Properties of the QGP with hard probes Oliver Busch for the ALICE - - PowerPoint PPT Presentation

▶
properties of the qgp with hard probes
SMART_READER_LITE
LIVE PREVIEW

Properties of the QGP with hard probes Oliver Busch for the ALICE - - PowerPoint PPT Presentation

Sep 24, 2022 40 likes •325 views

Properties of the QGP with hard probes Oliver Busch for the ALICE collaboration 1 Oliver Busch TGSW 2016 /09/17 Outline introduction jet azimuthal anisotropy jet shapes 2 Oliver Busch TGSW 2016 /09/17 Introduction 3

slide-1
SLIDE 1

Oliver Busch – TGSW 2016 /09/17

Oliver Busch for the ALICE collaboration

Properties of the QGP with hard probes

1

slide-2
SLIDE 2

Oliver Busch – TGSW 2016 /09/17

  • introduction
  • jet azimuthal anisotropy
  • jet shapes

Outline

2

slide-3
SLIDE 3

Oliver Busch – TGSW 2016 /09/17

Introduction

3

slide-4
SLIDE 4

Oliver Busch – TGSW 2016 /09/17

Jets: seeing quarks and gluons

  • jet: collimated bunch of hadrons
  • quasi-free parton scattering at high Q2:

the best available experimental equivalent to quarks and gluons

4

slide-5
SLIDE 5

Oliver Busch – TGSW 2016 /09/17

Jet fragmentation

  • initial hard scattering: high-pT partons
  • cascade of (anti-)quarks and gluons: parton shower
  • at soft scale (O(ΛQCD)): hadronization

5

slide-6
SLIDE 6
  • in heavy-ion collisions at ultra-relativistic energies,

a quasi macroscopic fireball of hot, strongly interacting matter in local thermal equilibrium is created

  • lattice QCD predicts phase transition to deconfined,

chirally symmetric matter

  • energy density

from the lattice: rapid increase around TC, indicating increase of degrees of freedom (pion gas -> quarks and gluons)

  • TC = 154 +/- 9 MeV

εC = 340 +/- 45 MeV/fm3

QCD phase transition

HotQCD, PRD 90, 094503

slide-7
SLIDE 7

Partons in heavy-ion collisions

  • hard partons are produced early and traverse the hot and dense QGP
  • expect enhanced parton energy loss: ‘jet quenching’ (mostly) due to

medium-induced gluon radiation

  • ‘vacuum’ expectation calculable by pQCD : ‘calibrated probe of QGP’
  • jets sensitive to properties of

the medium (energy density, , mean free path, coupling ... )

  • ... but also jet-medium

interaction not trivial (strong / weak coupling, parton mass / type, fireball dynamics ...)

JET collaboration, arXiv: 1312.5003 7

slide-8
SLIDE 8

LHC aerial view

8

slide-9
SLIDE 9

Jets at ALICE (LHC run 1)

  • jet trigger with EMCal and TRD
  • ‘charged’ (tracking) jets and ‘full’ jets
  • full jets from charged particle tracking and EM energy:

conceptually different and complementary to traditional approach

  • charged particle tracking:
  • Inner Tracking System (ITS)
  • Time Projection Chamber
  • full azimuth, |η |< 0.9

pT > 150 MeV/c

  • EMCal :
  • neutral particles
  • Δφ = 107°, |η|<0.7

cluster ET > 300 MeV

9

slide-10
SLIDE 10

central peripheral

  • jet reconstruction in heavy-ion collisions :

difficult due to the high underlying event background not related to hard scattering

  • correct spectra for background fluctuations and detector effects

via unfolding

  • not possible down to lowest jet pT

jet area ~ 0.5 (R = 0.4)

