Measurement of inclusive charged jet cross sectionin pp collisions at 𝑠 = 5.02 TeV with ALICE at the LHC
Ritsuya Hosokawa for the ALICE collaboration
University of Tsukuba, University Grenoble Alpes
Physics motivation
The measurement of jet cross sections with the ALICE detector is of twofold interest. First, the study of jet
production in pp collisions provides a test for perturbative Quantum Chromo Dynamics (pQCD). Second, jets
measured in heavy-ion collisions are a well established tool to probe the Quark Gluon Plasma (QGP). We canobtain a reference for heavy ion collisions from the measurement of the pp collisions.

Analysis details

ALICE experiment

TITS•

Consists of 3 typesilicon detectors•Silicon Pixel Detector (SPD)Silicon Drift Detector (SDD)
Silicon Strip Detector (SSD)• TPC (Time projection chamber)

10− 2

pp s = 5.02 TeV, Charged jet, anti-k T, R=0.2
Detector response: PYTHIA8+GEANT3
10− 3Generator level (PYTHIA6)−410− 5

ALICE Simulation

Unfolded / MCgenerator level

10− 6

d2σ/dp dη (mb c /GeV)

10(b)1010−3T

ALICE Preliminary

pp s = 5.02 TeV
anti-k T , R=0.4

10− 5

1.4
1.2

0.80.80.6
100.6104050pjet,chT60

T> 0.15 GeV/ c20304050p(GeV/ c )ALI−PREL−113801

25jet,chσ(R=0.2)/σ(R=0.4)

pp s = 5.02 TeV

0.8

anti-k T, |η |<0.50.7ptrack,chT

T

0.50.4

ALICE

0.3

POWHEG (UE subtracted)

0.2

PYTHIA6 (Perugia-2011)

0.1

PYTHIA8 (Monash-2013)

ALI−PREL−113830

4050pjet,chT

NLO calculations.
60•••(GeV/ c )Fig.5: Charged jet cross section ratio of R=0.2 jets to R=0.4 jets

•10−3ALICE Simulation

10−4jet50

10−54010−63010−72010−81010−91035

40

4550(GeV/ c )jet,chT,MC

20

30

40

50

60

70

p80

jet,chT,det90 100

10−10(GeV/c )Fig.2: Detector response matrix of true versus
reconstructed jet pT from full detector simulation

Sources of systematic uncertainties:
••
•
•
•
•

Tracking efficiency
Tracking resolution
Secondary contribution
UE subtraction
Unfolding
Cross section normalization

Summary and prospects• The charged jet crosssections are welldescribed by POWHEG> 0.15 GeV/ c30

R=0.4, |η | < 0.5(GeV/ c )ALICE Preliminaryjet

20

Charged jets, anti-k T

10−2

ALI−PREL−113806

0.610> 5 GeV/c60

Fig.4: Charged jet cross section (a) R=0.2 (b) R=0.4

0.930[1] JHEP 0804:063,2008[2] Eur.Phys.J. C72 (2012) 1896
[3] Nucl. Instrum. Meth. A 372 (1996) 469

1.2130jet
track,ch1.4

120|η |<0.5p> 0.15 GeV/ cMC/Data

MC/Datap20

Fig. 3:MC closure test: unfolded •detector level spectrum comparedto the generator truth. Particle anddetector level spectra fromdifferent event generators(PYTHIA8 and PYTHIA6 + GEANT3)
are used.

ALICE
POWHEG (UE subtracted)
PYTHIA6 (Perugia-2011)
PYTHIA8 (Monash-2013)−2

anti-k T , R=0.2
jettrack,ch15

ALI−SIMUL−113759−110− 4|η |<0.710p

TT

d2σ/dp dη (mb c /GeV)ALICE
POWHEG (UE subtracted)
PYTHIA6 (Perugia-2011)
PYTHIA8 (Monash-2013)

pp s = 5.02 TeV

10− 5T80

ALI−SIMUL−113549

0.6

ALICE Preliminary

10− 4hard0010.8

10− 11010−1pp s = 5.02 TeVPYTHIA8 p1

1.2

5−39060

Unfolded (SVD)

10Results
10− 2Detector response matrix70

1.4(a)

100Detector level (PYTHIA6+GEANT3)

Filled with Ar-CO2 (9:1)• Acceptance
Max drift time: 92 μs
Acceptance (Full tracking): |η|<0.9 (Full tracking w/ TPC): |η|<0.9•••(GeV/c )

• ITS

T,gen

32+32 scintillators
Acceptance:
2.8<η<5.1 (V0A)−3.7<η<−1.7 (V0C)••

1/Nevents dN/dp

Fig.1: ALICE detectorjet,chwith as main goal to study the QGP. In thisstudy, the ALICE V0 detector is used to trigger
minimum bias events. The central barrel
charged particle tracking system is used todetect charged particles. The tracking system
consists of a Time Projection Chamber (TPC)and Inner Tracking System (ITS)• V0• For this study, 25.5 M minimum bias events are analyzed.
[1]• Jet reconstruction: Anti-kT algorithm implemented in the[2]
FastJet .
• Track selection: Charged track pT > 0.15 GeV/c,a uniform efficiency in 𝜂 and 𝜑.
• The measurements are corrected to the particle level.
)'*,+,• Figure 2 shows the jet response matrix of true(𝑝$,&'( ) versus)'*,+,
reconstructed(𝑝$,-'* ) jet pT from a full detector simulation,used for the Singular Value Decomposition unfolding
method[3].
• The validity of the unfolding is demonstrated by an MC
closure test shown in Figure 3. Good agreement between
the truth and unfolded spectrum is found.
p

ALICE is one of the major LHC experiments,

The cross section ratio R=0.2 / R = 0.4 is sensitive to the jetstructure and rises as function of jet pT, indicating stronger
collimation at high pT,jet. The ratio is well described byPYTHIA6, PYTHIA8 as well as POWHEG NLO calculations.

••

Charged jet cross sections for R=0.2 andR = 0.4 are presented.
The cross sections are well described by
POWHEG NLO calculations.
The charged jet cross section ratio is welldescribed by PYTHIA6, PYTHIA8 and POWHEG.
The measurements serve as a reference forPbPb collisions at the same √sNN.
The ALICE calorimeters will be included toextend the analysis to full jets.