Search Results (22 total)

This Letter reports results from the MINOS experiment based on its initial exposure to neutrinos from the Fermilab NuMI beam. The rates and energy spectra of charged current ν_μ interactions are compared in two detectors located along the beam axis at distances of 1 and 735 km. With 1.27×10²⁰ 120 GeV protons incident on the NuMI target, 215 events with energies below 30 GeV are observed at the Far Detector, compared to an expectation of 336±14 events. The data are consistent with ν_μ disappearance via oscillations with |Δm₃₂²|=2.74_-0.26^+0.44×10^-3  eV² and sin⁡²(2θ₂₃)>0.87 (68% C.L.).

The complete 5.4 kton MINOS far detector has been taking data since the beginning of August 2003 at a depth of 2070 meters water-equivalent in the Soudan mine, Minnesota. This paper presents the first MINOS observations of ν_μ and ν̅ _μ charged-current atmospheric neutrino interactions based on an exposure of 418 days. The ratio of upward- to downward-going events in the data is compared to the Monte Carlo expectation in the absence of neutrino oscillations, giving R_up/down^data/R_up/down^MC=0.62_-0.14^+0.19(stat.)±0.02(sys.). An extended maximum likelihood analysis of the observed L/E distributions excludes the null hypothesis of no neutrino oscillations at the 98% confidence level. Using the curvature of the observed muons in the 1.3 T MINOS magnetic field ν_μ and ν̅ _μ interactions are separated. The ratio of ν̅ _μ to ν_μ events in the data is compared to the Monte Carlo expectation assuming neutrinos and antineutrinos oscillate in the same manner, giving R_{ν̅ μ/νμ}^data/R_{ν̅ μ/νμ}^MC=0.96_-0.27^+0.38(stat.)±0.15(sys.), where the errors are the statistical and systematic uncertainties. Although the statistics are limited, this is the first direct observation of atmospheric neutrino interactions separately for ν_μ and ν̅ _μ.

We report on a precision measurement of the parity-violating asymmetry in fixed target electron-electron (Møller) scattering: A_PV=[-131±14(stat)±10(syst)]×10^-9, leading to the determination of the weak mixing angle sin⁡²θ_W^eff=0.2397±0.0010(stat)±0.0008(syst), evaluated at Q²=0.026  GeV². Combining this result with the measurements of sin⁡²θ_W^eff at the Z⁰ pole, the running of the weak mixing angle is observed with over 6σ significance. The measurement sets constraints on new physics effects at the TeV scale.

We report a measurement of the parity-violating asymmetry in fixed target electron-electron (Møller) scattering: A_PV=[-175±30(stat)±20(syst)]×10^-9. This first direct observation of parity nonconservation in Møller scattering leads to a measurement of the electron’s weak charge at low energy Q_W^e=-0.053±0.011. This is consistent with the standard model expectation at the current level of precision: sin⁡²θ_W(M_Z)_MS̅ =0.2293±0.0024(stat)±0.0016(syst)±0.0006(theory).

We report on the extraction of R  =  σ_L / σ_T from CCFR ν_μ-Fe and ν̅ _μ-Fe differential cross sections. The CCFR differential cross sections do not show the deviations from the QCD expectations that are seen in the CDHSW data at very low and very high x. R as measured in ν_μ scattering is in agreement with R as measured in muon and electron scattering. All data on R for Q²>1 GeV² are in agreement with a NNLO QCD calculation which uses NNLO parton distribution functions and includes target mass effects. We report on the first measurements of R in the low x and Q²<1 GeV² region (where an anomalous large rise in R for nuclear targets has been observed by the HERMES Collaboration).

A new structure function analysis of CCFR deep inelastic ν-N and ν̅ -N scattering data is presented for previously unexplored kinematic regions down to Bjorken x  =  0.0045 and Q²  =  0.3 GeV². Comparisons to charged lepton scattering data from NMC and E665 experiments are made and the behavior of the structure function F₂^ν is studied in the limit Q²→0.

We report on the extraction of the structure functions F₂ and ΔxF₃  =  xF₃^ν-xF₃^ν̅ from CCFR ν_μ-Fe and ν̅ _μ-Fe differential cross sections. The extraction is performed in a physics model-independent (PMI) way. This first measurement of ΔxF₃, which is useful in testing models of heavy charm production, is higher than current theoretical predictions. The ratio of the F₂ (PMI) values measured in ν_μ and μ scattering is in agreement (within 5%) with the predictions of next-to-leading-order parton distribution functions using massive charm production schemes, thus resolving the long-standing discrepancy between the two sets of data.

