1. Azimuthal distribution of diffractive pions in DIS Richard Polifka, Charles University, Prague 8. - 9.12.2005, Antverpen

2. motivation Study of diffractive DIS of non resonant di pions in invariant mass range 1.1 – 3 GeV (between  and J/Ψ) Looking at angular distribution of pion and lepton plane in gamma-p CMS to distinguish between 2 gluon exchange model and pomeron exchange model

3. motivation Picture 1. Definition of pion and lepton plane Picture 2. Schematic diagram of 2 gluon exchange Pi+ Pi- Pion plane

4. sources DATA – 99/00, still using only 00 MC – rapgap inclusive diffraction at medium Q 2 from Tinne Anthonis for 99/00 Pomeron uds – 12 500/1 500 000 Pomeron c – 0/500 000 Meson – 350/3 000 000 => Pomeron uds

5. basic cuts Q 2 = GeV 2 Run Quality < 3 Y björken = | ZVTX | < 35 cm E-Pz = GeV Good electron cuts: only 1 electon in elmg candidates, E in SpaCal > 8 GeV, RSpaCal > 9.1 cm, excluded some runs because of unfunctional clusters…

6. pion cuts Based on Light VM Finder by X. Janssen and C. Gwilliam 2 opposite charged tracks in central region coming from primary vertex P t > 0.1 GeV  = No neutral particle with E > 0.4 GeV in Lar or SpaCal

7. diffractive and noise cuts Usually  MAX < 3.2, but here not needed X pom < 0.04 Invariant Mass = GeV No noise in PRT In first 2 plates of Forward Muon Detector allowed some noise

8. comparison of data & mc 12 500 mc x 776 data events => big error for data, my mc more or less describe data => look into mc to see what’s happening weighting with L4 and L5 weights ( standard HAT vars)

9. looking into hadron & parton level to see what in the event is going on Good event record Background event record

10. realisation Comparing several variables and trying to find some, which can on detector level distinguish between good and background events Not much differencies

11. comparison of good and background events

13. E – Pz > 50 GeV Ionisation < 2.3

14. effects ( from 776 data events) VariableCutEffect E – Pz> 50 GeV88 cutted > 0.757 cutted Ionisation< 2.35 cutted => 626 events left

15. comparison of data before (old) and after cuts (new)

16. comparison of data and monte carlo

18. subtriggers s0 is on in only 24%, s61 in 100% cases 146 from 626 !!

19. outlook Too small statistics => idea of cone in SpaCal ( no need to exclude whole SpaCal, many good events with radiated gamma) Cut on s0 = true would brutally decrease statistics => ? Add data 99 Put data and mc in better agreement