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

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王亚平 : LHC能区 ALICE实验及其 PHOS触发选判

王亚平王亚平( ( 华中师大粒子物理研究所华中师大粒子物理研究所 ))

LHC 能区 ALICE 实验及其PHOS 触发选判


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实验：超高能核 - 核碰撞0) initial conditions: target/projectile mass collision energy impact parameter

1) hard interactions (jets, heavy quarks, J/)

2) pre-equilibrium thermal system of partons

3) quark-gluon plasma Phase transition formation of hadrons

4) Hadron gas freeze-out interacting hadronic matter


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BRAHMSPHOBOS

PHENIX

STAR

Heavy ion 实验 @ BNL/RHIC(4km)

Heavy ion 实验 @BNL/AGS

RHIC 隧道

Heavy ion 实验 @ CERN/LHC (27km)

Heavy ion 实验 @CERN/SPS (6.7km)LHCLHC 隧道隧道

ALICE 探测器

STAR 探测器


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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

< 0.2~0.5~1τ0 (fm/c)

4 - 101.5-4.0<1τQGP (fm/c)

2×104(?)7x103103Vf(fm3)

15 - 403.5-7.52.5ε(GeV/fm3)

2-6×103700-1500430dNch/dy

550020017s1/2 (GeV)

LHCRHICSPSCentral collisions

expect conditions to be significantly different

碰撞的实验初始环境

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


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√s[GeV]

Ycm

RHIC

LHC

SPS

AGS

Initial ConditionsInitial Conditions

pre-RHIC guess still expect conditions to be significantly different


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RHIC LHC 200 GeV 5500 GeVNNs

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 。

s

NNs

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

ALICE @ LHCALICE @ LHC


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Size: 16 x 26 meters

Weight: 10,000 tonsALICE Set-up

HMPID

Muon Arm

TRD

PHOS

PMD

ITS

TOF TPC


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10-6 10-4 10-2 100

x

108

106

104

102

100

M2 (

GeV

2 ) 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

Novel aspects: Qualitatively new regime


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LHC

RHIC

SPS

(h+

+h-)/20

17 GeV

200 GeV

5500 GeV=√ s

• 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

(, Z0, W±).

Novel aspects: Qualitatively new regime


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ALICE/PHOton SpectrometerALICE/PHOton Spectrometer

PHOton SpectrometerPHOton Spectrometer ( (PHOSPHOS),), will detect electromagnetic particles in a limited acceptance domain at central rapidity and provide photon identificationphoton identification as well as neutral mesons identificationneutral mesons identification via the 2-photon decay channel.

Testing thermal and dynamical properties of the initial phase of collision, Testing thermal and dynamical properties of the initial phase of collision, in particular the initial temperature and space-time dimensions of hot in particular the initial temperature and space-time dimensions of hot zone.zone.

Main physical goals:Main physical goals:

– 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 Investigating jet quenching as a probe of deconfinement, studied via high high ppTT ππ0 0 spectrum, and identifying jets through gamma-jet and jet-jet spectrum, and identifying jets through gamma-jet and jet-jet correlations measurements.correlations measurements.

signals of chiral-symmetry restoration.signals of chiral-symmetry restoration.


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• 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

Physical goalsPhysical goals


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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).


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Assembly of PHOS module

Strip unit of 16 detectors

FEE cardin cooling cassette

ALICE-PHOS 前端电子学系统主板 FEE( 武汉组完成 )

PbW04 crystal


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Energy and spatial resolution of PHOS

能量分辨率从 1 GeV/c时的 4% 变化到 100 GeV/c时的 1%

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


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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。

Trigger system of ALICE


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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。

Trigger signals: L0, L1, L2


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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。

Trigger decision criterion of PHOS

7 FEE cards 7 FEE cards

7 FEE cards

TRU card

64 crystals ( 20 degree sector)

TRUregion

3584 Xtals8 TRU domains

16

28

56 crystals

One TRU region

Fast OR cables from FEE to TRU

1 trigger region ( 1 TRU) = 448 crystals1 Fast OR for 2*2 crystal signals 8 Fast OR generated per FEE 112 Fast OR inputs to each TRU

PHOS module


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P r e am p

sha per

summ ing shape r

M E B

2 usH V(i )

F E E ca r ds

HV (j)

L 1 L2

100 ns

Fast OR

A D C

1 0

x 1 / x 1 6

1 Trigger channel

Energy channels

1 0

P r e am p

H V(k )

AP D

HV (l )

= analog OR 2*2

P re a m p P r e a m p

A P D

A P DA PD

PWOrow A

PWOrow B

1 0

high/low

TRULevel-0

..Level-1

112 inputs

58 Gbits/s permanent input!

FEE->TRU signal routingFEE->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


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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 。

Trigger decision criterion of PHOS

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。

Interaction time t=0

12 bit ADC130ns

CTP

max. 800 ns (L0)

~ 40 m = 200 ns

fixed delay

FPGA40 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 25 ns 25 ns 25 ns

40 MHz

40 MHz NRZ serial Trigger

4*4 spaceSum25ns

Over Samp

15 ns

600 ns out of FPGA

160 ns

FEE


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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


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Trigger efficiency of PHOS

触发效率分布满足方程：

Trigger efficiency loss about ~ 4% due to the TRU boundaries

Trigger threshold


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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 module1 module

3 modules3 modules

5 modules5 modules

1 module = 20

y = 0.25

3 modules = 60

y = 0.25

5 modules = 100

y = 0.25


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Trigger rate of PHOS for Pb-Pb collision

1 module1 module

3 modules3 modules

5 modules5 modules

● 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 = 20

y = 0.25

3 modules = 60

y = 0.25

5 modules = 100

y = 0.25


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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.


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Thanks!Thanks!


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Modular structure 5 independent modules each of 3584 crystal detector units:PWO crystal+ APD+ preamp.

PHOS moduleWorking temperature: -25 oC

PHOS Cradle

Crystal detector unit

Strip unit of 16 detector units

PHOS mechanics

王亚平 ( 华中师大 粒子物理研究所 )

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王亚平 ( 华中师大粒子物理研究所 )