Total cross sections for the pp --> pp eta' reaction have been measured in the excess energy range from Q = 1.53 MeV to Q = 23.64 MeV. The experiment has been performed at the internal installation COSY-11 using a stochastically cooled proton beam of the COoler SYnchrotron COSY and a hydrogen cluster target. The determined energy dependence of the total cross section weakens the hypothesis of the S-wave repulsive interaction between the eta' meson and the proton. New data agree well with predictions based on the phase-space distribution modified by the proton-proton final-state-interaction (FSI) only.
Total cross sections w.r.t the excess energy in the CM system. Statistical errors only are given. As well as the 15 PCT overall systematic uncertainty there is an uncertainty on the energy of 0.44 MeV.
The eta-prime meson production in the reaction pp-->pp eta-prime has been studied at excess energies of Q = 26.5, 32.5 and 46.6 MeV using the internal beam facility COSY-11 at the cooler synchrotron COSY. The total cross sections as well as one angular distribution for the highest Q-value are presented. The excitation function of the near threshold data can be described by a pure s-wave phase space distribution with the inclusion of the proton-proton final state interaction and Coulomb effects. The obtained angular distribution of the eta-prime mesons is also consistent with pure s-wave production.
Angular distribution of the ETAPRIME in the CM system at an excess energy of 46.6 MeV. There is an additional systematic error of +24%/-35%.
We present results on vector-meson photoproduction via γp→Vp in the LBL-SLAC 82-in. hydrogen bubble chamber exposed to a linearly polarized photon beam at 2.8, 4.7, and 9.3 GeV. We find ρ0 production to have the characteristics of a diffractive process, i.e., a cross section decreasing slowly with energy and a differential cross section with slope of ∼ 6.5 GeV−2. Within errors the ρ0 production amplitudes are entirely due to natural-parity exchange. s-channel helicity is conserved to a high degree in the γ→ρ0 transition. We find evidence for small helicity-flip amplitudes for ππ pairs in the ρ0 region. Photoproduction of ω mesons is separated into its natural- (σN) and unnatural- (σU) parity-exchange contributions. The Eγ and t dependence and the spin density matrix of the unnatural-parity-exchange contribution are consistent with a one-pion-exchange process. The natural-parity-exchange part has characteristics similar to ρ0 production. At 9.3 GeV the ratio of σ(ρ0) to σN(ω) is ∼ 7. The slope of the φ differential cross section is ∼ 4.5 GeV−2, smaller than that of ρ0 and ω production. Natural-parity exchange is the main contributor to φ production. No evidence for higher-mass vector mesons is found in ππ, πππ, or KK¯ final states. The s and t dependences of Compton scattering as calculated from ρ, ω, and φ photoproduction using vector-meson dominance agree with experiment, but the predicted Compton cross section is too small by a factor of 2.
CALCULATED BY THE METHOD OF MOMENTS IN THE OMEGA MASS REGION. BACKGROUND NOT SUBTRACTED (ESTIMATED TO BE <5 PCT).
Di-jet event rates have been measured for deep-inelastic scattering in the kinematic domain ~5 < Q^2 < ~100 GeV^2 and ~10^(-4) < x_Bj < ~10^(-2), and for jet transverse momenta squared p_t^2 > ~Q^2. The analysis is based on data collected with the H1 detector at HERA in 1994 corresponding to an integrated luminosity of about 2 pb^(-1). Jets are defined using a cone algorithm in the photon-proton centre of mass system requiring jet transverse momenta of at least 5 GeV. The di-jet event rates are shown as a function of Q^2 and x_Bj. Leading order models of point-like interacting photons fail to describe the data. Models which add resolved interacting photons or which implement the colour dipole model give a good description of the di-jet event rate. This is also the case for next-to-leading order calculations including contributions from direct and resolved photons.
Di-jet rates for 'Symmetric' and 'Asymmetric' scenarios for jet energy cuts.
Di-jet rates for 'Sum' scenario for jet energy cuts.
Di-jet rates for 'Symmetric' and 'Asymmetric' scenarios for jet energy cuts.
The transition between photoproduction and deep-inelastic scattering is investigated in jet production at the HERA ep collider, using data collected by the H1 experiment. Measurements of the differential inclusive jet cross-sections dsigep/dEt* and dsigmep/deta*, where Et* and eta* are the transverse energy and the pseudorapidity of the jets in the virtual photon-proton centre of mass frame, are presented for 0 < Q2 < 49 GeV2 and 0.3 < y < 0.6. The interpretation of the results in terms of the structure of the virtual photon is discussed. The data are best described by QCD calculations which include a partonic structure of the virtual photon that evolves with Q2.
The inclusive virtual photon-proton jet cross section.
We present a study of events with Z bosons and hadronic jets produced in $\overline{p}p$ collisions at a center-of-mass energy of 1.8 TeV. The data consist of 6708 $Z \rightarrow e~+e~-$ decays from 106 pb$~{-1}$ of integrated luminosity collected using the CDF detector at the Tevatron Collider. The Z $+ \ge n$ jet cross sections and jet production properties have been measured for n = 1 to 4. The data compare well to predictions of leading order QCD matrix element calculations with added gluon radiation and simulated parton fragmentation.
