Electromagnetic processes in elementary reactions. Béatrice Ramstein Institut de Physique Nucléaire d Orsay, France

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1 Recent results from HADES : Electromagnetic rocesses in elementary reactions Béatrice Ramstein Institut de Physique Nucléaire d Orsay, France

2 The Collaboration SIS 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 München (TUM), Germany Moscow (ITEP,MEPhI,RAS), Russia Nicosia (Univ.), Cyrus Orsay (IPN), GSI France Rez (CAS, NPI), Czech Re. Sant. de Comostela (Univ.), Sain Valencia (Univ.), Sain Coimbra (Univ.), LIP, Portugal Béatrice Ramstein, IPN Orsay, France 2

3 Motivations of HADES exeriment SPS RHIC AGS hadrons QGP SIS 100 SIS 300 CBM SIS 18 HADES KEK,JLAB,TAPS G7 Di letons : enetrating robes medium modifications of vector meson roerties (ρ,ω) electromagnetic structure of hot and dense baryonic matter From B.J. Schäfer, J. Wambach riv. communication ρ/ρ o ~ 1-3, T < 100 MeV N π /A art 10% Béatrice Ramstein, IPN Orsay, France 3

4 Secificity of A GeV energy range long life time of the dense system (u to 15 fm/c) τ ρ ~ 1.3 fm/c, τ ω ~ 23 fm/c dominance of Δ resonance resonance matter (Δ 33 ) ρ/ρ 0 UrQMD calculations Au+Au 1 AGeV 1-2 GeV ρ/ρ 0 n, Δ Δ tot 15 fm/c π Δ π Δ Δ π N π Dalitz γe + e - N -1 N -1 Δ N e + e - Δ Dalitz Béatrice Ramstein, IPN Orsay, France 4

5 ! inconsistent formula can be found in the litterature Clarified by J. Van de Wiele Δ Dalitz decay: what is known? exact QED calculation : 3 amlitudes: e.g. Magnetic, Electric and Coulomb dγ(δ Ne 2 dq + - e ) = f 2 ( ) ( ) ( ) ( ) q m, q + 3 q + q 2 Δ q G M G E G C 2m Δ Δ + e + e - Δ + q 2 = M 2 inv (e+ e - ) = M γ* 2 > 0 Not measured γ* e - Dalitz decay e + Form factors G M (q 2 ), G E (q 2 ), G C (q 2 ) q 2 0 : «Time like «electromagnetic structure of N - Δ transition known only at q 2 =0 ( γn Δ πn) G M (0)=3, G E (0)=0.04, G C (0)=0.2 radiative decay: Δ Nγ BR=0.56%±0.06% Δ + Δ + γ γ q 2 = 0 Radiative decay Béatrice Ramstein, IPN Orsay, France 5

6 Δ Dalitz decay : form factors dγ/dm Form factors G M (q 2 ), G E (q 2 ), G C (q 2 ) «hoton oint» G M (0)=3, G E (0)=0.04, G C (0)=0.2 in transort models : constant G M : HSD, IQMD, UrQMD M Δ =1232 MeV/c 2 G M =3.0 G M (q 2 ) Iachello M Δ =1480 MeV/c 2 (E th =1.25 GeV) extended-vdm model: : RQMD G M (q 2 ) 0.6m 2 ρ two comonent Iachello model = «VMD like» Wan & Iachello, int.. J. Mod.. Phys. A 20(2005) M Δ =1830 MeV/c 2 (E th =2.2 GeV) M ee (GeV/c 2 ) Δ Dalitz decay branching ratio BR ~ Béatrice Ramstein, IPN Orsay, France 6

7 HADES 2 nd generation dileton sectrometer Side View Accetance: Full azimuth, olar angles 18 o -85 o Pair accetance 0.35 Particle identification: RICH, Time Of Flight, Pre-Shower (ad chambers & lead converter) ( also MDC (K ± )) Trigger: 1st Level: charged article multilicity (~10 khz) 2' Level: single electron trigger (~2.5 khz) START FW Momentum measurement Magnet: Bdl = Tm MDC: 24 Mini Drift Chambers Letons: Δx~ 140 μ er cell, Δ/ ~ 1-2 % ΔM/M ~ 2% at ρ mass Béatrice Ramstein, IPN Orsay, France 7

8 C+C dileton sectra 1/N π 0 dn/dm [1/GeV /c 2 ] C+C, 1.0 A GeV no medium effects HADES DLS Transort model: HSD (Giessen) HSD: π 0 Dalitz η Dalitz Δ Dalitz ω Dalitz ω ρ Brems. NN Brems. πn All 1/N π 0 dn/dm [1/GeV /c 2 ] C+C, 2.0 A GeV no medium effects 10-2 HADES HSD: π 0 Dalitz η Dalitz Δ Dalitz ω Dalitz ω ρ Brems. NN Brems. πn All M [GeV/c²] data: PLB 663 (2008) M [GeV/c²] PhD M.Sudol Phys. Rev. Lett. 98 (2007) C+C 1 AGeV data in agreement with DLS data (unexlained over years) Porter et al., Phys. Rev. Lett 79 (1997) Both sets of data are comatible with new transort model calculations E. Bratkovskaya and W.Cassing, nucl-th/ new treatments of Bremsstrahlung: R. Shyam & U.Mosel, PRC67 (2003) L.P. Katari, B. Kämfer, NPA 764 (2006) 338 Béatrice Ramstein, IPN Orsay, France 8

