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Systematic Studies of Jet–Medium Interactions in STAR

Investigate di-jet momentum imbalance, centrality dependence, and away-side correlations in high-energy collisions using systematic methodologies. Explore path-length dependent energy loss and jet shapes.

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Systematic Studies of Jet–Medium Interactions in STAR

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  1. Systematic Studies of Jet–medium Interactions in STAR Kun Jiang University of Science and Technology of China (USTC) & Purdue University (for the STAR Collaboration) Kun Jiang 1

  2. Tomography with Jets Path-length dependent energy loss Hard scattering selection High-pT hadron High-pT direct g Hard-core jets Surface bias Less bias No bias T. Renk PRC 88, 054902 (2013) • Di-jet momentum imbalance • shorter path length? (tangential biased di-jets) • Di-hadron correlations • maximum path length (trigger surface bias) Kun Jiang Quark Matter 2018, Venice, Italy 2

  3. Geom. matching Method for Di-jet Imbalance Study pTLead>20 GeV/c, pTSubLead>10 GeV/c, |Df-p|<0.4 HT: Neutral particle with pT>5.4 GeV/c Geom. matching Matched Di-jets Constituents pTCut=0.2 GeV/c Hard-Core Di-jets Constituents pTCut = 2 GeV/c Geom. matching: DR<0.4 Calculate “matched” momentum imbalance with constituentpTcut>0.2 GeV/c. Keep this jet selection Kun Jiang Quark Matter 2018, Venice, Italy 3

  4. Di-jet Imbalance STAR PRL 119, 062301 (2017) • Hard-core di-jets in central Au+Au significantly more imbalanced than p+p • Momentum balance restored to p+p baseline for R = 0.4 with soft particles included Kun Jiang Quark Matter 2018, Venice, Italy 4

  5. Centrality Dependence of AJ RUN7: STAR PRL 119, 062301 (2017) • Comparable between Au+Au Run 14 and Run 7 in 0-20% centrality (detector level) • Run14: large increase in statistics enable to study centrality dependence • Apparent evolution of AJ to more balanced jets in peripheral Au+Au collisions Kun Jiang Quark Matter 2018, Venice, Italy 5

  6. Enhanced Away-side Momentum Flow Projection of away-side pT onto trigger axis e: single-particle acceptance × efficiency STAR preliminary Au+Au 200 GeV STAR preliminary • For each centrality, cut on the lowest 10% of events to enhance away-side momentum flow  “jet” = jet + jet-like hotspots Kun Jiang Kun Jiang Quark Matter 2018, Venice, Italy 6 6

  7. Methodology for Two-particle Correlations Trigger particle |h| < 1 • Away-side: large recoil momentum region opposite to trigger particle • Analyze correlations in close-region and far-region, respectively • Flow contributions to close-region and far-region are equal cancelled in their difference close-region = flow + near-side “jet” + away-side “jet” * fractionclose far-region = flow + near-side “jet” + away-side“jet” * fractionfar diff = away-side “jet” * fraction Kun Jiang Quark Matter 2018, Venice, Italy 7

  8. Flow Subtracted Away-side Correlation STAR TPC STAR preliminary f-ftrig close- region far- region away-side “jet” h close-region = flow + near-side “jet” + away-side “jet” * fractionclose far-region = flow + near-side “jet” + away-side“jet” * fractionfar diff = away-side “jet” *fraction p STAR preliminary preliminary Gaussian fit • Near-side equal as expected • Away-side yield contains unknown “fraction” factor • Away-side shape can be quantified by Gaussian fit width, s p Df(rad) Kun Jiang Quark Matter 2018, Venice, Italy 8

  9. Away-side Jet-like Correlation Shape 50-80% 0.15<pTassoc<0.5 GeV/c 0-10% 0.15<pTassoc<0.5 GeV/c c2/ndf 44.8/46 STAR preliminary STAR preliminary c2/ndf 39.0/46 3<pTtrig<10 GeV/c 50-80% 2<pTassoc<3 GeV/c 0-10%2<pTassoc<3 GeV/c c2/ndf 38.1/46 STAR preliminary c2/ndf 42.3/46 STAR preliminary • The away-side correlation shape is consistent with Gaussian for all centrality and pT bins. Quark Matter 2018, Venice, Italy

  10. Away-side Jet-like Correlation Widths STAR preliminary saway-side(rad) pTassoc: 0.15 - 0.5 GeV/c 0.5 - 1 GeV/c 1 - 2 GeV/c 2 - 3 GeV/c 3<pTtrig:<10 GeV/c Au+Au 200 GeV More central  Centrality (%) • Moderate to high pT assoc. particles: broadening with increasing centrality • Shape for all pT more similar in central than in peripheral collisions Kun Jiang Quark Matter 2018, Venice, Italy 10

  11. Medium-induced Away-side Broadening • Width decreases rapidly with increasing pTassoc  expected for jet-like correlations • In central collisions the decrease is not as large  stronger broadening at higher pT • Different from jet-hadron correlations: • Different “jet” kinematics? • Different trigger biases? STAR preliminary saway-side(rad) STAR preliminary 3<pTtrig:<10 GeV/c Au+Au 200 GeV STAR PRL 112, 122301 (2014) Kun Jiang Quark Matter 2018, Venice, Italy 11

  12. Conclusions • Di-jet momentum imbalance: • Much improved statistics allow first measurement of centrality dependence at RHIC • AJ more balanced for peripheral Au+Au data • Away-side jet-like correlations: • Away-side shape with robust flow background subtraction • Correlation broadens with increasing centrality except low pT • Stronger centrality dependence of broadening at higher pT Kun Jiang Quark Matter 2018, Venice, Italy 12

  13. Outlook • g-jet and p0-jet • p+A hadron-jet • Heavy-flavor tagged jet(Saehanseul Oh poster #375) STAR preliminary STAR preliminary Kun Jiang Quark Matter 2018, Venice, Italy 13

  14. zg in Au+Au • Groomed momentum sharing zg of hard-core di-jets:Theory calculations show good agreement • More differential measurements of zg and jet sub-structure coming soon STAR preliminary STAR preliminary Ning-Bo Chang #137 May 15 Li & VitevarXiv: 1801.00008 N.-B. Chang et al. PLB 781 (2018) 423 Kun Jiang Quark Matter 2018, Venice, Italy 14

  15. Thank you！ Kun Jiang Quark Matter 2018, Venice, Italy 15

  16. Backup slides Kun Jiang Quark Matter 2018, Venice, Italy 16

  17. γ+jet and π0+jet in the STAR Experiment Au+Au 200 GeV, 0-15% central collisions Good trigger statistics after QA (9 < pTtrig< 30 GeV/c) π0γrich Raw Trigger pT spectrum Events Analysis is underway and will be updated soon. Kun Jiang Quark Matter 2018, Venice, Italy 17

  18. Jet-hadron PRL 112, 122301 (2014) Kun Jiang Quark Matter 2018, Venice, Italy 18

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