Search Results (62 total)

The Cryogenic Dark Matter Search (CDMS) is an experiment to detect weakly interacting massive particles (WIMPs), which may constitute the universe’s dark matter, based on their interactions with Ge and Si nuclei. We report the results of an analysis of data from the first two runs of CDMS at the Soudan Underground Laboratory in terms of spin-dependent WIMP-nucleon interactions on ⁷³Ge and ²⁹Si. These data exclude new regions of WIMP parameter space, including regions relevant to spin-dependent interpretations of the annual modulation signal reported by the DAMA/NaI experiment.

We report new results from the Cryogenic Dark Matter Search (CDMS II) at the Soudan Underground Laboratory. Two towers, each consisting of six detectors, were operated for 74.5 live days, giving spectrum-weighted exposures of 34 (12) kg d for the Ge (Si) targets after cuts, averaged over recoil energies 10–100 keV for a weakly interacting massive particle (WIMP) mass of 60  GeV/c². A blind analysis was conducted, incorporating improved techniques for rejecting surface events. No WIMP signal exceeding expected backgrounds was observed. When combined with our previous results from Soudan, the 90% C.L. upper limit on the spin-independent WIMP-nucleon cross section is 1.6×10^-43  cm² from Ge and 3×10^-42  cm² from Si, for a WIMP mass of 60  GeV/c². The combined limit from Ge (Si) is a factor of 2.5 (10) lower than our previous results and constrains predictions of supersymmetric models.

The Cryogenic Dark Matter Search (CDMS-II) employs low-temperature Ge and Si detectors to seek weakly interacting massive particles (WIMPs) via their elastic-scattering interactions with nuclei. Simultaneous measurements of both ionization and phonon energy provide discrimination against interactions of background particles. For recoil energies above 10 keV, events due to background photons are rejected with >99.99% efficiency. Electromagnetic events very near the detector surface can mimic nuclear recoils because of reduced charge collection, but these surface events are rejected with >96% efficiency by using additional information from the phonon pulse shape. Efficient use of active and passive shielding, combined with the 2090 m.w.e. overburden at the experimental site in the Soudan mine, makes the background from neutrons negligible for this first exposure. All cuts are determined in a blind manner from in situ calibrations with external radioactive sources without any prior knowledge of the event distribution in the signal region. Resulting efficiencies are known to ∼10%. A single event with a recoil of 64 keV passes all of the cuts and is consistent with the expected misidentification rate of surface electron recoils. Under the assumptions for a standard dark matter halo, these data exclude previously unexplored parameter space for both spin-independent and spin-dependent WIMP-nucleon elastic scattering. The resulting limit on the spin-independent WIMP-nucleon elastic-scattering cross section has a minimum of 4×10^-43  cm² at a WIMP mass of 60  GeVc^-2. The minimum of the limit for the spin-dependent WIMP-neutron elastic-scattering cross section is 2×10^-37  cm² at a WIMP mass of 50  GeVc^-2.

We report the first results from a search for weakly interacting massive particles (WIMPs) in the Cryogenic Dark Matter Search experiment at the Soudan Underground Laboratory. Four Ge and two Si detectors were operated for 52.6 live days, providing 19.4 kg d of Ge net exposure after cuts for recoil energies between 10 and 100 keV. A blind analysis was performed using only calibration data to define the energy threshold and selection criteria for nuclear-recoil candidates. Using the standard dark-matter halo and nuclear-physics WIMP model, these data set the world's lowest exclusion limits on the coherent WIMP-nucleon scalar cross section for all WIMP masses above 15  GeV/c², ruling out a significant range of neutralino supersymmetric models. The minimum of this limit curve at the 90% C.L. is 4×10^-43  cm² at a WIMP mass of 60  GeV/c².

