1 / 20

Jet studies in STAR via 2+1 correlations

This paper explores jet quenching in heavy ion collisions using statistical studies of di-jets with a 2+1 correlation technique. It analyzes high-energy photon and charged hadron triggered data, jet shapes, spectra, and comparison between d+Au and Au+Au analyses. Preliminary tests of theory models are also conducted for comparison with samples.

mosterman
Download Presentation

Jet studies in STAR via 2+1 correlations

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Jet studies in STAR via 2+1 correlations Hua Pei For the STAR Collaboration Winter Workshop on Nuclear Dynamics 2011

  2. Outline • Jet quenching in heavy ion collisions • Statistical studies of di-jets: 2+1 correlation technique • Analysis technique • High-energy photon and charged hadron triggered data • Jet shapes, spectra, and comparison between • d+Au analysis • Au+Au analysis • Preliminary test of theory models, comparison with samples. • Outlook Winter Workshop on Nuclear Dynamics 2011

  3. Start from 2-particle correlations • We have learned a lot from 2-particle correlation: • Head-shoulder shape on the away-side • Ridge at near-side Phys. Rev. C 77, 011901(R) (2008) Phys. Rev. C 80 (2009) 64912 Winter Workshop on Nuclear Dynamics 2011

  4. The long “Mach-cone” legend • Many theory models have calculated how parton-medium interaction (energy-loss) can form such “cone” structure. • On the other hand, di-jet structure re-appear at high-pT Au+Au correlations, with similar shapes to those in vacuum. PRL 97, 162301 (2006) PRL 104, 252301 (2010) Winter Workshop on Nuclear Dynamics 2011

  5. Introduction of “2+1” correlation • If we already observe high and low-pT associates each forming a peak on the away-side of a high-pT trigger, do they correlate with each other, so as to reform a jet-like structure? • And how will that test the existing theory models on energy-loss? • Both PHENIX and STAR reported their “2+1” work on QM08, using a second high-pT (“conditional”) particle on the away-side of the first high-pT trigger, then study the low-pT associates around both high-pT particles. Winter Workshop on Nuclear Dynamics 2011

  6. The “2+1” correlation associates primary trigger (T1) “jet-axis” trigger (T2) associates • Use two back-to-back high-pT triggers as proxy of dijets • “pin” the ‘jet axis’ selecting back-to-back triggers • study correlation w.r.t. this axis Courtesy of R .Hollis Winter Workshop on Nuclear Dynamics 2011

  7. The “2+1” correlation technique Signal Background • The trigger-associated pairs may be correlated due to flow effect instead of jets. • We subtract such background by using ZYAM method. • The back-to-back trigger pairs may be random combination. • This probability is estimated from trigger 1 & 2 correlation at the required back-to-back region. • Such pairs will contribute two independent “normal” 2-particle correlation, which are subtracted. (S+B)/S * Raw 2+1 correlation (near-side) – B/S * T1-A (near-side) – B/S * T2-A (away-side) = “True” 2+1 correlation (near-side) Winter Workshop on Nuclear Dynamics 2011

  8. STAR detector layout High energy gammas Charged tracks Winter Workshop on Nuclear Dynamics 2011

  9. Direct view of “2+1” correlation T1: 5 GeV/c < pT < 10 GeV/c T2: 4 GeV/c < pT < pTT1 A1: 1.5 GeV/c < pT < pTT1 Paper to be submitted Au+Au vs. d+Au STAR Preliminary • No appreciable difference between same side and away side, or between Au+Au and d+Au. • Significantly harder spectra than inclusive background (dash-line). Winter Workshop on Nuclear Dynamics 2011

  10. A test of theory model – Surface emission • If the jet-like structure from associate particles at this selected low-pT region is intact even at away-side, how will these “dijet-like” event help to explore medium properties? • A preliminary test: Assume full parton-absorption/escape area of medium (“core/corona”), both of elliptic shapes. • Go back to look at the back-to-back high-pT triggers. • Use the single-particle RAA to tune the size of core/corona (central panel), • Calculate the expected dijets absorption relative to single-jets (band at right panel). • Other tuning method exists:, e.g., v2 K. Werner, Phys. Rev. C 82, 034906 (2010) • It agrees with data (points at right panel), which comes from our 2+1 measurement (ratio of points at left panel, high-pT triggers with jet-like associates serve as proxy of jets). Winter Workshop on Nuclear Dynamics 2011

