Study on associated low pT hadronproduction with di-jet in Pb-Pb collisions at√sNN = 2.76 TeV in LHC-ALICE
Taiyo Kobayashi
High Energy Nuclear Physics Groupat University of Tsukuba(for the ALICE collaboration)

2013年9月20日金曜日

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Low PT particle production with di-jets

Lost energy of jets: distributed to the large angle of the away-side of the jet and it produces
low momentum particles at large angle (CMS).

Advantage of ALICE: one can measure low pT particles down to 150 MeV/c (w/ PID), together with jets.
→ Detailed study of medium response by quenched jets.
Disadvantage of ALICE: limited statistics of high energy di-jet sample in Pb-Pb.
(need to wait Run-2)

2013年9月20日金曜日

2Data set
• Event Selection:- PbPb, 2.76TeV, 13.6 M MB events, |Vz| < 10 [cm]• Track Selection:- TPC+ITS (Hybrid track cut), |η|< 0.9• Jet Reconstruction:- Charged jet only
- Used FASTJET package.
- Jet cone radius(R) = 0.2.
- pT min > 0.15 GeV/c.
• Centrality classes:- Used V0 detector• Central: 0-10 [%]• Semi central: 20-40 [%]• Peripheral: 60-90 [%]2013年9月20日金曜日

Centrality (%)

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Jet background in Pb-Pb★ Used event-by-event jet BG subtraction method for ρ calculations

jet cone areaρ (GeV/c)

ρ (GeV/c)# of TPC tracks

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Centrality (%)
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BG subtracted jet pT spectrapT jet (= pT jet, raw - ρA ) [GeV]2013年9月20日金曜日

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Leading jet,sub-leading jet∆φ = φpjet1 − φpjet2TT

pT jet1 = leading jet pT
pT jet2 = sub-leading jet pTleading
sub-leading

0-10%

pT jet1 > 30 GeV
pT jet2 > 0 GeV

pT jet1 > 40 GeV
pT jet2 > 20 GeV

dφdφ

pT jet (= pT jet, raw - ρA ) [GeV]The lower jet pT selection has Many Back ground.
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6Hadron distribution (w.r.t. jet axis)
pT jet1 > 30 GeV
pT jet2 > 10 GeV

jet1
jet2
pT − pT
Aj = jet1
pT + pjet2
TNo cut on Aj
Centrality dep.

Central 0-10%
Aj dep.

0-10 %
20-40 %
60-90 %

0.0 < Aj < 0.2
0.2 < Aj < 0.4
0.4 < Aj < 0.6
0.6 < Aj < 0.8pTtrack > 0.15 (GeV/c)

In-Jet, subleading•If we can select many higher jet pT
dφ = φjet1 - φh
2013年9月20日金曜日(jet pT > 40,50...)event in ALICE, wewill under stand lost energy of jets.

pT track (GeV/c)7

Summary and outlook• Studied low pT hadron production with di-jet in Pb-Pb collisions.
• Seen a effect of the background of di-jet Δφ distribution.
-The lower jet pT selection has many background.
• Low pT hadron production with di-jets:• I will use event cuts by (1) jet axis, (2) Aj, I think.
- The jet pT > 30 GeV sample used in the first, But these sample may
contain a large fraction of back ground.
➡So It is necessary for us to use higher jet pT sample.

[ Outlook ]• Comparison with other pT jet1 threshold. I have to check “fake jets”(BG) completely removed.
• Comparison with MC data, p-p data.
• Study of particle composition of “In-jet, sub-leading side”.
• Need Run-2 data for better statistics.

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Backup slides

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2. Data set• Event Selection:- LHC10h (PbPb, 2.76TeV), pass2, AOD file (AOD086)- Minimum bias Trigger (13.6 M MB events), |Vz| < 10 [cm]• Track Selection:- TPC+ITS (Hybrid track cut), |η|< 0.9• Jet Reconstruction:- Charged jet only
- Used FASTJET package.
- Anti-kT algorithm, R = 0.2.
- pT min > 0.15 GeV/c.
• Centrality classes:- Used V0 detector• Central: 0-10 [%]• Semi central: 20-40 [%]• Peripheral: 60-90 [%]2013年9月20日金曜日

Centrality (%)

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Run list (LHC10h)
139510,139507,139505,139503,139465,139438,139437,139360,139329,139328,139314,139310,139309,139173,139107,139105,139038,139037,139036,139029,139028,138872,138871,138870,138837,138732,138730,138666,138662,138653,
138652,138638,138624,138621,138583,138582,138579,138578,138534,138469,
138442,138439,138438,138396,138364,138275,138225,138201,138197,138192,138190,137848,137844,137752,137751,137724,137722,137718,137704,137693,137692,137691,137686,137685,137639,137638,137608,137595,137549,137546,137544,137541,137539,137531,137530,137443,137441,137440,137439,137434,137432,137431,137430,137366,137243,137236,137235,137232,137231,137230,137162,137161,137135

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11Hybrid Track Cut

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TPC acceptance2013年9月20日金曜日

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Raw charged jet pT spectra, η vs. φ for jets
0-10%

20-40%

20~40

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60-90%

60~90

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FASTJET algorithm

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BG jet pT (Divide Cone Radius)
jetjetreal PT = pT − ρ ∗ A•The result of Gaussian fit.

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