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Studying Time-like electromagnetic Baryonic Transitions with HADES

Explore the sensitivity of baryonic resonances to electromagnetic structure. Study dilepton emission in dense matter using HADES collab. Analyze time-like form factors and vector meson dominance.

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Studying Time-like electromagnetic Baryonic Transitions with HADES

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  1. N R e+  e- Studying Time-like electromagnetic Baryonic Transitions with HADES Béatrice Ramstein, IPN Orsay, France for the HADES collaboration Nucleon and Resonance structure in hard exclusive processes Orsay, 29 May 2017 B. Ramstein

  2. Outline • Introduction: • Motivations of measuringe+e-emissionwith HADES at GSI • Resultsfrom ppreactions • Sensitivity of e+e- emission to the electromagnetic structure • of baryonicresonances • Resultsobtainedwith the GSI pion beam • π+π- , e+e- production • Conclusions B. Ramstein

  3. HADES experimental program: e+e- production • hadronicmatterstudies: • A+A (E/A<2 GeV), p+A (E<3.5 GeV), π+A (0.5<E<1.6 GeV) (SIS18) • Study modifications of in-medium vectormeson spectral functions • depends on NN* coupling - main players: N(1520),  (1620), • N(1720) Elementaryreactions: p+p, d(n)+p, π+p Constraininterpretation of in-medium dileptonspectra by elementaryprocesses • Inclusive e+e- production: referencespectra • Dilepton exclusive channelse.g. ppppe+e-,π-pne+e- • Dalitzdecay of baryonicresonancesRNe+e- • Sensitivity to Time-likeelectromagnetic structure • Role of VectorMeson Dominance B. Ramstein

  4. Electromagneticbaryonictransitions in Time-Like and Space-Likeregion: towards a global picture ? Time-Likeelectromagneticformfactors Space-Like electromagnetic form factors Precise data from JLab/CLAS up to -q2=4 GeV2 No data Inverse pion electroproduction q2 <0 fixed e- n F(q2) - e- R p * R * e+ p - F(q2) e- p q2 =(Mee)2> 0 Workshop « Space-Like and Time-likeelectromagneticbaryonic transitions » 8-12 May 2017, Trento P. Cole, B. R., A. Sarantsev B. Ramstein

  5. Theoretical description of Dalitzdecayprocess SpaceLike: q2<0 Time Like: q2>0 complex GTL(q2) Analytic continuation real GSL(q2) Modelsconstrained by data In the Dalitzdecayprocess: • q2stayssmall,q2 < (MR -Mp)2 e.g. at M =1232 MeV/c2 ,q2 < 0.09 GeV/c2 • influence of vectormesonpoles for large MR For N-: 2 options: • takeconstant formfactors (photon point value) • + vectormeson contribution addedincoherently • use models for formfactors GE(q2),GM(q2),GC(q2) Béatrice Ramstein

  6. Time-likeform factor models Models: fitted to space-like (q2 0) formfactors data analyticallycontinued to time-likeregion (q2>0) q2 • Two-component model (direct coupling+VDM) • Zetenyiand Wolf, Phys. Rev. C 86 (2012) 065209 • e-VDM model (,’,’’,…) M. Krivoruchenko, Ann. Phys. 296 (2002) 299 • Currentlybeingextended(workin progress) to recentdata • - SL transition FF (CLAS) • - ρ/ωNN* couplings (PWA) SpaceLike • constituent quark-core+ meson cloud • existing for N-Δ(1232) and N-N(1520) • G. Ramalho, T. PenaPhys.Rev. D85 (2012), 113014 • G. Ramalho, T. PenaPhys.Rev. D95 (2017), 014003 Time Like B. Ramstein

  7. HADES High AcceptanceDiElectron Spectrometer at GSI, Darmstadt Acceptance:Full azimuth, polar angles 18o - 85o Particle identification:e+/e-, +/- , K+/K-, p RICH,Time Of Flight, Pre-Shower (pad chambers & lead converter) ( also MDC (K)) Trigger: ~ 50 kHz Momentum measurement Magnet: ∫Bdl = 0.1- 0.34 Tm MDC: 24 Mini Drift Chambers Leptons: x~ 140  per cell, p/p ~ 1-2 % • M/M ~ 2% at peak • ElectromagneticCalorimeter • ForwardDetector (0.5-7°) • to beready in 2018 7 B. Ramstein

