Full Jet Reconstruction in Heavy Ion Collisions Sevil

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Full Jet Reconstruction in Heavy Ion Collisions Sevil Salur

Full Jet Reconstruction in Heavy Ion Collisions Sevil Salur

Charge for this talk: 1) Update on the latest results on jet-medium interactions as

Charge for this talk: 1) Update on the latest results on jet-medium interactions as seen in A+A collisions at RHIC. 2) New techniques for full jet reconstruction. 1) Results that help move our understanding forward, (this is not an experiment-specific talk). Quark Matter 2009, Knoxville TN Sevil Salur 2

Why Pursue Full Jet Reconstruction? • Enables study of jet quenching at the partonic

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 3

Jets: a theorist’s view Final State Radiation Detector {p , K, p, n Initial

Jets: a theorist’s view Final State Radiation Detector {p , K, p, n Initial State Radiation , … } Jet Hadronization Beam Remnants p Beam Remnants JETS: Colored partons from the hard scatter (2 n) • Fragmentation via gluon radiation • Hadronization: “spray” of colorless hadrons p Parton Level: Calculable with p. QCD 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 4

Jets: an experimentalist’s view Final State Radiation Initial State Radiation Detector {p , K,

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

Jet Reconstruction Algorithms: Goal: re-associate hadrons to accurately reconstruct the partonic kinematics. Jet Cone

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 p. T KT jet 4. KT (starting point: low p. T particles) 5. Anti-KT (starting point: high p. T particles) Cone jet Anti-k. T jet Kinematic ambiguity e. g. , E-scheme vs p-scheme: 6. Gaussian filtering. Y. Lai, B. Cole ar. Xiv: 0806. 1499 See QM 2009 S 2 A Talk by Y. Lai Quark Matter 2009, Knoxville TN Sevil Salur 6

The Fast. Jet Algorithms Suite of modern Collinear and infrared safe jet algorithms •

The Fast. Jet Algorithms Suite of modern Collinear and infrared safe jet algorithms • sequential recombination: k. T, Cambridge/Aachen, anti-k. T • 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: 1. Large improvements to processing time vs. event multiplicity 2. Rigorous definition of jet area for subtraction of diffuse event background p (Jet Measured) ~ p (Parton) + × A(Jet) ± A(Jet) T T A= Jet Area = Diffuse noise, =noise fluctuations A, ρ, σ are all measurable quantities! iminary l e r P R STA Central u A + u A M. Cacciari, G. Salam 0707. 1378 [hep-ph] M. Cacciari, G. Salam, G. Soyez 0802. 1188 [hep-ph] Fast. Jet – http: //www. lpthe. jussieu. fr/~salam/fastjet Quark Matter 2009, Knoxville TN Sevil Salur 7

Heavy Ion Background Discussion p. T (Jet Measured) ~ p. T(Parton) + × A(Jet)

Heavy Ion Background Discussion p. T (Jet Measured) ~ p. T(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. 2. Different Algorithms respond differently to background. (k. T and Anti-k. T) KT jet Quark Matter 2009, Knoxville TN Sevil Salur Cone jet Anti-k. T jet 8

Jets in p+p at the Tevatron Cone and k. T jet spectra are consistent

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

Jets in p+p at the Tevatron Cone and k. T jet spectra are consistent

Jets in p+p at the Tevatron Cone and k. T 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 10

Jets in p+p at RHIC Phys. Rev. Lett. 97 (2006) 252001 Reconstructed by a

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 11

Towards Jets in A+A at RHIC Phys. Rev. Lett. 91 (2003) 072304 Phys. Rev.

