Physics @ ALICE with J-Cal

JSPS Research Fellow / University of TsukubaT. Horaguchi

Nov .05 2009 for the workshop for ALICE upgrades by Asian Countries2009/11/5The Workshop ALICE Upgredes by Asian Countries @ Yonsei University1Photon Analysis & J-CalOutline2009/11/5The Workshop ALICE Upgredes by Asian Countries @ Yonsei University2IntroductionLarge Hadron ColliderALICE ExperimentJet-CalorimeterJet Finding AlgorithmPhysics in pp CollisionsInclusive Jet ProductionDijet productionPrompt Photon ProductionPhoton-Jet ProductionUnderlying EventSummaryIntroduction2009/11/5The Workshop ALICE Upgredes by Asian Countries @ Yonsei University3Large Hadron ColliderPowerful QCD Machine !ALICE ExperimentFocus Heavy Ion Physicspp physics is also important topicJet-Calorimeter @ ALICE Enhance physics message from ALICEIncrease physics topics @ ALICEThis talk is entitled Photon Analysis and J-Cal; however, jet as a QCD physics in pp collisions are also discussed.And this talk focuses about pp physics @ ALICE LHC. Large Hadron Collider @ CERN2009/11/5The Workshop ALICE Upgredes by Asian Countries @ Yonsei University4LHC can accelerate up to14 TeV pp collisions5.5 TeV PbPb collisions2009Commissioning @ 450GeVCollisions @ 450GeV20103months : 7TeV pp5months : 8~10TeV pp1month : Heavy Ion RunLHC will run from this November !

ALICE

CMSLHC-bATLASALICE Detector5TPC (Time Projection Chamber)Main tracking device|h| < 0.9, full azimuthLargest ever88 m3, 10 m long, 5.6 m diameter, 570 k channels3 % X0, Ne (86)/CO2 (9.5)/ N2 (4.5), O2 ~ 1 ppmmax. 80 MB/event (after compression)ITS(Inner Tracking System)Tracking (|h|< 1) + multiplicity (|h|< 2)Si pixel/drift/strip; 2 layers each rf resolution: 12, 38TRD(Transition Radiation Detector)Tracking and particle identification|h| < 0.9, full azimuth400 600 mm resolution in rf, 23 mm in ze/p separation > 100 at pT > 3 GeV/cTrack finding efficiency ~ 90 % @ pT > 1GeV/cMomentum resolution of electrons ~ 2% @ pT > 4GeV/c

PHOS (Photon Spectrometer)EMCAL (ElectroMagnetic Calorimeter)Photon & electron measurement|h| < 0.7, 120 degree azimuthJ-Cal (Jet Calorimeter)Same as EMCAL, but located at oppositeSee nest page

2009/11/5The Workshop ALICE Upgredes by Asian Countries @ Yonsei University

J-cal for LHC-ALICE experimentfor back-to-back jets measurementsJ-Cal construction talk by Tatsuya Chujo on Nov. 6Jet Calorimeter (J-Cal)2009/11/56The Workshop ALICE Upgredes by Asian Countries @ Yonsei University6LHC : QCD Machine2009/11/5The Workshop ALICE Upgredes by Asian Countries @ Yonsei University7Jet PhysicsInclusive Jet production, Dijet production, Dijet angle distribution, Jet structureMonte Carlo TuningConstraints on PDFs and strong coupling constant at ultra high Q2Photon + JetsTest pQCDMonte Carlo TuningUnderlying EventScaling from lower energy experiments to LHCBasis for high pT physics program

Tevatron -> LHC Parton Kinematics2009/11/5The Workshop ALICE Upgredes by Asian Countries @ Yonsei University8

Jet Production @ ALICE2009/11/5The Workshop ALICE Upgredes by Asian Countries @ Yonsei University9Test pQCDBased on pQCDExtract PDFs Strong coupling constantStudy & test matrix element calculations

Underlying event makes the measurement complicatedGood place to study nature of underlying event

Boson + Jet Production @ ALICE2009/11/5The Workshop ALICE Upgredes by Asian Countries @ Yonsei University10

Test pQCDBased on pQCDExtract PDFsStrong coupling constantStudy & test matrix element calculationsLow statistics, so its challenging measurementsFor a time, photon-jet will be a main physics topic in a few yearsUnderlying event makes the measurement complicatedGood place to study nature of underlying eventJet Production & Measurement2009/11/5The Workshop ALICE Upgredes by Asian Countries @ Yonsei University11

Tracking Detector (ITS+TPC+TRD)EMCAL+PHOS+J-CalJet Finding Algorithm2009/11/5The Workshop ALICE Upgredes by Asian Countries @ Yonsei University12Two main categories of jet finding algorithmsCone AlgorithmsMidpoint Algorithm : Extensive use at Tevatron in Run (hep-ex/0005012).Cluster objects based on their proximity - space.Identify stable cones (kinematic direction = geometric center).Advantage: Simpler for underlying-event & pileup corrections.Disadvantage: Infrared-unsafe in high order pQCD & overlapping stable cones.Successive Combination AlgorithmsKt Algorithms : Extensive use at HERA. A few Tevatron analyses.Cluster objects based on a certain metric. Relative Kt for Kt algorithm.Advantage: Infrared-safe in all order of pQCD calculations.Disadvantages: Jet geometry can be complicated. Complex corrections.

