Search Results (888 total)

We present measurements of the branching fraction B and longitudinal polarization fraction f_L for B⁰→a₁(1260)⁺a₁(1260)^- decays, with a₁(1260)^±→π^-π⁺π^±. The data sample, collected with the BABAR detector at the SLAC National Accelerator Laboratory, represents 465×10⁶ produced BB̅ pairs. We measure B(B⁰→a₁(1260)⁺a₁(1260)^-)×[B(a₁(1260)⁺→π^-π⁺π⁺)]²=  (11.8±2.6±1.6)×10^-6 and f_L=0.31±0.22±0.10, where the first uncertainty is statistical and the second systematic. The decay mode is measured with a significance of 5.0 standard deviations including systematic uncertainties.

We present measurements of the top quark mass (m_t) in tt̅ candidate events with two final state leptons using 1  fb^-1 of data collected by the D0 experiment. Our data sample is selected by requiring two fully identified leptons or by relaxing one lepton requirement to an isolated track if at least one jet is tagged as a b jet. The top quark mass is extracted after reconstructing the event kinematics under the tt̅ hypothesis using two methods. In the first method, we integrate over expected neutrino rapidity distributions, and in the second we calculate a weight for the possible top quark masses based on the observed particle momenta and the known parton distribution functions. We analyze 83 candidate events in the data and obtain m_t=176.2±4.8(stat)±2.1(sys)  GeV and m_t=173.2±4.9(stat)±2.0(sys)  GeV for the two methods, respectively. Accounting for correlations between the two methods, we combine the measurements to obtain m_t=174.7±4.4(stat)±2.0(sys)  GeV.

We present the result from a precision measurement of the mass of the τ lepton, M_τ, based on 423  fb^-1 of data recorded at the Υ(4S) resonance with the BABAR detector. Using a pseudomass endpoint method, we determine the mass to be 1776.68±0.12(stat)±0.41(syst)  MeV. We also measure the mass difference between the τ⁺ and τ^-, and obtain (M_τ⁺-M_τ^-)/M_AVG^τ=(-3.4±1.3(stat)±0.3(syst))×10^-4, where M_AVG^τ is the average value of M_τ⁺ and M_τ^-.

We present an analysis of the decays B⁰→K^*0(892)γ and B⁺→K^*+(892)γ using a sample of about 383×10⁶ BB̅ events collected with the BABAR detector at the PEP-II asymmetric energy B factory. We measure the branching fractions B(B⁰→K^*0γ)=(4.47±0.10±0.16)×10^-5 and B(B⁺→K^*+γ)=(4.22±0.14±0.16)×10^-5. We constrain the direct CP asymmetry to be -0.033<A(B→K^*γ)<0.028 and the isospin asymmetry to be 0.017<Δ_0-<0.116, where the limits are determined by the 90% confidence interval and include both the statistical and systematic uncertainties.

We present evidence of D0-D̅ 0 mixing using a time-dependent amplitude analysis of the decay D0→K+π-π0 in a data sample of 384  fb-1 collected with the BABAR detector at the PEP-II e+e- collider at the Stanford Linear Accelerator Center. Assuming CP conservation, we measure the mixing parameters xKππ0′=[2.61-0.68+0.57(stat)±0.39(syst)]%, yKππ0′=[-0.06-0.64+0.55(stat)±0.34(syst)]%. This result is inconsistent with the no-mixing hypothesis with a significance of 3.2 standard deviations. We find no evidence of CP violation in mixing.

