Centrality in nucleus-nucleus collisions A.Kurepin, A.Litvinenko, - - PowerPoint PPT Presentation

Centrality in nucleus-nucleus collisions

A.Kurepin, A.Litvinenko, E.Litvinenko Institute for Nuclear Research RAS, Moscow Joint Institute for Nuclear Research, Dubna

EMIN2018, October 8 - 11, 2018 , INR, Moscow, Russia.

Contents:

• Introduction
• Conception of centrality in collider and fixed target experiments
• Methods of centrality determination
• Accuracy of the centrality and impact parameter measurements
• Simulation of possible multiplicity detector for MPD/NICA
• Conclusions

1

Centrality dependence of dNch=dh per participant pair as a function of Npart, measured in the Pb–Pb data at psNN = 2:76 TeV fitted with various parametrizations of Npart and Ncoll, calculated with the Glauber model. The fit parameters are given in the figure

Phys.Rev. C88 (2013) no.4, 044909 ALICE Collaboration

Nch=dh per centrality bin from each

• f the three detectors used. The error

bars correspond to the total statistical and systematic error

Phys.Lett. B726 (2013) 610-622 ALICE Collaboration

dNch=dh per centrality class compared to model predictions

Phys.Lett. B726 (2013) 610-622

Centrality dependence of the nuclear modification factor, RAA, of inclusive J=y production in Pb-Pb collisions at psNN =2:76TeV, measured at mid-rapidity and at forward-rapidity

Phys.Lett. B734 (2014) 314-327 ALICE Collaboration

Distribution of the neutron energy spectrum measured in the Pb- remnant side ZN calorimeter. The distribution is compared with the corresponding distribution from the SNM-Glauber model shown as a line. Centrality classes are indicated in the figure. The inset shows a zoom-in on the most peripheral events.

Phys.Rev. C91 (2015) no.6, 064905 ALICE Collaboration

Comparison of dNch=dh in the 0– 5% (0–6% for KLN) most central collisions of two versions of HIJING, KLN, and EPOS-LHC model calculations to the measured distribution.

Phys.Lett. B772 (2017) 567-577 ALICE Collaboration

Comparison of dNch=dh as a function of h in the 0–5% central class to model predictions. The bottom panel shows the ratio of the models to the data. Boxes around the points reflect the total uncorrelated systematic uncertainties.

Centrality and pseudorapidity dependence of the charged-particle multiplicity density in Xe-Xe collisions at 5.44 TeV ALICE Collaboration arXiv:1805.04432

The cross section as a function of Nhits TOF+RPC for the sum of TOF and RPC hits. The panel shows a simulation based

• n UrQMD eventsnfiltered through

the detailed detector simulation (blue symbols) and in addition through an emulator

• f the PT3 trigger (green symbols)

in comparison with the Glauber MC model (red histogram)

Eur.Phys.J. A54 (2018) no.5, 85 Centrality determination of Au + Au collisions at 1.23A GeV with HADES

Sketches of VZERO-A and VZERO-C arrays showing their segmentation. Scintillator thicknesses are 2.5 and 2 cm respectively.

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Distribution of the sum of amplitudes in the two VZERO arrays (black histogram) in Pb–Pb collisions at √sNN = 2.76 TeV. The red line shows the fit with a Glauber model. The shaded areas define the different centrality classes of hadronic collisions. The inset shows the low amplitude part of the distribution.

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,,

The ALICE Diffractive detector

• AD is formed by two main stations, each station consists of 2 layers

with 4 plastic scintillator pads each (8 pads per side).

• Each scintillator measures roughly 18cm x 21cm.
• Each scintillator plastic is coupled to a PMT through a wave length

shifting bar and an array of clear optic fibers.

