Azimuthal distribution of diffractive pions in DIS

Richard Polifka, Charles University, Prague8. - 9.12.2005, Antverpen

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

motivation

Picture 1. Definition of pion and lepton plane

Picture 2. Schematic diagram of 2 gluon exchange

Pi+

Pi- Pion plane

sources

DATA – 99/00, still using only 00MC – rapgap inclusive diffraction at medium Q2 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

basic cuts

Q2 = < 3.5,100> GeV2

Run Quality < 3Ybjörken = < 0.05 , 0.7 >

| ZVTX | < 35 cmE-Pz = < 35, 70> GeVGood electron cuts: only 1 electon in elmg candidates, E in SpaCal > 8 GeV, RSpaCal > 9.1 cm, excluded some runs because of unfunctional clusters…

pion cuts

Based on Light VM Finder by X. Janssen and C. Gwilliam2 opposite charged tracks in central region coming from primary vertexPt > 0.1 GeV

= < 20° , 160° >No neutral particle with E > 0.4 GeV in Lar or SpaCal

diffractive and noise cuts

Usually MAX < 3.2, but here not needed

Xpom < 0.04

Invariant Mass = <1.1 , 3 > GeVNo noise in PRTIn first 2 plates of Forward Muon Detector allowed some noise

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 happeningweighting with L4 and L5 weights ( standard HAT vars)

looking into hadron & parton level to see what in the event is going on

Good event record

Background event record

realisation

Comparing several variables and trying to find some, which can on detector level distinguish between good and background eventsNot much differencies

comparison of good and background events

comparison of good and background events

E – Pz > 50 GeV

Ionisation < 2.3

effects ( from 776 data events)

Variable Cut Effect

E – Pz > 50 GeV 88 cutted

> 0.7 57 cutted

Ionisation < 2.3 5 cutted

)(

)(

ePt

Pt

=> 626 events left

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

comparison of data and monte carlo

comparison of data and monte carlo

subtriggerss0 is on in only 24%, s61 in 100% cases

146 from 626 !!

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 99Put data and mc in better agreement