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Jet finding in p+p at STAR

Jet finding in p+p at STAR. Elena Bruna Yale University. Yale - Columbia Day, May 2 nd 2008. OUTLINE. Jet studies in p+p at STAR Motivations Recent results Future goals Jet finding algorithm in p+p at STAR Method Performance First studies on PYTHIA events Conclusions.

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Jet finding in p+p at STAR

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  1. Jet finding in p+p at STAR Elena Bruna Yale University Yale - Columbia Day, May 2nd 2008

  2. OUTLINE • Jet studies in p+p at STAR • Motivations • Recent results • Future goals • Jet finding algorithm in p+p at STAR • Method • Performance • First studies on PYTHIA events • Conclusions Elena Bruna, Yale University

  3. JET RECONSTRUCTION IN p+p AT RHIC: GOALS • Study the longitudinal asymmetry for inclusive jet production in polarized proton collisions at 200 GeV  sensitivity to gluon polarization [Phys. Rev. Lett. 97 (2006) 252001, arXiv:0710.2048] • Fragmentation functions of charged and identified particles provide: • comparison with MLLA formalism • baseline for jet quenching in Au+Au Elena Bruna, Yale University

  4. RECENT RESULTS AND PERSPECTIVES • Inclusive differential cross section for p+pjet + X measured by STAR with polarized proton beams. • Increased L in 2006: • High-pT jets • PID of jet fragments • GOALS for STAR: 2003-2004 data Elena Bruna, Yale University • Study of the fragmentation functions for particles inside jets in p+p for different jet energies and opening angles • Measure jets in Au+Au • Study the hadrochemical modifications of jets in the nuclear medium

  5. JETS IN VACUUM • MLLA (modified leading logarithmic approximation) formalism provides a good description of fragmentation functions in e+e- and ppbar collisions. e+e-√s=29 GeV H. Aihara et al. (TPC/2g coll.), PRL 52, 577 (1984) • STAR p+p 2006 data: • Measure fragmentation functions in p+p at 200 GeV as baseline for Au+Au • test pQCD models (MLLA, …)

  6. JET QUENCHING IN HOT NUCLEAR MATTER • Signatures: • Modification of jet energy distributions • Modification of jet fragmentation functions • Modification of the hadrochemical composition of the jet fragments [Sapeta, Wiedemann arXiv:0707.3494] • Medium-modified MLLA (includes hadrochemistry predictions): • IDEA: in-medium gluon radiation implies an enhancement of the parton splitting • MODEL: the parton splitting functions are enhanced by a common factor [Sapeta, Wiedemann arXiv:0707.3494] Elena Bruna, Yale University

  7. MODEL PREDICTIONS [Sapeta, Wiedemann arXiv:0707.3494] Elena Bruna, Yale University Full jet reconstruction and PID inside jets in both p+p and A-A is required

  8. JET FINDING ALGORITHM IN p+p • Cone algorithm: • A ‘seed’ defines the approximate jet direction • seed = track with E>Ethreshold • Tracks which are within a radius of R<Rcone are taken (R=√(ΔΦ2+Δη2)) • The centroid of the cone is given by summing the momenta of the particles inside the cone • The centroid becomes the new seed : procedure iterated until the seed position is stable • Additional features: • Midpoint algorithm: search for missing jets using the midpoint of all the pairs of found jets as seed • Splitting/merging: disentangle jets which share common towers in the calorimeter detector particle Elena Bruna, Yale University parton

  9. JET FINDING PERFORMANCES • Simulated PYTHIA events • Jet finding algorithm applied to: • PYTHIA particles (charged and neutral), no detector effect  PARTICLE jets • PYTHIA+GEANT+RECONSTRUCTED particles (tracks+towers in the calorimeter)  DETECTOR jets • PARTICLE jets and DETECTOR jets are compared arXiv:0710.2048 STAR MC simulations Elena Bruna, Yale University

  10. PARTICLE & DETECTOR JETS (1 of 2) 10<E(PYTHIA)<10.3 GeV 20<E(PYTHIA)<20.5 GeV BLACK = DETECTOR jet RED = PYTHIA jet BLACK = DETECTOR jet RED = PYTHIA jet • SETUP: • R=0.7 (ϑc~0.49 rad) • seed: ET>0.5 GeV • |ηjet|<0.3 30<E(PYTHIA)<30.5 GeV Elena Bruna, Yale University BLACK = DETECTOR jet RED = PYTHIA jet JET R=0.7 η=+1 η=-1 z

  11. PARTICLE & DETECTOR JETS (2 of 2) 10<E(PYTHIA)<10.3 GeV 20<E(PYTHIA)<20.5 GeV Elena Bruna, Yale University 30<E(PYTHIA)<30.5 GeV BLACK = DETECTOR jet RED = PYTHIA jet

  12. DETECTOR JETS: MULT VS EJET 10<E(PYTHIA)<10.3 GeV 20<E(PYTHIA)<20.5 GeV Elena Bruna, Yale University 30<E(PYTHIA)<30.5 GeV

  13. PARTICLE JETS:ξ (1of 2) 10<E(PYTHIA)<10.3 GeV 20<E(PYTHIA)<20.5 GeV • Only charged particles, no PID Elena Bruna, Yale University 30<E(PYTHIA)<30.5 GeV

  14. PARTICLE JETS:ξ (2of 2) 10<E(PYTHIA)<10.3 GeV 20<E(PYTHIA)<20.5 GeV 30<E(PYTHIA)<30.5 GeV Elena Bruna, Yale University PIONS KAONS

  15. SUMMARY AND OUTLOOK • Full jet reconstruction in p+p at RHIC is needed as a baseline to study hadrochemical modifications of jets in Au+Au collisions • The standard jet finding algorithm (midpoint cone) has been tested on PYTHIA events with different settings of the parameters (seed, Radius) • Test other algorithms: kT, … • Analysis on p+p (run 2006): in progress • Trigger effects are being studied • Correction factor from ‘detector jet’ to ‘particle jet’ • Fragmentation functions: charged particles, p, K, π, e, Λ, … Elena Bruna, Yale University

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