WIXLIB

Jet Measurements with STARwith a focus on jet reconstructionKolja Kauder for the STAR CollaborationJune 8, 2016

STARHigh Tower: Online TriggerET 5.4 GeVin one towerΔφ x Δη 0.05 x 0.05BEMCCharged and neutral particles: Full azimuthal acceptance Extended pseudorapidityacceptance h 1MagnetTPC Maria & Alex Schmah2Au Au, 200 GeVKolja Kauder, WSU - RHIC/AGS Meeting6/8/2016

Correlations: Jet Quenching beyond RAADi-hadronSTAR, PRL 91, 072304 (2003)STAR, PRL 95,152301 (2005)Di-Jets2 1STAR, PRL 97, 162301 (2006)STAR, PRC 83, 061901 (2011)Jet-hadronSTAR, PRL 112, 122301 (2014)3 Hadron Correlations: Dependence onhadronizationGoal: partonic E-loss All Correlations: Ensemble-based Goal: jet-by-jet E-loss “jets lose x amount of energy on average”“this jet lost x amount of energyKolja Kauder, WSU - RHIC/AGS Meeting6/8/2016

Implementation:FastJet3Jet FindingM. Cacciari and G. SalamPhys. Lett. B 641, 57 (2006)Sequential Clustering:- anti-kT, R 0.2—0.5 Resulting clusters are jets. Operational definition. Nounambiguous jet definition exists! Advantages: - average energy density:kT algorithm, same R 4Minimize sensitivity to hadronization:IR-safe and collinear-safe algorithmand instrumentationMeasure energy flow: connect todynamics of partonsComparison to QCD calculationsbeyond event generatorsKolja Kauder, WSU - RHIC/AGS Meeting6/8/2016

The Underlying Heavy Ion Eventpp@200 GeVCentral Au Au@ 200 GeVCan still find a “jet”, butdoes it come from a hardscattering?And if so, how to determinethe parton energy? 5 S pT in an R 0.4 cone is on theorder of 25 GeV/cIntra-event fluctuations:Kolja Kauder, WSU - RHIC/AGS Meeting 6 GeV/c6/8/2016

Background- Subtract average density:20 GeV fluctuations are rare ( 3s)– but 20 GeV jets are rare as well- Fluctuations and DetectorEffects: Embed reference inAuAu How to select hard scatters?pp @ Au Au Compare on detector level Or unfold response matrixto particle level6Focus on “coincidence” measurements Hadron-Jet correlationsSurface bias for trigger, but awayside is bias-free Di-Jet Asymmetrytangential bias jet geometry engineeringKolja Kauder, WSU - RHIC/AGS MeetingAlternative: direct g see Nihar Sahoo’s talk6/8/2016

Semi-Inclusive Recoil JetsA. Schmah, HP 2015Semi-Inclusive Recoil JetsSemi-inclusive yield of (charged) jetsrecoiling from a high-pT hadron triggerRecoil jet(s)search areaMeasuredCalculable in pQCDPhys.Rev. D79 (2009) 114014arXiv:0904.4402Triggerparticle- Trigger on high pT hadron Selection of a high pT process- Use all jet candidates on the other azimuthal hemispherewithin /- 45 degrees no fragmentation bias on recoil side!- Combinatorial background determined via mixed events7Kolja Kauder, WSU - RHIC/AGS Meeting6/8/2016

Charged Raw Recoil Jet Spectrum:Central Au AuCentral- Excellent description oflow pT SE spectrum with MEPreliminary- Normalization region variedsystematically- Significant jet signal atpT - A 10 GeV/cCombinatorial jet background statistically described bymixed event technique8Kolja Kauder, WSU - RHIC/AGS Meeting6/8/2016

Comparison Central-Peripheral: ICP- Significant suppression ( 0.2)at pT 10 GeV/c, close to 1 at low pTPreliminary- Larger suppression compared toLHC energies! (caveat: different R)ALICE Errors show combined systematics9Kolja Kauder, WSU - RHIC/AGS MeetingarXiv:1506.03984 [nucl-ex]6/8/2016

Large Angle Scattering off the QGP?JHEP 1305 (2013) 031DfDiscrete scattering centers oreffectively continuous medium?“Weak”“Strong”multiple scattering Continuous E-loss10 Scattering probability can give usimportant information about coupling strongly/weakly coupled QGP quasiparticles?Kolja Kauder, WSU - RHIC/AGS Meeting6/8/2016

Df at R 0.3PeripheralCentralHigh recoil jet pT:12 pT-rA 20 Same width for bothcentralitiesPreliminaryPreliminary8 pT-rA 125 pT-rA 8 GeV/c:5 pT-rA 8 f ftrig – fjet11 f ftrig – fjet Significant difference Normalization? BG? Flow? More studies neededKolja Kauder, WSU - RHIC/AGS Meeting6/8/2016

Trigger and Away-Side Jets(Biased) Di-Jet SelectionConstituent pTCut 0.2 GeV/cConstituent pTCut 2 GeV/c Reduce BG Reduce combinatorial jetsDi-jet Selection:Jet pTLead 20 GeV/cJet pTSubLead 10 GeV/c Df-p 0.4ATLAS, PRL 105, 252303CMS, PRC 84, 024906 (2011)12Kolja Kauder, WSU - RHIC/AGS Meeting6/8/2016

