Search Results (78 total)

Correlations in the azimuthal angle between the two largest transverse momentum jets have been measured using the D0 detector in pp̅ collisions at a center-of-mass energy sqrt[s]=1.96  TeV. The analysis is based on an inclusive dijet event sample in the central rapidity region corresponding to an integrated luminosity of 150  pb^-1. Azimuthal correlations are stronger at larger transverse momenta. These are well described in perturbative QCD at next-to-leading order in the strong coupling constant, except at large azimuthal differences where contributions with low transverse momentum are significant.

Using the exclusive decay B_s⁰→J/ψ(μ⁺μ^-)ϕ(K⁺K^-), we report the most precise single measurement of the B_s⁰ lifetime. The data sample corresponds to an integrated luminosity of approximately 220  pb^-1 collected with the D0 detector at the Fermilab Tevatron Collider in 2002–2004. We reconstruct 337 signal candidates, from which we extract the B_s⁰ lifetime, τ(B_s⁰)=1.444_-0.090^+0.098(stat)±0.020(sys)  ps. We also report a measurement for the lifetime of the B⁰ meson using the exclusive decay B⁰→J/ψ(μ⁺μ^-)K^*0(892)(K⁺π^-). We reconstruct 1370 signal candidates, obtaining τ(B⁰)=1.473_-0.050^+0.052(stat)±0.023(sys)  ps, and the ratio of lifetimes, τ(B_s⁰)/τ(B⁰)=0.980_-0.071^+0.076(stat)±0.003(sys).

We report the results of a search for supersymmetry (SUSY) with gauge-mediated breaking in the missing transverse energy distribution of inclusive diphoton events using 263  pb^-1 of data collected by the D0 experiment at the Fermilab Tevatron Collider in 2002–2004. No excess is observed above the background expected from standard model processes, and lower limits on the masses of the lightest neutralino and chargino of about 108 and 195 GeV, respectively, are set at the 95% confidence level. These are the most stringent limits to date for models with gauge-mediated SUSY breaking with a short-lived neutralino as the next-to-lightest SUSY particle.

We report the observation of the X(3872) in the J/ψπ⁺π^- channel, with J/ψ decaying to μ⁺μ^-, in pp̅ collisions at sqrt[s]=1.96  TeV. Using approximately 230  pb^-1 of data collected with the Run II D0 detector, we observe 522±100 X(3872) candidates. The mass difference between the X(3872) state and the J/ψ is measured to be 774.9±3.1(stat)±3.0(syst)  MeV/c². We have investigated the production and decay characteristics of the X(3872) and find them to be similar to those of the ψ(2S) state.

A search for pair production of doubly charged Higgs bosons in the process pp̅ →H⁺⁺H^--→μ⁺μ⁺μ^-μ^- is performed with the D0 run II detector at the Fermilab Tevatron. The analysis is based on a sample of inclusive dimuon data collected at an energy of sqrt[s]=1.96  TeV, corresponding to an integrated luminosity of 113  pb^-1. In the absence of a signal, 95% confidence level mass limits of M(H_L^±±)>118.4  GeV/c² and M(H_R^±±)>98.2  GeV/c² are set for left-handed and right-handed doubly charged Higgs bosons, respectively, assuming 100% branching into muon pairs.

We present the first measurement of the D^*+ width using 9/fb of e⁺e^- data collected near the Υ(4S) resonance by the CLEO II.V detector. Our method uses advanced tracking techniques and a reconstruction method that takes advantage of the small vertical size of the CESR beam spot to measure the energy release distribution from the D^*+→D⁰π⁺ decay. We find Γ(D^*+)=96±4 (statistical)±22 (systematic) keV. We also measure the energy release in the decay and compute Δm≡m_D^*+-m_D⁰=145.412±0.002 (statistical)±0.012 (systematic) MeV/c².

We have searched for the charmless hadronic decay of B⁰ mesons into two neutral pions. Using 9.13 fb^-1 taken at the Υ(4S) with the CLEO detector, we obtain an improved upper limit for the branching fraction B(B⁰→π⁰π⁰)<5.7×10^-6 at the 90% confidence level.

