The cross section for the elastic photoproduction of \r0\ mesons ($\gamma p \rightarrow \rho~0 p$) has been measured with the H1 detector at HERA for two average photon-proton centre-of-mass energies of 55 and 187GeV. TheFcenterline lower energy point was measured by observing directly the $\rho~{0}$ decay giving a cross section of $9.1\pm 0.9\,(\stat)\pm 2.5\,(\syst)\;\mu$b. The logarithmic slope parameter of the differential cross section, ${\rm d}\sigma/{\rm d}t$, is found to be $10.9 \pm 2.4\,(\stat) \pm 1.1\,(\syst)\;$GeV$~{-2}$. The \r0\ decay polar angular distribution is found to be consistent with s-channel helicity conservation. The higher energy cross section was determined from analysis of the lower part of the hadronic invariant mass spectrum of diffractive photoproduction and found to be $13.6\pm 0.8\,(\stat)\pm 2.4\,(\syst)\;\mu$b.
PI+ PI- cross section.
RHO0 cross section by selecting Mpipi to lie between 2Mpi and Mrho + 5width0.
No description provided.
We have studied single photon production in e + e − annihilation based on a data sample corresponding to an integrated luminosity of 164.1 pb −1 at s =58 GeV . The single photon yield is consistent with the prediction of the standard model with three light neutrino species. No anomalous signal has been observed. From this result left- and right-handed scalar electrons in the mass degenerate case are excluded at 90% CL below 44.4 GeV/ c 2 for the massless photino.
No description provided.
None
No description provided.
No description provided.
None
CROSS SECTION WAS ESTIMATED ASSUMING IT'S INDEPENDENCE OF THE ANTIPROTON M OMENTUM.
The production of neutral pions has been studied in the reactions 40 Ar + nat Ca , 86 Kr + nat Zr and 197 Au + 197 Au at 1 A GeV. For high energy pions emitted from the heavier systems a steeper than linear rise of the pion multiplicity with the centrality of the reaction is observed, indicating a pion production process other than binary nucleon-nucleon collisions. At low transverse momenta an enhancement of the π 0 -multiplicity increasing with the mass of the collision system is found. Systematic discrepancies between the experimental results and recent BUU, QMD and Cascade calculations are discussed.
No description provided.
RESULTS OF AN EXTRAPOLATION TO THE FULL SOLID ANGLE TAKING THE EXPERIMENTALTEMPERATURES INTO ACCOUNT.
No description provided.
The reaction γ+d → π++π−+p + n has been measured in a kinematically complete way at incident photon energies from 570 to 850 MeV in steps of 40 MeV. From detailed comparison of measured data with results of event simulations, it is concluded that three different mechanisms, the quasi-free, double-delta and phase space productions, contribute to the reaction. Each of the cross sections corresponding to these mechanisms is determined separately.
SYSTEMATIC ERRORS ARE NOT INCLUDED.
SYSTEMATIC ERRORS ARE NOT INCLUDED.
We report measurements of charm particle production asymmetries from the Fermilab photoproduction experiment E687. An asymmetry in the rate of production of charm versus anticharm particles is expected to arise primarily from fragmentation effects. We observe statistically significant asymmetries in the photoproduction of D + , D ∗+ and D 0 mesons and find small (but statistically weak) asymmetries in the production of the D s + meson and the Λ c + baryon. Our inclusive photoproduction asymmetries are compared to predictions from nonperturbative models of charm quark fragmentation.
Production asymmetry. E-gamma = 200 GeV is mean energy. Only reactions for charm particle production are present in the table. SIG(C=ANTI-CHARM) denotes the reaction with anti-charm production.
Antiparticle/particle production ratio. E-gamma = 200 GeV is mean energy. Only reactions for charm particle production are present in the table. SIG(C=ANTI-CHARM) denotes the reaction with anti-charm production.
Production asymmetry for particles produced in association with a D*(2010)+-. E-gamma = 200 GeV is mean energy. Only reactions for charm particle production are present in the table.
The interaction cross sections (σI) of ANa isotopes (A=20–23,25–32) on a carbon target have been measured at 950AMeV. The effective root-mean-square matter radii of these isotopes were deduced from σI by a Glauber-type calculation. By combining the isotope-shift data with the present data the radii of neutrons have been compared with those of protons for the first time along a chain of stable and unstable isotopes. A monotonic increase in the neutron skin thickness has been observed as the neutron number increases in Na isotopes.
ERRORS INCLUDE BOTH STATISTICAL AND SYSTEMATIC ERRORS.
The reaction p p → Λ Λ → p π + pπ − is studied in the experiment PS185 at the CERN Low Energy Antiproton Ring (LEAR). A precise measurement of the excitation function in the immediate threshold region below 6 MeV excess energy was achieved. The total cross section shows an unexpected behaviour around 1 MeV excess energy.
The values are calculated using M(p)=M(pbar) = 938.27231 Mev and M(lambda)=M(lambdabar) = 1115.63 MeV.
D(SIG)/D(OMEGA) as a function of COS(THETA(RF=CM)) for the nine intervals of the excess energy. Excess energy is SQRT(S)-M(lambda)-M(lambdabar).
We describe the sample of energetic single-photon events ( E γ > 15 GeV) collected by L3 in the 1991–1993 LEP runs. The event distributions agree with expectations from the Standard Model. The data are used to constrain the ZZ γ coupling and to set an upper limit of 4.1 × 10 −6 , μ B (90% C.L.) on the the magnetic moment of the τ neutrino.
The number of events expected from Standard Model is 8.2. Here UNSPEC is 'invisible' particle.
90 PCT C.L. limit on an anomalous magnetic moment for tau-neutrino from '1GAMMA + nothing' events. Magnetic moment in Bohr magnetons.
Forum