Event FractionDi-Jet Imbalance AJCentral Au Au, R 0.4KK, HP 2015Anti-kT R 0.4, pTLead 20 GeV & pTSubLead 10 GeV with pTcut 2 GeV/cCentral Au Auanti-kT, R 0.4Sys. Uncertainties:- tracking eff. 6%- tower energyscale 2%Preliminaryp-value 10-4(stat. error only)Pearson’s c2-testN.D. Gagunashvili,arXiv:physics/0605123 AJ Au Au di-jets more imbalanced than p p for pTcut 2 GeV/cCan the balance be restored?13Kolja Kauder, WSU - RHIC/AGS Meeting6/8/2016

Matched Di-jets w/o Constituent pT CutpTCut 2 GeV/cpTLead 20 GeV/cpTSubLead 10 GeV/c Df-p 0.4Rerun jet-finding algorithmanti-kT on these eventspTCut 0.2 GeV/cpTLead 20 GeV/c (pTCut 2 GeV/c)pTSubLead 10 GeV/c (pTCut 2 GeV/c)Geom. matchingGeom. matchingCalculate “matched” AJ withconstituent pT,cut 0.2 GeV/c.Geom. matching: DR 0.4Keep this jet selection14Kolja Kauder, WSU - RHIC/AGS Meeting6/8/2016

Event FractionDi-Jet Imbalance AJCentral Au Au, R 0.4Sys. Uncertainties:- tracking eff. 6%- tower energyscale 2%Anti-kT R 0.4, pTLead 20 GeV & pTSubLead 10 GeV with pTcut 2 GeV/cCentral Au Auanti-kT, R 0.4Preliminaryp-value 10-4(stat. error only)p-value 0.8(stat. error only) AJ Au Au di-jets more imbalanced than p p for pTcut 2 GeV/cAu Au AJ p p AJ for matched di-jets (R 0.4)15Kolja Kauder, WSU - RHIC/AGS Meeting6/8/2016

Differential MeasurementsR 0.4R 0.4R 0.2Matched topTCut 0.2 GeV/cMatched topTCut 2 GeV/cpTCut 1 GeV/cPreliminaryPreliminaryBalance can not berecovered in smallercone,or harder constituents16Kolja Kauder, WSU - RHIC/AGS Meeting6/8/2016

A Consistent (Qualitative) PictureFocus on: Jet Softening- All measurements p0, h-jet, gdir, AJ, and jet-h consistent withsuppression of high-z fragments Particularly jet-h and AJ suggest balancing at low-z Near-side is affected differently, but recoil always has long pathlength Need to compare at the same parton pT and hadron zT17Kolja Kauder, WSU - RHIC/AGS Meeting6/8/2016

A Consistent (Qualitative) PictureFocus on: Jet BroadeningPreliminary- h-Jet: Away-Side Jet cross section ofnarrow jets is suppressed Suggests broadening beyond R 0.3- Differential Di-Jet Imbalance: BroadeningPRL 112 (2014)12, 12230118Kolja Kauder, WSU - RHIC/AGS Meeting6/8/2016

A Tool to Control Path LengthBiased Di-Jet AJ: “Lost” energy of thedijets is recovered in a jet of R 0.4for pTCut 0.2 GeV/cInterpretation:(Constituent) pTCut 2 GeV/c High Tower (5.5 GeV) (Jet) pTLead 20 GeV/c Surface BiasContrast to LHC:CMS, PRC 84,024906 (2011)Large imbalance, balanced at large anglesSTAR:pTlead 15 GeV/cpTcut 2 GeV/cLHC:AJ Dijet TriggerT. Renk, PRC 85,064908 (2012)T. Renk, PRC 87,024905 (2013) (Recoil) pTSubLead 10 GeV/c Path Length Control19“Unbiased” di-jet selection longer path lengths& Larger energy loss at early times more diffusion in mediumKolja Kauder, WSU - RHIC/AGS Meeting6/8/2016

Unique Opportunity forJet Geometry Engineering at RHIC pTSubLead & Constituent pT systematically dial in thepath length of the recoil jetR 0.4,pTCut 2 GeV/cT. Renk, PRC 87,024905 (2013)20A RHIC Strength!Good correlation between jet and partonenergy for these jetsKolja Kauder, WSU - RHIC/AGS Meeting6/8/2016

Summary Hadron-Jet: Jet reconstruction of recoil jet no fragmentation bias on recoil side Suppression at 20 GeV/c ( 0.2) is larger compared to LHCenergies (caveat: different R) Df shows no difference between central and peripheral,except for lowest pT (interpretation needs more studies) AJ: Jet reconstruction of leading and recoil jet Energy loss jet-by-jet instead of ensemble-based “Lost” energy seems contained within R 0.4 and low pT Imbalance remains for smaller cone or higher constituentcutoff Observed Broadening and Softening jet-by-jet21Kolja Kauder, WSU - RHIC/AGS Meeting6/8/2016