Transverse energy distribution of the first highest ET jet in >= 1jet events.. Data read from plots.
Transverse energy distribution of the second highest ET jet in >= 2jet events.. Data read from plots.
Transverse energy distribution of the third highest ET jet in >= 3jet events.. Data read from plots.
The production of the Lambda and Sigma0 hyperons has been measured via the pp->pK+Lambda / Sigma0 reaction at the internal COSY-11 facility in the excess energy range between 14 and 60 MeV. The transition of the Lambda/Sigma0 cross section ratio from about 28 at Q<=13 MeV to the high energy level of about 2.5 is covered by the data showing a strong decrease of the ratio between 10 and 20 MeV excess energy. Effects from the final state interactions in the p-Sigma0 channel seem to be much smaller compared to the p-Lambda one. Estimates of the effective range parameters are given for the N-Lambda and the N-Sigma systems.
Cross section for LAMBDA production.. Statistical errors only.
Cross section for SIGMA0 production.. Statistical errors only.
Energy dependence of the LAMBDA/SIGMA0 ratio.
The ratio of the yields of antiprotons to protons in pp collisions has been measured by the ALICE experiment at $\sqrt{s} = 0.9$ and $7$ TeV during the initial running periods of the Large Hadron Collider(LHC). The measurement covers the transverse momentum interval $0.45 < p_{\rm{t}} < 1.05$ GeV/$c$ and rapidity $|y| < 0.5$. The ratio is measured to be $R_{|y| < 0.5} = 0.957 \pm 0.006 (stat.) \pm 0.014 (syst.)$ at $0.9$ TeV and $R_{|y| < 0.5} = 0.991 \pm 0.005 (stat.) \pm 0.014 (syst.)$ at $7$ TeV and it is independent of both rapidity and transverse momentum. The results are consistent with the conventional model of baryon-number transport and set stringent limits on any additional contributions to baryon-number transfer over very large rapidity intervals in pp collisions.
The central rapidity pbar/p ratio as a function of the rapidity interval Ybeam-Ybaryon and centre-of-mass energy. As well as the present ALICE measurements this table also lists the values from other experiments (see the text of the paper for details).
The first measurements of the invariant differential cross sections of inclusive $\pi^0$ and $\eta$ meson production at mid-rapidity in proton-proton collisions at $\sqrt{s}=0.9$ TeV and $\sqrt{s}=7$ TeV are reported. The $\pi^0$ measurement covers the ranges $0.4<p_T<7$ GeV/$c$ and $0.3<p_T<25$ GeV/$c$ for these two energies, respectively. The production of $\eta$ mesons was measured at $\sqrt{s}=7$ TeV in the range $0.4<p_T<15$ GeV/$c$. Next-to-Leading Order perturbative QCD calculations, which are consistent with the $\pi^0$ spectrum at $\sqrt{s}=0.9$ TeV, overestimate those of $\pi^0$ and $\eta$ mesons at $\sqrt{s}=7$ TeV, but agree with the measured $\eta/\pi^0$ ratio at $\sqrt{s}=7$ TeV.
The measured invariant differential section for inclusive PI0 production at a centre-of-mass energy of 7 TeV.
The measured invariant differential section for inclusive PI0 production at a centre-of-mass energy of 0.9 TeV.
The measured invariant differential section for inclusive ETA production at a centre-of-mass energy of 7 TeV.
Using the BES-II detector at the BEPC Collider, we measured the lowest order cross sections and the $R$ values ($R=\sigma^0_{e^+e^- \to {\rm hadrons}}/\sigma^0_{e^+e^- \to \mu^+\mu^-}$) for inclusive hadronic event production at the center-of-mass energies of 3.650 GeV, 3.6648 GeV and 3.773 GeV. The results lead to $\bar R_{uds}=2.224\pm 0.019\pm 0.089$ which is the average of these measured at 3.650 GeV and 3.6648 GeV, and $R=3.793\pm 0.037 \pm 0.190$ at $\sqrt{s}=3.773$ GeV. We determined the lowest order cross section for $\psi(3770)$ production to be $\sigma^{\rm B}_{\psi(3770)} = (9.575\pm 0.256 \pm 0.813)~{\rm nb}$ at 3.773 GeV, the branching fractions for $\psi(3770)$ decays to be $BF(\psi(3770) \to D^0\bar D^0)=(48.9 \pm 1.2 \pm 3.8)%$, $BF(\psi(3770) \to D^+ D^-)=(35.0 \pm 1.1 \pm 3.3)%$ and $BF(\psi(3770) \to D\bar{D})=(83.9 \pm 1.6 \pm 5.7)%$, which result in the total non-$D\bar D$ branching fraction of $\psi(3770)$ decay to be $BF(\psi(3770) \to {\rm non}-D\bar D)=(16.1 \pm 1.6 \pm 5.7)%$.
The Ruds value obtained by averaging the first two energy points.. The first error is the combined statistical and point-to-point systematic error and the DSYS error is the common systematic error.
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