nucl-ex digest · May 5, 2017

Measurements of

e p \to e^{'} π^{+} π^{-} p^{'}

Cross Sections with CLAS at

1.40 < W < 2.0

GeV and

2.0 < Q^{2} < 5.0

GeV

^{2}

E.L. Isupov · V.D. Burkert · D.S. Carman · R.W. Gothe · K. Hicks · B.S. Ishkhanov · V.I. Mokeev · the CLAS Collaboration

This paper reports new exclusive cross sections for

e p \to e^{'} π^{+} π^{-} p^{'}

using the CLAS detector at Jefferson Laboratory. These results are presented for the first time at photon virtualities 2.0 GeV^2 < Q^2 < 5.0 GeV^2 in the center-of-mass energy range 1.4 GeV < W < 2.0 GeV, which covers a large part of the nucleon resonance region. Using a model developed for the phenomenological analysis of electroproduction data, we see strong indications that the relative contributions from the resonant cross sections at W < 1.74 GeV increase with

Q^{2}

. These data considerably extend the kinematic reach of previous measurements. Exclusive

e p \to e^{'} π^{+} π^{-} p^{'}

cross section measurements are of particular importance for the extraction of resonance electrocouplings in the mass range above 1.6 GeV.

nucl-exPRC(2017)·51 citations

02*

Validity of the Weizsäcker-Williams Approximation and the Analysis of Beam Dump Experiments: Production of an axion, a dark photon, or a new axial-vector boson

Yu-Sheng Liu🇺🇸 · Gerald A. Miller🇺🇸

Beam dump experiments have been used to search for new particles, $ϕ$ , with null results interpreted in terms of limits on masses $m_{ϕ}$ and coupling constants $ϵ$ . However these limits have been obtained by using approximations [including the Weizsäcker-Williams (WW) approximation] or Monte-Carlo simulations. We display methods to obtain the cross section and the resulting particle production rates without using approximations on the phase space integral or Monte-Carlo simulations. In our previous work we examined the case of the new scalar boson production; in this paper we explore all possible new spin-0 and spin-1 particles. We show that the approximations cannot be used to obtain accurate values of cross sections. The corresponding exclusion plots differ by substantial amounts when seen on a linear scale. Furthermore, a new region ( $m_{ϕ} < 2 m_{e}$ ) of parameter space can be explored without using one of the common approximations, $m_{ϕ} ≫ m_{e}$ . We derive new expressions for the three photon decays of dark photon and four photon decays of new axial-vector bosons. As a result, the production cross section and exclusion region of different low mass ( $m_{ϕ} < 2 m_{e}$ ) bosons are very different. Moreover, our method can be used as a consistency check for Monte-Carlo simulations.

↳ hep-phhep-exnucl-exnucl-thPRD(2017)·111 citations

Measurements of ep→e′π+π−p′ Cross Sections with CLAS at 1.40<W<2.0 GeV and 2.0<Q2<5.0 GeV2

Validity of the Weizsäcker-Williams Approximation and the Analysis of Beam Dump Experiments: Production of an axion, a dark photon, or a new axial-vector boson

Measurements of $e p \to e^{'} π^{+} π^{-} p^{'}$ Cross Sections with CLAS at $1.40 < W < 2.0$ GeV and $2.0 < Q^{2} < 5.0$ GeV $^{2}$