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

2. Mike Miller 2 04/23/2006 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 (E cm 200-500 GeV, 5<p T <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. Mike Miller 3 04/23/2006 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 (E cm 200-500 GeV, 5<p T <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. Mike Miller 4 04/23/2006 Particle level jets parton particle detector 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 E overlap Add track/tower 4-momenta DataSimulation GEANT “geant” jets “pythia” jets Correction philosophy Use Pythia+GEANT to quantify detector response Estimate corrections to go from “detector” to the “particle” level pythia *(hep-ex/0005012)

5. Mike Miller 5 04/23/2006 Last Week at RHIC peak average  design L 2.5 1.2 6.0 P 67% 61% 70% Luminosity in 10 31 cm -2 s -1 The RHIC complex

6. Mike Miller 6 04/23/2006 2004 p+p commissioning run p T (track/tower) > 0.2 GeV |vertex-z|<60 cm p T (seed)>0.5 GeV, r cone =0.4, f merge =0.5 0.2< η jet <0.8 Neutral energy fraction<0.9 (and E T-trig >3.5 GeV/c for HT) High Tower Trigger BBC coincidence + one tower above threshold ε Trig (η=0.0)=1: E T-tower = 2.5 GeV ε Trig (η=0.8)=1: E T-tower = 3.3 GeV TPC 0<φ<2π 1< η<1 BEMC 0<φ<2π 0< η<1 in situ MIP/e calibration Sampled luminosity: ~0.16 pb -1 1.4 M High tower (HT) events 0.8 M highly pre-scaled minimum bias (MB) events  ~220k p T >5 GeV jets in HT sample before cuts Commissioned 1x1 jet patch trigger– main jet trigger in 2005+

7. Mike Miller 7 04/23/2006 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 Single Tower MIP

8. Mike Miller 8 04/23/2006 Monte Carlo model Pythia 6.203 (CDF Tune A) + GEANT3 + Reconstruction  (  r) = fraction of jet p T 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. Mike Miller 9 04/23/2006 Correction factors Jet p T resolution ~ 25% Efficiency of HT trigger changes by 2 orders of magnitude! Consistent results from both PYTHIA and HERWIG ε jet : decreases c(p T ) resolution: increases c(p T ) ε Trig : ~1 e-2 at p T-jet = 5 GeV ~1 at p T-jet = 50 GeV “measured” “true” Simulation

10. Mike Miller 10 04/23/2006 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. Mike Miller 11 04/23/2006 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. Mike Miller 12 04/23/2006 Summary and Outlook Much work to develop methods and techniques for jet triggering, reconstruction, and analyses First glimpse: Significant p T 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. Mike Miller 13 04/23/2006 Backup slides

14. Mike Miller 14 04/23/2006 Consider detector response (measured) to known input (true) Simulation: ~25% ± 5% for 10<p T <50 GeV/c Consistent number derived from (modest) sample of di-jet events  Choose bin width = resolution “geant jets”“pythia jets” Response Function Simulation p T (measured) 17 < p T (thrown) < 21 GeV/c reco Bin = thrown bin:  35-40% reco Bin = thrown ± 1:  ~80%  Motivates use of bin-by-bin correction factor

15. Mike Miller 15 04/23/2006 * Under Study Dominant systematic uncertainty estimates Normalization Pythia slope Statistics of c(pt) Background BBC Trigger Energy Scale Dominant uncertainty: 10% change in ECal  ~40% change in yield More under long term study (see last slide) Fractional Change in x-section

16. Mike Miller 16 04/23/2006 Consider detector response (measured) to known input (true) “geant jets”“pythia jets” Response & bin quality factors Simulation

17. Mike Miller 17 04/23/2006 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. Response & bin quality factors Simulation

18. Mike Miller 18 04/23/2006 Charged Track Momentum  p/p TPC 1% Charged Track Inefficiency10% x 60% jet6% * Neutral Tower Energy  G ain /G ain = 10% 40% in yield Neutral Energy Inefficiency ∑E T from n+K 0 L/S +  +  + 6-10% * MIP Subtraction10% Correction to Jet E T 1% Fiducial Detector EffectsEdges/Dead regions2% Jet  calculation1 tower =  =0.05 3% Background TriggerBackground trigger +MINBIAS event5% in yield Background EnergyJet + underlying Background 0 Underlying EventWork in Progress NA FragmentationComparison to HERWIG ongoing NA * Included in Correction Factor Jet Energy Scale Systematics

19. Mike Miller 19 04/23/2006 Theory Systematics Changing the pdf Changing the scale

20. Mike Miller 20 04/23/2006 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 p T >5 GeV jets in HT sample before cuts Commissioned 1x1 jet patch trigger– main jet trigger in 2005+ p T (track/tower) > 0.2 GeV |vertex-z|<60 cm r cone =0.4, f merge =0.5 0.2< η jet <0.8 Neutral energy fraction<0.9 (and E T-trig >3.5 GeV/c for HT) High Tower Trigger BBC coincidence + one tower above threshold ε Trig (η=0.0)=1: E T-tower = 2.5 GeV ε Trig (η=0.8)=1: E T-tower = 3.3 GeV TPC 0<φ<2π 1< η<1 BEMC 0<φ<2π 0< η<1 in situ MIP/e calibration AGS PHOBOSBRAHMS PHENIX STAR RHIC: unique pp collider designed for 70% beam polarization and 50<√s<500 GeV Runs: 03/04 “commissioning”, 2005/2006 physics running

21. Mike Miller 21 04/23/2006 Data vs. MC

22. Mike Miller 22 04/23/2006 Data vs. MC Red  pythia + gstar Black  data All error bars statistical High tower trigger pt (jet) >10 GeV/c

23. Mike Miller 23 04/23/2006 Data vs. MC Red  pythia + gstar Black  data All error bars statistical High tower trigger pt (jet) >10 GeV/c