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ALICE Experiment at LHC
Hiroshima UniversityT. Horaguchi
03/18/’09 for the Recent Topics in Hadron Physics
Outline
• Introduction– Motivation in Quark Physics– History of Universe & QCD– Theoretical Background
• Proton-Proton collisions• Heavy Ion Collisions
– History of QGP Search– What did we learn at RHIC ?
• ALICE Experiment• Contribution from Japan• Summary & Future Plan
2009/3/18
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Introduction• Motivation in “Quark Physics”
– State of early Universe • Matter state around 10-5 s after Big Bang• Evolution of the universe• Differentiation of each interaction
– Fundamental property in Strong Interaction • Quark confinement• Quark deconfinement ?
– Property of material of deconfined partons ?
– Origin of Mass• 2 Stage Mechanism
– Mass of quarks with Higgs Mechanism– Mass of hadrons with Chiral Symmetry Breaking
• LHC with ALICE – LHC : Strong QCD Machine– ALICE : Wide purpose Heavy Ion Experiment
2009/3/18
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History of the Universe & QCD
2009/3/18
15 by
1 by
1012 s
Birth of Life
Formation of Galaxy
Formation of Atom
Formation of Nucleus102 s
10-6 s
10-35
s
0.00s Big Bang
Inflation
Quark ConfinementAnti-Quark
AnnihilationProduction of
Quark
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Theoretical Background
• Perturvative QCD (pQCD)– QCD (Quantum ChromoDynamics)– Basement for proton-proton & heavy ion
collisions at high energy• Lattice QCD
– Predict new state of Quark Matter• Quark Gluon Plasma (QGP)
2009/3/18
Karsch,Lect. Notes Phys. 583
(2002) 209
Recent Topics in Hadron Physics @ TITECH
Proton-Proton Collisions with pQCD
• The cross section for a hard scattering process in proton-proton collisions, for example the production of a hadron “h” (pp→hX) , can be written as follows;
• The cross section can be factorize the three parts.
),(),,,(ˆ),(),( 222
21
,,
2121
21
21
21
zDxxpdxfxf
dxdxd
hfh
Xfffpp
fff
hXpp
Parton Distribution
Function (PDF)
Fragmentation Function (FF)
Subprocess cross section calculated with pQCD
2009/3/18
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Heavy Ion Collisions
Pre-equilibriumThermalization
QGP phase?
Mixed phaseHadronization (Freeze-out) + Expansion
2009/3/18
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Glauber Model
A
BSpectator
Participant
8 2009/3/18
Impact Parameter : b
• Spectator– Nucleon which do not
participate in Reaction• Participant (Npart)
– Nucleon which participates in Reaction
• Number of Binary Collisions (Ncoll)– Number of total
nucleon-nucleon collisions in heavy ion collisions
ypσσN
ypN=R
Tcoll
TAB ddd
ddd
ppinelNN
AB
//
/
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History of QGP Search• Bevalac @LBNL
– p=0.8 GeV/A, sNN=1.8 GeV• E802/859/866 @AGS-BNL
– p=14.6 GeV/A, sNN=5.4 GeV• NA44/WA98 @SPS-CERN
– p=160 GeV/A, sNN=17 GeV• PHENIX @RHIC-BNL
– p=100+100 GeV/A, sNN=200 GeV• ALICE @LHC-CERN
– p=2750+2750GeV/A, sNN=5500 GeV
2009/3/18
What do we learn from RHIC ?