9 NN Bremsstrahlung: Soft hoton aroximation γ* γ* Full OBE: meson exchange currents Amlitude calculated for real hoton + hase sace correction Half off-shell nucleon form factors Effects of VDM form factors in Katari & Kämfer model R. Shyam & U.Mosel, PRC67 (2003) no FF + Katari&Kämfer, NPA 764 (2006) 338 Gauge invariance contact terms n Bremsstrahlung by Katari & Kämfer factor 4 larger than SPA and Syam& & Mosel Bremsstrahlung also higher, but still much smaller than n Δ grahs : same tye of discreancies arxiv:nucl-th Béatrice Ramstein, IPN Orsay, France 9

10 More transort models results... BUU Barz et al. UrQMD Bleicher et al. IQMD Thomere et al. RQMD: E.Santini et al Δ Dalitz n C+C 2 AGeV n Bremsstrahlung and Delta Dalitz decay Imortant issues for understanding intermediate mass dileton yield Need for elementary, n reactions Béatrice Ramstein, IPN Orsay, France 10

11 reaction at 1.25 GeV: Δ Dalitz decay LH2 target, normalisation to elastic scattering (syst.error ~ 30 %) E=1.25 GeV < η threshold Bremsstrahlung is small reliminary Pluto simulations 1) Δ + σ( Δ + ) = 6 mb ~ 3/2 σ( π ) Δ Dalitz decay from QED vertex a) G M =3 b) Iachello G M (q 2 ) G M (q 2 ) Δ + γ* e -- e + 2) dσ/dmd dm from OBE model (Katari( & Kämfer) K with assumtion on γ* angular distribution a) Delta grahs only b) all grahs ( bremstrahlung +FSI) Dalitz decay from simle model + Iachello G M (q 2 ) OK BR ~ sensitivity to N-Δ electromagnetic structure! Even better in exclusive e + e - events.. Béatrice Ramstein, IPN Orsay, France 11

12 reaction at E=1.25 GeV: e + e - events only Δ + Bremstrahlung for M e+e- > 140 MeV/c events π π γe + e - M ee (GeV/c 2 ) missing mass MM(e + e - ) (GeV/c 2 ) About 2200 events from Δ Dalitz decay + Bremstrahlung but π background to be rejected (resolution on MM(e + e - )!) Interest of exclusive events: M inv (,e +,e - ) γ* angular distribution more efficient constraints on models and larger form factors sensitivity G M (q 2 ) Δ + Béatrice Ramstein, IPN Orsay, France 12 γ* e -- e + (Tingting Liu s PHD ) +. Small? γ* e -- e +

13 d at 1.25 GeV: n Bremstrahlung sensitivity deuteron beam HADES 2 m sectator roton 7 m Forward Wall ( ) PRELIMINARY Test of n bremsstrahlung contribution Fermi momentum η contribution normalisation to elastic scattering (syst.error ~ 30 %) PRELIMINARY HADES n data: a new uzzle?? PLUTO simulations: «quasi-free» n 1) σ (n nδ + ) = σ (n Δ )= 6 mb ~ 3/4 σ(n nπ ) η roduction (COSY/CELSIUS) added 2) Katari and Kämfer full OBE Béatrice Ramstein, IPN Orsay, France 13

14 HADES exerimental rogram 2001/ C + C 2 AGeV C + C 1 AGeV GeV elastic, exclusive e+e- (π,η) Ar + KCl 1.75 AGeV GeV exclusive e+e- (π,δ) GeV d AGeV +Nb 3.5 GeV 1 PRL (e+e-) + 1 submitted (hadron) 1 PLB (e+e-) + 1 submitted (hadron) Analysis finished (draft) Validation of detector erformance, measures of π and η Dalitz decays (helicity distribution), free cocktail Analysis ongoing dielectron sectra, medium effects inclusive analysis finished (draft) Δ Dalitz decay first measurement ω line shae and cocktail (π, Δ, η, ω, ρ, φ...)! Contribution of n Bremstrahlung / Δ Dalitz decay Reference for medium effects Béatrice Ramstein, IPN Orsay, France 14

15 First eaks at 3.5 GeV ω e + e - decay observed for a first time at SIS/Bevalac energy Cocktail normalized to π (no abs. norm.) at 3.5 GeV Mass resolution in the ω region < 2,7 % Ar 2007 Nb at 3.5 GeV On-line Nb sectrum PRELIMINARY Δ η π 0 ρ ω PRELIMINARY φ Oct 2008 Béatrice Ramstein, IPN Orsay, France 15

