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Exclusive  +  –  +  – and  +  0  –  0 production in two photon

Exclusive  +  –  +  – and  +  0  –  0 production in two photon collisions at LEP. O. Fedin, S. Nesterov, G. Sultanov, I. Vorobiev representing the L3 collaboration. April, 23-27 DIS 2003. e + e –  e + e –  +  –  +  – e + e –  e + e –  +  0  –  0.

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Exclusive  +  –  +  – and  +  0  –  0 production in two photon

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  1. Exclusive  + – + –and  + 0 – 0 production in two photon collisions at LEP O. Fedin, S. Nesterov, G. Sultanov, I. Vorobiev representing the L3 collaboration April, 23-27 DIS 2003 Exclusive +–+– and +0–0production in two photon collision at L3 (page 1)

  2. e+e–  e+e– + – + – e+e–  e+e–  + 0 – 0 Outline • Exclusive r 0r 0and r +r –production at Q2 0 • Exclusive r 0r 0 production for 1.2 < Q2 < 30 GeV2[Subm. to Phys. Lett.] •  + – + – and + 0 – 0 at W> 2.4 GeV Exclusive +–+– and +0–0production in two photon collision at L3 (page 2)

  3. Exclusive r 0r 0production at Q2 0 • high energy data (161 < s < 208 GeV), integrated luminosity 686.7 pb-1 • e+e–  e+e– + – + – • 4 tracks with zero charge • no photons • dE/dx CL(4) > 6% • e+e–  e+e–  + 0 – 0 • two tracks with zero charge • dE/dx CL(2) > 6% • 4 photons E > 100 MeV • two best  0 from constraintfit • p2t(4) < 0.02 GeV2 Sample of  + – + – — 69542 events (66838 in 1.0 < W<3.0 GeV) Sample of  + 0 – 0—5253 events (4740 in 1.0 < W  < 3.0 GeV) Exclusive +–+– and +0–0production in two photon collision at L3 (page 3)

  4. Efficiency and detector acceptance Detector acceptance and selection efficiency  determined from MC (EGPC generator[F.Linde, PhD Thesis, 1988] ) • Trigger efficiency calculated from the data: • 91.8% for  + – + – • 51.8% for + 0 – 0 Exclusive +–+– and +0–0production in two photon collision at L3 (page 4)

  5. Two pion mass spectra Exclusive +–+– and +0–0production in two photon collision at L3 (page 5)

  6. Partial Wave Analysis method • Performed in 1.0 < Wgg < 3.0 GeV • Model with rrin different spin-parity states and isotropic 4p[M.Althoff et al. Z.Phys. C16, 1982] • Arr BW12BW34JPJz+ perm. • A4p 1 • rr(JP,Jz) = (0+, 0), (2+, 2), (0–, 0), (2+, 0), (2–, 0(1,2)) and 4p isotropic, no interference, significant rr only 0+ and (2+, 2); 4pisotropic is effective background • MC integration of |Arr|2 • Likekihood fit to the data in each Wggbin Exclusive +–+– and +0–0production in two photon collision at L3 (page 6)

  7. Fit results for • M(p +p –) and M(p p 0) M(p +p –) spectrum M(p p 0) spectrum Exclusive +–+– and +0–0production in two photon collision at L3 (page 7)

  8. Fit results for • Angle of pion in C.M.S. of r with respect to the beam axis (Adair angle) angle of p + in r 0CMS angle of p  in rCMS Exclusive +–+– and +0–0production in two photon collision at L3 (page 8)

  9. Cross section for   • Total  and dominant partial waves cross sections • Isospin ratio of the  cross section is incompatible with I=0, 1 Exclusive +–+– and +0–0production in two photon collision at L3 (page 9)

  10. Cross section for   Broad enhancement near threshold of    Exclusive +–+– and +0–0production in two photon collision at L3 (page 10)

