Azimuthal#correlaons#of#neutral# pions#and#charged#jets...
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2 0 1 5 K O B E JAPAN (rad) ϕ ∆ -1 0 1 2 3 4 ) -1 (rad ϕ ∆ /d ch,jet N d trig 0 π N 1/ 0 5 10 15 ALICE Preliminary = 7 TeV s pp EMCal-triggered c > 10 GeV/ assoc T,ch,jet p (rad) ϕ ∆ -1 0 1 2 3 4 ) -1 (rad ϕ ∆ /d ch,jet N d trig 0 π N 1/ 0 2 4 6 c < 12 GeV/ trig 0 π T, p 8 < c < 20 GeV/ trig 0 π T, p 16 < c < 36 GeV/ trig 0 π T, p 24 < Systematic uncertainty c > 20 GeV/ assoc T,ch,jet p (rad) ϕ ∆ -1 0 1 2 3 4 ) -1 (rad ϕ ∆ /d ch,jet N d trig 0 π N 1/ 0 1 2 c > 30 GeV/ assoc T,ch,jet p ALI−PREL−71751 1. Select a neutral cluster with λ 0 2 > 0.3, track matching etc. (λ 0 : ellip=cal shower shape long axis) 2. Find local maxima: cells inside the clusters with higher energy than adjacent cells. Used clusters with NLM(Number of Local Maxima) <= 2. 3. Split the cluster in two new subclusters taking the two highest local maxima and aggregate all towers around them (form a 3x3 cluster). 4. Selected clusters with subclusters having an invariant mass at most 3 sigma from the π 0 mass. ALI-PERF-29549 Azimuthal correla=ons of neutral pions and charged jets in pp collisions at 7 TeV and PbPb collisions at 2.76 TeV Daisuke Watanabe for the ALICE Collabora=on Jet measurements play a cri=cal role in probing the hot and high energydensity ma^er created in heavyion collisions through parton energy loss via the observa=on of the jet structure modifica=on or jet suppression. Figure 1 shows the posi=on of hardsca^ering centers in the transverse plane generated in qPYTHIA. Assuming no inmedium energy loss per unit path length (q = 0 GeV 2 /fm), the distribu=on follows the unbiased distribu=on of hardsca^erings, whereas for large q values and high energe=c π 0 s it is strongly biased towards short jet path lengths [1]. In fact, the same effect maximizes the path length for jet recoiling from a high transverse momentum trigger hadron that mainly comes from the surface of the medium. In this poster, we report π 0 charged jet azimuthal correla=ons with high p T neutral pion triggers measured in pp collisions at √s = 7 TeV and the π 0 charged hadron correla=on results in PbPb collisions at √s NN = 2.76 TeV as the forthcoming results of π 0 jet analysis in PbPb collisions. TPC ITS EMCal The ALICE detector [3] was built to exploit the unique physics poten=al of nucleusnucleus interac=on at the LHC and is capable of studying jet quenching effects via par=cle iden=fica=on and jet reconstruc=on. This analysis used two types of detectors, the central tracking devices, the inner tracking system ITS and =me projec=on chamber TPC, for charged par=cle tracks measurement, and the electromagne=c calorimeter EMCal for π 0 measurements. The EMCal was also used as a trigger detector selec=ng events with energy deposi=ons larger than 4 and 5.5 GeV (the threshold changed during data taking). Charged par=cles measured in the TPC and ITS were used to reconstruct jets. We u=lized the an=k T algorithm [4] from the FastJet package [5]. • An=k T algorithm • Resolu=on parameter R = 0.4 • Minimum track p T > 0.15 GeV/c • Jet p T > 10 GeV/c • Jet pseudorapidity |η jet | < 0.5 • Reconstructed jet area A > 0.4 Mo=va=on ALICE experiment Jet reconstruc=on π 0 iden=fica=on method Cluster spli+ng method π 0 – charged hadron correla=on in PbPb 2.76 TeV • π 0 jet correla=ons have been measured in pp collisions at √s = 7 TeV with cluster splinng method • Two clear jet peaks are observed, indica=ng that high p T produc=on is correlated with jet produc=on • Both near and awayside widths are decreasing with increasing p T of the trigger π 0 . The decrease is stronger for the awayside correla=on width • Enhancement of nearside and suppression of awayside yields in PbPb collisions in π 0 hadron correla=on observed • The next step is to extend the π 0 hadron analysis to π 0 jet analysis and measure the trigger π 0 p T dependence of the ra=o of per trigger jet