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Summary from lecture I

Summary from lecture I. Meson line shape modifications seen in p+A/ +A reactions: E325/KEK : downward  mass shift (~ 9%) E325/KEK: downward  mass shift (~3%) and broadening CBTAPS : downward  mass shift (~14%) and 10-fold! broadening. Strong momentum dependece m(p). No sensitivity to 

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Summary from lecture I

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  1. Summary from lecture I • Meson line shape modifications seen in p+A/+A reactions: • E325/KEK : downward  mass shift (~ 9%) • E325/KEK: downward  mass shift (~3%) and broadening • CBTAPS : downward  mass shift (~14%) and 10-fold! broadening. Strong momentum dependece m(p). No sensitivity to  • .. but • G7/CLAS: no mass shift of  (~45% broadening)  contradiction to E325/KEK but CB problem in E325? • G7/CLAS: no effect on  mass shift ... but CLAS acceptance is not sensitive to CBTAPS no contradiction to CPTABS • New HADES experiment @ GSI : will be sensitive to both / 

  2. Dielectrons from HI: SIS (HADES) and Bevelac (DLS) P. Salabura Jagiellonian University/GSI

  3. First chance collisions Freeze-out Dense matter SIS (BEVALAC) energy regime: 1-2 AGeV • Final state (Freeze-out) in heavy ion collisions • approximately 10-15 % pions, baryon resonances ((1232)) dominated • up to 200 charged particles (Au+Au) • Enhancement of baryon density in "fireball" • Comparable to \ life times : V=1.3\23 fm/c Au + Au @ 1 AGeV UrQMD: J. Phys. G: Nucl. Part. Phys. 25 (1999) 1859– T60=80MeV r/r0 15 fm/c

  4. Meson production at SIS/Bevelac energies • Production of vector mesons close to the threshold :SNN< STHR=2MN + m (Ekinthresh = 1.92 GeV) • co-operative process :NN N, N NN/ or  N, N N*()  N/ • production confined to high density phase • Low production rates: One vector meson decaying into lepton pair per 10 Million reactions ! • Investigation of NN and N collisions is prerequisite for HI ! W. Cassing, E.L. Bratkovskaya / Phys.Rep. 308 (1999) 65Ð233 Yield (arb. units) mT=( m2 + p2 T)1/2

  5. e+e- : example thermal source • A(m)- Breit-Wigner resonace formula •  (m) Mass dependent decay width • for e+e- reads • fB(M,T)Boltzmann thermal factor • fB(M,T) ~ p E exp(-E/T) →e+e- from C+C @ 2AGeV + thermal source • no cut-off at M=2m

  6. e+ e- Line shape modification of  :intermediate resonaces D. Schumacher , S. Vogel et.al (UrQMD) •  produced through Baryonic resonance • N*(1520), N*(1720) and • (1700), (1905) involved N  N*()

  7. DLS puzzle: Data: R.J. Porter et al.: PRL 79(97)1229 Model: E.L. Bratkovskaya et al.: NP A634(98)168,BUU, vacuum spectral function DLS puzzle: Strong dilepton enhancement over hadronic cocktails comparable to top SPS energies (CERES)! • Not explained even by in-medium mass shifts and broadening • Shape of enhancement consistent with e+e- but cross section to low (TAPS)

  8. TAPS TAPS – Two Arms Photon Spectrometer Electromagnetic calorimeter : m =(2E1E2(1-cos(12))1/2 C+C @ 1 AGeV • small acceptance (mid rapidity) • Acc~10-3

  9.  and  from TAPS Cross sections measured and extrapolated to full solid assuming isotropic thermal source at rest in NN CM frame Converted into pair yields:

  10. The DiLepton Spectrometer at LBL • 1988-1993 at Bevalac • 2 Arm-Spectrometer • Minimum opening angle: 40° • Each arm: 40° in Φ, 7.5° in Θ • Trigger on electron-pairs • Mass resolution • 30-40% systematical error • pp/pd, Ca+Ca • 1993 C+C 1.04 AGeV, • Mid-Rapidity: 0.69 • Acceptance • Statistics

