1. Recent Results on Diffraction and Exclusive Production from CDF Christina Mesropian The Rockefeller University

2. DIS 2007 MunichChristina Mesropian2 Outline Introduction Diffractive Structure Function Exclusive Production –Exclusive Dijet Production –Exclusive e + e - Production –Exclusive Di-Photon Production

3. DIS 2007 MunichChristina Mesropian3 Introduction Diffractive: vacuum exchange Non-diffractive: color exchange Goals of Diffractive Program at CDF: To understand the nature of colorless exchange To test the feasibility of diffraction as a tool to search for new physics at the LHC

4. DIS 2007 MunichChristina Mesropian4 GAP X Diffraction at the Tevatron Kinematic Variables - t - 4-momentum transfer squared  - momentum fraction of antiproton carried by the diffractive exchange M X - mass of system X Goal: To study the partonic structure of diffractive exchange

5. DIS 2007 MunichChristina Mesropian5 SingleDiffractionDoubleDiffraction Double Pomeron Exchange Single + Double Diffraction Diffraction in Run I at CDF Published 14 papers

6. DIS 2007 MunichChristina Mesropian6 Forward Detectors in Run II RPS – Roman Pot Spectrometers 0.02 <  < 0.1 0 < |t| < 2 GeV 2 BSC – Beam Shower Counters 5.4 <  < 7.4 MPCAL – MiniPlug Calorimeters 3.5 <  < 5.2

7. DIS 2007 MunichChristina Mesropian7 Nucl. Instrum. Meth. A518 (2004) 42. Nucl. Instrum. Meth. A496 (2003) 333. designed to measure the energy and lateral position of both electromagnetic and hadronic showers “towerless” geometry – no dead regions MiniPlug Calorimeters

8. DIS 2007 MunichChristina Mesropian8 Diffractive Structure Function Hard diffraction: production of high p T dijets Study the diffractive structure function Dataknown PDF Diffractive dijets

9. DIS 2007 MunichChristina Mesropian9 Diffractive Structure Function: x Bj dependence Confirms Run I results different jet acceptance

10. DIS 2007 MunichChristina Mesropian10 Diffractive Structure Function: Q 2 dependence 100 GeV jets No significant Q 2 dependence in 100 < Q 2 < 10000 GeV 2 Pomeron evolves like proton?

11. DIS 2007 MunichChristina Mesropian11 same slope at t=0 for entire region of Q 2 < 4500 GeV 2 Diffractive Structure Function t dependence arbitrary normalization

12. DIS 2007 MunichChristina Mesropian12 Attractive channel for Higgs discovery at LHC Standard Model light Higgs:  “exclusive channel” →clean signal (no underlying event)  suppression at LO of the background sub-processes (J z =0 selection rule) Exclusive Higgs Production

13. DIS 2007 MunichChristina Mesropian13 Method: Select diffractive dijet events produced by DPE (Double Pomeron Exchange) Reconstruct Compare background with DPE Monte Carlo POMWIG uncertainty from different Pomeron PDFs Exclusive Dijet Production 0 not detected gap to calibrate theoretical calculations for exclusive Higgs production at LHC : study similar processes with higher cross sections: exclusive dijet, di-photon production

14. DIS 2007 MunichChristina Mesropian14 Exclusive Dijet Production CDF Run II Preliminary Excess in data over MC predictions for high R jj values Signal at R jj =1 is smeared due to shower/hadronization effects, NLO contributions

15. DIS 2007 MunichChristina Mesropian15 Exclusive Dijet Production MC fit to R jj data bkgd signal fit Binned likelihood fits (MC normalizations as free parameters) ExHuME CPC 175,232 (2006) Exclusive DPE as input to DPEMC CPC 167,217 (2005) Signal MC

16. DIS 2007 MunichChristina Mesropian16 Exclusive Dijet Production The two results are consistent with each other F1 F1 F2 F2  Look for heavy flavor jet suppression at high Rjj

17. DIS 2007 MunichChristina Mesropian17 Exclusive Dijet Cross Section Exclusive DPE (DPEMC) – exclusive DPE model (based on non –pQCD Bialas Landshoff model) as an input to DPE MC KMR x1/3 – Khoze, Martin, Ryskin at LO (factor 3 uncertainty) hep-ph/0507040 ExHuME – ExHuME Monte Carlo Data prefers ExHuME and KMR calculations

18. DIS 2007 MunichChristina Mesropian18 Exclusive Dijet Mass Distribution Higgs mass range!

19. DIS 2007 MunichChristina Mesropian19 Exclusive e + e - Production Select e + e - events: reconstruct e + e - with E T >5 GeV, |  |<2 request no additional calorimeter activity protons are not tagged 16 similar events are found PRL 98, 112001 (2007) QED mediated process, cross section is well known good control sample for search of

20. DIS 2007 MunichChristina Mesropian20 Exclusive e + e - Production

21. DIS 2007 MunichChristina Mesropian21 Exclusive di-photon events: select in the same way as e + e -, (except for tracking veto) with E T >5 GeV, |  |<1 agreement of exclusive e + e - cross section provides cross check of the methodology factor of 3 ~ 4 uncertainty in the cross section Exclusive  Production

22. DIS 2007 MunichChristina Mesropian22 Exclusive  Production

23. DIS 2007 MunichChristina Mesropian23 CDF results on Diffraction Diffractive Structure function Extended Run I results using single diffractive dijets no Q 2 dependence slope at t=0 is independent of Q 2 Exclusive Production Observed excess events at high R jj being consistent with exclusive dijets Observed events being consistent with exclusive  production Observed exclusive e + e - production – cross check for di-photons More interesting results are coming… Summary

24. DIS 2007 MunichChristina Mesropian24 Work in Progress Diffractive W ProductionExclusive Di-muon Production Rapidity Gaps between Jets

25. DIS 2007 MunichChristina Mesropian25 Pile-up Events One of the main problems: multiple interactions – spoil diffractive events L inst ~ 210 31 cm -2 s -1

26. DIS 2007 MunichChristina Mesropian26 discrepancy in normalization QCD factorization breakdown Pomeron exchange ~10 1/ξ behavior Regge factorization holds Diffractive Structure Function