Proton to Pion ratio in Jet and Bulk
region in Heavy Ion collisions
Measured by the ALICE detector, sNN = 2.76TeV
Misha Veldhoen (Utrecht University)
For the ALICE collaboration
Hard Probes 2012
Cagliari, Italy
Hadronization at high and low pT
L / KS0
• In p—p collisions the dominant particle production
mechanism is fragmentation.
2.5
Pb-Pb at
2
sNN = 2.76 TeV, |y|<0.75
0-5 % centrality
20-40 % centrality
40-60 % centrality
60-80 % centrality
80-90 % centrality
(pp at s = 7 TeV)
(pp at s = 0.9 TeV)
data points include stat. errors
estimated syst. error ~10 %
Preliminary
1.5
1
0.5
0
0
1
2
3
4
5
7
6
8
p (GeV/c)
T
• In A–A collisions, for pT < 6 GeV/c, a significantly enhanced
Baryon to Meson ratio is observed.
1
Reproducing the Baryon Enhancement
103
102
10
1
10-1
10-2 0
1.5
1
0.5
0
0
2
ALICE preliminary
PbPb, 2.76 TeV
1
p+
+
K
p
X
W
VISH2+1
VISHNU
T
Hydro normalized to
data for p < 3 GeV/c
3
T
STAR: Au-Au 200 GeV ´ L/ L
4
8
p (GeV/c)
ALICE preliminary:
6
ALICE, |y|<0.75
Pb-Pb 0-5%
Pb-Pb 60-80%
pp s = 7 TeV
STAR
Au-Au 0-5%
Au-Au 60-80%
Hydro VISH2+1
Recombination
x 0.85
with 10% feed-down correction
4
Pb-Pb sNN = 2.76 TeV
stat. errors only
syst. error ~10 %
2
T
p (GeV/c)
2
Hydrodynamics
Recombination and Hydro
Thermal Recombination
arXiv:1202.3233
arXiv:1202.3233
dN/dpTdy (GeV/c)
0
L / KS
Hot matter
• Hydrodynamic models reproduce the
charged particle spectra and ratios
for pT < 2 GeV/c.
Meson
Baryon
pT = 2pT,parton pT = 3pT,parton
• One possible hadronization mechanism at
pT < 6 GeV is coalescence/recombination.
Hadronization in Jets
Ratio
• What about hadronization in Jets? Several predictions have
- ±
been made.
K±/π±
p(p)/π
• Shower-Thermal Recombination,
(enhanced B/M should be
observed in Jets) [Hwa, Yang]
Hard parton
Meson
pT=2pT,parton
Baryon
pT=3pT,parton
Hot matter
• Medium effects, MLLA+LPHD
formalism [Sapeta, Wiedemann]
also predicts enhanced B/M
ratio in Jets.
arXiv:0707.3494 pT (GeV/c)
We will present a measurement of the p/π ratio in the
3
Jet peak and Bulk region of a di-hadron correlation.
Di-Hadron Correlations
• 1.4M central (0-10%) Pb—Pb.
• Associated particles: 1.5 < pT < 4.5 GeV/c,
Trigger particles: 5.0 < pT < 10.0 GeV/c.
• |η| < 0.8.
• PID using TOF and TPC.
• Corrections
– Mixed event correction (pair acceptance).
– Efficiency (tracking and PID) as function of pT and particle species.
– No feed-down correction, Λ spectrum in jets not known.
4
Selecting Peak and Bulk Regions
• Five-dimensional histogram:
Jet = Peak – Bulk
, dE / dx- dE / dx
st
p ,K, p
Pb-Pb, sNN = 2.76TeV
0-10% central
2.0 < pT < 2.5 GeV/c, |h| < 0.8
)
Peak
Bulk I
Bulk II
Count
May 21 , 2012
Δη
Dh
• Peak- and Bulk regions can
be selected by integrating
over Δϕ and Δη.
p ,K, p
Count
(
N Dj, Dh, pT,assoc, tTOF - tTOF
1.5
28000
1
27000
26000
0.5
25000
0
24000
Bulk
0
π
Δϕ
-0.5
23000
-1
22000
21000
-1.5
-1
0
1
2
3
4
D f (rad)
Δϕ (rad)
5
Combined PID: TPC and TOF
800
600
p
400
200
K
0
102
800
600
10
0
-400
-400
-10
p
K π
200
-200
-20
102
400
π
1
0
10
20
dE/dx - <dE/dx>p (a.u.)
dE/dx – <dE/dx>π (a.u.)