We have studied two-body charmless decays of the B meson into the final states ρ⁰ρ⁰, K^*0ρ⁰, K^*0K^*0, K^*0K̅ ^*0, K^*+ρ⁰, K^*+K̅ ^*0, and K^*+K^*- using only decay modes with charged daughter particles. Using 9.7×10⁶ BB̅ pairs collected with the CLEO detector, we place 90% confidence level upper limits on the branching fractions (1.4–14.1)×10^-5, depending on final state and polarization.

We have searched for the two-body decay of the B meson to a light pseudoscalar meson h  =  π^±,K^±,K_S⁰ and a massless neutral feebly interacting particle X⁰ such as the familon, the Nambu-Goldstone boson associated with a spontaneously broken global family symmetry. We find no significant signal by analyzing a data sample containing 9.7×10⁶ BB̅ mesons collected with the CLEO detector at the Cornell Electron Storage Ring, and set 90% C.L. upper limits B(B^±→h^±X⁰)  =  4.9×10^-5 and B(B⁰→K_S⁰X⁰)  =  5.3×10^-5. These limits correspond to a lower bound of approximately 10⁸ GeV on the family symmetry breaking scale with vector coupling involving the third generation of quarks.

We report on the observation of B⁰→D^*0π⁺π⁺π^-π^- decays. The branching ratio is (0.30±0.07±0.06)%. Interest in this particular mode was sparked by Ligeti, Luke and Wise who propose it as a way to check the validity of factorization tests in B⁰→D^*+π⁺π^-π^-π⁰ decays.

We have measured the first and second moments of the hadronic mass-squared distribution in B→X_cℓν, for P_lepton>1.5 GeV/c. We find 〈M_X²-M̅ _D²〉  =  0.251±0.066 GeV², 〈(M_X²-〈M_X²〉)²〉  =  0.576±0.170 GeV⁴, where M̅ _D is the spin-averaged D meson mass. From that first moment and the first moment of the photon energy spectrum in b→sγ, we find the heavy quark effective theory parameter λ₁ (in the modified minimal subtraction renormalization scheme, to order 1/M_B³ and β₀α_s²) to be -0.24±0.11 GeV². Using these first moments and the B semileptonic width, and assuming parton-hadron duality, we obtain |V_cb|  =  0.0404±0.0013.

We have measured the branching fraction and photon energy spectrum for the radiative penguin process b→sγ. We find B(b→sγ)  =  (3.21±0.43±0.27_-0.10^+0.18)×10^-4, where the errors are statistical, systematic, and from theory corrections. We obtain first and second moments of the photon energy spectrum above 2.0 GeV, 〈E_γ〉  =  2.346±0.032±0.011 GeV, and 〈E_γ²〉-〈E_γ〉²  =  0.0226±0.0066±0.0020 GeV², where the errors are statistical and systematic. From the first moment, we obtain (in the modified minimal subtraction renormalization scheme, to order 1/M_B³ and β₀α_s²) the heavy quark effective theory parameter Λ̅  =  0.35±0.08±0.10 GeV.

We present the first measurement of the D^*+ width using 9/fb of e⁺e^- data collected near the ϒ(4S) resonance by the CLEO II.V detector. Our method uses advanced tracking techniques and a reconstruction method that takes advantage of the small vertical size of the Cornell Electron-positron Storage Ring beam spot to measure the energy release distribution from the D^*+→D⁰π⁺ decay. We find Γ(D^*+)  =  96±4 (stat)±22 (syst) keV. We also measure the energy release in the decay and compute Δm≡m_D^*+-m_D⁰  =  145.412±0.002 (stat)±0.012 (syst) MeV/c².

We have searched a sample of 9.6×10⁶ BB̅ events for the flavor-changing neutral current decays B→Kℓ⁺ℓ^- and B→K^*(892)ℓ⁺ℓ^-. We subject the latter decay to the requirement that the dilepton mass m_ℓℓ exceed 0.5 GeV. There is no indication of a signal. We obtain the 90% confidence level upper limits B(B→Kℓ⁺ℓ^-)<1.7×10^-6 and B(B→K^*(892)ℓ⁺ℓ^-)_{mℓℓ>0.5 GeV}<3.3×10^-6. We also obtain an upper limit on the weighted average 0.65B(B→Kℓ⁺ℓ^-)+0.35B(B→K^*(892)ℓ⁺ℓ^-)_{mℓℓ>0.5 GeV}<1.5×10^-6. The weighted-average limit is only 50% above the standard model prediction.

