We report the first measurement of the cross section for Z boson pair production at a hadron collider. This result is based on a data sample corresponding to 1.9 fb-1 of integrated luminosity from ppbar collisions at sqrt{s} = 1.96 TeV collected with the CDF II detector at the Fermilab Tevatron. In the llll channel, we observe three ZZ candidates with an expected background of 0.096^{+0.092}_{-0.063} events. In the llnunu channel, we use a leading-order calculation of the relative ZZ and WW event probabilities to discriminate between signal and background. In the combination of llll and llnunu channels, we observe an excess of events with a probability of $5.1\times 10^{-6}$ to be due to the expected background. This corresponds to a significance of 4.4 standard deviations. The measured cross section is sigma(ppbar -> ZZ) = 1.4^{+0.7}_{-0.6} (stat.+syst.) pb, consistent with the standard model expectation.
Measured cross section. Errors are combined statistics and systematics.
We report on measurements of the inclusive jet production cross section as a function of the jet transverse momentum in pp-bar collisions at sqrt{s} = 1.96 TeV}, using the k_T algorithm and a data sample corresponding to 1.0 fb^-1 collected with the Collider Detector at Fermilab in Run II. The measurements are carried out in five different jet rapidity regions with |yjet| < 2.1 and transverse momentum in the range 54 < \ptjet < 700 GeV/c. Next-to-leading order perturbative QCD predictions are in good agreement with the measured cross sections.
Measured inclusive jet differential cross section as a function of PT for the rapidity range -0.1 to 0.1 with the jet resolution parameter D = 0.7.
Measured inclusive jet differential cross section as a function of PT for the absoloute rapidity range 0.1 to 0.7 with the jet resolution parameter D = 0.7.
Measured inclusive jet differential cross section as a function of PT for the absolute rapidity range 0.7 to 1.1 with the jet resolution parameter D = 0.7.
This Letter describes the current most precise measurement of the $W$ boson pair production cross section and most sensitive test of anomalous $WW\gamma$ and $WWZ$ couplings in $p \bar p$ collisions at a center-of-mass energy of 1.96 TeV. The $WW$ candidates are reconstructed from decays containing two charged leptons and two neutrinos, where the charged leptons are either electrons or muons. Using data collected by the CDF II detector from 3.6 fb$^{-1}$ of integrated luminosity, a total of 654 candidate events are observed with an expected background contribution of $320 \pm 47$ events. The measured total cross section is $\sigma (p \bar p \to W^+ W^- + X) = 12.1 \pm 0.9 \textrm{(stat)} ^{+1.6}_{-1.4} \textrm{(syst)}$ pb, which is in good agreement with the standard model prediction. The same data sample is used to place constraints on anomalous $WW\gamma$ and $WWZ$ couplings.
Measured cross section for inclusive W+ W- production.
We present a measurement of the top quark pair production cross section in ppbar collisions at sqrt(s)=1.96 TeV using 318 pb^{-1} of data collected with the Collider Detector at Fermilab. We select ttbar decays into the final states e nu + jets and mu nu + jets, in which at least one b quark from the t-quark decays is identified using a secondary vertex-finding algorithm. Assuming a top quark mass of 178 GeV/c^2, we measure a cross section of 8.7 +-0.9 (stat) +1.1-0.9 (syst) pb. We also report the first observation of ttbar with significance greater than 5 sigma in the subsample in which both b quarks are identified, corresponding to a cross section of 10.1 +1.6-1.4(stat)+2.0-1.3 (syst) pb.
Measured cross section where at least one B quark from the TOP quark decays is identified.
Measured cross section where both B quarks from the TOP quark decays are identified.
In this Letter, we report the first measurement of the inelastic cross section for antideuteron-nucleus interactions at low particle momenta, covering a range of $0.3 \leq p < 4$ GeV/$c$. The measurement is carried out using p-Pb collisions at a center-of-mass energy per nucleon-nucleon pair of $\sqrt{s_{\rm{NN}}}$ = 5.02 TeV, recorded with the ALICE detector at the CERN LHC and utilizing the detector material as an absorber for antideuterons and antiprotons. The extracted raw primary antiparticle-to-particle ratios are compared to the results from detailed ALICE simulations based on the GEANT4 toolkit for the propagation of antiparticles through the detector material. The analysis of the raw primary (anti)proton spectra serves as a benchmark for this study, since their hadronic interaction cross sections are well constrained experimentally. The first measurement of the inelastic cross section for antideuteron-nucleus interactions averaged over the ALICE detector material with atomic mass numbers $\langle A \rangle$ = 17.4 and 31.8 is obtained. The measured inelastic cross section points to a possible excess with respect to the Glauber model parameterization used in GEANT4 in the lowest momentum interval of $0.3 \leq p < 0.47$ GeV/$c$ up to a factor 2.1. This result is relevant for the understanding of antimatter propagation and the contributions to antinuclei production from cosmic ray interactions within the interstellar medium. In addition, the momentum range covered by this measurement is of particular importance to evaluate signal predictions for indirect dark-matter searches.
Raw primary antiproton-to-proton ratio as a function of the momentum p_primary.
Raw primary antiproton-to-proton ratio from Geant4-based MC simulations as a function of the momentum p_primary.
Raw primary antideuteron-to-deuteron ratio as a function of the momentum p_primary.