-30
Pb-Pb, sNN = 2.76TeV, 0-10% central
4.0 < pT < 4.5 GeV/c, |h| < 0.8
- p/2 < Df < 3p/2, -1.5 < Dh < 1.5 Count
1400
10
1200
1000
800
102
600
400
10
3
TOF
3
1000
-200
-30
10
1200
TOF
TOF
1000
3
1400
st
May 21 , 2012
TOF
10
Count
Count
Count
1200
Pb-Pb, sNN = 2.76TeV, 0-10% central
3.5 < pT < 4.0 GeV/c, |h| < 0.8
- p/2 < Df < 3p/2, -1.5 < Dh < 1.5
TOF p
Count
1400
st
May 21 , 2012
4.0 < pT < 4.5 GeV/c
tTOF–t <t-TOF
<t >π>(ps)
p (ps)
Count
TOF
tTOFt– <t- <tTOF>>πp (ps)
(ps)
Pb-Pb, sNN = 2.76TeV, 0-10% central
3.0 < pT < 3.5 GeV/c, |h| < 0.8
- p/2 < Df < 3p/2, -1.5 < Dh < 1.5
tTOF– <t
> Count
(ps)
t TOF
- <t π > (ps)
st
May 21 , 2012
3.5 < pT < 4.0 GeV/c
p
200
K
0
10
π
-200
-20
-10
0
10
20
dE/dx - <dE/dx>p (a.u.)
1
dE/dx – <dE/dx>π (a.u.)
-400
-30
-20
-10
1
0
10
20
dE/dx - <dE/dx>p (a.u.)
dE/dx – <dE/dx>π (a.u.)
• Specific energy loss, Time Projection Chamber (TPC)
• Time Of Flight (TOF)
• Good separation between pions, kaons and protons at
intermediate pT.
6
Count
Count
3.0 < pT < 3.5 GeV/c
Combined PID: Peak Shapes
10
3
1500
104
p
1000
10
K
500
π
0
-500
-30
-20
-10
0
dE/dx
10
20
30
dE/dx - <dE/dx>p (a.u.)
– <dE/dx>π (a.u.)
10
1
3
102
K
0
π
-500
-1000
-20 -15 -10 -5
0
5 10 15 20 25 30
dE/dx - <dE/dx>K (a.u.)
dE/dx – <dE/dx>K (a.u.)
5
500
p
0
104
-500
10
K
-1500
3
102
π
-2000
10
10
-2500
1
-3000
-30
-20
-10
0
dE/dx
10
20
30
dE/dx - <dE/dx>p (a.u.)
– <dE/dx>p (a.u.)
• Expected PID signals depend on pT and η  NonGaussian peak shapes.
• Generated templates to fit non-Gaussian peaks.
7
1
Count
10
-1000
500
1000
102
5
Count
1000
TOF p
10
Count
Count
2000
st
May 21 , 2012
Pb-Pb, sNN = 2.76TeV, 0-10% central
1.5 < pT < 2.0 GeV/c, |h| < 0.8
- p/2 < Df < 3p/2, -1.5 < Dh < 1.5
TOF
TOF
p
1500
Count
TOF
10
2000
4
Pb-Pb, sNN = 2.76TeV, 0-10% central
1.5 < pT < 2.0 GeV/c, |h| < 0.8
- p/2 < Df < 3p/2, -1.5 < Dh < 1.5
tTOF– <t
>p (ps)
t TOF
- <t
> (ps)
2500
st
May 21 , 2012
Mass Assumption: Protons
TOF
10
5
Count
Count
Count
3000
TOF
tTOFt– <t- <tTOF>>πp (ps)
(ps)
Pb-Pb, sNN = 2.76TeV, 0-10% central
1.5 < pT < 2.0 GeV/c, |h| < 0.8
- p/2 < Df < 3p/2, -1.5 < Dh < 1.5
tTOF–t <t-TOF
<t >K>K(ps)
(ps)
st
May 21 , 2012
Mass Assumption: Kaons
Count
Mass Assumption: Pions
Combined PID: Fit Example I
Count
Count
tTOF– t<t
>
<t
π >(ps)
p (ps)
TOFTOF TOF
1400
1.
1200
TOF
tTOF– t<tTOF
- <t>π >(ps)
p (ps)
1400
TOF
1400
10
p
600
1000
2
400
10
800
2
600
K
0
10
π
200
10
π
0
-200
-20
-10
1
0
10
20
dE/dx - <dE/dx>p (a.u.)
dE/dx – <dE/dx>π (a.u.)
K
200
10
π
-200
-400
-400
-30
102
p
600
0
-200
-400
800
400
400
200
3.
1200
1000
800
Count
st
May 21 , 2012
2.
