strangeness production in high multiplicity pp collisions€¦ · •n part-scaling does not hold...
TRANSCRIPT
Strangeness production in high multiplicity pp collisions
Marek Bombara on behalf of the ALICE Collaboration(Pavol Jozef Šafárik University, Košice, Slovakia)
Critical Point and Onset of Deconfinement 2017 Stony Brook University, USA
7-11 August 2017
1
• Historically, an enhanced production of strangeness was proposed as a signature of QGP in nucleus-nucleus collisions [J. Rafelski, B. Müller, Phys. Rev. Lett. 48 (1982) 1066–1069]
• However, the measured effect can be qualitatively explained as a strangeness suppression in reference sample (pp and p−A collisions)
Strangeness enhancement
Marek Bombara, Critical Point and Onset of Deconfinement 2017, Stony Brook, August 7, 2017
⟩part
N⟨1 10 210
re
lativ
e t
o p
p⟩
pa
rtN⟨
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ld /
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10
= 2.76 TeVNNsPb-Pb at
+Ω+
-Ω
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⟩part
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re
lativ
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ield
/
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10
+Ω+
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NA57 Pb-Pb, p-Pb at 17.2 GeV
STAR Au-Au at 200 GeV
ALI−DER−80680
2
ALICE, Phys. Lett. B 728 (2014) 216
• Npart-scaling does not hold at LHC energies, ratios to pions (as the most abundant particle) are studied
• hyperon-to-pion ratios for pp higher at LHC than at RHIC energies
• for A−A - no obvious collision energy dependence
Marek Bombara, Critical Point and Onset of Deconfinement 2017, Stony Brook, August 7, 2017
⟩part
N⟨1 10 210
Hyp
ero
n-t
o-p
ion
ra
tio
-410
-310
π/Ξ
π/Ω
ALICE Pb-Pb at 2.76 TeV
ALICE pp at 7 TeV
ALICE pp at 900 GeV
STAR Au-Au, pp at 200 GeV
ALICE Pb-Pb at 2.76 TeV
ALICE pp at 7 TeV
STAR Au-Au, pp at 200 GeV
(c)
ALI−PUB−78357
3
LHC offers not only unprecedented energies, but also unprecedented collision statistics in small systems ⇒ allows extensive multiplicity study of the reference samples (pp and p−Pb).
ALICE, Phys. Lett. B 728 (2014) 216
Strangeness enhancement
Multiplicity studies at the LHC
Marek Bombara, Critical Point and Onset of Deconfinement 2017, Stony Brook, August 7, 2017
η∆-4-2
02
4
φ∆ 02
4
φ∆
dη∆d
pair
N2 d tri
gN1 1.6
1.71.8
110≥ trkoffline = 5.02 TeV, NNNsCMS pPb
< 3 GeV/cT
1 < p(b)
(rad)
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0.80
0.85
c < 4 GeV/T,trig
p2 <
c < 2 GeV/T,assoc
p 1 <
= 5.02 TeVNN
sp-Pb
(0-20%) - (60-100%)
ALI−PUB−46246
η∆-4
-20
24
φ∆0
2
4
)φ
∆,η
∆R
( -202
>0.1GeV/c T
(a) CMS MinBias, p
η∆-4
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φ∆0
2
4)
φ∆,
η∆
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-101