We present a measurement of the inclusive jet cross section in p-pbar collisions at sqrt{s}=1.96 TeV based on data collected by the CDF II detector with an integrated luminosity of 1.13 fb^-1. The measurement was made using the cone-based Midpoint jet clustering algorithm in the rapidity region of |y|<2.1. The results are consistent with next-to-leading-order perturbative QCD predictions based on recent parton distribution functions (PDFs), and are expected to provide increased precision in PDFs at high parton momentum fraction x. The results are also compared to the recent inclusive jet cross section measurement using the k_T jet clustering algorithm, and we find that the ratio of the cross sections measured with the two algorithms is in agreement with theoretical expectations over a large range of jet transverse momentum and rapidity.
Measured inclusive jet cross section as a function of jet transverse momentum in the absolute rapidity region < 0.1. The bin-by-bin correction factors from parton to hadron-level are also tabulated.
Measured inclusive jet cross section as a function of jet transverse momentum in the absolute rapidity region 0.1 to 0.7. The bin-by-bin correction factors from parton to hadron-level are also tabulated.
Measured inclusive jet cross section as a function of jet transverse momentum in the absolute rapidity region 0.7 to 1.1. The bin-by-bin correction factors from parton to hadron-level are also tabulated.
The first measurement of dielectron ($\mathrm{e}^{+}\mathrm{e}^{-}$) production in central (0$-$10$\%$) Pb-Pb collisions at $\mathbf{\sqrt{{\textit{s}}_{\mathrm{NN}}}}$ = 2.76 TeV at the LHC is presented. The dielectron invariant-mass spectrum is compared to the expected contributions from hadron decays in the invariant-mass range $0 < m_{\mathrm{ee}}<3.5\ \mathrm{GeV}/\textit{c}^{2}$. The ratio of data and the cocktail of hadronic contributions without vacuum $\rho^{0}$ is measured in the invariant-mass range $0.15 < m_{\mathrm{ee}}<0.7\ \mathrm{GeV}/\textit{c}^{2}$, where an excess of dielectrons is observed in other experiments, and its value is $1.40 \pm 0.28\ (\mathrm{stat.}) \pm 0.08\ (\mathrm{syst.}) \pm 0.27\ (\mathrm{cocktail})$. The dielectron spectrum measured in the invariant mass range $0 < m_{\mathrm{ee}}<1\ \mathrm{GeV}/\textit{c}^{2}$ is consistent with the predictions from two theoretical model calculations that include thermal dielectron production from both partonic and hadronic phases with in-medium broadened $\rho^{0}$ meson. The fraction of direct virtual photons over inclusive virtual photons is extracted for dielectron pairs with invariant mass $0.1 < m_{\mathrm{ee}}<0.3\ \mathrm{GeV}/\textit{c}^{2}$, and in the transverse-momentum intervals $1<p_{\mathrm{T}, \mathrm{ee}}<2\ \mathrm{GeV}/\textit{c}$ and $2<p_{\mathrm{T}, \mathrm{ee}}<4\ \mathrm{GeV}/\textit{c}$. The measured fraction of virtual direct photons is consistent with the measurement of real direct photons by ALICE and with the expectations from previous dielectron measurements at RHIC within the experimental uncertainties.
Dielectron invariant-mass spectrum measured in central Pb-Pb collisions at $\sqrt{s_{NN}}$ = 2.76 TeV. The statistical and systematic uncertainties of the data are represented by vertical bars and boxes.
Data-to-cocktail ratio. Statistical uncertainties are represented by vertical bars and systematic uncertainties by boxes.
Dielectron invariant-mass spectrum divided by the hadronic cocktail without the contribution from the vacuum $\rho^{0}$. The statistical and systematic uncertainties of data are represented by vertical bars and boxes.
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.
Measurements of inclusive jet suppression in heavy ion collisions at the LHC provide direct sensitivity to the physics of jet quenching. In a sample of lead-lead collisions at $\sqrt{s_{NN}}$ = 2.76 TeV corresponding to an integrated luminosity of approximately 7 inverse microbarns, ATLAS has measured jets with a calorimeter over the pseudorapidity interval |$\eta$| < 2.1 and over the transverse momentum range 38 < pT < 210 GeV. Jets were reconstructed using the anti-$k_t$ algorithm with values for the distance parameter that determines the nominal jet radius of R = 0.2, 0.3, 0.4 and 0.5. The centrality dependence of the jet yield is characterized by the jet "central-to-peripheral ratio," $R_{cp}$. Jet production is found to be suppressed by approximately a factor of two in the 10% most central collisions relative to peripheral collisions. $R_{cp}$ varies smoothly with centrality as characterized by the number of participating nucleons. The observed suppression is only weakly dependent on jet radius and transverse momentum. These results provide the first direct measurement of inclusive jet suppression in heavy ion collisions and complement previous measurements of dijet transverse energy imbalance at the LHC.
Glauber model calculation of the mean numbers of Npart and its associated errors, the mean Ncoll ratios, and Rcoll with fractional errors as a function of the centrality bins.
The Rcp values as a function of jet PT for the four R values, 0.2, 0.3, 0.4 and 0.5 for the collision centrality in the range 0 - 10 %.
The Rcp values as a function of jet PT for the four R values, 0.2, 0.3, 0.4 and 0.5 for the collision centrality in the range 10 - 20 %.
We report the first observation of the associated production of a W boson and a Z boson. This result is based on 1.1 fb-1 of integrated luminosity from ppbar collisions at sqrt{s} = 1.96 TeV collected with the CDF II detector at the Fermilab Tevatron. We observe 16 WZ candidates passing our event selection with an expected background of 2.7 +/- 0.4 events. A fit to the missing transverse energy distribution indicates an excess of events compared to the background expectation corresponding to a significance equivalent to six standard deviations. The measured cross section is sigma(ppbar -> WZ) = 5.0^{+1.8}_{-1.6} pb, consistent with the standard model expectation.
Measured cross section.
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