Recent Jet Measurements in Heavy-ion Collisions at STAR in ... · Nihar"Sahoo,"Texas"A&MUniversity"...

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1 Nihar Sahoo, Texas A&M University Recent Jet Measurements in Heavy-ion Collisions at STAR in a Nutshell Nihar Sahoo Texas A&M University 2017 RHIC & AGS Annual Users’ Meeting

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Page 1: Recent Jet Measurements in Heavy-ion Collisions at STAR in ... · Nihar"Sahoo,"Texas"A&MUniversity" 1 Recent Jet Measurements in Heavy-ion Collisions at STAR in a Nutshell Nihar Sahoo

1  Nihar  Sahoo,  Texas  A&M  University  

Recent Jet Measurements in Heavy-ion Collisions at STAR

in a Nutshell

Nihar Sahoo Texas A&M University

2017 RHIC & AGS Annual Users’ Meeting

Page 2: Recent Jet Measurements in Heavy-ion Collisions at STAR in ... · Nihar"Sahoo,"Texas"A&MUniversity" 1 Recent Jet Measurements in Heavy-ion Collisions at STAR in a Nutshell Nihar Sahoo

•  Jet-like correlation

•  γ+hadron and π0+hadron [PLB 760 (2016) 689]

•  Semi-inclusive recoil charged jet •  h±+jet [arXiv:1702.01108] •  γ+jet and π0+jet [ongoing work: preliminary results:QM2017]

•  Di-jet •  AJ measurement (momentum imbalance) [accepted in PRL, arXiv:1609.03878] •  Di-jet+hadron correlations [preliminary results:QM2017] •  Di-jet zg (Splitting function) [ongoing work: preliminary results:QM2017 and

HP2016]

20/06/17   Nihar  Sahoo,  RHIC&AGS  Users'  meeDng  

2017   2  

Recent jet measurements in Heavy-Ion collisions

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•  Jet-like correlation •  γ+hadron and π0+hadron [PLB 760 (2016) 689]

20/06/17   Nihar  Sahoo,  RHIC&AGS  Users'  meeDng  2017   3  

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γ-hadrons and π0-hadrons correlations

•  On  ave.  γ-­‐triggered  parton  (jet)  loses  less  energy  than  that  of  π0-­‐trigger  •  due  to  path  length  (surface  biased  of  π0-­‐trigger)  

 •  γ-­‐triggered  parton  (jet)  loses  less  energy    than  π0-­‐trigger  recoil  

•  due  to  color  factor  (  CA/CF  =  9/4)                                      (dominant  γ  producDon:  qg  -­‐>qγ)  

Hadron  (π0)  Ideal  jet/  Direct-­‐photon  

20/06/17   Nihar  Sahoo,  RHIC&AGS  Users'  meeDng  2017  

YaJEM: T. Renk arXiv:1212.0646

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STAR: PLB 760 (2016) 689

Jet-like correlation: γ+hadron and π0+hadron

•  Large suppression at high zT and pTassoc

•  Within large uncertainty, no clear signature of color factor and path length dependence of energy loss

•  Precision measurements, like γ+jet and π0+jet, are needed for better understanding (different method and also higher statistics)

20/06/17   Nihar  Sahoo,  RHIC&AGS  Users'  meeDng  2017   5  

IAA(x) =Y

Au+Au(x)

Y

p+p(x)

=pTassoc/pTtrig  

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W. Chen, et al. arxiv:1704.03648 Coupled linear Boltzmann Transport and 3+1D hydro (CoLBT-hydro)

Jet-like correlation: γ+hadron

20/06/17   Nihar  Sahoo,  RHIC&AGS  Users'  meeDng  2017   6  

•  enhancement  of  so]  hadrons  due  to  jet-­‐induced  medium  excitaDon  

•  medium  enhances  producDon  of  so]  parDcles  in  parton  fragmentaDon,  relaDve  to  pp,  preferenDally  at  large  angles  

Wei  Chen,  QM2017  talk      

Similar  effect  from  low  to  high  pTγ  ?  

