Event Shapes, Alexander Savin University of WisconsinDIS 2006, April 21, Event Shapes in NC DIS at ZEUS Alexander A. Savin University of Wisconsin On Behalf of the ZEUS Collaboration DIS 2006, Tsukuba, Japan

Event Shapes, Alexander Savin University of WisconsinDIS 2006, April 21, HERA Kinematic Variables Breit Frame Definition: q + 2x B P = 0 Q 2, x Bj, y 920 GeV 27.5 GeV ZEUS (82.2 pb -1 ) 80 < Q 2 < GeV < x < 0.6 DESY , hep-ex/

Event Shapes, Alexander Savin University of WisconsinDIS 2006, April 21, Power Corrections Use power corrections to correct for non-perturbative effects in infrared and collinear safe event shape variable. Used to determine the hadronization corrections Universal non-perturbative constant Similar for the means and differential distributions

Event Shapes, Alexander Savin University of WisconsinDIS 2006, April 21, Test validity of the power correction method by extracting from a fit to the data. For means: NLO + PC as a function of Q (DISASTER++/DISENT) For differentials: NLO + NLL + PC in bins of (x,Q 2 ) (DISASTER++/DISPATCH/DISRESUM) Hessian method was used Analysis Method

Event Shapes, Alexander Savin University of WisconsinDIS 2006, April 21, Event-shape variables ThrustBroadening C Parameter Jet Mass Sums are over all momenta in the current hemisphere of the Breit frame Axis Dependent:T T, B T, T , B  Axis Independent:C, M 2

Event Shapes, Alexander Savin University of WisconsinDIS 2006, April 21, Mean Event Shapes Comparison with the ARIADNE Parton level should be taken as indicative only

Event Shapes, Alexander Savin University of WisconsinDIS 2006, April 21, Mean Event Shapes Results of the NLO+PC fit Simultaneous fit for  s and  0 Each shape fit separately NLO calculation using DISASTER++ Negative power correction

Event Shapes, Alexander Savin University of WisconsinDIS 2006, April 21, Mean Event Shapes Extracted parameters: Consistent with the previous measurement Extracted  0 are consistent (except T  ) with each other, slightly lower than H1 Extracted  s values are consistent with each other, except B T and T  High sensitivity of T  to PDF Theoretical errors dominate. World Average

Event Shapes, Alexander Savin University of WisconsinDIS 2006, April 21, Shape Distributions ARIADNE describes data well Only high Q region is used

Event Shapes, Alexander Savin University of WisconsinDIS 2006, April 21, Shape Distributions The differential distributions are fitted over a limited range. Bins for which theoretical calculations are not expected to be valid are omitted from fit. NLO+NLL+PC NLO+NLL

Event Shapes, Alexander Savin University of WisconsinDIS 2006, April 21, Shape Distributions The differential distributions are fitted over a limited range. Bins for which theoretical calculations are not expected to be valid are omitted from fit.

Event Shapes, Alexander Savin University of WisconsinDIS 2006, April 21, Extracted Parameters Extracted parameters Extracted  s values are consistent with each other and H1 Major theoretical uncertainties Fit range ; Theoretical parameters: renormalization scale, logarithmic rescale factor, power factor in modification term etc

Event Shapes, Alexander Savin University of WisconsinDIS 2006, April 21, Test of Q-independency Consistent with being independent of the Q range

Event Shapes, Alexander Savin University of WisconsinDIS 2006, April 21, y 2 – resolution cut parameter (2+1) to (1+1) ; K OUT – out-of-plane momentum Event Shapes With Jets Momentum out of plane 2 jets

Event Shapes, Alexander Savin University of WisconsinDIS 2006, April 21, y 2 parameter ARIADNE describes data well at high Q ; NLO describes data without hadronization correction

Event Shapes, Alexander Savin University of WisconsinDIS 2006, April 21, Out-of-plane momentum ARIADNE describes data well indicating significant hadronization corrections

Event Shapes, Alexander Savin University of WisconsinDIS 2006, April 21, SummarySummary Mean values and differential distributions of event- shape variables have been measured at ZEUS in the kinematic region 80 < Q2 < GeV 2 and < x < 0.6 The data are well described by the ARIADNE MC Power-correction method provides a reasonable description of the data for all event-shape variables with  for most of the variables. The lack of consistency in the (  S,  0 ) extraction suggests the importance of high-order processes that are not yet included in the model Need some theoretical input to proceed with the jets event shapes