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
Slide 2
Outline Motivation and strategy Datasets, jet algorithms,
correction schemes Observables Inclusive jet cross-section + Jet R
AA Jet radius systematics (di-)Hadron-jet recoil spectrum and Jet I
AA Discussion: implications for jet quenching 2Mateusz Ploskon
(LBNL), STAR, QM'09
Slide 3
Motivation and Strategy 1 Cross-section ratio AuAu/pp Physics
of full jet reconstruction in heavy ion collisions p+p Au+Au Energy
shift? Absorption? R=0.4 Measure energy flow into cone of radius R
o Total momentum is conserved even for strongly quenched jets o
Unbiased jet reconstruction: recover the full jet energy within
cone radius R o Compare Au+Au and p+p jet spectra o Inclusive cross
section: RAA jet ~1 o 0 +jet conditional yield: IAA jet ~1 o
Caveat: initial state nuclear effects 3Mateusz Ploskon (LBNL),
STAR, QM'09 R RJet
Slide 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 x 10 6 events)
p+p (2006): online Jet Patch trigger (int lumi 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 4Mateusz Ploskon (LBNL), STAR, QM'09
Slide 5
Jet algorithms Algorithms: k t and anti-k t from FastJet*
Resolution parameter R = 0.4, 0.2 Jet acceptance: | JET | < 1.-R
Recombination scheme: E-scheme with massless particles *Cacciari,
Salam and Soyez, JHEP 0804 (2008) 005 [arXiv:0802.1188] Anti-k t
expected to be less susceptible to background effects in heavy ion
collisions 5Mateusz Ploskon (LBNL), STAR, QM'09 Sequential
recombination algorithms Sequential recombination algorithms Cone
based algorithms Cone based algorithms
Slide 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 6Mateusz Ploskon (LBNL), STAR,
QM'09
Slide 7
Heavy Ions and background characterization 7Mateusz Ploskon
(LBNL), STAR, QM'09
Slide 8
STAR Preliminary Au+Au Central Underlying event 8 Single di-jet
event from a central Au+Au: - Two jet peaks on top of the HI
background Single di-jet event from a central Au+Au: - Two jet
peaks on top of the HI background Event background is characterized
with median p T per unit area ( ). in R = 0.4 is ~45 GeV/c. S/B~0.5
at 20 GeV/c. Event background is characterized with median p T per
unit area ( ). in R = 0.4 is ~45 GeV/c. S/B~0.5 at 20 GeV/c.
Central assumption: Signal and background can be factorized Central
assumption: Signal and background can be factorized with
resolution: True jet distribution smeared: DATA ~ 6.8 GeV True jet
distribution smeared: DATA ~ 6.8 GeV Mateusz Ploskon (LBNL), STAR,
QM'09 Systematic studies indicate variation of sigma +/-1 is a
conservative bracketing of systematic uncertainties. Error bands
indicate these limits. Systematic studies indicate variation of
sigma +/-1 is a conservative bracketing of systematic
uncertainties. Error bands indicate these limits.
Slide 9
Fake jet contamination 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 Fake jets: signal in excess of
background model from random association of uncorrelated soft
particles (i.e. not due to hard scattering) STAR Preliminary
9Mateusz Ploskon (LBNL), STAR, QM'09
Slide 10
Fake jet contamination 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 10Mateusz Ploskon
(LBNL), STAR, QM'09 Fake jets: signal in excess of background model
from random association of uncorrelated soft particles (i.e. not
due to hard scattering)
Slide 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 Procedure is numerically stable Correction depends
critically on background model main systematic uncertainty for
Au+Au Procedure is numerically stable Correction depends critically
on background model main systematic uncertainty for Au+Au unfolding
11Mateusz Ploskon (LBNL), STAR, QM'09 Pythia Pythia smeared Pythia
unfolded
Slide 12
Spectrum unfolding Corrections for smearing of jet p T due to
HI backround non- uniformities 1) raw spectrum STAR Preliminary
12Mateusz Ploskon (LBNL), STAR, QM'09
Slide 13
Spectrum unfolding Corrections for smearing of jet p T due to
HI backround non- uniformities 1) raw spectrum 2) removal of fake-
correlations STAR Preliminary 13Mateusz Ploskon (LBNL), STAR,
QM'09
Slide 14
Spectrum unfolding Corrections for smearing of jet p T due to
HI backround non- uniformities 1) raw spectrum 2) removal of fake-
correlations 3) unfolding STAR Preliminary 14Mateusz Ploskon
(LBNL), STAR, QM'09
Slide 15
Spectrum unfolding Corrections for smearing of jet p T due to
HI backround non- uniformities 1) raw spectrum 2) removal of fake-
correlations 3) unfolding 4) correction for p T resolution STAR
Preliminary 15Mateusz Ploskon (LBNL), STAR, QM'09
