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Exclusive Production of Hadron Pairs in Two-Photon Interactions

Bertrand Echenard University of Geneva on behalf of the LEP collaborations Hadronic Physics Session EPS, Aachen, 17-23 July 2003 contact: bertrand.echenard@cern.ch. Exclusive Production of Hadron Pairs in Two-Photon Interactions. Outline. q p and K pair production

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Exclusive Production of Hadron Pairs in Two-Photon Interactions

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  1. Bertrand Echenard University of Geneva on behalf of the LEP collaborations Hadronic Physics Session EPS, Aachen, 17-23 July 2003 contact: bertrand.echenard@cern.ch Exclusive Production of Hadron Pairs in Two-Photon Interactions

  2. Outline qp and K pair production ?p and K meson pair production[ALEPH:CERN-EP:2003-030] q Baryon pair production ?pp [L3: CERN-EP:2003-014 OPAL: Eur. Phys. J. C28 (2003) 45 ] ?LL and S0S0[L3: PLB 536 (2002) 24] qr0r0 and r+r- pair production ?r0r0 and r+r- pair production at Q20 [L3: submitted to EPS] ?r0r0 pair production at high Q2[L3: CERN-EP:2003-020] EPS 2003, Aachen

  3. Hadron pair production in gg collisions Tests of QCD calculations Handbag model qp and K pair production ?Handbag model (1) based on the Brodsky and Lepage approach (2) • Amplitude gggHH factorized into: • ? Hard part : gggqq scattering • ? Soft part: qq gHH transition (1) M. Diehl, P. Kroll and C. Vogt, PLB 532 (2002) 99, hep-ph/0112274. (2) S. J. Brodsky and J. P. Lepage, PRD 22 (1980) 2157 . EPS 2003, Aachen

  4. Hadron pair production in gg collisions Three quark & Diquark models Tests of QCD calculations • Baryon pair production Three quark model ?Handbag model (1) ?Three quark model (2) ?Quark-diquark model (3) Diquark Quark-diquark model (1) M. Diehl, P. Kroll and C. Vogt, hep-ph/0206288. (2) G. Farrar et al., Nucl Phys B 259 (1985) 702. (3) C. F. Berger, B. Lechner and W. Schweiger, Fizika B8 (1999) 371; C. F. Berger and W. Schweiger hep-ph/0212066. EPS 2003, Aachen

  5. p and K pair selection ALEPH event selection: ? 2 tracks of opposite charge ? Electron rejection criteria ? Muon rejection criteria ? Cut on dE/dx to select pions and kaons ? Exclusive event selection cut EPS 2003, Aachen

  6. Fit with power law: AW-6 • ? p+p- : A=200±40 nb•GeV6 • K+K-: A=220±40 nb•GeV6 gggp+p- and gggK+K- cross sections gggp+p- gggK+K- • q s(gggp+p-) = s(gggK+K- ) within uncertainty • Shape well described by QCD predictions • Disagreement in normalization and ratio K/p(QCD: s(gggK+K- ) / s(gggp+p-) 2 ) EPS 2003, Aachen

  7. qL3: ? Antiproton Neural network: P, dE/dx, Et/pt & shower shape ?Proton dE/dx and Et/pt qOPAL: ?dE/dx and E/P Proton-antiproton pair selection EPS 2003, Aachen

  8. gggpp cross section q q Results compatible with previous measurements Extend Wgg range q q Good agreement with quark-diquark model Three quark model excluded EPS 2003, Aachen

  9. gggpp angular distribution Low mass Intermediate mass High mass • Agreement in the intermediate and high Wgg region • Disagreement with diquark model in the low Wgg region • Low mass region well described by spherical harmonics : 92% Y20 and 8% Y00 EPS 2003, Aachen

  10. LL L and S0-pairselection Decay channel: Lgpp-Lgpp+S0gLg EPS 2003, Aachen

  11. gggLL and gggS0S0 cross sections LL S0S0 q Good agreement with diquark model predictions q Three quark model excluded EPS 2003, Aachen

  12. gggLL and gggS0S0 cross sections LL S0S0 q Agreement with the handbag model predictionsusing gggpp as input data EPS 2003, Aachen

  13. m(p+p-) spectrum r0r0 mass spectrum m(pp0) spectrum r+r- mass spectrum r0r0 and r+r- pair production at Q20 q r0r0 channel ? High statistics (~70000 events) ? Clear r0r0 peak L3 L3 • q r+r- channel • ? Less statistics (~5000 events) • ? Clear r+r- peak L3 L3 EPS 2003, Aachen

  14. r0r0 and r+r- pair production at Q20 Partial Wave Analysis: L3 Model withrr in different spin-parity-helicity states and isotropic 4p Arr=BW12BW34YJ ,Jz + permutations A4p=1 p • (JP,Jz) = (2+,2) dominant state • (0+,0) small contribution • (0-,0), (2+,0), (2-,0(1,2)) negligible • Broad enhancement near threshold of gggr0r0 • Ratio of r+r- / r0r0 cross sections incompatible with formation of one Isospin 0 or 1 resonance EPS 2003, Aachen

  15. r0r0 pair production at high Q2 m(p+p-) spectrum • q Select 4p + tagged electron: • ?gg*gr0r0 • ?gg*gr0 p+p- • ?gg*gp+p-p+p- non-resonant • ? Separated by a box method • Q2 interval: 1.2 GeV2 < Q2 < 30 GeV2 r0 r0r0 mass spectrum L3 r0r0 EPS 2003, Aachen

  16. r0 p+p- + 4p (NR) r0 p+p- + 4p (NR) r0r0 r0r0 r0r0 pair production at high Q2 1.2 GeV2 < Q2 < 8.5 GeV2 8.8 GeV2 < Q2 < 30 GeV2 ? Broad enhancement near threshold of gggr0r0 as observed in Q20 measurement EPS 2003, Aachen

  17. q Low and high Q2 data are well described by GDVM form factor r-pole not sufficient q r0r0 pair production at high Q2 91 GeV 161-209 GeV q Fit with 1/(Qm(Q2+W2)2): ?QCD prediction(1) :m=2 ?Data:m=2.4 ± 0.3 (Wgg=1.95) (1) M. Diehl et al . PRD 62 073014 (2000); hep-ph/0003233 EPS 2003, Aachen

  18. Conclusions qp and K pair production ?s(gggp+p-) = s(gggK+K- ) ?Only Wggdependence agrees with QCD predictions ?Normalization and K/p ratio disagree with QCD predictions q Baryon pair production ?Data can be described by diquark model and handbag model ?Three quark model excluded qr0r0 and r+r- pair production ?Dominance of (JP,Jz) = (2+,2) for Q20 ?Broad enhancement near threshold of gggr0r0 ?Good agreement with QCD predictions for dse+e-/dQ2 ?GVDM form factor also describes well the Q2 dependence of sgg EPS 2003, Aachen

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