1. Hadron modifications seen with electromagnetic probes
Volker Metag
II. Physikalisches Institut
Universität Giessen
Germany
Observables in pp interactions and their relevance to QCD
Workshop at ECT*,Trento, Italy, July 3-7, 2006
motivation (predicted medium effects in the charm sector)
first observation of medium modifications of the  meson:
a.) mass shift
b.) in-medium width
in-medium spectral function s(,p)
first observation of an -nucleus bound state:
summary and outlook

2. Motivation hadrons = excitations of the QCD vacuum
Mass [GeV]
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
T.Hatsuda and S. Lee,
PRC 46 (1992) R34
G.E.Brown and M. Rho,
PRL 66 (1991) 2720
widespread experimental activities to search for
in-medium modifications of hadrons

3. possible in-medium modifications of hadrons
in-medium mass shift
(partial restoration of chiral symmetry, meson-baryon coupling)
in-medium broadening of hadron resonances
(meson-baryon coupling, collisional broadening)
hadron-nucleus bound states
(meson-nucleus attractive potential)

4. model predictions for in-medium masses of mesons
V. Bernard and U.-G. Meißner
NPA 489 (1988) 647
NJL-model
degeneracy of chiral partners
K. Saito, K. Tushima, and A.W. Thomas
PRC 55 (1997) 2637
Quark-meson coupling model (QMC)
decrease of  -mass by  15%;
decrease of D-mass by 3%
at normal nuclear matter density

5. predictions in the charm sector
consequences of a dropping D-meson mass
A. Hayashigaki, Phys. Lett. B 487 (2000) 96
QCD sum rules: mD - 50 MeV
 width of (3770) increases
(2s) may become instable
to DD-decay
on the other hand, Lee and Ko find:
(S.H.Lee and C.M.Ko PRC67 (2003) )
from D-meson loops

6. Model predictions for spectral functions of r and w mesons
F. Klingl et al. NPA 610 (1997) 297
NPA 650 (1999) 299
- meson
m [GeV]
q [GeV]
AT [GeV-2]
M. Post et al., nucl-th/
-meson
1.) lowering of in-medium mass ) broadening of resonance
for rB

7. -, -meson-nucleus potential
K. Saito, K. Tsushima, A.W. Thomas, hep-ph/
predictions within the quark meson coupling model (QMC)
: E(1s) = MeV; = 29 MeV
: E(1s) = -100 MeV; = 31 MeV
: E(1s) = MeV; = 33 MeV
: E(1s) = -118 MeV; = 33 MeV

8. Predictions of nuclear bound quarkonium states
S. Brodsky et al. , PRL 64 (1990) 1011
attractive cc – nucleon potential due to multi gluon exchange
 c binding energy to light nuclei of the order of  20 MeV
Klingl et al., PRL 82 (1999) 3396
QCD sum rules: attractive mass shift of  5-10 MeV for J/ and c
K. Saito et al., hep-ph/
D- - nucleus bound states (superposition of Coulomb + strong interaction)
D- 208Pb (1s) bound by 24 MeV

9. experimental approach: dilepton spectroscopy: r, w, f  e+e-
reconstruction of invariant mass from 4-momenta of decay products:
essential advantage: no final state interactions !!
KEK-E325: M. Naruki et al., PRL 96 (2006) :
no broadening in the medium!!
-meson:
p (12 GeV) A ,  +X
NA60: R. Arnaldi et al., PRL 96 (2006) : In + In (158 AGeV)
-spectral function shows strong broadening but no shift in mass
CLAS (Jlab): C. Tur et al., A , ,  +X
HADES (GSI): planned experiment - p   n on bound proton

10. -mass in nuclei from photonuclear reactions
J.G.Messchendorp et al., Eur. Phys. J. A 11 (2001) 95 g w p0 p
gA   + X 
p0g
fraction of -decays in the medium
(  0.1 0) :  35%
M. Effenberger et al.
advantage:
• p0g large branching ratio (8 %)
• no -contribution (  0 : 7  10-4)
disadvantage:
• p0-rescattering

11. Expected  in-medium signal
rescattering of pions in nuclei
predominantly proceeds through
(1232) excitation:
scattered pions have Ekin150 MeV
no distortion by pion rescattering expected in mass range of interest

12. 4 p detector system CB/TAPS @ ELSA
front view of TAPS
= 00 to 3600
 = 50 to 300
side view
Crystal Barrel
1290 CsI
 = 300 to 1680
E=
MeV
TAPS
528 BaF2

13. 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

14. inclusive 0 signal for LH2 and Nb target
D. Trnka et al., PRL 94 (2005)192303
after background subtraction
difference in line shape of  signal for proton and nuclear target
m = m0 (1 -  /0) for  = 0.13
mNb = 763 MeV;   0.110 consistent with

15. decomposition of  signal into
D. Trnka, PhD thesis,
Univ. Giessen 2006
decomposition of  signal into
in-medium and vacuum decay contributions
in-medium contribution
vacuum contribution
Nb: in-medium: 45%
C: in-medium: 40%
lineshape of vacuum contribution taken from LH2 experiment
shape of in-medium contribution taken from BUU simulation
(P. Mühlich and U. Mosel, NPA (2006)), assuming m = m0( /0)

16. access to in-medium  width
in-medium  width proportional to  absorption:   vabs
transparency ratio:
normalization to C!!
E= 1,5 GeV
P. Mühlich and U. Mosel
NPA (2006)
74 MeV
37 MeV
= 19 MeV
M. Kaskulov and E. Oset
priv. communication
= 34 MeV
94 MeV

