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Measurement of the inclusive jet cross section in p+p collisions at E CM =200 GeV

Measurement of the inclusive jet cross section in p+p collisions at E CM =200 GeV. Mike Miller (MIT) For the STAR collaboration. Why study inclusive jet production at RHIC?. RHIC is polarized! Jets provide direct access to gluon helicity

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Measurement of the inclusive jet cross section in p+p collisions at E CM =200 GeV

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  1. Measurement of the inclusive jet cross section in p+p collisions at ECM=200 GeV Mike Miller (MIT) For the STAR collaboration

  2. Why study inclusive jet production at RHIC? • RHIC is polarized! • Jets provide direct access to gluon helicity • Long-term: search for new physics in parity violating di-jet production* • Jet shapes and underlying event • Can extend previous UA1 results • Unique kinematic niche (Ecm 200-500 GeV, 5<pT<50 GeV) • Can further constrain large-x PDFs • But… • Use tracking + EMCal • Lower sqrt(s)  steeply falling cross section • Must control E-scale systematic * Eur.Phys.J.C24:149-157,2002

  3. Why study inclusive jet production at RHIC? • RHIC is polarized! • Jets provide direct access to gluon helicity • Long-term: search for new physics in parity violating di-jet production* • Jet shapes and underlying event • Can extend previous UA1 results • Unique kinematic niche (Ecm 200-500 GeV, 5<pT<50 GeV) • Can further constrain large-x PDFs • But… • Use tracking + EMCal • Lower sqrt(s)  steeply falling cross section • Must control E-scale systematic * Eur.Phys.J.C24:149-157,2002

  4. Particle level jets *(hep-ex/0005012) Data Simulation midpoint-cone algorithm* • Search over “all” possible seeds for stable groupings • Check midpoints between jet-jet pairs for stable groupings • Split/merge jets based on Eoverlap • Add track/tower 4-momenta detector “geant” jets GEANT “pythia” jets particle pythia Correction philosophy • Use Pythia+GEANT to quantify detector response • Estimate corrections to go from “detector” to the “particle” level parton

  5. RHIC pC Polarimeters Absolute Polarimeter (H jet) Siberian Snakes BRAHMS & PP2PP PHOBOS 2005 Complete! Siberian Snakes Spin Flipper PHENIX STAR Spin Rotators Partial Snake Strong Snake Helical Partial Snake Polarized Source Last Week at RHIC LINAC AGS BOOSTER 200 MeV Polarimeter peak average  design L 2.5 1.2 6.0 P 67% 61% 70% Rf Dipole AGS Polarimeter Luminosity in 1031cm-2s-1 The RHIC complex

  6. 2004 p+p commissioning run Sampled luminosity: ~0.16 pb-1 1.4 M High tower (HT) events 0.8 M highly pre-scaled minimum bias (MB) events  ~220k pT>5 GeV jets in HT sample before cuts Commissioned 1x1 jet patch trigger– main jet trigger in 2005+ TPC 0<φ<2π 1< η<1 BEMC 0<φ<2π 0< η<1 in situ MIP/e calibration pT (track/tower) > 0.2 GeV |vertex-z|<60 cm pT(seed)>0.5 GeV, rcone=0.4, fmerge=0.5 0.2< ηjet <0.8 Neutral energy fraction<0.9 (and ET-trig>3.5 GeV/c for HT) High Tower Trigger BBC coincidence + one tower above threshold εTrig(η=0.0)=1: ET-tower= 2.5 GeV εTrig(η=0.8)=1: ET-tower= 3.3 GeV

  7. Single Tower MIP 2004 EMCal calibration Limited test-beam calibration • in situ calibration of 2400 channels p+p statistics insufficient  use Au+Au events from earlier in 2004 run (same HV) Use TPC tracks MIPs: relative gain Electrons: energy scale Set E-scale using 1.8<p<8 GeV/c electrons

  8. Monte Carlo model • Pythia 6.203 (CDF Tune A) + GEANT3 + Reconstruction • (r) = fraction of jet pT in sub-cone r • Common jet shape variable • Study HT trigger bias • Study data/MC agreement Shaded region represents single tower size HT trigger  hot core Bias decreases with increasing jet pT, well described by MC