Bonus Slides22Kolja Kauder, WSU - RHIC/AGS Meeting6/8/2016

Bonus: Soft-Drop Grooming Remove wide anglesoft radiationInteresting for: groomed energy, groomed radius pp, jet mass, Focus here:“Groomed Momentum Sharing”J. ThalerALICE Jet Workshop,YaleLarkoski et al.,Phys. Rev. D 91, 111501 (2015)23pT fraction carried by smaller sub-jetafter groomingKolja Kauder, WSU - RHIC/AGS Meeting6/8/2016

Measuring the AP Splitting FunctionRole of b:b 0 IRC safeb 0 (IR)C unsafeb 0 IRC unsafe – but Sudakov-safe independent of asPi: Appropriate Altarelli-Parisisplitting function (symmetrized) independent of pT (in UV limit)(q- qg, g- gg, g- qg) same for quarks and gluons weak pT dependence at RHIC24Kolja Kauder, WSU - RHIC/AGS Meeting6/8/2016

PYTHIA @ RHICPYTHIA8 pp at 200 GeVLeading anti-kT Jets, R 0.4reclustered with C/ASame jets embeddedFake Au Au mocks up multiplicity, spectra,energy densiy- Some difference from theory- maybe due to “small” R- Zg becomes pT-indep. above 30 GeV25- Fairly benign background effect- Shape and mild pT dependence goodfor unfoldingKolja Kauder, WSU - RHIC/AGS Meeting6/8/2016

Backup26Kolja Kauder, WSU - RHIC/AGS Meeting6/8/2016

Mixed Event Generation for JetsMixed eventMix only similarcentrality, ΨEP ,z-vertex positionPick one randomtrack per real event add to mixedevent Real events27 Ev.1Ev. Kauder, WSU - RHIC/AGSEv.KoljaMeeting23Ev.7656/8/2016

Recoil yield suppressionR 0.3R 0.5PreliminaryPreliminaryCalculate spectrum shift requires distributions exponential, ratio flatRHIC: smaller shift for larger RSpectrum Shift Periph/pp CentralpchT,jet range[GeV]Shift R 0.3[GeV]Shift R 0.5[GeV]Au Au @ 200 GeV[10,20]-6.3 0.6 0.8-3.8 0.5 1.8Pb Pb @ 2.76 TeV[60,100]ALICE arXiv:1506.0398428-8 2R 0.5: smaller shift at RHIC than LHCOut-of-cone energy transport ? comparison requires similar triggerbias theory calculationKolja Kauder, WSU - RHIC/AGS Meeting6/8/2016

pp HT Reference and Systematic ErrorsEvent FractionReference:Preliminarypp HT AuAu MBEmbed pp HT randomlyinto AuAu 0-20% minimumbias event, adjusted forrelative tracking efficiencybetween pp HT Y06 andAuAu HT Y07STAR, PRL 112, 122301 (2014)Systematic Uncertainties (Analogous to Jet-Hadron Corr.)- Tracking efficiency uncertainties 6%- Relative Tower energy scale uncertainty 2%- Background/vn: Null-Hypothesis Method1 vs. Method2- Remaining uncertainties negligible29Kolja Kauder, WSU - RHIC/AGS Meeting6/8/2016

Null-Hypothesis:Balance Restored by Uncorrelated BG?Method 1: Random Cone (RC):Take di-jet pair pTCut 2 GeV/c (w/o low pT)pTCut 2 GeV/cpTLead 20 GeVpTSubLead 10 GeVEmbed randomlyCalculate AJ withpTCut 0.2 GeV/cusing cone of Rthe two Jet vectorsinto a centralAu Au MB eventEmbed the two JetMethod 2: EtaCone (EC): vectors into a Au Au HTTake di-jet pairpTCut 2 GeV/c (w/o low pT)30event, 2R away fromreconstructed di-jetpair in that eventηKolja Kauder, WSU - RHIC/AGS Meetingϕ6/8/2016

Event FractionEffect of Background FluctuationsSys. Uncertainties:- tracking eff. 6%- tower energyscale 2%Anti-kT R 0.4, pTLead 20 GeV & pTSubLead 10 GeV with pTcut 2 GeV/cCentral Au Auanti-kT, R 0.4PreliminaryMethod 2(EC)Method 1(RC) AJ Balancing of Au Au matched di-jets due tocorrelated signal yield in a cone of R 0.431Kolja Kauder, WSU - RHIC/AGS Meeting6/8/2016

Contrast and ComparePreliminary“Hard Core”: Similar to LHC:clear imbalance compared to ppATLAS, PRL 105, 252303CMS, PRC 84, 024906 (2011)32Kolja Kauder, WSU - RHIC/AGS Meeting6/8/2016

Contrast and Compare IIMissing EnergyLHC: Shifted to large anglesPreliminaryJet-like yieldout to DR 1RHIC: Contained in R 0.4Shifted to lower pT33Kolja Kauder, WSU - RHIC/AGS MeetingCMS, JHEP 01 (2016) 006CMS, JHEP 1602 (2016)6/8/2016