Feasibility studies of conserved charge fluctuations in Au-Au - - PowerPoint PPT Presentation

SLIDE 1

Feasibility studies of conserved charge fluctuations in Au-Au collisions with CBM

Subhasis Samanta (for the CBM Collaboration)

National Institute of Science Education and Research, HBNI, Jatni, India

Outline ⋆ Introduction ⋆ CBM experiment ⋆ Analysis details ⋆ Results

Net-proton cumulants Net-charge cumulants

⋆ Summary

S Samanta (For the CBM Collaboration) Quark Matter - 2019, Wuhan, China 1 / 14

SLIDE 2

QCD phase diagram

⋆ Study QCD phase diagram at high net-baryon density

At high net-baryon density and low temperature, first order phase transition is expected which will end at a critical point (CP) CBM program supplements the Beam Energy Scan Program at RHIC, NA61 at SPS, NICA at JINR

Ref: CBM: EPJA 53, 60 (2017); PRC 74, 047901 (2006) S Samanta (For the CBM Collaboration) Quark Matter - 2019, Wuhan, China 2 / 14

SLIDE 3

Observables for CP search

Cumulants C1 = Nq, C2 =

• (δNq)2

, C3 =

• (δNq)3

, C4 =

• (δNq)4

− 3

• (δNq)22

Nq = Nq+ − Nq− and δNq = Nq −

• Nq
• q can be any conserved quantum number

(net-baryon, net-charge, net-strangeness etc.)

Mean, variance, skewness, kurtosis M = C1, σ2 = C2, S = C3

σ3 ,

κ = C4

σ4

⋆ Higher moments of conserved quantities are sensitive to correlation length

• (δNq)2

∼ ζ2

• (δNq)3

∼ ζ4.5

• (δNq)4

∼ ζ7 ⋆ Non-monotonic variations of Sσ = C3/C2, κσ2 = C4/C2 with beam energy are believed to be good signatures of CP

Ref: STAR: PRL 112, 032302 (2014); PRL 102, 032301 (2009) S Samanta (For the CBM Collaboration) Quark Matter - 2019, Wuhan, China 3 / 14

SLIDE 4

CBM experiment

⋆ Fixed target experiment ⋆ SIS 100: Au + Au collision, √sNN = 2.7 − 4.9 GeV ⋆ High interaction rate ⋆ High statistics data ⋆ Density in the center of the fireball expected to exceed few times greater than density of nucleus Challenges of higher moments measurements at CBM ⋆ Particle identification ⋆ Non-trivial variations of efficiency × acceptance with pT and rapidity (proper method of corrections needed) ⋆ Proper vertex identification in multiple collisions

Ref: CBM overview talk at QM2019 by Viktor Klochkov; EPJA 53, 60 (2017); The CBM Physics Book, Lect. Notes Phys. 814, Springer 2011; PRC 75 (2007) 034902 S Samanta (For the CBM Collaboration) Quark Matter - 2019, Wuhan, China 4 / 14

SLIDE 5

Simulation details

⋆ Event generators: UrQMD ⋆ Collision: Au+Au ⋆ Energy: Elab = 10 AGeV (√sNN = 4.72 GeV) ⋆ Events: 5 M (minimum bias) Detectors used: MVD, STS, RICH, TOF MVD: Vertex information STS: Momentum information RICH: Electron identification TOF: Hadron identification Detector acceptance: 1.5 < η < 3.8 (25◦ > θ > 2.5◦) sis100 setup

S Samanta (For the CBM Collaboration) Quark Matter - 2019, Wuhan, China 5 / 14

SLIDE 6

Particle identification using TOF Centrality selection using STS

ch

N

20 40 60 80 100 120 140

• No. of events

1 10

2

10

3

10

4

10

5

10 0 - 5 % 5 - 10 % 10 - 20 % 20 - 30 % 30 - 40 % 40 - 50 % 50 - 60 %

= 10 AGeV

lab

Au + Au, E UrQMD + CBM GEANT3 )

4

/c

2

< 0.4 (GeV

2

m

(Multiplicities are uncorrected for efficiency and acceptance)

⋆ Clean particle identification for bulk properties studies ⋆ To remove auto correlation in net-proton study, charge particles selected excluding p, ¯ p

S Samanta (For the CBM Collaboration) Quark Matter - 2019, Wuhan, China 6 / 14

SLIDE 7

Proton (anti-proton) selection

Mass square cut: 0.6 < m2 < 1.2 GeV2/c4 Rapidity acceptance: ∆y = 1 (ymid = 1.58) pT acceptance: 0.2 < pT < 2 GeV/c

(GeV/c)

