Investigation of Microbunching instability in BERLinPro

BERLinPro is using the new energy recovery linac technology. As, maintaining the low emittance and energy spread is of major importance in an ERL, the deep understanding and control of effects which can degrade the emittance and energy spread such as space charge effects are of interest. The microbunching caused by the longitudinal space charge forces can lead to an increase in emittance and energy spread in the arcs of the loop. In this contribution, the impacts of the microbunching instability on the beam quality and its implication for BERLinPro are discusse

A Search for Selectrons and Squarks at HERA

Data from electron-proton collisions at a center-of-mass energy of 300 GeV are used for a search for selectrons and squarks within the framework of the minimal supersymmetric model. The decays of selectrons and squarks into the lightest supersymmetric particle lead to final states with an electron and hadrons accompanied by large missing energy and transverse momentum. No signal is found and new bounds on the existence of these particles are derived. At 95% confidence level the excluded region extends to 65 GeV for selectron and squark masses, and to 40 GeV for the mass of the lightest supersymmetric particle.Comment: 13 pages, latex, 6 Figure

A Measurement of the Proton Structure Function F ⁣2(x,Q2)F_{\!2}(x,Q^2)

A measurement of the proton structure function $F_{\!2}(x,Q^2)$ is reported for momentum transfer squared $Q^2$ between 4.5 $GeV^2$ and 1600 $GeV^2$ and for Bjorken $x$ between $1.8\cdot10^{-4}$ and 0.13 using data collected by the HERA experiment H1 in 1993. It is observed that $F_{\!2}$ increases significantly with decreasing $x$, confirming our previous measurement made with one tenth of the data available in this analysis. The $Q^2$ dependence is approximately logarithmic over the full kinematic range covered. The subsample of deep inelastic events with a large pseudo-rapidity gap in the hadronic energy flow close to the proton remnant is used to measure the "diffractive" contribution to $F_{\!2}$.Comment: 32 pages, ps, appended as compressed, uuencoded fil

Search for compositeness, leptoquarks and large extra dimensions in e q contact interactions at HERA

The reaction e+p --> e+X is studied with the H1 detector at Hera. The data cover momentum transfers Q^2 between 200 GeV^2 and 30,000 GeV^2 and correspond to an integrated luminosity of 35.6 pb^(-1). The differential cross section dsigma/dQ^2 is compared to the Standard Model expectation for neutral current scattering and analysed to search for bar(e)e bar(q)q contact interactions. No evidence for new phenomena is observed. The results are used to set limits on scales within models of electron--quark compositeness, quark form factors and the exchange of virtual heavy leptoquarks. A search for gravitational effects mediated through the exchange of virtual gravitons which propagate into large extra dimensions is presented.Comment: 21 pages, 6 figures, 2 tables, Update to reference

Search for odderon induced contributions to exclusive pi0 photoproduction at HERA

A search for contributions to the reaction ep-> e pi^0 N^* from photon-Odderon fusion in the photoproduction regime at HERA is reported, at an average photon-proton centre-of-mass energy = 215 GeV. The measurement proceeds via detection of the pi^0 decay photons, a leading neutron from the N^* decay, and the scattered electron. No pi^0 signal is observed and an upper limit on the cross section for the photon-Odderon fusion process of sigma(gamma p -> pi^0 N^*) < 49 nb at the 95% confidence level is derived, integrated over the experimentally accessible range of the squared four-momentum transfer at the nucleon vertex 0.02 < |t| < 0.3 Gev^2. This excludes a recent prediction from a calculation based on a non-perturbative QCD model of a photon-Odderon fusion cross section above 200 nb.Comment: 13 pages, 1 table and 4 figure

