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Dijet invariant mass distribution in top quark hadronic decay with QCD corrections
The dijet invariant mass distributions from the hadronic decay of unpolarized top quark (t{yields}bW{sup +} followed by W{sup +}{yields}ud) are calculated, including the next-to-leading order QCD radiative corrections. We treat the top decay in the complex mass scheme due to the existence of the intermediate state W boson. Our analytical expressions are also available in different dimensional regularization schemes and {gamma}{sub 5} strategies. Finally, in order to construct the jets, we use different jet algorithms to compare their influences on our results. The obtained dijet mass distributions from the top quark decay are useful to distinguish these dijets from those produced via other sources and to clarify the issue about the recent CDF Collaboration's Wjj anomaly.
LHC bounds on interactions of dark matter
We derive limits on the interactions of dark matter with quarks from ATLAS null searches for jets+missing energy based on {approx}1 fb{sup -1} of integrated luminosity, using a model-insensitive effective theory framework. We find that the new limits from the LHC significantly extend limits previously derived from CDF data at the Tevatron. Translated into the parameter space of direct searches, these limits are particularly effective for {approx} GeV mass weakly interacting massive particles. Our limits indicate tension with isospin-violating models satisfying minimal flavor violation which attempt to reconcile the purported CoGeNT excess with Xenon-100, indicating that either a light mediator or nontrivial flavor structure for the dark sector is necessary for a viable reconciliation of CoGeNT with Xenon.
Randall-Sundrum corrections to the width difference and CP-violating phase in B{sub s}{sup 0}-meson decays
We study the impact of the Randall-Sundrum setup on the width difference {Delta}{Gamma}{sub s} and the CP-violating phase {phi}{sub s} in the B{sub s}{sup 0}-B{sub s}{sup 0} system. Our calculations are performed in the general framework of an effective theory, based on operator product expansion. The results can thus be used for many new-physics models. We find that the correction to the magnitude of the decay amplitude {Gamma}{sub 12}{sup s} is below 4% for a realistic choice of input parameters. The main modification in the {Delta}{Gamma}{sub s}/{beta}{sub s}-plane is caused by a new CP-violating phase in the mixing amplitude, which allows for a better agreement with the experimental results of the CDF and D0 Collaborations from B{sub s}{sup 0}{yields}J/{psi}{phi} decays. The best-fit value of the CP asymmetry S{sub {psi}{phi}} can be reproduced, while simultaneously the theoretical prediction for the semileptonic CP asymmetry A{sub SL}{sup s} can enter the 1{sigma} range.
Signals of C P violation beyond the MSSM in Higgs and flavor physics
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Search for high-mass resonances decaying into Z Z in p p ¯ collisions at s = 1.96 TeV
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Study of substructure of high transverse momentum jets produced in proton-antiproton collisions at √s=1.96 TeV
A study of the substructure of jets with transverse momentum greater than 400 GeV/c produced in proton-antiproton collisions at a center-of-mass energy of 1.96 TeV at the Fermilab Tevatron Collider and recorded by the CDF II detector is presented. The distributions of the jet mass, angularity, and planar flow are measured for the first time in a sample with an integrated luminosity of 5.95 fb⁻¹. The observed substructure for high mass jets is consistent with predictions from perturbative quantum chromodynamics.
Production of Λ 0 , Λ̄ 0 , Ξ ± , and Ω ± hyperons in pp̄ collisions at √s=1.96 TeV
We report a set of measurements of inclusive invariant p T differential cross sections of Λ 0 , Λ̄ 0 , Ξ ± , and Ω ± hyperons reconstructed in the central region with pseudorapidity |η|<1 and p T up to 10 GeV/c. Events are collected with a minimum-bias trigger in pp̄ collisions at a center-of-mass energy of 1.96 TeV using the CDF II detector at the Tevatron Collider. As p T increases, the slopes of the differential cross sections of the three particles are similar, which could indicate a universality of the particle production in p T . The invariant differential cross sections are also presented for different charged-particle multiplicity intervals.
Search for a heavy vector boson decaying to two gluons in pp̄ collisions at √s=1.96 TeV
We present a search for a new heavy vector boson Z' that decays to gluons. Decays to on-shell gluons are suppressed, leading to a dominant decay mode of Z'→g*g. We study the case where the off-shell gluon g* converts to a pair of top quarks, leading to a final state of tt¯g. In a sample of events with exactly one charged lepton, large missing transverse momentum and at least five jets, corresponding to an integrated luminosity of 8.7 fb⁻¹ collected by the CDF II detector, we find the data to be consistent with the standard model. We set upper limits on the production cross section times branching ratio of this chromophilic Z' at 95% confidence level from 300 to 40 fb for Z' masses ranging from 400 to 1000 GeV/c², respectively.
Measurement of the B -c meson lifetime in the decay B -c →J/ψπ⁻
The lifetime of the B -c meson is measured using 272 exclusive B -c →J/ψ(→μ⁺μ⁻)π⁻ decays reconstructed in data from proton-antiproton collisions corresponding to an integrated luminosity of 6.7 fb⁻¹ recorded by the CDF II detector at the Fermilab Tevatron. The lifetime of the B -c meson is measured to be τ (B -c )=0.452±0.048(stat)±0.027(syst) ps. This is the first measurement of the B -c meson lifetime in a fully reconstructed hadronic channel, and it agrees with previous results and has comparable precision.
