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Full Jet Reconstruction in Heavy Ion Collisions

Full Jet Reconstruction in Heavy Ion Collisions. Sevil Salur. Charge for this talk:. Update on the latest results on jet-medium interactions as seen in A+A collisions at RHIC. New techniques for full jet reconstruction.

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Full Jet Reconstruction in Heavy Ion Collisions

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  1. Full Jet Reconstruction in Heavy Ion Collisions Sevil Salur

  2. Charge for this talk: • Update on the latest results on jet-medium interactions as seen in A+A collisions at RHIC. • New techniques for full jet reconstruction. • Results that help move our understanding forward, (this is not an experiment-specific talk). Quark Matter 2009, Knoxville TN Sevil Salur

  3. Why Pursue Full Jet Reconstruction? • Enables study of jet quenching at the partonic level. • Uniquely large kinematic reach • In A+A much reduced geometric biases, full exploration of quenching. • Multiple channels for consistency checks: Inclusive, di-jets, h-jets, gamma-jets • Qualitatively new observables: energy flow, jet substructure, fragmentation function Quark Matter 2009, Knoxville TN Sevil Salur

  4. Jets: a theorist’s view Final State Radiation Initial State Radiation Hadronization Beam Remnants Beam Remnants • JETS: Colored partons from the hard scatter (2n) • Fragmentation via gluon radiation • Hadronization: “spray” of colorless hadrons Detector {p,K,p,n,…} Jet p p Parton Level: Calculable with pQCD Underlying Event: Beam remnants  Soft Background S.D Drell, D.J.Levy and T.M. Yan, Phys. Rev. 187, 2159 (1969) N. Cabibbo, G. Parisi and M. Testa, Lett. Nuovo Cimento 4,35 (1970) J.D. Bjorken and S.D. Brodsky, Phys. Rev. D 1, 1416 (1970) Sterman and Weinberg, Phys. Rev. Lett. 39, 1436 (1977) … and many more Quark Matter 2009, Knoxville TN Sevil Salur

  5. Jets: an experimentalist’s view Final State Radiation Initial State Radiation Hadronization Beam Remnants Beam Remnants Detector {p,K,p,n,…} Jet p p JETS: Collection of 4-vectors of calorimeter energy clusters and charged track momentum Quark Matter 2009, Knoxville TN Sevil Salur

  6. Jet Reconstruction Algorithms: Goal: re-associate hadrons to accurately reconstruct the partonic kinematics. Jet Cone Algorithm: 1. Mid Point Cone: Merging & Splitting 2. SIS CONE 3. Leading Order High Seed Cone (LOHSC) Fragmentation process outgoing parton Hard scatter Sequential recombination: Cluster pairs of objects close in relative pT 4. KT (starting point: low pT particles) 5. Anti-KT (starting point: high pT particles) Kinematic ambiguity e.g., E-scheme vs p-scheme: 6. Gaussian filtering. Y. Lai, B. Cole arXiv:0806.1499 See QM 2009 S2A Talk by Y. Lai KT jet Cone jet Anti-kT jet Quark Matter 2009, Knoxville TN Sevil Salur

  7. The FastJet Algorithms • Suite of modern Collinear and infrared safe jet algorithms • sequential recombination: kT, Cambridge/Aachen, anti-kT • cone: SISCone (Seedless Infrared-safe Cone) • Motivated by high precision jets in high luminosity p+p at LHC (pileup) • but directly applicable to heavy ion collisions • Two important algorithmic advances: • Large improvements to processing time vs. event multiplicity • Rigorous definition of jet area for subtraction of diffuse event background pT (Jet Measured) ~ pT(Parton) +  × A(Jet) ± A(Jet) A= Jet Area  = Diffuse noise, =noise fluctuations STAR Preliminary Au+Au Central A, ρ, σ are all measurable quantities! M. Cacciari, G. Salam 0707.1378 [hep-ph] M. Cacciari, G. Salam, G. Soyez 0802.1188 [hep-ph] FastJet – http://www.lpthe.jussieu.fr/~salam/fastjet Quark Matter 2009, Knoxville TN Sevil Salur

