Dielectron production in C+C collisions at 2AGeV with HADES Jochen Markert For the HADES Collaboration

Jochen Markert - QM November Reconstruction of the electron signal Results from C+C collisions at 2AGeV Comparison with models Comparison with DLS Dielectron production in C+C collisions at 2AGeV with HADES

Jochen Markert - QM November Introduction C+C at 2AGeV Large pair acceptance ~35% Trigger  1 st level : charged particle mult. > 4 (60%  reaction )  2 nd level: RICH+TOF/PreSHOWER → enhancement ~10 9% dM/M resolution at 0.8 GeV/c 2 M ee Total statistic: 650 M 1 st level events Opening angle > 9 o Averaged over 0 < Y < 2

Jochen Markert - QM November Selection criteria Hit matching  RICH rings ↔ MDC tracks  MDC tracks ↔ TOF and PreShower hits PID : e +, e -  β vs momentum correlation  PreShower condition Background rejection cuts  Opening angle > 9° DATA Single e +,e -

Jochen Markert - QM November Spectra before efficiency correction ~ signal pairs for full M ee range 2000 ~ 2000 signal pairs for full M ee > 150 MeV/c 2

Jochen Markert - QM November Event generator PLUTO : thermal source (T=80MeV)  polar angle distribution from charged  analysis η (TAPS data) ρ, ω : m  -scaling Δ scales with  Comparison of the data with cocktail 18 % 21 % systematic errors: 15 % - efficiency correction 10 % - combinatorial background 11 % -  0 normalization Cocktail A:  0 + η + ω “long lived components“ Cocktail B: Cocktail A + Δ + ρ

Jochen Markert - QM November Yield over Cocktail A Cocktail B/ Cocktail A factor 2 below data in 200< M ee <500 MeV/c 2 factor 4 below data in 500< M ee < 650 MeV/c 2 Comparison of the data with models RQMD: M. D. Cozma, C. Fuchs, E. Santini, A. Faessler, Phys. Lett. B 640, 150 (2006) UrQMD: D. Schumacher, S. Vogel, M. Bleicher, nucl-th/ HSD (v2.5): W. Cassing and E. L. Bratkovskaya, Phys. Rep. 308, 65 (1999). “free” spectral function Closer to data than cocktail B But model calculations Undershoot between 200<M ee <500 MeV/c 2 Overshoot for M ee > 700 MeV/c 2 C+C at 2AGeV

Jochen Markert - QM November P ┴ and Y distributions comparison data vs. cocktail ω η  M ee < 150 MeV/c 2 : Data well described (  0 -Dalitz region)  150 < M ee < 550 MeV/c 2 : Underestimation over whole p  range (factor 2). preliminary

Jochen Markert - QM November Comparison of C+C of DLS (1.04AGeV) and HADES (2.0AGeV) F(1.04) = 6.5 ± 0.5(stat) ± 2.1(sys)F(2.0) = 2.07 ± 0.21(stat) ± 0.38(sys) HADES DLS η Enhancement factor F over η for 150<M ee <500 MeV/c 2 : R. J. Porter et al., Phys. Rev. Lett (1997)

Jochen Markert - QM November Comparison of C+C of DLS (1.04AGeV) and HADES (2.0AGeV) F(1.04) = 6.5 ± 0.5(stat) ± 2.1(sys) F(2.0) = 2.07 ± 0.21(stat) ± 0.38(sys) Y exc (2.0)/Y exc (1.04) = 2.5 ± 0.5(stat) ± 1.5(sys) DLS HADES η DLS R. Averbeck et al., TAPS coll., Z. Phys. A 359, 65 (1997) R. Holzmann et al., TAPS coll., Phys. Rev. C 56, R2920 (1997)

Jochen Markert - QM November A closer look to the excess yield TAPS, KaoS measurements: Excess yield : Excess yield scales like  0 !

