[PPT] - Charged-particle pseudorapidity density N part versus N coll PowerPoint Presentation

SLIDE 1

U N I V E R S I T Y O F C O P E N H A G E N N I E L S B O H R I N S T I T U T E

faculty of science

Charged-particle pseudorapidity density

Npart versus Ncoll Christian Holm Christensen

Niels Bohr Institute

COST Workshop on interplay of hard and soft QCD probes for collectivity in heavy–ion collisions — 27th of February, 2019

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U N I V E R S I T Y O F C O P E N H A G E N N I E L S B O H R I N S T I T U T E

Disclaimer

I am an ALICE collaborator, so many results will be from the ALICE collaboration

Slide 2/30 — C.H.Christensen —

dNch dη

— COST’19 — 2019/02/27

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U N I V E R S I T Y O F C O P E N H A G E N N I E L S B O H R I N S T I T U T E

Overview

1 Measurements of dNch dη

Other measurements of interest Take-away

2 Scaling

Midrapidity dNch

dη

and total Nch Natural Centrality Glauber modelling

3 Summary

Slide 2/30 — C.H.Christensen —

dNch dη

— COST’19 — 2019/02/27

SLIDE 4

U N I V E R S I T Y O F C O P E N H A G E N N I E L S B O H R I N S T I T U T E

Wealth of measurements

pp(pp) results

From √s = 200 GeV to

13 TeV

Inelastic
with Nch > 0
with Nch > 1
Non-single diffractive
Mostly |η| < 2

η 8 − 6 − 4 − 2 − 2 4 6 η /d

ch

N d 1 2 3 4 5 6 7 8

) collisions p pp(p >100MeV

T

p ATLAS, 13TeV, INEL>1, ALICE, 13TeV, INEL>0 CMS, 13TeV, INEL >100MeV

T

p ATLAS, 8TeV, INEL>1, CMS & TOTEM, 8TeV, INEL TOTEM, 8TeV, INEL>0 TOTEM, 7TeV, INEL>0 CMS, 7TeV, NSD >100MeV

T

p ATLAS, 7TeV, INEL>1, CMS, 2.36TeV, NSD CDF, 1.8TeV, MB >100MeV

T

p ATLAS, 900GeV, INEL>1, CMS, 900GeV, NSD P238, 630GeV, MB CDF, 630GeV, MB UA1, 540GeV, NSD PHOBOS, 410GeV, INEL PHOBOS, 200GeV, INEL

HepData Slide 3/30 — C.H.Christensen —

dNch dη

— COST’19 — 2019/02/27

SLIDE 5

U N I V E R S I T Y O F C O P E N H A G E N N I E L S B O H R I N S T I T U T E

Wealth of measurements

AA at RHIC energies

Au–Au & Cu–Cu
From

√sNN = 20 GeV to 200 GeV

Mostly PHOBOS

Also results from BRAHMS, STAR

dNch/dη 10

2

10

3

10

Cu-Cu √sNN = 22.4GeV η 6 − 4 − 2 − 2 4 dNch/dη 10

2

10

3

10 Au-Au √sNN = 19.6Ge V 10

2 3 Cu-Cu √sNN = 62.4Ge

V η 6 − 4 − 2 − 2 4 10

2 3 Au-Au √sNN = 62.4GeV

10

2 3 Cu-Cu √sNN = 200Ge

V η 6 − 4 − 2 − 2 4 10

2 3 Au-Au √sNN = 200GeV

PHOBOS 0- 6% 6- 15% 15- 25% 25- 35% 35- 45% 45- 55%

PRC83(2011)024913 Slide 4/30 — C.H.Christensen —

dNch dη

— COST’19 — 2019/02/27

SLIDE 6

U N I V E R S I T Y O F C O P E N H A G E N N I E L S B O H R I N S T I T U T E

Wealth of measurements

AA at LHC energies

Xe–Xe & Pb–Pb
From

√sNN = 2.76 TeV to 5.44 TeV

Here ALICE

−3.5 < η < 5

Also ATLAS, CMS

Pb–Pb, √sNN = 2.76 TeV

PLB754(2016)373-385

Pb–Pb, √sNN = 5.02 TeV

PLB772(2017)567-577

Xe–Xe, √sNN = 5.44 TeV

PLB790(2019)35 Slide 5/30 — C.H.Christensen —

dNch dη

— COST’19 — 2019/02/27

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U N I V E R S I T Y O F C O P E N H A G E N N I E L S B O H R I N S T I T U T E

Wealth of measurements

d–Au & p–Pb results

From

√sNN = 200 GeV to 5.02 TeV

Here, PHOBOS &

ALICE |η| < 5.3

−5 < η < 3.5, resp.