  8. Heavy Ion Background Discussion pT (Jet Measured) ~ pT(Parton) +  × A(Jet) ± A(Jet) A= Jet Area  = Diffuse noise, =noise fluctuations • Fundamental Assumption: Two separable components: signal and background. • How might it be violated? • 1. Biases in background estimation due to presence of a jet. • a) Initial state radiation (Expected to be small compared to jet energy). • b) Final state “out-of-cone” radiation. • Different Algorithms respond differently to background. (kT and Anti-kT) KT jet Cone jet Anti-kT jet Quark Matter 2009, Knoxville TN Sevil Salur

  9. Jets in p+p at the Tevatron Cone and kT jet spectra are consistent kT Algorithm Cone Algorithm http://www-cdf.fnal.gov/physics/new/qcd/QCD.html Quark Matter 2009, Knoxville TN Sevil Salur

  10. Jets in p+p at the Tevatron Cone and kT jet spectra are consistent Cone Algorithm http://www-cdf.fnal.gov/physics/new/qcd/QCD.html Inclusive jet cross section over many orders of magnitude consistent with the NLO QCD Quark Matter 2009, Knoxville TN Sevil Salur

  11. Jets in p+p at RHIC Phys. Rev. Lett. 97 (2006) 252001 Reconstructed by a mid-point jet cone algorithm with R = 0.4 • STAR jet reconstruction: • neutral energy from Barrel EMC • charged hadrons from TPC Experimental uncertainty ~50% Agrees with NLO p-QCD Quark Matter 2009, Knoxville TN Sevil Salur

  12. Towards Jets in A+A at RHIC Phys. Rev. Lett. 91 (2003) 072304 Phys. Rev. Lett. 97 (2006) 162301 Phys.Rev.Lett.97:162301,2006 High pThadron suppressiondescribed by pQCD+partonic energy loss Medium seems to be transparent to photons colored medium. Conclusive evidence for large partonic energy loss in dense matter (final state effect) Phys. Rev. Lett 96 202301 (2006) Quark Matter 2009, Knoxville TN Sevil Salur

  13. Jet quenching via inclusive hadrons: Quantitative Understanding? Theory: Modifications of jets in a 3-D hydrodynamic medium All calculations have same initial structure, final vacuum fragmentation, nuclear geometry. Parameters can be adjusted to describe data well: varies between 4-18 GeV/c2 S. A. Bass, C. Gale, A. Majumder , C. Nonaka, G. Qin, T. Renk, J. Ruppert 0808.0908 [nucl-th] Good fit of theory to data but limited discrimination of underlying physics. TECHQM! Quark Matter 2009, Knoxville TN Sevil Salur

  14. Di-Hadrons : Quantitative Understanding? recoil yield per trigger zT=pTrecoil/pTtrig Vary energy loss parameter H. Zhang, J. F. Owens, E. Wang, X.N. Wang Phys. Rev. Lett. 98, 212301 (2007) J.L. Nagle arXiv:0805.0299 [nucl-ex] J. Adams, et al Phys Rev. Lett. 97, 162301 (2006) See the next talk by J. Nagle • Di-hadron suppression not yet well-described by NLO theory Quark Matter 2009, Knoxville TN Sevil Salur

  15. Di-Hadrons : Quantitative Understanding? recoil yield per trigger recoil yield per trigger zT=pTrecoil/pTtrig ZOWW arXiv:0902.4000 Vary energy loss parameter e0 H. Zhang, J. F. Owens, E. Wang, X.N. Wang Phys. Rev. Lett. 98, 212301 (2007) J.L. Nagle arXiv:0805.0299 [nucl-ex] J. Adams, et al Phys Rev. Lett. 97, 162301 (2006) See the next talk by J. Nagle See the talks in S3A by A. Hamed, M. Connors, A. Hanks • New developments are in progress!  Quark Matter 2009, Knoxville TN Sevil Salur

