The cross section for the reaction p¯N→μ+μ−X with muon pairs in the mass range 4<M<9 GeV/c2 and xF>0 was measured to be σ=0.104±0.005±0.008 nb/nucleon. The distributions dσdxF and M3dσdM were compared to the QCD-improved Drell-Yan model and to calculations including first-order QCD corrections, with use of deep-inelastic structure functions. Excellent agreement with the data was obtained if the calculations were multiplied by factors of 2.45 and 1.41, respectively.
We have studied muon pairs with an invariant mass between 4 and 9 GeV/c2 produced in p¯N and π−N interactions at an incident momentum of 125 GeV/c. The experiment was performed at Fermilab using a tungsten target and a special beam enriched to contain 18% antiprotons. We compare differential distributions as functions of the dimuon invariant mass, Feynman x, transverse momentum, and decay angles of the dimuon to the predictions of the Drell-Yan model including QCD corrections. Quark structure functions for the p¯ and π− are extracted. Comparisons of the antiproton data to the Drell-Yan model are significant because the cross sections depend principally on the valence-quark structure functions which are accurately determined by deep-inelastic scattering measurements. The measured absolute cross section (integrated over positive Feynman x and all transverse momenta) is 0.106±0.005±0.008 nb/nucleon for the p¯N interaction and 0.107±0.003±0.009 nb/nucleon for the π−N interaction, where the quoted errors are statistical and systematic, respectively. Normalization (K) factors that are required to bring the naive Drell-Yan and first-order QCD predictions into agreement with the measurements are extracted, and the uncertainties involved in such comparisons are examined.
We present results for the reactions νp→μ−π+p and νp→μ−K+p at energies above 5 GeV. The average cross section for the first reaction between 15 and 40 GeV is (0.80±0.12) × 10−38 cm2 and for events with Mπ+p<1.4 GeV is (0.55±0.08) × 10−38 cm2. The ratio of the cross section for the second reaction to that for the first is 0.017±0.010.
A search is presented for the pair production of light scalar top quarks in sqrt(s) = 7 TeV proton-proton collisions recorded with the ATLAS detector at the Large Hadron Collider. This analysis uses the full data sample collected during 2011 that corresponds to a total integrated luminosity of 4.7 fb-1. Light scalar top quarks are searched for in events with two opposite-sign leptons (e, mu), large missing transverse momentum and at least one jet in the final state. No excess over Standard Model expectations is found, and the results are interpreted under the assumption that the light scalar top decays to a b-quark in addition to an on-shell chargino whose decay occurs through a virtual W boson. If the chargino mass is 106 GeV, light scalar top quark masses up to 130 GeV are excluded for neutralino masses below 70 GeV.
The ATLAS detector at the Large Hadron Collider is used to search for high-mass resonances decaying to an electron-positron pair or a muon-antimuon pair. The search is sensitive to heavy neutral Z' gauge bosons, Randall-Sundrum gravitons, Z* bosons, techni-mesons, Kaluza-Klein Z/gamma bosons, and bosons predicted by Torsion models. Results are presented based on an analysis of pp collisions at a center-of-mass energy of 7 TeV corresponding to an integrated luminosity of 4.9/fb in the dielectron channel and 5.0/fb in the dimuon channel. A Z' boson with Standard Model-like couplings is excluded at 95 percent confidence level for masses below 2.22 TeV. A Randall-Sundrum graviton with coupling k/Mbar = 0.1 is excluded at 95 percent confidence level for masses below 2.16 TeV. Limits on the other models are also presented, including Technicolor and Minimal Z' Models.
This Letter reports a search for a heavy particle that decays to WW using events produced in pp collisions at sqrt(s) = 7 TeV. The data were recorded in 2011 by the ATLAS detector and correspond to an integrated luminosity of 4.7 fb-1. WW to l nu l' nu'(l, l' = e or mu) final states are considered and the distribution of the transverse mass of the WW candidates is found to be consistent with Standard Model expectations. Upper limits on the production cross section times branching ratio into W boson pairs are set for Randall-Sundrum and bulk Randall-Sundrum gravitons, which result in observed 95% CL lower limits on the masses of the two particles of 1.23 TeV and 0.84 TeV, respectively.
A search for supersymmetry (SUSY) in events with large missing transverse momentum, jets, and at least one hadronically decaying tau lepton, with zero or one additional light lepton (e/mu), has been performed using 4.7 fb-1 of proton-proton collision data at sqrt(s) = 7 TeV recorded with the ATLAS detector at the Large Hadron Collider. No excess above the Standard Model background expectation is observed and a 95% confidence level visible cross-section upper limit for new phenomena is set. In the framework of gauge-mediated SUSY-breaking models, lower limits on the mass scale Lambda are set at 54 TeV in the regions where the stau is the next-to-lightest SUSY particle (tan(beta) > 20). These limits provide the most stringent tests to date of GMSB models in a large part of the parameter space considered.
The ArgoNeuT collaboration presents measurements of inclusive muon neutrino and antineutrino charged current differential cross sections on argon in the Fermilab NuMI beam operating in the low energy antineutrino mode. The results are reported in terms of outgoing muon angle and momentum at a mean neutrino energy of 9.6 GeV (neutrinos) and 3.6 GeV (antineutrinos), in the range $0^\circ < \theta_\mu < 36^\circ$ and $0 < p_\mu < 25$ GeV/$c$, for both neutrinos and antineutrinos.
The NuTeV experiment at Fermilab has used a sign-selected neutrino beam to perform a search for the lepton number violating process $\bar{\nu}_mu e^- \to \mu^- \bar{\nu}_e$, and to measure the cross-section of the Standard Model inverse muon decay process $\nu_{\mu} e^- \to \mu^- \nu_e$. NuTeV measures the inverse muon decay asymptotic cross-section $\sigma/E$ to be 13.8 $\pm$ 1.2 $\pm$ 1.4 x $10^{-42} cm^2$/GeV. The experiment also observes no evidence for lepton number violation and places one of the most restrictive limits on the LNV/IMD cross-section ratio at $\sigma (\bar{\nu}_{\mu} e^- \to \mu^- \bar{\nu}_e) /\sigma (\nu_{\mu}e^- \to \mu^- \nu_e$) $\le$ 1.7% at 90% C.L. for V-A couplings and $\le$ 0.6% for scalar couplings.
We present data on inclusive negative-hadron production from charged-current antineutrino interactions in a 21% Ne-H mixture. Inclusive single-particle distributions are presented and are shown to be insensitive to the momentum transferred to the hadron vertex. Comparisons made to inclusive data from π−p and π−n interactions indicate a close similarity between the hadrons resulting from π-nucleon and ν¯-nucleus interactions. The general features of the ν¯-nucleus data are found to be similar to those seen in ν¯p interactions. This last observation implies that ν¯p and ν¯n interactions are similar and that nuclear effects are small.
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