Measurements of the azimuthal anisotropy of high-p_T neutral pion (π⁰) production in Au+Au collisions at sqrt[s_NN]=200 GeV by the PHENIX experiment are presented. The data included in this article were collected during the 2004 Relativistic Heavy Ion Collider running period and represent approximately an order of magnitude increase in the number of analyzed events relative to previously published results. Azimuthal angle distributions of π⁰ mesons detected in the PHENIX electromagnetic calorimeters are measured relative to the reaction plane determined event-by-event using the forward and backward beam-beam counters. Amplitudes of the second Fourier component (v₂) of the angular distributions are presented as a function of π⁰ transverse momentum (p_T) for different bins in collision centrality. Measured reaction plane dependent π⁰ yields are used to determine the azimuthal dependence of the π⁰ suppression as a function of p_T, R_AA(Δϕ,p_T). A jet-quenching motivated geometric analysis is presented that attempts to simultaneously describe the centrality dependence and reaction plane angle dependence of the π⁰ suppression in terms of the path lengths of hypothetical parent partons in the medium. This set of results allows for a detailed examination of the influence of geometry in the collision region and of the interplay between collective flow and jet-quenching effects along the azimuthal axis.

We present an all-sky search for gravitational waves in the frequency range 1 to 6 kHz during the first calendar year of LIGO’s fifth science run. This is the first untriggered LIGO burst analysis to be conducted above 3 kHz. We discuss the unique properties of interferometric data in this regime. 161.3 days of triple-coincident data were analyzed. No gravitational events above threshold were observed and a frequentist upper limit of 5.4  year^-1 on the rate of strong gravitational-wave bursts was placed at a 90% confidence level. Implications for specific theoretical models of gravitational-wave emission are also discussed.

We present the results obtained from an all-sky search for gravitational-wave (GW) bursts in the 64–2000 Hz frequency range in data collected by the LIGO detectors during the first year (November 2005—November 2006) of their fifth science run. The total analyzed live time was 268.6 days. Multiple hierarchical data analysis methods were invoked in this search. The overall sensitivity expressed in terms of the root-sum-square (rss) strain amplitude h_rss for gravitational-wave bursts with various morphologies was in the range of 6×10^-22  Hz^-1/2 to a few×10^-21  Hz^-1/2. No GW signals were observed and a frequentist upper limit of 3.75 events per year on the rate of strong GW bursts was placed at the 90% confidence level. As in our previous searches, we also combined this rate limit with the detection efficiency for selected waveform morphologies to obtain event rate versus strength exclusion curves. In sensitivity, these exclusion curves are the most stringent to date.

We observe the decays D_s1^*(2710)⁺→D^*K and D_sJ^*(2860)⁺→D^*K and measure their branching fractions relative to the DK final state. We also observe, in the D^*K mass spectrum, a new broad structure at a mass of (3044±8_stat(+30 / -5)_syst)  MeV/c² having a width Γ=(239±35_stat(+46 / -42)_syst)  MeV. To obtain this result we use 470  fb^-1 of data recorded by the BABAR detector at the PEP-II asymmetric-energy e⁺e^- storage rings at the Stanford Linear Accelerator Center running at center-of-mass energies near 10.6 GeV.

We present the first measurement of dijet angular distributions in pp̅ collisions at sqrt[s]=1.96  TeV at the Fermilab Tevatron Collider. The measurement is based on a dataset corresponding to an integrated luminosity of 0.7  fb^-1 collected with the D0 detector. Dijet angular distributions have been measured over a range of dijet masses, from 0.25 TeV to above 1.1 TeV. The data are in good agreement with the predictions of perturbative QCD and are used to constrain new physics models including quark compositeness, large extra dimensions, and TeV^-1 scale extra dimensions. For all models considered, we set the most stringent direct limits to date.

