Exploring Jet Properties in p+p Collisions at 200 GeV with STAR

Exploring Jet Properties in p+p Collisions at 200 GeV with SAR Helen Caines - Yale University - for the SAR Collaboration Outline Quark Matter 2009 Knoxville,N, USA March 30 th -April 4 th What we know already Jets and our data set z and ξ distributions he underlying event Summary and outlook &'"%(!"##$% 3445 ()*+,-../01#/))/22//

Jets a calibrated probe PHENIX SAR : PRL 97 (2006) 252001 K.Reygers QM2008 SAR : PLB 637 (2006) 161 S. Albino et al, NPB 725 (2005) 181 Jet cross-section in p+p is well described in pqcd framework over 7 orders of magnitude. Minimum bias particle production in p+p also well modeled. What about fragmentation? Helen Caines SAR Collaboration QM2009 2

Fragmentation functions (FF) MLLA heory CDF No previous comparisons at RHIC energies available. Measurements at higher s agree well with theory. est energy scaling of fragmentation functions. Sapeta&Wiedemann, hep-ph/0707.3494 Helen Caines SAR Collaboration QM2009 3

he p+p data set PC tracks to identify charged particles contribution. Barrel EMCal for neutral energy contribution. 2006 Run Sampled luminosity for Jet-Patch triggers: ~8.7 pb -1 (~8 M events) Jet-Patch rigger: BBC coincidence + EMCal Jet-Patch Jet-Patch: E > 8 GeV in Δη x Δφ = 1x1 Helen Caines SAR Collaboration QM2009 4

Jet reconstruction - algorithms Seedless Cone - SISCone Fastjet package - [Cacciari, Soyez, arxiv:0704.0292] Rcone= (Δφ 2 +Δη 2 ) all particles used. Splitting/Merging destroys cone shape. Recombination k Anti-k starts from lowest p. merges weighted by 1/p i.e. high p is dis-favored. starts from high p. merges weighted by p i.e. low p is dis-favored. [Cacciari, Salam, Soyez, arxiv:0802.1189] Helen Caines SAR Collaboration QM2009 5

Jet reconstruction - algorithms Seedless Cone - SISCone Fastjet package - [Cacciari, Soyez, arxiv:0704.0292] Rcone= (Δφ 2 +Δη 2 ) all particles used. Splitting/Merging destroys cone shape. Recombination k Anti-k starts from lowest p. merges weighted by 1/p i.e. high p is dis-favored. starts from high p. merges weighted by p i.e. low p is dis-favored. Compare results to explore systematics. [Cacciari, Salam, Soyez, arxiv:0802.1189] Helen Caines SAR Collaboration QM2009 5

Jet reconstruction - the resolution parameter Fraction of Energy within Jet Cone Radius 1 0.8 0.6 0.4 0.2 η jet <1-R 20 < Jet p < 30 GeV/c 30 < Jet p < 40 GeV/c 40 < Jet p < 50 GeV/c 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 Radius of Jet Cone Compare FF using different radii. Helen Caines SAR Collaboration QM2009 % Energy within resolution parameter R p (GeV/c) R 0.4 R 0.7 20-30 77% 94% 30-40 83% 96% 40-50 89% 98% Consistent with CDF > 80% within R~0.3. Larger energy more focussed jet. 6

Energy resolution - the jet energy scale Calculated in two way: Simulation MC input compared to reconstructed output. (GeV) Jet Reconstructed p 60 50 40 30 20 E jet Pythia vs E jet Reco Anti-k R<0.7 η jet <1-R -1-2!(p )/p 0.35 0.3 0.25 0.2 0.15 η jet <1-R 0 0 20 30 40 50 60 Input p Jet (GeV) Offset due to missing energy: Detector efficiencies. Undetected particles (n, K 0 L). -3 0.1 0.05 SISCone k Anti-k 00 5 15 20 25 30 35 40 45 50 Input p Jet (GeV/c) Resolution ~15-20% for pjet>15gev/c. Helen Caines SAR Collaboration QM2009 7

