au+au collisions at gev by the star experiment snn = 200 · 2019. 10. 18. · measurement of...
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Measurement of semi-inclusive +jet and π0+jet distributions in central Au+Au collisions at GeV by the STAR experiment
γdirsNN = 200
Nihar Ranjan Sahoo, for the STAR Collaboration Shandong University, Qingdao, China
Email Id: [email protected] The STAR Collaboration: https://drupal.star.bnl.gov/STAR/presentations/
JetJet
Abstract
MTD TOF Magnet upVPD BBC EEMCBEMC TPC
§ Special High Tower trigger for π0/γ event [BEMC] § Discrimination between π0 γγ and γdir
§ By Transverse Shower Profile (TSP) method § Using Barrel Shower Maximum Detector [BSMD]
2. STAR detector setup1. Motivation
5. Summary and outlook• First γdir+jet and π0+jet measurement at RHIC within 9 < ETtrig < 15 GeV is presented in central Au+Au collisions at
center of mass energy 200 GeV• Recoil jet with jet radius 0.2 is strongly suppressed at high jet pT whereas a noticeable recovery of jet energy loss is
observed at jet radius 0.5 for both the γdir and π0 trigger cases• Recoil jet suppression is seen to be independent of ET
trig; whereas γdir+jet and π0+jet show similar level of suppression.• The measurement within 15 < ET
trig < 20 GeV for γdir+jet is ongoing
• Jet quenching is an important signature of the hot and denseQCD matter produced in heavy-ion collisions [1].
• A direct photon (γdir) produced in coincidence with a recoiljet (γdir+jet) is a good probe to study the parton energy lossin the QGP [2].
• Comparison between γdir+jet vs π0+jet provides quantitativeunderstanding of parton energy loss in the QCD medium
• Energy loss as a function of path length, colorfactor, parton energy, etc.
• Redistribution of lost energy inside themedium [Jet radius]
1-0.5-
00.5
1h 3-2-
1-0
12
3
f
0
2
4
6
8
10
[GeV
/c]
Tp
-Trigger EventgAu+Au 200 GeV [Run14], Event number=37362, Run number=15098037
- Triggerg
3. Analysis details
γrich trigger event
Full analysis chain:
1. Discrimination between π0/γrich-triggered events
Transverse Shower Profile method [4]
2. Recoil jets from high-tower-triggered events (SE)
Using FastJet package [3]; Recoil jet region:[π-π/4,
π+π/4]; Jet radius = 0.2 and 0.5; |ηjet| < 1-R
3. Subtraction of uncorrelated jet background in recoil region
Based on h+jet analysis[5], event-mixing technique
4. Correction for detector and heavy-ion background
fluctuations effects
5. Conversion from γrich+jet to γdir+jet [4]
Using π0+jet yield and purity of γdir
6. Major sources of systematic uncertainty
Unfolding, mixed-event normalization region, detector
effects, γdir background subtraction [contributes only to γdir+jet]
Purity of direct photon for different trigger ETtrig bins
γrich trigger events: enriched-γdir trigger events with someadmixture of photons from π0.
8 10 12 14 16 18 20 [GeV]trig
TE10
15
20
25
30
35
sam
ple
rich
γBa
ckgr
ound
(%) i
n
STAR Preliminary
Au+Au 200 GeV [year 2014], 0%-15% Uncertaintyσ1±
References1. J. Adams et al. (STAR Collaboration), Nucl. Phys. A 757, 102 (2005)2. X.-N. Wang, Z. Huang, and I. Sarcevic, Phys. Rev. Lett. 77, 231 (1996)3. M. Cacciari, G. P. Salam, and G. Soyez, Eur. Phys. J. C (2012) 72:18964. L. Adamczyk et al. (STAR Collaboration), Phys. Lett. B 760 (2016) 689-6965. L. Adamczyk et al. (STAR Collaboration), Phys. Rev. C 96 (2017) no.2, 024905
We present the semi-inclusive measurement of charged jets recoiling from direct-photon and π0 triggers in central Au+Au collisions at 200 GeV center of mass energy, using a dataset with integratedluminosity 13 nb−1 recorded by the STAR experiment in 2014. The photon and π0 triggers have 9 < ETtrig < 15 GeV. Charged jets are reconstructed with the anti-kT algorithm with resolutionparameters R=0.2 and 0.5. A mixed Event technique developed previously by STAR is used to correct the recoil jet yield for uncorrelated background, enabling recoil jet measurements over a broadpT,jet range with large jet radius. We report the corrected semi-inclusive recoil jet yields for both triggers and compare them to those for p+p collisions. These measurements have different trigger bias,in terms of both the path-length distribution and quark/gluon mix of the recoil jet population, and their corrected recoil spectra are compared.
