Vector Mesons in the Nuclear Medium Volker Metag
- Slides: 20
Vector Mesons in the Nuclear Medium Volker Metag II. Physikalisches Institut, Universität Gießen introduction medium modifications of vector-mesons: 1) -meson: CERES, KEK-PS 325 2) -meson: CB/TAPS@ELSA outlook: medium modification in the charm sector: D-mesons: PANDA@FAIR summary invited talk given at CHIRAL-05, RIKEN, Tokyo, Japan, 15. – 17. February 2005
Motivation Mass [Ge. V] Hadrons = excitations of the QCD vacuum QCD-vacuum: complicated structure characterized by condensates In the nuclear medium: condensates are changed change of the hadronic excitation energy spectrum Þ widespread experimental activities to search for in-medium modifications of hadrons
theoretical predictions for mass changes of vector mesons in the nuclear medium T. Renk et al. , PRC 66 (2002) 014902 1. ) lowering of in-medium mass 2. ) broadening of resonance for B , T experimental approach: dilepton spectroscopy: , , f e+ereconstruction of invariant mass from 4 -momenta of decay products: essential advantage: no final state interaction
W. Schön et al. Act. Phys. Pol. B 27 (96) 2959 -p bound n at rest -mass in nuclei ne+e- “at rest”: | p | | p. F | exp: detect e+e- HADES M. Effenberger et al. PRC 60 (1999) 044614 expected signal: -A at p = 1. 3 Ge. V/c
-mass in nuclei from photonuclear reactions J. G. Messchendorp et al. , Eur. Phys. J. A 11 (2001) 95 p 0 A + X 0 advantage: • 0 large branching ratio (8 %) • no -contribution ( 0 : 7 10 -4) disadvantage: • 0 -rescattering
expected mass distribution for p, Nb (including detector resolution and 2 0 background) after cut on 0 kinetic energy within 0. 6 < M 0 < 0. 8 :
The accelerator facility ELSA at Bonn ELSA = Elektron Strecher Anlage
The Crystal Barrel/ TAPS detector @ELSA tagging spectrometer: tagging range: 31% -94% of Ebeam E = Ebeam - Ee CB: 1280 Cs. I modules TAPS: 540 Ba. F 2 modules
4 detector system CB/TAPS @ ELSA Crystal Barrel 1290 Cs. I side view TAPS 528 Ba. F 2 front view of TAPS F = 00 to 3600 = 300 to 1680 F = 00 to 3600 = 50 to 300
comparison of meson masses and lineshapes for LH 2 and nuclear targets 0 No change of mass and lineshape for longlived mesons ( 0, , ) decaying outside nuclei
inclusive 0 signal for LH 2 and Nb target D. Trnka (Giessen) after background subtraction difference in line shape of signal for proton and nuclear target
contribution from in-medium decays in vacuum removed by subtracting mass distribution measured with LH 2 target (64%) strength of in-medium decays concentrated around masses of 725 Me. V Þ mass drop by about 7% at estimated baryon density of about 0. 55 0 consistent with m = m 0 (1 - / 0); for = 0. 15
momentum dependence of signal mass modification only for p 0. 5 Ge. V/c first indication for an in-medium modification of the meson mass !!
photoproduction of mesons off nuclei A A at E 1. 2 Ge. V (CB/TAPS@ELSA) in-medium mass distribution ( 0 ) exp: D. Trnka (Giessen) theo: P. Mühlich et al. , nucl-th/0310067 comparison to BUU calculation assuming m = m 0 (1 - / 0); for = 0. 16 first experimental indication for a dropping mass in the nuclear medium
CB/TAPS @ MAMI C TAPS forward wall 528 Ba. F 2 - modules -Beam Crystal Ball 672 Na. I - modules
Charmed mesons in the medium @ PANDA in-medium spectral function of charmonia: consequence of dropping D-mass (cu) in the medium A. Hayashigaki, PLB 487 (2000) 96 Ye. S. Golubeva et al. , nucl-th/0212074 (3770)
FAIR Facility for Antiproton and Ion Research SIS 100 SIS 300 GSI as of today CBM PP HESR Super-FRS Elec. Cooler Atom. Phys. CR+RESR NESR FLAIR PANDA
summary vector mesons: : first evidence for medium modifications from e+e- in ultra-relativistic nucleus-collisions (CERES/CERN); indications for medium modifications at normal nuclear matter density from e+e- in p. A collisions at 12 Ge. V (KEK); : • first evidence for medium-modifications at normal nuclear matter density from 0 by comparison of p( , ) and A( , ) (CB/TAPS @ ELSA); • -p n on bound protons, planned at HADES/GSI; mesons with charm: D: planned experiments at FAIR
conclusion Experiments so far are in accordance with theoretical scenarios for changes of hadron properties in the nuclear medium. Studying the in-medium behaviour of hadrons is a promising approach to learn more about the origin of their mass. We have come a little closer to understanding the mass of matter Thanks: CBELSA/TAPS collaboration (Bonn) A 2 -collaboration (Mainz) Giessen-team: in particular Johan Messchendorp, Susan Schadmand, David Trnka Giessen-Theory: W. Cassing, St. Leupold, U. Mosel, P. Mühlich
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- Suma de dos vectores
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- Define
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