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Register a new userExclusive Hard Processes for Studying Hadron Structures at J-PARC
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Wen-Chen Chang
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With an appropriate hard scale, exclusive hadronic processes could provide novel information of the internal quark-gluon configurations of hadrons. The availability of 10-20 GeV secondary meson beam in the coming high-momentum beam line of Hadron Hall at J-PARC offers an unique opportunity to carry out the measurements of the exclusive hard processes. We address this interesting approach by two possibilities: (a) $pi^- p to K^0 Lambda(1405)$ for the constituent quark structure of $Lambda(1405)$, and (b) exclusive pion-induced Drell-Yan process $pi^- p to gamma^* n to l^+ l^- n$ for the generalized parton distributions (GPDs) of nucleons. Realization of such measurements at J-PARC will open up a new way of accessing the internal quark structure of exotic hadrons and also the nucleon GPDs based on a solid theoretical foundation of perturbative QCD.
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The pentaquark $Theta^+$ has been searched for via the $pi^-p to K^-X$ reaction with beam momenta of 1.92 and 2.01 GeV/$c$ at J-PARC. A missing mass resolution of 2 MeV (FWHM) was achieved but no sharp peak structure was observed. The upper limits on the production cross section averaged over the scattering angle from 2$^{circ}$ to 15$^{circ}$ in the laboratory frame were found to be less than 0.28 $mu$b/sr at the 90% confidence level for both the 1.92- and 2.01-GeV/$c$ data. The systematic uncertainty of the upper limits was controlled within 10%. Constraints on the $Theta^+$ decay width were also evaluated with a theoretical calculation using effective Lagrangian. The present result implies that the width should be less than 0.36 and 1.9 MeV for the spin-parity of $1/2^+$ and $1/2^-$, respectively.
The committee for the study of the extension of the Hadron Experimental Facility was formed under the Hadron Hall Users Association in August, 2015. This document is a summary of the discussions among the committee members, and documented by a part of the members listed below.
This write-up document is a summary of International workshop on the project for the extended hadron experimental facility which was held from March 26 to 28, 2018 at KEK Tokai Campus. This document is a collection of Letter Of Intents (LOIs) related to the proposed beam lines in the extended hadron experimental facility at J-PARC.
We report on the first measurement of cross sections for exclusive deeply virtual pion electroproduction off the proton, $e p to e^prime n pi^+$, above the resonance region at backward pion center-of-mass angles. The $varphi^*_{pi}$-dependent cross sections were measured, from which we extracted three combinations of structure functions of the proton. Our results are compatible with calculations based on nucleon-to-pion transition distribution amplitudes (TDAs) and shed new light on nucleon structure.
We first present an introduction to the theory of hard exclusive processes. We then illustrate this theory by a few selected examples. The last part is devoted to the most recent developments in the asymptotical energy limit.
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