Measurement of dijet cross sections in <Emphasis Type="Italic">ep</Emphasis> interactions with a leading neutron at HERA

Measurements are reported of the production of dijet events with a leading neutron in ep interactions at HERA. Differential cross sections for photoproduction and deep inelastic scattering are presented as a function of several kinematic variables. Leading order QCD simulation programs are compared with the measurements. Models in which the real or virtual photon interacts with a parton of an exchanged pion are able to describe the data. Next-to-leading order perturbative QCD calculations based on pion exchange are found to be in good agreement with the measured cross sections. The fraction of leading neutron dijet events with respect to all dijet events is also determined. The dijet events with a leading neutron have a lower fraction of resolved photon processes than do the inclusive dijet data.Received: 31 January 2005, Revised: 7 March 2005, Published online: 28 April 2005     

A study of the forward production of charm particle pairs in p-Fe and π−-Fe interactions

The hadronic production of charm particle pairs produced in the forward direction has been investigated in study of μ⁺μ^? pairs with large missing energy (indicative of final-state neutrinos). These events result primarily from two semileptonic decays of charm-anticharm states. A comparison of the data with the prediction of the intrinsic charm diffractive model indicates that diffractive production cross sections are small (of the order of a few μb) in both 350 GeV proton and 278 GeV pion interactions.     

Pion exchange and the H1 forward spectrometer data

We point out that the component of the nucleon wave function is vital to the interpretation of the recent H1 data for leading baryon production. While the n/p ratio is equal to two with the component alone, the inclusion of the component brings this ratio very near to unity, as observed in the experiment. This result demonstrates that pion exchange can not only account for leading neutron but also for a large fraction of the leading proton production. Received: 4 December 1998 / Revised version: 1 February 1999 / Published online: 27 April 1999     

Ep≤63 GeV 质子入射铅、铋引起的中子产生双微分截面的模拟(英文)

加速器驱动次临界系统(ADS) 液态Pb-Bi 散裂靶的设计中,需要可靠的理论计算工具精确地预言几个GeV 能量范围的质子引起的散裂反应产生的各种粒子和核素。利用蒙特卡罗模拟软件包Geant4 计算研究了800 MeV至3 GeV 质子入射铅、铋材料引起的中子产生双微分截面。比较了Geant4 不同物理模型得到的模拟结果与现有的实验数据。其中,Geant4 的QGSP BERT和QGSP INCL ABLA 物理模型模拟结果很好地再现了实验数据。本工作证实了Geant4 蒙特卡罗模拟软件包适合用于能量高达3 GeV 的质子入射铅、铋引起的中子产生双微分截面的模拟计算。A detailed design of the liquid Pb-Bi spallation target of the Accelerator Driven Systems (ADS) requires powerful and reliable computational tools that can accurately predict particles and nuclides production by the proton induced spallation reactions in the energy range of a few GeV. In this paper, the neutron production double-differential cross sections for Pb and Bi target materials at incident proton kinetic energies between 800 MeV and 3 GeV are studied by calculations with Monte Carlo simulation package Geant4. The simulated results of Geant4 with several physics models are compared with available experimental data. The simulated results generated by QGSP BERT and QGSP INCL ABLA physics models of Geant4 well reproduce the available experimental data. The present results validated that Geant4 Monte Carlo simulation package is suitable for simulations of neutron production double-differential cross sections of proton induced reaction on Pb and Bi targets in the incident energy range up to 3 GeV.     

Measurement of Upsilon production for p + p and p + d interactions at 800 GeV/c

We report a high statistics measurement of Upsilon production with an 800 GeV/c proton beam on hydrogen and deuterium targets. The dominance of the gluon-gluon fusion process for Upsilon production at this energy implies that the cross section ratio, sigma(p+d-->Upsilon)/2sigma(p+p-->Upsilon), is sensitive to the gluon content in the neutron relative to that in the proton. Over the kinematic region 0相似文献   

Inclusive production of protons, anti-protons and neutrons in p+p collisions at 158 GeV/c beam momentum

New data on the production of protons, anti-protons and neutrons in p+p interactions are presented. The data come from a sample of 4.8 million inelastic events obtained with the NA49 detector at the CERN SPS at 158 GeV/c beam momentum. The charged baryons are identified by energy loss measurement in a large TPC tracking system. Neutrons are detected in a forward hadronic calorimeter. Inclusive invariant cross sections are obtained in intervals from 0 to 1.9 GeV/c (0 to 1.5 GeV/c) in transverse momentum and from ?0.05 to 0.95 (?0.05 to 0.4) in Feynman x for protons (anti-protons), respectively. p _T integrated neutron cross sections are given in the interval from 0.1 to 0.9 in Feynman x. The data are compared to a wide sample of existing results in the SPS and ISR energy ranges as well as to proton and neutron measurements from HERA and RHIC.     

