Study of inclusive production of π± and protons in\bar p p interactions at 32 GeV/c

Results are presented on the inclusive production of π^± mesons and protons in \(\bar p\) p interactions at an incident antiproton momentum of 32 GeV/c in the MIRABELLE bubble chamber, based on a sample of 55,000 inelastic events. The spectra of π⁺(π^?) andp( \(\bar p\) ) are separated in the whole kinematically admitted region of phase space by a statistical method. The semi-inclusive and inclusive cross sections and the main average characteristics of π andp production are calculated. The invariant differential cross sections are studied as functions of the Fevnman scaling variablex, the rapidity and the transverse momentum. Thex distribution of π^± mesons in the proton fragmentation region does not show any significant contribution from quark exchange or annihilation processes. A possible contribution of hard quark scattering on mesons or baryons is observed for large transverse momenta.     

Inclusive cross section ratios in highp T proton-proton scattering at ISR energies

Ratios of inclusive cross sections σ(π⁺)/σ(π⁺+K ⁺+p) and \(\sigma (\pi ^ - )/\sigma (\pi ^ - + K^ - + \bar p)\) were measured for proton-proton interactions with a highp _T hadron in the final state around c.m.s. scattering angles θ?20°, 20° and 45° at two ISR energies \(\sqrt s = 31\) Gev and 62 GeV. Results are shown as functions of transverse and longitudinal momentum and are compared with parton model predictions. The different dependences of positive and negative pion fractions atp _T ?2–3 GeV/c on longitudinal momenta is similar to that observed in soft hadronic interactions at low values ofp _T where the leading proton effect (diquark fragmentation) is known to contribute. The quantitative agreement of the data with diquark model predictions indicates the presence of diquark fragmentation also in highp _T jets.     

Spin transfer to Λ and \bar \Lambda hyperons in deep inelastic scattering at HERMES

Preliminary results on the spin transfer to the Λ and $\bar \Lambda$ hyperons measured by the HERMES Collaboration are presented. Longitudinal spin transfer directed along the virtual-photon momentum in the Λ rest frame is found to be D _LL ^Λ = 0.19 ± 0.04_stat ± 0.02_syst, the transverse component being compatible with zero. For $\bar \Lambda$ both longitudinal and transverse components are compatible with zero within statistical errors of ±0.1.     

QCD scattering processes with hard gluon emission

2→3 QCD scattering processes are studied in kinematical regions which are free from infrared and mass singularities. Anomalously large hard gluon emission corrections are found to gluon-gluon annihilation \(gg \to q\bar q\) . It is pointed out that in a kinematical region where azimuthal angel correlations of large transverse momentum π⁰'s have been measured at ISR, the 3-jet production rate is large and the contribution of the subprocessgq→ggq is greater than the contributions from quark-quark scatteringqq→qqg.     

Studies in\bar p p annihilation

Evidence is presented that \(\bar p\) p annihilation proceeds via the formation of two jets, with average transverse momentum of the order of the nucleon mass. The implications of this behaviour is linked to the measured cross sections and multiplicities, and explanations for it have been sought in the underlying gluon and quark constituents of the \(\bar p\) p system. The confrontation of the suggested constituent mechanisms and experimental data lead to the concept that charm meson production may play a significant role in the \(\bar p\) p experiments at the highest available energies.     

Influence of cone algorithm parameters on efficiency and characteristics of reconstructed jets in p-p interactions at \sqrt s = 200 GeV

The influence of the cone algorithm parameters (E _cut, E _seed, R) on efficiency and characteristics of reconstructed jets in p-p collisions at the energy $\sqrt s $ = 200 GeV is studied. Event generation was carried out using the Monte Carlo code PYTHIA. The fraction of dijet event production as a function of transverse momentum of the hard process $\hat p_ \bot $ for different algorithm parameters is studied. The dependence of energy and parton direction reconstruction accuracy for dijet events and two leading jets in N-jet (N _Jet ≥ 2) events on the algorithm parameters is found. The results of jet modeling are compared with predictions obtained in the framework of z-scaling and experimental data obtained at RHIC. It is proved that the slope parameter of the scaling function is independent of the algorithm parameters in the transverse jet energy range E _T ^Jet = 25–60 GeV. It is shown that in the region E _T ^Jet < 25 GeV, strong dependence of invariant cross sections and the slope of the scaling function on the algorithm parameters is observed, and this dependence is enhanced with decreasing E _T ^Jet .     

Exploring the nuclear potential of antihyperons with antiprotons at {\overline{\rm\bf P}}{\rm\bf ANDA}

A schematic Monte Carlo simulation is used to examine the potential of the ${\overline{\rm P}} {\rm ANDA}$ experiment to extract information on the interaction of antihyperons in nuclei by exclusive hyperon-antihyperon pair production close to threshold in antiproton nucleus interactions. Due to energy and momentum conservation event-by-event transverse momentum correlations of the produced hyperon and antihyperons contain information on the difference between their potentials. It is demonstrated that for ${{\Lambda}{\overline{\Lambda}}}$ and ${{{\Xi}}{{\overline{\Xi}}}}$ pairs produced at antiproton momenta of 1.66 GeV/c and 2.9 GeV/c, respectively, the asymmetry is sufficiently sensitive even if the density as well as the momentum dependencies of the potentials are considered.     