Also BRAHMS,

ALTAS, CMS

d–Au, √sNN = 200 GeV

PRC83(2011)024913

p–Pb, √sNN = 5.02 TeV

5 10 15 20 25 30 35 40

dNch/dη η

5
4
3
2
1

1 2 3 4 5

ALICE Preliminary

Comb. Uncorr.syst.unc. Corr.syst.unc. p-Pb√sNN = 5.02TeV(ZNA) 0- 5% 5-10% 10-20% 20-40% 40-60% 60-80% 80-100%

ALI-PREL-99869 ALI-PREL-99869 ALI-PREL-99869 ALI-PREL-99869 Slide 6/30 — C.H.Christensen —

dNch dη

— COST’19 — 2019/02/27

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U N I V E R S I T Y O F C O P E N H A G E N N I E L S B O H R I N S T I T U T E

Models have room for improvement

Generally OK

near η = 0

Most deviate

for |η| > 0

PLB754(2016)373-385 EPJC76(2016)502 JHEP10(2018)134 PLB790(2019)35 Slide 7/30 — C.H.Christensen —

dNch dη

— COST’19 — 2019/02/27

SLIDE 9

U N I V E R S I T Y O F C O P E N H A G E N N I E L S B O H R I N S T I T U T E

Models have room for improvement

Generally OK

near η = 0

Most deviate

for |η| > 0

Good news for

Lund: Pythia/Angantyr not the worst

PLB754(2016)373-385 EPJC76(2016)502 JHEP10(2018)134 PLB790(2019)35 Slide 7/30 — C.H.Christensen —

dNch dη

— COST’19 — 2019/02/27

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U N I V E R S I T Y O F C O P E N H A G E N N I E L S B O H R I N S T I T U T E

The (not-so) transparent glass

Fit CGC

expression

PLB523(2001)79-87

Good fit of

dNch dη

λ parameter
ff

However . . .

6 − 4 − 2 − 2 4 6 y, η 1000 2000 3000 dNch/d(y, η) Pb-Pb √sNN = 5.02 Te V 0 − 5% Pb-Pb √sNN = 2.76 Te V 0 − 5% Au-Au √sNN = 200 GeV 0 − 6% Au-Au √sNN = 130 GeV 0 − 6%

Phys.Lett.B523(2001)79-87 CGC dNch/dη fit 0.95 C.L.

0.25 0.3 0.35 λ 1000 2000 3000

CGC exp. λ 0.95 C.L.

Slide 8/30 — C.H.Christensen —

dNch dη

— COST’19 — 2019/02/27

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U N I V E R S I T Y O F C O P E N H A G E N N I E L S B O H R I N S T I T U T E

The (not-so) transparent glass

Fit CGC

expression

PLB523(2001)79-87

Good fit of

dNch dη

λ parameter
ff

However . . .

6 − 4 − 2 − 2 4 6 y, η 1000 2000 3000 dNch/d(y, η) Pb-Pb √sNN = 5.02 Te V 0 − 5% Pb-Pb √sNN = 2.76 Te V 0 − 5% Au-Au √sNN = 200 GeV 0 − 6% Au-Au √sNN = 130 GeV 0 − 6%

Phys.Lett.B523(2001)79-87 CGC dNch/dη fit 0.95 C.L. CGC dNch/dy from dNch/dη

0.25 0.3 0.35 λ 1000 2000 3000

CGC exp. λ 0.95 C.L.

Sharp peak in dNch

dy

at y = 0

Caveat: older paper, but mechanism the same AFAIK

Slide 8/30 — C.H.Christensen —

dNch dη

— COST’19 — 2019/02/27

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U N I V E R S I T Y O F C O P E N H A G E N N I E L S B O H R I N S T I T U T E

Normality and transparency

BRAHMS Results:

dNπ,K

dy

∼ N[0, σ]

similar for p

Small decrease in pT
ver y

similar for p,p

Au–Au,0 − 10% √sNN = 200 GeV

PRL94(2005)032301

dN/dy

100 200 300

beam

y

(a)

+

π

π

+

K- K

4) × ( 4) × (

y

1 2 3 4 5

> [GeV/c]

T

<p

0.4 0.6 0.8

(b)

Slide 9/30 — C.H.Christensen —

dNch dη

— COST’19 — 2019/02/27

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U N I V E R S I T Y O F C O P E N H A G E N N I E L S B O H R I N S T I T U T E

Normality and transparency

BRAHMS Results:

dNπ,K

dy

∼ N[0, σ]

similar for p

Small decrease in pT
ver y

similar for p,p

Small rapidity loss δy
ver SPS energies

Increased transparency for √sNN 17 GeV

Au–Au,0 − 10% √sNN = 200 GeV

PRL94(2005)032301

Au–Au,Pb–Pb, central

PLB677(2009)267-271

dN/dy

100 200 300

beam

y

(a)

+

π

π

+

K- K

4) × ( 4) × (

y

1 2 3 4 5

> [GeV/c]