Energy resolution - the jet energy scale!(p )/p Calculated in two way: Simulation MC input compared to reconstructed output. Real data Energy balance of di-jets. 0.35 0.3 0.25 0.2 0.15 η jet <1-R (GeV) Jet Reconstructed p 60 50 40 30 20 E jet Pythia vs E jet Reco Anti-k R<0.7 η jet <1-R 0 0 20 30 40 50 60 Input p Jet (GeV) Offset due to missing energy: Detector efficiencies. Undetected particles (n, K 0 L). -1-2 -3 0.1 0.05 SISCone k Anti-k Simulation Read data di-jets 0 0 5 15 20 25 30 35 40 45 50 Input p Jet (GeV/c) Resolution ~15-20% for pjet>15gev/c. Helen Caines SAR Collaboration QM2009 7

ξ and z distributions for charged hadrons 1/N jet dn/d! 2 1.8 1.6 1.4 1.2 1 0.8 0.6 0.4 0.2 SISCone K Anti-K η jet <1-R Pythia 6.4 p-p data Data not corrected to particle level. 1/N jet dn/d! 2.2 2 1.8 1.6 1.4 1.2 1 0.8 0.6 0.4 0.2 SISCone K Anti-K η jet <1-R Pythia 6.4 p-p data 0 1 2 3 4 5! (=ln(p jet /p Part 20 <Jet preco< 30 GeV/c ) R=0.4 0 1 2 3 4 5! (=ln(p jet /p Part ) 30 <Jet preco< 40 GeV/c dn/dz Jet 1/N 1-1 -2 SISCone K Anti-K Simulation p-p data η jet <1-R PYHIA = PYHIA +GEAN dn/dz Jet 1/N 1-1 -2 SISCone K Anti-K Simulation p-p data η jet <1-R -3 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Z -3 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Z Reasonable agreement Helen Caines between SAR Collaboration data QM2009 and PYHIA+GEAN. 8

Charged hadrons ξ for different R and jet p 1/N jet dn/d! 1/N jet dn/d! 2 1.8 1.6 1.4 1.2 1 0.8 0.6 0.4 0.2 0 1 2 3 4 5! (=ln(p jet 2.2 SISCone K 2 Anti-K 1.8 1.6 1.4 1.2 1 0.8 0.6 0.4 0.2 SISCone K Anti-K 20<p reco <30 GeV/c Pythia 6.4 p-p data Pythia 6.4 p-p data 0 1 2 3 4 5! (=ln(p jet /p Part /p Part ) ) R<0.4 η jet <1-R ptrack > 0.2 1/N jet dn/d! Data not corrected to particle level. PYHIA = PYHIA +GEAN R<0.7 2.2 2 1.8 1.6 1.4 1.2 1 0.8 0.6 0.4 0.2 SISCone K Anti-K Pythia 6.4 p-p data 0 1 2 3 4 5! (=ln(p jet /p Part ) 30<p reco <40 GeV/c Agreement similar between PYHIA and data for both radii. Helen Caines SAR Collaboration QM2009 9

What about the Underlying Event? p-p events are complicated. More than just hard scattering. Underlying Event: soft or semi-hard multiple parton interactions, initial & final state radiation, beam-beam remnants Figure from Rick Field he Underlying Event is everything BU the hard scattering Helen Caines SAR Collaboration QM2009

Measuring the Underlying Event Define: Δφ Angle relative to leading jet oward Δφ < 60 o Away Δφ > 120 o. ransverse 60 o < Δφ < 120 o ransmax - rans. region with highest Σp or ΣN track ransmin rans. region with least Σp or ΣN track Underlying Event is the data in the ransverse regions. Helen Caines SAR Collaboration QM2009 11