We search for CP nonconservation in the decays of τ leptons produced via e⁺e^- annihilation at sqrt[s]∼10.6 GeV. The method uses correlated decays of pairs of τ leptons, each decaying to the ππ⁰ν_τ final state. The search is done within the framework of a model with a scalar boson exchange. In an analysis of a data sample corresponding to 12.2×10⁶ produced τ pairs collected with the CLEO detector, we find no evidence of violation of CP symmetry. We obtain a limit on the imaginary part of the coupling constant parametrizing the relative contribution of diagrams that would lead to CP violation to be -0.046<Im(Λ)<0.022 at 90% C.L. This result provides a restriction on CP nonconservation in tau lepton decays. As a cross-check, we study the decay angular distribution and perform a model-independent search for a CP violation effect of a scalar exchange in single τ→ππ⁰ν_τ decays. The limit on the imaginary part of the τ scalar coupling is -0.033<Im(Λ)<0.089 at 90% C.L.

We report on the observation of B̅ →D^*π⁺π^-π^-π⁰ decays. The branching ratios for D^*+ and D^*0 are (1.72±0.14±0.24)% and (1.80±0.24±0.27)%, respectively. Each final state has a D^*ωπ^- component, with branching ratios (0.29±0.03±0.04)% and (0.45±0.10±0.07)% for the D^*+ and D^*0 modes, respectively. We also observe B̅ →Dωπ^- decays. The branching ratios for D⁺ and D⁰ are (0.28±0.05±0.04)% and (0.41±0.07±0.06)%, respectively. A spin parity analysis of the ωπ^- system in the Dωπ^- final state shows a preference for a wide 1^- resonance. A fit to the ωπ^- mass spectrum finds a central mass of (1349±25_-5⁺¹⁰) MeV and width of (547±86_-45⁺⁴⁶) MeV. We identify this object as the ρ(1450) or the ρ^′.

We report on a search for the decay B⁺→D^*+K_S⁰ and its charge conjugate with the CLEO detector at the Cornell Electron Storage Ring (CESR). No candidates are found in 9.10 fb^-1 of data. The background is estimated to be 0.29±0.05 leading to an upper limit B(B⁺→D^*+K⁰)=9.5×10^-5 (90% confidence level).

We present an observation and time-integrated rate measurement of the decay D⁰→K⁺π^-π⁰ produced in 9 fb^-1 of e⁺e^- collisions near the ϒ(4S) resonance. The signal is inconsistent with an upward fluctuation of the background by 4.9 standard deviations. We measured the time-integrated rate of D⁰→K⁺π^-π⁰ normalized to the rate of D⁰̅ →K⁺π^-π⁰ to be 0.0043_-0.0010^+0.0011 (stat)±0.0007 (syst). This decay can be produced by doubly Cabibbo-suppressed decays or by the D⁰ evolving into a D⁰̅ through mixing, followed by a Cabibbo-favored decay to K⁺π^-π⁰. We also found the CP asymmetry A  =  (9_-22⁺²⁵)% be consistent with zero.

Using 12.7 fb^-1 of data collected with the CLEO detector at CESR, we observed two-photon production of the cc̅ states χ_c0 and χ_c2 in their decay to π⁺π^-π⁺π^-. We measured Γ_γγ(χ_c)×B(χ_c→π⁺π^-π⁺π^-) to be 75±13(stat)±8(syst) eV for the χ_c0 and 6.4±1.8(stat)±0.8(syst) eV for the χ_c2, implying Γ_γγ(χ_c0)  =  3.76±0.65(stat)±0.41(syst)±1.69(br) keV and Γ_γγ(χ_c2)  =  0.53±0.15(stat)±0.06(syst)±0.22(br) keV. Also, cancellation of dominant experimental and theoretical uncertainties permits a precise comparison of Γ_γγ(χ_c0)/Γ_γγ(χ_c2), evaluated to be 7.4±2.4(stat)±0.5(syst)±0.9(br), with QCD-based predictions.