T

<p

0.4 0.6 0.8

(b)

p

y

1 2 3 4 5 6 7 8 9 10

y> δ Rapidity loss <

0.5 1 1.5 2 2.5 3 3.5

E917 E802/E866 NA49 (PbPb) BRAHMS 62.4 GeV BRAHMS 200 GeV

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 10 20 30 40 50 60

net-baryons 62.4 GeV

Slide 9/30 — C.H.Christensen —

dNch dη

— COST’19 — 2019/02/27

SLIDE 14

U N I V E R S I T Y O F C O P E N H A G E N N I E L S B O H R I N S T I T U T E

Normality and transparency

BRAHMS Results:

dNπ,K

dy

∼ N[0, σ]

similar for p

Small decrease in pT
ver y

similar for p,p

Small rapidity loss δy
ver SPS energies

Increased transparency for √sNN 17 GeV

Slow pT

increase with √s

PLB693(2010)53-68

Au–Au,0 − 10% √sNN = 200 GeV

PRL94(2005)032301

Au–Au,Pb–Pb, central

PLB677(2009)267-271

dN/dy

100 200 300

beam

y

(a)

+

π

π

+

K- K

4) × ( 4) × (

y

1 2 3 4 5

> [GeV/c]

T

<p

0.4 0.6 0.8

(b)

p

y

1 2 3 4 5 6 7 8 9 10

y> δ Rapidity loss <

0.5 1 1.5 2 2.5 3 3.5

E917 E802/E866 NA49 (PbPb) BRAHMS 62.4 GeV BRAHMS 200 GeV

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 10 20 30 40 50 60

net-baryons 62.4 GeV

Slide 9/30 — C.H.Christensen —

dNch dη

— COST’19 — 2019/02/27

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U N I V E R S I T Y O F C O P E N H A G E N N I E L S B O H R I N S T I T U T E

Transforming to rapidity

ALICE Results:

dNch

dy ∼ N[0, σ] in Pb–Pb

For √sNN = 2.76 TeV
and √sNN = 5.02 TeV
Landau-like hydrodynamics

not consistent

“Extended longitudinal scaling” Pb–Pb,0 − 5% √sNN = 2.76 TeV

PLB726(2013)610-622

Pb–Pb,0 − 5% √sNN = 5.02 TeV

PLB754(2016)373-385

y

6
5
4
3
2
1

1 2 3 4 5 6 y /d

ch

N d 200 400 600 800 1000 1200 1400 1600 1800 2000 2200

ALICE 0-5% most central Gaussian+Gaussian Fit Gaussian Fit Landau-Carruthers Landau-Wong

[GeV]

NN

s 10

2

10

3

10

Carrut.

σ /

data

σ 1 1.5 AGS SPS RHIC LHC

π

+

π All charged particles 500 1000 1500 2000 2500 dNch/dy y

5
4
3
2
1

1 2 3 4 5 ALICE Data (symmetrised) Reflected

Uncorr. syst. unc.
Corr. syst. unc.

Gaussian fit Double-Gaussian fit Landau-Carruthers Landau-Wong √sNN = 5.02TeV 0–5% Pb–Pb

Landau-Carruthers:

dNch dy

∼ N

0, log √sNN/(2mp)
Landau-Wong:

dNch dy

∝ e

y2

beam−y2

Slide 10/30 — C.H.Christensen —

dNch dη

— COST’19 — 2019/02/27

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U N I V E R S I T Y O F C O P E N H A G E N N I E L S B O H R I N S T I T U T E

Fill up phase-space

A–A,central

PLB754(2016)373-385

√sNN [GeV]

10 102 103

σdNX/dy/σL−C

1 1.5

AGS SPS RHIC LHC √sNN [GeV]

10 102 103

σdNX/dy/(2ybeam)

0.2 0.3

π+ h±PHOBOS π− h±BRAHMS h±ALICE

Nch production fill phase-space for √sNN 17 GeV

Slide 11/30 — C.H.Christensen —

dNch dη

— COST’19 — 2019/02/27

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U N I V E R S I T Y O F C O P E N H A G E N N I E L S B O H R I N S T I T U T E

Take-away from these results

Lots of dNch

dη

measurements

Au–Au, Pb–Pb, Xe–Xe
d–Au, p–Pb
pp, pp
√s, √sNN ∈ {0.9, 2.76, 5.02, 5.44} TeV
Challenge for theory

Slide 12/30 — C.H.Christensen —

dNch dη

— COST’19 — 2019/02/27

SLIDE 18

U N I V E R S I T Y O F C O P E N H A G E N N I E L S B O H R I N S T I T U T E

Take-away from these results

Lots of dNch

dη

measurements

Au–Au, Pb–Pb, Xe–Xe
d–Au, p–Pb
pp, pp
√s, √sNN ∈ {0.9, 2.76, 5.02, 5.44} TeV
Challenge for theory
Shift at end of SPS (√sNN 17 TeV)
(Almost) Net-baryon free over extended rapidity

does not imply flat dNch

dη

Nch fill up phase-space

Particles more spread-out

AFAICT: Easier for theory?

