Event Shape Variables in DIS Update

1. Event Shape Variables in DIS Update A. Everett, A. Savin University of Wisconsin S. Hanlon, I. Skillicorn, A. Doyle University of Glasgow June 18, 2003

2. Used to determine the hadronization corrections Approach to Non-Perturbative Calculations • pQCD prediction → measured distribution • Correction factors for non-perturbative (soft) QCD effects • Separates out non-perturbative corrections for any infrared safe event shape variable, F: • Power Correction • independent of any fragmentation assumptions • “non-perturbative parameter” – (Dokshitzer, Webber, Phys. Lett. B 352(1995)451)

3. Event Shape Variables • Previous event shape variables not well correlated with • Study: • New Variables in DIS* • Kout • Azimuthal Correlation (following slides) *hep-ph/0111157 and hep-ph/0207072 • Previous Variables from previous event shape analysis (differential distributions)

4. Kinematic Bins • Mean of Event Shape Variables has a Q dependence. • Analysis done in bins of x and Q2.

5. Breit Frame Cuts Multiplicitycurrent ≥ 2 Ecurrent/Q > 0.25 For KOut, Acorr: At least 2 Jets in Breit Frame: E1,T > 6 GeV E2,T > 5 GeV PT,i,Lab 2 GeV Zufo Cuts Pt>0.15 GeV |η|<2.2 good acceptance region Selection Cuts Q2DA 80 GeV2 yJB > 0.04 yel < 0.95 Vertex with |z| < 40 cm |x| > 14 cm or |y| > 14 cm 38 < E-pZ < 65 GeV 44 < E-pZ for forward electron Good positron Sinistra Probability > 0.9 Ee’> 10 GeV Event Selection

6. C Parameter • Compare previous event shape variables between two analyses • Some small disagreement for uncorrected monte carlo at the detector level, perfect agreement at the “truth” level Uncorrected Ariadne at detector level Everett • Hanlon ┌ • Collimated: values tend towards minimum • Isotropic: values tend towards maximum

7. Invariant Jet Mass Everett • Hanlon ┌ Analyses Comparison Detector level Ariadne • Collimated: values tend towards minimum • Isotropic: values tend towards maximum

8. axis TT axis TZ axis TM axis Tm axis Energy Flow and Dijets: TT Everett • Hanlon ┌ Detector Level Ariadne • Collimated: values tend towards maximum • Isotropic: values tend towards minimum

9. axis TT axis TZ axis TM axis Tm axis Energy Flow and Dijets: T Detector Level Ariadne Everett • Hanlon ┌ • Collimated: values tend towards maximum • Isotropic: values tend towards minimum

10. BT 0 Thrust Axis BT 0.5 Broadening: BT • Broadening of particles in transverse momentum wrt. thrust axis Everett • Hanlon ┌ Detector Level Ariadne • Collimated: values tend towards minimum • Isotropic: values tend towards maximum

11. B 0 Photon Axis B 0.5 Broadening: B • Broadening of particles in transverse momentum wrt. photon axis Detector Level Ariadne Everett • Hanlon ┌ • Collimated: values tend towards minimum • Isotropic: values tend towards maximum

12. Out-of-plane Momentum • Examine New Variable: • Energy flow out of event plane defined by proton direction and thrust major axis • Sensitive to perturbative &non-perturbative contributions

13. Prediction by Banfi, Marchesini, Smye, Zanderighi (hep-ph/0111157) Plot ln(Kout/Q) since powers of ln(Kout/Q) used in resummation. Theoretical Prediction for Kout xB = 0.1 Q = 30 GeV y- = 0.1 < ykt < 2.5

14. Kout/Q Comparison • Good agreement between Data and Ariadne ’98 – ’00 Data (Everett) • Ariadne ┌ Kout/Q 0.0024 < x < 0.010 320 < Q2 < 640 GeV2

15. h h’ pth’ pth Azimuthal Correlation • Examine New Variable: • Momentum weighted function of the azimuthal angle around the photon-proton axis in the Breit frame between pairs (h,h’) of hadrons.

16. ACorr Comparison • Good initial agreement between Data and Ariadne ’98 – ’00 Data (Everett) • Ariadne ┌ Add Data vs MC Plots Here 0 /2   0.0024 < x < 0.6 80 < Q2 < 10240 GeV2

17. Summary • Good agreement between Glasgow and Wisconsin Analyses • Complementary analyses • Agreement of differential distributions • Early look at new variables • Acceptable level of agreement • Plan : • Systematic studies • Different monte carlo models • Extract S,