  16. Full Jet Reconstruction in Heavy Ion Collisions trigger • Multi-hadronic Observables: • Geometric Biases: dominated by jets that have not interacted! • Limited kinematic reach. • Jet energy not constrained. recoil • Why Pursue Full Jet Reconstruction? • Enables study of jet quenching at the partonic level. • Uniquely large kinematic reach • In A+A much reduced geometric biases, full exploration of quenching. • Multiple channels for consistency checks: Inclusive, di-jets, h-jets, gamma-jets • Qualitatively new observables: energy flow, jet substructure, fragmentation function Goal is Unbiased Jet Reconstruction: Reconstruct partonic kinematics independent of fragmentation details - quenched or unquenched. Quark Matter 2009, Knoxville TN Sevil Salur

  17. Can we see jets at RHIC? STAR Preliminary p+p   QM 2009 Talks by E. Bruna, H. Caines, M. Ploskon, J. Putschke Quark Matter 2009, Knoxville TN Sevil Salur

  18. Can we see jets at RHIC? PHENIX Preliminary Cu+Cu STAR Preliminary Au+Au Central   QM 2009 Talks by E. Bruna, M. Ploskon, J. Putschke, Y. S. Lai Quark Matter 2009, Knoxville TN Sevil Salur

  19. Reconstructed Spectra in p+p and Cu+Cu Large pT range within restricted PHENIX acceptance! Unfolding of the spectra is last step! Forthcoming soon! QM 2009 Talk by Y. S. Lai Quark Matter 2009, Knoxville TN Sevil Salur

  20. Extracting di-jet angular width No centrality dependence on the widths! QM 2009 Talk by Y. S. Lai Quark Matter 2009, Knoxville TN Sevil Salur

  21. Reconstructed Jet Spectra & Corrections: MB-Trig: Minimum Bias Trigger p+p: Phys. Rev. Lett. 97 (2006) 252001 Nbin scaled p+p Au+Au 0-10% STAR Preliminary MB-Trig dNJet/dET (per event) LOHSC R=0.4 pT cut =1 GeV Seed=4.6 GeV S. Salur [STAR Collaboration], arXiv:0809.1609 [nucl-ex] ET [GeV] Agreement with Nbin Scaled p+p (~50%). Quark Matter 2009, Knoxville TN Sevil Salur

  22. Suppression of backgrounds in heavy ions: Limit jet resolution parameter R Cut on track/calorimeter pT Reconstructed Jet Spectra & Corrections: p+p: Phys. Rev. Lett. 97 (2006) 252001 Nbin scaled p+p Au+Au 0-10% STAR Preliminary MB-Trig: Minimum Bias Trigger MB-Trig dNJet/dET (per event) LOHSC R=0.4 pT cut =1 GeV Seed=4.6 GeV S. Salur [STAR Collaboration], arXiv:0809.1609 [nucl-ex] ET [GeV] Agreement with Nbin Scaled p+p (~50%). Quark Matter 2009, Knoxville TN Sevil Salur

  23. Reconstructed Jet Spectra & Corrections: p+p: Phys. Rev. Lett. 97 (2006) 252001 Nbin scaled p+p Au+Au 0-10% STAR Preliminary MB-Trig: Minimum Bias Trigger MB-Trig O HT-Trig dNJet/dET (per event) Suppression of backgrounds in heavy ions: Limit jet resolution parameter R Cut on track/calorimeter pT LOHSC R=0.4 pT cut =1 GeV Seed=4.6 GeV HT-Trig: Satisfied Minimum Bias and requires a pion/photon with pT>7.5 GeV Large HT-trigger bias persists at least to 30 GeV. Similar to leading particle bias. S. Salur [STAR Collaboration], arXiv:0809.1609 [nucl-ex] ET [GeV] MB-Trigger: Agreement with Nbin Scaled p+p (~50%). HT-Trigger: Bias towards hard fragmentation: Bad for quenching Studies! What about other algorithms? Quark Matter 2009, Knoxville TN Sevil Salur

  24. PTCut Dependence Bias PT Cut Au+Au 0-10%MB-Trig  Nbin Scaled p+p Au+Au 0-10%MB-Trig  Nbin Scaled p+p Au+Au 0-10%MB-Trig  Nbin Scaled p+p STAR Preliminary STAR Preliminary STAR Preliminary KT KT KT p+p: Phys. Rev. Lett. 97 (2006) 252001 S. Salur [STAR Collaboration], arXiv:0810.0500 [nucl-ex] STAR Preliminary Au+Au Central pTcut Imprecise subtraction of underlying event? Do we introduce a bias with pT-cuts? Sensitivity to fragmentation model?   Quark Matter 2009, Knoxville TN Sevil Salur