Slide 12/30 — C.H.Christensen —

dNch dη

— COST’19 — 2019/02/27

SLIDE 19

U N I V E R S I T Y O F C O P E N H A G E N N I E L S B O H R I N S T I T U T E

Power-law systematic of Nch production

Mid rapidity dNch

dη

vs √sNN

Total Nch vs √sNN
Ntotal

ch

increase faster than

dNch

dη

|η|<0.5
Both faster than pp(pp)

〉 η /d

ch

N d 〈 〉

part

N 〈 2

2 4 6 8 10 12 14

), NSD p pp(p AA, central ALICE ALICE Xe-Xe CMS ALICE Pb-Pb CDF CMS UA5 ATLAS UA1 PHENIX STAR PHOBOS BRAHMS ), INEL p pp(p STAR ALICE NA50 CMS UA5 PHOBOS ISR pA(dA), NSD ALICE PHOBOS

| < 0.5 η |

0.103(2)

s ∝

0.155(4)

s ∝

0.114(3)

s ∝

(GeV)

NN

s

1 10

2

10

3

10

4

10

tot ch

N 〉

part

N 〈 2

20 40 60 80 100 120

AA, central ALICE Xe-Xe ALICE Pb-Pb PHOBOS BRAHMS NA50 E895 s log

0.123(6)

s ∝ PLB790(2019)35 Slide 13/30 — C.H.Christensen —

dNch dη

— COST’19 — 2019/02/27

SLIDE 20

U N I V E R S I T Y O F C O P E N H A G E N N I E L S B O H R I N S T I T U T E

Per participant production

Consistent increase from

pp to most central

ALICE:

dNch

dη

|η|<0.5 and

Ntotal

ch

scaled by s0.155 and s0.123 log(s) to match Xe–Xe

〉

part

N

〈

1 2 3 4 5 6

〉

part

N

〈

⁄

0.5 <  η 



〉

η /d

ch

N d

〈

50 100 150 200 250 300 350 400

CMS

CMS XeXe 5.44 TeV ALICE XeXe 5.44 TeV PbPb 5.02 TeV PbPb 2.76 TeV PbPb 2.76 TeV ) unc.

〉

part

N

〈

total (expt. +

expt. unc.

arXiv:1902.03603

100 200 300 400

〉 η /d

ch

N d 〈 〉

part

N 〈 2

4 6 8 10 12

| < 0.5 η | ALICE

= 5.44 TeV

NN

s Xe-Xe, 1.02) × = 5.02 TeV (

NN

s Pb-Pb, 1.02) × = 5.02 TeV (

NN

s p-Pb, 1.02) × = 5.02 TeV (

NN

s pp, 1.23) × = 2.76 TeV (

NN

s Pb-Pb, 1.15) × = 2.76 TeV (

NN

s pp,

RHIC (PHOBOS)

2.73) × = 0.2 TeV (

NN

s Au-Au, 2.73) × = 0.2 TeV (

NN

s Cu-Cu,

〉

part

N 〈

100 200 300 400

ch tot

N 〉

part

N 〈 2

40 60 80 100 120

3.77) × = 0.2 TeV (

NN

s Au-Au, 3.77) × = 0.2 TeV (

NN

s Cu-Cu,

RHIC (PHOBOS) ALICE

= 5.44 TeV

NN

s Xe-Xe, 1.03) × = 5.02 TeV (

NN

s Pb-Pb, 1.29) × = 2.76 TeV (

NN

s Pb-Pb,

PLB790(2019)35 Slide 14/30 — C.H.Christensen —

dNch dη

— COST’19 — 2019/02/27

SLIDE 21

U N I V E R S I T Y O F C O P E N H A G E N N I E L S B O H R I N S T I T U T E

Per participant production

Consistent increase from

pp to most central

ALICE:

dNch

dη

|η|<0.5 and

Ntotal

ch

scaled by s0.155 and s0.123 log(s) to match Xe–Xe

However, “rapid” increase

for most central (Npart ≈ 2A).

Also “up-tick” in total Nch

100 200 300 400

〉 η /d

ch

N d 〈 〉

part

N 〈 2

4 6 8 10 12

| < 0.5 η | ALICE

= 5.44 TeV

NN

s Xe-Xe, 1.02) × = 5.02 TeV (

NN

s Pb-Pb, 1.02) × = 5.02 TeV (

NN

s p-Pb, 1.02) × = 5.02 TeV (

NN

s pp, 1.23) × = 2.76 TeV (

NN

s Pb-Pb, 1.15) × = 2.76 TeV (

NN

s pp,

RHIC (PHOBOS)

2.73) × = 0.2 TeV (

NN

s Au-Au, 2.73) × = 0.2 TeV (

NN

s Cu-Cu,

〉

part

N 〈

100 200 300 400

ch tot

N 〉

part

N 〈 2

40 60 80 100 120

3.77) × = 0.2 TeV (

NN

s Au-Au, 3.77) × = 0.2 TeV (

NN

s Cu-Cu,

RHIC (PHOBOS) ALICE

= 5.44 TeV

NN

s Xe-Xe, 1.03) × = 5.02 TeV (

NN

s Pb-Pb, 1.29) × = 2.76 TeV (

NN

s Pb-Pb,

PLB790(2019)35 Slide 14/30 — C.H.Christensen —

dNch dη

— COST’19 — 2019/02/27

SLIDE 22

U N I V E R S I T Y O F C O P E N H A G E N N I E L S B O H R I N S T I T U T E

Production versus“natural centrality”

Scale abscissa by

max

Npart

= 2A

ALICE: Subtract 2 to line up pp

A 2

⁄

〉

part

N

〈

1 2 3 4 5 6

〉

part

N

〈

⁄

0.5 <  η 



〉

η /d

ch

N d

〈

0.2 0.4 0.6 0.8 1

CMS

CMS XeXe 5.44 TeV ALICE XeXe 5.44 TeV PbPb 5.02 TeV PbPb 2.76 TeV PbPb 2.76 TeV ) unc.

