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

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

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

-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-

-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

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]

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

The accelerator facility ELSA at Bonn 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 CsI modulesTAPS: 540 BaF2 modules

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

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

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

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%)

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 !!

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

CB/TAPS @ MAMI CCB/TAPS @ MAMI C

TAPS forward wall528 BaF2 - modules

Crystal Ball672 NaI - modules

-Beam

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

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

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

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