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 p. T hadron suppression described by p. QCD+partonic energy loss Medium seems to be transparent to photons colored medium. Phys. Rev. Lett 96 202301 (2006) Quark Matter 2009, Knoxville TN Conclusive evidence for large partonic energy loss in dense matter (final state effect) Sevil Salur 12

Jet quenching via inclusive hadrons: Quantitative Understanding? Theory: Modifications of jets in a 3

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. S. A. Bass, C. Gale, A. Majumder , C. Nonaka, G. Qin, T. Renk, J. Ruppert 0808. 0908 [nucl-th] Parameters can be adjusted to describe data well: varies between 4 -18 Ge. V/c 2 Good fit of theory to data but limited discrimination of underlying physics. TECHQM! Quark Matter 2009, Knoxville TN Sevil Salur 13

recoil yield per trigger Di-Hadrons : Quantitative Understanding? z. T=p. Trecoil/p. Ttrig Vary energy

recoil yield per trigger Di-Hadrons : Quantitative Understanding? z. T=p. Trecoil/p. Ttrig Vary energy loss parameter H. Zhang, J. F. Owens, E. Wang, X. N. Wang Phys. Rev. Lett. 98, 212301 (2007) J. L. Nagle ar. Xiv: 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 14

recoil yield per trigger Di-Hadrons : Quantitative Understanding? z. T=p. Trecoil/p. Ttrig Vary energy

recoil yield per trigger Di-Hadrons : Quantitative Understanding? z. T=p. Trecoil/p. Ttrig Vary energy loss parameter e 0 H. Zhang, J. F. Owens, E. Wang, X. N. Wang Phys. Rev. Lett. 98, 212301 (2007) J. L. Nagle ar. Xiv: 0805. 0299 [nucl-ex] J. Adams, et al Phys Rev. Lett. 97, 162301 (2006) ZOWW ar. Xiv: 0902. 4000 See the next talk by J. Nagle See the talks in S 3 A by A. Hamed, M. Connors, A. Hanks New developments are in progress! Quark Matter 2009, Knoxville TN Sevil Salur 15

Full Jet Reconstruction in Heavy Ion Collisions trigger recoil Multi-hadronic Observables: • Geometric Biases:

Full Jet Reconstruction in Heavy Ion Collisions trigger recoil Multi-hadronic Observables: • Geometric Biases: dominated by jets that have not interacted! • Limited kinematic reach. • Jet energy not constrained. 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 16

Can we see jets at RHIC? elimin r P R A T S p+p

Can we see jets at RHIC? elimin r P R A T S p+p ary QM 2009 Talks by E. Bruna, H. Caines, M. Ploskon, J. Putschke Quark Matter 2009, Knoxville TN Sevil Salur 17

Can we see jets at RHIC? liminary e r P X I PHEN Cu+Cu

Can we see jets at RHIC? liminary e r P X I PHEN Cu+Cu ry elimina r P R A T S entral C u A + Au QM 2009 Talks by E. Bruna, M. Ploskon, J. Putschke, Y. S. Lai Quark Matter 2009, Knoxville TN Sevil Salur 18

Reconstructed Spectra in p+p and Cu+Cu Large p. T range within restricted PHENIX acceptance!

Reconstructed Spectra in p+p and Cu+Cu Large p. T 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 19

Extracting di-jet angular width No centrality dependence on the widths! QM 2009 Talk by

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 20

STAR Preliminary d. NJet/d. ET (per event) Reconstructed Jet Spectra & Corrections: p+p: Phys.

STAR Preliminary d. NJet/d. ET (per event) Reconstructed Jet Spectra & Corrections: p+p: Phys. Rev. Lett. 97 (2006) 252001 Nbin scaled p+p MB-Trig: Minimum Bias Trigger Au+Au 0 -10% MB-Trig LOHSC R=0. 4 p. T cut =1 Ge. V Seed=4. 6 Ge. V S. Salur [STAR Collaboration], ar. Xiv: 0809. 1609 [nucl-ex] ET [Ge. V] Agreement with Nbin Scaled p+p (~50%). Quark Matter 2009, Knoxville TN Sevil Salur 21

STAR Preliminary d. NJet/d. ET (per event) Reconstructed Jet Spectra & Corrections: p+p: Phys.

STAR Preliminary d. NJet/d. ET (per event) Reconstructed Jet Spectra & Corrections: p+p: Phys. Rev. Lett. 97 (2006) 252001 Nbin scaled p+p Au+Au 0 -10% MB-Trig: Minimum Bias Trigger Suppression of backgrounds in heavy ions: Limit jet resolution parameter R Cut on track/calorimeter p. T LOHSC R=0. 4 p. T cut =1 Ge. V Seed=4. 6 Ge. V S. Salur [STAR Collaboration], ar. Xiv: 0809. 1609 [nucl-ex] ET [Ge. V] Agreement with Nbin Scaled p+p (~50%). Quark Matter 2009, Knoxville TN Sevil Salur 22

STAR Preliminary d. NJet/d. ET (per event) Reconstructed Jet Spectra & Corrections: p+p: Phys.