ξ  

ξ  

Hard                                                                            so]  Hard                                                                            so]  

pTγ:  5-­‐7  GeV/c  

pTγ:  12-­‐20  GeV/c  

pTγ:  9-­‐12  GeV/c  

pTγ:  7-­‐9  GeV/c  

Page 7: Recent Jet Measurements in Heavy-ion Collisions at STAR in ... · Nihar"Sahoo,"Texas"A&MUniversity" 1 Recent Jet Measurements in Heavy-ion Collisions at STAR in a Nutshell Nihar Sahoo

•  Semi-inclusive recoil charged jet •  h±+jet [arXiv:1702.01108]

•  γ+jet and π0+jet [ongoing work: preliminary results:QM2017]

20/06/17   Nihar  Sahoo,  RHIC&AGS  Users'  meeDng  2017   7  

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Trigger particle

Recoil jet(s) search area

Courtesy  of  Alex    Schmah    

1

Nhtrig

dNjet

dpT,jet=

1

�pp!h+X

d�pp!h+jet+X

dpT,jet

Semi-inclusive yield of jets* recoiling from a high pT hadron trigger

Measured   Calculable  in  fixed-­‐order  pQCD  

20/06/17   Nihar  Sahoo,  RHIC&AGS  Users'  meeDng  2017   8  

Semi-­‐inclusive  hadron+jet  

•  Use all jet candidates on the other azimuthal hemisphere within +/- 45 degree •  no fragmentation bias on recoil side

•  Mixed event correction for uncorrelated background jets in HIC •  allow to reach low jet pT

[arXiv:1702.01108]  

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•  Energy transported to larger jet R è interaction of jet with the medium •  Medium-induced energy transport to large anglesèlesser at RHIC than LHC

Note:  PYTHIA  p+p  in  ALICE  vs.  Peripheral  Au+Au  in  STAR  

ALICE:  JHEP09(2015)170    

20/06/17   Nihar  Sahoo,  RHIC&AGS  Users'  meeDng  2017   9  

h+Jet yield suppression [h+jet: arXiv:1702.01108]

 

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20/06/17   Nihar  Sahoo,  RHIC&AGS  Users'  meeDng  2017   10  

Lin  Chen,  et.  al,  arXiv:1607.01932  

Transverse Momentum Broadening in HIC

•  For a quark jet: the amount of medium-induced pT broadening describes the Au+Au central collisions from RHIC data.(Using  global  χ2  analysis) •  Higher statistics and low beam energy (e.g, 62.4 GeV) helpful for

better insight of pT broadening

< p2? >⇠ 13 GeV2

STAR: h+jet, π0+hadron PHENIX: charge dihadrons

Vacuum  so]  gluon  radiaDon  +  medium  induced  pT  broadening    

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π0+jet vs. h±+jet  

•  Applying correction due to detector and background fluctuations effects

•  Singular value decomposition (SVD) method for unfolding

•  Taking into account systematic

effects, π0 +jet and h±+jet show agreement within uncertainties

•  Any new information ? •  Icp, IAA, •  Different hadron trigger

What  about  comparison  between   γ+jet  and  π0 +jet    ?      

(h±+jet:  arXiv:1702.01108)  

20/06/17   Nihar  Sahoo,  RHIC&AGS  Users'  meeDng  2017   11  

(Ongoing  analysis)  

N.  Sahoo[QM2017  talk]  

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 π  –  π/4  

 π  +  π/4  

 π0/  γ    

Trigger  Tower  

Recoil  Jet  

•  Charged jet reconstruction (using FastJet3.0.6)

•  kt algorithm for background subtraction •  Anti-kt algorithm for jet reconstruction

•  π0/ϒ discrimination in heavy-ion experiment •  STAR barrel electromagnetic calorimeter

(BEMC) and shower maximum detector (BSMD)