We have measured the CP asymmetry A_CP≡[Γ(b→sγ)-Γ(b̅ →s̅ γ)]/[Γ(b→sγ)+Γ(b̅ →s̅ γ)] to be A_CP  =  (-0.079±0.108±0.022) (1.0±0.030), implying that, at 90% confidence level, A_CP lies between -0.27 and +0.10. These limits rule out some extreme non-standard-model predictions, but are consistent with most, as well as with the standard model.

We have measured the charge asymmetry in like-sign dilepton yields from B⁰B̅ ⁰ meson decays using the CLEO detector at the Cornell Electron Storage Ring. We find a_ℓℓ⁰≡[N(ℓ⁺ℓ⁺)-N(ℓ^-ℓ^-)]/[N(ℓ⁺ℓ⁺)+N(ℓ^-ℓ^-)]  =  +0.013±0.050±0.005. We combine this result with a previous, independent measurement and obtain Re(ε_B)/(1+|ε_B|²)  =  +0.0035±0.0103±0.0015 (uncertainties are statistical and systematic, respectively) for the CP impurity parameter, ε_B.

Using 13.7 fb^-1 of data recorded by the CLEO detector at the Cornell Electron Storage Ring, we investigate the spectrum of charmed baryons which decay into Λ_c⁺π^-π⁺ and are more massive than the Λ_c⁺(2625) baryon. We find evidence for two new states: one is broad and has an invariant mass roughly 480 MeV above that of the Λ_c⁺ baryon; the other is narrow with an invariant mass of 596±1±2 MeV above the Λ_c⁺ mass.

The τ decays to six-pion final states have been studied with the CLEO detector at the Cornell Electron Storage Ring. The measured branching fractions are B(τ^-→2π^-π⁺3π⁰ν_τ)  =  (2.2±0.3±0.4)×10^-4 and B(τ^-→3π^-2π⁺π⁰ν_τ)  =  (1.7±0.2±0.2)×10^-4. A search for substructure in these decays shows that they are saturated by intermediate states with η or ω mesons. We present the first observation of the decay τ^-→2π^-π⁺ων_τ and the branching fraction is measured to be (1.2±0.2±0.1)×10^-4. The measured branching fractions are in good agreement with the isospin expectations but somewhat below the conserved-vector-current predictions.

Using 13.7 fb^-1 of data recorded by the CLEO detector at Cornell Electron Storage Ring, we report evidence of two new charmed baryons: one decaying into Ξ_c^0′π⁺ with the subsequent decay Ξ_c^0′→Ξ_c⁰γ, and its isospin partner decaying into Ξ_c^+′π^- followed by Ξ_c^+′→Ξ_c⁺γ. We measure the following mass differences for the two states: M(Ξ_c⁰γπ⁺)-M(Ξ_c⁰)  =  318.2±1.3±2.9 MeV and M(Ξ_c⁺γπ^-)-M(Ξ_c⁺)  =  324.0±1.3±3.0 MeV. We interpret these new states as the J^P  =  1 / 2^- Ξ_c1 particles, the charmed-strange analogs of the Λ_c1⁺(2593).

Using 13.6 fb^-1 of continuum two-jet e⁺e^-→cc̅ events collected with the CLEO detector, we have searched for baryon number correlations at the primary quark level. We have measured the likelihood for a Λ_c⁺ charmed baryon to be produced in the hemisphere opposite a Λ̅ _c^- relative to the likelihood for a Λ_c⁺ charmed baryon to be produced opposite an anticharmed meson D̅ ; in all cases, the reconstructed hadrons must have momentum greater than 2.3 GeV/c. We find that, given a Λ̅ _c^- (reconstructed in five different decay modes), a Λ_c⁺ is observed in the opposite hemisphere (0.72±0.11)% of the time (not corrected for efficiency). By contrast, given a D̅ in one hemisphere, a Λ_c⁺ is observed in the opposite hemisphere only (0.21±0.02)% of the time. Normalized to the total number of either Λ̅ _c^- or D̅ “tags,” it is therefore 3.52±0.45±0.42 times more likely to find a Λ_c⁺ opposite a Λ̅ _c^- than a D̅ meson. This enhancement is not observed in the JETSET 7.3 e⁺e^-→cc̅ Monte Carlo simulation.