First measurements of the differential cross sections for the inclusive production of a photon in association with a heavy quark (c, b) jet are presented, covering photon transverse momenta 30-150 GeV, photon rapidities | y_gamma| < 1.0, jet rapidities |y_jet| < 0.8, and jet transverse momenta pT_jet > 15 GeV. The results are based on an integrated luminosity of 1 fb^-1 in ppbar collisions at sqrt(s)=1.96 TeV recorded with the D0 detector at the Fermilab Tevatron Collider. The results are compared with next-to-leading order perturbative QCD predictions.
Differential cross section for (GAMMA BJET X) production in the region YRAP(GAMMA)*YRAP(JET) > 0.
Differential cross section for (GAMMA BJET X) production in the region YRAP(GAMMA)*YRAP(JET) < 0.
Differential cross section for (GAMMA CJET X) production in the region YRAP(GAMMA)*YRAP(JET) > 0.
We present a measurement of the $\ttbar$ production cross section in $\ppbar$ collisions at $\sqrt{s}=1.96$ TeV using events containing a high transverse momentum electron or muon, three or more jets, and missing transverse energy. Events consistent with $\ttbar$ decay are found by identifying jets containing candidate heavy-flavor semileptonic decays to muons. The measurement uses a CDF Run II data sample corresponding to $2 \mathrm{fb^{-1}}$ of integrated luminosity. Based on 248 candidate events with three or more jets and an expected background of $79.5\pm5.3$ events, we measure a production cross section of $9.1\pm 1.6 \mathrm{pb}$.
Measured cross section assuming a top quark mass of 175 GeV. The second systematic error is the uncertainty on the luminosity.
A measurement of the $\bjet$ production cross section is presented for events containing a $Z$ boson produced in $p\bar{p}$ 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.
Ratio of integrated Z0 + bjet cross section to inclusive Z0 production.
Ratio of the Z0 + bjet to Z0 cross section as a function of the bjet ET.
Ratio of the Z0 + bjet to Z0 cross section as a function of the bjet pseudorapidity.
We present a search for new particles whose decays produce two jets (dijets) using proton-antiproton collision data corresponding to an integrated luminosity of 1.13 fb-1 collected with the CDF II detector. The measured dijet mass spectrum is found to be consistent with next-to-leading-order perturbative QCD predictions, and no significant evidence of new particles is found. We set upper limits at the 95% confidence level on cross sections times the branching fraction for the production of new particles decaying into dijets with both jets having a rapidity magnitude |y| < 1. These limits are used to determine the mass exclusions for the excited quark, axigluon, flavor-universal coloron, E6 diquark, color-octet technirho, W', and Z'.
The measured dijet mass spectrum for both jets having rapidity from -1 to 1.
In ultra-peripheral relativistic heavy-ion collisions, a photon from the electromagnetic field of one nucleus can fluctuate to a quark-antiquark pair and scatter from the other nucleus, emerging as a $\rho^0$. The $\rho^0$ production occurs in two well-separated (median impact parameters of 20 and 40 fermi for the cases considered here) nuclei, so the system forms a 2-source interferometer. At low transverse momenta, the two amplitudes interfere destructively, suppressing $\rho^0$ production. Since the $\rho^0$ decay before the production amplitudes from the two sources can overlap, the two-pion system can only be described with an entangled non-local wave function, and is thus an example of the Einstein-Podolsky-Rosen paradox. We observe this suppression in 200 GeV per nucleon-pair gold-gold collisions. The interference is $87% \pm 5% {\rm (stat.)}\pm 8%$ (syst.) of the expected level. This translates into a limit on decoherence due to wave function collapse or other factors, of 23% at the 90% confidence level.
Rapidity (left) and $M_{\pi\pi}$ (right) of the $\pi^{+}\pi^{-}$ distributions for the topology (exclusive $\rho^0$, top) and MB (Coulomb breakup, bottom) samples. The points with statistical error bars are the data, and the histograms are the simulations. The ’notch’ in the topology data around y = 0 is due to the explicit rapidity cut to remove cosmic-ray backgrounds.
