Scalar and Axial-Vector Mesons in a Three- Flavour Sigma Model
Vector Mesons in the Nuclear Medium
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Transcript of Vector Mesons in the Nuclear Medium
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Vector Mesons in the Nuclear MediumVector Mesons in the Nuclear Medium
Volker MetagII. Physikalisches Institut, Universität Gießen
invited talk given at CHIRAL-05, RIKEN, Tokyo, Japan, 15. –17. February 2005
medium modifications of vector-mesons:1) -meson: CERES, KEK-PS3252) -meson: CB/TAPS@ELSA
summary
introduction
outlook:medium modification in the charm sector:D-mesons: PANDA@FAIR
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MotivationMotivation
widespread experimental activities to search for in-medium modifications of hadrons
Mas
s [G
eV]
Hadrons = excitations of the QCD vacuumQCD-vacuum: complicated structure characterized by condensates
In the nuclear medium: condensates are changed
change of the hadronic excitation energy spectrum
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theoretical predictions for mass changes of vector mesons in the nuclear medium
theoretical predictions for mass changes of vector mesons in the nuclear medium
1.) lowering of in-medium mass 2.) broadening of resonance for B, T
essential advantage: no final state interaction
221 ppm
reconstruction of invariant mass from 4-momenta of decay products:dilepton spectroscopy: , , e+e-experimental approach:
T. Renk et al.,
PRC 66 (2002) 014902
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-mass in nuclei-mass in nuclei
HADES
M. Effenberger et al.
“at rest”: | p| | pF |
exp: detect e+e-
W. Schön et al. Act. Phys. Pol. B 27 (96) 2959
2i2
i pEm
PRC 60 (1999) 044614
expected signal: -A at p = 1.3
GeV/c
-pbound nat rest ne+e-
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-mass in nuclei from photonuclear reactions-mass in nuclei from photonuclear reactions
disadvantage:
• 0-rescattering
advantage:
• 0 large branching ratio (8 %)
• no -contribution ( 0 : 7 10-4)
J.G.Messchendorp et al., Eur. Phys. J. A 11 (2001) 95
p
A + X
0
2ppm
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Suppression of 0 rescattering eventsSuppression of 0 rescattering events
after rescattering 0 kinetic energy below 150 MeV 250 MeV/c (-decay kinematics) cut on 0 kinetic energy
P. Mühlich (Giessen)nucl-th/0310067
J.G.Messchendorp et al.Eur. Phys. J. A11 (2001) 95
Nb
m(0)[GeV]
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expected mass distribution for p, Nbexpected mass distribution for p, Nb
(including detector resolution and 20 background)
within 0.6 < M0 < 0.8 :
outside 76%
inside no 0-rescat. 22%
inside 0-rescat. 1%
double-0 1%
after cut on 0 kinetic energy
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The accelerator facility ELSA at Bonn The accelerator facility ELSA at Bonn
ELSA = Elektron Strecher Anlage
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The Crystal Barrel/ TAPS detector @ELSA
tagging spectrometer: tagging range: 31% -94% of Ebeam
E = Ebeam - Ee
CB: 1280 CsI modulesTAPS: 540 BaF2 modules
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front view of TAPSside view
Crystal Barrel TAPS 1290 CsI 528 BaF2
= 00 to 3600
= 50 to 300
detector system CB/TAPS @ ELSAdetector system CB/TAPS @ ELSA
= 00 to 3600 = 300 to 1680
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comparison of meson masses and lineshapesfor LH2 and nuclear targets
comparison of meson masses and lineshapesfor LH2 and nuclear targets
No change of mass and lineshape for longlived mesons (0, , ) decaying outside nuclei
0
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inclusive 0 signal for LH2 and Nb targetinclusive 0 signal for LH2 and Nb target
difference in line shape of signal for proton and nuclear target
D. Trnka (Giessen)after background subtraction
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contribution from in-medium decayscontribution from in-medium decays
strength of in-medium decays concentratedaround masses of 725 MeV mass drop by about 7% at estimated baryon density of about 0.55 0
consistent with m = m0 (1 - /0); for = 0.15
decays in vacuum
removed by subtracting mass distribution measured with LH2 target (64%)
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momentum dependence of signalmomentum dependence of signal
mass modification only for p 0.5 GeV/c
first indication for an in-medium modificationof the meson mass !!
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photoproduction of mesons off nucleiphotoproduction of mesons off nucleiA A at E 1.2 GeV (CB/TAPS@ELSA)
exp: D. Trnka (Giessen)
m = m0 (1 - /0); for = 0.16 comparison to BUU calculation assuming
in-medium mass distribution (0)
first experimental indication for a dropping mass in the nuclear medium
theo: P. Mühlich et al., nucl-th/0310067
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CB/TAPS @ MAMI CCB/TAPS @ MAMI C
TAPS forward wall528 BaF2 - modules
Crystal Ball672 NaI - modules
-Beam
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Charmed mesons in the medium @ PANDACharmed mesons in the medium @ PANDA
Ye.S.Golubeva et al.,nucl-th/0212074
(3770)
in-medium spectral function of charmonia:consequence of dropping D-mass (cu) in the medium
A. Hayashigaki, PLB487 (2000) 96
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SIS 100
HESR
SIS 300
CBM
PP Super-FRS
Atom. Phys.
GSI as of today
Elec.CoolerPANDA
CR+RESR
NESRFLAIR
FAIRFacility for Antiprotonand Ion Research
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vector mesons:: first evidence for medium modifications from e+e- in ultra-relativistic nucleus-nucleus-collisions (CERES/CERN); indications for medium modifications at normal nuclear matter density from e+e- in pA collisions at 12 GeV (KEK);
: • first evidence for medium-modifications at normal nuclear matter density from 0 by comparison of p(,) and A(,)
(CB/TAPS @ ELSA);
• -pn on bound protons, planned at HADES/GSI;
summarysummary
mesons with charm:D: planned experiments at FAIR
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conclusionconclusion
Experiments so far are in accordance with theoretical scenarios forchanges 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)A2-collaboration (Mainz)
Giessen-team: in particular Johan Messchendorp, Susan Schadmand, David Trnka
Giessen-Theory: W. Cassing, St. Leupold, U. Mosel, P. Mühlich