We performed a measurement of differential and integral jet shapes in proton-carbon, proton-tungsten and proton-aluminium collisions at 920 GeV/c proton momentum with the HERA-B detector at HERA for ...the jet transverse energies in the range 4 GeV<ET(jet)< 12 GeV. Jets were identified using the kT-clustering algorithm. The measurements were performed for the hardest jet in the event, directed towards the opposite side with respect to the trigger direction. Jets become narrower with increasing transverse energy and measured distributions agree well with predictions of the PYTHIA 6.2 model. We do not observe any significant difference in the jet shape for the carbon and the aluminium targets. Nevertheless, the transverse energy flow at small and large radii for the tungsten sample is slightly less than for light nuclei. This observation indicates some influence of the nuclear environment on the formation of jets in heavy nuclei, especially at lower transverse energies, 5 GeV<ET(jet)< 6 GeV.
Inclusive doubly differential cross sections d super(2) s sub(pA )/dx sub(F ) dp sub(T ) super(2) as a function of Feynman-x (x sub(F )) and transverse momentum (p sub(T )) for the production of K ...sub(S ) super(0) , and $\bar{\varLambda}$ in proton-nucleus interactions at 920 GeV are presented. The measurements were performed by HERA-B in the negative x sub(F )range (-0.12<x sub(F )<0.0) and for transverse momenta up to p sub(T )=1.6 GeV/c. Results for three target materials: carbon, titanium and tungsten are given. The ratios of production cross sections are presented and discussed. The Cronin effect is clearly observed for all three V super(0) species. The atomic number dependence is parameterized as s sub(pA )=s sub(pN ); A super(a )where s sub(pN )is the proton-nucleon cross section. The measured values of a are all near one. The results are compared with EPOS 1.67 and PYTHIA 6.3. EPOS reproduces the data to within -20% except at very low transverse momentum.
Inclusive doubly differential cross sections d2σpA/dxF dpT2 as a function of Feynman-x (xF) and transverse momentum (pT) for the production of KS0, Λ and \(\bar{\varLambda}\) in proton-nucleus ...interactions at 920 GeV are presented. The measurements were performed by HERA-B in the negative xF range (−0.12<xF<0.0) and for transverse momenta up to pT=1.6 GeV/c. Results for three target materials: carbon, titanium and tungsten are given. The ratios of production cross sections are presented and discussed. The Cronin effect is clearly observed for all three V0 species. The atomic number dependence is parameterized as σpA=σpN⋅Aα where σpN is the proton-nucleon cross section. The measured values of α are all near one. The results are compared with EPOS 1.67 and PYTHIA 6.3. EPOS reproduces the data to within ≈20% except at very low transverse momentum.
The inclusive production cross sections of the strange vector mesons K*0, K̄*0, and φ have been measured in interactions of 920 GeV protons with C, Ti, and W targets with the HERA-B detector at the ...HERA storage ring. Differential cross sections as a function of rapidity and transverse momentum have been measured in the central rapidity region and for transverse momenta up to pT = 3.5 GeV/c. The atomic number dependence is parametrised as σpA=σpN*Aα, where σpN is the proton–nucleon cross section. Within the phase space accessible, α(K*0)=0.86±0.03, α(K̄*0)=0.87±0.03, and α(φ)=0.96±0.02. The total proton–nucleon cross sections, determined by extrapolating the differential measurements to full phase space, are σpN→K*0=(5.06±0.54) mb, σpN→K̄*0=(4.02±0.45) mb, and σpN→φ=(1.17±0.11) mb. For all resonances the Cronin effect is observed; compared to the measurements of Cronin et al. for K± mesons, the measured values of α for φ mesons coincide with those of K+ mesons for all transverse momenta, while the enhancement for K*0/K̄*0 mesons is smaller.
Collective behaviour of final-state hadrons, and multiparton interactions are
studied in high-multiplicity $ep$ scattering at a centre-of-mass energy
$\sqrt{s}=318$ GeV with the ZEUS detector at ...HERA. Two- and four-particle
azimuthal correlations, as well as multiplicity, transverse momentum, and
pseudorapidity distributions for charged-particle multiplicities $N_{\textrm
ch} \geq 20$ are measured. The dependence of two-particle correlations on the
virtuality of the exchanged photon shows a clear transition from
photoproduction to neutral current deep inelastic scattering. For the
multiplicities studied, neither the measurements in photoproduction processes
nor those in neutral current deep inelastic scattering indicate significant
collective behaviour of the kind observed in high-multiplicity hadronic
collisions at RHIC and the LHC. Comparisons of PYTHIA predictions with the
measurements in photoproduction strongly indicate the presence of multiparton
interactions from hadronic fluctuations of the exchanged photon.
PDF
