1 / 27

Motivation for studies of pion induced dilepton production

Motivation for studies of pion induced dilepton production. Motivation for pion experiments (perspective from 2001): Subthreshold /  production amplitudes in  N V N a)Key measurement for in-medium / mass modification? b) unique tool to study Vector Meson coupling to baryon resonances

sloane-nixon
Download Presentation

Motivation for studies of pion induced dilepton production

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. Motivation for studies of pion induced dilepton production • Motivation for pion experiments (perspective from 2001): • Subthreshold /  production amplitudes in NVN a)Key measurement for in-medium / mass modification? • b) unique tool to study Vector Meson coupling to baryon resonances • Vector mesons production off nucleus

  2. one example W. Peters et.al. NPA 632(1998)109: r =r0 Nuclearmatter: additionalterms    N(1520)  r r r r D(1232) + ... + N-1 N-1 dominant role of baryons (also for SPS) ! important for future CBM Spectral function of  meson Vacuum: even at high T int. with baryons is dominant !

  3. In medium vector meson properties and  N scattering B.Friman N.PhysA610(1996) R. Rapp and J.Wambach • Direct -N Interactions (‘Rhosobars’) • low density theorem forward scattering amplitude • Optical and detailed balance theorem In medium properties are related to elementary TVN !

  4. Resonance contribution at vector mass region- off shell contributions? URQMD: arXiv:0811.4073v2: resonance model HSD : arXiv:0712.0635v2

  5. Resonance contribution at vector mass region- off shell contributions? • data seems to favour smaller VM contribution at the pole

  6. p-n puzzle?pp vs “quasi-free” pn @ 1.25 Model Calculations: a) NN-bremsstrahlung Kaptari & Kämpfer (K&K) b)  , yield constraint by data.  Dalitz decay Krivoruchenko et al. Phys.Rev.D 65 (2001) 017502+VMD form-factor (Q. Wan and F. Iachello, Int. J. Mod. Phys. A20 (2005) 1846) • pn data are not (yet) described by calculations ! • off –shell  contribution with strong isospin depend.?

  7. Vector meson production in πN π- + p n e+e- reactions in Isospin space I=1/2 (N*) I=3/2()  + n : exit channel  + n : exit channel I=1 isovector I=1 isoscalar TVN π- + n= TI=0() +TI=1() • different resonance probed via  /  2. π+ + n : π- + p rotated in Isospin space around Y by 1800 TVN π+ +n= TI=0() - TI=1() • opposite sign of iso-vector part (-1)I • access to vector-meson Baryon interaction !

  8. pp->ppX Ethresh [GeV]  /  -p->Xn  Mx [GeV/c2] Meson and resonanseproductionwith pion beams s 1.21 1.52 1.68 Meson production thresholds N, / M. Effenberger et al. PHYS. REV. C 60(1999) 044614 • direct resonance excitation: second, third res. region • strong off-shell contribution for  production D13(1520) •  partial wave analysis of Nππ channel. • What about  ? D. M. Manley et al.Phys. Rev. D 30(1984) 904 • p>0.5 GeV/c weak contribution from (1232) • (1232)->Ne+e- small !! p~1.3 GeV/c

  9. / productionin-n reactions VDM model: f/ decay couplings Relative phase of Tp->()Ndetermines interference pattern Exclusive:  -p ->e+e- n  +n ->e+e- p (via  ++d)?

  10. T/ amplitudes in  N  (/)N reactions -p (/)n+n (/)p M.F.M. Lutz , B. Froman, M. Sayuer . / Nuclear Physics A 713 (2003) 97–118 TVN • Coupled channels calculations(N,N,N,,…) • - opposite sign of T/: • destructive interferences in π- p and positive in +n • Large influence of I=1/2 below threshold: S11(1535) and D13(1520)

  11. / interference yieldin -n (published-2003) M.F.M. Lutz , B. Friman, M. Sayuer Nuclear Physics A 713 (2003) 97–118  -n e+e- n  +p e+e- p

  12. / interference: different models M.F.M. Lutz , B. Friman, M. Sayuer Nuclear Physics A 713 (2003) 97–118 • B. Kaempfer , A Titov , R.Reznik • Nucl. Phys. A721(2003)583 • Titov, B.Kaempfer • EPJA 12(2001)217 me+e-=0.6 GeV • quantitatively same picture but differs in details: • resonance contributions • (i.e D15(1520) not important) • coupling strengths (quark model vs coupled chann.) • Virtual photon angular distributions in CM sensitive to res.contributions

  13. pion beams @GSI • Becondarybeams (C+Be, N+Be,..): • Primarybeamintensity ? (~0.5*SCL) ~ 6.5*1010 N2ions/cyclereachedintests (2005) • duty factor(fast ramping of SIS magnets)? • extractionefficiency (~0.85) ? • Pion Beam profile atthe target • Pion momentump/p =4% : inbeamdetectors X1/X2 and Y3 (start) isnecessary for pionmometum determination (p/p =0.1% ) see Bjoern & Jurek talks

  14. Proton & pion beams @GSI • Intensity of pions/spill : expectations for SCL and 100% exctraction efficiency • 0.6 < p <1.5 GeV/c operation region • reached (2005 with N2 beam-0.5 SCL): 1.8*106/spill (4 sec long- 4 sec spill off ) @ p= 1.3 GeV/c • fast ramping of SIS magnets : 1.5-2 increase in duty factor possible ?

