件的L1触发。 高能物理学会第七届学术年会, 2006/10/27-2006/11/1, 桂林

FEE->TRU signal routing 112 analog sums are fanned in, via 14 FEE to 1 TRU due to 2*2 sums one TRU covers 448 crystals 1 level-0 output 3 level-1 outputs TRU Level-0 . Level-1 112 inputs 58 Gbits/s permanent input! 高能物理学会第七届学术年会, 2006/10/27-2006/11/1, 桂林

Trigger decision criterion of PHOS ALICE实验运行时，允许PHOS产生L0触发信号的等待时间只有800 ns，产生L1触发信号的等待时间只有6200 ns。 Interaction time t=0 12 bit ADC 130ns CTP max. 800 ns (L0) ~ 40 m = 200 ns fixed delay FPGA 40 MHz ~ 300 ns DeSer 25ns 20ns 20ns 10 ns 80 ns TOF shower APD analog Sum ~ 350 ns Analog -> Digital peak thresh. compare ~ 400 ns NRZ pipeline 4-deep time summing 25 ns 40 MHz NRZ serial Trigger 4*4 space Sum Over Samp 15 ns 600 ns out of FPGA 160 ns FEE PHOS采用TRU单元及其移动窗算法产生触发信号L0或L1，大幅度的缩短PHOS产生触发信号的时间。 高能物理学会第七届学术年会, 2006/10/27-2006/11/1, 桂林

Energy reconstruction performance 高斯分布的平均值μ=5.510 GeV，方差σ=0.104 GeV，σE/E=1.89%； 高斯分布的平均值μ=5.660 GeV，方差σ=0.099 GeV，σE/E=1.75%。 在大横动量范围里PHOS对电子的重建能量与电子的入射能量表现出理想的线性关系 高能物理学会第七届学术年会, 2006/10/27-2006/11/1, 桂林

Trigger efficiency of PHOS Trigger threshold 触发效率分布满足方程： Trigger efficiency loss about ~ 4% due to the TRU boundaries 高能物理学会第七届学术年会, 2006/10/27-2006/11/1, 桂林

Trigger rate of PHOS for P-P collision ● pp run: L = 5×1030 cm-2s-1, √sNN=14 TeV, mini-bias events σtotal~0.1 b; Pythia6.2, 6×106 pp collision events. 1 module 3 modules 5 modules 1 module Df = 20 Dy = 0.25 3 modules Df = 60 5 modules Df = 100 高能物理学会第七届学术年会, 2006/10/27-2006/11/1, 桂林

Trigger rate of PHOS for Pb-Pb collision ● PbPb run: L = 5×1026 cm-2s-1, √sNN=5.5 TeV,σtotal~7.7 b; Hijing1.36, 1×105 PbPb collision events, impact parameters (0, 3 fm). 1 module 3 modules 5 modules 1 module Df = 20 Dy = 0.25 3 modules Df = 60 5 modules Df = 100 高能物理学会第七届学术年会, 2006/10/27-2006/11/1, 桂林

Summary ○ LHC/ALICE is a powerful next generation detector first truly general purpose HI experiment addresses most relevant observables: from super-soft to ultra-hard many evolutionary developments： SSD, SDD, TPC, em cal, … some big advances in technology：electronics, pixels, TOF, computing ○ ALICE/PHOS performs well in trigger decision with good performance of energy reconstruction in a broad transverse momentum range from 0.5 GeV/c to 100 GeV/c trigger efficiency: 1) showed a first order exponential decay versus pT, 2) showed a loss about 4% due to the TRU boundaries trigger rate: 1) for direct photons was much higher than it for π0 and η-mesons, 2) PHOS could provide L0 trigger by its FEE card to low pT photon events and ALICE/CTP provide L0 trigger to high pT photon events, 3) PHOS could provide L1 trigger by its FEE card. 高能物理学会第七届学术年会, 2006/10/27-2006/11/1, 桂林

Thanks! 高能物理学会第七届学术年会, 2006/10/27-2006/11/1, 桂林

PHOS mechanics Modular structure Crystal detector unit PHOS module Working temperature: -25 oC Modular structure 5 independent modules each of 3584 crystal detector units: PWO crystal+ APD+ preamp. Strip unit of 16 detector units PHOS Cradle 高能物理学会第七届学术年会, 2006/10/27-2006/11/1, 桂林