  11. Side View START HADES detector • Acceptance: • Full azimuth, polar angles 18o - 85o • Pair acceptance  0.35 • Particle identification: • RICH: CsI solid photo cathode, C4F10 radiator, • TOF: 384 scintillator rods • TOFino: 24 scintillator paddles  MUL limitation, high granularity RPC from 2008 • Pre-Shower: 18 pad chambers & lead converters) • 2' Level single leg electron trigger (Me>=1) • e+e->=92%, evt. reduction : 20(pp) -3(ArKCl) • Momentum measurement • Magnet: B = 0.36 Tm + • MDC: 24 midi drift chambers, single-cell resolution  140 mm, 2005-6: set-up completed (MDC IV) FW

  12. mid-rapidity mid-rapidity Phase space coverage: HADES vs. DLS Red dashed lines: constant pair momenta in steps of 100 MeV/c • Thermal π0 and ηevents: HADES and DLS acceptance • HADES acceptance larger but for low masses (M<0.14 GeV/c2) part of phase space covered by DLS not covered by HADES !

  13. Hadron Id • momentum vs velocity (β) measurement: 180 <<450 TOFINO 450 <<850 TOF ~450 ps ~120 ps

  14. g g e+ e+ Q~ 2.20 p0 Q~ 15.20 e- Conversion e- Dalitz decay 20% electrons: pi0 Dalitz 70% : electrons conv. • hadron blind • 3 ~ ghad < gt < glep • C4F10 : gt = 18.3 • pp> 3 GeV/c Electron identification-RICH One ring: Two rings (if Q>40) • needs high res. MDC!

  15. DATA velocity vs. momentum e+ e- Electron Id • Spatial correlations • RICH rings ↔ MDC tracks • MDC tracks ↔ TOF and PreShower hits • PID : e+, e- • β vs momentum correlation • PreShower condition C + C @ 2AGeV • hadron admixture < 3% at 1000 MeV/c

  16. Relative suppression C1 C2 C3 Pair Analysis C + C @ 2 AGeV Signal/ Background rejection <9o TOF/Shower <90 MDC I-II RICH C1 C2 C3 close conversion candidate Shared detector hit Close pair C1 – the only pair cut C2 – selection of "clean" tracks C3- conversion rejection Signal= Ne+e- - CB CB – Combinatorial Background

  17. C + C @ 2 AGeV • Spectra before efficiency correctionnormalizated to ½(+ + -) yield  (Mee) ~9 % @ Mee~0.8 GeV/c2 2002 set-up with 2 inner MDC only ~ 23000 signal pairs for full Mee range ~ 3000 signal pairs for full Mee > 150 MeV/c2

  18. CB Reconstruction Mee > 150MeV/c2 Combinatorial background: M < 150 MeV/c2 - sLS sLs = 2 (checked with MC for HADES ) M > 150 MeV/c2 - mixed Opposite Sign (mOS) CC 2AGeV • Normalization done between 150-550 MeV/c2 Mee • sLS and mOS background show same behavior for Mee > 150 MeV/c2 • For Mee < 150 MeV/c2 deviations due to correlated background eeX Mee > 150MeV/c2

  19. Experiment Physics HADES dN/dM RawData Analysis Efficiency Correction PairSpectra Comparison to Physics Generators Event Generator time consuming but done to cross-check eff.corrections and acc. filters AcceptanceFilter Acc± (p,, Φ) final comparison: only in HADES acceptance comparison incl. efficiency factors

  20. Acceptance and Efficiency matrices • pair production and decay is described by 6 dof (3 production and 3 decay) • p (0 – 2 GeV/c), • Φ (0o – 60o), • Θ (0o – 90o) and similarly CC @ 2 AGeV

  21. Cocktail A: 0 + η + ω • Cocktail B: Cocktail A + Δ(Ne+e-) + ρ • short lived component 18 % 21 % C+C @ 2 AGeV A. Agakichiev Phys.Rev. Lett 98(2007) 052302 • Coctail A (long lived mesonic components) • 0 thermal source, anisotropic angular distribution according to measured +- •  isotropic •  mT scaling systematic errors: 15 % - efficiency correction 10 % - combinatorial background 11 % - 0 normalization