16 Hadronic channels: high quality by-roducts!! M nπ+ nπ + E=1.25 GeV Δ roduction mechanism n FSI elastic scattering Data normalisation and consistency checks Δ ++ Tingting Liu s PHD Submitted to EPJA C+C 1 and 2 AGeV π ± mt sectra M π+ First φ mt sectrum at SIS Ar+KCl 1.75 AGeV SQM08 Béatrice Ramstein, IPN Orsay, France 16

17 Exclusive reconstruction of the π,η γe + e - Δ1232 π e + e - detected N1440 N1535 Δ1600 η π,η γ γ* γ γe + e - Helicity distributions γ* e + e - dσ/dω e ~ 1+cos 2 θ (QED rediction, first measurement! Yields and invariant mass agree with resonance model Teis et al, ZPA356 (97) 421 Refinements: Δ Decay ang. Distr. (Wicklund et al.) N(1440) roduction angle ( Aichelin et al.) Béatrice Ramstein, IPN Orsay, France 17

18 Conclusions and outlook HADES is in a very roductive eriod C+C data have confirmed DLS data and triggered new theoretical calculations which are much closer to data E=1.25 GeV : data as exected from π and Δ contributions n data unexlained critical test for theoretical inuts check contribution of n Bremsstrahlung and Δ Dalitz decay A lot of other romising data (exclusive channels, strangeness, ) Focus on «high recision hadronic hysics tests» electromagnetic structure of hadrons Inclusive roduction of mesons (off-shell effects) Necessary (and interesting!) ste before studying medium effects.. Béatrice Ramstein, IPN Orsay, France 18

19 A rogram for the future 2008/ Ugrade RPC, DAQ, MDC Ni + Ni, Au+Au 2010 π+ + N π + A Planned > 2013 Hades goes FAIR ( 8 AGeV) Béatrice Ramstein, IPN Orsay, France 19

20 Thank You Béatrice Ramstein, IPN Orsay, France 20

21 nucleon elastic form factors in the two comonent model SU sf (6) sin flavor symmetry 4 arameters a 2, γ, g,v G M /μ F d G E /F d G Mn /μ n F d G E n ( Q 2 ) G = ( 1 ) 2 d Q Béatrice Ramstein, 0.71 IPN Orsay, France 21

22 Sace-like N-Δ transition form factors ( SU sf (6) symmetry) SU sf G M (Q 2 ) 3 arameters Direct couling strength γ fixed to the value from nucleon elastic form factors 2 free arameters : a size arameter of the N-ΔN transition octet or deculet g 10 /g 8 ratio of gyromagnetic factors for meson couling to G M N-Δ /3G D «elastic values» a 2 = 0.18 GeV -2 g 10 /g 8 =1 a 2 =0.29 GeV -2 g 10 /g 8 =1 a 2 =0.18 GeV -2 g 10 /g 8 =1.28 best fit a 2 =0.29 GeV -2 g 10 /g 8 =1.28 Béatrice Ramstein, IPN Orsay, France 22

23 Dileton sectra in OBE : a «hot» and controversial subject.. news from last week. arxiv:nucl-th Shyam and Mosel «Dileton roduction in nucleon-nucleon revisited» including Δ contribution Katari and Kämfer Shyam and Mosel Δ from our model: Δ + ~ 6 mb n nδ + ~ 12 mb Δ Dalitz decay : G M =3 G M (q 2 ) Δ + γ* e -- e + Dileton sectra in 4π accetance M(GeV/c 2 ) Béatrice Ramstein, IPN Orsay, France 23

24 90% of η η Production cross sections Q CM = s 1/2 -s th Data: Celsius/WASA Calen et al. Phys.Rev.C58(1998)2667 Phys.Rev.Lett 80(1998)2069 Phys.Rev.Lett.79(1997)2642 Béatrice Ramstein, IPN Orsay, France 24

25 Momentum vs velocity (β)( + examle: Ar A GeV TOF: θ >45 0 Hadron Id ) + de/dx in MDC & TOF: article mass sectra with de/dx (TOF & MDC) selection kaon identifcation Béatrice Ramstein, IPN Orsay, France 25

26 Medium Effects in Ar+KCl HSD: E.L. Bratkovskaya and W. Cassing arxiv: v1 and rivate communication Béatrice Ramstein, IPN Orsay, France 26

27 HSD/IQMD HSD IQMD IQMD results Larger Δ yield than HSD Slightly larger n Bremstrahlung although SPA is used!! HSD IQMD Béatrice Ramstein, IPN Orsay, France 27

28 How to measure «n-» reactions? HADES deuteron beam 2 m sectator roton FW 7 m contribution of + in +n after FW selection less than 12% (M < M π0 ) less than 2% (M > M π0 ) Béatrice Ramstein, IPN Orsay, France 28

29 Sensitivity to Δ Dalitz decay/ n Bremstrahlung Invariant mass are not enough selective Pt are more selective! IQMD M e+e- (GeV/c 2 ) Need for elementary,n reactions! Béatrice Ramstein, IPN Orsay, France 29