• dense: energy loss of (even heavy) quarks– jet quenching (high pT suppression)– jet modification
• partonic: quarks’ degrees of freedom, screening– constituent quark number scaling of collective
motion– J/Y suppression
• strongly coupled: perfect fluidity– hydro-dynamical collective motion
• hot: thermally radiative– thermal (virtual) photons
2009/3/18
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RHIC Outcomes: New State of Matter (1)
2009/3/18
ypσσN
ypN=R
Tcoll
TAB ddd
ddd
ppinelNN
AB
//
/
•pedestal and flow subtracted
• dense: energy loss of (even heavy) quarks– jet quenching (high pT suppression)– jet modification
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RHIC Outcomes: New State of Matter (2)
QGP
Hadron
27
Universal quark distribution; w
w (1 2v2,q cos2)
Beam axis
x
z
YReaction Plan
Not Central Collision
• partonic: quarks’ degrees of freedom, screening– constituent quark number scaling of
collective motion• strongly coupled: perfect fluidity
– hydro-dynamical collective motion
2009/3/18
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RHIC Outcomes: New State of Matter (3)
2009/3/18
• partonic: quarks’ degrees of freedom, screening– J/Y suppression
• hot: thermally radiative– thermal (virtual) photons
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labcm mEEs 2
ALICE
CMS
LHC-b
ATLAS
labcm mEEs 2
A Large Ion Collider Experiment
• The heavy ion experiment at LHC• Collider Experiment
– Advantage:– Disadvantage : Difficulty of covering the
acceptance• Circumstance : 27km• 30 countries; ~ 100 institutes; > 1,000
membersSweden
PolandNorway
Russia
JINR
Japan BrazilRomaniaSpain/Cuba
South AfricaUSA
ChinaCroatia
ArmeniaIndia
Korea
UkraineMexico
Czech Rep.Slovak Rep.
CERNDenmark
Finland
Germany
France
Italy
GreeceUK
HungaryNetherlands
2009/3/18
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ALICE : “ Wide-Purpose” Detector
• Central barrel spectrometer: -0.9 < h < 0.9– Tracking and particle identification in full
azimuth– Partial coverage of HMPID, PHOS, EMCal
• Forward muon spectrometer: - 4 < h < -2.4
• Multiplicity: - 3 < h < 5.4
(charged particles)
µ arm
2009/3/18
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ALICE (L3) Magnet + Detector Cage
2009/3/18
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Time Projection Chamber• Main tracking device
– |h| < 0.9, full azimuth• Largest ever
– 88 m3, 10 m long, 5.6 m diameter, 570 k channels
– 3 % X0, Ne (86)/CO2 (9.5)/ N2 (4.5), O2 ~ 1 ppm
– max. 80 MB/event (after compression)
2009/3/18
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Inner Tracking System
• Tracking (|h|< 1) + multiplicity (|h|< 2)• Si pixel/drift/strip; 2 layers each
– rf resolution: 12, 38, 20 mm
2009/3/18
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Transition Radiation Detector
• Tracking and particle identification– |h| < 0.9, full azimuth– 400 – 600 mm resolution in rf, 23 mm in z– e/p separation > 100 at pT > 3 GeV/c
2009/3/18
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Time of Flight
• Hadron identification– |h| < 0.9, full azimuth; 3.7 m flight path
• Multi-gap resistive plate chamber– Time resolution ~ 50 ps, 160 k channels
2009/3/18
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High Momentum PID
• Ring imaging Cherenkov with CsI photo-cathode– gth = 1.57, |h| < 0.6, Df = 58; 11 m2, 16.1 k
channels
2009/3/18
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Photon Spectrometer
• High granularity, high resolution EM calorimeter
• (details later)2009/3/18
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Forward (Di-)Muon Spectrometer
• Quarkonia and heavy flavor in forward region– 2.4 < h < 4.0– Mass resolution: < 70 MeV at J/Y, < 100 MeV
at – Momentum cutoff: 4 GeV/c
2009/3/18
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Trigger, DAQ, Offline• 1.2 GB/s (500 MB/s initially); 2.5 PB/y• Multi-layered trigger