  22. Cocktail B: Cocktail A + Δ + ρ  Contribution from short lived resonances (ρ, Δ, N*) • Reduced discrepancy for Mee>0.15 GeV/c2 • Cocktail B underestimates data C+C @ 1 AGeV • Good agreement in π0 region • Underestimates the data for Mee > 0.15 GeV/c2 Cocktail A:0 + η + ω = “long-lived” components only PRELIMINARY  Large excess yield

  23. η ω C+C @ 2AGeV pT , Y distributions • Mee < 150 MeV/c2 :Data well described, • 150 < Mee < 550 MeV/c2 :Underestimation over whole p range (factor 2). • Mee > 550 MeV/c2 : Underestimation for high p

  24. Pt Spectra @ 1 AGeV PRELIMINARY • Good agreement in π0 region • Underestimation for Mee> 0.15 GeV/c2 • Excess over Cocktail A (0+ η + ω) enhancement at low Pt PRELIMINARY No Off-shell, multi-step processes  Transport models

  25. RQMD Tübingen C.Fuchs, D. Cozma • UrQMD Frankfurt M. Bleicher, D. Schumacher • HSD Gießen (v2.5) E. Bratkovskaya, W. Cassing vacuum results Comparison to transport models for CC @ 2AGeV (status 2006) • Large variation of yield in models due to uncertainties in Baryon decays  must be fixed by data

  26. PRELIMINARY C + C 2 AGeV Phys. Rev. Lett. 98, 052302 (2007) Yield above  for C+C @ 2 and 1 AGeV Yield above : F(1.0) = 7.06 ± 0.6(stat) ± 1.58(sys) F(2.0) = 2.07 ± 0.21(stat) ± 0.38(sys)

  27. DLS η Yexc F(1.04) = 6.5 ± 0.5(stat) ± 2.1(sys) TAPS Yexc(2.0)/Yexc(1.04) = 2.5 ± .5(stat) ± 1.5(sys) Excitation function of Pair Excess (Yexc) DLS excess scales like pion production !

  28. Fit: Mee < 0.15 GeV/c² 0.15 GeV/c² ≤ Mee≤ 0.55 GeV/c² PRELIMINARY Pt [GeV/c] Pt [GeV/c] HADES vs DLS : direct comparison for CC at 1 AGeV

  29. PRELIMINARY PRELIMINARY  HADES and DLS Data agree J. Carroll – presentation International Workshop on Soft Dilepton ProductionAugust 20-22,1997, LBNL DLS Data: R.J. Porter et al.: PRL 79(97)1229 Direct Comparison: HADES vs DLS • HADES Data incl. extrapolation in DLS acceptance

  30. HADES and DLS agree with each other: Do we have now HADES/DLS puzzle for the next 10 years? • Hopefully not. • Do we understand elementary sources contributing to dielectron cocktail at SIS/Bevelac energies? • Radiation from baryonic matter ? • NNNNe+e- bremsstrahlung • NNNN*() NNe+e- bramsstrahlung with resonance excitation i.e  (1232)Ne+e- Delta Dalitz decay

  31. dp and pp @ 1.25 GeV Strategy: study of e+e- sources in pp and pn at s<sthres (Ekin =1.25 GeV) for  production Only 0,  and bremsstrahlung contribute: • Measure pp+pppe+e- (fix +) - assuming brems (pp) is small • Measure pn e+e-X with dp reactions – determine brems (pn)

  32.  () production in pp, pn @ 1.25 GeV Resonance model and isospin symmetry: •  dominant at 1.25 GeV 2/3+p0 1/30p- pp  p+ 6.0 mb pn n+ + pn  p0 =12. mb (assuming isospin symmetry) ++ =3 + 2/3+p0 2/30n0 2/3+,0 = p(n)0 S. Teis et al., Z. Phys. A 356 (1997) 421-435

  33. baryon resonances 1‘ 1 e+ 2‘ 2 1‘ 1 e- 2‘ 2 NN - bremstrahlung • Strong + electromagnetic process Kaptari, Kampfer Nucl. Phys. A 764 (2006) 338 Shyam & Mosel (2003) One Boson Exchange Model + = +

