Exclusive electroproduction of two pions at HERA

Abstract

The exclusive electroproduction of two pions in the mass range 0.4 < M ππ < 2.5 GeV has been studied with the ZEUS detector at HERA using an integrated luminosity of 82 pb −1 . The analysis was carried out in the kinematic range of 2 < Q 2 < 80 GeV 2 , 32 < W < 180 GeV and |t| < 0.6 GeV 2 , where Q 2 is the photon virtuality, W is the photon-proton centre-of-mass energy and t is the two-pion invariant-mass distribution is interpreted in terms of the pion electromagnetic form factor, |F (M ππ )|, assuming that the studied mass range includes the contributions of the ρ, ρ and ρ vector-meson states. The masses and widths of the resonances were obtained and the Q 2 dependence of the cross-section ratios σ (ρ → ππ)/σ (ρ) and σ (ρ → ππ)/σ (ρ) was extracted. The pion form factor obtained in the present analysis is compared to that obtained in e + e − → π + π − . a

Gauge field theories with Lorentz-violating operators of arbitrary dimension

“…f kkq . In principle, data from the H1 and ZEUS collaborations at HERA [51] and perhaps from a future electron-ion collider [52] could be analyzed to obtain constraints on the various coefficients a (5)µαβ . Given that the HERA energies lie in the range 1-100 GeV, the estimated constraints obtained in Ref.…”

PROSA PDFs and Astrophysical Applications

“…These data are directly sensitive to the valence and sea quark distributions and allow to put constraints on the gluon distribution through scaling violations (down to x 10 −3 ). The fit also includes combined H1 and ZEUS semi-inclusive data on charm production in NC DIS [3], plus ZEUS data on bottom production in DIS [4]. These data allow to further constrain gluon and sea distributions (down to x 10 −4 ), as well as the values of the charm and bottom masses.…”

Collinear and Transverse Momentum Dependent parton densities obtained with a Parton Branching Method

“…We used precision measurements in neutral and charged current interactions at various beam energies from HERA 1+2 [18] of σ red = d 2 σ ep /dxdQ 2 · Q 4 x/(2πα 2 (1 + (1 − y) 2 )) (which is the DIS cross section where the photon flux is removed) in the range 3.5 < Q 2 < 30000 GeV 2 , with α s (m Z ) = 0.118, at a starting scale µ 2 0 = 2 GeV 2 , masses for heavy quarks as m c = 1.73 GeV, m b = 5.0 GeV and m t = 175 GeV together with a fixed z M = 1 − 10 −5 . The fit of integrated TMDs was performed at LO and NLO with experimental uncertainties, for all flavours.…”