– Central trigger processor L0, L1, L2– High level trigger
• 1 K CPU; scalable to 20 K CPU
• LHC computing grid (LCG)– Tested world wide in 2007
• whole collected data systematically reconstructed• 18 TB of reconstructed data shared world wide• 7.5 K CPU, 1 PB disks at 65 sites in 4 continents
2009/3/18
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ALICE Data Flow
DAQ
CASTOR @ T0
T0
Buffer
CAF
T1
ESDT2
T2
ESD AOD
On lineAnalysis
First Reco 2-3 Reco
User Analysis
CERN
JP-HIROHSIMA-WLCG etc.…
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ALICE in Japan
• Full membership since 2006– Hiroshima University
• Physics primarily via photon channels• PHOS R&D and construction• “Tier 2” analysis facility
– CNS, University of Tokyo• Physics primarily via electron channels• Photon/electron trigger R&D• TRD construction
– University of Tsukuba• Physics primarily via collective behavior (?)• TRD construction• CERN branch office• J-Cal construction
2009/3/18
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Photons Physics @ Hiroshima University
• ALICE photon spectrometer: PHOS– photons, nuetral mesons, jet tagging
• + L0, L1 trigger capability• wide coverage from 100 MeV to 100 GeV
– high eneregy resolution, high granularity• s/E ~ 3 %/E up to 100 GeV • PbWO4 crystals of 22 (1.0 RMoliere)×22×180 (20 X0)
mm3
• APD + charge sensitive pre-amplifier readout• cooled and controlled at -250.1 C
– |h| < 0.12, Df = 100 at 4.6 m• 56×64×5 modules; 17,920 channels, 12.5 t
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Photon Physics #1: Neutral Mesons
thermal ~ e-E/T
hadron decays
jet-medium interaction jet-photon conversion bremsstrahlung
pQCD processes ~ pT-n
compton scattering annihilation fragmentation
• “day-1” physics program– enough acceptance with initial 3 PHOS
modules
• higher pT reach + stronger suppression than RHIC– clearer measurement of quark energy loss– less background for direct photon
measurement
2009/3/18
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• direct photon at RHIC: consistent with pQCD– consistent with simple p+p superposition– consistent w/ and w/o nuclear modification of
PDF– consistent w/ and w/o string fragmentation
quenching• hard photons at ALICE/LHC
– # prompt photons ~ # decay photons at > 60 GeV
– large rate up to very high pT
Photon Physics #2: pQCD Photons
K.J.Eskola et al.,NPB535 (1998) 351
F.Arleo,hep-ph/0601075 (2006)
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Quenched String Fragmentation
~ 60 % suppression at 10 GeV/c
F.Arleo,hep-ph/0707.2320 (2007)
• significant suppression of pQCD photons expected– independent measurement of quark energy
loss– less background for thermal photon
measurement
2009/3/18
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Photon Physics #3: Thermal Photons
• RHIC outcome– radiation at 300 – 500 MeV implied
• indirect measurement via g*• cf. critical temperature ~ 170 MeV
– models not strongly constrained
• LHC prospect– direct measurement of thermal photons
• higher temperature + longer life time• reduced background due to quenching• ALICE-PHOS detector
– understanding of thermal properties of partonic system
2009/3/18
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Computing @ Hiroshima University• GRID Computing• Local Cluster
– PHENIX / ALICE– Cluster
• Xeon 3.0GHz– 16node x 2cpu x
2core• Xeon X5355 2.66GHz
– 31nodex 2cpu x 4core • Xeon X5356 3.oGHz
– 20nodex2cpux2core– Storage Server
• 26TByte– Band Width
• 1GBps– OS
• SL4.4 or SLC4.5– Batch Job System
• Condor• ALICE Analysis
– Physics Simulation– Simulation for PHOS
Calibration• Production
– ALICE Full Simulation• 1G Event32
NFS
NFS
Library & Condor Server
Strage Server
Local Cluster
2009/3/18
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Computing GRID @ Hiroshima University