STAR Preliminary d. NJet/d. ET (per event) Reconstructed Jet Spectra & Corrections: p+p: Phys. Rev. Lett. 97 (2006) 252001 Nbin scaled p+p Au+Au 0 -10% MB-Trig O HT-Trig MB-Trig: Minimum Bias Trigger Suppression of backgrounds in heavy ions: Limit jet resolution parameter R Cut on track/calorimeter p. T LOHSC R=0. 4 p. T cut =1 Ge. V Seed=4. 6 Ge. V HT-Trig: Satisfied Minimum Bias and requires a pion/photon with p. T>7. 5 Ge. V Large HT-trigger bias persists at least to 30 Ge. V. Similar to leading particle bias. S. Salur [STAR Collaboration], ar. Xiv: 0809. 1609 [nucl-ex] ET [Ge. V] 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 23

PT Cut Dependence Bias Au+Au 0 -10% MB-Trig Nbin Scaled p+p KT STAR Preliminary

PT Cut Dependence Bias Au+Au 0 -10% MB-Trig Nbin Scaled p+p KT STAR Preliminary Au+Au 0 -10% STAR Preliminary PT Cut Nbin Scaled p+p KT KT p+p: Phys. Rev. Lett. 97 (2006) 252001 S. Salur [STAR Collaboration], ar. Xiv: 0810. 0500 [nucl-ex] liminary e r P R A ST Central Au+Au p. Tcut Imprecise subtraction of underlying event? Do we introduce a bias with p. T-cuts? Sensitivity to fragmentation model? Quark Matter 2009, Knoxville TN Sevil Salur 24

Un-Biased Jet Measurements Cross-Section d. NJet/d. ET (a. u. ) 1) Minimize the kinematic

Un-Biased Jet Measurements Cross-Section d. NJet/d. ET (a. u. ) 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 seed=4. 6 Ge. V R=0. 4 LOHSC Py. Det Py. Embed Py. True Unfolding bgd from signal STAR Preliminary S. Salur [STAR Collaboration], ar. Xiv: 0809. 1609 [nucl-ex] See QM 2009 S 2 A Talk by: M. Ploskon Quark Matter 2009, Knoxville TN ET ET [Ge. V] Correct via “unfolding” for the “min-bias” jet reconstruction. Sevil Salur 25

Au+Au BEMC calibration Uncertainty Unfolding Uncertainty STAR Preliminary Inclusive jet spectrum: p+p STAR Preliminary

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

RAA of Jets R = 0. 4 A large fraction of jets are reconstructed!

RAA of Jets R = 0. 4 A large fraction of jets are reconstructed! (Compare pion RπAA = 0. 2) BEMC calibration Uncertainty STAR Preliminary See QM 2009 S 2 A Talk by: M. Ploskon Quark Matter 2009, Knoxville TN Sevil Salur 27

What happens at high p. T? Relative contribution of sub-processes to inclusive jet production

What happens at high p. T? 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 28

What happens at high p. T? Relative contribution of sub-processes to inclusive jet production

What happens at high p. T? Relative contribution of sub-processes to inclusive jet production σΑ/σd SLAC E 139 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, ar. Xiv: hep-ph/0702101 What about other high x effects? Quark Matter 2009, Knoxville TN Sevil Salur 29

Au+Au BEMC calibration Uncertainty STAR Preliminary Jet Energy Profile: p+p STAR Preliminary See QM

Au+Au BEMC calibration Uncertainty STAR Preliminary Jet Energy Profile: p+p STAR Preliminary See QM 2009 S 2 A 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 30

Jet Energy Profile: STAR Preliminary Cross-section ratios in p+p and Au+ Au with R=0.