  15. Beamfocusatthe target position 25mm LH2 Target: entrance part diamter 15 mm LH2 cell diameter 25 mm d=2*1023 atoms/cm2

  16. Bunch mark:  production in -p reactions • large cross sections AND kinematically complete measurement ! • Reaction rates • total rates : LH2 at top Iπ =0.5*106/sec and reac =80 mb • e+e- @ 1.3 GeV ( = 2.5mb * 7.2 * 10-5 =180 nb) rec. in HADES : • Yield per day (24 day)= R*0.5(DAQ)*0.7(DF machine)=54/day • (~ 10/day measured for pp run) measured in 2006 !

  17. / interference yieldin -n (in times when HADES proposal was prepared-2001) Optimal energy @ s=1.55GeV 80 nb

  18. /productionin- N reactions Ekin= 1.3 GeV (s=1.89) E.Bratkovskaya Phys.Rev.C60(1999) • - p  n • Me+,e- >0.5 GeV dominated by  and  e+e- decays • Note: very small ->Ne+e- ! • - n  -,- n  n - is subthreshold ! • Me+,e- >0.5 GeV dominated by  ->e+e- • F37(1930), D35(1950) with I3/2= -1/2 • important for π-A reactions ! • (see Elena’s talk)

  19. Simulations HADES proposal-2001 cocktail 4 cocktail HADES acc • e+e- missing mass: • - + n e+e- n + X • selection of  /  • suppression: • ->e+e-, 00, …. e+e- missing mass e+e- miss. Mass

  20. PLUTO simulation’s (HADES proposal 2003) missing mass cut on nutron ! e+e- suppressed! 8o nb: ~20 day 180 nb: ~50 day Landolt-Boernstein, New Series I / 12b

  21. e+ -p boundn e+e-n M.Effenberger et al. Nucl-th/9901039  „at rest”: pe+e-< 300 MeV/c • mass modifications in 0 208Pb - W.Schoen et al. Acta Phys.PolB27(1996)2959  HADES e- Omega production in A • in‘99 spectacular effects predicted…

  22. incident photon energy range E = 900 – 2200 MeV Preliminary Measured: +A (CBTAPS/CLAS) CLAS arXiv:0707.2324v3 pe+e- >0.8 GeV/c 0 () =217 14 V.Metag priv. comm. • no mass shift • in-medium broadenning: transparency measurement •  ~ absorption =vabs  90 MeV !

  23. Theory’2008: Sensitivity to an in-medium mass shift Gi-BUU simulations: K. Gallmeister et al. Prog. Part. Nucl. Phys. 61 (2008) 283 3 scenarios: 1.) no in-medium modification 2.) broadening 3.) broadening and mass shift E= 900 – 1200 MeV E= 1500 – 2200 MeV • possible mass shift observable • near threshold even without cut • on ω momentum for E= 1500 – 2200 MeV effect only observable for extremely hard cut on ω momentum:

  24. Any chance for HADES? HADES proposal 2006 HSD: calculations (E. Bratkovskaya, D. Mishra) p+Nb @ 3.5 GeV/c rates: expected 40/day measured 10/day 3.5 GeV • experiment exp. rates: • 25 day at 1.3 GeV/c and maximal luminosity 1.17 GeV

  25. PRELIMINARY p+ 92Nb 3.5 GeV 40Ar+ 38KCl1.75 AGeV 2008 “on-line spectrum!” resonance contribution? 2007 2005 Vector mesons / at SIS h w D r p+p at 3.5 GeV • Data are available! • No quick answer to the question on in-medium / spectral function ! • Only comprehensive analysis (in progress) of the pp/p+A/andA+A can give answer

  26. Conclusions (to be work-out during this meeting) • π- p (π+ n ) reactions below  threshold – sensitive tool to study baryon-vector meson dynamics : • relevant for in-medium properties (SIS/18/300->SPS) • separation of vector/isovector em.current (intereference pattern) • πA reactions –probe for in-medium vector meson properties and low momentum + see other contributions (Madaleine , Laura, Elena, Gyuri,…) • Experiments: very challenging !!! beam intensity, in-beam pion tracking, broad focus->large background

  27. Di-electrons from -A reactions E.Bratkovskaya et.al. Phys.Rev.C60(1999) - Pb @ Ekin= 1.3 GeV R-> R-> No mass modifications R-> and mass modifications Final result depend on unknown elementary cross sections !!

More Related