  9. Correction factors “measured” Simulation “true” εjet : decreases c(pT) resolution: increases c(pT) εTrig: ~1 e-2 at pT-jet = 5 GeV ~1 at pT-jet = 50 GeV • Jet pT resolution ~ 25% • Efficiency of HT trigger changes by 2 orders of magnitude! • Consistent results from both PYTHIA and HERWIG

  10. Corrected cross section results • Good agreement between MB and HT data • Good agreement with NLO over 7 orders of magnitude • Error bars • statistical uncertainty from data • Error band • leading systematic uncertainty • 10% E-scale uncertainty 50% uncertainty on yield • Need di-jet, photon-jet to reduce sys. error • Agree with NLO calculation within systematic uncertainty

  11. Corrected cross section results • Good agreement between MB and HT data • Good agreement with NLO over 7 orders of magnitude • Error bars • statistical uncertainty from data • Error band • leading systematic uncertainty • 10% E-scale uncertainty 50% uncertainty on yield • Need di-jet, photon-jet to reduce sys. error • Agree with NLO calculation within systematic uncertainty UA1 at 200 GeV

  12. Summary and Outlook • Much work to develop methods and techniques for jet triggering, reconstruction, and analyses • First glimpse: • Significant pT reach (~50 GeV/c) • Agreement within large systematics with NLO calculations • A few primary issues under study: • Luminosity determination • Refined corrections • NLO clustering scheme • Goal: • Bring 2004 (and 2003) analyses to efficient closure • Bright Future • 2005: first real p+p run 3 pb-1 collected • 2006: first dedicated p+p run (goal 15 pb-1) with complete EMCal and commissioned jet and di-jet triggers QCD jet physics at RHIC: coming of age

  13. Backup slides

  14. Simulation: ~25% ± 5% for 10<pT<50 GeV/c Consistent number derived from (modest) sample of di-jet events  Choose bin width = resolution reco Bin = thrown bin: 35-40% reco Bin = thrown ± 1:  ~80%  Motivates use of bin-by-bin correction factor Response Function 17 < pT(thrown) < 21 GeV/c Simulation pT (measured) • Consider detector response (measured) to known input (true) “geant jets” “pythia jets”

  15. Dominant uncertainty: 10% change in ECal  ~40% change in yield • More under long term study (see last slide) Dominant systematic uncertainty estimates BBC Trigger Normalization Energy Scale * Under Study * Under Study Fractional Change in x-section Background Pythia slope Statistics of c(pt) * Under Study

  16. Response & bin quality factors Simulation Simulation • Consider detector response (measured) to known input (true) “geant jets” “pythia jets”

  17. Response & bin quality factors Simulation Simulation • Consider detector response (measured) to known input (true) “geant jets” “pythia jets” • Bins of width 1-sigma  “purity” of ~35% over range on the diagonal. • Motivates application of bin-by-bin correction factors.

  18. Jet Energy Scale Systematics * Included in Correction Factor

  19. Theory Systematics Changing the pdf Changing the scale

  20. PHOBOS BRAHMS PHENIX STAR AGS 2004 p+p commissioning run RHIC: unique pp collider designed for 70% beam polarization and 50<√s<500 GeV Runs: 03/04 “commissioning”, 2005/2006 physics running Sampled luminosity: ~0.16 pb-1 1.4 M High tower (HT) events 0.8 M highly pre-scaled minimum bias (MB) events  ~220k pT>5 GeV jets in HT sample before cuts Commissioned 1x1 jet patch trigger– main jet trigger in 2005+ TPC 0<φ<2π 1< η<1 BEMC 0<φ<2π 0< η<1 in situ MIP/e calibration pT (track/tower) > 0.2 GeV |vertex-z|<60 cm rcone=0.4, fmerge=0.5 0.2< ηjet <0.8 Neutral energy fraction<0.9 (and ET-trig>3.5 GeV/c for HT) High Tower Trigger BBC coincidence + one tower above threshold εTrig(η=0.0)=1: ET-tower= 2.5 GeV εTrig(η=0.8)=1: ET-tower= 3.3 GeV

  21. Data vs. MC

  22. Data vs. MC Red  pythia + gstar Black  data All error bars statistical High tower trigger pt (jet) >10 GeV/c

  23. Data vs. MC Red  pythia + gstar Black  data All error bars statistical High tower trigger pt (jet) >10 GeV/c

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