Experimental results on π−p interactions in the cm energy range 1.50–1.74 GeV

Channel cross sections, elastic differential cross sections and single pion production mass spectra and angular distributions are presented for π^?p interactions, based on 139 000 events observed at six energies in the center of mass region 1.50–1.74 GeV.     

A total energy trigger at large angles used in a calorimetric study of 150 GeV and 300 GeV pion and proton interactions on hydrogen

Hard hadronic scattering was studied by selecting 150 GeV and 300 GeV π^?p and pp events with large energy in a 240 cell calorimeter covering 452 to 1352 in the c.m.s. polar angle and the full 2π azimuth. A downstream calorimeter measured the remaining energy flow at smaller angles. For large energy deposited in the segmented calorimeter the proton induced cross section drops below the pion induced cross section, as expected in a constituent scattering picture. However, neither a simple energy scaling of the cross section nor a dominant jet structure of the events is observed. No evidence was found for recently proposed higher-twist mechanisms leading to events     

A study of charge distributions in inelastic proton-proton collisions

Charge distributions for the secondaries from inelastic proton-proton collisions are studied by means of new data from an experiment at 12 and 24 GeV/c (2 m HBC at CERN). By comparison with π^±p data at 16 GeV/c, the inclusive charge distributions for the fragments of an incident proton and pion, respectively, are analysed. In addition, the cross sections for charge exchange between cms hemispheres are presented for the various charged-particle multiplicities. For events with no more than one neutral particle, charge and baryon exchange between cms hemispheres are compared to those between clusters. For the inelastic two-prong reactions, the two-dimensional distributions in longitudinal phase space are presented.     

Strange baryons production and projectile fragmentation in p−A collisions at the AGS

Experiment 910 (E910) has studied proton-nucleus collisions at 12.3 and 17.5 GeV incident energies using a variety of targets. Centrality selection is provided via “grey” track multiplicity which can be statistically related to ν, the number of scatterings of the proton in the target nucleus. Previously published semi-inclusive measurements of Ν production are discussed and preliminary measurements of “leading” Ν production in 17.5 GeV p-Au collisions are presented as a function of ν. The data indicate that the probability for the projectile to fragment into a strange baryon increases significantly with increasing ν for ν≤3; an extrapolation of the E910 data to nucleus-nucleus collisions can reproduce most of the enhancement in Ν production observed in Pb-Pb collisions at 40, 80 and 160 A. GeV. Preliminary measurements of Ξ^? production in 17.5 GeV p-Au collisions show a rapid increase in yield with increasing ν. The data are discussed in the context of the Van Hove fragmentation model. Preliminary proton and pion spectra are presented for 12.3 GeV p-Be collisions. The data show a rapid degradation of outgoing proton momenta with increasing N _grey while only modest changes are observed in the pion fragmentation spectra.     

Search for coherent charged pion production in neutrino-carbon interactions

We report the result from a search for charged-current coherent pion production induced by muon neutrinos with a mean energy of 1.3 GeV. The data are collected with a fully active scintillator detector in the K2K long-baseline neutrino oscillation experiment. No evidence for coherent pion production is observed, and an upper limit of is set on the cross section ratio of coherent pion production to the total charged-current interaction at 90% confidence level. This is the first experimental limit for coherent charged pion production in the energy region of a few GeV.     

Investigation of neutron emission in the interaction of relativistic protons and deuterons with lead targets

Measurements of neutron double-differential cross sections and yields in time-of-flight experiments with various lead targets and beams of protons and deuterons with an energy of about 2 GeV are discussed. Space and energy distribution of neutrons in an extended lead target is studied by threshold detectors in the proton energy range of 1–3.7 GeV. The average multiplicity of neutrons, neutron energy, and neutron multiplication in lead as functions of target dimension, type, and energy of the beam particle are analyzed.     