We study the decay B^-→DK^*- using a sample of 379×10⁶ Υ(4S)→BB̅ events collected with the BABAR detector at the PEP-II B factory. We perform a Gronau-London-Wyler analysis where the D meson decays into either a CP-even (CP+) eigenstate (K⁺K^-, π⁺π^-), CP-odd (CP-) eigenstate (K_S⁰π⁰, K_S⁰ϕ, K_S⁰ω) or a non-CP state (K^-π⁺). We also analyze D meson decays into K⁺π^- from a Cabibbo-favored D̅ ⁰ decay or doubly suppressed D⁰ decay [Atwood-Dunietz-Soni (ADS) analysis]. We measure observables that are sensitive to the Cabibbo-Kobayashi-Maskawa angle γ: the partial-rate charge asymmetries A_CP±, the ratios R_CP± of the B-decay branching fractions in CP± and non-CP decay, the ratio R_ADS of the charge-averaged branching fractions, and the charge asymmetry A_ADS of the ADS decays: A_CP+=0.09±0.13±0.06, A_CP-=-0.23±0.21±0.07, R_CP+=2.17±0.35±0.09, R_CP-=1.03±0.27±0.13, R_ADS=0.066±0.031±0.010, and A_ADS=-0.34±0.43±0.16, where the first uncertainty is statistical and the second is systematic. Combining all the measurements and using a frequentist approach yields the magnitude of the ratio between the Cabibbo-suppressed and favored amplitudes, r_B=0.31 with a one (two) sigma confidence level interval of [0.24, 0.38] ([0.17, 0.43]). The value r_B=0 is excluded at the 3.3 sigma level. A similar analysis excludes values of γ in the intervals [0, 7]°, [55, 111]°, and [175, 180]° ([85, 99]°) at the one (two) sigma confidence level.

We provide the most precise measurement of the WW production cross section in pp̅ collisions to date at a center of mass energy of 1.96 TeV, and set limits on the associated trilinear gauge couplings. The WW→ℓνℓ^′ν (ℓ, ℓ^′=e, μ) decay channels are analyzed in 1  fb^-1 of data collected by the D0 detector at the Fermilab Tevatron Collider. The measured cross section is σ(pp̅ →WW)=11.5±2.1(stat+syst)±0.7(lumi)  pb. One- and two-dimensional 95% C.L. limits on trilinear gauge couplings are provided.

We search for a light Higgs boson A⁰ in the radiative decay Υ(3S)→γA⁰, A⁰→τ⁺τ^-, τ⁺→e⁺ν_eν̅ _τ, or τ⁺→μ⁺ν_μν̅ _τ. The data sample contains 122×10⁶ Υ(3S) events recorded with the BABAR detector. We find no evidence for a narrow structure in the studied τ⁺τ^- invariant mass region of 4.03<m_τ⁺τ^-<10.10  GeV/c². We exclude at the 90% confidence level (C.L.) a low-mass Higgs boson decaying to τ⁺τ^- with a product branching fraction B(Υ(3S)→γA⁰)×B(A⁰→τ⁺τ^-)>(1.5–16)×10^-5 across the m_τ⁺τ^- range. We also set a 90% C.L. upper limit on the τ⁺τ^- decay of the η_b at B(η_b→τ⁺τ^-)<8%.

We measure the rate of D⁰-D̅ ⁰ mixing with the observable y_CP=(τ_Kπ/τ_KK)-1, where τ_KK and τ_Kπ are, respectively, the mean lifetimes of CP-even D⁰→K⁺K^- and CP-mixed D⁰→K^-π⁺ decays, using a data sample of 384  fb^-1 collected by the BABAR detector at the SLAC PEP-II asymmetric-energy B Factory. From a sample of D⁰ and D̅ ⁰ decays where the initial flavor of the decaying meson is not determined, we obtain y_CP=[1.12±0.26(stat)±0.22(syst)]%, which excludes the no-mixing hypothesis at 3.3σ, including both statistical and systematic uncertainties. This result is in good agreement with a previous BABAR measurement of y_CP obtained from a sample of D^*+→D⁰π⁺ events, where the D⁰ decays to K^-π⁺, K⁺K^-, and π⁺π^-, which is disjoint with the untagged D⁰ events used here. Combining the two results taking into account statistical and systematic uncertainties, where the systematic uncertainties are assumed to be 100% correlated, we find y_CP=[1.16±0.22(stat)±0.18(syst)]%, which excludes the no-mixing hypothesis at 4.1σ.