Jet Energy Profile: STAR Preliminary Cross-section ratios in p+p and Au+ Au with R=0. 2/R=0. 4 p+p Increase in the ratio with increasing p. T. more focused cone with increasing jet p. T Au+Au Decrease in the ratio with increasing p. T. Quantitative differences due to jet resolution parameter R. See QM 2009 S 2 A Evidence of broadening of the jet energy profile due to quenching! Talk by: M. Ploskon Is R=0. 4 large enough to reconstruct the jets in an unbiased way? Quark Matter 2009, Knoxville TN Sevil Salur 31

Quantitative analysis of data requires model building… JEWEL (Jet Evolution with Energy Loss): K.

Quantitative analysis of data requires model building… JEWEL (Jet Evolution with Energy Loss): K. Zapp, G. Ingelman, J. Rathsman, J. Stachel, U. A. Wiedemann ar. Xiv: 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 ar. Xiv: 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 Ya. JEM: T. Renk ar. Xiv: 0808. 1803 QM 2009 Talk by T. Renk Analytic Calculations: Nicolas Borghini ar. Xiv: 0902. 2951 Many more…. PYQUEN (Lokhtin, Snigriev), PQM (Dainese, Loizides, Paic), HIJING (Gyulassy, Wang)… See other QM 2009 talks. Quark Matter 2009, Knoxville TN Sevil Salur 32

Analytic Calculations vs New Monte Carlos QM 2009 Talk by K. Zapp Nicolas Borghini

Analytic Calculations vs New Monte Carlos QM 2009 Talk by K. Zapp Nicolas Borghini ar. Xiv: 0902. 2951 Strong broadening of shower in transverse momentum with respect to jet axis. Angular distribution becomes wider! K. Zapp, G. Ingelman, J. Rathsman, J. Stachel, A. Wiedemann ar. Xiv: 0805. 4759 No strong broadening of shower when PTcut >2 Ge. V is selected. (limitations of broadening observable) We need to confront the calculations with data! Quark Matter 2009, Knoxville TN Sevil Salur 33

Fragmentation Functions from di-jets “trigger” jet Large HT-trigger bias in FF No-trigger bias in

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 34

Fragmentation Functions from di-jets “trigger” jet Large HT-trigger bias in FF p. T(trigger) >

Fragmentation Functions from di-jets “trigger” jet Large HT-trigger bias in FF p. T(trigger) > 10 Ge. V & PTcut=2 Ge. V 20<p. T(recoil jet) < 25 Ge. V & PTcut=0. 1 Ge. V large uncertainties due to background (further systematic evaluation needed) 20<pt, rec(Au. Au)<25 Ge. V ⇒ < pt, rec(pp)> ~ 18 Ge. V No-trigger bias in FF STAR Preliminary “recoil” jet Apparent modification in the z of Au+Au with respect to p+p. See QM 2009 S 2 A: Talk by E. Bruna Quark Matter 2009, Knoxville TN But a biased population of jets. Sevil Salur 35

Parton vs Hadron K. Zapp, G. Ingelman, J. Rathsman, J. Stachel, U. A. Wiedemann

Parton vs Hadron K. Zapp, G. Ingelman, J. Rathsman, J. Stachel, U. A. Wiedemann ar. Xiv: 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 36

QCD JET Observables In vacuum (LEP) data well understood in p. QCD KT jet

QCD JET Observables In vacuum (LEP) data well understood in p. QCD KT jet Cone jet Anti-k. T jet K. Zapp, G. Ingelman, J. Rathsman, J. Stachel, U. A. Wiedemann ar. Xiv: 0804. 3568 QM 2009 Talk by K. Zapp Medium Induced Radiation More Coarser Jet Structure p. T cut infrared safe insensitive observables! : number of subjets, thurst … Quark Matter 2009, Knoxville TN Sevil Salur 37

Another way to do it: Jet quenching at the LHC Pb+Pb at 5. 5

Another way to do it: Jet quenching at the LHC Pb+Pb at 5. 5 Te. V: enormous jet energy range qualitatively new probes P. Jacobs and M. van Leeuwen Nucl. Phys A 774, 237 (2006) N. Grau for ATLAS Copious production of hard probes : Jets, charm & bottom… High p. T Jets well above the background at LHC Quark Matter 2009, Knoxville TN Sevil Salur 38

LHC • Pb+Pb background seems to be under control for the reconstructed jet-energy. ALICE

