1. M.Baznat1, K.K.Gudima1, A.G.Litvinenko2, E.I.Litvinenko2
The centrality determination for the NICA/MPD using the LAQGSM generator
M.Baznat1, K.K.Gudima1, A.G.Litvinenko2, E.I.Litvinenko2
1Institute of Applied Physics, Academy of Science of Moldova, Moldova
2JINR Dubna, Russia

2. The centrality determination – the observables:
The number of particles produced in the region of rapidity close to zero
The total energy of spectators

3. The centrality classification
Geometrical cross section
Geometrical cross section
for the fixed impact parameter
Interval of impact parameter values
Interval given in percents from the geometrical cross section
Centrality
corresponds to the region of the impact parameter:

4. Jet Quenching – nuclear modification
The importance of the centrality study
elliptic flow scaling
with space eccentricity
short equlibration time
Jet Quenching – nuclear modification
factor vs centrality

5. Experimental data : the deposited energy for different types of spectators in dependence of the centrality
The NA49 collaboration. Eur. Phys. J., A2, 383, (1998)
At large impact parameters the most of spectator nucleons are bound in fragments.

6. Obvious requirements to a Zero Degree Calorimeter aimed to determine the centrality
The calorimeter should measure deposited energy of all types of the spectators: protons, neutrons and nuclear fragments;
In order to reach good geometrical acceptance, the calorimeter sensitive areas should be placed to the positions where it is expected to catch the biggest part of the spectators energy;
Detailed simulations with the transport of all types of spectators should be performed for each experiment individually taking into account the value and the configuration of magnetic field of the experiment;
Event generator for such simulations should produce all types of the spectators with the reasonable yield, and transport code should be able to transport all types of the spectators.

7. ZDC for NICA/MPD (standard geometry)
The technical design of ZDC for NICA/MPD proposed by the group of A.B.Kurepin (INR, Moscow)
ZDC consists from the modules 10x10x120cm3 (or 5x5x120cm3) . Each module consists of 60 lead-scintillator sandwiches 10x10cm2 with thicknesses 16 and 4mm. Main attention in the technical design was paid to the method of light readout from the scintillator tiles that should provide good efficiency and uniformity of light collection.

8. Fast evaluations: the movement of spectators at NICA/MPD
The conclusion:
Magnetic field of MPD will not change the polar angles
for spectators at ZDC position
it will only slightly changes the azimutal angles

9. LAQGSM high-energy event generator
LAQGSM describes reactions induced by both particles and nuclei at incident energies up to about 1 TeV/nucleon, generally, as a three-stage process:
IntraNuclear Cascade (INC), followed by pre-equilibrium emission of particles
during the equilibration of the excited residual nuclei formed after the
INC, followed by evaporation of particles from and/or fission of the compound nuclei.

11. LAQGSM intranuclear cascade model

12. The latest improvements of LAQGSM code

13. LAQGSM related publicaitons
LAQGSM03.03: a) “CEM03.03 and LAQGSM03.03 Event Generators for the MCNP6, MCNPX, and MARS15 Transport Codes” S. G. Mashnik, K. K. Gudima, R. E. Prael, A. J. Sierk, M. I. Baznat, and N. V. Mokhov, LANL Report LA-UR ; E-print: arXiv: v2 [nucl-th] 12 May 2008 b) S. G. Mashnik et al., LANL Report LA-UR ; E-print: arXiv: v1 [nucl-th] 12 Sep c) K. K. Gudima and S. G. Mashnik, Proc. 11th Internat. Conf. on Nuclear Reaction Mechanisms, Varenna, Italy, June 12–16, 2006, edited by E. Gadioli (2006) pp. 525–534; E-print: nucl-th/
LAQGSM03.01: S. G. Mashnik et al., LANL Report LA-UR , Los Alamos (2005).
LAQGSM: K. K. Gudima, S. G. Mashnik, A. J. Sierk, LANL Report LA-UR , Los Alamos, 2001.
Quark-Gluon String Model (QGSM): N. S. Amelin, K. K. Gudima, V. D. Toneev, Sov. J. Nucl. Phys. 51 (1990) 327–333; [Yad. Fiz. 51 (1990) 512–523]. Sov. J. Nucl. Phys. 51 (1990) 1093–1101; [Yad. Fiz. 51 (1990) 1730–1743]. Sov. J. Nucl. Phys. 52 (1990) 1722–178, [Yad. Fiz. 52 (1990) 272–282]

14. LAQGSM rapidity and pseudorapidity
sqrt(S)=9
sqrt(S)=9
sqrt(S)=5
sqrt(S)=5

15. URQMD and LAQGSM AuAu mbias data - theta:Ekin/A
URQMD sqrt(S)=9 GeV/u
LAQGSM sqrt(S)=9 GeV/u
free nucleons + fragments
free nucleons
all nucleons
pions + …
pions
fragments

16. LAQGSM AuAu, A:b, Pt/A:Pz/A
Sqrt(S)=5
Arest_of_projectile
Pt/A
Sqrt(S)=9 A b b
Pz/A

17. LAQGSM AuAu, sqrt(S)=9, Pt:Pz per nucleon

18. Optimistic results with UrQMD
URQMD generator, Sqrt(S)=5: all nucleons in 1000 events
Total kinetic energy of all nucleons for each URQMD event
Total kinetic energy of all nucleons directed to ZDC

