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Reaction plane reconstruction in extZDC

Reaction plane reconstruction in extZDC. • Reaction plane reconstruction using extended ZDC: beam energy, ZDC cell size, ZDC length, magnetic field Reconstruction of impact parameter b TPC track data vs energy in extended ZDC. Position of extZDC within MPD set-up. extZDC.

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Reaction plane reconstruction in extZDC

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  1. Reaction plane reconstruction in extZDC • • Reaction plane reconstruction using extended ZDC: • beam energy, ZDC cell size, ZDC length, magnetic field • Reconstruction of impact parameter b • TPC track data vs energy in extended ZDC Reaction plane peconstruction

  2. Position of extZDC within MPD set-up extZDC Reaction plane peconstruction

  3. Methods of reaction plane reconstruction • Using 1-st Fourier harmonics → directed flow in a collision in Lab frame: Method 1: b φR Method 2: → Optimize weight wi to increase sensitivity to RP → combine measurements for η<0 and η>0 to improve precision, study as a function of impact parameter b Reaction plane peconstruction

  4. Extended ZDC detector dcell = 5x5 cm, 420 cells in each side of MPD • Simulation of extended ZDC within mpdroot: • L = 120 (60, 40) cm • 5 < R < 61 cm, z0=270 cm, 1<θ<12.5o (2.2<η<4.8) • dcell = 5x5,10x10 cm • wi=ΣEvis in active layers of 1 module → use methods 1 and 2 for RP reconstruction • No π vs p/ion identification • Geant 4 , QGSP_BIC physics model dcell = 10x10 cm, 121 cells in each side of MPD Reaction plane peconstruction

  5. b = 0 – 16 fm in 8 bins, 2 fm / bin Resolution δφRP vs b δφRPo = φZDC-φRP Extended ZDC, QGSM 9 AGeV AuAu, Geant4 QGSP_BIC model dcell = 5x5cm, L=120cm 2.2 < η < 4.8, method 1, w=Evis No PID (π vs p/ion) Reaction plane peconstruction

  6. b = 0 – 16 fm in 8 bins, 2 fm / bin cos δφRP vs b cos(δφRP) = cos(φZDC-φRP) Extended ZDC, QGSM 9 AGeV AuAu, Geant4 QGSP_BIC model dcell = 5x5cm, L=120cm 2.2 < η < 4.8, method 1, w=Evis No PID (π vs p/ion) Reaction plane peconstruction

  7. Resolution δφRP vs b • methods 1 and 2 give consistent results for RP resolution in azimuthal angle φ • RP resolution for the case if only ZDC from one side of MPD set-up is used vs full ZDC set-up (lower plot) Reaction plane peconstruction

  8. Resolution δφRP and <cos δφRP> vs b Effects of ZDC cell size and length, beam energy and interaction model Reaction plane peconstruction

  9. Effect of magnetic field: <φZDC-φRP> vs b → Systematic effect of magnetic field increases from ~1o at 9 AGeV to ~3o at 3 AGeV, QGSM and UrQMD model give consistent results QGSM UrQMD Reaction plane peconstruction

  10. Effect of magnetic field: <φZDC-φRP> vs b • Systematic effect of magnetic field increases from ~1o at 9 AGeV to ~3o at 3 AGeV • Magnetic field systematics is small compared to RP resolution • QGSM and UrQMD models give consistent results → systematics could be corrected based on model predictions • For precise measurements of asymmetries at the lowest beam energy reduced magnetic field would decrease RP systematics Reaction plane peconstruction

  11. Extended ZDC: Evis vs impact parameter b QGSM, 9 AGeV b measurement using Evis (ZDC): QGSM model: Evis has peak at b=8-10 fm, → double solution in b measurement based on Evis UrQMD model: monotonic dependence of Evis on b Reaction plane peconstruction b = 0 – 16 fm in 8 bins, 2 fm / bin

  12. Extended ZDC: Fvis(R<25cm) vs b QGSM, 9 AGeV b measurement using Fvis=Evis(R<25cm)/Evis(full zdc): QGSM model: Fvis is monotonic except at highest b>12fm → large fluctuations of Fvis → double solution for b measurement based on Fvis UrQMD model: monotonic dependence of Fvis on b Reaction plane peconstruction b = 0 – 16 fm in 8 bins, 2 fm / bin