LHC • Pb+Pb background seems to be under control for the reconstructed jet-energy. ALICE • Detector Upgrades: 2 super modules are installed for ALICE Full azimuthal calorimetric coverage for ATLAS & CMS 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 39

Conclusions: Why Pursue Full Jet Reconstruction? Full jet reconstruction gives access to the full

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 Ge. V). – Nbin scaling (50% Syst Uncert. ) observed for the least biased case, R=0. 4 and p Tcut=0. 1 Ge. V • In A+A much reduced geometric biases, full exploration of quenching. – But beware of biases: data taking and selection of particles (p. Tcut, R) – Path length and jet radius dependencies. • Multiple channels for consistency checks: Inclusive, di-jets, h-jets, γ-jets – Session 2 A • Qualitatively new observables: energy flow, jet substructure, fragmentation function “When you have completed 95 percent of your journey, you are only halfway there. ” Japanese Proverb Quark Matter 2009, Knoxville TN Sevil Salur 40

Thank you! Nestor Armesto Elena Bruna Matteo Cacciari Helen Caines Brian Cole Nathan Grau

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

Sevil Salur 42

Sevil Salur 42

RAA of Jets R = 0. 4 R = 0. 2 STAR Preliminary See

RAA of Jets R = 0. 4 R = 0. 2 STAR Preliminary See QM 2009 S 2 A Talk by: M. Ploskon Jets are reconstructed in an unbiased way for the R=0. 4 Sevil Salur 43

The Fast. Jet Measurement of the Jet Area 1. Add randomly distributed ghost particles

The Fast. Jet Measurement of the Jet Area 1. Add randomly distributed ghost particles of known density d to the event 2. Run the jet algorithm 3. Count the number n of ghost particles assigned to the jet 4. Jet area A= n/d Jets are irregular objects! Jet area is non-trivial (≠ πR 2) Accounts for event-wise fluctuations in shape and area of jet Sevil Salur 44

Nuclear Modification Factors of Di-jets “trigger” jet Large HT-trigger bias in FF “recoil” jet

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! p. T(recoil jet) large suppression See QM 2009 S 2 A: Talk by E. Bruna Quark Matter 2009, Knoxville TN Significant suppression in di-jet coincidence Sevil Salur 45

The Fast. Jet Algorithms: Background Subtraction in Pb+Pb M. Cacciari, G. Salam, G. Soyez

The Fast. Jet Algorithms: Background Subtraction in Pb+Pb M. Cacciari, G. Salam, G. Soyez 0802. 1188 [hep-ph] Fast. Jet – 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 46

The Fast. Jet Algorithms: Background Subtraction in p+p M. Cacciari, G. Salam, G. Soyez

The Fast. Jet Algorithms: Background Subtraction in p+p M. Cacciari, G. Salam, G. Soyez 0802. 1189 [hep-ph] Anti-k. T is resistant to absorption by background of jet energy at large radius Sevil Salur 47

Modified Fragmentation Function Modified Leading Logarithmic Approximation: - good description of vacuum fragmentation (basis

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

Fragmentation-function in Au+Au 0 -20% and p+p STAR Preliminary LOCone Fast. Jet k. T

Fragmentation-function in Au+Au 0 -20% and p+p STAR Preliminary LOCone Fast. Jet k. T STAR Preliminary J. Putschke [STAR Collaboration], ar. Xiv: 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 S 2 A: Talks by E. Bruna, H. Caines Where is the jet quenching? Biases: Online triggering, PT cut Sevil Salur 49

Quantitative Understanding: Di-Hadrons? z. T=p. Trecoil/p. Ttrig H. Zhang, J. F. Owens, E. Wang,

Quantitative Understanding: Di-Hadrons? z. T=p. Trecoil/p. Ttrig H. Zhang, J. F. Owens, E. Wang, X. N. Wang Phys. Rev. Lett. 98, 212301 (2007) J. L. Nagle ar. Xiv: 0805. 0299 [nucl-ex] J. Adams, et al Phys Rev. Lett. 97, 162301 (2006) vary model parameter e 0 Di-hadron suppression not yet well-described by NLO theory Sevil Salur 50

p+p @ s = 200 Ge. V Jets at RHIC & LHC: Au+Au @

p+p @ s = 200 Ge. V Jets at RHIC & LHC: Au+Au @ s. NN = 200 Ge. V Pb+Pb @ s. NN = 5. 5 Te. V A. Pulvirenti schematic view of jet production in quark matter hadrons leading particle q q leading particle q hadrons Multiple interaction inside the collision region Lose energy through medium induced gluon radiation Early production from parton-parton scatterings Direct probes of partonic phase Sevil Salur 51