1200
1000
-30
Count
st
May 21 , 2012
Count
Count
tTOF– <t
tTOFTOF
- <t>TOF
>p (ps)
π (ps)
Count
st
May 21 , 2012
Pb-Pb, sNN = 2.76TeV, 0-10% central
2.5 < pT < 3.0 GeV/c, |h| < 0.8
Final Fit Result
Pb-Pb, sNN = 2.76TeV, 0-10% central
2.5 < pT < 3.0 GeV/c, |h| < 0.8
Data - Templates (K,p)
Count
Count
Pb-Pb, sNN = 2.76TeV, 0-10% central
2.5 < pT < 3.0 GeV/c, |h| < 0.8
Data
-20
-10
1
0
10
20
dE/dx - <dE/dx>p (a.u.)
dE/dx – <dE/dx>π (a.u.)
-30
-20
-10
1
0
10
20
dE/dx - <dE/dx>p (a.u.)
dE/dx – <dE/dx>π (a.u.)
1. Data, mass assumption: pions.
2. Kaon and Proton templates subtracted, remaining
peak fitted with a function (Gauss+Tail).
3. Final fit, pions (function), kaons and protons (template)
8
Combined PID: Fit Example II
Count
Count
Data
800
4.
Fit Result
st
May 21 , 2012
Count
Count
st
May 21 , 2012
Pb-Pb, sNN = 2.76TeV, 0-10% central
2.5 < pT < 3.0 GeV/c, |h| < 0.8
Final Fit Result
-0.30 < dE/dx - <dE/dx>p < 0.25 (a.u.)
Pb-Pb, sNN = 2.76TeV, 0-10% central
2.5 < pT < 3.0 GeV/c, |h| < 0.8
Final Fit Result
0 < t TOF - <t TOF>p < 20 ps
900
5.
Data
800
700
Fit Result
600
600
500
400
400
300
200
200
100
0
-400 -200 0
200 400 600 800 100012001400
t
- <tTOF>p (ps)
tTOFTOF– <tTOF
>π (ps)
0
-30
-20
-10
0
10
20
dE/dx - <dE/dx>p (a.u.)
dE/dx – <dE/dx>π (a.u.)
4. Slice through the pion peak (TOF).
5. Slice through the proton peak (TPC).
9
Proton and Pion Yields in Peak and Bulk
Pb-Pb, sNN = 2.76TeV, 0-10% central
-1
(GeV/c) -1
1/Ntrig dN/dpNtirg
dp (GeV/c)
T,assoc
T,assoc
-1
(GeV/c)-1
1/Ntrig dN/dpNT,assoc
(GeV/c)
tirg dpT,assoc
Pb-Pb, sNN = 2.76TeV, 0-10% central
p + p Bulk Yield
(Normalized)
1
1
1
-
p + p Peak Yield
p + p Bulk Yield
(Normalized)
dN
+
dN
π
1
p
Correlated Uncertainty
10
Correlated Uncertainty
Uncorrelated Uncertainty
-1
10
Uncorrelated Uncertainty
-1
5.0 < pT,trig < 10.0 GeV/c
2
2.5
3
5.0 < pT,trig < 10.0 GeV/c
3.5
p
4
(GeV/c)
2
2.5
3
pT,assoc (GeV/c)
1
Count
T,assoc
p+ + p- Yield Difference
(Peak - Bulk)
Pb-Pb, sNN = 2.76TeV, 0-10% central
p + p Yield Difference
(Peak - Bulk)
p
tirg
π
-1
2
2.5
3
-1
10-2
5.0 < pT,trig < 10.0 GeV/c
3.5
p
4
(GeV/c)
pT,assoc (GeV/c)
T,assoc
4
(GeV/c)
pT,assoc (GeV/c)
10
10
3.5
p
T,assoc
T,assoc
Count
Pb-Pb, sNN = 2.76TeV, 0-10% central
Ntirg dp
-1
dN
1
-1
1/Ntrig dN/dp
(GeV/c)
T,assoc(GeV/c)
T,assoc
dN
-1
1
-1
1/Ntrig dN/dp
(GeV/c)
T,assoc(GeV/c)
N dp
• Bulk yield
normalized
to peak region:
-0.52 < Δϕ < 0.52,
-0.6 < Δη < 0.6
• Correlated and
uncorrelated
uncertainties
shown
separately.
p+ + p- Peak Yield
5.0 < pT,trig < 10.0 GeV/c
2
2.5
3
3.5
p
4
(GeV/c)
pT,assoc (GeV/c)
T,assoc
10
p/π Ratio
(p+p)/(p++p-)
Pb-Pb, sNN = 2.76TeV, 0-10% central
Bulk Ratio (-0.52 < D f < 0.52, ± 0.6 < D h < ± 1.5)
1.4
1.2
5.0 < pT,trig < 10.0 GeV/c
1
0.8
• p/π Ratio in Bulk region
(-0.52 < Δφ < 0.52 rad,
±0.60 < Δη < ± 1.50)
• Results not feed-down
corrected.