We combine measurements of the top quark pair production cross section in pp̅ collisions in the ℓ+jets, ℓℓ, and τℓ final states (where ℓ is an electron or muon) at a center of mass energy of sqrt[s]=1.96  TeV in 1  fb^-1 of data collected with the D0 detector. For a top quark mass of 170  GeV/c², we obtain σ_tt̅ =8.18_-0.87^+0.98  pb in agreement with the theoretical prediction. Based on predictions from higher order quantum chromodynamics, we extract a mass for the top quark from the combined tt̅ cross section, consistent with the world average of the top quark mass. In addition, the ratios of tt̅ cross sections in different final states are used to set upper limits on the branching fractions B(t→H⁺b→τ⁺νb) and B(t→H⁺b→cs̅ b) as a function of the charged Higgs boson mass.

We have performed a search for the η_b(1S) meson in the radiative decay of the Υ(2S) resonance using a sample of 91.6×10⁶ Υ(2S) events recorded with the BABAR detector at the PEP-II B factory at the SLAC National Accelerator Laboratory. We observe a peak in the photon energy spectrum at E_γ=609.3_-4.5^+4.6(stat)±1.9(syst)  MeV, corresponding to an η_b(1S) mass of 9394.2_-4.9^+4.8(stat)±2.0(syst)  MeV/c². The branching fraction for the decay Υ(2S)→γη_b(1S) is determined to be [3.9±1.1(stat)_-0.9^+1.1(syst)]×10^-4. We find the ratio of branching fractions B[Υ(2S)→γη_b(1S)]/B[Υ(3S)→γη_b(1S)]=0.82±0.24(stat)_-0.19^+0.20(syst).

We present a measurement of the W boson mass in W→eν decays using 1  fb^-1 of data collected with the D0 detector during Run II of the Fermilab Tevatron collider. With a sample of 499830 W→eν candidate events, we measure M_W=80.401±0.043  GeV. This is the most precise measurement from a single experiment.

Bose-Einstein correlations of charged kaons are used to probe Au+Au collisions at sqrt[s_NN]=200  GeV and are compared to charged pion probes, which have a larger hadronic scattering cross section. Three-dimensional Gaussian source radii are extracted, along with a one-dimensional kaon emission source function. The centrality dependences of the three Gaussian radii are well described by a single linear function of N_part^1/3 with a zero intercept. Imaging analysis shows a deviation from a Gaussian tail at r≳10  fm, although the bulk emission at lower radius is well described by a Gaussian. The presence of a non-Gaussian tail in the kaon source reaffirms that the particle emission region in a heavy-ion collision is extended, and that similar measurements with pions are not solely due to the decay of long-lived resonances.

We present a search for charged Higgs bosons in decays of top quarks, in the mass range 80<m_H^±<155  GeV, assuming the subsequent decay H⁺→τ⁺ν_τ (and its charge conjugate). Using 0.9  fb^-1 of lepton+jets data collected with the D0 detector at the Fermilab Tevatron pp̅ collider, operating at a center of mass energy sqrt[s]=1.96  TeV, we find no evidence for a H^± signal. Hence we exclude branching ratios B(t→H⁺b)>0.24 for m_H^±=80  GeV and B(t→H⁺b)>0.19 for m_H^±=155  GeV at the 95% C.L.

We report on a matched-filter search for gravitational wave bursts from cosmic string cusps using LIGO data from the fourth science run (S4) which took place in February and March 2005. No gravitational waves were detected in 14.9 days of data from times when all three LIGO detectors were operating. We interpret the result in terms of a frequentist upper limit on the rate of gravitational wave bursts and use the limits on the rate to constrain the parameter space (string tension, reconnection probability, and loop sizes) of cosmic string models. Many grand unified theory-scale models (with string tension Gμ/c²≈10^-6) can be ruled out at 90% confidence for reconnection probabilities p≤10^-3 if loop sizes are set by gravitational back reaction.