• Site name– JP-HIROSHIMA-WLCG
• Site Administrator – T. Sugitate– T. Horaguchi
• Site Security Officer– T. Sugitate– T. Horaguchi
• Site Component– VOBOX– Computing Element– Storage Elemet
• ~200TByte– Monitoring– User Interface– Worker Node
• Intel Xeon5160 2cpu x 2core x 16• Network Bandwidth
– 1GBit Ethernet on SINET3• Regional Supported by ASGC in Taiwan• Possible associated Tier-1 in Lyon
WN
VOBOX
CE
SE
UI
Router
SINET-3
2009/3/18
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J-Cal (EM) @ University of Tsukuba
• J-Cal (EM) for back-to back jets in ALICE
• Define back-to back jets• Trigger back-to back jets
• Why back-to back jets?– Origins clean– Kinematically clean
• Energy balance• back-to back in phi
• Physics Goal– Modification of soft particles
with high E jet• Mach Cone, Ridge, etc
– Tomography of QGPJ-Cal
ALICE EMCAL
J as Jet, Japanese, EMCAL
~1 supermodule(ΔΦ
,Δη) ~(0.4,0.4)
2009/3/18
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ALICE Status and Plan• Initial configuration in 2009
– Full: ITS, TPC, HMPID, muon, trigger detectors– Partial: TRD (> 8/18), TOF (> 8/18), PHOS
(3/5)– Reduced: high level trigger (30%)
• i.e. Initially:– Almost full hadron/muoncapability– Partial electron/photon capability
• Mid-term (a few years) plan for completion– Full TRD, TOF, PHOS– EMCal– Enhanced higher level trigger 2009/3/18
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• Vital reference for Pb+Pb– Elementary processes at unknown energy
region• s, c, b, quarkonia, …
• Own physics in p+p– Particle production mechanisms at highest ever
energy• Multiplicity, baryon transport, …
– ALICE advantages• pT coverage from < 100 MeV/c (XT < 10-5) to > 100
GeV/c• Good particle identification• Trigger capability including minimum-bias, multiplicity,
…
• Physics in high multiplicity p+p events
Initial Strategy : p+p Physics
2009/3/18
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Boundary Condition: LHC Schedule
• LHC start-up schedule– 2008/09 first beam– 2009/09 re-commissioning (p+p)– 2009/10 p+p, s = 10 TeV?, 1032 cm-2s-1
– 2010? Pb+Pb, sNN = 5.5 TeV, 5×1025 cm-
2s-1
• expectations in initial years– p+p s = 14 TeV, 1031 cm-2s-1 (ALICE), 107 s/y
s = 5.5 TeV, 1031 cm-2s-1, 106 s/y×1 y
– Pb+Pb sNN = 5.5 TeV, 1027 cm-2s-1, 106 s/y
– p+Pb sNN = 8.8 TeV, 1029 cm-2s-1, 106 s/y×1 y
– Ar+Ar sNN = 6.3 TeV, 1029 cm-2s-1, 106 s/y×1 y
2009/3/18
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• Discovery of deconfined partonic matter at RHIC
• Not end of story; new prospects at LHC– global understanding of hot partonic matter
• ALICE at LHC starting in months– Uniquely suitable for hard/heavy probes– Opening new ground for “soft” photonic probes– ALICE-J in full commitment (along with RHIC)
• ALICE : “ wide-purpose” heavy ion experiment– Broad prospect coverage + high capacity for
“unknown”• Physics harvests around corner (even in
initial p+p)
Summary & Future Plan
2009/3/18
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Backup
2009/3/18
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40Dec.2008, Wuhan
View from RHICians
• Nothing much changes from what we see at RHIC.
• Nevertheless,– Larger/longer QGP– High pt jets
become available!
RHIC LHC
√ sNN (GeV) 200 5500
T/Tc 1.9 3.0-4.2
ε(GeV/fm3) 5 15-60
τQGP (fm/c) 2-4 >10
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Backup (v2)
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V2 ってなに?
ビーム軸
x
z
反応平面
非中心衝突
Y
生成粒子と反応平面の為す角度 Φ
x ( 反応平面 )
Y
φ
粒子の収量が、( x 方向) > ( y 方向)なら、 v2>0
v2 は、生成される粒子の方位角方向の異方性( Azimuthal anisotropy )の強度をあらわしている???
の分布をフーリエ展開
=
dN/d(-Ψ) = N (1 + 2v2cos(2(-Ψ)))
ex. Φ-Ψ の分布
v2 ・・・ 生成粒子の反応平面に対しての楕円率
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楕円型フロー( Elliptic Flow )ってなに?
• フロー ・・・ 粒子の集団運動• 楕円型 ・・・ x方向とy方向に流れるフローの
量が違う。
Y
XR.P.
