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In-medium Properties of the r, w, and f

In-medium Properties of the r, w, and f. PAC33 Proposal PR08-018 M. H. Wood (spokesperson), C. Djalali (spokesperson), R. Gothe, D. Tedeschi, S. Strauch Univ. of South Carolina R. Nasseripour (spokesperson) George Washington Univ. D. Weygand (spokesperson) Jefferson Lab

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In-medium Properties of the r, w, and f

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  1. In-medium Properties of the r, w, and f PAC33 Proposal PR08-018 M. H. Wood (spokesperson), C. Djalali (spokesperson), R. Gothe, D. Tedeschi, S. Strauch Univ. of South Carolina R. Nasseripour (spokesperson) George Washington Univ. D. Weygand (spokesperson) Jefferson Lab and the CLAS Collaboration

  2. Quark-gluon level: • Chiral symmetry is broken by the small u,d masses. • In hot/dense medium, • Chiral symmetry restoration. • Many-body effects: • Modified coupling constants • Modified loops • Opening of decay channel • … Seminal work on scaling law: G. E. Brown and M. Rho, PRL 66,2720, (1991) Cited 786 times in SPIRES database Mesons in the Medium Hadronic structure is going to be altered due to the proximity of other hadrons. Predicted modifications can be viewed :

  3. r meson r meson r=0 r0/2 r0 r Meson in the Medium vacuum state Calculations by the Valencia group - hybrid of quark effects and nuclear many-body effects. Chiral symmetry restoration: T. Hatsuda and S. H. Lee, Phys. Rev. Lett. 66, 2720 (1992) • = 0 • = 0.5r0 • = r0 Many-body effects: R. Rapp, G. Chanfray, J Wambach, Nucl Phys. A617 (1997) 472 JLab densities

  4. w Meson in the Medium Quark-Meson Coupling Model (A. W. Thomas): K. Saito et al., Phys. Lett. B 433 (1998) 243 K. Saito et al., Phys. Rev. C 59 (1998) 1203 K. Saito et al.,Prog. Part. Nucl. Phys. 58 (2007) 1 Considers the w meson as a quark-anitquark pair coupled to the nucleons through s-meson exchange. Applied to w-nucleus bound states and meson propagation in the medium. Does not include absorption of the w meson in the nucleus. JLab densities

  5. Experimental Results Rel. Heavy-Ion Elementary Reactions M.Naruki et al., PRL 96 (2006) R. Muto et al., PRL 98 (2007) D. Adamova et al., PRL 91 (2003) R. Arnaldi et al., PRL 96 (2006) *D. Trnka et al, PRL 94 (2005)

  6. ct~23.4 fm ct~1.3 fm ct~44.4 fm CLAS Experiment at Jefferson Lab(T~0 MeV and r~0.5r0) • Predicted medium modifications are large enough to be observed at normal nuclear density. • Vector mesons produced in various nuclei. • Photon beam probes the interior of the nucleus. • e+e- decay : no final state interactions, 10-5 branching ratio • CLAS detector rejection of pion pairs: 107 • Detect all three mesons simultaneously. • Measure the r meson directly and cleanly. • r meson – decays inside the nucleus (direct properties). • w and f mesons – interact inside nucleus (many-body effects).

  7. w r f e+e- Mass Spectra and Background Determination Mixed event background determination: Shape – random mixing of e+ and e- from single lepton events. Absolute normalization - pairs of identical (e+e+, e-e-) leptons, which are produced only by uncorrelated processes provide an absolute normalization. m+m-measurement: at CERN-SPS IPNO-DR-02.015 (2002) p+p- measurement: at CERN-ISR (Nucl. Phys. B124 (1977) 1-11). e+e- measurement: at RHIC (arXiv:nucl-ex/0510006 v1 3 Oct 2005). Proton Femtoscopy of eA interactions:ITEP group, CLAS Analysis 2003-103

  8. C Fe D2 Fit with Breit-Wigner/M3, where M and G are free parameters. e+e- Invariant Mass (GeV) The r Mass Spectra After removing the w, f, and background contributions: Broadening of the width is consistent with many-body effects.