0.6
0.4
0.2
0
1
1.5
2
2.5
3
3.5
p
4
T,assoc
4.5
(GeV/c)
11
p/π Ratio
(p+p)/(p++p-)
Pb-Pb, sNN = 2.76TeV, 0-10% central
Bulk Ratio (-0.52 < D f < 0.52, ± 0.6 < D h < ± 1.5)
1.4
Inclusive (Feed Down Corr.), |y| < 0.5, 0-5%
1.2
5.0 < pT,trig < 10.0 GeV/c
1
0.8
0.6
0.4
• Comparison with feeddown corrected p/π
ratio, from inclusive
spectra (0-5%),
(QM2010 prel.)
• Inclusive spectra used
|y| < 0.5 instead of
|η| < 0.8.
0.2
0
1
1.5
2
2.5
3
3.5
p
4
T,assoc
4.5
(GeV/c)
12
p/π Ratio
(p+p)/(p++p-)
Pb-Pb, sNN = 2.76TeV, 0-10% central
Bulk Ratio (-0.52 < D f < 0.52, ± 0.6 < D h < ± 1.5)
1.4
Peak-Bulk Ratio (-0.52 < D f < 0.52, -0.4 < D h < 0.4)
1.2
5.0 < pT,trig < 10.0 GeV/c
1
0.8
0.6
0.4
0.2
0
1
1.5
2
2.5
3
3.5
p
4
T,assoc
• Comparison with the
p/π Ratio in the Jet
(Peak – Bulk)
(-0.52 < Δφ < 0.52 rad,
-0.40 < Δη < 0.40)
• Jet ratio not feeddown corrected.
• Significant difference
between Bulk and Jet
ratio.
4.5
(GeV/c)
13
p/π Ratio
(p+p)/(p++p-)
Pb-Pb, sNN = 2.76TeV, 0-10% central
Bulk Ratio (-0.52 < D f < 0.52, ± 0.6 < D h < ± 1.5)
1.4
Peak-Bulk Ratio (-0.52 < D f < 0.52, -0.4 < D h < 0.4)
1.2
Pythia (Peak-Bulk Ratio)
5.0 < pT,trig < 10.0 GeV/c
1
0.8
0.6
0.4
0.2
0
1
1.5
2
2.5
3
3.5
p
4
T,assoc
4.5
(GeV/c)
• Comparison with
Pythia p/π ratio in Jet.
(Pythia v6.4.21,
default tune)
• Pythia p/π ratio agrees
with measured Pb–Pb
p/π ratio in Jet.
• Particle production in
Jet dominated by
fragmentation.
• No evidence for
medium modification.
14
Summary and Conclusions
• p/π Ratios in the Jet and Bulk of a di-hadron correlation were
presented.
• Particles identified using both TPC and TOF.
• The p/π ratio in Bulk is compatible with the p/π ratio from
feed down corrected inclusive spectra in the range 1.5 < pT <
3.0 GeV/c.
• The p/π ratio in the Jet is compatible with a Pythia curve in
the range 2.0 < pT < 4.0 GeV/c. (Pythia v6.4.21, default tune)
• Our measurement suggests that particle production
mechanism in jets is dominated by fragmentation. No
evidence for medium modification.
15
BACKUP
16
Fit Quality
Pb-Pb, sNN = 2.76TeV, 0-10% central
2.5 < pT < 3.0 GeV/c, |h| < 0.8
(Data - Final Fit Result)/Data
st
st
0.08
1200
0.06
1000
0.04
800
0.02
600
0
400
-0.02
200
-0.04
0
-0.06
-200
-0.08
-400
-30
-20
-10
0
10
20
dE/dx - <dE/dx>p (a.u.)
(Data-Fit)/Data
-0.1
4
1400
3
1200
1000
2
800
1
600
0
400
-1
200
0
-2
-200
-3
-400
-30
-20
-10
0
10
20
dE/dx - <dE/dx>p (a.u.)
-4
(Data-Fit)/σstat
17
(Data - Final Fit Result)/ sstat
1400
May 21 , 2012
tTOF - <tTOF>p (ps)
0.1
(Data - Final Fit Result)/Data
tTOF - <tTOF>p (ps)
May 21 , 2012
Pb-Pb, sNN = 2.76TeV, 0-10% central
2.5 < pT < 3.0 GeV/c, |h| < 0.8
(Data - Final Fit Result)/ s stat