衝突関与部の初期の幾何学的な異方性が運動量空間における方位角異方性となって検出されている。→ 衝突で生成された物質の性質を反映している測定量
???
???
Y
X
λ >> R ; 等方的(Isotropic)
λ << R ; 異方的(anisotropic)
粒子の平均自由行程( λ )が衝突関与部の半径 Rより十分大きければ、相互作用せず、粒子は等方的に広がる。 ( 圧力勾配もうまれない )
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• QGP 中でのパートンの平均自由行程 λ が衝突関与部の半径 Rに比べて十分に小さいと、系が局所的熱平衡に達して圧力勾配をうむ 粒子の運動量空間での方位角異方性– λ>> R ; isotropic 自由ガスのように振舞う– λ<< R ; anisotropic 流体のように振舞う
もし平均自由行程( λ )が衝突関与部の半径 R より十分小さければ・・・
圧力勾配 小
圧力勾配 大粒子放出 大
粒子放出 小原子核の 非
中心衝突では、衝突部の初期の形はアーモンド形(幾何学的異方性をもつ)
ビーム軸
x
z
反応平面
非中心衝突
Y
QGP物質の相互作用 圧力勾配 楕円型フロー v2 が有限 v2 測定は、衝突関与部の初期の幾何学的な異方性が運動量空間における方位角異
方性となって検出されている。→ 衝突で生成された物質の性質を反映している測定量
v2は衝突関与部の楕円率と1対1対応と考えられていた。
2009/3/18
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相互作用があればv 2 は、発達する可能性がある。
衝突後の時間発展の描像
衝突
QGP
パートン熱平衡
化学的凍結
熱的凍結
ハドロン化v 2 が増える。
v 2は、いつ作られたのか?
2009/3/18
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反応関与部の楕円率 ( 説明 )
22
22 -
xy
xy
Eccentricity =
Participant Eccentricity がより実験室の状態に近い。
2009/3/18
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Elliptic flow @ Low pT
RHIC 実験では様々な粒子の v2 が
測定され、有限な値を示している!
運動量が 1.5 GeV/c 以下では 質量が軽い粒子ほど v2 が大きく
なることが観測されている。 v2(π)>v2(K)>v2(p)
=> 流体力学モデルで説明。 非常に早い時間での熱平衡を仮定
τ0 = 0.6 fm/c
=> 系が熱平衡状態になっていることを示唆 強く相互作用する物質の存在
meson(π,K) と baryon(p) の v2 の振る舞いが
mid pT で異なる
Hydro;Phys. Rev. C 67 (03) 044903v2; Phys.Rev.Lett.91 182301 (2003) PHENIX
金+金、√ s =200GeV
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Elliptic flow @ Mid pT
v2: Au+Au, √s = 200GeV , MB
KET = mT-m0
Mid pT (~1.5GeV/c<pT <~4.0GeV/c)• 流体力学モデルで説明できない。• meson(π,K) と baryon(p) で v2 の振る
舞いが異なり、クォーク数でスケールする。– クォーク数でスケールすると v2 は同じ
カーブを描く (universal v2 の存在 )• KET scaling で、質量の効果を取り除く
と低い pT 領域から一致する。• v2 の横運動エネルギー依存が粒子種に
よらずに一致する。(なぜか?)• Φ メソンもクォーク数でスケールする。• u,d,s クォークに比べて重い c クォーク
も、 u,d,s クォークと同程度に flow しているという解析結果もある。( Shingo’s D-thesis )
PRL 98, 162301
Recombination の描像と一致する。クォークレベルで flow が決まっている
ことを示唆している。 2009/3/18
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Quark Number Scaling
)3(
)2(
33
3
23
3
tB
B
tM
M
pwCpd
NdE
pwCpd
NdE
QGP
Hadron
ハドロン化のメカニズムの一つで、近くにある同じぐらいの運動量を持つクォークがくっついてハドロンをつくるというモデル
qq => Meson (π,K)qqq => Baryon (p) Universal なパートン分布 w(pT) を仮
定
mesonbaryon
w(pT)
パートン分布
)3(3
)2(2
,2,2
,2,2
tqB
tqM
pvv
pvv
v2 がパートンレベルで決まっていれば以下の式が成り立つ
p/π ratio をよく再現している。
recombination
Recombination model
fragmentation
v2 (200GeV Au+Au ) のbaryon とMeson の違いを再現している。 2009/3/18
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v2(KET/nq)/nq/epar/Npart1/3
Universal Scaling Different System (Au+Au, Cu+Cu) Different Energy (200GeV ~
62.4GeV) Different Centrality (0-50%) Different particles (π/ K /p ・・・ )
Universal Curve !!