Jochen Markert - QM November C+C at 1 AGeV (HADES) before efficiency correction HADES preliminary Spectrum before efficiency correction Enhancement factor F(1.0) ≈ 5.8 (in 150<M ee <500 MeV/c 2 range) Enhancement within errors in agreement with DLS

Jochen Markert - QM November Summary & outlook Summary 2 AGeV C+C dielectron spectra  excess yield established  no specific p  dependence for enhancement Comparison to models ongoing Comparison to DLS:  Preliminary 1 AGeV spectra shows no contradiction to DLS data  Excess of yield for 150<M ee <500 MeV/c 2 measured at 1.04 and 2 AGeV scales like  0 multiplicity OutLook Ongoing analysis of  p+p at 2.2 GeV (Jan. 04)  exp. check of η reconstruction eff.  C+C at 1 AGeV (Aug. 04)  direct comparison with DLS  Ar+KCl at AGeV (Sep. 05)  p+p at 1.25 GeV (Jan. 06)  Δ production Next physics runs  p/d+p, at 3.5/1.25 AGeV (Spring. 07)  ω production/isospin dependence  p+A (2007+)  Heavy systems, pion beam (2008/9)

Jochen Markert - QM November The HADES collaboration  Bratislava (SAS, PI), Slovakia  Catania (INFN - LNS), Italy  Cracow (Univ.), Poland  Darmstadt (GSI), Germany  Dresden (FZD), Germany  Dubna (JINR), Russia  Frankfurt (Univ.), Germany  Giessen (Univ.), Germany  Milano (INFN, Univ.), Italy  Munich (TUM), Germany  Moscow (ITEP,MEPhI,RAS), Russia  Nicosia (Univ.), Cyprus  Orsay (IPN), France  Rez (CAS, NPI), Czech Rep.  Sant. de Compostela (Univ.), Spain  Valencia (Univ.), Spain  Coimbra (Univ.), Portugal

The END Thank you for your attention

Jochen Markert - QM November and  design  π 0, η acceptance  1AGeV  Comparison with Pluto cocktail preliminary Pluto vs Hades data π 0 π 0 →e + e – γ Hades DLS DLS mid-rapidity η→e + e – γ Hades DLS DLS mid-rapidity

Jochen Markert - QM November Phase space coverage: HADES vs DLS A direct Comparison between HADES and DLS dielectron results not feasible π 0 π 0 →e + e – γ η→e + e – γ

Jochen Markert - QM November Efficiency corrections Efficiency matrix is created for single leptons (e+, e - ) in p (0 – 2 GeV/c), Θ (0 o – 90 o ), Φ (0 o – 360 o ) averaged over momentum averaged over all sectors

Jochen Markert - QM November Acceptance matrix Acceptance matrix is created in p (0 – 2 GeV/c), Φ (0 o – 60 o ), Θ (0 o – 90 o ) for the single leptons. Integrating over internal dilepton angle → Pair acceptance matrix: M ee, P T and Y

Jochen Markert - QM November Acceptance matrix Opening angle > 9 o Acceptance matrix is created in p (0 – 2 GeV/c), Φ (0 o – 60 o ) and Θ (0 o – 90 o ) for the single leptons. Integrating over internal dilepton angle one can create pair acceptance matrix in 3D: M ee, P T and Y

Jochen Markert - QM November Experiment RawData Raw Data HADES Analysis Physics PairSpectra Pair SpectraSimulation Monte-Carlo Data Detector Simulation Analysis Event Generator Pair Spectra Efficiency Correction Correction dN/dM AcceptanceFilter Acceptance Filter Theory Analysis flow

Jochen Markert - QM November Days of data taking Events all files all good files only M4 events only events with >=1 track Evaluation of the statistics 242 M - recorded events 217 M – trigger M4 events 6 % of LVL1 events are also LVL2 46% - LVL2 60% - LVL1

Jochen Markert - QM November UrQMD impact parameter [fm] σ tot σ reac σ trigger LVL1 trigger - centrality selection σ geom - Π b 2 max * in agreement with Kox et all. 864 ± 45 mbarn

