Transverse momentum spectra of π, K and p in small collision systems:search for collective phenomena

Nicolò Jacazio for the ALICE collaborationUniversity of Turin and INFN

The ALICE detectorI VZERO detectors

trigger and

centrality/multiplicity

Main detectors for PID:

I Inner tracking system (ITS) I Time projection chamber (TPC)

I Time of flight (TOF) I High momentum PID (HMPID)

Measuring the event multiplicityVZERO percentiles

Event multiplicity at forward-rapidity obtained measuring the signal in the

two V0 detectors and dividing its distribution into percentile-based classes

Counting tracksEvent multiplicity at mid-rapidity (|η| < 0.8) obtained by counting tracksreconstructed in the barrel detectors and segments of tracks reconstructed

with the SPD detector to increase the acceptance

VZERO Amplitude (a.u.)0 5000 10000 15000 20000

Ev

en

ts

-210

-110

1

10

210

Data

Glauber fit

0-5

%

5-1

0%

10

-20

%

20

-30

%

30

-40

%

40

-50

%

50

-60

%

0 500 1000

10

210

70

-80

%

60

-70

%

ALI−PUB−8808 [2]

VZERO-A amplitude (a.u.)0 100 200 300 400 500 600 700 800 900

Events

(a.u

.)

1

10

210

310

410

0-5%

5-10%

10-20%

20-40%

40-60%

60-80%

80-100%

= 5.02 TeVNN

sALICE p-Pb at 0-5%5-10%10-20%20-40%40-60%60-80%80-100%

03/05/2013

ALI−PERF−51387

chN0 10 20 30 40 50 60 70

)ch

NP

(

-710

-610

-510

-410

-310

-210

-110

1

ALICE pp

> 0.15 GeVT

p| < 0.8, η > 0, |chN = 7 TeV, s

ALI−PUB−59106 [3]

PID strategiesITS

)c (GeV/p

0.07 0.1 0.2 0.3 0.4 0.5 1 2 3 4 5

m)

µ (

ke

V/3

00

x/d

EIT

S d

0

100

200

300

400

500

600

700

05/03/2013

TeV 5.02 = NN

sp-Pb

π

e

K p

ALI−PERF−46922

I Specific energy-loss in the ITS vs momentumI dE/dx resolution for the ITS ∼ 10% (p–Pb)

TPC

)c (GeV/p

0.2 0.3 0.4 1 2 3 4 5 6 7 8 910

(arb

. u

nits)

x/d

ET

PC

d

0

100

200

300

400

500

600

700

π

e

K

p d t

05/03/2013

TeV 5.02 = NNsp-Pb

ALI−PERF−46927

I Specific energy-loss in the TPC vs momentumI dE/dx resolution for the TPC ∼ 5% (p–Pb)

TOF

p-Pb minimum bias

p

K

π

p

K

π

= 5.02 TeVNN

sp-Pb

5/03/2013

(GeV/c)p0 1 2 3 4 5

βT

OF

0.2

0.4

0.6

0.8

1

= 5.02 TeVNN

sp-Pb

5/03/2013

π

K

p

K

p

ALI−PERF−46936

I Particle velocity β measured by TOF vsmomentum

I TOF time resolution ∼ 85− 120 ps depending

on multiplicity (p–Pb)

HMPID

)cp (GeV/0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5

HM

PID

Chere

nkov a

ngle

(ra

d)

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

π

K

p

TeV 7 = spp

ALI−PUB−72451 [5]

I Mean Cherenkov angle vs momentumI 3σ separation for π-K for pT < 3 GeV/c

I 3σ separation for p-K for pT < 5 GeV/c

ResultsSpectra in pp

The multiplicity in pp can

be quantified by the ratio:

zraw =(N rawch )limit〈N rawch 〉mult>0

〈N rawch 〉 = 9.6, |η| < 0.8

N rawch zraw

7-12 0.7-1.313-19 1.4-2.020-28 2.1-2.929-39 3.0-4.140-49 4.2-5.150-59 5.2-6.260-71 6.3-7.472-82 7.5-8.6

I Multiplicity dependenceof the spectral shape

I Spectra becomeprogressively harder as a

function of multiplicity

and particle mass

→ Mass ordering asexpected from

hydrodynamics

-1 )c

) (G

eV

/T

pd

y/(

dN

2 d

ev

N1/

-210

-110

1

10

rawz

mult > 0

[0.7-1.4)

[1.4-2.1)

[2.1-3.0)

[3.0-4.2)

[4.2-5.2)

[5.2-6.3)

[6.3-7.5)

[7.5-8.6]

+π

= 7 TeVspp -110

1

Uncertainty

statistical

total systematic

mult. related syst.