  25. Un-Biased Jet Measurements • 1) Minimize the kinematic cuts, e.g PTCut • 2) Data driven corrections : • a. Experimental characterization of background fluctuations. • b. Detailed unfolding of fluctuations.  Correcting for smearing dNJet/dET (a.u.) seed=4.6 GeV R=0.4 Cross-Section LOHSC PyDet PyEmbed PyTrue Unfolding bgd from signal STAR Preliminary ET ET [GeV] S. Salur [STAR Collaboration], arXiv:0809.1609 [nucl-ex] See QM 2009 S2A Talk by: M. Ploskon Correct via “unfolding” for the “min-bias” jet reconstruction. Quark Matter 2009, Knoxville TN Sevil Salur

  26. Inclusive jet spectrum: Au+Au STAR Preliminary Unfolding Uncertainty BEMC calibration Uncertainty BEMC calibration Uncertainty p+p STAR Preliminary Unfolding uncertainty corresponds to a factor of 2 in jet cross-section. See QM 2009 S2A Talk by: M. Ploskon Anti-kT and kT jet spectra are consistent. Quark Matter 2009, Knoxville TN Sevil Salur

  27. RAA of Jets A large fraction of jets are reconstructed! (Compare pion RπAA = 0.2) R = 0.4 BEMC calibration Uncertainty STAR Preliminary See QM 2009 S2A Talk by: M. Ploskon Quark Matter 2009, Knoxville TN Sevil Salur

  28. What happens at high pT? Relative contribution of sub-processes to inclusive jet production p+p W. Vogelsang Private Communication Relative contributions of quark and gluon vary. What about quenching dependence on parton species? Quark Matter 2009, Knoxville TN Sevil Salur

  29. What happens at high pT? Relative contribution of sub-processes to inclusive jet production SLAC E139 σΑ/σd p+p W. Vogelsang Private Communication The EMC Effect: Deviation between structure Functions of Au and deuterium. Relative contributions of quark and gluon vary. Initial state effects at large x ~15% J. Gomez et al., SLAC–PUB–5813 June 7, 2001 D.F. Geesaman et al., Ann. Rev. Nucl. Part. Sci. 45, 337 (1995) B. A. Cole. et al, arXiv:hep-ph/0702101 What about other high x effects? Quark Matter 2009, Knoxville TN Sevil Salur

  30. Jet Energy Profile: Au+Au STAR Preliminary BEMC calibration Uncertainty BEMC calibration Uncertainty p+p STAR Preliminary See QM 2009 S2A Talk by: M. Ploskon Au+Au: Stronger decrease in yield within R=0.2 as compared to R=0.4 Quark Matter 2009, Knoxville TN Sevil Salur

  31. Jet Energy Profile: Cross-section ratios in p+p and Au+ Au with R=0.2/R=0.4 STAR Preliminary STAR Preliminary p+p Increase in the ratio with increasing pT. more focused cone with increasing jet pT Au+Au Decrease in the ratio with increasing pT. Quantitative differences due to jet resolution parameter R. Evidence of broadening of the jet energy profile due to quenching! Is R=0.4 large enough to reconstruct the jets in an unbiased way? See QM 2009 S2A Talk by: M. Ploskon Quark Matter 2009, Knoxville TN Sevil Salur

  32. Quantitative analysis of data requires model building… JEWEL (Jet Evolution with Energy Loss): K. Zapp, G. Ingelman, J. Rathsman, J. Stachel, U. A. Wiedemann arXiv:0805.4759 Parton shower with microscopic description of interactions with medium QM 2009 Talk by K. Zapp Q-Pythia: N. Armesto, L. Cunqueiro and C. A. Salgado arXiv:0809.4433[hep-ph] MC implementation in Pythia of medium-induced gluon radiation through an additive term in the vacuum splitting functions. QM 2009 Talks by N. Armesto and Salgado YaJEM: T. Renk arXiv:0808.1803 QM 2009 Talk by T. Renk Analytic Calculations: Nicolas Borghini arXiv: 0902.2951 Many more…. PYQUEN (Lokhtin, Snigriev), PQM (Dainese, Loizides, Paic), HIJING (Gyulassy, Wang)… See other QM2009 talks. Quark Matter 2009, Knoxville TN Sevil Salur