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(b) CMS MinBias, 1.0GeV/c<p
η∆-4
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24
φ∆0
2
4
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∆,η
∆R
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>0.1GeV/c T
110, p≥(c) CMS N
η∆-4
-20
24
φ∆0
2
4
)φ
∆,η
∆R
( -2-101
<3.0GeV/cT
110, 1.0GeV/c<p≥(d) CMS N
• structures previously connected to collectivity in Pb−Pb collisions
• many other observables in high multiplicity pp and p−Pb resemble those in A−A
4
CMS, JHEP 09 (2010) 091
CMS, PLB 718 (2013) 795
ALICE, PLB 719 (2013) 29
It all started with ridges:
Multiplicity studies at the LHC
Marek Bombara, Critical Point and Onset of Deconfinement 2017, Stony Brook, August 7, 2017
η∆-4-2
02
4
φ∆ 02
4
φ∆
dη∆d
pair
N2 d tri
gN1 1.6
1.71.8
110≥ trkoffline = 5.02 TeV, NNNsCMS pPb
< 3 GeV/cT
1 < p(b)
(rad)
ϕ∆
-1
0
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2
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trig
N1
0.75
0.80
0.85
c < 4 GeV/T,trig
p2 <
c < 2 GeV/T,assoc
p 1 <
= 5.02 TeVNN
sp-Pb
(0-20%) - (60-100%)
ALI−PUB−46246
η∆-4
-20
24
φ∆0
2
4
)φ
∆,η
∆R
( -202
>0.1GeV/c T
(a) CMS MinBias, p
η∆-4
-20
24
φ∆0
2
4)
φ∆,
η∆
R(
-101
<3.0GeV/cT
(b) CMS MinBias, 1.0GeV/c<p
η∆-4
-20
24
φ∆0
2
4
)φ
∆,η
∆R
(
-4-202
>0.1GeV/c T
110, p≥(c) CMS N
η∆-4
-20
24
φ∆0
2
4
)φ
∆,η
∆R
( -2-101
<3.0GeV/cT
110, 1.0GeV/c<p≥(d) CMS N
5
CMS, JHEP 09 (2010) 091
CMS, PLB 718 (2013) 795
ALICE, PLB 719 (2013) 29
It all started with ridges:
• structures previously connected to collectivity in Pb−Pb collisions
• many other observables in high multiplicity pp and p−Pb resemble those in A−A
Are there any unusual trends also in strangeness production in high multiplicity pp collisions?
Multiplicity studies at the LHC
Marek Bombara, Critical Point and Onset of Deconfinement 2017, Stony Brook, August 7, 2017
η∆-4-2
02
4
φ∆ 02
4
φ∆
dη∆d
pair
N2 d tri
gN1 1.6
1.71.8
110≥ trkoffline = 5.02 TeV, NNNsCMS pPb
< 3 GeV/cT
1 < p(b)
(rad)
ϕ∆
-1
0
1
2
3
4
η∆
-2
-1
0
1
2
)-1
(ra
dϕ
∆d
η∆
dasso
cN
2d
trig
N1
0.75
0.80
0.85
c < 4 GeV/T,trig
p2 <
c < 2 GeV/T,assoc
p 1 <
= 5.02 TeVNN
sp-Pb
(0-20%) - (60-100%)
ALI−PUB−46246
η∆-4
-20
24
φ∆0
2
4
)φ
∆,η
∆R
( -202
>0.1GeV/c T
(a) CMS MinBias, p
η∆-4
-20
24
φ∆0
2
4)
φ∆,
η∆
R(
-101
<3.0GeV/cT
(b) CMS MinBias, 1.0GeV/c<p
η∆-4
-20
24
φ∆0
2
4
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∆,η
∆R
(
-4-202
>0.1GeV/c T
110, p≥(c) CMS N
η∆-4
-20
24
φ∆0
2
4
)φ
∆,η
∆R
( -2-101
<3.0GeV/cT
110, 1.0GeV/c<p≥(d) CMS N
6
CMS, JHEP 09 (2010) 091
CMS, PLB 718 (2013) 795
ALICE, PLB 719 (2013) 29
It all started with ridges:
• structures previously connected to collectivity in Pb−Pb collisions
• many other observables in high multiplicity pp and p−Pb resemble those in A−A
Are there any unusual trends also in strangeness production in high multiplicity pp collisions?
