1 / 36

Analysis of Dileptons in Ar+KClR

This analysis focuses on the investigation and characterization of dileptons in Ar+KClR collisions at 1.756 GeV/u. The study includes independent lepton analyses and explores various observables such as mass spectra, transverse mass, rapidity, polar angles, and helicity. The results are compared with statistical models and a reference data set to understand the origin of the observed excess. Further investigations into baryonic contributions and the impact of other channels are also discussed.

jchapman
Download Presentation

Analysis of Dileptons in Ar+KClR

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Dileptons in Ar+KClR. Holzmann for the e+e- Team Sep05 run: 1.756 GeV/u Ar on KCl target • 2.2 · 109 LVL1 events inspected (10 Tbyte!) • 3 independent lepton analyses finished (hard cut, Bayesian, MVA) Combined e+e- mass spectrum (HC+Bayes+MVA)/3 : • π0 Dalitz • continuum • omega peak

  2. MVA Hard Cut e- e+ optimization (by Manuel Lorenz) Optimized MVA Status 2009 After optimization of MVA pid:

  3. Omega production gaus + expo bkg fit → ω yield = (3.9±1.6) ·10-8 30 - 40 counts! • Corrected for • BR = 7.16 ·10-5 • acceptance = 0.29 (for T = 85 MeV) • ► MLVL1(ω) = (6.7±2.7) ·10-3 Systematic error: - background ? - medium effects ?

  4. Comparison with statistical model THERMUS calculation (T, μB and RC fit to HADES data) ω and  described in statistical model, but…

  5. Statistical model fits (at 1.76 GeV/u) • Manuel’s fit to Ar+KCl: T = 75, μB = 790 MeV [to be written and published] • Cleymans parametrization: T = 67, μB = 763 MeV [Phys. Rev. C73 (2006) 034905] • Andronic parametrization: T = 63, μB = 746 MeV [Phys. Lett. B673 (2009) 142] • Averbeck fit to TAPS data: T = 80, μB = 710 MeV [Phys. Rev. C67 (2003) 024903]

  6. / ratio: OZI in Ar+KCl vs. NN • Using yields from •  → K+K-: (2.6 ± 0.7) ·10-4 •  → e+e- : (6.7 ± 2.7) ·10-3 • ► • >> R/ in NN and πN reactions ! • Impact of other channels besides NN and πN ? • (e.g. ρN, ρΔ, …) >> OZI allowed

  7.  production in BUU Schade, Wolf & Kämpfer, in Phys. Rev. C 81 (2010) 034902 exotic ch. standard ch.

  8. retuned HSD (Nov09 release) • M/Mπ0 = 0.0019 (exp = 0.0020) • for M>0.65 GeV: ω+ρ = 70%

  9. Continuum pairs in Ar+KCl • How to characterize the continuum? • Look at many observables! • yield: dN/dm • transverse mass: dN/dmt • rapidity: dN/dy • polar angles: dN/dθcm • helicity: dN/dα • Look at their systematics vs. Ebeam and Apart See my Sesimbra talk 2009

  10. “Excess” vs. beam energy and system size Yield/Apart • baryonic contrib. in Ar+KCl >> C+C • scales with Ebeam like π production • scales with Apart stronger than linear • ≈ <Apart>1.4 Compare A+A with N+N, but properly normalized. π0 and η from TAPS (min. bias) e+e-continuum pairs: HADES (LVL1) DLS (min. bias)

  11. Preparing a “reference” for Ar+KCl Definition of a ”reference” based on pp and np data: Compare excess over η in Ar+KCl with excess over η in reference x2.5 - 3 • η contributions subtracted ! • yield normalized to M(π0) ►► Excess over NN!

  12. Characterizing the excess: dn/dmt A reminder: dn/dmt of a thermal source given by ► Use 1/mt3/2 dn/dmt to extract slope parameters

  13. Definition of mass slices mid high low mostly 3-body ! mostly 2-body ?

  14. A+A Transverse-mass spectra: Mee<0.15 GeV(efficiency and acceptance corrected) A+A vs. 1.25 GeV N+N ► Low-mass bin is well described by π0 Dalitz ► 1.25 GeV/u NN reference

  15. A+A Transverse mass: 0.15<Mee<0.50 GeV A+A vs. 1.25 GeV N+N ► Mid-mass bin: T of baryonic component changes only weakly with Ebeam ! ► 1.25 GeV/u NN reference … ?