• For trigger generation, a coincidence between adjacent pads is

required. Not to scale

XeXe run

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Used data:

– pass1 AOD data – ADC saturation was corrected in CPass1 – charges were normalized to have the same 90% quantile

Event selection:

– CINT7ZAC (CINT7 + ZDC) – ADAND (online+offline BB) Glauber ntuples for XeXe (thanks to Alberica Toia)

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Evo volution o

• f FHCAL

Compact ZDC of 20 modules with high granularity. Extended HCAL of 120 modules with high granularity Simplicity, cheap. Low acceptance. Poor event plane angular resolution. High acceptance, perfect event plane resolution. Very expensive, complicated . FHCAL of 45 modules: Moderate segmentation, High acceptance, Nice event plane resolution, Reasonably simple and cheap. transverse sizes 10x10 cm2 transverse sizes 15x15 cm2

Centrality determination from the energy depositions in calorimeter.

M.Golubeva et al. “ Nuclear-Nuclear Collision Centrality Determination by the Spectators Calorimeter for the MPD Setup at the NICA Facility “ Yad.Fiz. 76 ( 2013 ) 2-17 The ambiguity in centrality determination can be resolved by taking track multiplicity in TPC.

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GeV 11 =

NN

S

The correlation between energy deposition in FHCal and charged tracks multiplicity in TPC for the Au-Au collisions with energy 5 GeV (left) and 9 GeV (right) Место для уравнения.

11 GeV 5 GeV

FHCAL alone can measure the centrality (without any other detectors).

Energy asymmetry Energy asymmetry By taking the horizontal cut at asymmetry and the vertical bins at energy deposition one can resolve the ambiguity in centrality determination.

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Ein Eout Together with energy deposition Edep in FHCAL another

• bservable “ energy asymmetry” is introduced:

As=(Ein-Eout)/(Ein+Eout).

The resolution of impact parameter obtained in separate bins of the energy depositions in FHCal for beam energy √ s = 5 GeV (left) and √ s= 11 GeV (right). Blue and red points correspond to the one and two parts of FHCal, respectively. Green points - estimation with allowance for spectator number fluctuations.

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• V. Klochkov, I Seluuzhenkov,

Acta Physica Polonica 10 ( 2017 ) 919

CBM centrality determination procedure with PSD

Multiplicity distribution for STS at CBM ( left ). Impact parameter resolution with different centrality estimators ( right )

Number of primary particles/event hitting FWALL surface (hole d=10 cm) Including neutrons

M.Golubeva, A.Ivashkin, A.Kurepin “Study of nuclear fragmentation at MPD/NICA “ EPJ Web of Conferences 138, 11001 ( 2017 ) Baldin ISHEPP XXIII

Au+Au √s = 5 AGeV Au+Au √s = 11 AGeV

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Number of primary particles/event hitting FWALL surface Without neutrons (from generator) Au+Au √s = 5 AGeV Hole d=10 cm Hole d=70 cm Hole d=0.5 cm

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Without neutrons Au+Au √s = 11 AGeV Number of primary particles/event hitting FWALL surface

(Using info from MC tracks category)

Hole d=10 cm Hole d=70 cm

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Sketch of FMD array showing their segmentation. Scintillator thicknesses are 2.5 cm. Radius of the hole is 6 cm. Outer radius is 70 cm.

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Multiplicity and energy distributions of protons, pions and fragments hitting the FMD detector

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Multiplicity and energy distributions of protons, pions and fragments with energy less 3.5 GeV hitting the FMD detector

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Dependence of the total energy in GeV of protons on the impact parameter b in fm

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Conclusions

1. Centrality in nucleus-nucleus collisions is the important conception in the relativistic nuclear collisions. However due to the multiple interactions by passing the nuclei the impact parameter could not be determined with accuracy better than 10 % 2. Additional constraints arise at energies of the order of 3-10 AGeV because of the contribution of spectators 3. For MPD/NICA by using the Forward Multiplicity Detector the determination

• f the impact parameter could be obtained with accuracy better than

with Forward Hadron Calorimeter of the order of 10 % for the central and semi- central collisions

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