A Large Ion Collider Experiment
Marek Bombara, Critical Point and Onset of Deconfinement 2017, Stony Brook, August 7, 2017 7
Data: - pp √s = 7 TeV, 100 M 2010 - pp √s = 13 TeV, 50 M 2015
ITS (Inner Tracking System): primary vertex reconstruction, tracking, particle identification
V0: triggering, background suppression, event multiplicity determination
TPC (Time Projection Chamber): main tracking detector, particle identification
Multiplicity definition
Marek Bombara, Critical Point and Onset of Deconfinement 2017, Stony Brook, August 7, 2017
(h/)
(h/)ppINEL>0
= 1 + aSb log
hdNch/di
hdNch/dippINEL>0
Class name I II III IV V
/INEL>0 0 0.95% 0.95 4.7% 4.7 9.5% 9.5 14% 14 19%
hdNch/di 21.3± 0.6 16.5± 0.5 13.5± 0.4% 11.5± 0.3 10.1± 0.3
Class name VI VII VIII IX X
/INEL>0 19 28% 28 38% 38 48% 48 68% 68 100%
hdNch/di 8.45± 0.25 6.72± 0.21 5.40± 0.17% 3.90± 0.14 2.26± 0.12
1
• analysed events have at least one charged particle in |η|<1 (INEL>0)
• event sample divided into 10 classes according to ionisation energy (~ proportional to the charged particle multiplicity) deposited in V0 detectors, covering the regions 2.8 < η < 5.1 and −3.7 < η < −1.7
• ⟨dNch/dη⟩ - average pseudorapidity density of primary charged particles in |η|< 0.5
Multiplicity classes used in pp@7TeV analysis:
8
(Multi-)Strange particle identification
Marek Bombara, Critical Point and Onset of Deconfinement 2017, Stony Brook, August 7, 2017
)2) (GeV/cπ, Λ(invM
1.28 1.3 1.32 1.34 1.36
)2
Counts
/(M
eV
/c
0
5
10
15
20
25
310×
> 0.6 GeV/cT
p
)±Ξ(PDGM
(a)
-Ξ
+Ξ
)2, K) (GeV/cΛ(invM
1.64 1.66 1.68 1.7
)2
Counts
/(M
eV
/c
0
0.2
0.4
0.6
0.8
1
1.2
1.43
10×
> 0.8 GeV/cT
p
)±Ω(PDGM
(b)
-Ω
+Ω
ALI−PUB−14756
Ξ− Ω−
ΛΛ
π−
π−
K−
π−
p
p
⊗ B
• the (multi-)strange particle candidates are identified in the ALICE detector via decay topology
• in order to distinguish between signal and background, many geometrical selection criteria were applied on the candidates
• the yield is extracted by analysing invariant mass distributions of the decay products
Example of multi-strange decay topology
9
Physics Letters B Volume 712, 12 June 2012, Page 309
Identified particle pT spectra at 7 TeV
Marek Bombara, Critical Point and Onset of Deconfinement 2017, Stony Brook, August 7, 2017
-1 )c
(G
eV
/T
p/d
yd
N2
devt
N1
/
7−10
6−10
5−10
4−10
3−10
2−10
1−10
1
10
210
310
410 -π++π
7
6
5
4
3
2
1
1
10
2
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4 -+K
+K
0 5 10 15 20
8−10
7−10
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5−10
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1
10
210
310 pp+
7
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2
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0 5 10 15 20
8
7
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3
2
1
1
10
2
3
Λ+Λ
0 2 4 6 8 10 12
8
7
6
5
4
3
2
1
1
10
2
3 +Ξ+
-Ξ
)c (GeV/T
p0 2 4 6 8 10
8
7
6
5
4
3
2
1
1
10
2
3
ALICE Preliminary
=7 TeVspp at
V0M Mult. Evt. Classes
+Ω+
-Ω
7
6
5
4
3
2
1
1
10
2
3
4
*KK*+p, p+
-+K
+, K-
π++π :
+Ξ+
-Ξ, Λ+Λ, S
0 K
)0
X (x 2)1IX (x 2
)2VIII (x 2)
3VII (x 2
)4VI (x 2)
5V (x 2
)6