Jet fragmentation getting more diffuse as jet propagate in the medium? Jet Sevil Salur

Jet fragmentation getting more diffuse as jet propagate in the medium? Jet Sevil Salur 52

STAR Preliminary p+p Au+Au BEMC calibration Uncertainty STAR Preliminary Inclusive jet spectrum: See QM

STAR Preliminary p+p Au+Au BEMC calibration Uncertainty STAR Preliminary Inclusive jet spectrum: See QM 2009 S 2 A Talk by: M. Ploskon New analysis (k. T & anti-k. T) agrees with published STAR data (Mid-point cone) Quark Matter 2009, Knoxville TN Sevil Salur 53

Di-hadrons? z. T=p. Trecoil/p. Ttrig Zhang et al. (ZOWW) PRL 98, 212301 See the

Di-hadrons? z. T=p. Trecoil/p. Ttrig Zhang et al. (ZOWW) PRL 98, 212301 See the next talk by Jamie Nagle Di-hadrons not yet well-constrained by NLO theory Sevil Salur 54

What’s happening! Effect A: Biased sample of jets due to the High-Tower Trigger: d.

What’s happening! Effect A: Biased sample of jets due to the High-Tower Trigger: d. N/dξ the HT trigger favors “surface” jets that are not modified by the medium Ejet (Au. Au) = Ejet (pp) FF unmodified If this is true HT jets should not binary scale even without Ptcut! Effect B: B Biased sample of jets due to energy loss and p. Tcut d. N/dξ The jet softens in the medium Its energy is not recovered with p. Tcut AND assuming PYTHIA fragmentation Its energy is UNDERESTIMATED ξ=ln(ptjet/pt) should be larger If this is true Quenching models could address this issue Sevil Salur Au+Au p+p ξ 55

Fragmentation Functions Trigger jet Recoil jet STAR Preliminary p. T(trigger) > 10 Ge. V

Fragmentation Functions Trigger jet Recoil jet STAR Preliminary p. T(trigger) > 10 Ge. V & PTcut=2 Ge. V p. T(recoil jet) > 25 Ge. V & PTcut=0. 1 Ge. V No apparent modification in the z of Au+Au with respect to p+p. See QM 2009 S 2 A: Talk by E. Bruna Sevil Salur 56

Fragmentation Functions Trigger jet Recoil jet STAR Preliminary p. T(trigger) > 10 Ge. V

Fragmentation Functions Trigger jet Recoil jet STAR Preliminary p. T(trigger) > 10 Ge. V & PTcut=2 Ge. V 20<p. T(recoil jet) < 25 Ge. V & PTcut=0. 1 Ge. V Apparent modification in the z of Au+Au with respect to p+p. See QM 2009 S 2 A: Talk by E. Bruna Jets look more softer and more diffuser! Sevil Salur 57

STAR Preliminary Mateusz Ploskon, LBNL, STAR, QM'09 Increasing Path Length H – recoil jet

STAR Preliminary Mateusz Ploskon, LBNL, STAR, QM'09 Increasing Path Length H – recoil jet coincidences 58

q-PYTHIA (http: //igfae. usc. es/Qat. MC) Carlos Salgado Talk 2009 QM Sevil Salur 59

q-PYTHIA (http: //igfae. usc. es/Qat. MC) Carlos Salgado Talk 2009 QM Sevil Salur 59

Q-Pythia Sevil Salur 60

Q-Pythia Sevil Salur 60

QCD Observables: (Analytic Calculations) Number of subjets vs Opening Angle Gluon Jet Multiplicity is

QCD Observables: (Analytic Calculations) Number of subjets vs Opening Angle Gluon Jet Multiplicity is sensitive to hadronisation. observe a strong broadening of the shower in k. T Nicolas Borghini ar. Xiv: 0902. 2951 Increase in the subjet distributions Need theoretical understanding of jet energy loss Sevil Salur 61

QCD JET Observables In vacuum (LEP) data well understood in p. QCD 100 Ge.

