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Title: SEARCH FOR IN-MEDIUM MODIFICATIONS OF THE ρ MESON

Abstract

The photoproduction of vector mesons on various nuclei has been studied using the CEBAF Large Acceptance Spectrometer (CLAS) at Jefferson Laboratory, and here we present preliminary results. All three vector mesons, ρ, ω,and φ, are observed via their decay to e +e -, in order to reduce the effects of final state interactions in the nucleus. Of particular interest is possible in-medium effects on the properties of the ρ meson. The ρ spectral function is extracted from the data on various nuclei, carbon, iron, and titanium, and compared to the spectrum from liquid deuterium, which is relatively free of nuclear effects. We observe no effects on the mass of the ρ meson, however, there is some widening of the resonance in titanium and iron, which is consistent with expected collisional broadening.

Authors:
; ; ;
Publication Date:
Research Org.:
Thomas Jefferson National Accelerator Facility, Newport News, VA
Sponsoring Org.:
USDOE - Office of Energy Research (ER)
OSTI Identifier:
903314
Report Number(s):
JLAB-PHY-07-623; DOE/OR/23177-0045
TRN: US0703239
DOE Contract Number:
AC05-06OR23177
Resource Type:
Conference
Resource Relation:
Journal Name: Int.J.Mod.Phys.A; Journal Volume: 22; Conference: 9th International Workshop On Meson Production, Properties And Interaction (MESON 2006) 9-13 Jun 2006, Cracow, Poland
Country of Publication:
United States
Language:
English
Subject:
43 PARTICLE ACCELERATORS; CARBON; CEBAF ACCELERATOR; DECAY; DEUTERIUM; FINAL-STATE INTERACTIONS; IRON; MESONS; MODIFICATIONS; NUCLEI; PHOTOPRODUCTION; PRODUCTION; RESONANCE; SPECTRAL FUNCTIONS; SPECTROMETERS; TITANIUM; VECTOR MESONS; Vector mesons, medium modification effects

Citation Formats

WEYGAND, D P, DJALALI, C, NASSERIPOUR, R, and WOOD, M. SEARCH FOR IN-MEDIUM MODIFICATIONS OF THE ρ MESON. United States: N. p., 2007. Web. doi:10.1142/S0217751X07035562.
WEYGAND, D P, DJALALI, C, NASSERIPOUR, R, & WOOD, M. SEARCH FOR IN-MEDIUM MODIFICATIONS OF THE ρ MESON. United States. doi:10.1142/S0217751X07035562.
WEYGAND, D P, DJALALI, C, NASSERIPOUR, R, and WOOD, M. Mon . "SEARCH FOR IN-MEDIUM MODIFICATIONS OF THE ρ MESON". United States. doi:10.1142/S0217751X07035562. https://www.osti.gov/servlets/purl/903314.
@article{osti_903314,
title = {SEARCH FOR IN-MEDIUM MODIFICATIONS OF THE ρ MESON},
author = {WEYGAND, D P and DJALALI, C and NASSERIPOUR, R and WOOD, M},
abstractNote = {The photoproduction of vector mesons on various nuclei has been studied using the CEBAF Large Acceptance Spectrometer (CLAS) at Jefferson Laboratory, and here we present preliminary results. All three vector mesons, ρ, ω,and φ, are observed via their decay to e+e-, in order to reduce the effects of final state interactions in the nucleus. Of particular interest is possible in-medium effects on the properties of the ρ meson. The ρ spectral function is extracted from the data on various nuclei, carbon, iron, and titanium, and compared to the spectrum from liquid deuterium, which is relatively free of nuclear effects. We observe no effects on the mass of the ρ meson, however, there is some widening of the resonance in titanium and iron, which is consistent with expected collisional broadening.},
doi = {10.1142/S0217751X07035562},
journal = {Int.J.Mod.Phys.A},
number = ,
volume = 22,
place = {United States},
year = {Mon Jan 01 00:00:00 EST 2007},
month = {Mon Jan 01 00:00:00 EST 2007}
}

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  • The photoproduction of vector mesons on various nuclei has been studied using the CLAS detector at Jefferson Laboratory. The vector mesons, {rho}, {omega}, and {phi}, are observed via their decay to e{sup +}e{sup -}, in order to reduce the effects of final-state interactions in the nucleus. Of particular interest are possible in-medium effects on the properties of the {rho} meson. The {rho} mass spectrum is extracted from the data on various nuclei, {sup 2}H, C, Fe, and Ti. We observe no significant mass shift and some broadening consistent with expected collisional broadening for the {rho} meson.
  • Polarization transfer in quasi-elastic nucleon knockout is sensitive to the properties of the nucleon in the nuclear medium, including possible modification of the nucleon form factor and/or spinor. In our recently completed experiment E03-104 at Jefferson Lab we measured the proton recoil polarization in the 4He(e,e'p)3H reaction at a Q^2 of 0.8 (GeV/c)^2 and 1.3 (GeV/c)^2 with unprecedented precision. These data complement earlier data between 0.4 and 2.6 (GeV/c)^2 from both Mainz and Jefferson Lab. The measured ratio of polarization-transfer coefficients differs from a fully relativistic calculation, favoring either the inclusion of a medium modification of the proton form factorsmore » predicted by a quark-meson coupling model or strong charge-exchange final-state interactions. The measured induced polarizations agree well with the fully relativistic calculation and indicate that these strong final-state interactions may not be applicable.« less
  • There exist model calculations showing the modification of the hadronic parameters of ρ meson in the nuclear environment. From these parameters, we extract the ρ-meson-nucleus optical potential and show the medium effect due to this potential on the ρ-meson mass distribution spectra in the photonuclear reactions. The calculated results reproduced reasonably the measured e{sup +}e{sup −} invariant mass, i.e., ρ-meson mass, distribution spectra in γ, ρ{sup 0} → e{sup +}e{sup −} reactions on nuclei.
  • Rho meson propagation in hot hadronic matter is studied in a model with coupling to {pi}{pi} states. Medium modifications are induced by a change of the pion dispersion relation through collisions with nucleons and {Delta}{close_quote}s in the fireball. Maintaining gauge invariance dilepton production is calculated and compared to the recent data of the CERES Collaboration in central S+Au collisions at 200 GeV/u. The observed enhancement of the rate below the rho meson mass can be largely accounted for. {copyright} {ital 1996 The American Physical Society.}
  • We extend our recent study of dilepton invariant-mass spectra from the decays of {rho} mesons produced by photon reactions off nuclei. We specifically focus on experimental spectra as recently measured by the CLAS Collaboration at the Thomas Jefferson National Accelerator Facility using carbon and iron nuclei. Building on our earlier work, we broaden our description to a larger set of observables to identify sensitivities to the medium effects predicted by microscopic calculations of the {rho} spectral function. We compute mass spectra for several target nuclei and study the spectral shape as a function of the three-momentum of the outgoing leptonmore » pair. We also compute the so-called nuclear transparency ratio, which provides an alternative means (and thus consistency check) of estimating the {rho} width in the cold nuclear medium.« less