We report results from Experiment 871, performed at the BNL AGS, of a measurement of the branching ratio K_L⁰→μ⁺μ^- with respect to the CP-violating mode K_L⁰→π⁺π^-. This experiment detected over 6200 candidate μ⁺μ^- events, a factor of 6 more than that seen in all previous measurements combined. The resulting branching ratio Γ(K_L⁰→μ⁺μ^-)/Γ(K_L⁰→π⁺π^-)  =  (3.474±0.057)×10^-6 leads to a branching fraction B(K_L⁰→μ⁺μ^-)  =  (7.18±0.17)×10^-9, which is consistent with the current world average, and reduces the uncertainty in this decay mode by a factor of 3.

Data from the CCFR E770 neutrino deep inelastic scattering experiment at Fermilab contain events with a large Bjorken x (x>0.7) and high momentum transfer [Q²>50 (GeV/c)²]. A comparison of the data with a model based on no nuclear effects at large x shows a significant excess of events in the data. The addition of Fermi gas motion of the nucleons in the nucleus to the model does not explain the excess. Adding a higher momentum tail due to the formation of “quasi-deuterons” makes some improvement. An exponentially falling F₂∝e^-s(x-x₀) at large x, predicted by “multi-quark clusters” and “few-nucleon correlations,” can describe the data. A value of s=8.3±0.7(stat)±0.7(syst) yields the best agreement with the data.

We present new limits on v_e(v_e)→v_τ(v_τ) and v_e(v_e)→v_s oscillations by searching for v_e disappearance in the high-energy wideband CCFR neutrino beam. Sensitivity to v_τ appearance comes from τ decay modes in which a large fraction of the energy deposited is electromagnetic. The beam is composed primarily of v_μ(v_μ), but this analysis uses the 2.3% v_e(v_e) component of the beam. Electron neutrino energies range from 30 to 600 GeV and flight lengths vary from 0.9 to 1.4 km. This limit improves the sensitivity of existing limits for v_e→v_τ at high Δm² and obtains a lowest 90% confidence upper limit in sin² 2α of 9.9×10^-2 at Δm²∼125 eV².

The most sensitive experiment to date to search for the muon and electron lepton number violating decay K_L⁰→μ^±e^∓ has detected no events consistent with this process. Based on this result, the 90% confidence level upper limit on the branching fraction is B(K_L⁰→μ^±e^∓)<4.7×10^-12.

In an experiment designed to search for and study very rare two-body decay modes of the K_L⁰, we have observed four examples of the decay K_L⁰→e⁺e^-, where the expected background is 0.17±0.10 events. This observation translates into a branching fraction of 8.7_-4.1^+5.7×10^-12, consistent with recent theoretical predictions. This result represents by far the smallest branching fraction yet measured in particle physics.

We extract a set of values for the Gross–Llewellyn Smith sum rule at different values of 4-momentum transfer squared ( Q²), by combining revised CCFR neutrino data with data from other neutrino deep-inelastic scattering experiments for 1<Q²<15 GeV²/c². A comparison with the order α_s³ theoretical predictions yields a determination of α_s at the scale of the Z-boson mass of 0.114±_0.012^0.009. This measurement provides a new and useful test of perturbative QCD at low Q², because of the low uncertainties in the higher order calculations.

We present an improved determination of the proton structure functions F₂ and xF₃ from the Columbia-Chicago-Fermilab-Rochester Collaboration ν-Fe deep inelastic scattering experiment. Comparisons to corrected high-statistics charged-lepton scattering results for F₂ from the NMC, E665, SLAC, and BCDMS experiments indicate good agreement for x>0.1 but some discrepancy at lower x. The Q² evolution of both the F₂ and xF₃ structure functions yields a value of the strong coupling constant at the scale of mass of the Z boson of α_s(M_Z²)  =  0.119±0.002(expt)±0.004(theory). This is one of the most precise measurements of this quantity.

Limits on ν_μ(ν̅ _μ)→ν_e(ν̅ _e) oscillations based on a statistical separation of ν_eN charged current interactions in the CCFR detector at Fermilab are presented. Neutrino energies range from 30 to 600 GeV with a mean of 140 GeV, and ν_μ flight lengths vary from 0.9 to 1.4 km. The result excludes oscillations in the region with sin²2α>1.8×10^-3 for large Δm² (>1000 eV²) and Δm²>1.6 eV² for sin²2α  =  1. This result is the most stringent limit to date for Δm²>25 eV² and it excludes the high Δm² oscillation region favored by the LSND experiment. The ν_μ-to- ν_e cross-section ratio was measured as a test of ν_μ(ν̅ _μ)↔ν_e(ν̅ _e) universality to be 1.026±0.025(stat)±0.049(syst).