〉

part

N

〈

total (expt. +

expt. unc.

arXiv:1902.03603

0.2 0.4 0.6 0.8 1

〉 η /d

ch

N d 〈 〉

part

N 〈 2

4 6 8 10 12

| < 0.5 η | ALICE

= 5.44 TeV

NN

s Xe-Xe, 1.02) × = 5.02 TeV (

NN

s Pb-Pb, 1.02) × = 5.02 TeV (

NN

s p-Pb, 1.02) × = 5.02 TeV (

NN

s pp, 1.23) × = 2.76 TeV (

NN

s Pb-Pb, 1.15) × = 2.76 TeV (

NN

s pp,

RHIC (PHOBOS)

2.73) × = 0.2 TeV (

NN

s Au-Au, 2.73) × = 0.2 TeV (

NN

s Cu-Cu,

) A

2) / (2

〉

part

N 〈 (

0.2 0.4 0.6 0.8 1

ch tot

N 〉

part

N 〈 2

40 60 80 100 120

3.77) × = 0.2 TeV (

NN

s Au-Au, 3.77) × = 0.2 TeV (

NN

s Cu-Cu,

RHIC (PHOBOS) ALICE

= 5.44 TeV

NN

s Xe-Xe, 1.03) × = 5.02 TeV (

NN

s Pb-Pb, 1.29) × = 2.76 TeV (

NN

s Pb-Pb,

PLB790(2019)35 Slide 15/30 — C.H.Christensen —

dNch dη

— COST’19 — 2019/02/27

SLIDE 23

U N I V E R S I T Y O F C O P E N H A G E N N I E L S B O H R I N S T I T U T E

dNch dη

versus “natural centrality”

PHOBOS Result:

Constant Npart

show deviations

Constant

Npart/(2A) show scaling

PRL102(2009)142301 Slide 16/30 — C.H.Christensen —

dNch dη

— COST’19 — 2019/02/27

SLIDE 24

U N I V E R S I T Y O F C O P E N H A G E N N I E L S B O H R I N S T I T U T E

dNch dη

versus “natural centrality”

PHOBOS Result:

Constant Npart

show deviations

Constant

Npart/(2A) show scaling How can that be?

participants do not know “natural centrality”

PRL102(2009)142301 Slide 16/30 — C.H.Christensen —

dNch dη

— COST’19 — 2019/02/27

SLIDE 25

U N I V E R S I T Y O F C O P E N H A G E N N I E L S B O H R I N S T I T U T E

dNch dη

versus “natural centrality”

PHOBOS Result:

Constant Npart

show deviations

Constant

Npart/(2A) show scaling How can that be?

participants do not know “natural centrality”

Important: Npart from Glauber i.e., Model

PRL102(2009)142301 Slide 16/30 — C.H.Christensen —

dNch dη

— COST’19 — 2019/02/27

SLIDE 26

U N I V E R S I T Y O F C O P E N H A G E N N I E L S B O H R I N S T I T U T E

Glauber and Glauber–Gribov

Glauber:

Inputs:
Charge-distribution

(e.g., 3pF or 3pG)

Nucleon–nucleon

cross-section σNN

Black-disc:

P(bNN) = Θ(2r − bNN)

Impact parameter b
Outputs:
Npart, Ncoll, . . .
Nucleon distribution

Glauber–Gribov

Colour-state fluctuations

Fluctuation of σNN (δσNN)

15 − 10 − 5 − 5 10 15 (fm) x 10 − 5 − 5 10 (fm) z

Event # 8 = 10.4 fm b = 118

part

N = 261

coll

N = 69.7 mb

NN

σ

Normal Gribov:

Sample σNN once per event
OK for p–A, tricky for A–A

Slide 17/30 — C.H.Christensen —

dNch dη

— COST’19 — 2019/02/27

SLIDE 27

U N I V E R S I T Y O F C O P E N H A G E N N I E L S B O H R I N S T I T U T E

Individual nucleon fluctuations

Allow each nucleon to fluctuate in “size”

Simple approach, Angantyr/PYTHIA more evolved

Calculate σAB for any two nucleons A and B
Fix to reproduce σNN = σAB

not necessarily P(σNN)

Nucleon “sizes” fixed throughout

Frozen colour state

Based on TGlauberMC

PRC97(2017)054910

Work-in-progress: Apply skepticism here

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dNch dη

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SLIDE 28

U N I V E R S I T Y O F C O P E N H A G E N N I E L S B O H R I N S T I T U T E

“Up-tick” in AA collisions

Ansatz: Take Ncoll as proxy for dNch

dη

r total Nch

Pb–Pb, σNN = 70mb (√sNN = 5.02 TeV)