Production of Ξ−-Hypernuclei via the (K −, K +) Reaction in a Quark-Meson Coupling Model

We study the production of Ξ^?-hypernuclei, ${^{12}{_{\Xi^-}}}$ Be and ${^{28}{_{\Xi^-}}}$ Mg, via the (K ^?, K ⁺) reaction within a covariant effective Lagrangian model, employing the bound Ξ^? and proton spinors calculated by the latest quark-meson coupling model. The present treatment yields the 0° differential cross sections for the formation of simple s-state Ξ^? particle-hole states peak at a beam momentum around 1.0 GeV/c with a value in excess of 1 μb.     

Double parton scattering contribution toW+jets

We investigate the double parton scattering production ofW ^±+jets in proton colliders. At high energies an observable signal is expected from double parton collisions when events with small transverse momentumW together with two jets balancing inp _T are selected. Double parton scattering is also a potentially serious background to several rare processes whose signal is aW ⁺+W ^?(→ev+jets) final state. A simplep _T ^W cut seems to be sufficient to separate the genuineW-pair events from the double scattering background.     

Hadronic colliders as probes of the proton spin structure

We perform a systematic analysis of different processes with high energy polarized proton beams: jets, direct photon, lepton pairs (Drell-Yan) andWZ production. Different sets of polarized partonic densities are used that fit EMC and SLAC polarized deep inelastic scattering data with variable amount of quark and gluon components of the proton spin. The case of the future Relativistic Heavy Ion Collider (RHIC) used as a polarized collider at a maximum energy of \(\sqrt s = 500\) GeV is analyzed in detail.     

The Qweak: Precision Measurement of the Proton’s Weak Charge by Parity Violating Experiment

The Qweak experiment at the Thomas Jefferson National Accelerator Facility measures the parity violating asymmetry in longitudinally polarized electron scattering from the proton at very low momentum transfer, Q ² = 0.026 (GeV/c)², at an incident electron beam energy of 1.16 GeV. With this measurement and the earlier results of the parity violating elastic scattering experiments, the Qweak experiment determines the weak charge of the proton, ${Q^p_{\rm W}}$ , with a 4% combined statistical and systematic error. This measurement will be used to determine the weak mixing angle, ${\sin^2\theta_{\rm W}}$ , that is predicted by the Standard Model from the Z ⁰ pole down to lower energies. Qweak will determine ${\sin^2\theta_{\rm W}}$ to a 0.3% relative precision, providing a competitive measurement of the running of this quantity. Moreover, if there is a significant deviation of the weak mixing angle from the Standard Model prediction, then the Qweak experiment will give a glimpse of possible extensions of the Standard Model.     

Kaon production in\bar pp interactions at c.m. energies from 200 to 900 GeV

A detailed analysis ofK _s ⁰ production in \(\bar pp\) |<2.5 the average transverse momentum is found to be 0.53±0.07 GeV/c at 200 GeV and 0.62±0.08 GeV/c at 900 GeV, which is an increase with respect to data at c.m. energies below 60 GeV. TheK _s ⁰ production cross sections in inelastic collisions are 29±4 mb at 200 GeV and 63±6 mb at 900 GeV, showing an increase compared to lower energy data. The central kaon density is found to increase as a logarithmic function of energy. At 900 GeV, where statistics are sufficient to allow one to draw conclusions, the average transverse momentum is higher in events with large charged multiplicity than in events with low multiplicity.     

Effective spectral function for quasielastic scattering on nuclei

Spectral functions that are used in neutrino event, generators to model quasielastic (QE) scattering from nuclear targets include Fermi gas, Local Thomas Fermi gas (LTF), Bodek-Ritchie Fermi gas with high momentum tail, and the Benhar-Fantoni two dimensional spectral function. We find that the \(\nu \) dependence of predictions of these spectral functions for the QE differential cross sections ( \({d^2\sigma }/{dQ^2 d\nu }\) ) are in disagreement with the prediction of the \(\psi '\) superscaling function which is extracted from fits to quasielastic electron scattering data on nuclear targets. It is known that spectral functions do not fully describe quasielastic scattering because they only model the initial state. Final state interactions distort the shape of the differential cross section at the peak and increase the cross section at the tails of the distribution. We show that the kinematic distributions predicted by the \(\psi '\) superscaling formalism can be well described with a modified effective spectral function (ESF). By construction, models using ESF in combination with the transverse enhancement contribution correctly predict electron QE scattering data.     