  13. QGSM vs UrQMD: particle and energy flow extZDC • QGSM and UrQMD generate very different particle and energy flow spectra in pseudo-rapidity range of extZDC Reaction plane peconstruction

  14. ExtZDC: <Evis> and <Fvis> (R<25cm) vs b Effect of beam energy and AuAu interaction model QGSM vs UrQMD: • model dependence is big for Evis at large b (b>10fm) • effect is smaller for Fvis(ZDC, R<25cm), but is not negligible • QGSM and UrQMD predictions for particle and energy flow in ZDC pseudo-rapidity range are very different → energy flow measurement in extended ZDC will distinguish between models What can one get from TPC data? Reaction plane peconstruction

  15. Multiplicity and Σ p (π,K,p in TPC) vs b • Σ p of charged tracks in TPC (|η|<1.2) is a measure of impact parameter b or centrality of nucleus-nucleus interaction. It is less model dependent (QGSM vs UrQMD) in comparison with multiplicity of TPC tracks (lower plot) • Model dependence of b measurement with Σ p of charged particles in TPC decreases at low beam energies Reaction plane peconstruction

  16. Summary • Extended ZDC detector (2.2<η<4.8) provides RP measurement at medium b (4<b<10 fm) with resolution of δφRP~22-35o in AuAu collisions at energies 5-9 AGeV, RP resolution deteriorates to δφRP~45-65o at 3 AGeV • Sensitivity of extended ZDC to RP azimuthal angle in central (b<3 fm) and peripheral collisions (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: dcell=10x10cm, L=60cm are sufficient for RP measurement. ZDC length is more crucial for energy flow measurement • Magnetic field systematics to φRP is ~1o at 9 AGeV which increases to ~3o at 3 AGeV. Reduced magnetic field at the lowest energy would decrease systematics • Measurement of impact parameter b using Evis(ZDC) is strongly model dependent (QGSM vs UrQMD) at large b, Fvis(ZDC,R<25cm) is less model dependent, but Fvis is not monotonic at large b • Σ p of charged particles detected in TPC provides measurement of b with smaller model dependence, than TPC track multiplicity • Energy flow measurement with extended ZDC will distinguish between models in beam fragmentation region Reaction plane peconstruction

  17. Backup Reaction plane peconstruction

  18. Relation between b and centrality Impact parameter b: 0 - 3 fm 3 – 6 fm 6 – 9 fm 9 – 12 fm Fraction of σincltot : 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) Reaction plane peconstruction

  19. Directed Flow v1 vs Rapidity y nucleons π-mesons UrQMD QGSM Reaction plane peconstruction

  20. G4 physics model: QGSP_BIC vs QGSP_BERT Shower radius in ZDC: hadrons, light ions (A=2,3,4), em particles Gean4 physics models: QGSP_BERTuses Geant4 Bertini cascade for primary protons, neutrons, pions and Kaons below ~10GeV. In comparison to experimental data we find improved agreement to data compared to QGSP which uses the low energy parameterised (LEP) model for all particles at these energies. The Bertini model produces more secondary neutrons and protons than the LEP model, yielding a better agreement to experimental data. QGSP_BIC uses Geant4 Binary cascade for primary protons and neutrons with energies below ~10GeV, thus replacing the use of the LEP model for protons and neutrons In comparison to the LEP model, Binary cascade better describes production of secondary particles produced in interactions of protons and neutrons with nuclei. QGSP_BIC also uses the binary light ion cascade to model inelastic interaction of ions up to few GeV/nucleon with matter. QGSP_BIC is selected → more reasonable description of interactions of light ions (A=2,3,4) with medium, see also next slides Reaction plane peconstruction

  21. G4 physics model: QGSP_BIC vs QGSP_BERT Evis (0.1zdc) / Evis (full zdc) Evis (zdc) / Egen hadrons, light ions (A=2,3,4), em particles Reaction plane peconstruction

  22. G4 physics model: QGSP_BIC vs QGSP_BERT Evis (zdc) vs Egen Evis (zdc) / Egen vs Egen hadrons, light ions (A=2,3,4), em particles Non-linear response because of shower leakage Reaction plane peconstruction

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