1 / 37

Mateusz Ploskon For the STAR Collaboration

Inclusive jet cross-sections and correlations in Au+Au and p+p collisions at sqrt ( s NN ) = 200 GeV. Mateusz Ploskon For the STAR Collaboration. Outline. Motivation and strategy Datasets, jet algorithms, correction schemes Observables Inclusive jet cross-section + Jet R AA

casimir-lel
Download Presentation

Mateusz Ploskon For the STAR Collaboration

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Inclusive jet cross-sections and correlations in Au+Au and p+p collisions at sqrt(sNN) = 200 GeV Mateusz Ploskon For the STAR Collaboration

  2. Outline • Motivation and strategy • Datasets, jet algorithms, correction schemes • Observables • Inclusive jet cross-section + Jet RAA • Jet “radius” systematics • (di-)Hadron-jet recoil spectrum and Jet IAA • Discussion: implications for jet quenching Mateusz Ploskon (LBNL), STAR, QM'09

  3. Motivation and Strategy R Physics of full jet reconstruction in heavy ion collisions Jet R=0.4 Measure energy flow into “cone” of radius R Energy shift? p+p Absorption? p0 Au+Au • Total momentum is conserved even for strongly quenched jets • Unbiased jet reconstruction: recover the full jet energy within • cone radius R • Compare Au+Au and p+p jet spectra • → Inclusive cross section: RAAjet~1 • → p0+jet conditional yield: IAAjet~1 • Caveat: initial state nuclear effects Cross-section ratio AuAu/pp 1 Mateusz Ploskon (LBNL), STAR, QM'09

  4. Data sets Essential requirement: minimize trigger bias of jet population • Inclusive spectrum data: • Au+Au (2007): • online MinBias Trigger • offline select 10% most central events (8 x106events) • p+p (2006): • online “Jet Patch” trigger (intlumi 6.5 pb^-1) • offline correct bias at low ET • h+jet coincidence data: • Both p+p (2006) and Au+Au (2007): • Online “BEMC High Tower” trigger • Offline: hadron trigger energy from 3x3 tower cluster (ET>7 GeV) • Track and Tower cuts: • BEMC towers energy > 0.2 GeV • TPC track momentum pT > 0.2 GeV/c Mateusz Ploskon (LBNL), STAR, QM'09

  5. KT jet anti-kTjet Jet algorithms Anti-kt expected to be less susceptible to background effects in heavy ion collisions Algorithms: kt and anti-kt from FastJet* • Resolution parameter R = 0.4, 0.2 • Jet acceptance: |hJET|< 1.-R • Recombination scheme: E-scheme with massless particles R Sequential recombination algorithms Cone based algorithms Fragmentation Hard scattering *Cacciari, Salam and Soyez, JHEP 0804 (2008) 005 [arXiv:0802.1188] Mateusz Ploskon (LBNL), STAR, QM'09

  6. Systematic corrections Trigger corrections • p+p trigger bias correction Particle level corrections: • Detector effects: efficiency and pT resolution • “Double* counting” of particle energies • * electrons: - double; hadrons: - showering corrections • All towers matched to primary tracks are removed from the analysis Jet level corrections: • Spectrum shift: • Unobserved energy • TPC tracking efficiency • BEMC calibration (dominant uncertainty in p+p) • Jet patch trigger efficiency (only in p+p) • Jet pT resolution • Underlying event (dominant uncertainty in Au+Au) Full assessment of jet energy scale uncertainties Data driven correction scheme • Weak model dependence: only for single-particle response, p+p trigger response • No dependence on quenching models Mateusz Ploskon (LBNL), STAR, QM'09

  7. Heavy Ions and background characterization Mateusz Ploskon (LBNL), STAR, QM'09

  8. STAR Preliminary Au+Au Central   Underlying event Single di-jet event from a central Au+Au: - Two jet peaks on top of the HI background Central assumption: Signal and background can be factorized Event background is characterized with median pT per unit area (r). <pTBG> in R = 0.4 is~45 GeV/c. S/B~0.5 at 20 GeV/c. Systematic studies indicate variation of sigma +/-1 is a conservative bracketing of systematic uncertainties. Error bands indicate these limits. with resolution: True jet distribution smeared: sDATA ~ 6.8 GeV Mateusz Ploskon (LBNL), STAR, QM'09