Highp T hadrons as leading particles in jets produced at the ISR

The density of charged particles near a single highp _T trigger particle in proton-proton collisions has been studied with the SFM detector at the CERN-ISR. It is shown that:—the secondaries cluster in a jet-like manner about the trigger particle; —the momentum distributions in this trigger jet can be unambiguously separated from the spectator background distributions;—the momentum distributions in this trigger jet can be unambiguously separated from the spectator background distributions;—the momentum component transverse to the jet direction is exponentially damped;—the width of the transverse distributions increases with the momentum component along the jet;—the fractional longitudinal momentum density depends strongly on the trigger transverse momentum and scales with \(x_T = {{2p_T } \mathord{\left/ {\vphantom {{2p_T } {\sqrt s }}} \right. \kern-0em} {\sqrt s }}\) . All these findings support the hard constituent scattering origin of highp _T hadrons.     

Two-jet production inp\bar p collisions

The production of two quark/gluon jets in \(p\bar p\) collisions is analyzed. We determine the cross section dependence on the transverse momentum, the rapidities, and on the two-jet invariant mass, and we evaluate the sensitivity of the results on the theoretical input assumptions and the experimental cuts. We extrapolate these results into the TeV energy region.     

Charge-charge correlations and the detection of weak vector bosons by hadronic jets in\bar pp andpp collisions at collider energies

We study the charge properties of quark jets within a chain decay model for quark jet fragmentation. Using the charge properties of quark jets, we define charge-charge two-jet cross sections and correlations. In \(\bar pp\) collisions these correlations show significant structure due to the weak vector bosonsW ^± andZ ⁰.     

Charge asymmetry in W + jets production at the LHC

The charge asymmetry in W ^±+ jets production at the LHC can serve to calibrate the presence of New Physics contributions. We study the ratio $\sigma(W^{+}+n\mbox{ jets})/\sigma(W^{-}+n\mbox{ jets})$ in the Standard Model for n≤4, paying particular attention to the uncertainty in the prediction from higher-order perturbative corrections and uncertainties in parton distribution functions. We show that these uncertainties are generally of order a few percent, making the experimental measurement of the charge asymmetry ratio a particularly useful diagnostic tool for New Physics contributions.     

Weak boson plus jet production in 2nd-order QCD

We calculate cross sections for the production ofW ⁺ andZ bosons in association with 1 and 2 jets at \(p\bar p\) collider energies. The expected rates for these processes in second-order QCD are presented as a function of the cuts on the transverse momenta of the jets and are compared with jet rates measured by UA1.     

Production of isolated nucleons with large transverse momentum in nucleon-nucleon collisions

The cross section of isolated nucleon production with large transverse momentum in nucleonnucleon collisions is calculated. This process is due to the hard scatteringqq→B q. A general selection rule for helicity amplitudes of the processes involving mesons and baryons is established. In particular it leads to the vanishing of the amplitudesq ₊ q ₊ \( \to B_{ + 3/2} \bar q - ; \gamma _ + \gamma _ + \to M_{ + 1} M_{ - 1} ,B_{ + 3/2} \bar B_{ - 3/2} \) . The quantitative estimates using the nucleon wave function from [5] show that the selection of the events with isolated proton production is possible in ISR data.     

Measurements of the ratio Rdp of the quasi-elastic nd \rightarrow p(nn) to the elastic np \rightarrow pn charge-exchange process yields at zero proton emission angle over the 0.55-2.0 GeV neutron beam energy region

New experimental results on the ratio R_dp of the quasi-elastic charge-exchange yield at the outgoing proton angle $ \theta_{{p,{\rm Lab}}}^{}$ = 0^° for the nd $ \rightarrow$ p(nn) reaction to the elastic np $ \rightarrow$ pn charge-exchange yield are presented. The measurements were carried out at the Nuclotron of the Veksler and Baldin Laboratory of High Energies of the JINR (Dubna) at the neutron beam kinetic energies of 0.55, 0.8, 1.0, 1.2, 1.4, 1.8 and 2.0GeV. The intense neutron beam with small momentum spread was produced by break-up of deuterons which were accelerated and extracted to the experimental hall. In both reactions mentioned above the outgoing protons with the momenta p _p approximately equal to the neutron beam momentum p _{n, beam} were detected in the directions close to the direction of incident neutrons, i.e. in the vicinity of the scattering angle $ \theta_{{p,{\rm Lab}}}^{}$ = 0^° . Measured in the same data taking runs, the angular distributions of the charge-exchange reaction products were corrected for the well-known instrumental effects and averaged in the vicinity of the incident neutron beam direction. These corrected angular distributions for every of nd $ \rightarrow$ p(nn) and np $ \rightarrow$ pn charge-exchange processes were proportional to the differential cross-sections of the corresponding reactions. The data were accumulated by the Delta-Sigma set-up magnetic spectrometer with two sets of multiwire proportional chambers located upstream and downstream of the momentum analyzing magnet. Inelastic processes were considerably reduced by the additional detectors surrounding the hydrogen and deuterium targets. The time-of-flight system was applied to identify the detected particles. The new R_dp data are compared with the existing ones, which were obtained below 1GeV, and with the calculations which were made using the phenomenological NN amplitude sets.