In-medium Properties of the  and  PAC33 Proposal PR 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

Mesons in the Medium Hadronic structure is going to be altered due to the proximity of other hadrons. Predicted modifications can be viewed : Seminal work on scaling law: G. E. Brown and M. Rho, PRL 66,2720, (1991) Cited 786 times in SPIRES database 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 …

 Meson in the Medium Many-body effects: R. Rapp, G. Chanfray, J Wambach, Nucl Phys. A617 (1997) 472       meson vacuum state Chiral symmetry restoration: T. Hatsuda and S. H. Lee, Phys. Rev. Lett. 66, 2720 (1992) Calculations by the Valencia group - hybrid of quark effects and nuclear many-body effects.      JLab densities

 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  meson as a quark-anitquark pair coupled to the nucleons through -meson exchange. Applied to -nucleus bound states and meson propagation in the medium. Does not include absorption of the  meson in the nucleus. JLab densities

KEKCBELSA/TAPSCERES NA 60 Reaction pA  (  ) A’ VM  e+e-  A   A’    0  p+Au,Pb+Au   e+e- In+In    +  - Condition  =0.53  0, T~0 MeV  =0.55  0, T~0 MeV 158 A GeV Mass  m  ~  m  ~-9%  m  ~ -4%  m  ~ -14%*  m not favored  m not favored No mass shift Width   ~   ~ 0 MeV   (  =  0 ) = 47 MeV   (  =  0 )  140 MeV (unpublished) Broadening favored Strong broadening Issues No direct extraction of  meson  0 FSI Large background (100x) , T not constant M.Naruki et al., PRL 96 (2006) R. Muto et al., PRL 98 (2007) *D. Trnka et al, PRL 94 (2005) R. Arnaldi et al., PRL 96 (2006) D. Adamova et al., PRL 91 (2003) Experimental Results Elementary Reactions Rel. Heavy-Ion

CLAS Experiment at Jefferson Lab (T~0 MeV and  ~0.5    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, branching ratio CLAS detector rejection of pion pairs: 10 7 Detect all three mesons simultaneously. Measure the  meson directly and cleanly.  meson – decays inside the nucleus (direct properties). and  mesons – interact inside nucleus (many-body effects). c~1.3 fm c~23.4 fm c~44.4 fm

e + e - Mass Spectra and Background Determination  measurement: at CERN-SPS IPNO-DR (2002)  measurement: at CERN-ISR (Nucl. Phys. B124 (1977) 1-11). e+e- measurement: at RHIC (arXiv:nucl-ex/ v1 3 Oct 2005). Proton Femtoscopy of eA interactions: ITEP group, CLAS Analysis 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.   

The  Mass Spectra After removing the , , and background contributions: Target Mass (MeV/c 2 ) CLAS data Width(MeV/c 2 ) CLAS data Mass(MeV/c 2 ) Giessen Sim. Width(MeV/c 2 ) Giessen Sim. 12 C / / / / Fe / / / / Broadening of the width is consistent with many-body effects. Fit with Breit-Wigner/M 3, where M and  are free parameters. D2 CFe e + e - Invariant Mass (GeV)

Outcome Publish PRL published – R. Nasseripour et al., PRL 99 (2007) PRC article will be submitted in January Impact Result does not confirm the KEK results. Rule out  M 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.

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

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 Previous data 5x statistics

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

Additional Studies Previous -meson in Fe result: M – small and consistent with zero.  – broadening consistent with many-body effects. Proposal: Momentum dependence of M and  of  meson in Fe and Nb. Absorption studies: Although the detected  and  mesons decay outside the nucleus, the in-medium widths can be accessed through meson- nucleon interactions. c~1.3 fm c~23.4 fm c~44.4 fm

P. Mühlich and U. Mosel NPA 773 (2006) MeV 93 MeV  = 47 MeV M. Kaskulov, E.Hernandez and E. Oset EPJ A 31 (2007) 245  = 34 MeV 94 MeV Transparency ratio: The in-medium width is  =  0 +  * where  * =  v  * VN Absorption of  Meson and its In-medium Width Normalized to carbon

Comparison of  Meson Results Preliminary JLab result shows greater in-medium broadening. JLab (preliminary) TAPS (arXiv:nucl-ex v2, Dec 2007) TAPS latest:   ~ MeV Proposed JLab data

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

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

This Proposal Beam energy: 3 GeV Beam energy: 3 GeV Targets: LD2, C, Fe, Nb, Sn Targets: LD2, C, Fe, Nb, Sn LD2 – control LD2 – control Fe – quality check Fe – quality check Nb – new results on  meson Nb – new results on  meson C – normalization; ,  studies C – normalization; ,  studies Sn – new result; ,  studies Sn – new result; ,  studies Fe and Nb thicknesses: Fe and Nb thicknesses: 2.5 g/cm 2 (x2.5) Beam time: 36 days (x2) Beam time: 36 days (x2) Statistical improvement: x5 Statistical improvement: x5 Previous target LD2 CCCC Fe Ti Pb Proposed target (not to scale)

Summary Medium modifications are complicated with various interactions:  Fundamental : chiral symmetry restoration, quarks/gluons  Effective : nuclear many body effects  Hybrid : quark-meson couplings Proof of chiral symmetry restoration can only be achieved with an understanding of the vector-meson many-body effects. Proposal: 1.Momentum dependence of the in-medium properties of  meson in Fe and Nb. 2.Additional studies –  and  meson in-medium widths accessed through absorption.

Backup Slides

Effective Density J. G. Messchendorp, private communication

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

Momentum Dependence -  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. Integrating over momentum range Dividing into momentum bins Valencia group (no momentum dep.) TAPS data Giessen group (before TAPS result) Giessen group (after TAPS result)

Momentum Dependence –  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 Longitudinal Transverse Calculations at =2 0

Recent PAC Approved Photon-beam Experiments Run period Beam time (days) PAC rating g9/FROST 37A- g10 30A g11 35A- g12 35A g13 48A-

Phase Diagram Hadronic properties depend on the quark condensate can change with  (density) and T (temperature). As goes to zero, hadron masses go to zero. How to measure modifications? 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 Light vector meson in a stationary nucleus Latest predictions range from 5-20%.

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/cm 2 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.

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

e + e - Invariant Mass Spectra Same sector e+e- removed Momentum corrections Target energy loss corrections Lepton momentum > 500 MeV Mixed-event background (see next slide) Same sector events   

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 mesons  : M=768 MeV  = 149 MeV c  ~ 1.3 fm J P =1 -  : M=782 MeV  = 8 MeV c  ~ 23.4 fm  : M=1020 MeV  = 4 MeV c  ~ 44.4 fm

The  Mass Spectra Fit function: Photon propagator Breakup momentum phase space D2 CFe e + e - Invariant Mass (GeV) After removing the , , and background contributions:

Extracting the Result 1.Make ratio of mass spectra of heavy target to reference target. 2.Fit the slope in region of  meson. 3.Compare with relation of slope to the percentage change in mass. In Fe nucleus, g7a sets an upper limit with a 95% confidence level:  m~-21 MeV. Broadening of the width is consistent with nuclear many-body effects. Accepted by PRL, Oct PRC version in ad hoc committee.

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