international workshop on heavy ion physics at lhc photon physics with phos

International Workshop on Heavy Ion Physics at LHC

Photon Physics with PHOS at Center China of Normal University

Institute of Particle Physics May 21-24, 2008, Wuhan, China

Toru Sugitate / Hiroshima [email protected]

Outline of the Talk Photon sources and physics Lessons from RHIC Reality and strategy for the 1st years Conclusion

Toru Sugitate / Hiroshima Univ. / KEK-20080425

page 3Time Line of the UniversePhotons: the important probe to explore the nature


page 4

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zDxxpdxfxf

dxdxd

hfh

Xfffpp

fff

hXpp

hadronic photonsCalc. w/ pQCD, eg. PYTHIAmeson decays in jets

Parton Distribution Function (PDF)

Subprocess cross section calculated with pQCD

Fragmentation Function (FF)

Photons in pp & AA collisions

pQCD photonsPrecise calc. w/ pQCDIsolated photonsOnly little abundance

prompt photons in AACalc. w/ Lattice QCDThermal photons: QGP and HG

p~T~GeV


page 5

Global observables: Multiplicities, distributions

Degrees of freedom as a function of T: hadron ratios and spectra, dilepton continuum, direct thermal photons

Early state manifestation of collective effects: elliptic flow

Energy loss of partons in quark gluon plasma: jet quenching, high pt spectra, open charm and open beauty

Deconfinement: charmonium and bottonium spectroscopy

Chiral symmetry restoration: neutral to charged ratios, res. decays

Fluctuation phenomena - critical behavior: event-by-event particle comp. and spectra

Geometry of the emitting source: HBT, impact parameter via zero-degree energy flow

pp collisions in a new energy domain










Photon Physics in AA collisions

Pre-equilibrium

Hadronization (Freeze-out) + Expansion

Thermalization QGP phase? Mixed phase

direct pQCD photons

decay photonsdirect thermal photons



















Experimental advantages of Photon Measurement a single calorimeter measures photons and neutral mesons. a calorimeter identifies particles up to very high momentumImportant physics outcome on DAY-1

Most-cited single results from RHIC; 422 cited as of May 2008Suppression of hadrons with large transverse momentum in central Au+Au collisions at s(NN)**(1/2) = 130-GeV. By PHENIX Collaboration (K. Adcox et al.). Sep 2001. 6pp. Published in Phys.Rev.Lett.88:022301,2002 / e-Print Archive: nucl-ex/0109003


page 6Lesson-1 from RHIC

Find discrepancies in Au+Au from elementary processes at high pT.

The low pT feature has been known at SPS and understood as nuclear effects.

KKP

Kretzer

data vs pQCD

p+p->p0 + X

hep-ex/0305013 S.S. Adler et al.

h++h- p0


page 7The Jet Quenching at RHIC

Suppression is very strong (RAA=0.2!) and flat up to 20 GeV/c

Common suppression for p0 and ; it is at partonic level

e > 15 GeV/fm3; dNg/dy > 1100

陽子＋陽子衝突におけるジェット生成高運動量粒子

ｸｵｰｸｸｵｰｸ

ハドロン粒子多重生成（ジェット）

高運動量粒子

ハドロン粒子多重生成

真空

原子核衝突におけるジェット抑制

Both neutral mesons and photons are essential probes for

the jet quenching.

RAA at higher pT reveals new features.


page 8Lesson-2 from RHIC

Systematic error is dominant.


page 9Direct g via g* measurements

pQCD photons

decay photons

/g E Tethermal photons:

Schematic spectrum

PHENIX preliminary

First direct photon excess seen at PHENIX

The first promising result of direct photon measurement at low pT from low-mass electron pair analysis.

Are these thermal photons? The rate is above pQCD calculation. The method can be used in p+p collisions.

If it is due to thermal radiation, the data can provide the first direct measurement of the initial temperature of the matter.

T0max ~ 500-600 MeV !?T0ave ~ 300-400 MeV !?