  9. Outcome • Publish • PRL published – R. Nasseripour et al.,PRL 99 (2007) 262302 • PRC article will be submitted in January 2008. Impact Result does not confirm the KEK results. Rule out DM predictions of Brown/Rho and Hatsuda/Lee. Momentum Dependence Mass spectra – spectral function, branching ratio, production. Need more information - momentum dependence. Chiral symmetry restoration - expected to be momentum independent. Many-body effects – momentum dependent.

  10. Momentum Dependence – r Meson Giessen group (U. Mosel): W. Peters et al., NPA 632 (1998) 109 M. Post et al., NPA 741 (2004) 81 BUU model of r meson production and propagation with nucleon resonance-hole contributions.

  11. Previous data 5x statistics Momentum Dependence - Proposal With new measurement, we will obtain 4 bins of equal statistics in momentum. The sensitivity of each bin will be better than what was achieved over the entire previous CLAS experiment. Proposed improvement: 5x statistics Use Nb and Fe targets

  12. CLAS result - Fe Estimated error Esimated error – total Nb Momentum Dependence - Experiment Below are the projected errors for each momentum bin based on the previous CLAS results.

  13. ct~23.4 fm ct~1.3 fm ct~44.4 fm Additional Studies Previous r-meson in Fe result: DM – small and consistent with zero. DG – broadening consistent with many-body effects. Proposal: Momentum dependence of DM and DG of r meson in Fe and Nb. Absorption studies: Although the detected w and f mesons decay outside the nucleus, the in-medium widths can be accessed through meson-nucleon interactions.

  14. = 47 MeV = 34 MeV 93 MeV 94 MeV 180 MeV Absorption of w Meson and its In-medium Width The in-medium width is G=G0+G* where * = grv*VN Transparency ratio: Normalized to carbon Normalized to carbon M. Kaskulov, E.Hernandez and E. Oset EPJ A 31 (2007) 245 P. Mühlich and U. Mosel NPA 773 (2006) 156

  15. Proposed JLab data JLab (preliminary) TAPS (arXiv:nucl-ex0711.4709v2, Dec 2007) Comparison of w Meson Results TAPS latest: Gw~130-150 MeV Preliminary JLab result shows greater in-medium broadening.

  16. Giessen calculations Giessen calculations w/ Spring8 absorption strengths Proposed JLab data JLab (preliminary) Spring8 T. Ishikawa et al. Phys. Lett. B 608, 215 (2005) Comparison to Expt. – f Meson The Spring8 experiment was g A gf A’ g K+K- A’ (Eg=1.5-2.4 GeV). CLAS has the advantage of the e+e- detection. Proposed experiment will study momentum dependence.

  17. Unique Characteristics of CLAS The CLAS detector at 3 GeV is ideal for the study of the in-medium properties of the vector mesons. • Intense photon beam. • Vertex reconstruction for novel target design. • Excellent e+e- identification and p+p- rejection. • Clean mass spectra with all three vector mesons. • Low background which is determined accurately.

  18. Previous target Pb Fe Ti C C C C LD2 Proposed target (not to scale) This Proposal • Beam energy: 3 GeV • Targets: LD2, C, Fe, Nb, Sn • LD2 – control • Fe – quality check • Nb – new results on r meson • C – normalization; w,f studies • Sn – new result; w,f studies • Fe and Nb thicknesses: 2.5 g/cm2 (x2.5) • Beam time: 36 days (x2) • Statistical improvement: x5

  19. Proof of chiral symmetry restoration can only be achieved with an understanding of the vector-meson many-body effects. Summary Medium modifications are complicated with various interactions: • Fundamental : chiral symmetry restoration, quarks/gluons • Effective : nuclear many body effects • Hybrid : quark-meson couplings • Proposal: • Momentum dependence of the in-medium properties of r meson in Fe and Nb. • Additional studies – w and f meson in-medium widths accessed through absorption.