QCD JET Observables In vacuum (LEP) data well understood in p. QCD 100 Ge. V Jet K. Zapp, G. Ingelman, J. Rathsman, J. Stachel, U. A. Wiedemann ar. Xiv: 0804. 3568 p. T cut infrared safe insensitive observables! : number of subjets, broadening, energy flow… Need theoretical understanding of jet energy loss Sevil Salur 62

Theory: Jet Quenching – Energy Loss Elastic energy loss: Bjorken ’ 82 Bremsstrahlung: Gyulassy,

Theory: Jet Quenching – Energy Loss Elastic energy loss: Bjorken ’ 82 Bremsstrahlung: Gyulassy, Wang, Plumer ’ 92 jet quenching measures color charge density, plasma transport coefficients But quantitative analysis of data requires model building Current status: large discrepancies (factor~10) in extracted medium parameters (transport coefficients) → ongoing efforts to resolve this Renk: medium increases virtuality of partons during evolution PYQUEN (Lokhtin, Snigriev): PYTHIA afterburner reduces energy of final state partons and adds radiated gluons according to BDMPS expectations. PQM (Dainese, Loizides, Paic): MC implementation of BDMPS quenching weights HIJING (Gyulassy, Wang): jet and mini-jet production with induced splitting JEWEL (Zapp, Ingelman, Rathsman, Stachel, Wiedemann): parton shower with microscopic description of interactions with medium q-PYTHIA (Armesto, Cunquiero, Salgado, Xiang): includes BDMPS-like radiation in modified splitting function See many QM 2009 talks… Sevil Salur 63

Jet Reconstruction: connect theory and experiment schematic view of jet production hadrons q Goal:

Jet Reconstruction: connect theory and experiment schematic view of jet production hadrons q Goal: re-associate hadrons to accurately reconstruct the partonic kinematics (infrared and collinear safe) θ≈0 q hadrons • p. QCD theory calculates partons • experiment measures fragments of partons: hadrons and calorimeter towers (clusters of hadrons) Apply “same” jet clustering algorithm to data and theory. Sevil Salur 64

The Fast. Jet Algorithms Underlying event (UE) & pile-up are distributed uniformly in y

The Fast. Jet Algorithms Underlying event (UE) & pile-up are distributed uniformly in y and p. T(Jet Measured) ~ p. T(Parton) + <p. T(UE)> X A(Jet) / <Aj> 22 pile-up in p+p + Pythia 6. 325 dijet Aj M. Cacciari, G. Salam 0707. 1378 [hep-ph] = Diffuse noise (p. T added) Area Definition: Estimate the active area of each jet by filling event with many very soft particles then count how many are clustered into given jet Study of PT/Aj determine the noise density ρon an event-by-event basis Sevil Salur 65

Background in k. T Use the same approach for HI Study the p. T/Aj

Background in k. T Use the same approach for HI Study the p. T/Aj and remove the contribution Aj M. Cacciari, G. Salam 0707. 1378 [hep-ph] The scaled pp cross-section is recovered after the subtraction Looks promising: Has to be studied further for RHIC & LHC with experimentalist tools Sevil Salur 66

k. T Algorithms are not so slow after all Voronoi Diagram N 3 Nlog(N)

k. T Algorithms are not so slow after all Voronoi Diagram N 3 Nlog(N) Geometric nearest neighbor search Computational Geometry Algorithms Library M. Cacciari, G. Salam hep-ph/0512210 • Divide the plane into cells (one per vertex), • N points can be constructed with O (N ln N ) Orders of magnitude faster Large N region is feasible. Geometrical and minimum-finding of the kt jet-finder require O (N ln N ) Sevil Salur 67

Event Characteristics: Jet Area & Fluctuations M. Cacciari, G. Salam, G. Soyez 0802. 1188

Event Characteristics: Jet Area & Fluctuations M. Cacciari, G. Salam, G. Soyez 0802. 1188 [hep-ph] Background Fluctuations Au+Au 0 -10% MB-trig Py. Embed Py. True Counts Jet Area Au+Au 0 -10% MB-trig Py. Embed Py. True Jet ET> 20 Ge. V KT p. T cut = 0. 1 Ge. V R=0. 4 STAR Preliminary Jet Area KT R=0. 4 p. T cut = 0. 1 Ge. V STAR Preliminary Sigma Heavy-ion: Reduction in Jet Area & Increase in fluctuations Pythia Jets embedded in real Au+Au background events have the same area and fluctuations with that of Jets in real Au+Au data.