  9. Fake jet contamination “Fake” jets: signal in excess of background model from random association of uncorrelated soft particles (i.e. not due to hard scattering) “Fake” jet rate estimation: • Central Au+Au dataset (real data) • Randomize azimuth of each charged particle and calorimeter tower • Run jet finder • Remove leading particle from each found jet • Re-run jet finder STAR Preliminary Mateusz Ploskon (LBNL), STAR, QM'09

  10. Fake jet contamination “Fake” jets: signal in excess of background model from random association of uncorrelated soft particles (i.e. not due to hard scattering) “Fake” jet rate estimation: • Central Au+Au dataset (real data) • Randomize azimuth of each charged particle and calorimeter tower • Run jet finder • Remove leading particle from each found jet • Re-run jet finder STAR Preliminary Mateusz Ploskon (LBNL), STAR, QM'09

  11. Spectrum unfolding: method • Background non-uniformity (fluctuations) and energy resolution introduce pT-smearing • Correct via “unfolding”: inversion of full bin-migration matrix • Check numerical stability of procedure using jet spectrum shape from PYTHIA Pythia Pythia smeared Pythia unfolded unfolding • Procedure is numerically stable • Correction depends critically on background model • → main systematic uncertainty for Au+Au Mateusz Ploskon (LBNL), STAR, QM'09

  12. Spectrum unfolding • Corrections for smearing of jet pT due to HI backround non-uniformities • 1) raw spectrum STAR Preliminary Mateusz Ploskon (LBNL), STAR, QM'09

  13. Spectrum unfolding • Corrections for smearing of jet pT due to HI backround non-uniformities • 1) raw spectrum • 2) removal of “fake”-correlations STAR Preliminary Mateusz Ploskon (LBNL), STAR, QM'09

  14. Spectrum unfolding • Corrections for smearing of jet pT due to HI backround non-uniformities • 1) raw spectrum • 2) removal of “fake”-correlations • 3) unfolding STAR Preliminary Mateusz Ploskon (LBNL), STAR, QM'09

  15. Spectrum unfolding • Corrections for smearing of jet pT due to HI backround non-uniformities • 1) raw spectrum • 2) removal of “fake”-correlations • 3) unfolding • 4) correction for pT resolution STAR Preliminary Mateusz Ploskon (LBNL), STAR, QM'09

  16. Jet yields in p+pat sqrt(sNN) = 200 GeV Mateusz Ploskon (LBNL), STAR, QM'09

  17. Inclusive jet cross-section in p+p at sqrt(sNN) = 200 GeV • Fully corrected jet cross-section reconstructed with kt algorithm • Very good agreement between the algorithms STAR Preliminary Uncertainty due to BEMC calibration Mateusz Ploskon (LBNL), STAR, QM'09

  18. Inclusive jet cross-section in p+p at sqrt(sNN) = 200 GeV • Comparison to published STAR data • run 2003/2004 • Note: • published data reconstructed with different jet algorithm: • Mid-point cone (R=0.4) STAR Preliminary Phys. Rev. Lett. 97 (2006) 252001 Mateusz Ploskon (LBNL), STAR, QM'09

  19. Inclusive jet yields in 10% most central Au+Au at sqrt(sNN) = 200 GeV Mateusz Ploskon (LBNL), STAR, QM'09

  20. Inclusive jet yields in 10% most central Au+Au at sqrt(sNN) = 200 GeV • Fully corrected jet spectrum • Exactly the same algorithms and jet definitions used as compared to p+p • Bands on data points represent estimation of systematic uncertainties due to background subtraction STAR Preliminary Uncertainty due to BEMC calibration Mateusz Ploskon (LBNL), STAR, QM'09

  21. Inclusive jet spectrum: p+p and central Au+Au (R=0.4 and R=0.2) p+p Au+Au central STAR Preliminary STAR Preliminary Mateusz Ploskon (LBNL), STAR, QM'09