yields I AA in PbPb at √s NN = 2.76 TeV Summary [1] Thorsten Renk, arXiv:1408.6684v1[hepph], 28 Aug 2014 [2] ALICE Collabora=on, J. Allen, et al, CERNLHCC2010011, ALICETDR014ADD1 [3] ALICE Collabora=on, B. Abelev, et al, Int. J. Mod. Phys. A 29 (2014) 1430044 [4] M. Cacciari, G. P. Salam and G. Soyez et al, JHEP 0804 (2008) 063 [5] M. Cacciari, G. P. Salam and G. Soyez et al, CERNPHTH/2011297 [6] T. A. Trainor, Phys.Rev. C81 (2010) 014905 References Fig. 1 qPYTHIA simula=on of distribu=on of hardscaBering centers in the transverse plane [2]. Fig. 2 ALICE detector [3] Fig. 6 π 0 jet azimuthal correla=ons normalized by number of trigger π 0 for trigger π 0 p T regions 8 < p T,π0 trig < 12 GeV/c, 16 < p T,π0 trig < 20 GeV/c, 24 < p T,π0 trig < 36 GeV/c, and associated jet thresholds p T, ch,jet asso > 10, 20, 30 GeV/c. Fig. 7 Near and awayside Gaussian widths as a func=on of trigger p T for several charged jet p T thresholds (p T, ch,jet asso > 10, 20, 30 GeV/c ). Jet selec=on criteria Fig. 3 The reconstructed jet shape by using the an=k T algorithm [4]. Fig. 4 λ 0 2 vs E T for neutral clusters. x y π 0 charged jet azimuthal correla=ons Near and awayside width ^ ^ π 0 – jet correla=on results in pp 7 TeV ) c (GeV/ 0 π T, p 10 15 20 25 30 35 40 -1 ) c (GeV/ T p /d 0 π N d event N 1/ -5 10 -4 10 -3 10 -2 10 -1 10 spectra 0 π Uncorrected Raw +Mass cuts 2 0 λ 2 ≤ NLM = 7 TeV s pp > 4-5.5 GeV patch EMCal L0 trigger, E ALICE Preliminary ALI−PREL−71747 Fig. 5 Uncorrected π 0 distribu=on with NLM <=2 and applied analysis cuts. 1. Azimuthal correla=on: two clear jetlike peaks at near and away side of the trigger π 0 are observed in pp collisions. 2. Yields of jetlike peaks increase with increasing π 0 p T . 3. The near and awayside Gaussian widths decrease moderately with increasing π 0 p T . ) c (GeV/ trig 0 π T, p 10 15 20 25 30 35 (rad) near σ 0 0.05 0.1 0.15 0.2 = 7 TeV s pp EMCal-triggered Near side ALICE Preliminary ) c (GeV/ trig 0 π T, p 10 15 20 25 30 35 (rad) away σ 0 0.2 0.4 0.6 Away side c > 10 GeV/ assoc T,ch,jet p c > 20 GeV/ assoc T,ch,jet p c > 30 GeV/ assoc T,ch,jet p Systematic uncertainty ALI−PREL−71755 (GeV/c) T p 3 4 5 6 7 8 9 10 ) c -1 (GeV T p /d assoc dN trig 1/N -2 10 -1 10 1 =2.76 TeV NN s Pb-Pb 0-10% c < 16.0 GeV/ trig T p 8.0 < | < 0.7 ϕ ∆ Near side (NS) | | < 0.7 π - ϕ ∆ Away side (AS) | NS: Flat Background AS: Flat Background NS: Flow Background AS: Flow Background ALICE Preliminary ALI−PREL−79322 (GeV/c) T p 3 4 5 6 7 8 9 10 AA I 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 =2.76 TeV NN s Pb-Pb 0-10% c < 16.0 GeV/ trig T p 8.0 < | < 0.7 ϕ ∆ Near side | Flat Background ± -h 0 π Flat Background ± -h ± h Flow Background ± -h 0 π Flow Background ± -h ± h Black points: PRL 108, 092301 (2012) ALICE Preliminary ALI−PREL−79136 (GeV/c) T p 3 4 5 6 7 8 9 10 AA I 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 =2.76 TeV NN s Pb-Pb 0-10% c < 16.0 GeV/ trig T p 8.0 < | < 0.7 π - ϕ ∆ Away side | Flat Background ± -h 0 π Flat Background ± -h ± h Flow Background ± -h 0 π Flow Background ± -h ± h Black points: PRL 108, 092301 (2012) ALICE Preliminary ALI−PREL−79167 • Flat background subtrac=on: ZYAM method [6] • Flow background subtrac=on: C(Δϕ): per trigger normalized measured azimuthal correla=on func=on. J(Δϕ) : per trigger normalized jetlike correla=on aver ellip=c flow background subtrac=on. b 0 : background scale factor obtained from the ZYAM method [6]. Fig. 8 Near and awayside per trigger yields of charged hadrons for π 0 triggers with 8 < p T,π0 trig < 16 GeV/c. Fig. 9 Near and awayside ra=o of per trigger yields of charged hadrons (I AA ) for π 0 triggers with 8 < p T,π0 trig < 16 GeV/c. I AA ( p p 0 T , p h ± T )= Y PbPb ( p p 0 T , p h ± T ) Y pp ( p p 0 T , p h ± T ) J (Dj )= C(Dj ) - b 0 (1 + 2hu trig 2 u assoc 2 i cos(2Dj )) The Ra=o of per trigger yields I AA is defined as • Small enhancement of nearside and suppression of awayside yields observed in π 0 hadron analysis.
