1. Centrality Determination and Reaction plane reconstruction with MPD D.Dryablov, V. Zhezher, M.Kapishin, G.Musulmanbekov XIV GDRE Workshop, Dubna 12 - 14 December 2012

2. Topics  Motivation  Event Generators  MPD Layout  Reaction Plane Reconstruction with ExtZDC  Definitions  MC estimation of efficiency of ExtZDC  Determination of Centrality  by TPC  by ExtZDC  Results of RP reconstruction  Plans for the Future XIV GDRE Workshop, Dubna 12 - 14 December 2012

3. Motivation: Why do we need RP reconstruction? Physics Tasks at semi-central nucleus-nucleus collisions:  Elliptic Flow of mesons, nucleons and hyperons, hypernuclei  Direct Flow of nucleons, hyperons and hypernuclei  Femtoscopy Correlations w.r.t. RP  Global polarization (w.r.t. RP) of hyperons (Λ, Ξ, Ω)  Vector mesons alightment w.r.t. RP, measured by dilepton yield asymmety  Charge asymmetry w.r.t. RP, CME Selection of Semi-central collisions  Centrality Determination XIV GDRE Workshop, Dubna 12 - 14 December 2012

4. Event Generators: UrQMD vs LAQGSM QGSMUrQMD QGSM XIV GDRE Workshop, Dubna 12 - 14 December 2012

5. Event Generators LAQGSM K. Gudima et al. LA-UR-01-6804 minbias events: 10 5 for √s = 3, 5, 7, 9, 11 GeV semi-central events: 10 5 for √s = 7 GeV GLISSANDO – GlauberMC W. Broniowski et al., CPC, 2008 any statistics at any energy In prospect: UrQMD add-on: A. Polanski, G. Musulmanbekov, ISHEPP’2012 residual nucleus evaporation multifragmentation XIV GDRE Workshop, Dubna 12 - 14 December 2012

6. Length of TPC -340 cm, D=300cm ExtZDC Last MPD layout XIV GDRE Workshop, Dubna 12 - 14 December 2012

7. “Old” and Extended ZDC cell 10 x 10 (cm x cm) XIV GDRE Workshop, Dubna 12 - 14 December 2012

8. Extended ZDC detector XIV GDRE Workshop, Dubna 12 - 14 December 2012 Simulation of Extended ZDC within mpdroot: L ≈ 120 cm 5 < R < 61 cm (radius of the inscribe circle) d cell = 10x10 cm z 0 = 365 cm (distance from the int. point to ZDC) 0.8 o < θ < 9.3 o (covered zenith angle) 2.5 < η < 5.0 (covered pseudorapidity range) x y ExtZDC

9. Reaction Plane: Definitions initial spatial anisotropyanisotropy in momentum space x y z pypy pxpx -  /4 y x  /43  /4 -3  /4 “In-plane” region “Out-of-plane” region Reaction plane defined by (1) beam direction and (2) impact parameter XIV GDRE Workshop, Dubna 12 - 14 December 2012

10. Definitions: Flows 1-st Fourier harmonics → directed flow 2-nd Fourier harmonics → elliptic flow ψRψR XIV GDRE Workshop, Dubna 12 - 14 December 2012

11. Definitions: Reaction Plane reconstruction Reaction plane x y x y Σ w i *sin(2  i ) tan(2  2 ) = Σ w i *cos(2  i ) 22 11 Σ w i *sin(  i ) tan(  1 ) = Σ w i *cos(  i ) plane with the directed moment plane with the elliptic moment (w i : 1 or p T ) ii ii ShinIchi Esumi XIV GDRE Workshop, Dubna 12 - 14 December 2012

12. Method 1: Method 2: ; Reaction Plane reconstruction with ExtZDC x y ExtZDC XIV GDRE Workshop, Dubna 12 - 14 December 2012

13. Problem of identification: directed flows of pions and nucleons have opposite signs ! So are orientations of RPs defined by them! XIV GDRE Workshop, Dubna 12 - 14 December 2012

14. ΔΨ R vs impact parameter 200 GeV ­ Selection of Semi-Central Events XIV GDRE Workshop, Dubna 12 - 14 December 2012