Underlying event in heavy-ion collisions

slide-11
SLIDE 11

Jet nuclear modification factor

  • strong suppression observed, similar to hadron RAA

→ parton energy not recovered inside jet cone

  • increase of suppression

with centrality

  • weak pT

dependence

  • JEWEL and

YaJEM jet quenching models reproduce suppression

Phys.Lett. B746 (2015) 1 JEWEL: PLB 735 (2014) YaJEM:PRC 88 (2013) 014905

slide-12
SLIDE 12

Oliver Busch – TGSW 2016 /09/17

Jet azimuthal anisotropy

12

slide-13
SLIDE 13

Oliver Busch – TGSW 2016 /09/17

Reaction plane dependence

  • different medium thickness in- and out-of plane
  • sensitive to path length dependence of jet

quenching: pQCD radiative E-loss : ~L2

collisional E-loss : ~L

strong coupling (ADS/CFT) : ~L3

13

slide-14
SLIDE 14

Oliver Busch – TGSW 2016 /09/17

Jet v2 : results

  • quantify azimuthal asymmetry via 2nd Fourier harmonic v2ch jet
  • central collisions: 1.5 - 2 sigma from v2ch jet = 0

→ consistent with 0, but maybe hint for effect of initial density fluctuations ?

  • non-zero v2ch jet in semi-central collisions
  • Phys. Lett. B753 (2016) 511

) c (GeV/

ch jet T

p 20 30 40 50 60 70 80 90 100 |>0.9 } η ∆ {EP, |

ch jet 2

v 0.1 0.2

Syst (correlated)

ALICE (a)

= 2.76 TeV

NN

s Pb-Pb |<0.7

jet

η , |

T

k = 0.2 anti- R c > 3 GeV/

T, lead

p , c > 0.15 GeV/

T, track

p 0-5%, Stat unc.

ch jet 2

v Syst unc. (shape) Syst unc. (correlated)

) c (GeV/

ch jet T

p 20 30 40 50 60 70 80 90 100 |>0.9 } η ∆ {EP, |

ch jet 2

v 0.1 0.2

Syst (correlated)

ALICE (b)

= 2.76 TeV

NN

s Pb-Pb |<0.7

jet

η , |

T

k = 0.2 anti- R c > 3 GeV/

T, lead

p , c > 0.15 GeV/

T, track

p 30-50%, Stat unc.

ch jet 2

v Syst unc. (shape) Syst unc. (correlated)

14

slide-15
SLIDE 15

Oliver Busch – TGSW 2016 /09/17

Comparison to previous results

  • ALICE + CMS single particles, ATLAS full jets :

different energy scales !

  • non-zero v2 up to high pT

ALICE, Phys. Lett. B753 (2016) 511 ALICE, Phys. Lett. B719 (2013) 18 ) c (GeV/

jet T

p ,

part T

p 50 100 150

jet 2

v ,

part 2

v

0.1 0.2 0.3

ALICE

= 2.76 TeV

NN

s Pb-Pb |<0.7

jet

η , |

T

k = 0.2 anti- R c > 3 GeV/

T, lead

p , c > 0.15 GeV/

T, track

p 0-5%, Stat unc.

ch jet 2

v Syst unc. (shape) Syst unc. (correlated) 5-10%

calo jet 2

v ATLAS 0-10% |>3} η ∆ {|

part 2

CMS v 0-5% |>2} η ∆ {|

part 2

v ALICE

(a)

) c (GeV/

jet T

p ,

part T

p 50 100 150

jet 2

v ,

part 2

v

0.1 0.2 0.3

ALICE

= 2.76 TeV

NN

s Pb-Pb |<0.7

jet

η , |

T

k = 0.2 anti- R c > 3 GeV/

T, lead

p , c > 0.15 GeV/

T, track

p 30-50%, Stat unc.

ch jet 2

v Syst unc. (shape) Syst unc. (correlated) 30-50%

calo jet 2

v ATLAS 30-50% |>3} η ∆ {|

part 2

v CMS 30-50% |>2} η ∆ {|

part 2

v ALICE

(b)