We present a direct measurement of trilinear gauge boson couplings at γWW and ZWW vertices in WW and WZ events produced in pp̅ collisions at sqrt[s]=1.96  TeV. We consider events with one electron or muon, missing transverse energy, and at least two jets. The data were collected using the D0 detector and correspond to 1.1  fb^-1 of integrated luminosity. Considering two different relations between the couplings at the γWW and ZWW vertices, we measure these couplings at 68% C.L. to be κ_γ=1.07_-0.29^+0.26, λ=0.00_-0.06^+0.06, and g₁^Z=1.04_-0.09^+0.09 in a scenario respecting SU(2)_L⊗U(1)_Y gauge symmetry and κ=1.04_-0.11^+0.11 and λ=0.00_-0.06^+0.06 in an “equal couplings” scenario.

We present a measurement of the mass difference between t and t̅ quarks in lepton+jets final states of tt̅ events in 1  fb^-1 of data collected with the D0 detector from Fermilab Tevatron Collider pp̅ collisions at sqrt[s]=1.96  TeV. The measured mass difference of 3.8±3.7  GeV is consistent with the equality of t and t̅ masses. This is the first direct measurement of a mass difference between a quark and its antiquark partner.

We report the observation of the baryonic B-decay B̅ ⁰→Λ_c⁺p̅ K^-π⁺, excluding contributions from the decay B̅ ⁰→Λ_c⁺Λ̅ K^-. Using a data sample of 467×10⁶ BB̅ pairs collected with the BABAR detector at the PEP-II storage ring at SLAC, the measured branching fraction is (4.33±0.82_stat±0.33_syst±1.13_Λc⁺)×10^-5. In addition we find evidence for the resonant decay B̅ ⁰→Σ_c(2455)⁺⁺p̅ K^- and determine its branching fraction to be (1.11±0.30_stat±0.09_syst±0.29_Λc⁺)×10^-5. The errors are statistical, systematic, and due to the uncertainty in the Λ_c⁺ branching fraction. For the resonant decay B̅ ⁰→Λ_c⁺p̅ K̅ ^*0 we obtain an upper limit of 2.42×10^-5 at 90% confidence level.

We study the reaction e⁺e^-→e⁺e^-π⁰ in the single tag mode and measure the differential cross section dσ/dQ² and the γγ^*→π⁰ transition form factor in the momentum transfer range from 4 to 40  GeV². At Q²>10  GeV² the measured form factor exceeds the asymptotic limit predicted by perturbative QCD. The analysis is based on 442  fb^-1 of integrated luminosity collected at PEP-II with the BABAR detector at e⁺e^- center-of-mass energies near 10.6 GeV.

According to general relativity a perturbed black hole will settle to a stationary configuration by the emission of gravitational radiation. Such a perturbation will occur, for example, in the coalescence of a black hole binary, following their inspiral and subsequent merger. At late times the waveform is a superposition of quasinormal modes, which we refer to as the ringdown. The dominant mode is expected to be the fundamental mode, l=m=2. Since this is a well-known waveform, matched filtering can be implemented to search for this signal using LIGO data. We present a search for gravitational waves from black hole ringdowns in the fourth LIGO science run S4, during which LIGO was sensitive to the dominant mode of perturbed black holes with masses in the range of 10M_⊙ to 500M_⊙, the regime of intermediate-mass black holes, to distances up to 300 Mpc. We present a search for gravitational waves from black hole ringdowns using data from S4. No gravitational wave candidates were found; we place a 90%-confidence upper limit on the rate of ringdowns from black holes with mass between 85M_⊙ and 390M_⊙ in the local universe, assuming a uniform distribution of sources, of 3.2×10^-5  yr^-1 Mpc^-3=1.6×10^-3  yr^-1L₁₀^-1,where L₁₀ is 10¹⁰ times the solar blue-light luminosity.