15. Reaction Plane Reconstruction 3 GeV ­ ExtZDC acceptance XIV GDRE Workshop, Dubna 12 - 14 December 2012

16. Extended ZDC detector 5 GeV ­ ExtZDC acceptance XIV GDRE Workshop, Dubna 12 - 14 December 2012

17. Extended ZDC detector 7 GeV ­ ExtZDC acceptance XIV GDRE Workshop, Dubna 12 - 14 December 2012

18. Extended ZDC detector 9 GeV ­ ExtZDC acceptance XIV GDRE Workshop, Dubna 12 - 14 December 2012

19. Extended ZDC detector 11 GeV ­ ExtZDC acceptance XIV GDRE Workshop, Dubna 12 - 14 December 2012

20. Selection of events by centrality in TPC Impact parameter b: 0 - 3 fm 3 – 6 fm 6 – 9 fm 9 – 12 fm Fraction of σ incl tot : 0 - 5% 5 – 15% 15 – 30% 30 – 60% Total multiplicity of charged tracks is a measure of impact parameter b (and centrality of nucleus-nucleus interaction) Semi-Central Events XIV GDRE Workshop, Dubna 12 - 14 December 2012

21. Selection of events by centrality in TPC LAQGSM Minbias events, √s = 9 GeV XIV GDRE Workshop, Dubna 12 - 14 December 2012

22. Selection of events by centrality in TPC LAQGSM Minbias events, √s = 9 GeV - 5 – 9 fm, semi-central events XIV GDRE Workshop, Dubna 12 - 14 December 2012

23. Selection of centrality: N participants GlauberMC Minbias events, √s = 9 GeV - 5 – 9 fm, semi-central events XIV GDRE Workshop, Dubna 12 - 14 December 2012

24. Selection of events by centrality in ExtZDC LAQGSM Minbias events, √s = 9 GeV - 5 – 9 fm, semi-central events XIV GDRE Workshop, Dubna 12 - 14 December 2012

25. Selection of events by centrality in ExtZDC LAQGSM Minbias events, √s = 9 GeV XIV GDRE Workshop, Dubna 12 - 14 December 2012

26. Selection of events by centrality in ExtZDC LAQGSM Minbias events, √s = 9 GeV - 5 – 9 fm, semi-central events XIV GDRE Workshop, Dubna 12 - 14 December 2012

27. RP reconstruction by Extended ZDC detector No particle identification Geant 4, QGSP_BIC physics model Systematic effect of magnetic field: ~1 o at 9 AGeV increases to ~3 o at 3 AGeV x y ExtZDC XIV GDRE Workshop, Dubna 12 - 14 December 2012

28. Resolution δφ RP and vs b M. Kapishin 2012 RP reconstruction by Extended ZDC detector XIV GDRE Workshop, Dubna 12 - 14 December 2012

29. Extended ZDC detector (2.2<η<4.8) provides RP measurement at medium b (4<b<10 fm) with resolution of δφ RP ~22-35 o in AuAu collisions at energies 5-9 AGeV, RP resolution deteriorates to δφ RP ~45-65 o at 3 AGeV Sensitivity of extended ZDC to RP azimuthal angle in central (b 12 fm) is much weaker QGSM and UrQMD models give consistent results for RP resolution of extended ZDC, model dependence increases at low beam energies ZDC cell size and length is not critical: d cell =10x10cm, L=60cm are sufficient for RP measurement. ZDC length is more crucial for energy flow measurement Magnetic field systematics to φ RP is ~1 o at 9 AGeV which increases to ~3 o at 3 AGeV. Reduced magnetic field at the lowest energy would decrease systematics Summary M. Kapishin 2012 XIV GDRE Workshop, Dubna 12 - 14 December 2012

30. 7 GeV Protons + neutrons +pions protons + neutrons 7 GeV no particle identification RP reconstruction by MC in Extended ZDC acceptance 7 GeV = 34 o = 33.8 o R = 0.83 RP resolution, R = XIV GDRE Workshop, Dubna 12 - 14 December 2012

31. Dependence of RP resolution on size of Extended ZDC XIV GDRE Workshop, Dubna 12 - 14 December 2012 Protons + neutrons

32. Dependence of RP resolution on size of Extended ZDC XIV GDRE Workshop, Dubna 12 - 14 December 2012 Protons + neutrons+pions

33. Plans for RP reconstruction: 1.Include ExtZDC channel-by-channel E loss in DST, 2.Estimate the resolutions needed for the physical tasks. XIV GDRE Workshop, Dubna 12 - 14 December 2012

34. Thank You! XIV GDRE Workshop, Dubna 12 - 14 December 2012

35. Reaction plane resolution vs. numbers of particle and value of the flow XIV GDRE Workshop, Dubna 12 - 14 December 2012