Sensitivities of the variables leading : Most basic jet cut, one jet in our acceptance. back-to-back : Sub-set of leading jet collection. Require Δφ > 150, paway/plead > 0.7 Suppresses hard initial and final state radiation. ransmin : Sensitive to beam-beam remnants and soft multiple parton interactions. ransmax : Enhanced probability of containing hard initial and/or final state radiation component. Helen Caines SAR Collaboration QM2009 12

ransmin vs ransmax regions of UE CDF s=1.96 ev leading ransmax > backto-back ransmax Significant initial/final state radiation at large angles. Helen Caines SAR Collaboration QM2009 13

ransmin vs ransmax regions of UE CDF s=1.96 ev leading ransmax > backto-back ransmax Significant initial/final state radiation at large angles. dn ch /d"d! 0.7 0.6 0.5 SISCone,R=0.7, η jet < 1-R, ptrack > 0.2 GeV/c Max UE Min UE SAR s=200 GeV leading ransmax ~ back-to-back ransmax Small initial/final state radiation at large angles. 0.4 Lead Jet Data 0.3 Back-to-Back Jet data 0.2 0.1 0 5 15 20 25 30 35 40 Lead Jet p (GeV/c) Helen Caines SAR Collaboration QM2009 13

ransmin vs ransmax regions of UE CDF s=1.96 ev leading ransmax > backto-back ransmax Significant initial/final state radiation at large angles. dn ch /d"d! 0.7 0.6 0.5 0.4 0.3 SISCone,R=0.7, η jet < 1-R, ptrack > 0.2 GeV/c Lead Jet Data Back-to-Back Jet data Max UE Min UE SAR s=200 GeV leading ransmax ~ back-to-back ransmax Small initial/final state radiation at large angles. ransmax > ransmin 0.2 0.1 0 5 15 20 25 30 35 40 Lead Jet p (GeV/c) Helen Caines SAR Collaboration QM2009 13

dn ch /d"d! ransmin vs ransmax regions of UE CDF s=1.96 ev leading ransmax > backto-back ransmax Significant initial/final state radiation at large angles. dn ch /d"d! 0.7 0.6 0.5 0.4 0.3 0.2 0.1 SISCone,R=0.7, η jet < 1-R, ptrack > 0.2 GeV/c Lead Jet Data Back-to-Back Jet data Max UE Min UE 0 5 15 20 25 30 35 40 Lead Jet p (GeV/c) SAR s=200 GeV leading ransmax ~ back-to-back ransmax Small initial/final state radiation at large angles. ransmax > ransmin Poisson distribution with average dn ch /dηdφ = 0.36 UE ~independent of jet p. Helen Caines SAR Collaboration QM2009 13

p spectra in jet, UE, Min-Bias event dn/d "d!dp 1/N 1/p 1-1 -2-3 15<pjet<20 GeV/c, η jet <1-R Charged Jets ransverse Max particles ransverse Min Min-Bias dn/d "d!p 1/N 1/p -2-3 -4 All data raw K 0 s Jets ransverse Max ransverse Min Min-Bias -4-5 -5-6 -6-7 dn/d "d!dp 1/N 1/p -8-2 -3-4 0 2 4 6 8 Particle p (GeV/c) Λ Jets ransverse Max ransverse Min Min-Bias dn/d "d!dp 1/N 1/p -7-2 -3-4 0 2 4 6 8 Particle p (GeV/c) Jets ransverse Max ransverse Min Min-Bias -5-5 -6 0 2 4 6 8 Particle p (GeV/c) -6 0 2 4 6 8 Particle p (GeV/c) Helen Caines SAR Collaboration QM2009 14

Summary & outlook Charged hadron ξ and z distributions at s=200 GeV similar to PYHIA 6.4. Underlying Event largely decoupled from hard scattering. Large angle initial/final state radiation is small. Particle p spectra are significantly softer out of the jet cone compared to in the jet. p spectra of Underlying Event close to that of Min-Bias triggered events. Outlook Compare more jet-variables (k, j, etc) to pqcd models. Use relativistic rise and newly installed of to identify π, K, p. Repeat measurements at s=500 GeV. Measure PID FF in heavy ion collisions. See posters: 2-Hadron FF (M. Elnimr), d-au (J. Kapitan), UE (HC) Helen Caines SAR Collaboration QM2009 15