Jochen Markert - QM November Normalization factor NOV02 Yield/event0.79HADES acceptance – LVL1 trigger Correction to 4Π1.44 Yield corr to 4Π1.15 Corr. to trigger0.714Π – LVL1 trigger Min. bias yield0.814Π min. bias 6.5 ● 10 8respective number of LVL1 events * DS factor : 6.5 ●  0 multiplicity extrapolated into 4Π : efficiency of the LVL2 trigger : 0.92

Jochen Markert - QM November The spectrometer concept Geometry  Full azimuth, polar angles 18 o - 85 o  Pair acceptance  0.35  About detector channels Particle identification  RICH: CsI solid photo cathode, C 4 F 10 radiator, N o  80, pion suppression  10 4  TOF: 384 scintillator rods  TOFino: 24 scintillator paddles  temporary solution, RPC in future  Pre-Shower: 18 pad chambers & lead converters) Momentum measurement  Magnet: superconducting Toroid with B  = 0.36 Tm  MDC: 24 multi-wire drift chambers, single-cell resolution  140  m 1 m During run in November 2002 RICH, inner MDC’s, TOF and SHOWER ready outer MDC’s only partly installed In analysis presented here only inner MDC’s are used

Jochen Markert - QM November Lepton multiplicity per event ~7% of the events contain 2 opposite sign leptons ~7% of the events contain 2 like sign leptons ~83% of the events contain only 1 lepton

Jochen Markert - QM November Efficiency:  80% Purity:  85% Contamination:  lepton fakes  15% (mainly close pairs)  hadrons < 3% Single leptons: Efficiency and Purity Simulation p*q [MeV/c]

Jochen Markert - QM November Background rejection C1 C1 – the only pair cut C2C3 C2, C3 – lepton cuts TOF/Shower <9 o RICH MDC I-II C1 C2 C3 C1 C2 C3 <9 0 Close pair Shared detector hit close conversion candidate Relative suppression C1 C2 C3

Jochen Markert - QM November combinatorial background: M < 150 MeV/c 2 - sLS M > 150 MeV/c 2 - mOS M ee > 150MeV/c 2 Combinatorial background same event Like-Sign (sLS) vs. mixed event Opposite-Sign (mOS) Normalization done between MeV/c 2 M ee sLS and mOS background show same behavior for M ee > 150 MeV/c 2

Jochen Markert - QM November Summary of the eff corrections, normalization and systematic errors Components for the efficiency corrections: efficiency correction opening angle correlation tracking efficiency – 92% for each singles Components for the normalization: number of LVL1 * DS events second level trigger (LVL2) efficiency – 92%  0 multiplicity into 4 Components for the systematic errors: 15 % - efficiency correction (self-consistence check) 10 % - combinatorial background 11 % -  0 normalization 18 % 21 %

Jochen Markert - QM November Estimation of the systematic errors efficiency corrections at maximum 15% combinatorial background at maximum 10% Normalization to  0 multiplicity 11 % systematic error comes from: efficiency/purity corrections extrapolation to 4, full momenta

Jochen Markert - QM November Self-consistency check of efficiency correction SIMULATION THEORY Pluto data through HADES acceptance filter Pluto data through reconstruction chain and efficiency correction

Jochen Markert - QM November Comparison of C+C of DLS (1.04AGeV) and HADES (2.0AGeV) F(1.04) = 6.5 ± 0.5(stat) ± 2.1(sys) F(2.0) = 2.07 ± 0.21(stat) ± 0.38(sys) Y exc (2.0)/Y exc (1.04) = 2.5 ± 0.5(stat) ± 1.5(sys)

Jochen Markert - QM November P ┴ and Y distributions comparison Data vs. PLUTO Good agreement for the low masses ! No strong P ┴ dependence for enhancement ! ω η

Jochen Markert - QM November Comparison of the data with models RQMD Tübingen C.Fuchs, D. Cozma HSD Gießen (v2.5) E. Bratkovskaya, W. Cassing In-medium calculation Undershoot between 200<M ee <500 MeV/c 2 (HSD) Overshoot between 450<M ee <600 MeV/c 2 (RQMD) in-medium