4. Results and discussion
6-10
5-10
4-10
3-10
2-10
1-10
1
10
]-1) [
(GeV
/c)
jet
h d
reco
,ch
T,je
t/(d
pje
tsN2
) dtri
g(1
/N
Au+Au 200 GeV, 0-15% = 0.2jet RTanti-k
+jet0p
< 11 GeV [SE]Ttrig9 < E
< 15 GeV [SE]Ttrig11 < E
ME
= 0.5jetR
10- 0 10 20 30 A) [GeV/c]× r - raw,ch
T,jet (= preco,ch
T,jetp
1
10
ME
SE
10- 0 10 20 30 A) [GeV/c]× r - raw,ch
T,jet (= preco,ch
T,jetp
1
10
6-10
5-10
4-10
3-10
2-10
1-10
1
10]-1
) [(G
eV/c
)je
th
dre
co,c
hT,
jet
/(d p
jets
N2) d
trig
(1/N
Au+Au 200 GeV, 0-15% = 0.2jet RTanti-k
+jetrichg
< 11 GeV [SE]Ttrig9 < E
< 15 GeV [SE]Ttrig11 < E
ME
= 0.5jetR
10- 0 10 20 30 A) [GeV/c]× r - raw,ch
T,jet (= preco,ch
T,jetp
1
10
ME
SE
10- 0 10 20 30 A) [GeV/c]× r - raw,ch
T,jet (= preco,ch
T,jetp
1
10
STAR Preliminary STAR Preliminary
γrich+jet: SE and MEπ0+jet: SE and ME
γdir+jet vs π0+jet: Recoil jet suppression for Rjet = 0.2 and 0.5
5 10 15 20 251−10
1
PYTH
IAAAI Au+Au 200 GeV, 0-15%
= 0.5jet RTanti-k
STAR Preliminary
< 11 GeVtrigT9 < E
5 10 15 20 25 [GeV/c]ch
T,jetp
1−10
1
PYTH
IAAAI
< 15 GeVtrigT11 < E +jet0π +jet
dirγ
Caption- IAAPYTHIA as a function ofpT,jetch for γdir- (red band) and π0-trigger(blue band) recoil charged jet. Top: 9 <ETtrig< 11 GeV. Bottom: 11 < ETtrig< 15GeV. Lighter and darker bandsrepresent systematic and statisticaluncertainties, respectively. Right andleft panels represent Rjet=0.2 and 0.5,respectively.
A clear difference between recoil-jet spectra for different trigger ET: 9 < ETtrig < 11 GeV vs. 11 <
ETtrig < 15 GeV. Recoil jet pT is suppressed with respect to PYTHIA8. γdir+jet: downward arrow
represents upper limit in the yield at: pT,jetch = 11 GeV/c for 9 < ET
trig <11 GeV, pT,jetch = 15 GeV/c
for 11 < ETtrig <15 GeV.
Caption- γrich+jet :The reconstructed jet p T, jetreco distributions
are shown for the same event (SE) and mixed event (ME) fortwo triggers ETtrig bins: 9-11 GeV and 11-15 GeV. Left andright panels represent for Rjet =0.2 and 0.5, respectively. Lowerpanels shows the ratio between SE and normalized ME.
Recoil charged jets dominate (above ~10 GeV/c) overuncorrelated jet background from mixed events for differentETtrig bins and jet radii. A clear trigger dependence can beenseen.
0 5 10 15 20 25 [GeV/c]ch
T,jetp
4-10
3-10
2-10
1-10
-1) [
GeV
/c]
jet
h d
ch T,je
t/(d
pje
t2
dN
trig
1/N
Au+Au, 0-15%=0.5
jet, RTanti-k
< 30 GeV/cconstT
p+jet0p
PYTHIA < 15 GeVtrig
T11 < E < 11 GeVtrig
T9 < E
STAR Preliminary
π0+jet: Recoil jet pT spectra γdir+jet: Recoil jet pT spectraCaption- Fully corrected semi-inclusive γdir trigger recoil charged jetpT, jet spectra for the above two ETtrigbins. Dashed lines are PYTHIA8expectation. Left panel (R=0.2) andRight panel (R=0.5). Systematic(lighter band) and statistical (darkerband) uncertainty. γdir+jet: Downwardarrow represents the large uncertainty.