3/1
2 )/(
partq
qET
Nn
nKv
2009/3/18
Backup (Heavy Quark)
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• RHIC outcome– J/Y suppression as strong signature of
deconfinement– mechanism not uniquely identified
• no J/Y melting, but only Y’ and cc?• melting/regeneration balance?
• LHC prospect– systematic measurements of J/Y,, excited
states– unified understanding of suppression
mechanism(s)
Initial(?) Strategy #3 : Heavy Q’onia
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• LHC: hard/heavy QCD machinecharm/beauty sNN (mb) shadowing
multiplicity• p+p 14 TeV 11.2/0.5 1.0/1.0
0.16/0.007• central Pb+Pb 6.6/0.2 0.65/0.85 115/4.6
• fate of J/Y?– larger energy density leading to J/Y melting
at last?– larger charm yield leading to regeneration
dominance?– note 20 – 30% J/Y from B decay
• open beauty measurement important
J/ Y at ALICE/LHC
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• (1s) melting only at LHC• (2s) expected to melt approximately
with J/Y• pT dependence of (1s)/ (2s) interesting
– key to resolve possible melting/regeneration balance
Relevance of
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• ALICE uniquely down to pT = 0 and at large rapidity
Quarkonia Measurements at LHC
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• ALICE (and CMS) capable to separate substates– ~ 100 MeV resolution required
Quarkonia Resolution: Sub-States of
ALICE e+e-
s < 80 MeV
ALICE m+m-
s < 100 MeV
CMS m+m-
s ~ 80 MeV
ATLAS m+m-
s > 120 MeV
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• e.g. in 1 month of Pb+Pb– J/Y: good statistics
• up to ~ 20 GeV/c
– Y’: smaller S/B– (1s), (2s): good S/B
• up to ~ 8 GeV/c
– (3s): lower statistic
Quarkonia Statistics/Feasibility
S[103
]B[103
]S/B S/(S+B)
J/Y 130 680 0.20
150
Y’ 3.7 300 0.01
6.7
(1S) 1.3 0.8 1.7 29
(2S) 0.35 0.54 0.65
12
(3S) 0.20 0.42 0.48
8.1
m+m- raw spectra
m+m- after combinatorics subtraction
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pt direct/decay direct/decay thermal/decaythermal/decay
(GeV/c) w/o suppression 80% suppression w/o suppression 80% suppression
3 [1] 4 – 10 % 4 – 10 % 3 – 9 % 3 – 9 % [2] 5 – 9 % 5 – 9 % 5 – 9 % 5 – 9 % [3] 5 – 10 % 5 – 10 % 4 – 8 % 4 – 8 %
5 [1] 6 – 12 % 12 – 25 % 3 – 9 % 6 – 18 % [2] 6 – 10 % 12 – 20 % 3 – 5 % 6 – 10 % [3] 11 – 15 % 20 – 30 % 7 – 12 % 14 – 22 %
10 [1] ~ 10 % ~ 50 % ~ 5 % ~ 25 % [2] ~ 10 % ~ 50 % < 1 % < 5 % [4] 25 – 30 % 15 – 20 %
[1] F.Arleo et al., hep-ph/0311131[2] F.Arleo, D.d’Enterria, D.Peressounko,
nucl-th/0707.2357[3] S.Turbide, R.Rapp, C.Gale, hep-ph/0308085[4] S.Turbide, C.Gale, S.Y.Jeon, G.D.Moore,
hep-ph/0502248
Direct/Thermal Photon Expectations
