1 / 16

Exclusive rr production in tagged gg interactions at LEP

Exclusive rr production in tagged gg interactions at LEP. I. Vorobiev. Carnegie Mellon University. On behalf of the L3 collaboration. The XXXXth Rencontres de Moriond, QCD AND HIGH ENERGY HADRONIC INTERACTIONS La Thuile, Italy

abia
Download Presentation

Exclusive rr production in tagged gg interactions at LEP

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Exclusive rr production in tagged gg interactions at LEP I. Vorobiev Carnegie Mellon University On behalf of the L3 collaboration • The XXXXth Rencontres de Moriond, • QCD AND HIGH ENERGY HADRONIC INTERACTIONS • La Thuile, Italy • March 12 - 19, 2005

  2. e+ e-e+ e-g g* e+ e- r0 r0 e+ e-e+ e-g g* e+ e- r+ r- Reactions studied The L3 experiment performed study of exclusive r-pair production in the reactions: with one tagged electron or positron. Tagging devices: Luminosity Monitor (LUMI) Covers Q2 range at LEP I 1.2 - 8.5 GeV2 at LEP II 8.8 - 30 GeV2 Very Small Angle Tagger (VSAT) (available only at LEP II) Covers Q2 range 0.2 - 0.85 GeV2 LEP II Exclusive rho rho production in tagged gamma-gamma interactions at LEP

  3. LEP I : around 91 GeV < 209 GeV < 209 GeV 161 < 183 < LEP II : LEP II : Data samples Measurement with LUMI: Integrated luminosity L = 148.7 pb-1 L = 706.0 pb-1 Total L = 854.7 pb-1 Measurement with VSAT: L = 684.8 pb-1 Exclusive rho rho production in tagged gamma-gamma interactions at LEP

  4. Selected events: LUMI - 934 ev. VSAT - 1958 ev. Selected events: LUMI - 343 ev. VSAT - 414 ev. Underlying reactions Exclusive rho rho production in tagged gamma-gamma interactions at LEP

  5. Distributions: LUMI, - this cut is taken to measure cross section. Exclusive rho rho production in tagged gamma-gamma interactions at LEP

  6. Distributions: VSAT, - this cut is taken to measure cross section. Exclusive rho rho production in tagged gamma-gamma interactions at LEP

  7. for for Contributing processes (non resonant) For VSAT also: MC model: isotropic production and phase space decays. Maximum likelihood fit - set of 6 variables, all mass combinations, is calculated using box method. Exclusive rho rho production in tagged gamma-gamma interactions at LEP

  8. Result of fit : LUMI, Shadowed histograms – contribution of Exclusive rho rho production in tagged gamma-gamma interactions at LEP

  9. Result of fit : VSAT, a) cosineof the polar angle of thewith respect to the axis in the center-of-mass system b) cosine of the polar angle of thein its parent helicity-system c) angle between the decay planes of the two mesons in the center-of-mass system d) cosine of the opening angle between the two directions of flight, each one defined in its parent helicity-system Exclusive rho rho production in tagged gamma-gamma interactions at LEP

  10. Q2 dependence ( ) QCD model for high Q2 M.Diehl et al, Phys.Rev.Lett. 81 (1998) 1782. N.Kivel et al, Phys.Lett. B 467 (1999) 263. A.Freund, Phys.Rev. D 61(2000) 074010. M.Diehl et al, Phys.Rev. D 62 (2000) 073014. 2HDA – Two Hadron Distribution Amplitudes (or Generalized Distribution Amplitudes (GDA)) Fit to Simplified formula: In our case <W> = 1.95 GeV Exclusive rho rho production in tagged gamma-gamma interactions at LEP

  11. Dedicated theoretical analysis I.V.Anikin, B.Pire, O.V.Teryaev, Phys. Rev. D 69 (2004) 014018. Phenomenological parameter is defined from the fit, which gives normalization of Exclusive rho rho production in tagged gamma-gamma interactions at LEP

  12. Q2 dependence ( ) For the region and compatible with the factor 2 Expected for an isospin I=0 state. This is in contrast with measurements at , where cross section is few times higher. Exclusive rho rho production in tagged gamma-gamma interactions at LEP

  13. Full Q2 range The relative magnitude of and production changes in the vicinity of , suggesting different -pair production mechanisms at low and high . Exclusive rho rho production in tagged gamma-gamma interactions at LEP

  14. cross section Extrapolation of GVDM dependence to for gives Exclusive rho rho production in tagged gamma-gamma interactions at LEP

  15. dependence of cross section For and small there is an enhancement of production relative to . Exclusive rho rho production in tagged gamma-gamma interactions at LEP

  16. The measurements allow to follow the evolution of cross sections over a • - region of two orders of magnitude. • The dependence of the process is well reproduced by parametrisation • based on GVDM model over the entire - region. But data cannot be • satisfactory described by such a parametrisation in the whole - region. • A - pole description is excluded for both and data. • The relative magnitude of and production changes in the vicinity of • , suggesting different - pair production mechanisms at low and high . Conclusions L3 measurements: , LUMI Phys. Lett. B 568 (2003) 11. , LUMI Phys. Lett. B 597 (2004) 26. Phys. Lett. B 604 (2004) 48. , VSAT , VSAT In preparation. • A QCD - based form is found to provide a good parametrisation in the entire interval, • where the differential cross sections show a monotonic decrease of more than four • orders of magnitude (for range ). Exclusive rho rho production in tagged gamma-gamma interactions at LEP

More Related