Measurement of Event Shape Variables in Deep Inelastic e^+ Scattering

Abstract

Deep inelastic e^+ scattering data, taken with the H1 detector at HERA, are used to study the event shape variables thrust, jet broadening and jet mass in the current hemisphere of the Breit frame over a large range of momentum transfers Q between 7 GeV and 100 GeV. The data are compared with results from e^+e^- experiments. Using second order QCD calculations and an approach to relate hadronisation effects to power corrections an analysis of the Q dependences of the means of the event shape parameters is presented, from which both the power corrections and the strong coupling constant are determined without any assumption on fragmentation models. The power corrections of all event shape variables investigated follow a 1/Q behaviour and can be described by a common parameter alpha_0.

Figures (4)

• Figure 1: Differential event shape distributions of a) thrust $1/N\,dn/d(1 - T_c)$, b) thrust $1/N\,dn/d(1 - T_z)$, c) jet broadening $1/N\,dn/dB_c$ and d) jet mass $1/N\,dn/d\rho_c$. H1 DIS $e\,p$ data (full symbols, only statistical errors shown) are compared with LEPTO Monte Carlo simu-lations (---). The spectra for $\langle Q \rangle = 8.3 - 68~{\rm GeV}$ are multiplied by factors of $10^n$ ($n = 0, 4$)
• Figure 2: Mean event shape variables as a function of Q for a)$\langle 1 - T_c \rangle$, b)$\langle 1 - T_z \rangle / 2$, c)$\langle B_c \rangle$, and d)$\langle \rho_c \rangle$. H1 DIS $e\,p$ data ($\bullet$, errors include statistics and systematics) are compared with LEPTO Monte Carlo simulations for hadrons (---) and partons ($\cdot\cdot\cdot$). Data from $e^+e^-$ experiments ($\triangle$) are shown for thrust $\langle 1 - T_{ee} \rangle$, calculated for the whole event, and for the average of the heavy and light jet masses
• Figure 3: Differential event shape distributions of a) thrust $1/N\,dn/d(1 - T_c)$, b) thrust $1/N\,dn/d(1 - T_z)$, c) jet broadening $1/N\,dn/dB_c$ and d) jet mass $1/N\,dn/d\rho_c$. H1 DIS $e\,p$ data (full symbols, only statistical errors shown) are compared with second order QCD calculations (---). The spectra for $\langle Q \rangle = 8.3 - 68~{\rm GeV}$ are multiplied by factors of $10^n$ ($n = 0, 4$)
• Figure 4: Mean event shape variables as a function of Q for a)$\langle 1 - T_c \rangle$, b)$\langle 1 - T_z \rangle / 2$, c)$\langle B_c \rangle$, and d)$\langle \rho_c \rangle$. H1 DIS $e\,p$ data ($\bullet$, errors include statistics and systematics) are compared with QCD fits (---) and second order QCD calculations ($\cdot\cdot\cdot$)