19. Optimistic results with UrQMD
URQMD generator, Sqrt(S)=9: all nucleons in 1000 events
Total kinetic energy of all nucleons for each URQMD event
Total kinetic energy of all nucleons directed to ZDC

20. Taking into account spectator fragments
LAQGSM generator, Sqrt(S)=5: all nucleons in 1000 events
Total kinetic energy of all nucleons and fragments for each LAQGSM event
Total kinetic energy of all nucleons and fragments directed to ZDC

21. Taking into account spectator fragments
LAQGSM generator, Sqrt(S)=9: all nucleons in 1000 events
Total kinetic energy of all nucleons and fragments for each LAQGSM event
Total kinetic energy of all nucleons and fragments directed to ZDC

22. All nucleons directed to the hole of ZDC (rectangle 10x10cm2)
0 % - 60 %
60 % - 80 %
80 % %

23. The centrality determination: ZDC (energy) + number of charged barrel tracks

24. Interface between mpdroot and LAQGSM data
Class constructor:
MpdLAQGSMGenerator (const char* fileName, const Bool_t use_collider_system=kTRUE);
Class usage in simulation macro:
fRun->SetName("TGeant4");
MpdLAQGSMGenerator* guGen= new MpdLAQGSMGenerator(filename);
primGen->AddGenerator(guGen);

25. Conclusions
The LAQGSM data can be used for NICA/MPD simulations under mpdroot package based on fairroot software.
The LAQGSM angular distributions of the spectators differ from URQMD picture.
“The proposed ZDC can measure the centrality alone (without data from another detectors) for the cases when it is known that the impact parameter is smaller than 8 -9 fm.
One of the possible solutions is to use the particles multiplicity measured by TPC detector together with the value of energy deposition in ZDC. The selection of the most central and the most peripheral events in this case can be made by the corresponding large and small signal from the TPC.
Another solution for the selection of the peripheral events with a small signal in ZDC an additional Zero Degree Neutron (ZDN) calorimeter can be installed after the 1rst dipole magnet of NICA.
The selection of the most central and the most peripheral events can also be made by a small electromagnetic calorimeter placed out of the beam in front of ZDC,.
The experimental study of the spectator distributions have to be performed on the extracted beam of NUCLOTRON-M at the fixed target. For such study the beam energy equals to (or less than) one NICA ring energy (sqrt(S)=2) is enough.”

26. Backup slides

27. Примеры определения центральности в различных экспериментах
PHENIX
NA49
STAR
y=0
y=3
y>6
NA49
ZDC Only
STAR
TPC only
PHENIX
BBC & ZDC

28. Study of spectator-nucleons and spectator-fragments acceptance for new ZDC geometry
Generators: URQMD 1.3 and LAQGSM
Collision: mbias (bdb distribution), sqrt(S)=5 (GeV/u), events
Transport: Geant3 and Geant4
Software framework: mpdroot
ZDC special geometry: thin layers (0.5mm silicon each) – old and new cross-section
ZDC positions: cm from the collision point
Magnet: the latest geometry for MPD magnet
Magnetic field: Tesla
No pipe
Cave material: air

29. URQMD nucleons (directed and transported to ZDC entrance)
came to old ZDC
came to hole
came to new ZDC
Geant3
directed to
284772
15520
216888
286182
Geant4
288372
15639
218084

30. LAQGSM nucleons (directed and transported to ZDC entrance)
came to old ZDC
came to hole
came to new ZDC
directed to ? ? ?
79290
Geant4
56673
4944
38840

31. LAQGSM fragments (directed and transported to ZDC entrance)
came to old ZDC
came to hole
came to new ZDC
directed to ? ? ?
23110
Geant4
19680
1425
14466

32. All directions: Number of nucleons
Generator
All directions: Number of nucleons
Rectangle 90x90 without hole: Number of nucleons
Rectangle 90x90 with hole Number of nucleons
Rectangle 10x10 (“hole”): Number of nucleons
URQMD
(100%)
(78%)
(74%)
15553 (4%)
LAQGSM
(100%)
(69%)
(36%)
(33%)
Generator
New ZDC + hole: Number of nucleons
Hole: Number of nucleons
New ZDC: Number of nucleons
LAQGSM (p+n+A*fragments)
(100%)
(56.4%)
98676 (43.5%)

33. ZDC geometry A: (Lead-Scint sandwich: “Lead 16mm”)
ZDC geometry B: (Scint layer : “Lead 0”)
Geometry: cave, magnet, and ZDC (A and B). Cave material: air and vacuum.
Magnetic Field: 0 (no field) and 0.5T
Generator: LAQGSM sqrt(S) = 5
Transport: Geant4 and Geant3
Events:

34. LAQGSM AuAu, sqrt(S)=9, Pt/A and theta vs b

35. LAQGSM Sqrt(S)=9 GeV/u, rapidity

36. Statistical Multifragmentation Model (SMM)

37. MSDM generator in SHIELD code