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

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

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)

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

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) 038202) from D-meson loops

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/0309085 -meson 1.) lowering of in-medium mass 2.) broadening of resonance for rB

-, -meson-nucleus potential K. Saito, K. Tsushima, A.W. Thomas, hep-ph/0506314 predictions within the quark meson coupling model (QMC) : E(1s) = -39 MeV; = 29 MeV : E(1s) = -100 MeV; = 31 MeV : E(1s) = -56 MeV; = 33 MeV : E(1s) = -118 MeV; = 33 MeV

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/0506314 D- - nucleus bound states (superposition of Coulomb + strong interaction) D- 208Pb (1s) bound by 24 MeV

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) 092301: no broadening in the medium!! -meson: p (12 GeV) A ,  +X NA60: R. Arnaldi et al., PRL 96 (2006) 162302: 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

-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

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

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= 900-2200 MeV TAPS 528 BaF2

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

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

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(1 - 0.16 /0)

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

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 = 1.45-1.55 GeV (D.Trnka et al.(preliminary))

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

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

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)

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

correlation between  momentum and proton angle 5° 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

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

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:

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: 1.54 GeV  No chance for populating a state bound with 20 MeV!!!

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!!

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 !!

CBELSA/TAPS collaboration

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

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 

Flatte fit to TAPS data M. Pfeiffer et al., PRL 94 (2005) finer energy binning 2 poles: m-i/2 = (1487.7-i4.8) MeV; (1483.9-i8.9) MeV

Prediction of  mesic states in QMC and QHD models K. Saito, K. Tsushima, A.W. Thomas, hep-ph/0506314

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

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

Ye.S.Golubeva et al., nucl-th/0212074  (3770) A. Hayashigaki, PLB487 (2000) 96