Transcript of Azimuthal#correlaons#of#neutral# pions#and#charged#jets...
Quark Matter 2015 Official Logo
Created by Masakiyo Kitazawa, Oct. 2014
2 0 1 5 K O B E J A P A N
2015 KOBE JAPAN
2 0 1 5 K O B E J A P A N
(rad)ϕ∆-1 0 1 2 3 4
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N d
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= 7 TeVspp EMCal-triggered
c > 10 GeV/assocT,ch,jetp
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c > 20 GeV/assocT,ch,jetp
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ϕ∆
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N d
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N1/
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c > 30 GeV/assocT,ch,jetp
ALI−PREL−71751
1. Select a neutral cluster with λ02 > 0.3, track matching etc. (λ0: ellip=cal shower shape long axis) 2. Find local maxima: cells inside the clusters with higher energy than adjacent cells. Used clusters with NLM(Number of Local Maxima) <= 2. 3. Split the cluster in two new sub-‐clusters taking the two highest local maxima and aggregate all towers around them (form a 3x3 cluster). 4. Selected clusters with sub-‐clusters having an invariant mass at most 3 sigma from the π0 mass.
ALI-PERF-29549
Figure 1: A sample parton-level event (generated with Herwig [8]), together with many random soft“ghosts”, clustered with four different jets algorithms, illustrating the “active” catchment areas ofthe resulting hard jets. For kt and Cam/Aachen the detailed shapes are in part determined by thespecific set of ghosts used, and change when the ghosts are modified.
the jets roughly midway between them. Anti-kt instead generates a circular hard jet, which clips alens-shaped region out of the soft one, leaving behind a crescent.
The above properties of the anti-kt algorithm translate into concrete results for various quanti-tative properties of jets, as we outline below.
2.2 Area-related properties
The most concrete context in which to quantitatively discuss the properties of jet boundaries fordifferent algorithms is in the calculation of jet areas.
Two definitions were given for jet areas in [4]: the passive area (a) which measures a jet’ssusceptibility to point-like radiation, and the active area (A) which measures its susceptibility todiffuse radiation. The simplest place to observe the impact of soft resilience is in the passive area fora jet consisting of a hard particle p1 and a soft one p2, separated by a y − φ distance ∆12. In usualIRC safe jet algorithms (JA), the passive area aJA,R(∆12) is πR2 when ∆12 = 0, but changes when∆12 is increased. In contrast, since the boundaries of anti-kt jets are unaffected by soft radiation,
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Azimuthal correla=ons of neutral pions and charged jets in pp collisions at 7 TeV and Pb-‐Pb collisions at 2.76 TeV
Daisuke Watanabe for the ALICE Collabora=on
Jet measurements play a cri=cal role in probing the hot and high energy-‐density ma^er created in heavy-‐ion collisions through parton energy loss via the observa=on of the jet structure modifica=on or jet suppression. Figure 1 shows the posi=on of hard-‐sca^ering centers in the transverse plane generated in qPYTHIA. Assuming no in-‐medium energy loss per unit path length (q = 0 GeV2/fm), the distribu=on follows the unbiased distribu=on of hard-‐sca^erings, whereas for large q values and high energe=c π0s it is strongly biased towards short jet path lengths [1]. In fact, the same effect maximizes the path length for jet recoiling from a high transverse momentum trigger hadron that mainly comes from the surface of the medium. In this poster, we report π0-‐ charged jet azimuthal correla=ons with high pT neutral pion triggers measured in pp collisions at √s = 7 TeV and the π0-‐ charged hadron correla=on results in Pb-‐Pb collisions at √sNN = 2.76 TeV as the forthcoming results of π0-‐ jet analysis in Pb-‐Pb collisions.