Rapidity (left) and $M_{\pi\pi}$ (right) of the $\pi^{+}\pi^{-}$ distributions for the topology (exclusive $\rho^0$, top) and MB (Coulomb breakup, bottom) samples. The points with statistical error bars are the data, and the histograms are the simulations. The ’notch’ in the topology data around y = 0 is due to the explicit rapidity cut to remove cosmic-ray backgrounds.
Raw (uncorrected) ρ0 $t_{\perp}$-spectrum in the range 0.0 < |y| < 0.5 for the MB data. The points are data, with statistical errors. The dashed (filled) histogram is a simulation with an interference term (“Int”), while the solid histogram is a simulation without interference (“NoInt”). The handful of events histogrammed at the bottom of the plot are the wrong-sign ($\pi^{+}\pi^{+}+\pi^{-}\pi^{-}$) events, used to estimate the combinatorial background.
By analyzing the data sets of 17.3 pb$^{-1}$ taken at $\sqrt s= 3.773$ GeV and of 6.5 pb$^{-1}$ taken at $\sqrt s= 3.650$ GeV with the BES-II detector at the BEPC collider, we measure the observed cross sections for the exclusive light hadron final states of $K_S^0K^-\pi^+$, $K_S^0K^-\pi^+\pi^0$, $K_S^0K^-\pi^+\pi^+\pi^-$, $K_S^0K^-\pi^+\pi^+\pi^-\pi^0$, $K_S^0K^-\pi^+\pi^+\pi^+\pi^-\pi^-$ and $K_S^0K^-\pi^+\pi^0\pi^0$ produced in $e^+ e^-$ annihilation at the two energy points. We set the upper limits on the observed cross sections and the branching fractions for $\psi(3770)$ decay to these final states at 90% C.L..
Observed cross sections.
By analyzing the data sets of 17.3, 6.5 and 1.0 pb$^{-1}$ taken, respectively, at $\sqrt s= 3.773$, 3.650 and 3.6648 GeV with the BES-II detector at the BEPC collider, we measure the observed cross sections for $e^+e^-\to \pi^+\pi^-\pi^0\pi^0$, $K^+K^-\pi^0\pi^0$, $2(\pi^+\pi^-\pi^0)$, $K^+K^-\pi^+\pi^-\pi^0\pi^0$ and $3(\pi^+\pi^-)\pi^0\pi^0$ at the three energy points. Based on these cross sections we set the upper limits on the observed cross sections and the branching fractions for $\psi(3770)$ decay into these final states at 90% C.L..
Observed cross sections.
We study the beam-energy and system-size dependence of \phi meson production (using the hadronic decay mode \phi -- K+K-) by comparing the new results from Cu+Cu collisions and previously reported Au+Au collisions at \sqrt{s_NN} = 62.4 and 200 GeV measured in the STAR experiment at RHIC. Data presented are from mid-rapidity (|y|<0.5) for 0.4 < pT < 5 GeV/c. At a given beam energy, the transverse momentum distributions for \phi mesons are observed to be similar in yield and shape for Cu+Cu and Au+Au colliding systems with similar average numbers of participating nucleons. The \phi meson yields in nucleus-nucleus collisions, normalised by the average number of participating nucleons, are found to be enhanced relative to those from p+p collisions with a different trend compared to strange baryons. The enhancement for \phi mesons is observed to be higher at \sqrt{s_NN} = 200 GeV compared to 62.4 GeV. These observations for the produced \phi(s\bar{s}) mesons clearly suggest that, at these collision energies, the source of enhancement of strange hadrons is related to the formation of a dense partonic medium in high energy nucleus-nucleus collisions and cannot be alone due to canonical suppression of their production in smaller systems.
