Exclusive ρ 0 electroproduction

1. Exclusive ρ0 electroproduction H. Abramowicz, S. Kananov, A. Kreisel, A. Levy, O. Smith Tel Aviv University and S. Proskuryakov Moscow State University A. Levy: rho electroproduction

2. g g IP ‘hard’ ‘soft’ Why are we measuring • Expect  to increase from soft (~0.2, from ‘soft Pomeron’ value) to hard (~0.8, from xg(x,Q2)2) • Expect b to decrease from soft (~10 GeV-2)to hard (~4-5 GeV-2) A. Levy: rho electroproduction

3. ZEUS published results DESY 98-107, EPJ C6 (1999) 603 A. Levy: rho electroproduction

4. b(Q2) A. Levy: rho electroproduction

5. Preliminary results -2001 Arik  BaBar A. Levy: rho electroproduction

6. Decision: publish 96-00 data • Data: 96-97 (Arik, Sergey) + 98-00 (Sergey, Sasha) L ~ 120 pb-1 • MC: ρ0 – ZEUSVM, pdiss: EPSOFT(96-97), PYTHIA(98-00) using FPC and LPS • Kinematic region: 2 < Q2 < 160 GeV2 32 < W < 180 GeV 0 < |t| < 1 GeV2 • 0.65 < M() < 1.2 GeV - 65,000 evts A. Levy: rho electroproduction

7. M() - all A. Levy: rho electroproduction

8. M() – Q2, t A. Levy: rho electroproduction

9. Control plots Example: 98-00 data A. Levy: rho electroproduction

10. Control plots – SCHC reweighting Example: 98-00 data A. Levy: rho electroproduction

11. Control plots – 15ME reweighting A. Levy: rho electroproduction

12. Density matrix elements A. Levy: rho electroproduction

13. LPS FPC Proton dissociation MC: PYTHIA A. Levy: rho electroproduction

14. Systematics • E-PZ cut (default 45 GeV) was changed to 42 and 48 GeV • pT of the pions (default 0.15 GeV) was changed to 0.2 GeV • elasticity cut. The energy of unmatched island (default 0.3 GeV) was changed to 0.25 and 0.35 GeV • elasticity cut. The distance of closest approach of island and extrapolated track was changed from 30cm (default) to 20cm • Z-vertex cut (default |Z| < 50cm) was varied from 40 to 60 cm • Box cut (default 13.2X8 cm) was increased by 0.5 cm •  mass window (default 0.65-1.2 GeV) was changed to 0.6-1.1 GeV • generated W dependence in MC was reweighted by Wn, (n=±0.03) • generated t in MC was reweighted by exp(bt) b = ±0.5 GeV-2 • angular distributions in MC were reweighted according SCHC. Default reweighting comes from 15 matrix element fit. • generated Q2 in MC was reweighted by (Q2+Mρ2)k,where k = ±0.05 A. Levy: rho electroproduction

15. d/dt A. Levy: rho electroproduction

16. (Q2) Fit to whole Q2 range gives bad 2/df (~14) Good fit A. Levy: rho electroproduction

17. (Q2) A. Levy: rho electroproduction

18. (Q2) n=n(Q2) because b=b(Q2) In case of J/ b=const  n=const A. Levy: rho electroproduction

19. (W) A. Levy: rho electroproduction

20. R=L/T (Q2) SCHC A. Levy: rho electroproduction

21. R(W) • L has the same W dependence as T ?? L  qqbar in small configuration T  qqbar in small and large configurations small configuration  steep W dep large configuration  slow W dep   large qqbar configuration is supressed A. Levy: rho electroproduction

22. Comparison of analyses A. Levy: rho electroproduction

23. Outlook • Finish Pomeron trajectory on combined data • Present d/dt in finer bins • Put theory curves on results • ZEUS-note + draft of paper are being written • Try for “paper presentation” before DIS07 A. Levy: rho electroproduction