  8. The Collaboration SIS • Cracow(Univ.), Poland • Darmstadt (GSI), Germany • Dresden (FZD), Germany • Dubna (JINR), Russia • Frankfurt (Univ.), Germany • Giessen (Univ.), Germany • Jülich (FZJ), Germany • Milano (INFN, Univ.), Italy • München (TUM), Germany • Moscow (ITEP,MEPhI,RAS), Russia • Nicosia (Univ.), Cyprus • Orsay (IPN), France • Rez (CAS, NPI), Czech Rep. • Sant. de Compostela (Univ.), Spain • Wuppertal (BUG), Germany • Coimbra (Univ.), LIP, Portugal GSI 8 B. Ramstein

  9. Hades « strategy » • Studydileptonemissionin dense and hot matter • A+A reactions in the 1-2 AGeVenergy range C+C 1 and 2 GeV/nucleon, Ar+KCl 1.75 GeV/nucleon, Au+Au 1.25 GeV/nucleon • cold matterat normal nucleardensity p+Nb 3.5 GeV • (cf KEK, Jlab, CBELSA/TAPS) • Elementary collisions pp, dp and -p • reference to heavy-ion spectra • understanddilepton production mechanism (exclusive channels) • dileptonemissionisprobingtime-likeelectromagnetic structure of hadronic transitions! • Simultaneousmeasurements of hadronicchannels(inclusive and exclusive meson • production 1, 2, , ,  ,…) • production mechanism • Baryon spectroscopy (baryonicresonancecouplings,..) • Partial WaveAnalysis: pppp0, pppn+, -pn+ -, -pp 0- • …. strangenessmeasurement program: K- , K0,, (1385), (1405) Béatrice Ramstein

  10. (1232) Dalitzdecay: formfactors ppppe+e- E=1.25 GeV .  and 0 production cross section deduced from PWA of one pion production channels HADES coll.., Eur. Phys. J. A 51 (2015) 137 π° Dalitz: π°e+e- Shyam and Mosel, , PRC82 (2010)062201 Deviation from « point-like » transition HADES coll., arXiv:1703.07840[nucl-ex](PRC, accepted) B. Ramstein

  11. e-  * e+  N (1232) Dalitzdecay: angular distributions and branching ratio • ppppe+e- E=1.25 GeV Non-resonantBremsstrahlungsubtracted Acceptancecorrected  Production angle Helicity distributions *  e+e- scaled  contribution from pppp0(PWA)  Dalitzdecay simulation (Ramalho&Penaform factor) Only transverse :d/dΩe~ 1+cos2 Fit result : d/dcos ~ 1 + B cos2B=1.170.34 first measurement of (1232) Dalitzdecaybranching ratio BR( Ne+e-) = 4.19  0.42 (model)  0.46 (syst.)  0.34 (stat.) 10-5. B. Ramstein

  12. Higher lying resonances: meson production Cocktail of baryonic resonances Fitted to distributions in ppπ0 , pnπ+ and ppchannels HADES coll.. Eur.Phys.J. A50 (2014) 8 2 channelsunderstudy (A.Belounnas PHD Orsay) B. Ramstein

  13. Higher lying resonances: electromagnetic channels Effect of VDM like em transition FF for light baryonic resonances (N(1520),…) p+ppp e+e - 3.5 GeV ppe+e- ω R  Inclusive e+e- production reproduced by resonnace model withρNN* couplings ρ Dalitzdecays of point-like baryonic resonances constrained by ppπ0 and pnπ+ channels ppe+e- R  G. Agakishiev et al. Eur.Phys.J. A50 (2014) 8 ω J. Weil, et al., EPJA 48, 111 (2012) + “direct” ρ and ω B. Ramstein