•  Transverse shower profile (TSP) method

�� 2 [3⇡

4,5⇡

4]

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Semi-­‐inclusive  γ+jet  and  π0+jet    

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Purity of γdir : p+p ~40% Au+Au (0-10%) ~70%

•  PYTHIA predicts larger jet yield for π0 trigger than γdir (π0 carries ~85% energy of near side parton, STAR:PLB  760  (2016)  689)

•  In p+p, reasonable agreement with standalone PYTHIA considering purity of γdir

 p+p  

[STAR:PLB  760  (2016)  689]    

Raw Jet pT without background and detector effect correction

π0 +jet vs. γ+jet  

STAR  preliminary  

N.  Sahoo[QM2017  talk]  

[GeV/c]chT,jet

p5 10 15 20 25 30

+Jet

γ+J

et0 π

1−10

1

10

]dir

γ/0πPYTHIA[, Au+Au purity 70%]

richγ/0πPYTHIA[

, p+p purity 40%]rich

γ/0πPYTHIA[

[At particle level]

p+p  

Au+Au  

(Ongoing  analysis)  

PYTHIA  expectaLon(for  different  purity  of  γdir)  

Nihar  Sahoo,  RHIC&AGS  Users'  meeDng  2017  

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π0 +jet vs. γ+jet  

•  Medium effect ? (Color factor and/or path length effect) •  To extract medium effect for π0 +jet vs. γ+jet, need full corrections,

detailed study and large statistics

Au+Au  

[GeV/c]chT,jet

p5 10 15 20 25 30

+Jet

γ+J

et0 π

1−10

1

10

]dir

γ/0πPYTHIA[, Au+Au purity 70%]

richγ/0πPYTHIA[

, p+p purity 40%]rich

γ/0πPYTHIA[

[At particle level]

STAR  preliminary  

(Ongoing  analysis)  

N.  Sahoo[QM2017  talk]  

 p+p  Reference    

Raw Jet pT without background and detector effect correction

Purity of γdir : p+p ~40% Au+Au (0-10%) ~70%

PYTHIA  expectaLon(for  different  purity  of  γdir)  

[STAR:PLB  760  (2016)  689]    

Nihar  Sahoo,  RHIC&AGS  Users'  meeDng  2017  

p+p  

Au+Au  

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• Di-jet •  AJ measurements [accepted in PRL, arXiv:1609.03878]

•  Di-jet+hadron correlation [preliminary results:QM2017]

•  Di-jet zg (Groomed Momentum Sharing zg)

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R = 0.4

•  Stronger di-jet Imbalance in AuAu for pTCut > 2 GeV for hard core selection

•  But pp balance recovered for pTCut > 0.2 GeV for R=0.4 (Not for R=0.2!)

Di-jet imbalance

Charged + neutral constituents “Hard Core:” High Tower (HT) trigger ET>5.4 GeV pTCut = 2 GeV/c

How  do  we  understand  the  redistribuDon  of  energy  within  each  jets  ?  

20/06/17   Nihar  Sahoo,  RHIC&AGS  Users'  meeDng  2017   16  

Accepted by PRL arXiv:1609.03878

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φ∆0.8− 0.6− 0.4− 0.2− 0 0.2 0.4 0.6 0.8

φ∆

dN/d

Dije

ts1/

N

1−

0

1

2

3

4

5AuAu HT 0-20%p+p HTtracking unc. Au+Autracking unc. p+pJES unc.

< 2.0assocT

1.0 < p|<0.45η∆|

recoil jet

STAR Preliminary

φ∆0.8− 0.6− 0.4− 0.2− 0 0.2 0.4 0.6 0.8

φ∆

dN/d

Dije

ts1/

N

1−

0

1

2

3

4

5AuAu HT 0-20%p+p HTtracking unc. Au+Autracking unc. p+pJES unc.