Midrapidity $(|y| < 0.5)$ transverse momentum spectra of $\phi$ mesons for various collision centrality classes for $Cu+Cu$ collisions at $\sqrt{s_{NN}}=62.4$ and 200 GeV. To study the system size dependence, comparison of $40-50\%$ $Au+Au$ spectra to $10-20\%$ $Cu+Cu$ spectra at 200 GeV, and $40-60\%$ $Au+Au$ spectra to $20-30\%$ $Cu+Cu$ spectra at 62.4 GeV are shown. These centralities for the two colliding systems have similar $\langle N_{\scriptsize{\mbox{part}}}\rangle$ values as outlined in Table 2. The errors represent the statistical and systematic errors added in quadrature. They are found to be within the symbol size. The spectra are fitted to a Levy function discussed in the text.
Midrapidity $(|y| < 0.5)$ transverse momentum spectra of $\phi$ mesons for various collision centrality classes for $Cu+Cu$ collisions at $\sqrt{s_{NN}}=62.4$ and 200 GeV. To study the system size dependence, comparison of $40-50\%$ $Au+Au$ spectra to $10-20\%$ $Cu+Cu$ spectra at 200 GeV, and $40-60\%$ $Au+Au$ spectra to $20-30\%$ $Cu+Cu$ spectra at 62.4 GeV are shown. These centralities for the two colliding systems have similar $\langle N_{\scriptsize{\mbox{part}}}\rangle$ values as outlined in Table 2. The errors represent the statistical and systematic errors added in quadrature. They are found to be within the symbol size. The spectra are fitted to a Levy function discussed in the text.
Upper panels. $N_{\scriptsize{\mbox{part}}}$ scaled ($R^{N_{\scriptsize{\mbox{part}}}}_{AA}$) nuclear modification factors as a function of $p_{T}$ of $\phi$ mesons for $0-10\%$ and $20-30\%$ $Cu+Cu$ and $Au+Au$ collisions at $\sqrt{s_{NN}}=200$ GeV. Lower panel. Same as above for $N_{\scriptsize{\mbox{bin}}}$ scaled ($R^{N_{\scriptsize{\mbox{bin}}}}_{AA}$) nuclear modification factor. The error bars represent the statistical and systematic errors added in quadrature. The shaded band in upper panel around 1 at $p_{T}=4.5-5.5$ GeV/$c$ in the right side reflects the uncertainty in $N_{\scriptsize{\mbox{part}}}$ and that on the lower panel for $N_{\scriptsize{\mbox{bin}}}$ calculation for central $Au+Au$ collisions. The respective uncertainties for central $Cu+Cu$ collisions are of similar order.
We report e+e- --> b anti-b cross section measurements by the BABAR experiment performed during an energy scan in the range of 10.54 to 11.20 GeV at the PEP-II e+e- collider. A total relative error of about 5% is reached in more than three hundred center-of-mass energy steps, separated by about 5 MeV. These measurements can be used to derive precise information on the parameters of the Y(10860) and Y(11020) resonances. In particular we show that their widths may be smaller than previously measured.
Measured values of R(b) from the detailed scan in SQRT(S),. where R(b) is the ratio between the number of observed E+ E- --> B BBAR(GAMMA) normalized to luminosity divided to the bare dimuon cross-section.
We report a measurement of the single top quark production cross section in 2.2 ~fb-1 of p-pbar collision data collected by the Collider Detector at Fermilab at sqrt{s}=1.96 TeV. Candidate events are classified as signal-like by three parallel analyses which use likelihood, matrix element, and neural network discriminants. These results are combined in order to improve the sensitivity. We observe a signal consistent with the standard model prediction, but inconsistent with the background-only model by 3.7 standard deviations with a median expected sensitivity of 4.9 standard deviations. We measure a cross section of 2.2 +0.7 -0.6(stat+sys) pb, extract the CKM matrix element value |V_{tb}|=0.88 +0.13 -0.12 (stat+sys) +- 0.07(theory), and set the limit |V_{tb}|>0.66 at the 95% C.L.
Combined measured single top quark cross section in the s and t channels. The error is combined statistics and systematics.
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