Using improved Ge and Si detectors, better neutron shielding, and increased counting time, the Cryogenic Dark Matter Search (CDMS) experiment has obtained stricter limits on the cross section of weakly interacting massive particles (WIMPs) elastically scattering from nuclei. Increased discrimination against electromagnetic backgrounds and reduction of the neutron flux confirm WIMP-candidate events previously detected by CDMS were consistent with neutrons and give limits on spin-independent WIMP interactions which are >2× lower than previous CDMS results for high WIMP mass, and which exclude new parameter space for WIMPs with mass between 8 and 20 GeV/c².

The Cryogenic Dark Matter Search (CDMS) employs low-temperature Ge and Si detectors to search for weakly interacting massive particles (WIMPs) via their elastic-scattering interactions with nuclei while discriminating against interactions of background particles. For recoil energies above 10 keV, events due to background photons are rejected with >99.9% efficiency, and surface events are rejected with >95% efficiency. The estimate of the background due to neutrons is based primarily on the observation of multiple-scatter events that should all be neutrons. Data selection is determined primarily by examining calibration data and vetoed events. Resulting efficiencies should be accurate to ∼10%. Results of CDMS data from 1998 and 1999 with a relaxed fiducial-volume cut (resulting in 15.8 kg days exposure on Ge) are consistent with an earlier analysis with a more restrictive fiducial-volume cut. Twenty-three WIMP candidate events are observed, but these events are consistent with a background from neutrons in all ways tested. Resulting limits on the spin-independent WIMP-nucleon elastic-scattering cross section exclude unexplored parameter space for WIMPs with masses between 10–70 GeV/c². These limits border, but do not exclude, parameter space allowed by supersymmetry models and accelerator constraints. Results are compatible with some regions reported as allowed at 3σ by the annual-modulation measurement of the DAMA Collaboration. However, under the assumptions of standard WIMP interactions and a standard halo, the results are incompatible with the DAMA most likely value at >99.9% confidence level (C.L.), and are incompatible with the model-independent annual-modulation signal of DAMA at 99.99% C.L. in the asymptotic limit.

The Cryogenic Dark Matter Search (CDMS) employs Ge and Si detectors to search for weakly interacting massive particles (WIMPs) via their elastic-scattering interactions with nuclei while discriminating against interactions of background particles. CDMS data, accounting for the neutron background, give limits on the spin-independent WIMP-nucleon elastic-scattering cross section that exclude unexplored parameter space above 10 GeV/c² WIMP mass and, at >75% C.L., the entire 3σ allowed region for the WIMP signal reported by the DAMA experiment.

An upper limit on the branching ratio for the decay K⁺→e⁺νμ⁺μ^- is set at 5.0×10^-7 at a 90% confidence level, consistent with predictions from chiral perturbation theory.

We have observed the rare decay K⁺→π⁺μ⁺μ^- and measured the branching ratio γ(K⁺→π⁺μ⁺μ^-)/γ(K⁺→all)  =  [5.0±0.4(stat)±0.7(syst)±0.6(th)]×10^-8. We compare this result with predictions from chiral perturbation theory and estimates based on the decay K⁺→π⁺e⁺e^-.

The first observation of the decay K⁺→π⁺γγ is reported. A total of 31 events was observed with an estimated background of 5.1±3.3 events in the π⁺ momentum range from 100 to 180 MeV/c. The corresponding partial branching ratio, B(K⁺→π⁺γγ,100 MeV/c<P_π⁺<180 MeV/c), is [6.0±1.5(stat)±0.7(syst)]×10^-7. No K⁺→π⁺γγ decay was observed in the π⁺ momentum region greater than 215 MeV/c. The observed π⁺ momentum spectrum is compared with the predictions of chiral perturbation theory.

An upper limit on the branching ratio for the decay K⁺→π⁺νν̅ is set at 2.4×10^-9 at the 90% C.L. using pions in the kinematic region 214 MeV/c<P_π<231 MeV/c. An upper limit of 5.2×10^-10 is found on the branching ratio for decays K⁺→π⁺X⁰, where X⁰ is any massless, weakly interacting neutral particle. Limits are also set for cases where M_X⁰>0.