Diffractive photoproduction of ψ(2S) mesons at HERA

Results on diffractive photoproduction of ψ(2S) mesons are presented using data collected between 1996 and 2000 with the H1 detector at the HERA ep collider. The data correspond to an integrated luminosity of 77 pb-1. The energy dependence of the diffractive ψ(2S) cross section is found to be similar to or possibly somewhat steeper than that for J/ψ mesons. The dependences of the elastic and proton dissociative ψ(2S) photoproduction cross sections on the squared momentum transfer t at the proton vertex are measured. The t-dependence of the elastic channel, parametrised as ebt, yields bψ(2S) el = (4.31 ± 0.57 ± 0.46) GeV-2, compatible with that of the J/φ. For the proton dissociative channel the result bψ(2S) pd (0.59 ± 0.13 ± 0.12) GeV-2 is 2.3 standard deviations smaller than that measured for the J/ψ. With proper account of the individual wavefunctions theoretical predictions based on perturbative QCD are found to describe the measurements well. © 2002 Elsevier Science B.V. All rights reserved.0H1 Collaboration.info:eu-repo/semantics/publishe

Measurement of open beauty production at HERA

The first observation of open b production in ep collisions is reported. An event sample containing muons and jets has been selected which is enriched in semileptonic b quark decays. The visible cross section \sigma(ep -> b \bar{b}X -> \mu X') for Q^2 < 1 GeV^2, 0.1 < y < 0.8 is measured to be 0.176+-0.016(stat.)+0.026-0.017(syst.) nb for the muons to be detected in the range 35 deg 2.0 GeV in the laboratory frame. The expected visible cross section based on a NLO QCD calculation is 0.104+-0.017 nb. The cross sections for electroproduction with Q^2<1 GeV^2 and photoproduction are derived from the data and found to be \sigma(ep-> e b\bar{b}X) = 7.1+-0.6(stat.)+1.5-1.3(syst.) nb and \sigma(\gamma p-> b\bar{b} X) = 111+-10(stat.)+23-20(syst.) at an average \sim 180 GeV, respectively.Comment: 11 pages, 4 figures, 0 tables, submitted to Physics Letters

First measurement of the charged current cross-section at HERA

The cross section of the charged current process e − p → v e + hadrons is measured at HERA for transverse momenta of the hadron system larger than 25 GeV. The size of the cross section exhibits the W propagator

Photoproduction with a leading proton at HERA

The total cross section for the photoproduction process with a leading proton in the final state has been measured at γp centre-of-mass energies W of 91, 181 and 231GeV. The measured cross sections apply to the kinematic range with the transverse momentum of the scattered proton restricted to pT≤0.2GeV and 0.68≤z≤0.88, where z=Ep′/Ep is the scattered proton energy normalised to the beam energy. The cross section dσγp→Xp′(W,z)/dz is observed to be independent of W and z within the measurement errors and amounts to (8.05±0.06(stat)±0.89(syst)) μb on average. The data are well described by a Triple Regge model in which the process is mediated by a mixture of exchanges with an effective Regge trajectory of intercept αi(0)=0.33±0.04(stat)±0.04(syst). The total cross section for the interaction of the photon with this mixture (γαi→X) can be described by an effective trajectory of intercept αk(0)=0.99±0.01(stat)±0.05(syst). Predictions based on previous triple Regge analyses of pp→pX data assuming vertex factorisation are broadly consistent with the γp data. The measured cross sections are compared with deep inelastic scattering leading proton data in the same region of z and pT for photon virtuality Q2 > 2.5GeV2. The ratio of the cross section for leading proton production to the total cross section is found to rise with Q2. © 2001 Elsevier Science B.V.0H1 Collaboration.info:eu-repo/semantics/publishe

Measurement of dijet cross-sections in photoproduction and photon structure

The production of hard di-jet events in photoproduction at HERA is dominated by resolved photon processes in which a parton in the photon with momentum fraction x_gamma is scattered from a parton in the proton. These processes are sensitive to the quark and gluon content of the photon. The differential di-jet cross-section dsigma/dlog(x_gamma) is presented here, measured in tagged photoproduction at HERA using data taken with the H1 detector, corresponding to an integrated luminosity of 7.2 pb^(-1). Using a restricted data sample at high transverse jet energy, E_(T,jet)>6 GeV, the effective parton density f_gamma,eff(x_gamma) = [q(x_gamma) + bar(q)(x_gamma) +9/4g(x_gamma)] in the photon in leading order QCD is measured down to x_gamma=0.05 from which the gluon density in the photon is derived.Comment: 19 pages, 5 figures and 2 table