TPC
ITS
EMCal The ALICE detector [3] was built to exploit the unique physics poten=al of nucleus-‐nucleus interac=on at the LHC and is capable of studying jet quenching effects via par=cle iden=fica=on and jet reconstruc=on. This analysis used two types of detectors, the central tracking devices, the inner tracking system ITS and =me projec=on chamber TPC, for charged par=cle tracks measurement, and the electromagne=c calorimeter EMCal for π0 measurements. The EMCal was also used as a trigger detector selec=ng events with energy deposi=ons larger than 4 and 5.5 GeV (the threshold changed during data taking).
Charged par=cles measured in the TPC and ITS were used to reconstruct jets. We u=lized the an=-‐kT algorithm [4] from the FastJet package [5].
• An=-‐kT algorithm • Resolu=on parameter R = 0.4 • Minimum track pT > 0.15 GeV/c • Jet pT > 10 GeV/c • Jet pseudorapidity |ηjet| < 0.5 • Reconstructed jet area A > 0.4
Mo=va=on
ALICE experiment Jet reconstruc=on
π0 iden=fica=on method Cluster spli+ng method
π0 – charged hadron correla=on in Pb-‐Pb 2.76 TeV
• π0-‐ jet correla=ons have been measured in pp collisions at √s = 7 TeV with cluster splinng method • Two clear jet peaks are observed, indica=ng that high pT produc=on is correlated with jet produc=on • Both near and away-‐side widths are decreasing with increasing pT of the trigger π0. The decrease is stronger for the away-‐side correla=on width
• Enhancement of near-‐side and suppression of away-‐side yields in Pb-‐Pb collisions in π0-‐ hadron correla=on observed
• The next step is to extend the π0-‐hadron analysis to π0-‐ jet analysis and measure the trigger π0 pT dependence of the ra=o of per trigger jet yields IAA in Pb-‐Pb at √sNN = 2.76 TeV
Summary
[1] Thorsten Renk, arXiv:1408.6684v1[hep-‐ph], 28 Aug 2014 [2] ALICE Collabora=on, J. Allen, et al, CERN-‐LHCC-‐2010-‐011, ALICE-‐TDR-‐014-‐ADD-‐1 [3] ALICE Collabora=on, B. Abelev, et al, Int. J. Mod. Phys. A 29 (2014) 1430044 [4] M. Cacciari, G. P. Salam and G. Soyez et al, JHEP 0804 (2008) 063 [5] M. Cacciari, G. P. Salam and G. Soyez et al, CERN-‐PH-‐TH/2011-‐297 [6] T. A. Trainor, Phys.Rev. C81 (2010) 014905
References
Fig. 1 qPYTHIA simula=on of distribu=on of hard-‐scaBering centers in the transverse plane [2].
Fig. 2 ALICE detector [3]
Fig. 6 π0-‐ jet azimuthal correla=ons normalized by number of trigger π0 for trigger π0 pT regions 8 < pT,π0trig < 12 GeV/c, 16 < pT,π0trig < 20 GeV/c, 24 < pT,π0trig < 36 GeV/c, and associated jet thresholds pT, ch,jetasso > 10, 20, 30 GeV/c.
Fig. 7 Near and away-‐side Gaussian widths as a func=on of trigger pT for several charged jet pT thresholds (pT, ch,jetasso > 10, 20, 30 GeV/c ).
Jet selec=on criteria
Fig. 3 The reconstructed jet shape by using the an=-‐kT algorithm [4].
Fig. 4 λ02 vs ET for neutral clusters.
x
y
π0-‐ charged jet azimuthal correla=ons
Near and away-‐side width
^ ^
π0 – jet correla=on results in pp 7 TeV
)c (GeV/0πT, p
10 15 20 25 30 35 40
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spectra0πUncorrected Raw +Mass cuts2
0λ
2≤NLM
= 7 TeVspp > 4-5.5 GeV
patchEMCal L0 trigger, E
ALICE Preliminary
ALI−PREL−71747
Fig. 5 Uncorrected π0 distribu=on with NLM <=2 and applied analysis cuts.
