1. The Diffractive Structure Function:ξ dependence Christina Mesropian The Rockefeller University

2. - - p p P x p Study the diffractive structure function Regge factorization: The Diffractive Structure Function Subject of interest: Hard diffraction process: production of high pT dijets Single Diffractive dissociation Christina Mesropian

3. The Diffractive Structure Function 2 dijet samples: - SD: diffractive – leading p ND: non-diffractive Measure ratio of SD to ND then known ND structure function Christina Mesropian

4. The Diffractive Structure Function discrepancy in normalization factorization breakdown Power Law dependence Christina Mesropian

5. change in shape for R as a function of x SD ND The Diffractive Structure Function:Run I ξ dependence contributions from reggeon exchange in 0.035<ξ<0.095 range if reggeon has different structure than pomeron no ξ dependence Christina Mesropian

6. events without hits in BSC on the p or p side - The Diffractive Structure Function:Run 2: East dijets to study ξ dependence for low ξ (<0.035) values Goals rapidity gaps Means West BSC gap requirement Christina Mesropian

7. The Diffractive Structure Function:Run 2: Hardware Beam Shower Counters: scintillation counters around the beam pipe detect particles traveling in direction from interaction point along beam pipe 5.5 < |η| <7.5 coverage BSCs provide East and West gap triggers: Christina Mesropian

8. The Diffractive Structure Function:Run 2: Trigger gap trigger rate decreases with increasing luminosity – additional interactions “kill” gap MBR Monte Carlo simulation Christina Mesropian

9. _ p p η → X The Diffractive Structure Function:Run 2 information from calorimeters: forward calorimeters: MiniPlugs: 3.5<|η|<5.1 determination of ξ: from the information of final state particles in the diffractive mass system X low ξvalues 0.001 < ξ possibly… Christina Mesropian

10. The Diffractive Structure Function:Run 2 for cross reference with RP+Jet data sample Tighter cut on BSCW gap Christina Mesropian

11. The Diffractive Structure Function:Run 2 Cleaner sub-sample Request MP west gap 0-0 bin corresponds to BSCW+MPW gap sub-sample Christina Mesropian

12. The Diffractive Structure Function:Run 2 BSCW- Gap + Jet Sample 0.001 < ξ • Strategy for the analysis: • calculate ξ for each event • separate clean diffractive sample: • calculate x for dijet system • compare with ND Jet5 sample • cross checks with RP + Jet5 sample • different Q2 samples for the same trigger… Christina Mesropian

13. Summary FACT: New possibility to extend ξ range down to 0.001 for Q2 100 GeV2 QUESTION: Will the ξ distribution at the Tevatron be the same as at HERA at very low ξ? ANSWER: New results from CDF Run 2 data coming soon! Christina Mesropian