A lot of developments in recent years.SisCone, Cambridge-Aachen, Anti-Kt, etc.E.g. FastJet : http://www.lpthe.jussieu.fr/~salam/fastjetExtensively studied in LHC experiments. Will benefit future studies.

Cone jetKT jetJet Finding Algorithm 13FastJet: sequential clustering algorithmshttp://www.lpthe.jussieu.fr/~salam/fastjetkT algorithmCambridge/Aachen algorithmanti-kT algorithmCone jetKT jet

Parameters - R size - pT cut - Jet threshold

arXiv:0802.1189v2 [hep-pn] (2008)Algorithm2009/11/5The Workshop ALICE Upgredes by Asian Countries @ Yonsei UniversityCalculate particle distance : dijCalculate Beam distance : diB=kti2pFind the smallest distance (dij or diB)If dij is the smallest combine particlesIf diB is the smallest and the cluster momentum lager than threshold call the cluster a Jet.

13

Which is the best algorithm ?14

resolution resolutionmeasured energy pThard 100GeV/cJet threshold 20GeV/ckT algorithmanti-kT algorithmCambridge algorithm

Resolution : of sharp gaussianPerformance of energy reconstruction of Jet with anti-kT algorithm is about 50% better than kT algorithm!We analyze for closest Jet to parton , = parton axis jet axisThis work has been done by D. Sakata & T. Horaguchi.

2009/11/5The Workshop ALICE Upgredes by Asian Countries @ Yonsei UniversityInclusive Jet Production2009/11/5The Workshop ALICE Upgredes by Asian Countries @ Yonsei University15Test pQCD at highest Q^2.Constrain PDFs, especially gluons at high-x.Measure strong coupling constant J-Cal enhance the statistics of Jet events

Blue : GluonRed: Quarks=5.5TeV ppDiJet Production2009/11/5The Workshop ALICE Upgredes by Asian Countries @ Yonsei University16J-Cal improves the resolution of the dijet measurement.Dijet angular distribution is sensitive to the jets by pQCD higher order effect.

Jet Structure (qg Jet Separation)2009/11/5The Workshop ALICE Upgredes by Asian Countries @ Yonsei University17Broadness of the jets in direction compared with the closest partonGluon jet has wider structure than quark jet.Precise discussion will be presented by Hiroki Yokoyama on Nov. 7

pTRRed : QuarkBlue : GluonPDF with Recent Tevatron Jet Data2009/11/5The Workshop ALICE Upgredes by Asian Countries @ Yonsei University18Tevatron data reduced uncertainties of PDFs.LHC data also will lead to softer high-x gluons and help reducing uncertainties of PDFs.

Prompt Photon Production2009/11/5The Workshop ALICE Upgredes by Asian Countries @ Yonsei University19In Tevatron, Data/NLO pQC is in agreement at high pT, but enhancement at low pT.Need to treat the fragmentation function carefully.Wider acceptance of J-Cal can improve the quality of isolation cut, but fake photon (from merged 2 photons from 0) will increase in high pT.

Low pT Photon Measurement Any source of real g can emit g* with very low mass. Convert direct g* fraction to real direct photon yieldS : Process dependent factor

qg*gqe+e-

Kroll-Wada formula20

Direct g*/inclusive g* is determined by fitting the following function for each pT bin.

Reminder : fdirect is given by Kroll-Wada formula with S = 1.r : direct g*/inclusive g*2009/11/5The Workshop ALICE Upgredes by Asian Countries @ Yonsei University20Photon-Jet Production2009/11/5The Workshop ALICE Upgredes by Asian Countries @ Yonsei University21Data@Tevatron not well described by NLO pQCD calculationIntrinsic kt ? Resummation ?At LHC, fragmentation effect of prompt photon production will increase, so this topic is so important.

Underlying Event (UE)2009/11/5The Workshop ALICE Upgredes by Asian Countries @ Yonsei University22Underlying Event = Beam remnant + Multiple Parton Interaction (MPI)Jet ProductionTransverse region sensitive to UEHigh statistics jet sampleStudies in Various dijet topologies

Summary2009/11/5The Workshop ALICE Upgredes by Asian Countries @ Yonsei University23LHC is powerful QCD machine !Produced the highest pT particlesWider parton kinematics rangeJet productionTest pQCD at high Q2Extract PDFs, especially high-x gluonsMeasure strong coupling constantJet finding algorithm study almost donePrompt photon & Photon-Jet productionTest pQCDIt will challenge and polish the theoretical calculation.J-Cal will enhance physics message even if pp collisions !Physics harvests around corner even if initial pp collisions !

2009/11/5The Workshop ALICE Upgredes by Asian Countries @ Yonsei University24Backup Slides

0(hadron) triggerJet (small R) triggerJet (large R) triggerGamma triggerCloser and closer to the initial parton energymore and more surface biasgiven by energy loss

STAR PreliminaryAu+Au 0~10%,Jet,0 - hadron correlation Comparisons are the most important!RHIC-AGS09, Y. S. LaiQM09, M. Ploskon2009/11/525The Workshop ALICE Upgredes by Asian Countries @ Yonsei University25

Recoil Di-jet ETjet1>70GeV Recoil 0-jet ET0>30GeV Recoil -jet ET>30GeV in PHOS/J-calEM-caljet (R