arXiv subjects

M. Derrick et al

Publications and source records attributed to M. Derrick et al.

4 recordsLinked to original sources

arXiv1997

Search for Lepton Flavor Violation in ep Collisions at 300 GeV Center of Mass Energy

Using the ZEUS detector at the HERA electron-proton collider, we have searched for lepton flavor violation in ep collisions at a center-of-mass energy s^1/2 of 300 GeV. Events of the type e + p -> lepton + X with a final-state lepton (mu or tau) of high transverse momentum, were sought. No evidence was found for lepton flavor violation in the combined 1993 and 1994 data samples, for which the integrated luminosities were 0.84 pb^-1 for e- p collisions and 2.94 pb^-1 for e+ p collisions. Limits on coupling vs. mass are provided for leptoquarks and R-parity violating squarks. For flavor violating couplings of electromagnetic strength, we set 95% confidence level lower limits on leptoquark masses between 207 GeV and 272 GeV, depending on the leptoquark species and final-state lepton. For leptoquark masses larger than 300 GeV, limits on flavor-changing couplings are determined, many of which supersede prior limits from rare decay processes.

hep-ex↗

arXiv1997

Study of Photon Dissociation in Diffractive Photoproduction at HERA

Diffractive dissociation of quasi-real photons at a photon-proton centre of mass energy of W ~ 200 GeV is studied with the ZEUS detector at HERA. The process under consideration is gamma p -> X N, where X is the diffractively dissociated photon system of mass M_X and N is either a proton or a nucleonic system with mass M_N < 2GeV. The cross section for this process in the interval 3 < M_X < 24 GeV relative to the total photoproduction cross section was measured to be sigma^partial_D / sigma_tot = 6.2 +- 0.2(stat) +- 1.4(syst)%. After extrapolating this result to the mass interval of m_phi^2 < M_X^2 < 0.05 W^2 and correcting it for proton dissociation, the fraction of the total cross section attributed to single diffractive photon dissociation, gamma p -> X p, is found to be sigma_SD / sigma_tot = 13.3 +- 0.5(stat) +- 3.6(syst)%. The mass spectrum of the dissociated photon system in the interval 8 < M_X < 24 GeV can be described by the triple pomeron (PPP) diagram with an effective pomeron intercept of alpha_P(0) = 1.12 +- 0.04(stat) +- 0.08(syst). The cross section for photon dissociation in the range 3 < M_X < 8 GeV is significantly higher than that expected from the triple pomeron amplitude describing the region 8 < M_X < 24 GeV. Assuming that this discrepancy is due to a pomeron-pomeron-reggeon (PPR) term, its contribution to the diffractive cross section in the interval 3 < M_X < 24 GeV is estimated to be f_PPR = 26 +- 3(stat) +- 12(syst)%.

hep-ex↗

arXiv1996

Measurement of Elastic omega Photoproduction at HERA

The reaction $γp \rightarrow ωp$ $(ω\rightarrow π^+π^-π^0$ and $π^0\rightarrowγγ)$ has been studied in $ep$ interactions using the ZEUS detector at photon-proton centre-of-mass energies between $70$ and $90 GeV$ and $|t| < 0.6 GeV^2$, where $t$ is the squared four momentum transferred at the proton vertex.The elastic \ome photoproduction cross section has been measured to be $σ_{γp\rightarrow ωp} = 1.21\pm 0.12\pm 0.23 μb$. The differential cross section $dσ_{γp\rightarrow ωp} /d|t|$ has an exponential shape $e^{-b |t|}$ with a slope $b = 10.0\pm 1.2\pm 1.3 GeV^{-2}$. The angular distributions of the decay pions are consistent with s-channel helicity conservation. When compared to low energy data, the features of $ω$ photoproduction as measured at HERA energies are in agreement with those of a soft diffractive process. Previous measurements of the $ρ^0$ and $ϕ$ photoproduction cross sections at HERA show a similar behaviour.

hep-ex↗

arXiv1996

Observation of Events with an Energetic Forward Neutron in Deep Inelastic Scattering at HERA

In deep inelastic neutral current scattering of positrons and protons at the center of mass energy of 300 GeV, we observe, with the ZEUS detector, events with a high energy neutron produced at very small scattering angles with respect to the proton direction. The events constitute a fixed fraction of the deep inelastic, neutral current event sample independent of Bjorken $x$ and $Q^2$ in the range $ 3 \cdot 10^{-4} < \xbj < 6\cdot 10^{-3}$ and $10 < Q^2 <100$~GeV$^2$.

hep-ex↗