  11. Exclusive r0r0production for 1.2 < Q2 < 30 GeV2 • Single tage+e– e+e–taggg*  e+e–tagr 0r 0 • tagged electron 25 mrad <  < 68 mrad • p2t (etagp+p–p+p –) < 0.2 GeV2 • Etag> 80% Ebeam  Z-pole (s  91 GeV) 1.2 < Q 2 < 8.5 GeV2, Le+e– = 148.7 pb-1  high energy data (s  195 GeV) 8.8 < Q 2 < 30 GeV2, L e+e– = 706.0 pb-1  at Z-pole sample of 851 events withWgg > 1 GeV  at high energy sample of 498 events with Wgg > 1 GeV Exclusive +–+– and +0–0production in two photon collision at L3 (page 11)

  12. M( + –) spectrum Exclusive +–+– and +0–0production in two photon collision at L3 (page 12)

  13. Box method[D.M.Schmidt et al. NIM A328(1993)] • 2 million MC events for channel • * 0 0 • * 0 + – • * + – + – • Likelihood fit to thedata Exclusive +–+– and +0–0production in two photon collision at L3 (page 13)

  14. Fit results for 0 0 • M( + –) in different Q2 and Wregions Points represent the data, histogram shows fit results, hatched area shows  0 0 component Exclusive +–+– and +0–0production in two photon collision at L3 (page 14)

  15. Fit results for 0 0 • Production angle and angle between decay planes Points represent the data, histogram shows fit results, hatched area shows  0 0 component Exclusive +–+– and +0–0production in two photon collision at L3 (page 15)

  16. Cross section of *  0 0 Z-pole data High energy data • Broad enhancement near threshold of gg  r0r0as seen in measurements at Q2  0 • Interval 1.1 < Wgg < 3.0 GeV is chosen for Q2-dependence Exclusive +–+– and +0–0production in two photon collision at L3 (page 16)

  17. Cross section of *  0 0 • Fit with 1/(Qn(Q2+<W>2)2) • n = 2.4  0.3(<W> = 1.945) • Agrees with QCD expectation n= 2 [M.Diehl et al. PRD 62 073014] • Agrees well with GVDM form • factor,r-pole is not sufficient Exclusive +–+– and +0–0production in two photon collision at L3 (page 17)

  18. High Wtwo pion mass spectra M= 763  4 GeV  = 170  21 GeV Mf2 = 1282  15 GeV f2 = 273  130 GeV M = 1738  19 GeV  = 130  61 GeV • (770), f2(1270),  (1700) are clearly seen Exclusive +–+– and +0–0production in two photon collision at L3 (page 18)

  19. Breit-Wigner fit for high W M= 763  4 GeV  = 170  21 GeV Mf2 = 1282  15 GeV f2 = 273  130 GeV Exclusive +–+– and +0–0production in two photon collision at L3 (page 19)

  20. Summary • Exclusive rrproduction at Q2 0 • Dominance of(JP, Jz) = (2+, 2) spin-parity state • Broad enhancement of rr near threshold • Cross section ratio s(r0r0)/s(r+r-) is incompatible with isospin I=0,1 • Exclusive r0r0 production at high Q2 • Broad enhancement of rrnear threshold as for Q2 ~ 0 • Good agreement with the QCD expectation for differential cross section ds e+e-/dQ2 • GDVM form factor describes well Q2 dependence of sgg • Measurements of the sgg at Q2 ~ 0 and for Q2 > 1.2 GeV are consistent • Low and high Q2 data are consistent with the same QCD prediction • High Wggregion • In  + – + –(770), f2 (1270) and (1700) are clearly seen • In  + 0 – 0(770) and f2 (1270) are seen Exclusive +–+– and +0–0production in two photon collision at L3 (page 20)

  21. Cross section    + – + –  Comparison of total   + –+ – cross section Exclusive +–+– and +0–0production in two photon collision at L3 (page 21)

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