50 100 150 200 250 300 350 400

part

N 2 4 6 8 10 12 14 16 〉 /2)

part

N /(

coll

N 〈

=70.0mb

NN

σ Pb-Pb, No fluctuations Gribov Per-nucleon =0.5mb

NN

σ δ =0.5mb

NN

σ δ =1mb

NN

σ δ =1mb

NN

σ δ =2mb

NN

σ δ =2mb

NN

σ δ =3mb

NN

σ δ =3mb

NN

σ δ

Xe–Xe, σNN = 68.4mb (√sNN = 5.44 TeV)

50 100 150 200 250

part

N 2 4 6 8 10 12 14 〉 /2)

part

N /(

coll

N 〈

=68.4mb

NN

σ Xe-Xe, No fluctuations Gribov Per-nucleon =0.5mb

NN

σ δ =0.5mb

NN

σ δ =1mb

NN

σ δ =1mb

NN

σ δ =2mb

NN

σ δ =2mb

NN

σ δ =3mb

NN

σ δ =3mb

NN

σ δ

Glauber–Gribov: “up-tick”
individual nucleon fluctuation: More smooth increase
“Up-tick” possible sign of σNN fluctuations

Fluctuations a la p–A

Slide 19/30 — C.H.Christensen —

dNch dη

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SLIDE 29

U N I V E R S I T Y O F C O P E N H A G E N N I E L S B O H R I N S T I T U T E

So where are we?

Lots of result on Nch production
Cu–Cu,Xe–Xe,Au–Au,Pb–Pb,d–Au,p–Pb,pp
√s, √sNN ∈ {0.9, 2.76, 5.02, 5.44, 7, 8, 13} TeV

Slide 20/30 — C.H.Christensen —

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SLIDE 30

U N I V E R S I T Y O F C O P E N H A G E N N I E L S B O H R I N S T I T U T E

So where are we?

Lots of result on Nch production
Cu–Cu,Xe–Xe,Au–Au,Pb–Pb,d–Au,p–Pb,pp
√s, √sNN ∈ {0.9, 2.76, 5.02, 5.44, 7, 8, 13} TeV
Above top SPS
Normal distributed in measured range
Fill up phase space (wide dNch

dy )

√sNN-scaling pretty solid

Slide 20/30 — C.H.Christensen —

dNch dη

— COST’19 — 2019/02/27

SLIDE 31

U N I V E R S I T Y O F C O P E N H A G E N N I E L S B O H R I N S T I T U T E

So where are we?

Lots of result on Nch production
Cu–Cu,Xe–Xe,Au–Au,Pb–Pb,d–Au,p–Pb,pp
√s, √sNN ∈ {0.9, 2.76, 5.02, 5.44, 7, 8, 13} TeV
Above top SPS
Normal distributed in measured range
Fill up phase space (wide dNch

dy )

√sNN-scaling pretty solid
Nch fluctuate up in central A–A
Significant σNN fluctuations at small b?

Similar to p–Pb

“Up-tick” not centrality bias

Probably need better Glauber or Core-Corona approach?

Npart “scaling” not necessarily broken

But Ncoll strongly dependent on Npart, so hard to tell

Slide 20/30 — C.H.Christensen —

dNch dη

— COST’19 — 2019/02/27

SLIDE 32

U N I V E R S I T Y O F C O P E N H A G E N N I E L S B O H R I N S T I T U T E

So where are we?

Lots of result on Nch production
Cu–Cu,Xe–Xe,Au–Au,Pb–Pb,d–Au,p–Pb,pp
√s, √sNN ∈ {0.9, 2.76, 5.02, 5.44, 7, 8, 13} TeV
Above top SPS
Normal distributed in measured range
Fill up phase space (wide dNch

dy )

√sNN-scaling pretty solid
Nch fluctuate up in central A–A
Significant σNN fluctuations at small b?

Similar to p–Pb

“Up-tick” not centrality bias

Probably need better Glauber or Core-Corona approach?

Npart “scaling” not necessarily broken

But Ncoll strongly dependent on Npart, so hard to tell

Nch production still a challenge

Slide 20/30 — C.H.Christensen —

dNch dη

— COST’19 — 2019/02/27

SLIDE 33

U N I V E R S I T Y O F C O P E N H A G E N N I E L S B O H R I N S T I T U T E

Back-ups

Slide 21/30 — C.H.Christensen —

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— COST’19 — 2019/02/27

SLIDE 34

U N I V E R S I T Y O F C O P E N H A G E N N I E L S B O H R I N S T I T U T E

Limiting fragmentation

dNch

dη

at large |η| independent of √sNN.

