alice results on light flavour hadron production in p-pb...
TRANSCRIPT
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
ALICE | Rencontres de Moriond | 28.03.2014 | Philipp Lüttig 3
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)
ALICE | Rencontres de Moriond | 28.03.2014 | Philipp Lüttig 4
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
ALICE | Rencontres de Moriond | 28.03.2014 | Philipp Lüttig 5
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
ALICE | Rencontres de Moriond | 28.03.2014 | Philipp Lüttig 6
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
ALICE | Rencontres de Moriond | 28.03.2014 | Philipp Lüttig 7
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,
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
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
ALICE | Rencontres de Moriond | 28.03.2014 | Philipp Lüttig 8
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,
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
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
ALICE | Rencontres de Moriond | 28.03.2014 | Philipp Lüttig 9
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,
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
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
ALICE | Rencontres de Moriond | 28.03.2014 | Philipp Lüttig 10
| < 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
ALICE | Rencontres de Moriond | 28.03.2014 | Philipp Lüttig 11
)c (GeV/T
p
)-!
+
+!
) / (
p(p
+
0
0.2
0.4
0.6
0.8
1
0 1 2 3
0-5%
60-80%
= 5.02 TeVNNsALICE, p-Pb,
V0A Multiplicity Classes (Pb-side)
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%
= 5.02 TeVNNsALICE, p-Pb,
V0A Multiplicity Classes (Pb-side)
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
ALICE | Rencontres de Moriond | 28.03.2014 | Philipp Lüttig 12
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
ALICE | Rencontres de Moriond | 28.03.2014 | Philipp Lüttig 13
)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-
• 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, stronger
than for pions
ALICE | Rencontres de Moriond | 28.03.2014 | Philipp Lüttig 14
)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 < 2.8 GeV/
Tp<0.5 for
cmsy0<
c > 2.8 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)
- + K+K
ALI!PREL!60966
Transverse Momentum Spectra Identified Particles – p + p
• 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, even
stronger than for K
ALICE | Rencontres de Moriond | 28.03.2014 | Philipp Lüttig 15
)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 < 3.0 GeV/
Tp<0.5 for
cmsy0<
c > 3.0 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)
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)
ALICE | Rencontres de Moriond | 28.03.2014 | Philipp Lüttig 16
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
ALICE | Rencontres de Moriond | 28.03.2014 | Philipp Lüttig 17
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
ALICE | Rencontres de Moriond | 28.03.2014 | Philipp Lüttig 18
)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
ALICE | Rencontres de Moriond | 28.03.2014 | Philipp Lüttig 19
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