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• extrapolated from PHENIX/EMC to ALICE/PHOS– based on expected PHOS performance
Systematic Errors on Photons
p0 pt (GeV/c) 2 6 10 16
Peak extraction (%) 3.7 2.5 2.4 2.3
Acceptance (%) 1.0 1.0 1.0 1.0
PID efficiency (%) 5.8 4.1 4.3 4.1
Energy scale linear (%) 4.0 4.0 4.0 4.0
Energy scale non linear (%) 1.7 0.7 0.5 0.5
Merging (%) 0.0 0.0 0.0 0.0
Non vertex (%) 2.0 2.0 2.0 2.0
Conversion (%) 3.4 3.4 3.4 3.4
Total (%) 9.1 7.5 7.8 7.0
gpt (GeV/c) 2 6 10 16
Peak extraction (%) 3.7 2.5 2.4 2.3
Charged contamination (%) 2.4 2.4 2.4 2.4
Neutron contamination (%) 2.0 0.1 0.1 0.1
Other mesons contribution (%) 6.0 3.0 3.0 3.0
Acceptance (%) 0.7 0.7 0.7 0.7
PID efficiency (%) 3.0 2.0 2.0 2.0
Energy scale non linear (%) 1.7 0.7 0.5 0.5
Merging (%) 0.0 0.0 0.0 0.0
Non vertex (%) 2.0 2.0 2.0 2.0
Conversion (%) 1.8 1.8 1.8 1.8
Total (%) 8.9 5.8 5.7 5.7
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Pre-equilibriumThermalizationQGP phase?
Mixed phaseHadronization (Freeze-out) + Expansion
Photons from Multi Stage
Compton/AnnihillationFragmentation
Prompt PhotonJet-Photon Conversion
Jet-Bremsstrahlung (QGP)
Jet+MediumThermal Photon (QGP)Thermal Photon (HG)
Thermal Photon
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Decay photons
+ Decay photon as huge background
The decay photon background strongly reduced due to jet suppression in A+A
Schematic Spectrum in A+A
Thermal Photon (QGP)Thermal Photon (HG)
Jet-Photon ConversionJet-Bremsstrahlung (QGP)
Thermal Photon
/g E Tethermal:nT
1
phard:
Jet+MediumCompton/Annihillation
Fragmentation
Prompt Photon
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Schematic Spectrum in A+A
Thermal Photon (QGP)Thermal Photon (HG)
Thermal Photon
Compton/AnnihillationFragmentation
Prompt Photon
pT ~ Tmedium
~ 1 GeV (QGP) ~ 200 MeV (HG)
pT ~ QCD
Tmedium ~ 1 GeV (QGP)
Jet-Photon ConversionJet-Bremsstrahlung (QGP)
Jet+Medium
pT ~ pT
q (Conversion)
< pTq (Brems)
Jet
Compton
Fragmentation
Conversion
Fries et.al.PRL90(2003)132301
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BNL-RHIC-PHENIX: Au+Au sNN=200 GeV
PHENIX
p+p 衝突の重ね合わせで記述できる。 2009/3/18
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100 xT
Au+Au minimum bias
gq ->q is main contribution
BNL-RHIC-PHENIX: Prompt Photon
x=0.1 から 0.2 にかけて 20 %の減少がみられた 次のページへ
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BNL-RHIC-PHENIX: Prompt Photon
• pQCD Photon = Direct Photon + Fragmentation
PRL98(2007)012002, PHENIX
direct
Fragmentation
calculation by W. Vogelsang
At RHIC energy, the fragmentation contribution is not negligible, ~30% at 10GeV/c photon.