17. access to in-medium  width
in-medium  width proportional to  absorption:   vabs
transparency ratio:
normalization to C!!
E=1.5 GeV
37 MeV
74 MeV
= 19 MeV
= 34 MeV
94 MeV
Comparison to data taken at E = GeV (D.Trnka et al.(preliminary))

18. dependence of  width on  momentum
P. Mühlich , private communication
taking the momentum dependence
of the  width into account,both
analyses agree:
 gets broadened in the medium by a factor 10!!
transparency ratio measurement also possible for charmed mesons in the
nuclear medium   inel (p)  (p); (J/-suppression in AA collisions)
experimental problem: luminosity L  A-2/3 (for Au factor 30 !!)
p - loss due to single Coulomb scattering  Z2

19. momentum dependence of  signal (Nb-target)
D. Trnka et al., PRL 94 (2005)192303 Nb
LH2
mass modification only for p 0.5 GeV/c
determination of momentum dependence of  - nucleus potential requires
finer momentum bins  improved 2nd. generation experiment

20. The population of meson-nucleus bound states in recoil-free kinematics
forward going nucleon takes over photon momentum
magic incident energies : E  930 MeV
: E  2750 MeV
(ELSA)

21. signature for  - mesic states no intensity for negative energies
quasifree
E. Marco and W. Weise, PLB 502 (2001) 59
quasifree
-mesic states
T. Nagahiro et al. N. Phys. A 761 (2005) 92
attractive
potential
signature for  - mesic states
repulsive
potential
no intensity for negative energies

22. correlation between  momentum and proton angle5°
15°
740 MeV/c
240 MeV/c p 
E = 2750 MeV
simulation
E = 1.5 –2.5 GeV
background
bound states expected for p < 140
|p| < 500 MeV/c for p < 140
candidates

23. comparison of data on LH2 and C
D. Trnka, PhD thesis,
Univ. Giessen 2006
comparison of data on LH2 and C
small proton angles
70 < p< 140
LH2
for small proton angles: difference between C and LH2 data for negative energies C
quasi-
free
large proton angles
180 < p< 280
for large proton angles: similar background distributions for C and LH2 data C
LH2

24. Evidence for carbon data after 70 < p< 140
background subtraction
70 < p< 140
quasifree
 mesic states
E.Marco and W.Weise
PLB 502 (2001) 59
theoretical prediction
first evidence for the existence
of an -nucleus bound state:
here:

25. population of charmed meson bound states??
p 4He  c3H (S. Brodsky et al., PRL 64 (1990) 1011)
c bound by  20 MeV; exp. signature -decay (branching 4•10-4)
in the laboratory: minimum c momentum: 2.1 GeV/c;
 c = 0.59; Ekin(c) = 400 MeV
minimum incident p-kinetic energy: GeV
 No chance for populating a state bound with 20 MeV!!!

26. kinematics for pp  (2s)  J/(1s) + 2 at threshold: Ekin(p) = 5
kinematics for pp  (2s)  J/(1s) + 2 at threshold: Ekin(p) = 5.37 GeV
(allowing for phase space of 3 GeV)
in the laboratory: minimum J/(1s) momentum: 4.4 GeV/c;
 J/ = 0.82; Ekin(J/) = 2.28 GeV
no chance of forming a J/- nucleus bound state!!

27. An in-medium dropping of the  meson mass has been observed
Summary and outlook
An in-medium dropping of the  meson mass has been observed
consistent with
major step forward towards understanding the origin
of hadron masses
first information on in-medium  width:
first evidence for  mesic 11B
 second generation experiments with improved statistics
are needed and in preparation
 difficult to transfer techniques and approaches
to the charm sector !!

28. CBELSA/TAPS collaboration

29. Decay of a bound -mesic state: 3He
excitation function: rise in cross section near threshold:
-mesic 3He state ? (N-final state interaction?)
 3He E EB G
E [MeV]
structure in excitation function for 0 p back-to-back emission
0p+X g
3He
S11
3He* p 2H h

30. pp – decay of g p h
S11
3He
3He* 2H
E [MeV]
structure in excitation function of p0p back-to-back emission near h-threshold: B(3He)= ( 5.5  5) MeV; = (39  21) MeV 

31. Flatte fit to TAPS data
M. Pfeiffer et al., PRL 94 (2005)
finer energy binning
2 poles: m-i/2 = ( i4.8) MeV; ( i8.9) MeV

32. Prediction of  mesic states in QMC and QHD models
K. Saito, K. Tsushima, A.W. Thomas, hep-ph/

33. Search for  mesic states in heavier nuclei
C. Garcia-Recio et al., PLB 550 (2002) 47
unitarized chiral model
preferably only 1s-state
24Mg: B=12.6 MeV; =33 MeV
experiment at COSY (ENSTAR/Big-Karl):
Roy et al. : p 12C  3He + 10B; p 6Li  3He + 4He
experiment at GSI:
Hayano et al., EPJ A6 (1999) 105; 7Li(d,3He)6He; Td = 3.6GeV

34. Prediction of  mesic states
E. Marco and W. Weise, PLB 502 (2001) 59

35. Ye.S.Golubeva et al.,
nucl-th/
 (3770)
A. Hayashigaki, PLB487 (2000) 96