+K-210

-110

p

ALICE Preliminary

)c(GeV/T

p

0.5 1 1.5 2 2.5

ratio to m

ult. >

0

1

10

)c(GeV/T

p

0.2 0.4 0.6 0.8 1 1.2 1.4

1

10

)c(GeV/T

p

0.5 1 1.5 2 2.5

1

10

ALI−PREL−81642

The Blast-Wave fitsThe blast-wave model is a simplified hydro model with the following functional form:

E d3Ndp3 ∼ f (pt) =

∫ R0 mTK1 (mT cosh ρ/Tfo) I0 (pT sinh ρ) rdr

mT =√m2 + p2T βr (r) = βs (r/R)

n ρ = tanh−1βr

0 1 2 3 4 5 6

]-2 )

c)

[(G

eV

/y

dT

p/(

dN

2 d

Tp

π 1

/2e

vN

1/ -510

-410

-310

-210

-110

1

10

210

310

410

510 = 2.76 TeV

NNsALICE, Pb-Pb,

PRC 88, 044909 (2013)Centrality Class: 0-5%

(100x)-π + +π

(10x)-

+ K+K

(1x)pp +

Blast-Wave

global fit range

c: 0.5-1.0 GeV/π

cK: 0.2-1.5 GeV/

cp: 0.3-3.0 GeV/

)c (GeV/T

p

0 1 2 3 4 5 6

data

/ m

odel

1

1.5 -π + +π

1

1.5-

+ K+

K

1

1.5 pp +

ALI−DER−67916 [4]

0 1 2 3 4 5 6

]-2 )

c)

[(G

eV

/y

dT

p/(

dN

2 d

Tp

π 1

/2e

vN

1/ -510

-410

-310

-210

-110

1

10

210

310

410 = 5.02 TeVNN

sALICE, p-Pb,

PLB 728 (2014) 25-38V0A Multiplicity Class (Pb-side): 0-5%

(100x)-π + +π

(10x)-

+ K+K

(1x)pp +

Blast-Wave

global fit range

c: 0.5-1.0 GeV/π

cK: 0.2-1.5 GeV/

cp: 0.3-3.0 GeV/

)c (GeV/T

p

0 1 2 3 4 5 6

data

/ m

odel

1

1.5 -π + +π

1

1.5-

+ K+

K

1

1.5 pp +

ALI−DER−67956 [1]

0 1 2 3 4 5 6

]-2 )

c)

[(G

eV

/y

dT

p/(

dN

2 d

Tp

π 1

/2e

vN

1/

-410

-310

-210

-110

1

10

210

310

= 7 TeVsALICE, pp,

ALICE Preliminary Multiplicity Class: [0.7, 1.4)rawz

(100x)+π

(10x)+K

p (1x)

Blast-Wave

global fit range

c: 0.5-1.0 GeV/π

cK: 0.3-1.5 GeV/

cp: 0.5-2.5 GeV/

)c (GeV/T

p

0 1 2 3 4 5 6

data

/ m

odel

1

1.5 +π

1

1.5 +K

1

1.5 p

ALI−PREL−72482

References

1. B.Abelev et Al. (ALICE Coll.) Phys. Lett. B728 (2014) 25-38

2. K. Aamodt et Al. (ALICE Coll.) Phys. Rev. Lett. 106 (2011), 032301

3. ALICE-PUBLIC-2013-001

4. B.Abelev et Al. (ALICE Coll.) Phys. Rev. C 88, 044910 (2013)

5. ALICE Coll. arXiv:1402.4476 [nucl-ex]

6. E. Schnedermann, J. Sollfrank, and U. Heinz Phys. Rev. C 48, 2462 (1993)

Spectra in p–Pb

)c (GeV/T

p

0 1 2 3 4 5

]

-2 )c

) [(

GeV

/y

dT

p/(

dN

2)

dT

pπ

1/(

2e

vN

1/

-410

-310

-210

-110

1

10

210

310

410

-

π + +

π

= 5.02 TeVNNsALICE, p-Pb,

< 0.5CMS

y0 <

V0A Multiplicity Classes(Pb-side)

0-5% (64x)

5-10% (32x)

10-20% (16x)

20-40% (8x)

40-60% (4x)

60-80% (2x)

80-100% (1x)

individual fit

ALI−PUB−58037 [1] )c (GeV/Tp0 0.5 1 1.5 2 2.5 3 3.5 4 4.5

]

-2 )c

) [(

GeV

/y

dT

p/(

dN

2)

dT

pπ

1/(

2e

vN

1/

-410

-310

-210

-110

1

10

210

- + K

+K

= 5.02 TeVNNsALICE, p-Pb,

< 0.5CMS

y0 <

V0A Multiplicity Classes(Pb-side)

0-5% (64x)

5-10% (32x)

10-20% (16x)

20-40% (8x)

40-60% (4x)

60-80% (2x)

80-100% (1x)

individual fit

ALI−PUB−58041 [1] )c (GeV/Tp0 1 2 3 4 5 6 7

]

-2 )c

) [(

GeV

/y

dT

p/(

dN

2)

dT

pπ

1/(

2e

vN

1/

-510

-410

-310

-210

-110

1

10

pp +

= 5.02 TeVNNsALICE, p-Pb,

< 0.5CMS

y0 <

V0A Multiplicity Classes(Pb-side)

0-5% (64x)

5-10% (32x)

10-20% (16x)

20-40% (8x)

40-60% (4x)

60-80% (2x)

80-100% (1x)

individual fit

ALI−PUB−58045 [1]

Spectra evolution with multiplicity in p–Pb: shown to exhibit behaviour that is qualitatively similar to both pp and

Pb–Pb

Particle ratios

)c (GeV/T

p

0 0.5 1 1.5 2 2.5 3

Ra

tio

0.5

1

1.5

2

2.5

3

3.5

)c (GeV/T

p

0 0.5 1 1.5 2 2.5 3

Ra

tio

0.5

1

1.5

2

2.5

3

3.5

ALICE Preliminary

2+syst2statuncert.=

= 2.76 TeVNN

sPb-Pb,

>=13.4η/dch

N>=1601/=45/