p+p
Au+Au
Isolation cut により直接光子の収量が減る。 Fragmentation + Underlying Event
により説明可能
Isospin effect + Fragmentation Quenching is consistent with data
Hep-ph/0601075, by F.Arleo
Arleo JHEP 0609 (2006) 015
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BNL-RHIC-PHENIX: Thermal Photon
• NLO pQCD
• A particular thermal Model– 2+1 hydro, t0=0.15 fm/c
– T0ave=360 MeV(T0
max=570 MeV)
– The data are consistent with thermal + pQCD
– pQCD questionable down to low pT
• needs confirmation from analysis of p+p data
L.E. Gordon, W. VogelsangPhys. Rev. D48, 3136 (1993)
D. d’Enterria, D. Peressounkonucl-th/0503054
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QGP-ThermalJet-photon
NLO-pQCD
All
• Interaction of hard-scattered parton with dense matter.– Compton scattering
(jet-photon conv.)• R.J. Fries, Phys.Rev. C72
(2005) 041902 – Over estimation at high-
pT• S. Turbide, Phys.Rev. C72
(2005) 014906– Reproduce data well
– Bremsstrahlung• B.G. Zakharov, JETP Lett.
80 (2004) 1
Jet-quenching effect for fragmentation photons are estimated with AMY formalism.
BNL-RHIC-PHENIX: Jet-Medium
もう少し理解が必要
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Direct Photon Measurement in ALICE Hard photon
Strong suppression of high pT hadrons will help to improve the S/N ratio
High pT photons can be found Thermal photon
Direct evidence of thermal equilibration
Created matter in LHC will have high temperature, high density and long life time matter comparison with RHIC, so we can expect large thermal photon component in ALICE
Primary contributor in low pT regionThermal photon measurement is
very challenging because it is very hard due to a large background from hadron decays.
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Low pT Photons
In ‘real’ photon measurement Measured yield with a large systematic
errorDifficulty on measuring low pT “real” direct photons
1. Finite energy resolution of the EMCal
2. Large hadron background
Advantages on measuring ‘virtual’ photons
1. High momentum resolution of the TPC
2. Reliable estimation of the hadron decay components using Kroll-Wada formula
Experimental determination is very important since applicability of pQCD is doubtable in low pT region
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Virtual Photon Measurement
71/16
Case of Hadrons
Obviously S = 0 at Mee > Mhadron
Case of g*
– If pT2>>Mee2
Possible to separate hadron decay
components from virtual photon in the proper mass window.
Any source of real g can emit g* with very low mass.
Convert direct g* fraction to real direct photon yield
S : Process dependent factor
3
2
222 1
hadron
eeee M
MMFS
1S
qg*
g q
e+e-
gp
SdNMM
m
M
m
dM
Nd
eeee
e
ee
e
ee
121
41
3
22
2
2
22
inclusive
direct
inclusive
direct
gg
gg
Kroll-Wada formula
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Evaluation the Statistics in First Year Evaluation from NLO pQCD
calculation Used INCNLO
http://wwwlapp.in2p3.fr/lapth/PHOX_FAMILY/readme_inc.htm
CTEQ6M, BFG √s : 14TeV pp μ : 0.5pT,1.0pT,2.0pT
Evaluation of the number of the virtual photon
Assumed DAQ rate :100KHz
1 Day : ~2M 1 Month : ~60M 3 Month: ~ 180M
Acceptance Correction Considered TRD
acceptance |h|< 0.9 f coverage: 8/18 x 2p72
30 Days90 Days
Enough Statics !
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• expected signal/background ratio– 4 ~ 10 % (3 GeV/c) – 25 ~ 50 % (10 GeV/c)
• expected systematic error with ALICE/PHOS– 8.9 % (2 GeV/c) – 5.7 % (10 GeV/c)
Direct/Thermal Photon Feasibility
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RHIC Outcomes: New State of Matter
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Backup (J-Cal)
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Plenty of high pt jets
• Many orders of magnitude!
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Technical details
• We like to increase #of mod. by sacrificing read outs• for larger yields and for jet
broadening
• Why not with PHOS?• Too narrow in eta for jet finding
1 super module =12 x 24
=288 modules
~ 1 Super Module16 x 16 =256 modules
(ΔΦ,Δη)~(0.4,0.4)
11 super module ΔΦ=110o (~1.9 rad)|η|<0.7
W. Current Our Budget
4 towers/module
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