IV (x 2)7III (x 2
)8
II (x 2)
9I (x 2
:+
Ω+-
Ω )
0IX + X (x 2
)1VII + VIII (x 2)2V + VI (x 2)
3III + IV (x 2
)4I + II (x 2
*:K K*+)
0X (x 2
)1IX (x 2)2VIII (x 2)
3VII (x 2
)4VI (x 2)
5IV + V (x 2
)6
III (x 2)7II (x 2)
8I (x 2
ALI−PREL−111017
• pT spectra get harder as the multiplicity increases
10
Baryon to meson ratios
Marek Bombara, Critical Point and Onset of Deconfinement 2017, Stony Brook, August 7, 2017
ALI-PREL-110561
11
• shift + increase of the peak in most central Pb−Pb collisions ⇒ radial flow + quark recombination
• B/M qualitatively similar in all three colliding systems: depletion at low pT, enhancement in mid pT and no change in high pT
• more-or-less smooth evolution across the systems in low and mid pT region, production is driven by final multiplicity
• high pT independent on multiplicity
Baryon to meson ratios
Marek Bombara, Critical Point and Onset of Deconfinement 2017, Stony Brook, August 7, 2017
ALI-PREL-110561
ALI-PREL-110566
12
• shift + increase of the peak in most central Pb−Pb collisions ⇒ radial flow + quark recombination
• B/M qualitatively similar in all three colliding systems: depletion at low pT, enhancement in mid pT and no change in high pT
• more-or-less smooth evolution across the systems in low and mid pT region, production is driven by final multiplicity
• high pT independent on multiplicity
• enhancement of strange particle w.r.t. non-strange yield clearly visible for high multiplicity pp collisions
• very nice overlap with p−Pb and Pb−Pb results
Strangeness enhancement in pp
Marek Bombara, Critical Point and Onset of Deconfinement 2017, Stony Brook, August 7, 2017
ALI-PREL-134502
13
Enhancement observed as a function of ⟨dNch/dη⟩ is independent of collision type!
• remarkable overlap of p−Pb and peripheral Pb−Pb with Cu−Cu and Au−Au - even for 25 times smaller energy the strangeness production is similar!
• need more data for pp from RHIC (either multiplicity dependence study or from Beam Energy Scan programme)
Is the enhancement dependent on collision energy?
Marek Bombara, Critical Point and Onset of Deconfinement 2017, Stony Brook, August 7, 2017
ALI-PREL-135175
14
ALI-PUB-106882
• The ratios of particle yields with a big mass difference do not show enhancement as a function of multiplicity
• no model* is able to reproduce the increase of the hyperon-to-pion ratios and the “flatness” baryon-to-meson ratios
Is the enhancement mass related?
Marek Bombara, Critical Point and Onset of Deconfinement 2017, Stony Brook, August 7, 2017 15
ALICE, Nature Physics 13 (2017) 535
* There is a very recent improvement of the DIPSY prediction for p/π ratio, see the talk of C. Bierlich at SQM’17
• can be fitted by empirical function with the number of valence quarks as a fixed parameter (S=1,2,3):
Marek Bombara, Critical Point and Onset of Deconfinement 2017, Stony Brook, August 7, 2017
ALI-PUB-106886
(h/)
(h/)ppINEL>0
= 1 + aSb log
hdNch/di
hdNch/dippINEL>0
16
Strangeness enhancement in pp
ALICE, Nature Physics 13 (2017) 535
Hierarchy of the enhancement determined by the hadron strangeness!