Search for the production of ZW and ZZ boson pairs decaying into charged leptons and jets in proton-antiproton collisions at sqrt[s]=1.96 TeV
We present a measurement of the production cross section for ZW and ZZ boson pairs in final states with a pair of charged leptons, from the decay of a Z boson, and at least two jets, from the decay of a W or Z boson, using the full sample of proton-antiproton collisions recorded with the CDF II detector at the Tevatron, corresponding to 8.9 fb^(-1) of integrated luminosity. We increase the sensitivity to vector boson decays into pairs of quarks using a neural network discriminant that exploits the differences between the spatial spread of energy depositions and charged-particle momenta contained within the jet of particles originating from quarks and gluons. Additionally, we employ new jet energy corrections to Monte Carlo simulations that account for differences in the observed energy scales for quark and gluon jets. The number of signal events is extracted through a simultaneous fit to the dijet mass spectrum in three classes of events: events likely to contain jets with a heavy-quark decay, events likely to contain jets originating from light quarks, and events that fail these identification criteria. We determine the production cross section to be 2.5 +2.0 -1.0 pb (< 6.1 pb at the 95% confidence level), consistent with the standard model prediction of 5.1 pb.
Search for a dijet resonance in events with jets and missing transverse energy in pp[over ¯] collisions at sqrt[s]=1.96 TeV
We report on a search for a dijet resonance in events with only two or three jets and large imbalance in the total event transverse momentum. This search is sensitive to the possible production of a new particle in association with a W or Z boson, where the boson decays leptonically with one or more neutrinos in the final state. We use the full data set collected by the CDF II detector at the Tevatron collider at a proton-antiproton center-of-mass energy of 1.96 TeV. These data correspond to an integrated luminosity of 9.1 fb^{-1}. We study the invariant mass distribution of the two jets with highest transverse energy. We find good agreement between data and standard model background expectations and measure the combined cross section for WW, WZ, and ZZ production to be 13.8^{+3.0}_{-2.7} pb. No significant anomalies are observed in the mass spectrum and 95% credibility level upper limits are set on the production rates of a potential new particle in association with a W or Z boson.
Measurement of the production and differential cross sections of W⁺W⁻ bosons in association with jets in p p ¯ collisions at s = 1.96 TeV
We present a measurement of the W-boson-pair production cross section in pp¯ collisions at 1.96 TeV center-of-mass energy and the first measurement of the differential cross section as a function of jet multiplicity and leading-jet energy. The W⁺W⁻ cross section is measured in the final state comprising two charged leptons and neutrinos, where either charged lepton can be an electron or a muon. Using data collected by the CDF experiment corresponding to 9.7 fb⁻¹ of integrated luminosity, a total of 3027 collision events consistent with W⁺W⁻ production are observed with an estimated background contribution of 1790 ± 190 events. The measured total cross section is σ(pp¯→ W⁺W⁻) = 14.0 ± 0.6(stat) ⁺1.2 ⁻1.0 (syst) ± 0.8(lumi) pb, consistent with the standard model prediction.
Measurement of the $B_c^{\pm}$ production cross section in $p\bar{p}$ collisions at $\sqrt{s}=1.96$ TeV
Here, 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 + → J/ψμ + ν to the B + meson in the decay mode B + → J/ψK + in proton-antiproton collisions at center-of-mass energy √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 fb -1 . The ratio of the production cross sections times branching fractions for B c + and B + mesons with momentum transverse to the beam greater than 6 GeV/c and rapidity magnitude smaller than 0.6 is 0.211 ± 0.012(stat) -0.020 +0.021 (syst). Using the known B + → J/ψK + branching fraction, the known B + production cross section, and a selection of the predicted B c + → J/ψμ + ν branching fractions, the range for the total B c + production cross section is estimated.
Measurement of the forward-backward asymmetry in low-mass bottom-quark pairs produced in proton-antiproton collisions
Here, we report a measurement of the forward-backward asymmetry, AFB, in $b\bar{b}$ pairs produced in proton-antiproton collisions and identified by muons from semileptonic b-hadron decays. The event sample is collected at a center-of-mass energy of √s = 1.96 TeV with the CDF II detector and corresponds to 6.9 fb –1 of integrated luminosity. We obtain an integrated asymmetry of A FB ($b\bar{b}$)=(1.2±0.7)% at the particle level for b-quark pairs with invariant mass, m $b\bar{b}$ , down to 40 GeV/c 2 and measure the dependence of A FB ($b\bar{b}$) on m $b\bar{b}$ . The results are compatible with expectations from the standard model.
Exclusion of an Exotic Top Quark with -4/3 Electric Charge Using Soft Lepton Tagging
We present a measurement of the electric charge of the top quark using pp collisions corresponding to an integrated luminosity of 2.7 fb{sup -1} at the CDF II detector. We reconstruct tt events in the lepton+jets final state. We use soft lepton taggers to determine the flavor of the b jets, which we use to reconstruct the top quark's electric charge and exclude an exotic top quark with -4/3 charge at 95% confidence level. This is the strongest exclusion of the exotic charge scenario and the first to use soft leptons for this purpose.
Direct Mass Limits for Chiral Fourth-Generation Quarks in All Mixing Scenarios
Present limits on chiral fourth-generation quark masses m{sub b}{sup '} and m{sub t}{sup '} are broadly generalized and strengthened by combining both t{sup '} and b{sup '} decays and considering a full range of t{sup '} and b{sup '} flavor-mixing scenarios with the lighter generations (to 1- parallel V{sub 44} parallel {sup 2{approx_equal}}10{sup -13}). Various characteristic mass-splitting choices are considered. With m{sub t}{sup '}>m{sub b}{sup '} we find that CDF Collaboration limits on the b{sup '} mass vary by no more than 10%-20% with any choice of flavor mixing, while for the t{sup '} mass, we typically find stronger bounds, in some cases up to m{sub t}{sup '}>430 GeV. For m{sub b}{sup '}>m{sub t}{sup '}, we find m{sub b}{sup '}>380-430 GeV, depending on the flavor mixing and the size of the m{sub t}{sup '}-m{sub b}{sup '} mass splitting.