1. The In-medium Widths of the  and  Mesons in Nuclei 17 Sep 20081 and the CLAS Collaboration M. H. Wood (Canisius College, Buffalo, NY, USA) M. Paolone, R. Nasseripour, D. P. Weygand, C. Djalali M. H. Wood, EMIN2009

2. Vector Meson-Nucleon Interaction  Elementary process –  experimentally studied by beam incident on hydrogen target. (T. H. Bauer, R. D. Spital, and D. R. Yennie, Rev. Mod. Phys. 50, 261 (1978))  In-medium interactions –  Sum of elementary interactions?  Medium effects (modified meson properties)?  Review of V-N properties in the medium  (S. Leupold, V. Metag, and U. Mosel, arXiv:nucl-th/0907.2388 (2009))  Mass decrease – more nucleon resonances to couple.  Width increase – modification of couplings and virtual loops. 17 Sep 2008M. H. Wood, EMIN20092

3. 17 Sep 20083 Mesons  : M=768 MeV  = 149 MeV J P =1 -  : M=782 MeV  = 8 MeV  : M=1020 MeV  = 4 MeV With the g7a experiment at Jefferson Lab (JLab), access to the in- medium meson widths. Reaction :   + A --> V X --> e + e - X ( no FSI) (E  < 4 GeV) (Talk on  meson modifications – D. P. Weygand, 19 Sep) The Widths of  and  Mesons in Nuclei M. H. Wood, EMIN2009 Nuclear transparency ratio T A =  A /A  N Measurement : nuclear transparency ratio provides access to in-medium  N and  N total cross sections. Get width from  * VN.

4. 17 Sep 2008 M. H. Wood, EMIN20094 C BA south linac north linac injector Superconducting e - Accelerator  I max =200 mA  E max =6 GeV, dE/E=10 -4.  1500 physicists, ~30 countries  operational since 1997 Jefferson Lab (JLab)

5. 17 Sep 20085 Particle Detection In CLAS M. H. Wood, EMIN2009 Excellent  /e discrimination: 5.4x10 -4 for one and 2.9x10 -7 for two leptons.

6. Superconducting Torus Magnet 6 Superconducting coils for deflecting charged particles Time-of-Flight Hodoscope 48 Scintillators/sector for measuring a particle’s travel time Electromagnetic Calorimeter Lead-Scintillator for detecting electrons Drift Chambers Ar-CO 2 6500 channels/sector to measure the path of a charged particle Gas Cherenkov Counter e/  separation CEBAF Large Acceptance Spectrometer (CLAS) e - : inbending tracks e + : outbending tracks EC e/  rejection factor : 10 -2 CC e/  rejection factor : 10 -1 EC/CC rejection factor : 10 -3 Rejection factor for e + e - : 10 -6 17 Sep 2008 6M. H. Wood, EMIN2009

7. 17 Sep 20087 Event Selection e+e+ e-e- p M. H. Wood, EMIN2009 Segmented target Foils of Carbon, Iron, Titanium, and Lead LD2 (LH2) as control Sample event LD2 C CC C Fe Ti Pb

8. 17 Sep 20088 e + e - Mass Spectra M. H. Wood, EMIN2009 Mass Spectra after subtraction of the  meson contribution. Mass Spectra with , , and  mesons simulation

9. 17 Sep 20089  Absorption SPring8  A   A’  K + K - A’ (E=1.5-2.4 GeV) T. Ishikawa et al. Phys. Lett. B 608, 215 (2005) JLab SPring8 Giessen calculations Giessen calculations w/ Spring8 absorption strengths Normalized to carbon Comparison to other workComparison to Glauber calculations M. H. Wood, EMIN2009 In-medium:    N ~ 25 – 55 mb Elementary:   N < 10 mb Needed for RHI calculations.

10. 17 Sep 200810  Absorption The in-medium width is  =  0 +  coll where  coll =  v  * VN Valencia calculations Kaskulov, Hernandez & Oset EPJ A 31, 245 (2007) Giessen calculations P. Mühlich and U. Mosel NPA 773, 156 (2006) Normalized to carbon M. H. Wood, EMIN2009 JLab (upper/lower limits) CBELSA_TAPS M. Kotulla eta al., PRL 100, 192302 (2008)

11. Momentum Dependence 17 Sep 2008M. H. Wood, EMIN200911 Possible explanation for disagreement is momentum dependence of the in- medium interactions. Average  meson momentum:  1.1 GeV (CBELSA-TAPS)  1.7 GeV (JLab) Instead of scaling each result, compare a common momentum bin. CBELSA-TAPS has data in five momentum bins.

12. 17 Sep 200812 In-medium  Interference Constructive Destructive M. H. Wood, EMIN2009 Decay channels JLab :  -> e + e - CBELSA-TAPS :  ->  0 

13. 17 Sep 200813  Interference Interference model after subtracting the  meson Data from the 2 H target M. H. Wood, EMIN2009

14. 17 Sep 200814 CLAS was an excellent tool for these studies: e + e - from rare leptonic decay of light vector mesons are identified. Clear ,  and  signals in the invariant mass spectrum. The  meson: From transparency ratios, width > 200 MeV! Disagreement with CBELSA-TAPS result momentum dependence? in-medium destructive  interference? The  meson: From transparency ratios, in medium total cross section ~ 25-55 mb Agreement with SPring8 result. Next at Jlab: High Statistics measurement of e + e - production on H 2 (on tape) Conditionally approved g7b high statistics data (LD 2, C, Fe, Nb, Sn)  Summary and Conclusions M. H. Wood, EMIN2009