Holds in pp and Cu–Cu
Study not feasible for

√sNN > 2.76 TeV

2 4 6 8 10 0-5 % /2) 〉

part

N 〈 /( η /d

ch

N d 2 4 6 8 10 10-20 %

Double Gaussian fit Linear extrapolation beam

y

η

= ' η

8
7
6
5
4
3
2
1

2 4 6 8 10

ALICE 2.76 TeV BRAHMS Si 200 GeV BRAHMS BB 200 GeV PHOBOS 200 GeV PHOBOS 62 GeV

20-30 % Slide 22/30 — C.H.Christensen —

dNch dη

— COST’19 — 2019/02/27

SLIDE 35

U N I V E R S I T Y O F C O P E N H A G E N N I E L S B O H R I N S T I T U T E

Comparing to pp

rX =

dNch dη

X
dNch

dη

pp

rPb–Pb

10 102

η

5
4
3
2
1

1 2 3 4 5 ALICE Pb–Pb, pp √sNN = 5.02TeV 0– 5% 5–10% 10–20% 20–30% 30–40% 40–50% 50–60% 60–70% 70–80% 80–90% Data (symmetrised)

Uncorr. syst. unc.
Corr. syst. unc.

Preliminary ALI-PREL-118148

Pb–Pb

×102 over pp
Increase as η → 0

Slide 23/30 — C.H.Christensen —

dNch dη

— COST’19 — 2019/02/27

SLIDE 36

U N I V E R S I T Y O F C O P E N H A G E N N I E L S B O H R I N S T I T U T E

Comparing to pp

2rx Npart = 2 Npart dNch dη

X
dNch

dη

pp

rPb–Pb/(Npart/2)

0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

η

5
4
3
2
1

1 2 3 4 5 ALICE Preliminary Pb–Pb, pp √sNN = 5.02TeV 0– 5% 5–10% 10–20% 20–30% 30–40% 40–50% 50–60% 60–70% 70–80% 80–90% Data (symmetrised)

Uncorr. syst. unc.
Corr. syst. unc.

ALI-PREL-118161

Pb–Pb

×102 over pp
Increase as η → 0
Scale by 2/Npart (Glauber)
Collimation near η = 0

Slide 23/30 — C.H.Christensen —

dNch dη

— COST’19 — 2019/02/27

SLIDE 37

U N I V E R S I T Y O F C O P E N H A G E N N I E L S B O H R I N S T I T U T E

Comparing to pp

2rx Npart = 2 Npart dNch dη

X
dNch

dη

pp

rPb–Pb/(Npart/2)

0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

η

5
4
3
2
1

1 2 3 4 5 ALICE Preliminary Pb–Pb, pp √sNN = 5.02TeV 0– 5% 5–10% 10–20% 20–30% 30–40% 40–50% 50–60% 60–70% 70–80% 80–90% Data (symmetrised)

Uncorr. syst. unc.
Corr. syst. unc.

ALI-PREL-118161

Pb–Pb

×102 over pp
Increase as η → 0
Scale by 2/Npart (Glauber)
Collimation near η = 0

rp–Pb

2 4 6 8 10 12 14

η

5
4
3
2
1

1 2 3 4 5 ALICE Preliminary p–Pb (V0A), pp √sNN = 5.02TeV 0– 5% 5–10% 10–20% 20–40% 40–60% 60–80% 80–100% Data

Uncorr. syst. unc.
Corr. syst. unc.

ALI-PREL-118157

p–Pb

Centrality: V0A
×10 over pp
Near-linear increase from

p- to Pb-going side

Slide 23/30 — C.H.Christensen —

dNch dη

— COST’19 — 2019/02/27

SLIDE 38

U N I V E R S I T Y O F C O P E N H A G E N N I E L S B O H R I N S T I T U T E

Nuclear modification

rX Ncoll = 1 Ncoll dNch dη

X
dNch

dη

pp

rPb–Pb/Ncoll

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

η

5
4
3
2
1

1 2 3 4 5 ALICE Preliminary Pb–Pb, pp √sNN = 5.02TeV 0– 5% 5–10% 10–20% 20–30% 30–40% 40–50% 50–60% 60–70% 70–80% 80–90% Data (symmetrised)

Uncorr. syst. unc.
Corr. syst. unc.

ALI-PREL-118165

ր as η → 0

rp–Pb/NPb−side

coll 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

η

5
4
3
2
1

1 2 3 4 5 ALICE Preliminary p–Pb (ZNA), pp √sNN = 5.02TeV 0– 5% 5–10% 10–20% 20–40% 40–60% 60–80% 80–100% Data

Uncorr. syst. unc.
Corr. syst. unc.

ALI-PREL-118169

N.B.: Centrality ZNA
Independent

proton-nucleon scattering

PRC72(2005)034907 PRL39(1977)1120

Similar level in ion for most central Pb–Pb events.

similar fluctuations in central Pb–Pb as in p–Pb?