1. Azimuthal correla=on: two clear jet-‐like peaks at near and away side of the trigger π0 are observed in pp collisions. 2. Yields of jet-‐like peaks increase with increasing π0 pT. 3. The near and away-‐side Gaussian widths decrease moderately with increasing π0 pT. )c (GeV/trig
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• Flat background subtrac=on: ZYAM method [6] • Flow background subtrac=on:
-‐ C(Δϕ): per trigger normalized measured azimuthal correla=on func=on. -‐ J(Δϕ) : per trigger normalized jet-‐like correla=on aver ellip=c flow background subtrac=on. -‐ b0 : background scale factor obtained from the ZYAM method [6]. Fig. 8 Near and away-‐side per trigger yields of charged
hadrons for π0 triggers with 8 < pT,π0trig < 16 GeV/c.
Fig. 9 Near and away-‐side ra=o of per trigger yields of charged hadrons (IAA) for π0 triggers with 8 < pT,π0trig < 16 GeV/c.
52 ALICE Analysis Note 2013
(GeV/c)T
p3 4 5 6 7 8 9 10
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(G
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ig1
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Fig. 59: Per-trigger yield of charged hadrons distributions subtracted flat background on near side |Dj|< 0.7 (left),away side |Dj �p|< 0.7 (right) in trigger pT at 8.0 < ptrig
T < 16.0 GeV/c in Pb-Pb 0-10% atp
sNN = 2.76 TeV.The blue boxes are the total systematic uncertainty.
Flow background:665
Taking into account the background of flow, the per-trigger yield of charged hadrons on near side, away666
side in in Pb-Pb collisions 0-10% centrality atp
sNN = 2.76 TeV are obtained, shown in Fig. 60.
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c)-1
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Fig. 60: Per-trigger yield of charged hadrons distributions subtracted flow background on near side |Dj| < 0.7(left), away side |Dj �p|< 0.7 (right) in trigger pT at 8.0 < ptrig
T < 16.0 GeV/c in Pb-Pb 0-10% atp
sNN = 2.76TeV. The blue boxes are the total systematic uncertainty.
667
Fig. 61 shows the same results of the per-trigger yield of charged hadrons on near side, away side in in668
Pb-Pb collisions 0-10% centrality atp
sNN = 2.76 TeV as Fig. 59 and Fig. 60, but in one figure.669
8.3 Yield modification factor670
In this section, the yield modification factors, IAA and ICP, are calculated. The factors can be written as671
IAA(pp0
T , ph±T ) =
Y PbPb(pp0
T , ph±T )
Y pp(pp0T , ph±
T ); (26)
22 ALICE Analysis Note 2013
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Fig. 18: The systematic uncertainty from the three pedestal subtractions of the yield on Near side |Dj| < 0.7(left), Away side |Dj �p| < 0.7 (right) in Pb-Pb 0-10% at
psNN = 2.76 TeV, respectively. The blue boxed is the
systematic uncertainty.
to fit the distribution in the pT range. The fit error is considered to estimate the systematic uncertainty431
at 8.0 < pT < 16.0 GeV/c. The fit result is 0.0347±0.0043, which gives the systematic uncertainty of432
⇠ 12.4%. To the charged hadron flow, it has ⇠ 2% systematic uncertainty at pT > 6.0 GeV/c. Finally,
GeV/c0 2 4 6 8 10 12 14
2υ
) -π
++
π(
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h+
(h
0
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sPb-Pb
0-10%
Fig. 19: u2 flow of charged pions (left) and charged hadrons (right) in Pb-Pb 0-10% atp
sNN = 2.76 TeV. In theleft, the blue line is the fit value at 8.0 < pT < 16.0 GeV/c with0.0347±0.0043. The fit error is used to estimatethe systematic uncertainty of flow.
433
the jet-like correlations is obtained by434
J(Dj) =C(Dj)�b0(1+2hu trig2 uassoc
2 icos(2Dj)) (13)
where J(Dj) and C(Dj) are the jet-like correlations and all correlations obtained by Eq. 10, respectively;435
u trig2 and uassoc
2 are the elliptic flow coefficients of trigger particles and associated particles, respectively;436
b0 is the background scaled factor, which is generally determined by a pedestal subtraction employing437
the zero-yield-at-minimum (ZYAM) method shown in Sec. 5.4.2.438
The Ra=o of per trigger yields IAA is defined as
• Small enhancement of near-‐side and suppression of away-‐side yields observed in π0-‐hadron analysis.