T

p 0.5 1 1.5 2 2.5 Purity 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 = 10 AGeV

lab

Au + Au, E UrQMD + CBM GEANT3 1.08 < y < 2.08 (GeV/c)

T

p 0.5 1 1.5 2 2.5 Efficiency 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.08 < y < 2.08 y 0.5 1 1.5 2 2.5 3 3.5 4 Efficiency 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 < 2.0 (GeV/c)

T

0.2 < p

y 0.5 1 1.5 2 2.5 3 3.5 (GeV/c)

T

p 0.5 1 1.5 2 2.5 3 3.5 4

1 10

2

10

3

10

Au + Au = 10 AGeV

lab

E UrQMD CBM GEANT3

⋆ Purity > 96 % ⋆ Efficiency decreases at high pT due to the detector acceptance ⋆ Efficiency for 0-5 % and 70 -80 % centralities are ≃ 62 % and ≃ 46 %

S Samanta (For the CBM Collaboration) Quark Matter - 2019, Wuhan, China 7 / 14

SLIDE 8

Proton (anti-proton) multiplicity distributions

)

p

(N

p

N 10 20 30 40 50 60 70 80

• No. of events

1 10

2

10

3

10

4

10

5

10

6

10 p p

(0 - 5) %

= 10 AGeV

lab

Au + Au, E UrQMD + CBM GEANT3 < 2.0 (GeV/c)

T

0.2 < p

1.08 < y < 2.08

)

p

(N

p

N 10 20 30 40 50 60 70 80

• No. of events

1 10

2

10

3

10

4

10

5

10

6

10

(5 - 10) %

)

p

(N

p

N 10 20 30 40 50 60 70 80

• No. of events

1 10

2

10

3

10

4

10

5

10

6

10

(10 -20) %

)

p

(N

p

N 10 20 30 40 50 60 70

• No. of events

1 10

2

10

3

10

4

10

5

10

6

10

(20 - 30) %

)

p

(N

p

N 10 20 30 40 50 60 70

• No. of events

1 10

2

10

3

10

4

10

5

10

6

10

(30 - 40) %

)

p

(N

p

N 10 20 30 40 50 60 70

• No. of events

1 10

2

10

3

10

4

10

5

10

6

10

(40 - 50) %

Uncorrected distributions for efficiency and acceptance

S Samanta (For the CBM Collaboration) Quark Matter - 2019, Wuhan, China 8 / 14

SLIDE 9

Proton (anti-proton) multiplicity distributions

)

p

(N

p

N 5 10 15 20 25 30 35 40

• No. of events

1 10

2

10

3

10

4

10

5

10

6

10 p p

(50 - 60) %

= 10 AGeV

lab

Au + Au, E UrQMD + CBM GEANT3

)

p

(N

p

N 5 10 15 20 25 30 35 40

• No. of events

1 10

2

10

3

10

4

10

5

10

6

10

(60 - 70) %

)

p

(N

p

N 5 10 15 20 25 30 35 40

• No. of events

1 10

2

10

3

10

4

10

5

10

6

10

(70 - 80) %

(Uncorrected distributions for efficiency and acceptance)

⋆ Proton multiplicities follow negative binomial distribution ⋆ Number of ¯ p is very less compared to p (¯ p/p = 7.8 × 10−5 (0 -5 %), ¯ p/p = 2.5 × 10−4 (70 - 80 %) from UrQMD) ⋆ Proton distributions are skewed more to the right side of the mean

S Samanta (For the CBM Collaboration) Quark Matter - 2019, Wuhan, China 9 / 14

SLIDE 10

Net-proton multiplicity distributions

)

p

• N

p

N (N ∆ 10 20 30 40 50 60 70 80 90

• No. of events

1 10

2

10

3

10

4

10

5

10

6

10

(0-5) % (5-10) % (10-20) % (20-30) % (30-40) % (40-50) % (50-60) % (60-70) % (70-80) %

= 10 AGeV

lab

Au + Au, E UrQMD + CBM GEANT3 < 2.0 (GeV/c)

T

0.2 < p 1.08 < y < 2.08

Uncorrected for efficiency and acceptance

Centrality (%) Nch (m2 < 0.4 GeV2/c4 ) 0-5 Nch ≥ 71 5-10 60 ≤ Nch < 71 10-20 44 ≤ Nch < 60 20-30 32 ≤ Nch < 44 30-40 23 ≤ Nch < 32 40-50 16 ≤ Nch < 23 50-60 10 ≤ Nch < 16 60-70 6 ≤ Nch < 10 70-80 4 ≤ Nch < 6 ⋆ Mean and variance decreases from central towards the peripheral collisions ⋆ Distributions are skewed more to the right side of the mean

S Samanta (For the CBM Collaboration) Quark Matter - 2019, Wuhan, China 10/ 14

SLIDE 11

Cn of net-proton vs centrality (%)