CMS, PRL 109 (2012) 022 ATLAS, PRL 111 (2013) 152

15

slide-16
SLIDE 16

Oliver Busch – TGSW 2016 /09/17

Comparison to JEWEL

  • in semi-central collisions, good agreement with JEWEL

(collisional + ‘pQCD’ radiative energy loss)

  • clear indication of path-length dependence of energy loss
  • Phys. Lett. B753 (2016) 511

) c (GeV/

ch jet T

p 20 30 40 50 60 70 80 90 100

ch jet 2

v

0.1 0.2

0-5%, JEWEL

ch jet 2

v 0-5%, Stat unc.

ch jet 2

v Syst unc. (shape) Syst unc. (correlated)

ALICE

= 2.76 TeV

NN

s Pb-Pb |<0.7

jet

η , |

T

k = 0.2 anti- R c > 3 GeV/

lead T

p , c > 0.15 GeV/

T, track

p

(a)

) c (GeV/

ch jet T

p 20 30 40 50 60 70 80 90 100

ch jet 2

v

0.1 0.2

30-50%, JEWEL

ch jet 2

v 30-50%, Stat unc.

ch jet 2

v Syst unc. (shape) Syst unc. (correlated)

ALICE

= 2.76 TeV

NN

s Pb-Pb |<0.7

jet

η , |

T

k = 0.2 anti- R c > 3 GeV/

lead T

p , c > 0.15 GeV/

T, track

p

(b)

16

slide-17
SLIDE 17

Oliver Busch – TGSW 2016 /09/17

Jet Shapes

17

slide-18
SLIDE 18

Oliver Busch – TGSW 2016 /09/17

  • radial moment ‘girth’ g, longitudinal dispersion pTD,

difference leading - subleading pT LeSub

  • shapes in Pb-Pb as probe of

quenching of low-pT jets:

characterise fragment distributions and are sensitive to medium induced

changes of intra-jet momentum flow

  • ‘event-by-event’ measure, sensitive to fluctuations

Jet shapes

18

slide-19
SLIDE 19

Oliver Busch – TGSW 2016 /09/17

Jet shapes in Pb-Pb

19

  • fully corrected to charged particle level
  • compare to PYTHIA reference, validated with results from pp collisions

at 7 TeV

  • g shifted to smaller values indicates more collimated jet core

g

0.02 0.04 0.06 0.08 0.1 0.12

g dN/d

jets

1/N

5 10 15 20 25 30

ALICE Data Shape uncertainty Correlated uncertainty PYTHIA Perugia 11 = 2.76 TeV

NN

s Pb-Pb = 0.2 R charged jets,

T

k Anti- c < 60 GeV/

jet,ch T

p 40 <

ALICE Preliminary

ALI−PREL−101580

→

slide-20
SLIDE 20

Oliver Busch – TGSW 2016 /09/17

20

  • larger pTD in Pb-Pb compared to PYTHIA

indicates fewer constituents in quenched jets

  • LeSub in Pb-Pb in good agreement with Pb-Pb:

hardest splittings likely unaffected

D

T

p

0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

D

T

p dN/d

jets

1/N

1 2 3 4 5 6

ALICE Data Shape uncertainty Correlated uncertainty PYTHIA Perugia 11 = 2.76 TeV

NN

s Pb-Pb = 0.2 R charged jets,

T

k Anti-

ALICE Preliminary

c <60 GeV/

jet,ch T

p 40 <

ALI−PREL−101584

) c (GeV/ LeSub

5 10 15 20 25 30

/GeV) c ( LeSub dN/d

jets

1/N

0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2

ALICE Data Shape uncertainty Correlated uncertainty PYTHIA Perugia 11 = 2.76 TeV

NN

s Pb-Pb = 0.2 R charged jets,

T

k Anti-

ALICE Preliminary

c < 60 GeV/

jet,ch T

p 40 <

ALI−PREL−101588

→ →

slide-21
SLIDE 21

Oliver Busch – TGSW 2016 /09/17

  • trends reproduced by JEWEL jet quenching model:

collimation through emission of soft particles at large angles

JEWEL: K.C. Zapp, F. Kraus, U.A. Wiedemann, JHEP 1303 (2013) 080

Jet shapes: model comparison

21

slide-22
SLIDE 22

Oliver Busch – TGSW 2016 /09/17

Summary

  • hard probes allow to probe properties of the QGP
  • first insights on dynamics parton of energy loss from jet nuclear

suppression factor and jet shape measurements

  • non-zero jet v2 indicates path-length

dependence of jet quenching

  • run2: extended calorimetry

allows to assess new observables

22

slide-23
SLIDE 23

Oliver Busch – TGSW 2016 /09/17

  • Backup -

23

slide-24
SLIDE 24
  • Establish correspondence between

detector measurements / final state particles / partons

  • two types of jet finder:
  • iterative cone
  • sequential recombination

(e.g. anti-kT)

  • resolution parameter R

Jet reconstruction

hep-ph/0802.1189

24

slide-25
SLIDE 25

Oliver Busch – TGSW 2016 /09/17

QCD matter at LHC

  • direct photons:

prompt photons from hard scattering + thermal radiation from QCD matter

  • low-pT inverse slope parameter:

Teff = 297 +/- 12stat. +/- 42syst. MeV/c

  • indicates initial temperature way

above TC

arXiv 1509.07324 [nucl-ex]

25

slide-26
SLIDE 26

Oliver Busch – TGSW 2016 /09/17

  • high- pT hadrons `proxy’ for jet
  • jet quenching for charged hadrons,

Pb-Pb collisions at √sNN = 2.76 TeV

  • hadron observables biased towards

leading fragment → study the effect for fully reconstructed jets

PLB 720 (2013) 250

Hadrons in heavy-ion collisions

26

slide-27
SLIDE 27

Oliver Busch – TGSW 2016 /09/17

Analysis details

  • charged jets, R = 0.2
  • account for flow-modulation of background via

event-by-event fit and subtraction of local background density

  • unfolding to account for

background fluctuations : separately for spectra in- and out-of-plane

  • Phys. Lett. B753 (2016) 511

(rad) ϕ 1 2 3 4 5 6 ) c ) (GeV/ ϕ (

ch

ρ 50 100 150 200

= 2.76 TeV

NN

s Pb-Pb Single event | < 0.9

track

η , | c < 5 GeV/

T, track

p 0.15 < ]))

EP, 2

Ψ

  • ϕ

cos(2[

2

(1+2v ρ ]))

EP, 3

Ψ

  • ϕ

cos(3[

3

(1+2v ρ ) ϕ (

ch

ρ ρ

ALICE

27

slide-28
SLIDE 28

10 20 30 40 50 60 70 80 90 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

g uncorrected

0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16

g dN/d

jet

1/N

9 −

10

8 −

10

7 −

10

6 −

10

5 −

10

4 −

10

3 −

10

2 −

10

1 −

10 1 10

Pythia Det. Level Pythia Embedded Area. Sub (2nd order) Pythia Embedded Const. Sub Pythia Embedded Unsubtracted ALICE simulation charged jets

T

R=0.2, Anti-k c <60 GeV/

jet,ch T

40 < p

ALI-SIMUL-101958

  • charged jets from charged particle tracks, pTconst > 150 MeV/c

in pp MinB at 7 TeV and Pb-Pb 10% central at 2.76 TeV

  • R=0.2, 40 < pTjet < 60 GeV/c, no leading constituent cut
  • novel background subtraction methods (Pb-Pb)
  • area subtraction (G. Soyez et al, Phys. Rev. Lett 110 (2013) 16)
  • constituent subtraction (P. Berta et al, JHEP 1406 (2014) 092)
  • 2D unfolding to correct

for background fluctuations and detector effects

Analysis details

28