  14. Interest of N reactionstudy • Electromagneticchannels • Exclusive -pn e+e- canbeeasilyselected • Resonanceproduced in s-channelwithfixed mass =s • (lessoverlapping contributions than in pp) • N interaction bettercontrolledthan pp • Imputs from pion photo/electro-production canbeused • Hadronicchannels: • Verypoor data base for pion beam data • New data needed to advanceknowledge in baryon • and mesonspectroscopy (J-PARC, projects of mesonbeam • facilitiesW. J. Briscoe et al., Eur. Phys. J. A51 (2015) 129) - n R * e+ p e- B. Ramstein

  15. Pion beam at GSI Pion beamtracker Diamond detectors HADES GSI pion beam momentum0.6 < p <1.5 GeV/c pion flux ~ 106/s at 1 GeV/c 2 Double-sidedSiliconsensors 100 x100mm2, 300μm thick 2 x128 channels η ω Pion momentumacceptance=2% ResolutionΔp/p < 0.3% B. Ramstein

  16. N R e+  e- Pion beamexperimentwith HADES • 2014 experiment: Limited beam time +intensity • Use of Polyethylene (CH2)n and Carbontargets • Motivations: investigate the N(1520) region • +  - and -° production in an energy scan (4 measurements s=1.46-1.55 GeV/c2) • Improve database for baryon spectroscopy: 2N (N,N, ) branchings • e+e- production s=1.49 GeV/c2 • Resonance Dalitz decays R→Ne+e- • (Link to time-like transition electromagnetic structure) • No existing data Subtraction of C contribution and Normalisation using π-+p elasticscattering B. Ramstein

  17. Bonn-Gatchina PWA: HADES data • collaboration with A. Sarantsev • 4 data samples from HADES (π-p nπ+π- and π-ppπ0π- ) • + photon (CB-ELSA,MAMI) and pion (Crystal Ball) data base One example: HADES data at p=683.5 MeV/c

  18. Bonn-Gatchina Partial WaveAnalysis in 2 production channels -p+- n -p-0p • Preliminary results •  production: •  1.3 mb at 0.69 GeV/c • N(1520): • N coupling =122 % • PDG 2015 : 15-25% • PDG 2016: no info n - total 3/2- (D13+..) 1/2- (S11+..) 3/2+ (P33+.. • OnlyN(1520) and N(1440) play a significantrolearounds=1.5 GeV • New HADES data are crucial for the determination of the  contribution • Still no data on  between 1.54 and 1.75 GeV/c2 (part of HADES future program) B. Ramstein

  19. Analysis of e+e-channels Rawe+e- invariant mass spectrum • Signal = Ne+e- -CB • CB: same-event like-sign pairs • CB rejection cuts: • Tracking optimized to reject  conversion • e+e- opening angle > 9° • Signal (M<140 MeV/c2) = 13138 • Signal (M>140 MeV/c2) = 3300 • Efficiency corrections based on • GEANT simulations Measurement on CH2 target: (d/dM)H+0.5 (d/dM)C C  4 H B. Ramstein

  20. Inclusive e+e- production • PLUTO eventgenerator • Fröhlich et al, POS (2007) 076 • π-p: • Meson production: Landolt-Börnstein • 0e+e-  e+e- • « N(1520) »: Point-likebaryonic contribution • cross section from n-p • e+e- distribution as N(1520)0 Ne+e- • π-C: • quasi-free process(momentumdistr. of • nucleonstakenintoaccount) scaledto C /H 4 • Simulations filtered by acceptance preliminary • Cocktail of point-like sources • underestimates the e+e-yieldat high invariant mass • Strongη contribution B. Ramstein

  21. Exclusive ne+e-channelwith pion beams: e+  e- 0.9 <Mmissee< 1.03 GeV/c2 Total π0 e+e-γ ηe+e-γ N(1520)ne+e- π-pne+e- π-pne+e- preliminary Minvee > 0.12 GeV/c2 PWA  ρe+e- ρπ+π- Vector Dominance Model (d/dMee)= (d/dM )* BR(Mee=M) * (M/Mee)3 Minvππ(GeV/c2) • Deviation from point-likebehaviour consistent with VDM (ρ e+e-) • ρ cross section and mass shapederived from π-pπ+π- n measured in the sameexperiment ! • Empiricalway of takingintoaccount VDM formfactors for electromagneticdecays B. Ramstein