  11. Questions and answers • Surface emission model works with correlation data. How will path-length dependent energy-loss models adapt to the 2+1 measurement? • A possible explanation from path-length dependent models: By selecting trigger pairs of similar pT (>5GeV/c vs. >4GeV/c), is it true that these triggers sample partons losing similar energy? • Then not only away-side, but also near-side partons, are not fully surface biased. The two partons travel similar length of medium then fragment, to reach similar energy loss or survival probability. • This can be tested by picking up those high-pT trigger pairs of big asymmetry in energy. A relative difference shall happen between Au+Au & d+Au when we compare near-/away-sides. Call that a double ratio? (e.g. T. Renk, Phys. Rev. C 80, 044904 (2009)) Winter Workshop on Nuclear Dynamics 2011

  12. Asymmetric triggers, correlation functions Red: Same-side,Blue: Away-side RHIC Run 2007/2008, STAR High Tower trigger data Trigger1 : ET>10 GeV (E-M calorimeter), mostly from g pairs of same p0 vs. Trigger2 : pT>4 GeV/c, Associate: pT>1.5 GeV/c Large DpT between the two triggers. Au+Au vs. d+Au STAR Preliminary Errors are statistical Df (|Dh|<1.0)Dh (|Df|<0.7) The correlations are of close shape/level from d+Au to central Au+Au collisions, at both same-/away-sides Winter Workshop on Nuclear Dynamics 2011

  13. Asymmetric triggers, spectra Au+Au d+Au Au+Au / d+Au STAR Preliminary STAR Preliminary STAR Preliminary Errors are statistical Same-side Away-side STAR Preliminary STAR Preliminary STAR Preliminary Errors are statistical The same-side spectra ratio is flat at unity. The away-side spectra ratio is also consistent with flat at unity. Winter Workshop on Nuclear Dynamics 2011

  14. Compare Au+Au with d+Au Spectra of Au+Au divided by d+Au STAR Preliminary STAR Preliminary Red: Same-side,Blue: Away-side If the surviving dijets (jet-like structure sustained) mainly come from partons losing energy or escape from deep within the medium then fragmentate in vacuum, sampling asymmetric trigger pairs meaning sampling asymmetric parton (jet) energies, i.e., different levels of surface-bias. The observation of same level of correlation functions and spectra seems not to indicate so. Winter Workshop on Nuclear Dynamics 2011

  15. Summary • The 2+1 correlation are used as proxy of dijets to study parton-medium interaction. • When two back-to-back high-pT particles are triggered, the whole associated particles sustain jet-like structures, at a close shape and magnitude, on both correlation functions and spectra, at Au+Au to d+Au. • Theory models are tested primarily: • Surface emission model (core/corona) agrees with data. • Path-length dependent energy loss mode are expected to: • Show a relative difference between near- and away-side Au+Au/d+Au (double ratio), • It is not observed in either symmetric or asymmetric trigger case. • Detailed study is going on. Winter Workshop on Nuclear Dynamics 2011

  16. Backup Winter Workshop on Nuclear Dynamics 2011

  17. More Trigger ET & pT bins RHIC Run 2007/2008, STAR High Tower trigger data Trigger1 : ET>10 GeV (E-M calorimeter) vs. Trigger2 : pT>4 GeV/c, Associate: pT>1.5 GeV/c Large DpT between the two triggers. Au+Au vs. d+Au STAR Preliminary Errors are statistical Df (radian)Dh The correlations are of close shape/level from d+Au to central Au+Au collisions, at both near-/away-sides Winter Workshop on Nuclear Dynamics 2011

  18. More Trigger ET & pT bins RHIC Run 2007/2008, STAR High Tower trigger data Trigger1 : ET>10 GeV (E-M calorimeter) vs. Trigger2 : pT>6 GeV/c, Associate: pT>1.5 GeV/c Large DpT between the two triggers. Au+Au vs. d+Au STAR Preliminary Errors are statistical Df (radian)Dh The correlations are of close shape/level from d+Au to central Au+Au collisions, at both near-/away-sides Winter Workshop on Nuclear Dynamics 2011

  19. More Trigger ET & pT bins RHIC Run 2007/2008, STAR High Tower trigger data Trigger1 : ET>8 GeV (E-M calorimeter) vs. Trigger2 : pT>4 GeV/c, Associate: pT>1.5 GeV/c Large DpT between the two triggers. Au+Au vs. d+Au STAR Preliminary Errors are statistical Df (radian)Dh The correlations are of close shape/level from d+Au to central Au+Au collisions, at both near-/away-sides Winter Workshop on Nuclear Dynamics 2011

  20. More Trigger ET & pT bins RHIC Run 2007/2008, STAR High Tower trigger data Trigger1 : ET>8 GeV (E-M calorimeter) vs. Trigger2 : pT>6 GeV/c, Associate: pT>1.5 GeV/c Large DpT between the two triggers. Au+Au vs. d+Au STAR Preliminary Errors are statistical Df (radian)Dh The correlations are of close shape/level from d+Au to central Au+Au collisions, at both near-/away-sides Winter Workshop on Nuclear Dynamics 2011

More Related