Marek Bombara, Critical Point and Onset of Deconfinement 2017, Stony Brook, August 7, 2017
0 2 4 6 8 10 12
]-1 )
c)
[(G
eV
/yd
Tp
/(d
N2 d
ev
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/
8−10
7−10
6−10
5−10
4−10
3−10
2−10
1−10
1
10
210
310
V0M multiplicity event classes)
9I (x 2 )
8II (x 2
)7III (x 2 )6
IV (x 2)
5V (x 2 )4VI (x 2
)3
VII (x 2 )2VIII (x 2IX (x 2) X
Lévy-Tsallis fit
= 13 TeVsALICE Preliminary - pp
S0K
|<0.5y|
)c (GeV/T
p
0 2 4 6 8 10 12
Ra
tio t
o I
NE
L>
0
1−10
1
10
ALI-PREL-116278
0 1 2 3 4 5 6 7 8
]-1 )
c)
[(G
eV
/yd
Tp
/(d
N2 d
ev
N1
/
8−10
7−10
6−10
5−10
4−10
3−10
2−10
1−10
1
10
210
V0M multiplicity event classes)
9I (x 2 )
8II (x 2
)7III (x 2 )6
IV (x 2)
5V (x 2 )4VI (x 2
)3
VII (x 2 )2VIII (x 2IX (x 2) X
Lévy-Tsallis fit
= 13 TeVsALICE Preliminary - pp
Λ+Λ|<0.5y|
)c (GeV/T
p
0 1 2 3 4 5 6 7 8
Ra
tio t
o I
NE
L>
0
1−10
1
10
ALI-PREL-116282
17
• hardening of the spectra with increasing multiplicity observed in the pT-region:| pT |<4 GeV/c
Strange particle pT spectra at 13 TeV
Marek Bombara, Critical Point and Onset of Deconfinement 2017, Stony Brook, August 7, 2017
0 1 2 3 4 5
]-1 )
c)
[(G
eV
/yd
Tp
/(d
N2 d
ev
N1
/
7−10
6−10
5−10
4−10
3−10
2−10
1−10
1
V0M multiplicity event classes)4I+II (x 2 )
3III+IV (x 2
)2V+VI (x 2 VII+VIII (x 2)
IX+X
Lévy-Tsallis fit
= 13 TeVsALICE Preliminary - pp +Ω+
-Ω
|<0.5y|
)c (GeV/T
p
0 1 2 3 4 5
Ratio
to IN
EL>
0
1−10
1
10
ALI-PREL-116290
0 1 2 3 4 5 6
]-1 )
c)
[(G
eV
/yd
Tp
/(d
N2 d
ev
N1
/
7−10
6−10
5−10
4−10
3−10
2−10
1−10
1
10
210
V0M multiplicity event classes)
9I (x 2 )
8II (x 2
)7III (x 2 )6
IV (x 2)
5V (x 2 )4VI (x 2
)3
VII (x 2 )2VIII (x 2IX (x 2) X
Lévy-Tsallis fit
= 13 TeVsALICE Preliminary - pp +Ξ+
-Ξ
|<0.5y|
)c (GeV/T
p
0 1 2 3 4 5 6
Ratio
to IN
EL>
0
1−10
1
10
ALI-PREL-116286
18
• hardening of the spectra seems to be species dependent
Multi-strange particle pT spectra at 13 TeV
⟨pT⟩ as a function of multiplicity
Marek Bombara, Critical Point and Onset of Deconfinement 2017, Stony Brook, August 7, 2017
ALI-PREL-116330 ALI-PREL-116336
ALI-PREL-116342 ALI-PREL-116346
19
• spectra harder in 13 TeV than in 7 TeV for the same multiplicity
Yield as a function of multiplicity
Marek Bombara, Critical Point and Onset of Deconfinement 2017, Stony Brook, August 7, 2017
ALI-PREL-116310 ALI-PREL-116318
ALI-PREL-116322 ALI-PREL-116326
20
• linear increase of the yields with multiplicity, yields are invariant with respect to collision energy for a given event multiplicity!
