alice results on light flavour hadron production in p-pb...

ALICE results on light flavour hadron production in p-Pb collisions at the LHC

Philipp Lüttig for the ALICE collaboration

Rencontres de Moriond March 2014

Motivation

•  differentiate between initial and final state effects •  challenge at LHC: dNch/dη in p-Pb comparable to semi-peripheral Au-Au

at RHIC Ø  final state dense matter effects cannot be neglected

•  extend probed part of nuclear wave function to very low x and high gluon

densities Ø  saturation, parton shadowing

•  probe different momentum transfer regions by selecting different particle masses

ALICE | Rencontres de Moriond | 28.03.2014 | Philipp Lüttig 2

The ALICE Experiment


Tracking: ITS + TPC PID: TPC/TOF Multiplicity: VZERO

VZERO

Inner Tracking

System (ITS)

Time Projection Chamber (TPC)

pT > 0.15 GeV/c |η| < 0.8

Time-of-Flight (TOF)


Spectra at low pT

Average Transverse Momentum of inclusive charged particles

•  clear difference between collision

systems

•  pp: difference in beam energy

small wrt. p-Pb

•  multiplicity dependence in p-Pb: –  Nch < 15: similar to pp –  Nch > 15: shape similar to Pb-Pb –  potential superposition of pp and

Pb-Pb


chN

0 20 40 60 80 100

)c

(G

eV

/!

Tp"

0.45

0.5

0.55

0.6

0.65

0.7

0.75

0.8

0.85

0.9 ALICE, charged particlesc<10.0 GeV/

Tp|<0.3, 0.15< #|

= 7 TeVspp

= 5.02 TeVNN

sp-Pb

= 2.76 TeVNN

sPb-Pb

ALI!DER!55987

Phys.Lett. B

727 (2013) 371-380

Average Transverse Momentum Model Comparison

•  pp: –  color reconnection needed to

describe data

•  p-Pb: –  EPOS fits data best –  Glauber MC (superposition of pp

collisions) underpredicts data

•  Pb-Pb: –  models cannot describe data –  most models reproduce shape,

but magnitude is underestimated


0 20 40 60 80 100

)c

(G

eV

/!

Tp"

0.5

0.6

0.7

0.8

0.9

1

Data

PYTHIA 8, tune 4C

without CR

with CR

ALICE,charged particles

c<10.0 GeV/T

p|<0.3, 0.15<#|

= 7 TeVspp

0 20 40 60 80 100

)c

(G

eV

/!

Tp"

0.45

0.5

0.55

0.6

0.65

0.7

0.75

0.8

0.85

Data

DPMJET

HIJING

AMPT

EPOS

Glauber MC

= 5.02 TeVNNsp-Pb

chN

0 20 40 60 80 100

)c

(G

eV

/!

Tp"

0.45

0.5

0.55

0.6

0.65

0.7

= 2.76 TeVNNsPb-Pb

Data

ALI!PUB!55948

Phys.Lett. B

727 (2013) 371-380

)2c) (GeV/-

!,+!M(

0.45 0.46 0.47 0.48 0.49 0.5 0.51 0.52 0.53 0.54 0.55

24/09/2012

= 5.02 TeVsp-Pb,

candidatesS0K

| < 0.5lab

|y

ALI!PERF!42699

Particle Identification

•  identify π, K, p via specific

energy loss in the TPC

and velocity in TOF

•  strange hadrons via

secondary decay vertex


0 2 4 6 8 10

]-2 )

c)

[(G

eV

/yd

Tp

/(d

N2

dT

p!

1/2

ev

N1/ -810

-710

-610

-510

-410

-310

-210

-110

1

10

210

310

410

(100x)-! + +!

(10x)- + K+K

(1x)pp +

(0.1x)0SK

(0.01x)" + "

= 5.02 TeVNN

sALICE, p-Pb,

V0A Multiplicity Class (Pb-side)5-10%

Blast-Wave

EPOS LHC

Krakow

DPMJET

< 0.5CMS

0 < y

)c (GeV/T

p

0 2 4 6 8 10

da

ta /

mo

de

l

0 2 4 6 8 10

0.51

1.5 -! + +!