  34. L.P. Kaptari, B. Kämpfer Nucl. Phys. A 764 (2006) 338 x2 total x4 NN- bremsstrahlung-dielectron yield • Large isospin (pn = pp ) effects

  35. pp/dp from DLS Data: DLS: W.Wilson Phys.Rev.C(1998) • Problems in description • Bremsstrahlung? •  contribution ? • No 0 visible in data ! cross-check with "known" physics" missing E. Bratkovskaya et al. nucl-th\0008037 (2000) 100 100 C. Fuchs et al. Phys. Rev. C68 014904(2003) 10-1 10-1 eVDM

  36. 10 S/B 1 pp/dp @ 1.25 GeV HADES preliminary (run 2006) • ~50% analyzed • 17008 signal pairs 0.5 1.0 Mee

  37. pp @ 1.25: comparison to simple model preliminary not eff. corrected • cocktail filtered with HADES acceptance and rec. efficiency • normalized to 0 yield • only 2 sources: • 0 e+e-  • +pe+e- decay (BR=4.4*10-5) • + yield fixed to 0 with isospin relation: N(+)=3/2 N(0) • factor ~2 missing yield for • M>0.15 GeV/c2

  38. pne+e- X with d+p @ 1.25 AGeV • forward p spectator tagging in Forward Wall  selection of pn reactions(10% contribution from pp, only) p_c p_spec pc d d+pp_c n  p_spec d+pp_c n 0 p_spec p_c p_c p_c p_spect ns p_spec p_spec

  39. 10 S/B 1 pn @ 1.25 AGeV "On-line spectrum" not efficiency corrected • (MUL=>2 && FW "p spectator") tag on np -> e+e- X reactions • ~50% analyzed "online" • 37800 signal pairs +- > 90 0.5 1.0 Mee

  40. pn @ 1.25 AGeV cocktail not efficiency corrected normalized to same 0 yield "online spectrum" p + n @ 1.25 AGeV e+e- >90 • cocktail filtered with HADES acceptance and rec. efficiency • cocktail with  and  only: • (same as for pp case) • factor 4-5 missing yield for M>150 MeV/c2 (~3 larger than for pp)! • larger at higher masses • clear evidence for additional sources • (bremsstrahlung !? pn>pp)

  41. factor ~3-4 p+n vs p+p vs C+C : scaling to VERY PRELIMINARY ! p+p vs p+n • p+n above p+p by a factor of 3 • stronger effect at higher masses  Contribution from bremsstrahlung?  pn Bremsstrahlung > pp Bremsstrahlung p+n vs C+C • fair agreement over whole range  NN – bremsstrahlung !?  Puzzle explained by bremsstrahlung?

  42. HADES – HSD vacuum (version'07) Inv. mass • Good agreement • Undershoot at ~ 0.4 GeV/c2 ? Pt Distributions • Mee < 0.15 GeV/c² - 0dominated • Mee > 0.15 GeV/c²: • Bremsstrahlung important at low pt

  43. Summary: • Low mass enhancement ("DLS puzzle") : a) HADES+ DLS fully consistent: b) dielectron enhancement scales with beam energy as pion production b) preliminary combined pp and pn data @1.25 GeV show enhancement (pn>pp) above "standard cocktail" : 0 e+e- , Ne+e- • Ne+e- BR? • NN bremstrahlung ? • e+e- (for pn – Fermi momentum) All components can be fixed from new HADES data Improved cocktail should be then compared to HI data... and finaly fix elementary dielectron cocktail • Vector meson production a) / region measured in pp @ 3.5 GeV with HADES b) in –medium modifications ? Ar+KCl measured in 2005 and analysis is almost complete c) p+Nb(Be) to hunt for / modification in nucleus – run scheduled for beginning of next year

  44. Quo Vadis HADES p+p 1,25 GeV EXP S201 p,d+p 1,25/3,5 AGeV EXP S201 p+A upgrade Ni+Ni p+N,A Au+Au 8 AGeV SIS Currently discussed in a committee SIS SIS

  45. back-up slides

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