Compare direct g and g* at LHC

schematic purpose only


page 10Another Ion Collider at CERN

s = 14 TeV for proton + protonsNN = 5.5 TeV for Pb + Pb

ＡＴＬＡＳ実験ＡＬＩＣＥ実験

ＣＭＳ実験

ＬＨＣ -ｂ実験

sNN at LHC = 28 x RHIC =320 x SPS = 1000 x AGS


page 11“Expected” Features at LHC

QGP formation X 2 TRHIC

X 10-20 eRHIC

X 3-5 VFORHIC

X 3-5 QGPRHIC

dominant hard process

heavy quark production

X 2000

~2% at SPS~50% at RHIC~98% at LHC

tothard /

RHICLHC 20

Thermo-dynamic feature

p~T~GeV

Thermal photon physics

High pT jet physics

Heavy flavor physics


page 12

Exp. ATLAS CMS ALICE

Name LAr Barrel LAr Endcap ECAL(EB) ECAL(EE) PHOS EMCal

Structure Liquid Ar PWO + APD~80,000ch

PWO + APD~18,000ch Pb + APD

Coverage 0<|h|<1.4, 2p

1.4<|h|<3.2, 2p

0<|h|<1.5, 2p

1.5<|h|<3.0, 2p

0<|h|<0.12, 0.6p

0<|h|<0.7, 0.6p

Dynamic Range 20MeV-2TeV upto 4TeV 5MeV-80GeV 16MeV-250GeV

Granularityx

0.003x0.100 0.025x0.025 0.025x0.050

0.025x0.100 0.025x0.025 0.025x0.050

0.0174x0.01740.0174x0.0174

to 0.05x0.05

0.004x0.004 0.0143x0.0143

Res. 10%/E0.5%

10%/E0.5%

2.7%/E0.55%

5.7%/E0.55%

3.3%/E 1.1%

7%/E1.5%

Photon Detectors at LHC


page 13Simulation Studies

Background photon source map

Event display with AliRoot


page 14Lots of PCB/frame/pipes there

ITS+TPC+TRD+TOFX/X0~”43%”80%


page 15Direct Photon Sensitivity

Direct photon sensitivity (sig/noise) along two scenarios; with and without jet quenching.

signal strength w/o quenching

Systematic error with a TRD/TOF hole

g all/g

dec

Thermal photons

thermal g enhanced range

A hole in TRD/TOF for 3 central PHOS modules, reducing X/Xo=80% down to

~20%, open the thermal photon sensitive window down to 3-4 GeV.

g all/g

dec

Thermal photon sensitive window

signal strength with quenching


page 16PHOS Strategy in 1st LHC year

Photon physics with PHOS is very promising from the 1st year, but

There are some issues to be cleared for the success: single warm PHOS in 2008 small acceptance; less yield, higher mgg cutoff,

and calibration strategy low LY/gain; larger missing energy, higher trigger

threshold, and increase non-linearity poor mgg resolution; increase sys. errors

p0 & acceptance by Takashi Iwasaki

1st Module as of 15 May, 2008

See Yuri’s TF list

* students’ working version

p0

p0

geometrical acceptance

1 PHOS module

3 PHOS modules

pT[GeV]

pT[GeV]

Mgg[GeV]

Mgg[GeV]


page 17PHOS Strategy in 2nd LHC year

p+p at 14TeV and 1st Pb+Pb run expected Install 3 cold PHOS modules for the 1st

Pb+Pb runs assemble two modules by this fall build the air-tight shells integrate photon triggers

Learn the spectrometer from p+p runs Tune the spectrometer for the best energy

and spatial performances to minimize the systematic uncertainties

Photon analysis in reality is not easy but fruitful output guaranteed

Subgroups are now being formed in PWG4 under Yves;

“You are very welcome to join the p0 team.” said by Hisa Torii, the convener.

~1000 p0

in 1-2 days500k p0/109 events w/ warm PHOS by HT


page 18Conclusion

ALICE is a versatile detector and PHOS is optimized for measurements of thermal photons and neutral mesons up to moderate energies.

Physics scope with PHOS in the 1st LHC years; pT spectra of neutral mesons in pp and AA

Seek new physics at the energy frontier! Promising outcome comparing with pQCD

RAA of neutral mesons & photons up to mod. pT

Promising outcome from 1st years RAA in d+A

Indispensable info. planned in 3rd year. Thermal photons from QGP/HG

Need good understanding of apparatus for accurate all photon and meson yields, and good AA runs pion yield from p+p in

30days by LB


page 19

Thank you for

your attention.

international workshop on heavy ion physics at lhc photon physics with phos

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