  22. Cross-section ratios in p+p and Au+ Au with R=0.2/R=0.4 Many systematics effects cancel in the ratio p+p Au+Au STAR Preliminary p+p: “Narrowing” of the jet structure with increasing jet energy Au+Au: Strong broadening of the jet energy profile Mateusz Ploskon (LBNL), STAR, QM'09

  23. Nuclear modification factor for jets Mateusz Ploskon (LBNL), STAR, QM'09

  24. RAA Jets • Significant energy recovered as compared to RAA~0.2 for hadrons • Visible trends: • different sensitivity of the algorithms • Central values drop as a function of jet pT R = 0.4 STAR Preliminary 5% uncertainty on BEMC calibration Mateusz Ploskon (LBNL), STAR, QM'09

  25. RAA Jets and Energy flow in smaller “cone” radii R=0.4 STAR Preliminary R=0.2 Significant drop of RAA as a function of jet pT for R=0.2 as compared to R=0.4 Jet energy not fully recovered in small “cones” – shift towards lower pT Mateusz Ploskon (LBNL), STAR, QM'09

  26. Hadron-jet coincidences Mateusz Ploskon (LBNL), STAR, QM'09

  27. STAR, PRL 97, 162301 (2006) Yield per trigger Df Di-hadron – jet correlations A STAR high pTdihadrons: bias towards non-interacting jet population Recoil B Mateusz Ploskon (LBNL), STAR, QM'09

  28. Hadron+jet coincidence Energy shift? R=0.4 p+p Conditional yield Absorption? Au+Au p0 • Trigger on hard, leading p0 (pT>6 GeV/c) • 3x3 tower cluster in BEMC • Construct spectrum of recoil jets • normalized per di-hadron trigger • This event selection will maximize • the recoil path length distribution • in matter R Jet Cond. yield ratio AuAu/pp 1 Mateusz Ploskon (LBNL), STAR, QM'09

  29. H – recoil jet coincidences A A Recoil jet Recoil jet B pT> 0.5 GeV/c B pT> 6 GeV/c Use jet fragmentation bias to vary jet path length distribution? Mateusz Ploskon (LBNL), STAR, QM'09

  30. H – recoil jet coincidences STAR Preliminary A (Au+Au: 10% central) Anti-kt R=0.4 B Mateusz Ploskon (LBNL), STAR, QM'09

  31. H – recoil jet coincidences STAR Preliminary A (Au+Au: 10% central) Anti-kt R=0.4 B Mateusz Ploskon (LBNL), STAR, QM'09

  32. H – recoil jet coincidences STAR Preliminary A (Au+Au: 10% central) Anti-kt R=0.4 B Mateusz Ploskon (LBNL), STAR, QM'09

  33. H – recoil jet coincidences STAR Preliminary A (Au+Au: 10% central) Anti-kt R=0.4 B Significant suppression of the bias free recoil jet spectrum Mateusz Ploskon (LBNL), STAR, QM'09

  34. Summary Au+Au 10% central STAR Preliminary • Qualitatively new measurement of jet quenching in terms of energy flow (rather than hadronic observables) has been established • What we have shown: • Minimum bias dataset: RAA~0.5 or larger • Significant broadening of jet energy profile R=0.2 -> R=0.4 • Strong suppression of recoil jet rate at maximum path-length • Consistent interpretation: • quenching induces jet broadening • R=0.4 (with the presented jet definitions) is insufficient for unbiased reconstruction RAu+Au 10% central STAR Preliminary STAR Preliminary STAR Preliminary Mateusz Ploskon (LBNL), STAR, QM'09

  35. Outlook • Rich new set of observables to confront calculations • New MC jet quenching models (qPythia, JEWEL, T. Renk) • New jet algorithms for HI collisions? • Post-processing – integration of significant energy flow outside the “initial” jet areas (however probably hard to calculate/resolve theoretically Mateusz Ploskon (LBNL), STAR, QM'09

  36. Extra slides Mateusz Ploskon (LBNL), STAR, QM'09

  37. Spectrum unfolding- correction for smearing of jet pt due to bgnonuniformities R=0.2 R=0.4 Mateusz Ploskon (LBNL), STAR, QM'09

More Related