We present limits on ν_μ(ν̅ _μ)→ν_τ(ν̅ _τ) and ν_μ(ν̅ _μ)→ν_e(ν̅ _e) oscillations based on a study of inclusive νN interactions performed using the CCFR massive coarse-grained detector in the Fermilab Tevatron Quadrupole Triplet neutrino beam. The sensitivity to oscillations is from the difference in the longitudinal energy deposition pattern of ν_μN vs ν_τN or ν_eN charged-current interactions. The ν_μ energies ranged from 30 to 500 GeV with a mean of 140 GeV. The minimum and maximum ν_μ flight lengths are 0.9 and 1.4 km, respectively. For ν_μ→ν_τ oscillations, the lowest 90% confidence upper limit in sin²2α of 2.7 × 10^-3 is obtained at Δm²∼50 eV². This result is the most stringent limit to date for 25<Δm²<90 eV². For ν_μ→ν_e oscillations, the lowest 90% confidence upper limit in sin²2α of 1.9 × 10^-3 is obtained at Δm²∼350 eV². This result is the most stringent limit to date for 250<Δm²<450 eV², and also excludes at 90% confidence much of the high Δm² region favored by the recent LSND observation.

We report a precise measurement of the weak mixing angle from the ratio of neutral current to charged current inclusive cross sections in deep-inelastic neutrino-nucleon scattering. The data were gathered at the CCFR neutrino detector in the Fermilab quadrupole-triplet beam, with neutrino energies up to 600 GeV. Using the on-shell definition, sin²θ_W==1-M_W²/M_Z², we obtain sin²θ_W=0.2218±0.0025(stat)±0.0036(expt syst)±0.0037(model).

The CCFR Collaboration presents a measurement of scaling violations of the nonsinglet structure function and a comparison to the predictions of perturbative QCD. The value of Λ_QCD, from the nonsinglet evolution with Q²>15 GeV² and in the modified minimal-subtraction renormalization scheme, is found to be 210±28(stat)±41(syst) MeV.

We present the first measurement of the left-right cross section asymmetry (A_LR) for Z boson production by e⁺e^- collisions. The measurement was performed at a center-of-mass energy of 91.55 GeV with the SLD detector at the SLAC Linear Collider which utilized a longitudinally polarized electron beam. The average beam polarization was (22.4±0.6)%. Using a sample of 10 224 Z decays, we measure A_LR to be 0.100±0.044(stat)±0.004(syst), which determines the effective weak mixing angle to be sin²θ_W^eff=0.2378 ±0.0056(stat)±0.0005(syst).

A high-statistics study by the Columbia-Chicago-Fermilab-Rochester Collaboration of opposite-sign dimuon events induced by neutrino-nucleon scattering at the Fermilab Tevatron is presented. A sample of 5044 ν_μ and 1062 ν¯_μ induced μ^∓μ^± events with P_μ1≥9 GeV/c, P_μ2≥5 GeV/c, 30≤E_ν≤600 GeV, and 〈Q²〉=22.2 GeV²/c² is observed. The data support the slow-rescaling model of charm production with a value of m_c=1.31±0.24 GeV²/c². The first measurement of the Q² dependence of the nucleon strange quark distribution xs(x) is presented. The data yield the Cabibbo-Kobayashi-Maskawa matrix element ‖V_cd‖=0.209±0.012 and the nucleon fractional strangeness content η_s=0.064_-0.007^+0.008.

The relative absence of ν¯_μ-induced charged current events with respect to ν_μ-induced events at large (>0.45) and large y (>0.70) enables us to limit the right handed coupling of the weak current. Our data restrict ‖η‖²=‖g_R/g_L‖²<0.0 015 with 90% C.L. Within the framework of left-right symmetric models, this measurement imposes a limit upon the mixing angle of the left and right handed bosons. Unlike the limits imposed by the μ-decay and nuclear β-decay experiments, our limit is valid irrespective of the mass of the right handed neutrino.

We present a measurement of neutrino tridents, muon pairs induced by neutrino scattering in the Coulomb field of a target nucleus, in the Columbia-Chicago-Fermilab-Rochester neutrino experiment at the Fermilab Tevatron. The observed number of tridents after geometric and kinematic corrections, 37.0±12.4, supports the standard-model prediction of 45.3±2.3 events. This is the first demonstration of the W-Z destructive interference from neutrino tridents, and rules out, at 99% C.L., the V-A prediction without the interference.