Centrality (%) 20 40 60 80

1

C 10 20 30 40

= 10 AGeV

lab

Au + Au, E UrQMD + CBM GEANT3 < 2.0 (GeV/c)

T

0.2 < p 1.08 < y < 2.08 Net-proton Without CBW correction With CBW correction

Centrality (%) 20 40 60 80

2

C 10 20 30 40 Centrality (%) 20 40 60 80

3

C 20 40 60 80 Centrality (%) 20 40 60 80

4

C 100 − 100 200

Centrality bin width correction Cn =

r wrCn,r

wr =

nr

• r nr
• r wr = 1

sum is over multiplicity bins ⋆ CBWC done to suppress volume fluctuations ⋆ Statistical error estimation is done using Delta theorem

Ref: Advanced Theory of Statistics: Vol.1, London (1945); Asymptotic Theory of Statistics and Probability, Springer (2008); JPG 39, 025008 (2012); JPG 40, 105104 (2013) S Samanta (For the CBM Collaboration) Quark Matter - 2019, Wuhan, China 11/ 14

SLIDE 12

Correction of cumulants of net-proton using Unfolding method

Algorithm used: RooUnfoldBayes

Relationship between measured and true distribution: y = Rx y = measured, x = true, R = response matrix ⋆ 50 % events are used to construct R

p

• N

p

N

20 40 60 80 100 120

• No. of events

1 10

2

10

3

10

4

10

5

10

Measured True Corrected

= 10 AGeV

lab

Au + Au, E (0 - 5) % < 2.0 (GeV/c)

T

0.2 < p 1.08 < y < 2.08

Centrality (%) 20 40 60 80

1

C 20 40 60

= 10 AGeV

lab

Au + Au, E UrQMD + CBM GEANT3 < 2.0 (GeV/c)

T

0.2 < p 1.08 < y < 2.08 Net-proton

Centrality (%) 20 40 60 80

2

C 20 40 60 80 100

Measured Corrected True

Centrality (%) 20 40 60 80

3

C 100 − 50 − 50 100 150 Centrality (%) 20 40 60 80

4

C 1000 2000 3000

⋆We are able to get back cumulants of ’True’, even if the efficiency is non-binomial and has non-trivial dependence on pT and rapidity

Ref: NIMA 362, 487 (1995) S Samanta (For the CBM Collaboration) Quark Matter - 2019, Wuhan, China 12/ 14

SLIDE 13

Net-charge multiplicity distributions and cumulants of net-charge

)

• N

+

N (N ∆ 20 40 60 80 100 No of events 1 10

2

10

3

10

4

10

5

10

6

10

(0-5) % (5-10) % (10-20) % (20-30) % (30-40) % (40-50) % (50-60) % (60-70) % (70-80) %

= 10 AGeV

lab

Au + Au, E UrQMD + CBM GEANT3 < 2.0 (GeV/c)

T

0.2 < p < 2.65 η 1.65 <

Uncorrected for efficiency and acceptance

Centrality (%) 20 40 60 80

1

C 20 40 60 80

= 10 AGeV

lab

Au + Au, E UrQMD + CBM GEANT3 < 2.0 (GeV/c)

T

0.2 < p < 2.65 η 1.65 < Net-charge

Centrality (%) 20 40 60 80

2

C 50 100 150 200 250

Measured Corrected True

Centrality (%) 20 40 60 80

3

C 500 1000 Centrality (%) 20 40 60 80

4

C 15000 − 10000 − 5000 − 5000 10000

⋆ We are able to get back cumulants of ’True’, except C4 in 0 − 5 % ⋆ More statistics needed

S Samanta (For the CBM Collaboration) Quark Matter - 2019, Wuhan, China 13/ 14

SLIDE 14

Summary ⋆ Studied the feasibility of doing fluctuation analysis with conserved charges in Au+Au collisions at 10 AGeV with CBM detector using simulated events from UrQMD. ⋆ Clean proton identification with high purity is possible and hence one can study the net-proton (proxy for net-baryon) higher order moments using CBM detector. ⋆ Centrality selection using charged particles other than proton and anti-protons is possible. ⋆ Efficiency and detector effects were corrected for using unfolding techniques and original distributions and cummulants recovered. This shows that using the CBM detector, higher moments of net-proton and net-charge can be studied. Outlook ⋆ Similar studies in other SIS100 energies ⋆ Look forward to data from CBM at SIS100 energies in the year 2025

S Samanta (For the CBM Collaboration) Quark Matter - 2019, Wuhan, China 14/ 14

SLIDE 15

Thank you

S Samanta (For the CBM Collaboration) Quark Matter - 2019, Wuhan, China 14/ 14