Energy Resolution LOHSC ET=35± 5 Ge. V ∆E KT p. Tcut =1 Ge. V

Energy Resolution LOHSC ET=35± 5 Ge. V ∆E KT p. Tcut =1 Ge. V R=0. 4 CAMB ET=35± 5 Ge. V STAR Preliminary p. Tcut =1 Ge. V R=0. 4 STAR Preliminary Seed=4. 6 Ge. V p. Tcut =1 Ge. V R=0. 4 STAR Preliminary Counts Event by event comparison of Py. True vs Py. Det vs Py. Embed. ∆E ∆E E = EPy. Det - EPy. True Shift of median due to un-measured particles (n, K 0 L) E = EPy. Embed – EPy. Det Eand the p. T cut. = EPy. Embed - EPy. True Smearing due to background subtraction in Au+Au. Tail at positive ∆E causes a kick in the spectrum. Sevil Salur 69

Effect of Resolution on Spectrum d. NJet/d. ET (a. u. ) p. Tcut =0.

Effect of Resolution on Spectrum d. NJet/d. ET (a. u. ) p. Tcut =0. 1 Ge. V seed=4. 6 Ge. V R=0. 4 LOHSC Py. Det Py. Embed Py. True STAR Preliminary p. Tcut =1. 0 Ge. V seed=4. 6 Ge. V R=0. 4 LOHSC Py. Det Py. Embed Py. True STAR Preliminary p. Tcut = 2. 0 Ge. V seed=4. 6 Ge. V R=0. 4 LOHSC Py. Det Py. Embed Py. True STAR Preliminary ET [Ge. V] -Increase p. T threshold: Reduce the effect of background fluctuations (jet reconstruction in 0 -10% Au+Au is similar in p+p) - The p. T cut is expected to produce biases. Similar effects also observed for KT & Cambridge/Aachen Sevil Salur 70

Resolution and Efficiency & Acceptance Corrections STAR Preliminary Py. True Py. Embed LOHSC p.

Resolution and Efficiency & Acceptance Corrections STAR Preliminary Py. True Py. Embed LOHSC p. T cut =0. 1 Ge. V R=0. 4 Seed=4. 6 Ge. V pol 5 STAR Preliminary ET [Ge. V] ET-dependent correction factors PTcut LOHSC KT CAMB 0. 1 Ge. V 0. 2 -10 1 -4 2 -6 1 Ge. V 0. 2 -1 0. 7 -1 1 -2 2 Ge. V 0. 2 -0. 3 0. 5 -1 Sevil Salur Py. Embed / Py. True d. NJet/d. ET (a. u. ) Resolution effect corrected assuming Pythia Fragmentation. Embed Pythia Jets in 0 -10% Central Events with MBtrig. ET [Ge. V] Use the fit functions from the ratio of Py. Embed to Py. True to correct for energy resolution, efficiency & acceptance. 71

ATLAS • Efficiency and ET resolution as a function of jet ET and eta.

ATLAS • Efficiency and ET resolution as a function of jet ET and eta. • Gamma-jet measurements possible ! • Di-jet correlation expectations, • D(z) determination • Effective RAA of jets (reco/input) Talk by N. Grau QM 2009 Sevil Salur 72

CMS g+jet (Z+jet) cleaner means to determine fragmentation function Talk by G. Veres QM

CMS g+jet (Z+jet) cleaner means to determine fragmentation function Talk by G. Veres QM 2009 CMS Eur. Phys. J. 50 (2007) 117 Sevil Salur 73

Fake jet contamination “Fake” jets: signal in excess of background model from random association

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 Sevil Salur STAR Preliminary 74