Vector Mesons in the Nuclear Medium
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Vector Mesons in the Nuclear Medium. Volker Metag II. Physikalisches Institut, Universität Gießen. introduction. medium modifications of vector-mesons: 1) -meson: CERES, KEK-PS325 2) -meson: [email protected] outlook: medium modification in the charm sector: D-mesons: [email protected] summary.

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Vector Mesons in the Nuclear Medium

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Vector mesons in the nuclear medium

Vector Mesons in the Nuclear Medium

Volker Metag

II. Physikalisches Institut, Universität Gießen

introduction

medium modifications of vector-mesons:

1) -meson: CERES, KEK-PS325

2) -meson: [email protected]

outlook:

medium modification in the charm sector:

D-mesons: [email protected]

summary

invited talk given at CHIRAL-05,

RIKEN, Tokyo, Japan, 15. –17. February 2005


Vector mesons in the nuclear medium

Mass [GeV]

Motivation

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

  • widespread experimental activities to search for

    in-medium modifications of hadrons


Vector mesons in the nuclear medium

1.) lowering of in-medium mass 2.) broadening of resonance

for rB, T 

theoretical predictions for mass changes of vector mesons in the nuclear medium

T. Renk et al.,

PRC 66 (2002) 014902

experimental approach:

dilepton spectroscopy: r, w, f e+e-

reconstruction of invariant mass from 4-momenta of decay products:

essential advantage: no final state interaction


Vector mesons in the nuclear medium

-mass in nuclei

M. Effenberger et al.

W. Schön et al.Act. Phys. Pol. B 27 (96) 2959

PRC 60 (1999) 044614

expected signal: -A at p = 1.3 GeV/c

-pbound  nat rest  ne+e-

“at rest”: | pw |  | pF |

exp: detect e+e-

HADES


Vector mesons in the nuclear medium

gA   + X

p

g

p0g

g



w

p0

g

g

-mass in nuclei from photonuclear reactions

J.G.Messchendorp et al., Eur. Phys. J. A 11 (2001) 95

advantage:

• p0g large branching ratio (8 %)

• no -contribution (  0 : 7  10-4)

disadvantage:

• p0-rescattering


Vector mesons in the nuclear medium

expected mass distribution for p, Nb

(including detector resolution and 2p0 background)

after cut on p0kinetic energy

within 0.6 < Mp0g< 0.8 :


Vector mesons in the nuclear medium

The accelerator facility ELSA at Bonn

ELSA = Elektron Strecher Anlage


Vector mesons in the nuclear medium

The Crystal Barrel/ TAPS detector @ELSA

tagging spectrometer:

tagging range: 31% -94% of Ebeam

CB: 1280 CsI modules

TAPS: 540 BaF2 modules

E = Ebeam - Ee


Vector mesons in the nuclear medium

4 p detector system CB/TAPS @ ELSA

Crystal BarrelTAPS

1290 CsI 528 BaF2

front view of TAPS

side view

g

  • = 00 to 3600

     = 300 to 1680

  • = 00 to 3600

     = 50 to 300


Vector mesons in the nuclear medium

comparison of meson masses and lineshapes

for LH2 and nuclear targets

0



No change of mass and lineshape for longlived mesons (0, , ) decaying outside nuclei


Vector mesons in the nuclear medium

inclusive 0 signal for LH2 and Nb target

D. Trnka (Giessen)

after background subtraction

difference in line shape of  signal for proton and nuclear target


Vector mesons in the nuclear medium

contribution from  in-medium decays

  • decays in vacuum

    removed bysubtracting 

    mass distribution measured

    with LH2 target (64%)

  • strength of in-medium

  • decays concentrated

    around 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


Vector mesons in the nuclear medium

momentum dependence of  signal

  • mass modification only

    for p 0.5 GeV/c

first indication for an

in-medium modification

of the  meson mass !!


Vector mesons in the nuclear medium

photoproduction of  mesons off nuclei

  • A   A at E  1.2 GeV ([email protected])

in-medium  mass distribution (0)

exp: D. Trnka (Giessen)

theo: P. Mühlich et al., nucl-th/0310067

m =m0 (1 -  /0); for  = 0.16

comparison to BUU calculation assuming

first experimental indication for a dropping  mass in the nuclear medium


Vector mesons in the nuclear medium

CB/TAPS @ MAMI C

g-Beam

TAPS forward wall

528 BaF2 - modules

Crystal Ball

672 NaI - modules


Vector mesons in the nuclear medium

Charmed mesons in the medium @ PANDA

in-medium spectral function of charmonia:

consequence of dropping D-mass (cu) in the medium

Ye.S.Golubeva et al.,

nucl-th/0212074

 (3770)

A. Hayashigaki, PLB487 (2000) 96


Vector mesons in the nuclear medium

FAIR

Facility for Antiproton

and Ion Research

SIS 100

SIS 300

GSI as of today

CBM

HESR

Super-FRS

PP

Elec.Cooler

PANDA

Atom. Phys.

CR+RESR

FLAIR

NESR


Vector mesons in the nuclear medium

summary

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);

• -pn on bound protons, planned at HADES/GSI;

  • mesons with charm:

  • D:planned experiments at FAIR


Vector mesons in the nuclear medium

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)

A2-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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