A measurement of the cross section for γγ→pp¯ is performed at two-photon center-of-mass energies between 2.00 and 3.25 GeV. These results are obtained using e⁺e^-→e⁺e^-pp¯ events selected from 1.31 fb^-1 of data taken with the CLEO II detector. The measured cross section is in reasonable agreement with previous measurements and is in excellent agreement with recent calculations based on a diquark model. However, leading order QCD calculations performed using the Brodsky-Lepage formalism are well below the measured cross section.

The CLEO II detector is used to search for the production of χ_c2 states in two-photon interactions. We use the signature χ_c2→γJ/ψ→γl⁺l^- with l=e,μ. Using 1.49 fb^-1 of data taken with beam energies near 5.29 GeV, the two-photon width of the χ_c2 is determined to be Γ(χ_c2→γγ)=1.08±0.30(stat)±0.26(syst) keV, in agreement with predictions from perturbative QCD.

Using data collected in the region of the γ(4S) resonance with the CLEO II detector operating at the Cornell Electron Storage Ring, we report on evidence for the production of Σ_c⁺⁺ and Σ_c⁰ baryons in B decays, with Σ_c→Λ_c⁺π. This observation is based on 77±19 Σ_c⁺⁺ and 76±21 Σ_c⁰ candidates from B decays. We find the product branching fractions B(B̅ →Σ_cX)B(Λ_c⁺→pK^-π⁺) for Σ_c=Σ_c⁺⁺, Σ_c⁰, and Σ_c⁺ to be (2.1 ± 0.8 ± 0.7) × 10^-4, (2.3 ± 0.8 ± 0.7) × 10^-4, and less than 4.8 × 10^-4 at 90% confidence level, respectively. A study of the Σ_c⁺⁺ and Σ_c⁰ momentum spectra indicates that B decays to two-body final states with Σ_c are suppressed.

A measurement of the cross section for the combined two-photon production of charged pion and kaon pairs is performed using 1.2 fb^-1 of data collected by the CLEO II detector at the Cornell Electron Storage Ring. The cross section is measured at invariant masses of the two-photon system between 1.5 and 5.0 GeV/c², and at scattering angles more than 53° away from the γγ collision axis in the γγ center-of-mass frame. The large background of leptonic events is suppressed by utilizing the CsI calorimeter in conjunction with the muon chamber system. The reported cross section is compared with leading order QCD models as well as previous experiments. Although the functional dependence of the measured cross section disagrees with leading order QCD at small values of the two-photon invaraint mass, the data show qualitatively a transition to perturbative behavior at an invariant mass of approximately 2.5 GeV/c².

Branching ratios for the dominant Cabibbo-suppressed decays of the τ lepton have been measured by CLEO II in e⁺e^- annihilation at the Cornell Electron Storage Ring (sqrt[s]∼10.6 GeV) using kaons with momenta below 0.7 GeV/c. The inclusive branching ratio into one charged kaon is (1.60 ± 0.12 ± 0.19)%. For the exclusive decays, B(τ^-→K^-ν_τ)=(0.66±0.07±0.09)%, B(τ^-→K^-π⁰ν_τ)=(0.51±0.10±0.07)%, and, based on three events, B(τ^-→K^-2π⁰ν_τ)<0.3% at the 90% confidence level. These represent significant improvements over previous results. B(τ^-→K^-π⁰ν_τ) is measured for the first time with exclusive π⁰ reconstruction.

We have measured the vector-pseudoscalar mass splitting M(D_s^*+)-M(D_s⁺)=144.22±0.47±0.37 MeV significantly more precisely than the previous world average. We minimize the systematic errors by also measuring the vector-pseudoscalar mass difference M(D^*0)-M(D⁰) using the radiative decay D^*0→D⁰γ, obtaining [M(D_s^*+)-M(D_s⁺)]-[M(D^*0)-M(D⁰)] =2.09±0.47±0.37 MeV. This is then combined with our previous high-precision measurement of M(D^*0)-M(D⁰), which used the decay D^*0→D⁰π⁰. We also measure the mass difference M(D_s⁺)-M(D⁺)=99.5±0.6±0.3 MeV, using the φπ⁺ decay modes of the D_s⁺ and D⁺ mesons.

