Double-tag events in two-photon collisions are studied using the L3 detector at LEP centre-of-mass energies from root(s)=189 GeV to 209 GeV. The cross sections of the e+e- -> e+e- hadrons and gamma*gamma* -> hadrons processes are measured as a function of the photon virtualities, Q1^2 and Q2^2, of the two-photon mass, W_gammagamma, and of the variable Y=ln(W_gammagamma^2/(Q1 Q2)), for an average photon virtuality <Q2> = 16 GeV2. The results are in agreement with next-to-leading order calculations for the process gamma*gamma* -> q qbar in the interval 2 <= Y <= 5. An excess is observed in the interval 5 < Y <= 7, corresponding to W_gammagamma greater than 40 GeV . This may be interpreted as a sign of resolved photon QCD processes or the onset of BFKL phenomena.
We have measured antiproton production cross sections as functions of centrality in collisions of 14.6 GeV/c per nucleon Si28 ions with targets of Al, Cu, and Pb. For all targets, the antiproton yields increase linearly with the number of projectile nucleons that have interacted, and show little target dependence. We discuss the implications of this result on the production and absorption of antiprotons within the nuclear medium.
Inclusive doubly differential cross sections d^2\sigma_{pA}/dx_Fdp_T^2 as a function of Feynman-x (x_F) and transverse momentum (p_T) for the production of K^0_s, Lambda^0 and anti-Lambda^0 in proton-nucleus interactions at 920 GeV are presented. The measurements were performed by HERA-B in the negative x_F range (-0.12<x_F<0.0) and for transverse momenta up to p_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^0 species. The atomic number dependence is parameterized as \sigma_{pA} = \sigma_{pN} \cdot A^\alpha where \sigma_{pN} is the proton-nucleon cross section. The measured values of \alpha are all near one. The results are compared with EPOS 1.67 and PYTHIA 6.3. EPOS reproduces the data to within \approx 20% except at very low transverse momentum.
The production of K_short mesons in pp collisions at a centre-of-mass energy of 0.9 TeV is studied with the LHCb detector at the Large Hadron Collider. The luminosity of the analysed sample is determined using a novel technique, involving measurements of the beam currents, sizes and positions, and is found to be 6.8 +/- 1.0 microbarn^-1. The differential prompt K_short production cross-section is measured as a function of the K_short transverse momentum and rapidity in the region 0 < pT < 1.6 GeV/c and 2.5 < y < 4.0. The data are found to be in reasonable agreement with previous measurements and generator expectations.
The ALICE experiment has measured low-mass dimuon production in pp collisions at $\sqrt{s} = 7$ TeV in the dimuon rapidity region 2.5<y<4. The observed dimuon mass spectrum is described as a superposition of resonance decays ($\eta$, $\rho$, $\omega$, $\eta^{'}$, $\phi$) into muons and semi-leptonic decays of charmed mesons. The measured production cross sections for $\omega$ and $\phi$ are $\sigma_\omega$ (1<$p_{\rm T}$<5 GeV/$c$,2.5<y<4) = 5.28 $\pm$ 0.54 (stat) $\pm$ 0.50 (syst) mb and $\sigma_\phi$(1<$p_{\rm T}$<5 GeV/$c$,2.5<y<4)=0.940 $\pm$ 0.084 (stat) $\pm$ 0.078 (syst) mb. The differential cross sections $d^2\sigma/dy dp_{\rm T}$ are extracted as a function of $p_{\rm T}$ for $\omega$ and $\phi$. The ratio between the $\rho$ and $\omega$ cross section is obtained. Results for the $\phi$ are compared with other measurements at the same energy and with predictions by models.
The inclusive single and double differential cross-sections for neutral and charged current processes with four-momentum transfer squared Q^2 between 150 and 30,000 GeV2 and with Bjorken x between 0.0032 and 0.65 are measured in e^+ p collisions. The data were taken with the H1 detector at HERA between 1994 and 1997, and they correspond to an integrated luminosity of 35.6 pb^-1. The Q^2 evolution of the parton densities of the proton is tested, yielding no significant deviation from the prediction of perturbative QCD. The proton structure function F_2(x,Q^2) is determined. An extraction of the u and d quark distributions at high x is presented. At high Q^2 electroweak effects of the heavy bosons Z0 and W are observed and found to be consistent with Standard Model expectation.
The inclusive e^-p single and double differential cross sections for neutral and charged current processes are measured with the H1 detector at HERA, in the range of four-momentum transfer squared Q^2 between 150 and 30000 GeV^2, and Bjorken x between 0.002 and 0.65. The data were taken in 1998 and 1999 with a centre-of-mass energy of 320 GeV and correspond to an integrated luminosity of 16.4 pb^(-1). The data are compared with recent measurements of the inclusive neutral and charged current e^+p cross sections. For Q^2>1000 GeV^2 clear evidence is observed for an asymmetry between e^+p and e^-p neutral current scattering and the generalised structure function xF_3 is extracted for the first time at HERA. A fit to the charged current data is used to extract a value for the W boson propagator mass. The data are found to be in good agreement with Standard Model predictions.
We have studied the processpp→γγ+X at\(\sqrt s= 63 GeV\) GeV in the central rapidity region. We report a positive signal at 96% C.L., a ratio γγ/e+e−=4.0±3.0 when the transverse momentum of each photon is above 2 GeV/c, and a cross-sectiondσ/dydMγγ=(5.5±2.7)×10−34 cm2/GeV when |y|<0.5,4<Mγγ<6 GeV.
This Letter describes a measurement of the muon cross section originating from b quark decay in the forward rapidity range 2.4 < y(mu) < 3.2 in pbarp collisions at sqrt(s) = 1.8 TeV. The data used in this analysis were collected by the D0 experiment at the Fermilab Tevatron. We find that NLO QCD calculations underestimate b quark production by a factor of four in the forward rapidity region. A cross section measurement using muon+jet data has been included in this version of the paper.
A precision measurement of the $Z$ boson production cross-section at $\sqrt{s} = 13$ TeV in the forward region is presented, using $pp$ collision data collected by the LHCb detector, corresponding to an integrated luminosity of 5.1 fb$^{-1}$. The production cross-section is measured using $Z\rightarrow\mu^+\mu^-$ events within the fiducial region defined as pseudorapidity $2.0<\eta<4.5$ and transverse momentum $p_{T}>20$ GeV/$c$ for both muons and dimuon invariant mass $60<M_{\mu\mu}<120$ GeV/$c^2$. The integrated cross-section is determined to be $\sigma (Z \rightarrow \mu^+ \mu^-)$ = 196.4 $\pm$ 0.2 $\pm$ 1.6 $\pm$ 3.9~pb, where the first uncertainty is statistical, the second is systematic, and the third is due to the luminosity determination. The measured results are in agreement with theoretical predictions within uncertainties.
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