  33. Analytic Calculations vs New Monte Carlos QM 2009 Talk by K. Zapp Nicolas Borghini arXiv: 0902.2951 K. Zapp, G. Ingelman, J. Rathsman, J. Stachel, U. A. Wiedemann arXiv:0805.4759 Strong broadening of shower in transverse momentum with respect to jet axis. Angular distribution becomes wider! No strong broadening of shower when PTcut >2 GeV is selected. (limitations of broadening observable) We need to confront the calculations with data! Quark Matter 2009, Knoxville TN Sevil Salur

  34. Fragmentation Functions from di-jets “trigger” jet Large HT-trigger bias in FF No-trigger bias in FF “recoil” jet Quark Matter 2009, Knoxville TN Sevil Salur

  35. Fragmentation Functions from di-jets large uncertainties due to background (further systematic evaluation needed) “trigger” jet pT(trigger) > 10 GeV & PTcut=2 GeV 20<pT(recoil jet) < 25 GeV & PTcut=0.1 GeV Large HT-trigger bias in FF 20<pt,rec(AuAu)<25 GeV ⇒ < pt,rec(pp)> ~ 18 GeV No-trigger bias in FF STAR Preliminary “recoil” jet Apparent modification in the z of Au+Au with respect to p+p. But a biased population of jets. See QM 2009 S2A: Talk by E.Bruna Quark Matter 2009, Knoxville TN Sevil Salur

  36. Parton vs Hadron K. Zapp, G. Ingelman, J. Rathsman, J. Stachel, U. A. Wiedemann arXiv:0804.3568 K. Zapp Talk 2009 QM Clear increase in multiplicity due to radiative energy loss Collisional energy loss when recoils are counted toward the jet Significant uncertainties due to the sensitivity to hadronisation: Look for new observables unaffected by the hadronisation. Quark Matter 2009, Knoxville TN Sevil Salur

  37. QCD JET Observables In vacuum (LEP) data well understood in pQCD K. Zapp, G. Ingelman, J. Rathsman, J. Stachel, U. A. Wiedemann arXiv:0804.3568 QM 2009 Talk by K. Zapp Medium Induced Radiation  More Coarser Jet Structure pT cut infrared safe insensitive observables! : number of subjets, thurst … KT jet Cone jet Anti-kT jet Quark Matter 2009, Knoxville TN Sevil Salur

  38. Another way to do it: Jet quenching at the LHC • Pb+Pb at 5.5 TeV: • enormous jet energy range •  qualitatively new probes P. Jacobs and M. van Leeuwen Nucl. Phys A774, 237 (2006) N. Grau for ATLAS Copious production of hard probes : Jets, charm & bottom… High pT Jets well above the background at LHC Quark Matter 2009, Knoxville TN Sevil Salur

  39. LHC • Pb+Pb background seems to be under control for the reconstructed jet-energy. • Detector Upgrades: • 2 super modules are installed for ALICE • Full azimuthal calorimetric coverage for ATLAS & CMS ALICE g+jet (Z+jet) cleaner means to determine FF ALICE EMCAL Physics Performance Update, CD-2 CMS Eur. Phys. J. 50 (2007) 117 ATLAS N. Grau for ATLAS QM 2009 Talks by: N. Grau, G. Veres Poster by M. Heinz … Quark Matter 2009, Knoxville TN Sevil Salur

