Energetic neutrons produced in ep collisions at HERA have been studied with the ZEUS detector in the photoproduction regime at a mean photon-proton center-of-mass energy of 220 GeV. The neutrons carry a large fraction 0.64 < x(L) < 0.925 of the incoming proton energy, and the four-momentum transfer squared at the proton-neutron vertex is small, vertical bar t vertical bar < 0.425 GeV(2). The x(L) distribution of the neutrons is measured in bins of t. The (1 - x(L)) distributions in the t bins studied satisfy a power law dN/dx(L) proportional to (1 - x(L))(a(t)), with the powers a(t) following a linear function of t: a(t) = 0.88 +/- 0.09(stat.)(-0.39)(+0.34) (syst.) - (2.81 +/- 0.42(stat.)(-0.62)(+1.13) (syst.) GeV(-2))t. This result is consistent with the expectations of pion-exchange models, in which the incoming proton fluctuates to a neutron-pion state, and the electron interacts with the pion.
Study of the pion trajectory in the photoproduction of leading neutrons at HERA
BASILE, MAURIZIO;CIFARELLI, LUISA;CONTIN, ANDREA;PALMONARI, FEDERICO;SARTORELLI, GABRIELLA;ZICHICHI, ANTONINO;
2005
Abstract
Energetic neutrons produced in ep collisions at HERA have been studied with the ZEUS detector in the photoproduction regime at a mean photon-proton center-of-mass energy of 220 GeV. The neutrons carry a large fraction 0.64 < x(L) < 0.925 of the incoming proton energy, and the four-momentum transfer squared at the proton-neutron vertex is small, vertical bar t vertical bar < 0.425 GeV(2). The x(L) distribution of the neutrons is measured in bins of t. The (1 - x(L)) distributions in the t bins studied satisfy a power law dN/dx(L) proportional to (1 - x(L))(a(t)), with the powers a(t) following a linear function of t: a(t) = 0.88 +/- 0.09(stat.)(-0.39)(+0.34) (syst.) - (2.81 +/- 0.42(stat.)(-0.62)(+1.13) (syst.) GeV(-2))t. This result is consistent with the expectations of pion-exchange models, in which the incoming proton fluctuates to a neutron-pion state, and the electron interacts with the pion.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.