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Register a new userMeasurement of central exclusive pi+pi- production in p-pbar collisions at sqrt(s) = 0.9 and 1.96 TeV at CDF
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We measure exclusive $pi^+pi^-$ production in proton-antiproton collisions at center-of-mass energies $sqrt{s}$ = 0.9 and 1.96 TeV in the Collider Detector at Fermilab. We select events with two oppositely charged particles, assumed to be pions, with pseudorapidity $|eta| < 1.3$ and with no other particles detected in $|eta| < 5.9$. We require the $pi^+pi^-$ system to have rapidity $|y|<$ 1.0. The production mechanism of these events is expected to be dominated by double pomeron exchange, which constrains the quantum numbers of the central state. The data are potentially valuable for isoscalar meson spectroscopy and for understanding the pomeron in a region of transition between nonperturbative and perturbative quantum chromodynamics. The data extend up to dipion mass $M(pi^+pi^-)$ = 5000 MeV/$c^2$ and show resonance structures attributed to $f_0$ and $f_2(1270)$ mesons. From the $pi^+pi^-$ and $K^+K^-$ spectra, we place upper limits on exclusive $chi_{c0}(3415)$ production.
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We have observed exclusive gammagamma production in proton-antiproton collisions at sqrt{s}=1.96 TeV, using data from 1.11 pm 0.07 fb^{-1} integrated luminosity taken by the Run II Collider Detector at Fermilab. We selected events with two electromagnetic showers, each with transverse energy E_T > 2.5 GeV and pseudorapidity |eta| < 1.0, with no other particles detected in -7.4 < eta < +7.4. The two showers have similar E_T and azimuthal angle separation Deltaphi sim pi; 34 events have two charged particle tracks, consistent with the QED process p bar{p} to p + e^+e^- + bar{p} by two-photon exchange, while 43 events have no charged tracks. The number of these events that are exclusive pi^0pi^0 is consistent with zero and is < 15 at 95% C.L. The cross section for pbar{p} to p+gammagamma+bar{p} with |eta(gamma)| < 1.0 and E_T(gamma) > 2.5$ GeV is 2.48^{+0.40}_{-0.35}(stat)^{+0.40}_{-0.51}(syst) pb.
We describe a measurement of the ratio of the cross sections times branching fractions of the $B_c^+$ meson in the decay mode $B_c^+ rightarrow J/psi mu u$ to the $B^+$ meson in the decay mode $B^+ rightarrow J/psi K^+$ in proton-antiproton collisions at center-of-mass energy $sqrt{s}=1.96$ TeV. The measurement is based on the complete CDF Run II data set, which comes from an integrated luminosity of $8.7,{rm fb}^{-1}$. The ratio of the production cross sections times branching fractions for $B_c^+$ and $B_c^+$ mesons with momentum transverse to the beam greater than $6~textrm{GeV}/c$ and rapidity magnitude smaller than 0.6 is $0.211pm 0.012~mbox{(stat)}^{+0.021}_{-0.020}~mbox{(syst)}$. Using the known $B^+ rightarrow J/psi K^+$ branching fraction, the known $B^+$ production cross section, and a selection of the predicted $B_c^+ rightarrow J/psi mu u$ branching fractions, the range for the total $B_c^+$ production cross section is estimated.
We present a measurement of the inclusive jet cross section using the Run II cone algorithm and data collected by the D0 experiment in p pbar collisions at a center-of-mass energy sqrt(s)=1.96 TeV, corresponding to an integrated luminosity of 0.70 fb^(-1). The jet energy calibration and the method used to extract the inclusive jet cross section are described. We discuss the main uncertainties, which are dominated by the jet energy scale uncertainty. The results cover jet transverse momenta from 50 GeV to 600 GeV with jet rapidities in the range -2.4 to 2.4 and are compared to predictions using recent proton parton distribution functions. Studies of correlations between systematic uncertainties in transverse momentum and rapidity are presented.
We report on a measurement of the $D^{+}$-meson production cross section as a function of transverse momentum ($p_T$) in proton-antiproton ($pbar{p}$) collisions at 1.96 TeV center-of-mass energy, using the full data set collected by the Collider Detector at Fermilab in Tevatron Run II and corresponding to 10 fb$^{-1}$ of integrated luminosity. We use $D^{+} to K^-pi^+pi^+$ decays fully reconstructed in the central rapidity region $|y|<1$ with transverse momentum down to 1.5 GeV/$c$, a range previously unexplored in $pbar{p}$ collisions. Inelastic $pbar{p}$-scattering events are selected online using minimally-biasing requirements followed by an optimized offline selection. The $K^-pi^+pi^+$ mass distribution is used to identify the $D^+$ signal, and the $D^+$ transverse impact-parameter distribution is used to separate prompt production, occurring directly in the hard scattering process, from secondary production from $b$-hadron decays. We obtain a prompt $D^+$ signal of 2950 candidates corresponding to a total cross section $sigma(D^+, 1.5 < p_T < 14.5~mbox{GeV/}c, |y|<1) = 71.9 pm 6.8 (mbox{stat}) pm 9.3 (mbox{syst})~mu$b. While the measured cross sections are consistent with theoretical estimates in each $p_T$ bin, the shape of the observed $p_T$ spectrum is softer than the expectation from quantum chromodynamics. The results are unique in $pbar{p}$ collisions and can improve the shape and uncertainties of future predictions.
A measurement of the $bjet$ production cross section is presented for events containing a $Z$ boson produced in $pbar{p}$ collisions at $sqrt{s}=1.96$ TeV, using data corresponding to an integrated luminosity of 2 fb$^{-1}$ collected by the CDF II detector at the Tevatron. $Z$ bosons are selected in the electron and muon decay modes. Jets are considered with transverse energy $E_T>20$ GeV and pseudorapidity $|eta|<1.5$ and are identified as $bjets$ using a secondary vertex algorithm. The ratio of the integrated $Z+bjet$ cross section to the inclusive $Z$ production cross section is measured to be $3.32 pm 0.53 {rm (stat.)} pm 0.42 {rm (syst.)}times 10^{-3}$. This ratio is also measured differentially in jet $E_T$, jet $eta$, $Z$-boson transverse momentum, number of jets, and number of $bjets$. The predictions from leading order Monte Carlo generators and next-to-leading-order QCD calculations are found to be consistent with the measurements within experimental and theoretical uncertainties.
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