  16. Transverse mass: Mee>0.50 GeV ► Large slopes: Tee >> Tchem = 75 MeV

  17. 3-body (!) 2-body (?) decays More mass cuts in ArKCl… Mee = 0.35 – 0.50 0.50 – 0.65 >0.65 GeV ► Indeed dominant, according to transport

  18. Comparison with in-medium HSD HSD vs. Ar+KCl at 1.76 GeV/u • low-mass bin is well described, except for mt >800 MeV • at mid-mass, slope is fine, but no selectivity • high-mass slope reproduced by neither ρ/ω, nor Δ !

  19. Systematics of slopes at 1.76 GeV/u π0 and η from TAPS Why are slopes of ρ/ω and  so different ?

  20. Summary • ω yield in Ar+KCl: • reproduced by statistical models and (updated) transport • R/ >> R/(NN) >> OZI allowed • dN/dmt vs. Mee: • low-mass region is well understood • mid-mass not very selective → origin of excess remains unclear • high-mass has surprisingly large T>>Tchem ► continue our systematics towards large A+A

  21. Thanks to the (still active) e+e- team: • Filip Krizek • Martin Jurkovic • Manuel Lorenz • Tatyana Galatyuk • Gosia Sudol … and let’s get those Au+Au data in!

  22. Some more details…

  23. dn/dmt in an isotropic thermal source Relativistic Boltzmann distribution: ► Integrating over θ and ɸ this gives: ► Integrating over pz: ► Integrating over mt:

  24. mt scaling vs. statistical models ► Integrating dn/dmt over mt gives full yield: ► mt scaling: ► equivalent togrand-canonical statistics in the classical limit (see e.g. Hagedorn 1965)

  25. 100 40 0.15<M<0.50 η Pair dN/dmtfrom thermal sources in Pluto(T = 40 –100 MeV) ω π0 Δ ρ M<0.15 ρ M>0.50

  26. Pluto mt acceptances 0.15<M<0.50 mt M<0.15 M>0.50

  27. Effect of Δ contribution on acceptance Compare acceptances for different cocktail compositions (M>0.50 GeV): T=125

  28. Cleaning up high-momentum tracks(by lowering the pe cut) Pair mt acceptances: ► This lowers the acceptance at high mt considerably

  29. Effect of p cut on slopes pe< 1.3 GeV/c pe< 0.9 GeV/c ► small reduction of slopes only

  30. y = y0 ± 0.1 all y Paradise Lost or Stranger Than Paradise ? Vector mesons dominate in acc. Δ dominates in acc. ► slopes decrease, still remain high

  31. Comparison of dσ/dmt and dσ/dEcm dσ/dE makes use of longitudinal component as well, but need to go to AA cm !

  32. Ar+KCl vs. C+C excess y = y0 all y ► After subtraction of first-chance part, T2 < T1

  33. Attempt to reproduce the HSD Δ tail

  34. y = yo 1/Mt2 dN2/dMtdy π0 η Mt [GeV/c2] Vector meson mt scaling beyond π0 and η • Mid-rapidity π0 and η data • from TAPS: • 1.5 GeV/u Ar+Ca • 2.0 GeV/u Ca+Ca • HADES dileptons with Mee>0.5: • 1.756 GeV/u Ar+KCl • y = yo± 0.1 (0.76 – 0.96) • <BRee> = 6 ∙10-5 Consistency with M(ω) ?

  35. CM helicity distributions Compatible with pseudoscalar π0 Large B’ points to polarized excess! Statistics!!!

  36. CM polar distributions M<0.15 anisotropy consistent with π± distributions Large 0.15<M<0.50 anisotropy requires excess to have A2 > 0! M>0.50 ??? Statistics!!!

More Related