  20. Backup Slides

  21. J. G. Messchendorp, private communication Effective Density

  22. Momentum Dependence – r Meson Giessen group (U. Mosel): W. Peters et al., NPA 632 (1998) 109 M. Post et al., NPA 741 (2004) 81 BUU model of r meson production and propagation with nucleon resonance-hole contributions. Transverse Longitudinal

  23. Integrating over momentum range Valencia group (no momentum dep.) Dividing into momentum bins TAPS data Giessen group (before TAPS result) Giessen group (after TAPS result) Momentum Dependence - w Meson • Preliminary CBELSA/TAPS results. • Wealth of information in the absorption measurement. • Issue with subtraction of large background. • These results need to be independently checked.

  24. Momentum Dependence – w Meson Quark-Meson Coupling Model (A. W. Thomas): K. Saito et al., Phys. Lett. B 433 (1998) 243 K. Saito et al., Phys. Rev. C 59 (1998) 1203 K. Saito et al., Prog. Part. Nucl. Phys. 58 (2007) 1 Calculations at r=2r0 Transverse Longitudinal

  25. Recent PAC Approved Photon-beam Experiments

  26. Light vector meson in a stationary nucleus Latest predictions range from 5-20%. • Relativistic Heavy Ion Collisions • collide heavy nuclei (Au+Au) at high speeds • compression of the 2 nuclei creates an environment of high temperature and density Phase Diagram Hadronic properties depend on the quark condensate can change with r (density) and T (temperature). As goes to zero, hadron masses go to zero. How to measure modifications?

  27. Multi-Segment Nuclear Target Contains materials with different average densities. LD2 and seven solid foils of C, Fe, Pb, and Ti. Each target material 1 g/cm2 and diameter 1.2 cm Approximately same number of nucleons/target Proper spacing 2.5 cm to reduce multiple scattering Deuterium target as reference, small nucleus, no modification is expected.

  28. p e+ e- Event Display Due to the magnetic field orientation, the positively-charged particles bend away from the beamline. The negatively-charged particles bend inward.

  29. w r f e+e- Invariant Mass Spectra Same sector events • Same sector e+e- removed • Momentum corrections • Target energy loss corrections • Lepton momentum > 500 MeV • Mixed-event background • (see next slide)

  30. Background Subtracted Fits Model the uncorrelated background using “mixed-events” technique. Monte-Carlo distributions of individual possible channels that contribute to e+e- mass spectrum are generated by Giessen BUU model and to fit the data. Nucl. Phys. A671, 503(2000) Vector mesonsr: M=768 MeV G= 149 MeV ct~1.3 fm JP=1- w: M=782 MeV G = 8 MeVct~23.4 fmf: M=1020 MeV G = 4 MeVct~44.4 fm

  31. C Fe D2 e+e- Invariant Mass (GeV) The r Mass Spectra After removing the w, f, and background contributions: Fit function: Photon propagator Breakup momentum phase space

  32. Extracting the Result • Make ratio of mass spectra of heavy target to reference target. • Fit the slope in region of r meson. • Compare with relation of slope to the percentage change in mass. In Fe nucleus, g7a sets an upper limit with a 95% confidence level: Dm~-21 MeV. Broadening of the width is consistent with nuclear many-body effects. Accepted by PRL, Oct. 2007. PRC version in ad hoc committee.

  33. Decay length L: p=momentum M=mass G=width Outcome • Publish • PRL published – R. Nasseripour et al.,PRL 99 (2007) 262302 • PRC article will be submitted in January 2008. Impact Result does not confirm the KEK results. Rule out DM predictions of Brown/Rho and Hatsuda/Lee. Momentum Dependence Mass spectra – spectral function, branching ratio, production. Need more information - momentum dependence. Chiral symmetry restoration is expected to be momentum independent. Momentum dependence addresses many-body effects.

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