Slide 24/30 — C.H.Christensen —

dNch dη

— COST’19 — 2019/02/27

SLIDE 39

U N I V E R S I T Y O F C O P E N H A G E N N I E L S B O H R I N S T I T U T E

Angantyr results

Same trends as data for

both dNch/dη||η|<0.5 and Ntotal

ch

Sophisticated σNN

fluctuations

“Up-tick” not centrality bias

Slide 25/30 — C.H.Christensen —

dNch dη

— COST’19 — 2019/02/27

SLIDE 40

U N I V E R S I T Y O F C O P E N H A G E N N I E L S B O H R I N S T I T U T E

Quark participants and component models

Nα

part over-shoots, no

“up-tick”

Nβ

coll over- and

under-shoots, no “up-tick”

f Npart + (1 − f )Ncoll
ver- and under-shoots, no

“up-tick”

Core-Corona over-shoots,

no “up-tick”

〉

part

N 〈

100 200 300 400

〉 η /d

ch

N d 〈 〉

q-part

N 〈 µ , 〉 η /d

ch

N d 〈 〉

part

N 〈 2

4 6 8 10 12 14

= 5.44 TeV

NN

s Xe-Xe = 5.02 TeV

NN

s Pb-Pb

part

N

part

N =3.5 µ =3,

q

N =3

q

N =4.3 µ =5,

q

N =5

q

N

| < 0.5 η ALICE, |

α part

N

β coll

N

coll

N ) f +(1-

part

N f

core part

N

core

〉 η /d

ch

N d 〈 +

corona part

N

pp

〉 η /d

ch

N d 〈

Quark participant scaling not much clear than Npart
Rise at low Npart?
Still rise at high Npart

σqq fluctuations?

Slide 26/30 — C.H.Christensen —

dNch dη

— COST’19 — 2019/02/27

SLIDE 41

U N I V E R S I T Y O F C O P E N H A G E N N I E L S B O H R I N S T I T U T E

Express dNch

dη

in terms of dNch

dy

500 1000 1500 2000 2500 dNch/dy y

5
4
3
2
1

1 2 3 4 5 ALICE Data (symmetrised) Reflected

Uncorr. syst. unc.
Corr. syst. unc.

Gaussian fit Double-Gaussian fit Landau-Carruthers Landau-Wong √sNN = 5.02TeV 0–5% Pb–Pb ALI-PUB-115105

PLB772(2017)567-577

Direct measurement
f dNch

dy :

Gaussian in measured region

Via mean Jacobian:

Gaussian in measured region dNch dy = 1 β dNch dη y ≈ η − cos ϑ 2a2 β ≈ 1

1 + 1/(a2 cosh2 η)

a: effective pT/m

pp and Pb–Pb Ansatz:

dNch/dη=βA/( √ 2πσ)e−y2/(2σ)

p–Pb Ansatz: A → (αy + a)

dNch/dη=β(αy+A)/( √ 2πσ)e−y2/(2σ)

Fit dNch

dη

to extract σ, effective pT/m

Slide 27/30 — C.H.Christensen —

dNch dη

— COST’19 — 2019/02/27

SLIDE 42

U N I V E R S I T Y O F C O P E N H A G E N N I E L S B O H R I N S T I T U T E

σy and effective pT/m

Npart

10 102

σdNch/dy

3 4 5 6 7 ALICE Preliminary, √sNN = 5.02TeV pp p–Pb Pb–Pb Pb–Pb (arXiv:1612.08966) DATA EPOS-LHC dNch/dy EPOS-LHC ALI-PREL-118360

Npart

10 102

Effective pT/m

1.4 1.6 1.8 2 2.2 2.4 2.6 2.8 ALICE Preliminary, √sNN = 5.02TeV pp p–Pb Pb–Pb DATA EPOS-LHC

pT/m||y|<0.5 EPOS-LHC

Effective pT/m × m

0.3 0.35 0.4 0.45 0.5 0.55 0.6 ALI-PREL-118372

σ decrease

Collimation of production

Peripheral similar

σ to pp

Limiting fragmentation

Effective pT/m

increase for Pb–Pb

consistent with pp

Slide 28/30 — C.H.Christensen —

dNch dη

— COST’19 — 2019/02/27

SLIDE 43

U N I V E R S I T Y O F C O P E N H A G E N N I E L S B O H R I N S T I T U T E

Back-of-the-envelope initial energy density

Bjorken formula:

εBjτ = 1/ST dET/dy

with

dET/dy ≈ 2mTdNch/dy 2m

1 + (pT/m)2 dNch/dy
ST from Glauber
part. Full area
part. Overlap

part.: part.:

Npart 10 102 ST (fm2) 1 10 102 √sNN = 5.02TeV Pb–Pb p–Pb participants participants SX1(2015)13

ALI-SIMUL-118412

εBjτ εLBτ ≡ 1/S∪,∩

T

2

1 + (pT/m)2 dNch/dy

Slide 29/30 — C.H.Christensen —

dNch dη

— COST’19 — 2019/02/27

SLIDE 44

U N I V E R S I T Y O F C O P E N H A G E N N I E L S B O H R I N S T I T U T E

The lower-bound of εBj

Npart

10 102

εLBτ (GeV/fm2)

10−1 1 10 102

ALICE Preliminary, √sNN = 5.02TeV pp p–Pb Pb–Pb Pb–Pb, √sNN = 2.76TeV Glauber area ∪part. ∩part. ALI-PREL-118408

PRC94(2016)034903

Fixed energy density at fixed Npart

Except for central p–Pb

For ∪ part, large increase over pp
If same initial ε in systems, then similar final state effects?

Slide 30/30 — C.H.Christensen —

dNch dη

— COST’19 — 2019/02/27