Slide 16
Jet yields in p+p at sqrt(s NN ) = 200 GeV 16Mateusz Ploskon
(LBNL), STAR, QM'09
Slide 17
Inclusive jet cross-section in p+p at sqrt(s NN ) = 200 GeV o
Fully corrected jet cross-section reconstructed with kt algorithm o
Very good agreement between the algorithms STAR Preliminary
17Mateusz Ploskon (LBNL), STAR, QM'09 Uncertainty due to BEMC
calibration
Slide 18
Inclusive jet cross-section in p+p at sqrt(s NN ) = 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 18Mateusz Ploskon (LBNL), STAR, QM'09
Phys. Rev. Lett. 97 (2006) 252001
Slide 19
Inclusive jet yields in 10% most central Au+Au at sqrt(s NN ) =
200 GeV 19Mateusz Ploskon (LBNL), STAR, QM'09
Slide 20
Inclusive jet yields in 10% most central Au+Au at sqrt(s NN ) =
200 GeV o Fully corrected jet spectrum o Exactly the same
algorithms and jet definitions used as compared to p+p o Bands on
data points represent estimation of systematic uncertainties due to
background subtraction STAR Preliminary 20Mateusz Ploskon (LBNL),
STAR, QM'09 Uncertainty due to BEMC calibration
Slide 21
Inclusive jet spectrum: p+p and central Au+Au (R=0.4 and R=0.2)
p+p Au+Au central STAR Preliminary 21Mateusz Ploskon (LBNL), STAR,
QM'09
Slide 22
Cross-section ratios in p+p and Au+ Au with R=0.2/R=0.4 p+p:
Narrowing of the jet structure with increasing jet energy Au+Au:
Strong broadening of the jet energy profile 22Mateusz Ploskon
(LBNL), STAR, QM'09 STAR Preliminary p+p Au+Au Many systematics
effects cancel in the ratio
Slide 23
Nuclear modification factor for jets 23Mateusz Ploskon (LBNL),
STAR, QM'09
Slide 24
R = 0.4 5% uncertainty on BEMC calibration o Significant energy
recovered as compared to R AA ~0.2 for hadrons o Visible trends: o
different sensitivity of the algorithms o Central values drop as a
function of jet p T STAR Preliminary 24Mateusz Ploskon (LBNL),
STAR, QM'09 R AA Jets
Slide 25
R AA Jets and Energy flow in smaller cone radii Significant
drop of R AA as a function of jet p T for R=0.2 as compared to
R=0.4 Jet energy not fully recovered in small cones shift towards
lower p T Significant drop of R AA as a function of jet p T for
R=0.2 as compared to R=0.4 Jet energy not fully recovered in small
cones shift towards lower p T 25Mateusz Ploskon (LBNL), STAR, QM'09
STAR Preliminary R=0.4 R=0.2
Di-hadron jet correlations 27 Yield per trigger STAR, PRL 97,
162301 (2006) STAR high pT dihadrons: bias towards non- interacting
jet population A A B B Recoil Mateusz Ploskon (LBNL), STAR,
QM'09
Slide 28
Hadron+jet coincidence 1 Cond. yield ratio AuAu/pp p+p Au+Au
Energy shift? Absorption? R=0.4 o Trigger on hard, leading (p T
>6 GeV/c) o 3x3 tower cluster in BEMC o Construct spectrum of
recoil jets o normalized per di-hadron trigger This event selection
will maximize the recoil path length distribution in matter
Conditional yield 28Mateusz Ploskon (LBNL), STAR, QM'09 R R
Jet
Slide 29
H recoil jet coincidences A A B p T > 0.5 GeV/c Recoil jet A
A B p T > 6 GeV/c Recoil jet Use jet fragmentation bias to vary
jet path length distribution? 29Mateusz Ploskon (LBNL), STAR,
QM'09
Slide 30
H recoil jet coincidences A A B B STAR Preliminary 30Mateusz
Ploskon (LBNL), STAR, QM'09 (Au+Au: 10% central) Anti-kt R=0.4
Slide 31
H recoil jet coincidences STAR Preliminary 31Mateusz Ploskon
(LBNL), STAR, QM'09 (Au+Au: 10% central) Anti-kt R=0.4 A A B B
Slide 32
H recoil jet coincidences STAR Preliminary 32Mateusz Ploskon
(LBNL), STAR, QM'09 (Au+Au: 10% central) Anti-kt R=0.4 A A B B
Slide 33
H recoil jet coincidences STAR Preliminary 33Mateusz Ploskon
(LBNL), STAR, QM'09 (Au+Au: 10% central) Anti-kt R=0.4 A A B B
Significant suppression of the bias free recoil jet spectrum
Slide 34
STAR Preliminary Summary o Qualitatively new measurement of jet
quenching in terms of energy flow (rather than hadronic
observables) has been established o What we have shown: o Minimum
bias dataset: RAA~0.5 or larger o Significant broadening of jet
energy profile R=0.2 -> R=0.4 o Strong suppression of recoil jet
rate at maximum path-length o Consistent interpretation: o
quenching induces jet broadening o R=0.4 (with the presented jet
definitions) is insufficient for unbiased reconstruction 34Mateusz
Ploskon (LBNL), STAR, QM'09 STAR Preliminary Au+Au 10% central R
Au+Au 10% central
Slide 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 35Mateusz Ploskon
(LBNL), STAR, QM'09
Slide 36
Extra slides 36Mateusz Ploskon (LBNL), STAR, QM'09
Slide 37
Spectrum unfolding - correction for smearing of jet p t due to
bg nonuniformities R=0.4 R=0.2 37Mateusz Ploskon (LBNL), STAR,
QM'09