0 2 4 6 8 10

0.51

1.5 - + K

+K

0 2 4 6 8 10

0.51

1.5 pp +

0 2 4 6 8 10

0.51

1.5 0SK

0 2 4 6 8 10

0.51

1.5" + "

ALI!PUB!58145

Transverse Momentum Spectra

0 2 4 6 8 10

]-2 )

c)

[(G

eV

/yd

Tp

/(d

N2

dT

p!

1/2

ev

N1

/ -810

-710

-610

-510

-410

-310

-210

-110

1

10

210

310

410

(100x)-! + +!

(10x)- + K+K

(1x)pp +

(0.1x)0SK

(0.01x)" + "

= 5.02 TeVNN

sALICE, p-Pb,


Blast-Wave

EPOS LHC

Krakow

DPMJET

< 0.5CMS

0 < y

)c (GeV/T

p

0 2 4 6 8 10

data

/ m

odel

0 2 4 6 8 10

0.51

1.5 -! + +!

0 2 4 6 8 10

0.51

1.5 - + K

+K

0 2 4 6 8 10

0.51

1.5 pp +

0 2 4 6 8 10

0.51

1.5 0SK

0 2 4 6 8 10

0.51

1.5" + "

ALI!PUB!58145

Identified Particles - Model Comparison

•  transverse momentum spectra

of different particles

•  comparison to models: –  Blast-Wave –  EPOS-LHC –  Krakow –  DPMJET


Phys.Lett. B

728 (2014) 25-38

0 2 4 6 8 10

]-2 )

c)

[(G

eV

/yd

Tp

/(d

N2

dT

p!

1/2

ev

N1

/ -810

-710

-610

-510

-410

-310

-210

-110

1

10

210

310

410

(100x)-! + +!

(10x)- + K+K

(1x)pp +

(0.1x)0SK

(0.01x)" + "

= 5.02 TeVNN

sALICE, p-Pb,


Blast-Wave

EPOS LHC

Krakow

DPMJET

< 0.5CMS

0 < y

)c (GeV/T

p

0 2 4 6 8 10

data

/ m

odel

0 2 4 6 8 10

0.51

1.5 -! + +!

0 2 4 6 8 10

0.51

1.5 - + K

+K

0 2 4 6 8 10

0.51

1.5 pp +

0 2 4 6 8 10

0.51

1.5 0SK

0 2 4 6 8 10

0.51

1.5" + "

ALI!PUB!58145

Transverse Momentum Spectra Identified Particles - Model Comparison

•  DPMJET as QCD-inspired

model can describe multiplicity

distribution in p-Pb (not shown),

but fails to describe pT spectra

•  Krakow: hydrodynamical model

including initial fluctuations

describes spectra for low pT

•  EPOS reproduces π and p over

measured range, but larger

deviations for K0s and Λ


Phys.Lett. B

728 (2014) 25-38

0 2 4 6 8 10

]-2 )

c)

[(G

eV

/yd

Tp

/(d

N2

dT

p!

1/2

ev

N1/ -810

-710

-610

-510

-410

-310

-210

-110

1

10

210

310

410

(100x)-! + +!

(10x)- + K+K

(1x)pp +

(0.1x)0SK

(0.01x)" + "

= 5.02 TeVNN

sALICE, p-Pb,


Blast-Wave

EPOS LHC

Krakow

DPMJET

< 0.5CMS

0 < y

)c (GeV/T

p

0 2 4 6 8 10

da

ta /

mo

de

l

0 2 4 6 8 10

0.51

1.5 -! + +!