  22. e+e- exclusive production: comparison to models • Lagrangian model : real γ + VDM coupling • Large Born term • Zetenyiand Wolf • Phys. Rev. C 86 (2012) 065209 • Cocktails from resonance models • (GiBUU) • N(1520)0 nne+e- • Overestimates contribution at low q2 • (related to too large • radiative decay BR (R N ) in • pure VDM models) • s channel model based on ρ/ωNN* couplings • Destructive • interference • toolowe+e-yield • B. Kaempfer , A Titov , R.Reznik NPA721(2003)583 • M. Lutz , B. Friman, M. SoyeurNPA 713 (2003) 97–118 B. Ramstein

  23. N R e+  e- Information on em structure from angular distributions • e+e- invariant mass distributions are only sensitive to • a linearcombination of |FF|2 • Additional information in angular distributions • Similarly to polarization in (e,e’) scattering Density matrix formalism: E.Speranza et al. Phys.Lett. B764 (2017) 282-288 A. Sarantsev (ECT* meeting, May2017)  |A|2= • 3 independentdensity matrix elements:11 , 10,1-1 depending on Mee and  • contain information on electromagnetic structure • e.g. pure transverse (E/M): 11 =1/2, 10 =0 • Related to helicity amplitudes and/or formfactors B. Ramstein

  24. Fit of helicity angle distribution s=1.49 GeV/c2 quasi-free -pne+e- Fitted to HADES data in HADES acceptance : Cos CM < 0 0<Cos CM < 0.5 Cos CM > 0.5 B. Ramstein

  25. Very first results on density matrix elements Quasi-free -pne+e- Microscopic model s and t channels: N(1440) and N(1520) with VDM formfactors: B. Friman, M. Zetenyi, E. SperanzaPhys.Lett. B764 (2017) 282-288 s=1.49 GeV/c2 Mee> 400 MeV/c2 • Despitelowstatistics, significant • information on the electromagnetic • structure of the transition • Presence of longitudinal contribution • Consistent with pure N(1520) in VDM • Model • Link to helicity amplitudes to beworked out Cos CM < 0 Cos CM > 0.5 Federico Scozzi (PHD IPNO/Darmstadt) EPJ Web Conf., 137 (2017) 05023 0<Cos CM < 0.5 B. Ramstein

  26. SL and TL transitions: towards a global picture? Still a long way to go in time likeregion… SL + TL B. Ramstein

  27. Outlook-Future plans for HADES •  Dalitzdecaymeasured for the first time • pioneeringpromisingstudieswith HADES and the GSI pion beam in the N(1520) region… • e+e-channels : Time-likebaryonic transitions • 2 channels: baryon spectroscopy • 2018: 3-4 year time slot for HADES experimentswithbeams (p,, A) at SIS 18 before the start of FAIR • Higheracceptance(Forward Detector)+ ElectromagneticCalorimeter • InvestigateheavierresonancesΔ(1620), N(1720),… • in e+e-channels and manyhadronicchannels, • e.g. -pn , K0, K,…. • Electromagneticdecays of hyperons • in pp reactions : Y, Ye+e- Pave the way for future mesonbeamfacilities W. J. Briscoe et al., Eur. Phys. J. A51 (2015) no.10, 129 • After 2022: HADES experiments at FAIR • (p and ion beams, possibly pions in future….) B. Ramstein

  28. Thankyou B. Ramstein

  29. Dalitz decaydifferentialdecaywidth: N(1520)Ne+e- =f(2 )(|GE|2+3|GM|2 + (Mee/MR)2|GC|2) MR=1.520 GeV/c2 B. Ramstein

  30. B. Ramstein

  31. B. Ramstein

  32. B. Ramstein

  33. Separation of channels elastic p-(normalization) n+- 791 938,8 MeV (= 1.7%) 939,4MeV(= 1.0%) beamtracker 791 PE C p PE C, C e.b.e p p-0 791 791 132,8 133,2beamtracker SAID

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