Outlook
• a special high-multiplicity trigger in pp at 13TeV was used during the data taking in 2016
• enough statistics to study 0−0.1% and 0−0.01% multiplicity samples
Marek Bombara, Critical Point and Onset of Deconfinement 2017, Stony Brook, August 7, 2017 21
ALI-PERF-131160
Summary
• intriguing trends observed in strangeness production in high multiplicity pp collisions resembling the trends from Pb−Pb, like e.g. hardening of pT spectra or similarities in B/M ratios
• enhancement of strange particle production w.r.t. pion production as a function of multiplicity seen in pp collisions
• for the same multiplicity: the strangeness production does not depend on collision system and (at least for LHC) also on collision energy
• production of particles with higher strangeness content is more enhanced in comparison with inclusive production
• stay tuned for the results obtained using data collected with a high-multiplicity trigger in pp collisions at 13 TeV
Marek Bombara, Critical Point and Onset of Deconfinement 2017, Stony Brook, August 7, 2017 22
Backup slides
23
(dNch/dη)/(⟨Npart⟩/2) as a function of the number of participants
Marek Bombara, Critical Point and Onset of Deconfinement 2017, Stony Brook, August 7, 2017 24
⟩part
N ⟨0 100 200 300 400
/2)
⟩p
art
N ⟨)/
(η
/dc
hN
(d
4
5
6
7
8
9
DPMJET III [10]HIJING 2.0 (sg=0.23) [11]HIJING 2.0 (sg=0.20) [11]Armesto et al. [12]Kharzeev et al. [13]Albacete et al. [14]
Pb-Pb 2.76 TeV ALICE
ALI−PUB−8816
ALICE, Phys. Rev. Lett. 106 (2011) 032301
Marek Bombara, Critical Point and Onset of Deconfinement 2017, Stony Brook, August 7, 2017
ALI-PREL-108831
• the hardening is more pronounced for heavier particles
• similar behaviour observed also in p−Pb and Pb−Pb collisions where it can be interpreted as a particle emission from a collectively expanding thermal source (radial flow)
• do we see a radial flow in pp as well?
25
pT spectra at 7 TeV
Blast-Wave fit
Marek Bombara, Critical Point and Onset of Deconfinement 2017, Stony Brook, August 7, 2017
-1 )c
(G
eV
/T
p/d
ydN
2 d
evt
N1/
-710
-610
-510
-410
-310
-210
-110
1
10
210
310
410 = 7 TeVsALICE Preliminary, pp
V0M Class I+II
100× π
50×K p
10× S0K
0.1× Λ
0.05× Ξ
0.05× Ω-5 10×K*
, K, pπBlast-Wave fit to
Blast-Wave prediction
0 1 2 3 4 5 6 7 8 9
11.5
π cfit range: 0.5-1.0 GeV/
0 1 2 3 4 5 6 7 8 91
1.5 Kc0.2-1.5 GeV/
0 1 2 3 4 5 6 7 8 91
1.5 pc0.3-3.0 GeV/
0 1 2 3 4 5 6 7 8 9
11.5
S0
K
0 1 2 3 4 5 6 7 8 91
1.5Λ
0 1 2 3 4 5 6 7 8 91
1.5Ξ
0 1 2 3 4 5 6 7 8 9
11.5
Ω
)c (GeV/T
p0 1 2 3 4 5 6 7 8 9
11.5
K*
ALI−PREL−109116
5
10
15
20
25
30
35
40
5 10 15 20 25 30 35 40 450
1
2
3
4
5
6
7
8
9
10
|< 0
.5η|
⟩η
/dch
Nd⟨
⟩T
β⟨
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7
(G
eV
)ki
nT
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0.16
0.18
0.2
)c) , p (0.3-3.0 GeV/c) , K (0.2-1.5 GeV/c (0.5-1 GeV/πGlobal Blast-Wave fit to
= 7 TeVsALICE Preliminary, pp,
= 5.02 TeVsALICE, p-Pb,
= 2.76 TeVNNsALICE, Pb-Pb,
= 5.02 TeVNNsALICE Preliminary, Pb-Pb,
ALI-PREL-122516
26
• for the similar multiplicity: the kinetic freeze-out temperature and the average transverse velocity are higher for pp than for Pb−Pb
• Spectra are harder for higher multiplicity event classes. Similar effect seen in p−Pb can be explained by collectivity.
• in HI such behaviour could be explained by models based on relativistic hydrodynamics
• blast-wave fit to all species for class I points to thermal source at kinetic freeze-out temperature 163 MeV and common transverse velocity 0.49
pT spectra at 7 TeV
Marek Bombara, Critical Point and Onset of Deconfinement 2017, Stony Brook, August 7, 2017
ALI-PUB-106874
27
ALICE, Nature Physics 13 (2017) 535