0 2 4 6 8 10

0.51

1.5 - + K

+K

0 2 4 6 8 10

0.51

1.5 pp +

0 2 4 6 8 10

0.51

1.5 0SK

0 2 4 6 8 10

0.51

1.5" + "

ALI!PUB!58145

Average Transverse Momentum of identified charged particles

•  multiplicity in V0A as

selector for different event

classes

•  good agreement between

charged and neutral K

•  increase with multiplicity

for all particle species

•  slope stronger for higher

particle masses

•  similar mass ordering seen

for pp and Pb-Pb


| < 0.5lab

!|"

lab!/d

chNd#

10 210

)c

(G

eV

/"

Tp#

0.4

0.6

0.8

1

1.2

1.4

1.6

$ + $

pp +

0SK

- + K

+K

-% + +%

= 5.02 TeVNNsALICE, p-Pb,

V0A Multiplicity Classes (Pb-side)

< 0.5CMS

y0 <

ALI!PUB!58097

Phys.Lett. B

728 (2014) 25-38

Particle Ratios of identified particles


)c (GeV/T

p

)-!

+

+!

) / (

p(p

+

0

0.2

0.4

0.6

0.8

1

0 1 2 3

0-5%

60-80%



0 1 2 3

0-5%

80-90%

= 2.76 TeVNNsALICE, Pb-Pb,

ALI!PUB!58061

•  p/π ratio vs. pT

p-Pb: increase at intermediate pT and depletion at low pT with multiplicity Pb-Pb: similar effects as in p-Pb, but more pronounced

•  Λ/K0s ratio vs. pT

similar for p-Pb and Pb-Pb: –  increase at intermediate pT for

larger multiplicity –  depletion at low pT

)c (GeV/T

p

S0 /

K!

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

2.2

2.4

0 2 4 6 8

0-5%

60-80%



0 2 4 6 8

0-5%

80-90%

= 2.76 TeVNNsALICE, Pb-Pb,

ALI!PUB!58065

Phys.Lett. B

728 (2014) 25-38

p-Pb Pb-Pb


High pT Results

Transverse Momentum Spectra Identified Particles – π+ + π-

•  multiplicity in V0A as selector for

different event classes

•  identification at high pT based on

statistical analysis of particle

abundance in the relativistic rise in

the TPC

•  hardening of spectra with

increasing multiplicity


)c (GeV/T

p

0 2 4 6 8 10 12 14

-2)]

cd

y) [

(Ge

V/

Tp

/(d

2N

) d

Tp

! 1

/(2

ev

1/N

-1010

-910

-810

-710

-610

-510

-410

-310

-210

-110

1

10

210

310

410

= 5.02 TeVNNsp-Pb, c < 2.0 GeV/

Tp<0.5 for

cmsy0<

c > 2.0 GeV/T

p|<0.3 for cms

y|

V0A multiplicity0-5% (64x)5-10% (32x)10-20% (16x)20-40% (8x)40-60% (4x)60-80% (2x)80-100% (1x)

-! + +

!

ALI!PREL!60962

Transverse Momentum Spectra Identified Particles – K+ + K-






the TPC


increasing multiplicity, stronger

than for pions


)c (GeV/T

p

0 2 4 6 8 10 12 14

-2)]

cd

y) [

(Ge

V/

Tp

/(d

2N

) d

Tp

! 1

/(2

ev

1/N

-1010

-910

-810

-710

-610

-510

-410

-310

-210

-110

1

10

210

310

410


Tp<0.5 for

cmsy0<

c > 2.8 GeV/T

p|<0.3 for cms

y|


- + K+K

ALI!PREL!60966

Transverse Momentum Spectra Identified Particles – p + p






the TPC


increasing multiplicity, even

stronger than for K


)c (GeV/T

p

0 2 4 6 8 10 12 14

-2)]

cd

y) [

(Ge

V/

Tp

/(d

2N

) d

Tp

! 1

/(2

ev

1/N

-1010

-910

-810

-710

-610

-510

-410

-310

-210

-110

1

10

210

310

410


Tp<0.5 for

cmsy0<

c > 3.0 GeV/T

p|<0.3 for cms

y|


pp +

ALI!PREL!60970

-2)