  40. Conclusions: Why Pursue Full Jet Reconstruction? • Full jet reconstruction gives access to the full spectrum of fragmentation topologies: • Enables study of jet quenching at the partonic level. – New theory developments FASTJET and New medium-modified shower MC codes… Q-Pythia, JEWEL,… • Uniquely large kinematic reach – First full jet reconstruction at RHIC (0-10% central heavy ion collisions - reach is up to 50 GeV). – Nbin scaling (50% Syst Uncert.) observed for the least biased case, R=0.4 and pTcut=0.1 GeV • In A+A much reduced geometric biases, full exploration of quenching. – But beware of biases: data taking and selection of particles (pTcut, R) – Path length and jet radius dependencies. • Multiple channels for consistency checks: Inclusive, di-jets, h-jets, γ-jets • Qualitatively new observables: energy flow, jet substructure, fragmentation function – Session 2A “When you have completed 95 percent of your journey, you are only halfway there.” Japanese Proverb Quark Matter 2009, Knoxville TN Sevil Salur

  41. Thank you! Nestor Armesto Elena Bruna Jana Bielcikova Matteo Cacciari Helen Caines Brian Cole David d'Enterria Nathan Grau John Harris Wolf G. Holzman Peter Jacobs Jan Kapitan Yue Lai Leticia Mendez Mateusz Ploskon Joern Putschke Thorsten Renk Gavin Salam Carlos Salgado Gregory Soyez Gabor Veres Urs Achim Wiedemann Korinna Zapp … Quark Matter 2009, Knoxville TN Sevil Salur

  42. Sevil Salur

  43. RAA of Jets R = 0.4 R = 0.2 STAR Preliminary STAR Preliminary See QM 2009 S2A Talk by: M. Ploskon Jets are reconstructed in an unbiased way for the R=0.4 Sevil Salur

  44. The FastJet Measurement of the Jet Area • Add randomly distributed ghost particles of known density d to the event • Run the jet algorithm • Count the number n of ghost particles assigned to the jet • Jet area A= n/d Jets are irregular objects! Jet area is non-trivial (≠ πR2) Accounts for event-wise fluctuations in shape and area of jet Sevil Salur

  45. Nuclear Modification Factors of Di-jets “trigger” jet Large HT-trigger bias in FF “recoil” jet No-trigger bias in FF STAR Preliminary • Maximum path length for the recoil! • pT(recoil jet)  large suppression See QM 2009 S2A: Talk by E.Bruna Significant suppression in di-jet coincidence Quark Matter 2009, Knoxville TN Sevil Salur

  46. The FastJet Algorithms: Background Subtraction in Pb+Pb M. Cacciari, G. Salam, G. Soyez 0802.1188 [hep-ph] FastJet – http://www.lpthe.jussieu.fr/~salam/fastjet M. Cacciari, G. Salam 0707.1378 [hep-ph] Pb+Pb jet cross-section is recovered after the subtraction Background subtraction works in the Heavy Ion environment. Sevil Salur

  47. The FastJet Algorithms: Background Subtraction in p+p M. Cacciari, G. Salam, G. Soyez 0802.1189 [hep-ph] Anti-kT is resistant to absorption by background of jet energy at large radius Sevil Salur

  48. Modified Fragmentation Function Modified Leading Logarithmic Approximation: - good description of vacuum fragmentation (basis of PYTHIA) - introduce medium effects at parton splitting Jet quenching: Low pT enhancement pT hadron~ 2 GeV =ln(EJet/phadron) Borghini and Wiedemann, hep-ph/0506218 Fragmentation is strongly modified at pThadron~1-5 GeV Sevil Salur

  49. Fragmentation-function in Au+Au 0-20% and p+p STAR Preliminary LOCone FastJet kT STAR Preliminary J. Putschke [STAR Collaboration], arXiv:0809. 1419[nucl-ex] No apparent modification in the ξ of Au+Au with respect to p+p. Good agreement between the algorithms! See QM 2009 S2A: Talks by E.Bruna, H.Caines Where is the jet quenching? Biases: Online triggering, PT cut Sevil Salur

  50. Quantitative Understanding: Di-Hadrons? Df zT=pTrecoil/pTtrig H. Zhang, J. F. Owens, E. Wang, X.N. Wang Phys. Rev. Lett. 98, 212301 (2007) J.L. Nagle arXiv:0805.0299 [nucl-ex] J. Adams, et al Phys Rev. Lett. 97, 162301 (2006) vary model parameter e0 • Di-hadron suppression not yet well-described by NLO theory Sevil Salur

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