< 2.0assocT

1.0 < p|<0.45η∆|

trigger jet

STAR Preliminary

Trigger  jet  

Recoil  jet  

Trigger  jet  

Recoil  jet  

Updated Hard Core selection: pTCut = 2 GeV/c and Jet pTLead>20 GeV/c Jet pTSubLead>10 GeV/c Trigger Jet contains HT with ET>6 GeV

20/06/17   Nihar  Sahoo,  RHIC&AGS  Users'  meeDng  2017   17  

Dijet+hadron correlation  

Similar  observaDon  in  Δη  correlaDon.  

Δφ  =  φtrig  –  φhadron     Δφ  =  φrecoil  –  φhadron    Nick  Elsey  QM2017  poster  

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•  Trigger jet +hadron: no significant difference (Surface biased) •  Recoil jet +hadron: hints of excess yields at low hadron pT < 2 GeV/c •  Expecting excess yields in Au+Au than p+p, but hints of balanced dijets

( because no AJ cut is used)

20/06/17   Nihar  Sahoo,  RHIC&AGS  Users'  meeDng  2017   18  

Updated Hard Core selection: pTCut = 2 GeV/c and Jet pTLead>20 GeV/c Jet pTSubLead>10 GeV/c Trigger Jet contains HT with ET>6 GeV

Jet yields in Au+Au and p+p collisions Trigger  jet  

Recoil  jet  

Trigger  jet  

Recoil  jet  

N.  Sahoo  [QM2017  talk]  Nick  Elsey  QM2017  poster  

Associated  hadron    pT  

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20/06/17   Nihar  Sahoo,  RHIC&AGS  Users'  meeDng  2017   19  

Jet grooming Removes  so]  divergences  and  uncorrelated  backgrounds  in  a  jet      

Marta  Verweij    QM2017  talk  

Shared momentum fraction (zg)

No flavor and (weak) jet pT dependence

Soft drop condition z > zcut θβ  

Momentum fraction carried by the subleading branch

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Di-jet zg in Au+Au and p+p

•  No significant splitting modification on near- or away-side (with hard-core jet selection but AJ is modified!)

•  Contrast to LHC (Note:No dijet selection)

gz0.1 0.2 0.3 0.4 0.5 0.6

Au+

Au

/ p+p

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2 = 10-20 GeV/cRecoil

TRecoil Jet, p

Au+Au MB⊕Au+Au HT / p+p HT

STAR Preliminary

gz0.1 0.2 0.3 0.4 0.5 0.6

Au+

Au

/ p+p

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2 = 20-30 GeV/cTrig

TTrigger Jet, p

Au+Au MB⊕Au+Au HT / p+p HT

STAR Preliminary

Trigger   Recoil  

20  

K.  Kauder[QM2017  talk]  

20/06/17   Nihar  Sahoo,  RHIC&AGS  Users'  meeDng  2017  

CMS  preliminary  

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20/06/17   Nihar  Sahoo,  RHIC&AGS  Users'  meeDng  2017   21  

What we learned so far ?

•  Jet-like correlation (γ+hadron and π0+hadron) •  Precision measurements to understand color factor and path

length effect •  CoLBT-Hydro: jet-induced medium excitation and soft particle

emission at large opening angle •  Extracting of medium induced pT broadening

•  Semi-inclusive recoil charged jet (h±+jet /γ+jet ) •  Energy transported to larger jet cone R due to interaction of jet

with the medium •  Lesser medium-induced energy transport to large angles at RHIC

than LHC (Lower RHIC energy, i.e. 62.4 GeV, may give more info) •  π0+jet vs. γ+jet: hints of medium effect ? Ongoing work…

•  Di-jet •  “Lost” energy contained within R=0.4 •  Splitting via zg not modified Stay  tuned….  

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20/06/17   Nihar  Sahoo,  RHIC&AGS  Users'  meeDng  2017   22  

Back  Up  

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23  Nihar  Sahoo,  RHIC&AGS  Users'  meeDng  2017  20/06/17  

Au+Au    p+p  Raw Jet pT without background and detector effect correction

π0 +jet vs. γ+jet