(Ge

V/c

)T

dp

!)/

(dch

N2

) (d

T p

" 1

/(2

evt

1/N

-710

-610

-510

-410

-310

-210

-110

1

10

210

= 5.02 TeVNN

sALICE, p-Pb

| < 0.3cms

!|

4)# < 0.8 (cms

!0.3 <

16)# < 1.3 (cms

!0.8 <

| < 0.3cms

!pp reference, |

(GeV/c)T

p1 10

ratio

0.8

1

1.2

| < 0.3cms

! < 0.8 / | cms

!0.3 <

| < 0.3cms

! < 1.3 / | cms

!0.8 <

ALI!PUB!44347

Transverse Momentum Spectra of inclusive charged particles

•  based on data from 2012

(pilot run)

•  limited statistics (only up

to pT = 20 GeV/c)


Phys. R

ev. Lett.110 (2013) 082302

2

c -2

) G

eV

! d

Tp

/(d

N2

) d

Tp

"1

/(2

-910

-810

-710

-610

-510

-410

-310

-210

-110

1

10

210 =5.02 TeV, NSDNNsp-Pb,

charged particles

16)#|<0.3 (cms

!|

4)#<0.8 (cms

!-0.3<

<0.8cms

! 0.3<

|<0.8!pp reference |

)c (GeV/T

p1 10

Ra

tio

0.850.9

0.951

1.051.1

1.15|<0.3

cms!<0.8/|

cms!-0.3<

|<0.3cms

!<0.8/|cms

! 0.3<

ALI!PREL!67300

Transverse Momentum Spectra of inclusive charged particles

•  higher statistics by

including data from 2013

•  forward η added, slightly

harder spectrum

•  measurement extended to

pT = 50 GeV/c

•  reduced statistical errors

•  in ratio, correlated

uncertainties are

cancelled


NB: pp Reference Spectrum

no measurement available at

√s = 5.02 TeV:

•  pT < 5 GeV/c: interpolation of

cross section for fixed pT as

function of energy

•  pT > 5 GeV/c: scaling of measured

data at √s = 7 TeV with relative

change from NLO-pQCD

•  pT > 20 GeV/c: parametrization

with power law


)2

c -2

) (m

b G

eV

Tp

d!

)/(d

ch"

2)

(dT

p #

1/(

2

-910

-810

-710

-610

-510

-410

-310

-210

-110

1

10

210

310

ALICE, pp references

| < 0.3! = 5.02 TeV, |s > 20 GeV/c)

Tpower-law fit (p

| < 0.8! = 2.76 TeV, |s

)c (GeV/T

p

-110 1 10

ref.

/ f

it

0.60.70.80.9

11.11.21.31.4 syst. uncert. reference

= 5.02 TeVs

ALI!PUB!60534

Eur.P

hys.J. C73 (2013) 2662

Nuclear Modification Factor for p-Pb collisions

•  reference in |η| < 0.8

•  pT < 1 GeV/c:

suppression

•  1 GeV/c < pT < 3 GeV/c:

Cronin-like enhancement

•  pT > 3 GeV/c:

consistent with unity


pP

bR

0.5

0.6

0.7

0.8

0.9

1

1.1

1.2

1.3=5.02 TeV NSDNNsp-Pb

charged particles

|<0.3cms

!|

)c (GeV/T

p

0 5 10 15 20 25 30 35 40 45 50

pP

bR

0.5

0.6

0.7

0.8

0.9

1

1.1

1.2

1.3

<0.8cms

!-0.3<

ALI!PREL!67304

RpPb =d 2N pPb / dpTd!TAA d 2" pp / dpTd!

Summary

Spectra at low pT:

•  <pT> as function of multiplicity for (un)identified charged hadrons •  increase with multiplicity •  rise stronger with higher particle mass

•  Models incorporating final state effects give a better description of the data

•  clear evolution with multiplicity of pT spectra, reminiscent of Pb-Pb behaviour

(usually attributed to collective phenomena)

High pT Results:

•  pT spectra of charged pions, Kaons and protons up to pT = 15 GeV/c for different

multiplicity classes

•  pT spectra and nuclear modification factor for inclusive charged hadrons •  up to pT = 50 GeV/c •  RpPb consistent with unity at high pT

20 ALICE | Rencontres de Moriond | 28.03.2014 | Philipp Lüttig

alice results on light flavour hadron production in p-pb...

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