171 research outputs found
Standard Model Large-E_T Processes and Searches for New Physics at HERA
Existing and missing calculations of standard model processes producing large
transverse energy in electron-proton interactions at HERA are reviewed. The
adequacy of the existing standard model Monte Carlo programs for generic
searches of exotic processes is analyzed.Comment: 9 pages, LaTeX, uses iop style files, Contribution to the 3rd UK
Phenomenology Workshop on HERA Physics, September 1998, Durha
Chiral effective field theories of the strong interactions
Effective field theories of the strong interactions based on the approximate
chiral symmetry of QCD provide a model-independent approach to low-energy
hadron physics. We give a brief introduction to mesonic and baryonic chiral
perturbation theory and discuss a number of applications. We also consider the
effective field theory including vector and axial-vector mesons.Comment: 22 pages, 9 figures, proceedings of "Many-Body Structure of Strongly
Interacting Systems", Mainz, Germany, Feb. 23-25 201
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
Energy Flow in the Hadronic Final State of Diffractive and Non-Diffractive Deep-Inelastic Scattering at HERA
An investigation of the hadronic final state in diffractive and
non--diffractive deep--inelastic electron--proton scattering at HERA is
presented, where diffractive data are selected experimentally by demanding a
large gap in pseudo --rapidity around the proton remnant direction. The
transverse energy flow in the hadronic final state is evaluated using a set of
estimators which quantify topological properties. Using available Monte Carlo
QCD calculations, it is demonstrated that the final state in diffractive DIS
exhibits the features expected if the interaction is interpreted as the
scattering of an electron off a current quark with associated effects of
perturbative QCD. A model in which deep--inelastic diffraction is taken to be
the exchange of a pomeron with partonic structure is found to reproduce the
measurements well. Models for deep--inelastic scattering, in which a
sizeable diffractive contribution is present because of non--perturbative
effects in the production of the hadronic final state, reproduce the general
tendencies of the data but in all give a worse description.Comment: 22 pages, latex, 6 Figures appended as uuencoded fil
Measurement of the pi^+ meson polarizabilities via the gamma p->gamma pi^+ n reaction
An experiment on the radiative pi^+ meson photoproduction from the proton
(gamma p->gamma pi^+ n) was carried out at the Mainz Microtron MAMI in the
kinematic region 537 MeV <E_{gamma}<817 MeV,
140^o<theta_{gamma-gamma'}^cm<180^o. The pi^+ meson polarizabilities have been
determined from a comparison of the data with the predictions of two different
theoretical models, the first one being based on an effective pole model with
pseudoscalar coupling while the second one is based on diagrams describing both
resonant and nonresonant contributions. The validity of the models has been
verified by comparing the predictions with the present experimental data in the
kinematic region where the pion polarizability contribution is negligible
(s_1<5 mu^2) and where the difference between the predictions of the two models
does not exceed 3%. In the region, where the pion polarizability contribution
is substantial (5<s_1/mu^2<15, -12<t/mu^2<-2), the difference
(alpha-beta)_{pi^+} of the electric (alpha) and the magnetic (beta)
polarizabilities has been determined. As a result we find:
(alpha-beta)_{pi^+}=(11.6\pm 1.5_{stat}\pm 3.0_{syst}\pm 0.5_{mod})x10^-4fm^3.
This result is at variance with recent calculations in the framework of chiral
perturbation theory.Comment: 34 pages, 12 figures, final version to appear in Eur. Phys. J. A;
typos have been correcte
Jets and energy flow in photon-proton collisions at HERA
Properties of the hadronic final state in photoproduction events with large transverse energy are studied at the electron-proton collider HERA. Distributions of the transverse energy, jets and underlying event energy are compared to \overline{p}p data and QCD calculations. The comparisons show that the \gamma p events can be consistently described by QCD models including -- in addition to the primary hard scattering process -- interactions between the two beam remnants. The differential jet cross sections d\sigma/dE_T^{jet} and d\sigma/d\eta^{jet} are measured
Разработка интерактивной моделирующей системы технологии низкотемпературной сепарации газа
We present a study of J ψ meson production in collisions of 26.7 GeV electrons with 820 GeV protons, performed with the H1-detector at the HERA collider at DESY. The J ψ mesons are detected via their leptonic decays both to electrons and muons. Requiring exactly two particles in the detector, a cross section of σ(ep → J ψ X) = (8.8±2.0±2.2) nb is determined for 30 GeV ≤ W γp ≤ 180 GeV and Q 2 ≲ 4 GeV 2 . Using the flux of quasi-real photons with Q 2 ≲ 4 GeV 2 , a total production cross section of σ ( γp → J / ψX ) = (56±13±14) nb is derived at an average W γp =90 GeV. The distribution of the squared momentum transfer t from the proton to the J ψ can be fitted using an exponential exp(− b ∥ t ∥) below a ∥ t ∥ of 0.75 GeV 2 yielding a slope parameter of b = (4.7±1.9) GeV −2
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