Title:
Measurement of inclusive charged-jet production in Au+Au collisions at sqrt(s_NN) = 200 GeV
Primary Authors:
Jana Bilecikova (NPI), Peter Jacobs (LBNL), Jan Rusnak (NPI)
Contact:
Jan Rusnak, rusn@email.cz
Target Journal: PRC
Version Submitted to PRC:
PRC paper v6
Almost Final Verison:
paper on arXiv
Previous Paper Drafts:
PRC paper v5
PRC paper v4
PRC paper v3
PRC paper v2
paper on arXiv
paper draft v5.0
paper draft v4.2
paper draft v3.6
paper draft v3.5
paper draft v3.4
paper draft v3.3
paper draft v2.11
paper draft v2.10
paper draft v 2.9
Analysis Note:
version 5.5
version 5.3
version 5.2
Editors's comments (to PRCv5)
Response to GPC comments to addressing PRC comments:
Response to GPC comments
Response to PRC Referee comments:
Response to PRC Referee comments round 1
Response to STAR Collaboration comments:
Response to collaboration comments round 2
Response to collaboration comments round 1
Response to GPC comments:
Response to grammar comments
Response to Paper comments Feb11
Response to paper comments Aug13
Response to AN comments Aug13
Response to PWG comments:
Response to comments to paper v2.9
Code description:
drupal.star.bnl.gov/STAR/blog/rusnak/inclusive-charged-jet-analysis-code-description
PAPER FIGURES (in .eps format):
EPS_Figures_PRCv6
YAML tables for figures:
YAML_tables_5-0
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ABSTRACT:
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The STAR Collaboration at the Relativistic Heavy Ion Collider reports the first measurement of inclusive charged-jet production in peripheral and central Au+Au collisions at sqrt(s_NN)=200 GeV. Jets are reconstructed using charged tracks within |eta|<1.0 and pT>0.2 GeV/c, with jet resolution parameter R=0.2, 0.3, and 0.4. The large background yield uncorrelated with the jet signal is observed to be dominated by statistical phase space, consistent with previous measurement. This background is suppressed by requiring a high transverse-momentum (high-pT) leading hadron in accepted jet candidates. The bias imposed by this requirement is assessed, and the pT-region in which this bias is small is identified.
Inclusive charged-jet distributions are reported for 5<pTjetch<25 GeV/c and 5<pTjetch<30 GeV/c, for peripheral and central Au+Au collisions respectively.
Charged-jet yield suppression is observed for central relative to peripheral Au+Au collisions, with the magnitude of suppression indicating similar
population-averaged energy loss due to medium-induced energy transport as that measured for a semi-inclusive recoil jet population. The inclusive jet yield is also suppressed in central Au+Au relative to p+p collisions, with the magnitude of suppression consistent with that measured for inclusive hadron production at high-pT. Comparison of inclusive charged-jet yields for different values of R shows no signficant evidence of
medium-induced broadening of the transverse jet profile in central Au+Au
collisions. The measured distributions are compared to theoretical model calculations incorporating jet quenching.
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CONCLUSIONS:
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We have reported the quasi-inclusive distribution of charged jets in central and peripheral Au+Au collisions at sqrt(s_NN)=200 GeV, over the range 5<pTjetch<30 GeV/c. The combinatorial background in such collisions is suppressed by the requirement that the leading charged hadron in the jet satisfy pTlead>pTleadmin, where pTleadmin=5 GeV/c in the primary analysis. The bias imposed by this requirement is quantified by comparing distributions for pTleadmin=5 and 7 GeV/c, and the region of the measurement where the bias is small is identified.
A Parametrized Model (PM), based on uncorrelated particle emission, is developed to describe the raw distributions, motivated by the excellent description by such an approach of event-by-event distribution of transverse energy in a limited acceptance in nucleus-nucleus collisions. The PM is found to describe the raw distributions well, indicating that the large background to jet measurements in central Au+Au collisions at RHIC is to a large extent statistically distributed, with dynamical QCD correlations such as jets playing a much lesser role. A similar conclusion was drawn from a Mixed Event analysis of semi-inclusive hadron-jet distributions at RHIC.
Suppression of the quasi-inclusive charged-jet yield is observed in central relative to peripheral Au+Au collisions, with magnitude of the suppression similar to that observed at the LHC. This is in contrast to the significant pT-dependence observed for inclusive hadron suppression.
The yield suppression in central Au+Au collisions can be expressed equivalently as a shift in pTjetch, corresponding to medium-induced energy loss out of the jet cone. The pTjetch-shift for the quasi-inclusive population is found to be consistent with that measured for semi-inclusive recoil jets, though both measurements currently have large systematic uncertainties that will be improved in future measurements.
Yield suppression in central collisions is also studied relative to the PYTHIA-simulated charged-jet spectrum in p+p collisions, RAA^pyth. The
PYTHIA calculation is validated by comparison to a STAR measurement of fully reconstructed jets in p+p collisions. Comparison is made to RAA predicted by several current theoretical calculations of jet quenching, with consistency found for the NLO and SCET models for R=0.2. For R=0.4, all models agree with the measurement.
Finally, medium-induced broadening of the jet transverse energy distribution is explored by measuring the ratio of quasi-inclusive yields for R=0.2 and 0.4. No significant medium-induced modification of the distribution is observed in central Au+Au collisions. In comparison to jet quenching calculations, NLO predicts a larger ratio than observed, but SCET and the Hybrid Model are consistent with the measurement.
The data presented here provide new constraints on jet quenching calculations, and promise new insights into the processes that drive it.
