Jet finding in p p at STAR

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Jet finding in pp at STAR

• Elena Bruna
• Yale University

Yale - Columbia Day, May 2nd 2008
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OUTLINE

• Jet studies in pp at STAR
• Motivations
• Recent results
• Future goals
• Jet finding algorithm in pp at STAR
• Method
• Performance
• First studies on PYTHIA events
• Conclusions

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JET RECONSTRUCTION IN pp 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,
  arXiv0710.2048
• Fragmentation functions of charged and identified
  particles provide
• comparison with MLLA formalism
• baseline for jet quenching in AuAu

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RECENT RESULTS AND PERSPECTIVES

• Inclusive differential cross section for pp?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

• Study of the fragmentation functions for
  particles inside jets in pp for different jet
  energies and opening angles
• Measure jets in AuAu
• Study the hadrochemical modifications of jets in
  the nuclear medium

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JETS IN VACUUM

• MLLA (modified leading logarithmic approximation)
  formalism provides a good description of
  fragmentation functions in ee- and ppbar
  collisions.

ee-vs29 GeV
H. Aihara et al. (TPC/2g coll.), PRL 52, 577
(1984)

• STAR pp 2006 data
• Measure fragmentation functions in pp at 200 GeV
  as baseline for AuAu
• test pQCD models (MLLA, )

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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
  arXiv0707.3494
• 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
  arXiv0707.3494

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MODEL PREDICTIONS
Sapeta, Wiedemann arXiv0707.3494
Full jet reconstruction and PID inside jets in
both pp and A-A is required
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JET FINDING ALGORITHM IN pp

• Cone algorithm
• A seed defines the approximate jet direction
• seed track with EgtEthreshold
• Tracks which are within a radius of RltRcone are
  taken (Rv(?F2??2))
• 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
parton
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JET FINDING PERFORMANCES

• Simulated PYTHIA events
• Jet finding algorithm applied to
• PYTHIA particles (charged and neutral), no
  detector effect ? PARTICLE jets
• PYTHIAGEANTRECONSTRUCTED particles
  (trackstowers in the calorimeter) ? DETECTOR
  jets
• PARTICLE jets and DETECTOR jets are compared

arXiv0710.2048 STAR MC simulations
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PARTICLE DETECTOR JETS (1 of 2)
10ltE(PYTHIA)lt10.3 GeV
20ltE(PYTHIA)lt20.5 GeV
BLACK DETECTOR jet RED PYTHIA jet
BLACK DETECTOR jet RED PYTHIA jet

• SETUP
• R0.7 (?c0.49 rad)
• seed ETgt0.5 GeV
• ?jetlt0.3

30ltE(PYTHIA)lt30.5 GeV
BLACK DETECTOR jet RED PYTHIA jet
JET
R0.7
?1
?-1
z
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PARTICLE DETECTOR JETS (2 of 2)
10ltE(PYTHIA)lt10.3 GeV
20ltE(PYTHIA)lt20.5 GeV
30ltE(PYTHIA)lt30.5 GeV
BLACK DETECTOR jet RED PYTHIA jet
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DETECTOR JETS MULT VS EJET
10ltE(PYTHIA)lt10.3 GeV
20ltE(PYTHIA)lt20.5 GeV
30ltE(PYTHIA)lt30.5 GeV
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PARTICLE JETS? (1of 2)
10ltE(PYTHIA)lt10.3 GeV
20ltE(PYTHIA)lt20.5 GeV
30ltE(PYTHIA)lt30.5 GeV

• Only charged particles, no PID

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PARTICLE JETS? (2of 2)
10ltE(PYTHIA)lt10.3 GeV
20ltE(PYTHIA)lt20.5 GeV
30ltE(PYTHIA)lt30.5 GeV
PIONS KAONS
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SUMMARY AND OUTLOOK

• Full jet reconstruction in pp at RHIC is needed
  as a baseline to study hadrochemical
  modifications of jets in AuAu 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 pp (run 2006) in progress
• Trigger effects are being studied
• Correction factor from detector jet to
  particle jet
• Fragmentation functions charged particles, p, K,
  p, e, ?,