# Photon Physics with PHOS

## Presentation on theme: "Photon Physics with PHOS"— Presentation transcript:

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 Univ.

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

Time Line of the Universe
Photons: the important probe to explore the nature

Photons in pp & AA collisions
pQCD photons Precise calc. w/ pQCD Isolated photons Only little abundance hadronic photons Calc. w/ pQCD, eg. PYTHIA meson decays in jets Parton Distribution Function (PDF) Subprocess cross section calculated with pQCD Fragmentation Function (FF) prompt photons in AA Calc. w/ Lattice QCD Thermal photons: QGP and HG p~T~GeV

Photon Physics in AA collisions
Hadronization (Freeze-out) + Expansion Pre-equilibrium Thermalization QGP phase? Mixed phase decay photons direct thermal photons direct pQCD photons 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 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 Experimental advantages of Photon Measurement a single calorimeter measures photons and neutral mesons. a calorimeter identifies particles up to very high momentum Important physics outcome on DAY-1 Most-cited single results from RHIC; 422 cited as of May 2008 Suppression 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 pp. Published in Phys.Rev.Lett.88:022301,2002 / e-Print Archive: nucl-ex/

Lesson-1 from RHIC p+p->p0 + X KKP Kretzer h++h- p0
data vs pQCD p+p->p0 + X hep-ex/ S.S. Adler et al. h++h- p0 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.

The Jet Quenching at RHIC
Both neutral mesons and photons are essential probes for the jet quenching. 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 ハドロン粒子多重生成 （ジェット） 真空 原子核衝突におけるジェット抑制 Suppression is very strong (RAA=0.2!) and flat up to 20 GeV/c Common suppression for p0 and h; it is at partonic level e > 15 GeV/fm3; dNg/dy > 1100 RAA at higher pT reveals new features.

Systematic error is dominant.
Lesson-2 from RHIC Systematic error is dominant.

Direct g via g* measurements
First direct photon excess seen at PHENIX Compare direct g and g* at LHC PHENIX preliminary decay photons thermal photons: Schematic spectrum T0max ~ MeV !? T0ave ~ MeV !? 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. pQCD photons schematic purpose only

Another Ion Collider at CERN
s = 14 TeV for proton + proton sNN = 5.5 TeV for Pb + Pb sNN at LHC = 28 x RHIC =320 x SPS = 1000 x AGS ＣＭＳ実験 ＬＨＣ-ｂ実験 ＡＴＬＡＳ実験 ＡＬＩＣＥ実験

Thermo-dynamic feature
“Expected” Features at LHC QGP formation X 2 TRHIC X RHIC 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 Thermo-dynamic feature p~T~GeV Thermal photon physics High pT jet physics Heavy flavor physics

Photon Detectors at LHC
Exp. ATLAS CMS ALICE Name LAr Barrel LAr Endcap ECAL(EB) ECAL(EE) PHOS EMCal Structure Liquid Ar PWO + APD ~80,000ch ~18,000ch Pb + APD Coverage 0<|h|<1.4, 2p 1.4<|h|<3.2, 0<|h|<1.5, 1.5<|h|<3.0, 0<|h|<0.12, 0.6p 0<|h|<0.7, Dynamic Range 20MeV-2TeV upto 4TeV 5MeV-80GeV 16MeV-250GeV Granularity x 0.003x x x0.050 0.025x x x0.050 0.0174x0.0174 to 0.05x0.05 0.004x0.004 0.0143x0.0143 Res. 10%/E 0.5% 2.7%/E 0.55% 5.7%/E 3.3%/E  1.1% 7%/E 1.5%

Simulation Studies Event display with AliRoot
Background photon source map

Lots of PCB/frame/pipes there
ITS+TPC+TRD+TOF X/X0~”43%”80%

Direct Photon Sensitivity
Direct photon sensitivity (sig/noise) along two scenarios; with and without jet quenching. Thermal photons gall/gdec thermal g enhanced range signal strength w/o quenching Systematic error with a TRD/TOF hole gall/gdec signal strength with quenching 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. Thermal photon sensitive window

PHOS 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 0 See Yuri’s TF list Mgg[GeV] 0 1st Module as of 15 May, 2008 Mgg[GeV] 3 PHOS modules geometrical acceptance 1 PHOS module pT[GeV] 0 &  acceptance by Takashi Iwasaki pT[GeV] * students’ working version

PHOS 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; ~1000 p0 in 1-2 days 500k p0/109 events w/ warm PHOS by HT “You are very welcome to join the p0 team.” said by Hisa Torii, the convener.

Conclusion 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
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