1. September 17-20, 2003.Kenichi Hatakeyama1 Soft Double Pomeron Exchange in CDF Run I Kenichi Hatakeyama The Rockefeller University for the CDF Collaboration Small-x and Diffraction 2003 Fermilab, Illinois, USA

2. September 17-20, 2003.Kenichi Hatakeyama2 Introduction Shaded Area : Region of Particle Production

3. September 17-20, 2003.Kenichi Hatakeyama3 Main Issue in Hadronic Diffraction : results from single diffractive (SD) dijet production  The diffractive structure function measured using SD dijet events at the Tevatron is smaller than that at HERA by approximately an order of magnitude.  The discrepancy is generally attributed to additional color exchanges which spoil the “diffractive” rapidity gap. ~10 Factorization Breakdown CDF Collaboration, Phys. Rev. Lett. 84, 5043-5048 (2000).

4. September 17-20, 2003.Kenichi Hatakeyama4 Dijet Production in DPE  Dijet production by double pomeron exchange was studied by CDF.  R[DPE/SD] is larger than R[SD/ND] by a factor of about 5. CDF Collaboration, Phys. Rev. Lett. 85, 4215-4220 (2000). The formation of the 2nd gap is not as suppressed as the 1st gap. Extract diffractive structure function from R[DPE/SD] and compare it with expectations from HERA results.

5. September 17-20, 2003.Kenichi Hatakeyama5 Diffractive Structure Function measured using DPE dijet events The diffractive structure function measured using DPE dijets is approximately equal to expectations from HERA! Factorization holds?

6. September 17-20, 2003.Kenichi Hatakeyama6 Unitarity problem : Soft Diffraction : Inclusive (Soft) SD Results  The measured SD cross section is smaller than the Regge theory prediction by approximately an order of magnitude at the Tevatron energy.  Normalizing the integral of the pomeron flux (f IP/p ) to unity yields the correct √s- dependence of σ SD. Is the formation of the second gap suppressed? Tevatron data Study DPE Similar results were obtained for double diffraction as well. Renormalization

7. September 17-20, 2003.Kenichi Hatakeyama7 Inclusive (Soft) DPE Cross Section  Regge theory prediction + factorization :  Flux renorm. model : (both gaps are suppressed.) K. Goulianos, Phys. Lett. B 353, 379 (1995).  Gap probability (P gap ) renorm. model : P gap is renormalized. (only one gap is suppressed.) K. Goulianos, e.g. hep-ph/0110240 (2001). = κ=g/β(0). g:triple-Pomeron coupling,

8. September 17-20, 2003.Kenichi Hatakeyama8 Analysis Strategy  Use events triggered on a leading antiproton.  ξ pbar is measured by Roman Pots : ξ pbar RPS.  Measure ξ p (ξ pbar ) from BBC and calorimeters : ξ p X (ξ pbar X ).  Calibrate ξ X by comparing ξ pbar RPS and ξ pbar X.  Plot ξ p X distribution and look for a DPE signal expected in the small ξ p X region.

9. September 17-20, 2003.Kenichi Hatakeyama9 Reconstruction of ξ p X Calorimeters : use E T and η of towers above noise level. BBC : use hits in BBC scintillation arrays. p T is chosen to follow the “known” p T spectrum : Use calorimeter towers and BBC hits to reconstruct ξ p : Calorimeters BBC

10. September 17-20, 2003.Kenichi Hatakeyama10 Calibration of ξ X ξ X distribution in every ξ RPS bin is fitted to P1 : Peak P2 : Width P2/P1 = 0.57 (ξ X resolution is ~60%.) ξ X = ξ RPS, (ξ X is calibrated so that ξ X = ξ RPS.)

11. September 17-20, 2003.Kenichi Hatakeyama11 ξ p X Distribution  The input ξ p distribution in DPE MC is 1/ξ p 1+ε (ε = 0.104 is obtained from p ± p/π ± p/K ± p total cross sections).  The DPE and SD MC distributions are independently normalized to the data distribution.  The measured ξ p X distribution is in agreement with the DPE+SD MC distribution.

12. September 17-20, 2003.Kenichi Hatakeyama12 DPE Fraction in SD Events R[DPE/SD(incl)] Source@ 1800 GeV@ 630 GeV Data0.195±0.001±0.0110.168±0.001±0.012 Regge + factorization0.360.25 Flux Renormalization0.041 P gap Renormalization0.210.17 In agreement with the renormalized gap predictions!

13. September 17-20, 2003.Kenichi Hatakeyama13 Soft Diffraction : Summary σ (mb) Gap Fraction Good Agreement with Renormalized Gap Predictions! SDDD DPE SDD

14. September 17-20, 2003.Kenichi Hatakeyama14 Conclusions  The measured ξ p X distribution exhibits ~1/ξ 1+ε behavior (ε = 0.104).  The measured DPE fraction in SD is : for 0.035 <ξ pbar < 0.095 and ξ p < 0.02 at √s = 1800 GeV.  in agreement with the renormalized gap prediction. In events with a rapidity gap, the formation of a second gap is “unsuppressed”!