Cross-section measurements of single pion production in charged current neutrino and antineutrino interactions

All six exclusive single pion production processes from neutrino and antineutrino charged current interactions are studied in the energy range between 3 and 30 GeV. Using a quark model for single pion production from Rein and Sehgal we fitted the aximal mass parameter from total cross sections and compare the results with values from other experiments and the world-averages.     

Single transverse-spin asymmetry in very forward and very backward neutral particle production for polarized proton collisions at

In the 2001–2002 running period of the Relativistic Heavy Ion Collider (RHIC), transversely polarized protons were accelerated to 100 GeV for the first time, with collisions at . We present results from this run for single transverse-spin asymmetries for inclusive production of neutral pions, photons and neutrons of the energy region 20–100 GeV for forward and backward production for angles between 0.3 mrad and 2.2 mrad with respect to the polarized proton direction. An asymmetry of was observed for forward neutron production, where the errors are statistical and systematic, and the scale error is from the beam polarization uncertainty. The forward photon and π⁰, and backward neutron, photon, and π⁰ asymmetries were consistent with zero. The large neutron asymmetry indicates a strong interference between a spin–flip amplitude, such as one pion exchange which dominates lower energy neutron production, and remaining spin–non-flip amplitudes such as reggeon exchange.     

The total photon deuteron hadronic cross section in the energy range 0.265–4.215 GeV

The total cross section for photoproduction of hadrons on the deutron, σ_T^d, has been measured for photon energies in the range 0.265–40215 GeV. From this, using results for the photon total cross section, obtained previously with the same apparatus, the neutron total cross section has been determined in the resonance region. The resonant structure is found to be quite different from that for the proton. Thereafter the neutron cross section falls off steadily with energy, and the values obtained are consistently lower than those for the proton. Forward scattering amplitudes have been evaluated for the deuteron.     

Determination of the total c\bar c production cross section in 340 GeV/c \Sigma^--nucleus interactions

The production of charmed particles by 340 GeV/c momentum was studied in the hyperon beam experiment WA89 at the CERN-SPS, using the -spectrometer. In two data-taking periods in 1993 and 1994 an integrated luminosity of on copper and carbon targets was recorded. From the reconstruction of charm particle decays in 10 decay channels production cross sections for D, , and were determined in the region . Assuming an dependence of the cross section on the nucleon number, we calculate a total production cross section of per nucleon. The last term is an upper limit on the unknown contribution from charmed-strange baryon production. Received: 3 September 1999 / Published online: 3 February 2000     

The photoproduction of neutral pions from protons at forward angles in the resonance region

Differential cross sections for the photoproduction of pi-zero mesons from protons have been measured at angles between 10° and 70° c.m. in the energy range 0.85 GeV to 1.30 GeV. The values are compared with the fits to pion photoproduction data from three recent partial-wave analyses.     

Limits on D0-D0 mixing and bottom particle production cross section from hadronically produced same-sign dimuon events

The rates for same-sign and opposite-sign dimuon events with missing energy (indicative of final-state neutrinos) have been measured in 278 GeV π^?-Fe and 350 GeV proton-Fe collisions. The main source of opposite-sign events is two semi-leptonic decays of hadronically produced charm states. The same-sign events are consistent with background from pion and kaon decays. We obtain a limit of 0.044 (90% CL) on the fraction of D⁰ semileptonic decays that result in the wrong-sign muon and conclude that less than 9% (90% CL) of same-sign dimuon events produced in neutrino interactions can be attributed to D⁰-$\text{D}$⁰ mixing. The data imply δm < 6.5 × 10^?4 eV and $\text{δλ}\text{λ}\text{< 0.55}$ for the difference in mass and inverse lifetime of the CP eigenstates of the D⁰. Limits on diffractive bottom production cross sections in proton and pion collisions are also presented.     

Cross sections and asymmetries for the reaction from threshold to 1 GeV

Total cross sections, differential cross sections and asymmetries for the reaction from threshold to 1 GeV have been measured. The outgoing π⁰ was detected by a 4π neutral meson spectrometer. Our data are compared with the corresponding np→NNπ^± reactions. The isoscalar partial cross sections are extracted from the relevant total cross sections. They are significant throughout the whole energy range. Below the Δ-region, energy-integrated differential cross sections show a large anisotropy difference between the neutral and charged pion channels, respectively. A partial-wave fit shows that the initial T = 0 state is dominated by the ³D₁ wave in this energy region. Finally, predictions of phenomenological models give reasonable good account of the measured observables but cannot reproduce the sign of the asymmetries.