We have fully reconstructed decays of both B¯⁰ and B^- mesons into final states containing either D, D^*, D^**, ψ, ψ’, or χ_c1 mesons. This allows us to obtain new results on many physics topics including branching ratios, tests of the factorization hypothesis, color suppression, resonant substructure, and the B^--B¯⁰ mass difference.

We have searched for B⁰ decays to two charged leptons and set 90% confidence level upper limits on the branching fractions: B(B⁰→e⁺e^-)<5.9×10^-6, B(B⁰→μ⁺μ^-)<5.9×10^-6, B(B⁰→e^±μ^∓)<5.9×10^-6, B(B⁰→e^±τ^∓)<5.3×10^-4, and B(B⁰→μ^±τ^∓)<8.3×10^-4.

We present a measurement of Γ(D_s⁺→μ⁺ν) / Γ(D_s⁺→φπ⁺)=0.245±0.052±0.074. Using this ratio and B(D_s⁺→φπ⁺)=(3.7±0.9)% we extract f_Ds=344±37±52±42 MeV, where the last error is due to the uncertainty in the D_s⁺→φπ⁺ absolute branching ratio. This result is larger than most theoretical predictions.

Using the CLEO II detector at the Cornell Electron Storage Ring we have measured the ratio of branching fractions, B(D⁺→K^-π⁺π⁺)/(D⁰→K^-π⁺)=2.35±0.16±0.16. Our recent measurement of scrB(D⁰→K^-π⁺) then gives scrB(D⁺→K^-π⁺π⁺)=(9.3±0.6±0.8)%.

Using the CLEO II detector, we have obtained evidence for a new meson decaying to D⁰K⁺. Its mass is 2573.2_-1.6^+1.7±0.8±0.5 MeV/c² and its width is 16_-4⁺⁵±3 MeV/c². Although we do not establish its spin and parity, the new meson is consistent with predictions for an L=1, S=1, J^P=2⁺ charmed strange state.

Using the CLEO II data sample, with an integrated luminosity of 1.8 fb^-1 at and near the Υ(4S) resonance, we have observed a signal for D⁰→K⁺π^-, which could be due to either D⁰D¯⁰ mixing or doubly Cabibbo suppressed decay, or a combination of the two. We find scrB(D⁰→K⁺π^-)/scrB(D⁰→K^-π⁺)=0.0077±0 .0025(stat) ±0.0025(syst).

Using the CLEO II detector, we have measured the branching fractions for ϒ(3S)→ππϒ(1S), ϒ(3S)→ππϒ(2S), and the cascade ϒ(3S)→ϒ(2S)+X, ϒ(2S)→π⁺π^-ϒ(1S), analyzing the exclusive mode where the daughter ϒ state decays to a e⁺e^- or μ⁺μ^- pair, as well as the inclusive π⁺π^- transitions where the final ϒ state decays into hadrons. Properties of the ππ system are analyzed. Searches for the cascade decay ϒ(3S)→π⁺π^-h_b, h_b→γη_b and ϒ(3S)→π⁰h_b were also performed.

Using the CLEO II detector and a sample of 955 000 Υ(4S) decays we have confirmed charmless semileptonic decays of B mesons. In the momentum interval 2.3–2.6 GeV/c we observe an excess of 107±15±11 leptons, which we attribute to b→ulν. This result yields a model-dependent range of values for ‖V_ub/V_cb‖ that is lower than has been obtained in previous studies. For the inclusive spectator model of Altarelli et al. we find ‖V_ub/V_cb‖=0.076±0.008. Models that describe b→ulν with a limited set of exclusive final states give ‖V_ub/V_cb‖=0.06-0.10.