Search Results (28 total)

Measurements of the double-differential π^± production cross section in the range of momentum 0.5≤p≤8.0 GeV/c and angle 0.025≤θ≤0.25 rad in collisions of protons on beryllium, carbon, nitrogen, oxygen, aluminum, copper, tin, tantalum, and lead are presented. The data were taken with the large-acceptance HAdRon Production (HARP) detector in the T9 beamline of the CERN Proton Synchrotron. Incident particles were identified by an elaborate system of beam detectors. Thin targets of 5% of a nuclear interaction length were used. The tracking and identification of the produced particles were performed using the forward system of the HARP experiment. Results are obtained for the double-differential cross sections d²σ/dp dΩ mainly at four incident proton beam momenta (3, 5, 8, and 12 GeV/c). Measurements are compared with the GEANT4 and MARS Monte Carlo generators. A global parametrization is provided as an approximation of all the collected datasets, which can serve as a tool for quick yield estimates.

Single charged pion production in charged-current muon neutrino interactions with carbon is studied using data collected in the K2K long-baseline neutrino experiment. The mean energy of the incident muon neutrinos is 1.3 GeV. The data used in this analysis are mainly from a fully active scintillator detector, SciBar. The cross section for single π⁺ production in the resonance region (W<2  GeV/c²) relative to the charged-current quasielastic cross section is found to be 0.734_-0.153^+0.140. The energy-dependent cross section ratio is also measured. The results are consistent with a previous experiment and the prediction of our model.

Measurements of the double-differential π^± production cross section in the momentum range 100≤p≤800 MeV/c and angle range 0.35≤θ≤2.15 rad in proton-beryllium, proton-carbon, proton-aluminium, proton-copper, proton-tin, proton-tantalum, and proton-lead collisions are presented. The data were taken with the large-acceptance HARP detector in the T9 beam line of the CERN PS. The pions were produced by proton beams in a momentum range from 3 to 12.9 GeV/c hitting a target with a thickness of 5% of a nuclear interaction length. Tracking and identification of the produced particles was performed by using a small-radius cylindrical Time Projection Chamber (TPC) placed inside a solenoidal magnet. Incident particles were identified by an elaborate system of beam detectors. Results are obtained for the double-differential cross sections d²σ/(dpdθ) at six incident proton beam momenta [3, 5, 8, and 8.9 GeV/c (Be only) and 12 and 12.9 GeV/c (Al only)]. They are based on a complete correction of static and dynamic distortions of tracks in the HARP TPC, which allows the complete statistics of the collected data set to be used. The results include and supersede our previously published results and are compatible with these. Results are compared with the GEANT4 and MARS Monte Carlo simulation.

The atmospheric neutrino background for proton decay via p→e⁺π⁰ in ring imaging water Cherenkov detectors is studied with an artificial accelerator neutrino beam for the first time. In total, 3.14×10⁵ neutrino events corresponding to about 10 megaton-years of atmospheric neutrino interactions were collected by a 1000 ton water Cherenkov detector (KT). The KT charged-current single π⁰ production data are well reproduced by simulation programs of neutrino and secondary hadronic interactions used in the Super-Kamiokande (SK) proton decay search. The obtained p→e⁺π⁰ background rate by the KT data for SK from the atmospheric neutrinos whose energies are below 3 GeV is 1.63_-0.33^+0.42(stat)_-0.51^+0.45(syst)(megaton-year)^-1. This result is also relevant to possible future, megaton-scale water Cherenkov detectors.

We present measurements of ν_μ disappearance in K2K, the KEK to Kamioka long-baseline neutrino oscillation experiment. One-hundred and twelve beam-originated neutrino events are observed in the fiducial volume of Super-Kamiokande with an expectation of 158.1_-8.6^+9.2 events without oscillation. A distortion of the energy spectrum is also seen in 58 single-ring muonlike events with reconstructed energies. The probability that the observations are explained by the expectation for no neutrino oscillation is 0.0015% (4.3σ). In a two-flavor oscillation scenario, the allowed Δm² region at sin⁡²2θ=1 is between 1.9 and 3.5×10^-3  eV² at the 90% C.L. with a best-fit value of 2.8×10^-3  eV².

The weak nucleon axial-vector form factor for quasielastic interactions is determined using neutrino interaction data from the K2K Scintillating Fiber detector in the neutrino beam at KEK. More than 12 000 events are analyzed, of which half are charged-current quasielastic interactions ν_μn→μ^-p occurring primarily in oxygen nuclei. We use a relativistic Fermi gas model for oxygen and assume the form factor is approximately a dipole with one parameter, the axial-vector mass M_A, and fit to the shape of the distribution of the square of the momentum transfer from the nucleon to the nucleus. Our best fit result for M_A=1.20±0.12  GeV. Furthermore, this analysis includes updated vector form factors from recent electron scattering experiments and a discussion of the effects of the nucleon momentum on the shape of the fitted distributions.

We performed an improved search for ν_μ→ν_e oscillation with the KEK to Kamioka (K2K) long-baseline neutrino oscillation experiment, using the full data sample of 9.2×10¹⁹ protons on target. No evidence for a ν_e appearance signal was found, and we set bounds on the ν_μ→ν_e oscillation parameters. At Δm²=2.8×10^-3  eV², the best-fit value of the K2K ν_μ disappearance analysis, we set an upper limit of sin⁡²2θ_μe<0.13 at a 90% confidence level.

We report the result from a search for charged-current coherent pion production induced by muon neutrinos with a mean energy of 1.3 GeV. The data are collected with a fully active scintillator detector in the K2K long-baseline neutrino oscillation experiment. No evidence for coherent pion production is observed, and an upper limit of 0.60×10^-2 is set on the cross section ratio of coherent pion production to the total charged-current interaction at 90% confidence level. This is the first experimental limit for coherent charged pion production in the energy region of a few GeV.

We present results for ν_μ oscillation in the KEK to Kamioka (K2K) long-baseline neutrino oscillation experiment. K2K uses an accelerator-produced ν_μ beam with a mean energy of 1.3 GeV directed at the Super-Kamiokande detector. We observed the energy-dependent disappearance of ν_μ, which we presume have oscillated to ν_τ. The probability that we would observe these results if there is no neutrino oscillation is 0.0050% (4.0σ).

We describe the status of our effort to realize a first neutrino factory and the progress made in understanding the problems associated with the collection and cooling of muons towards that end. We summarize the physics that can be done with neutrino factories as well as with intense cold beams of muons. The physics potential of muon colliders is reviewed, both as Higgs factories and compact high-energy lepton colliders. The status and time scale of our research and development effort is reviewed as well as the latest designs in cooling channels including the promise of ring coolers in achieving longitudinal and transverse cooling simultaneously. We detail the efforts being made to mount an international cooling experiment to demonstrate the ionization cooling of muons.

The status of the research on muon colliders is discussed and plans are outlined for future theoretical and experimental studies. Besides work on the parameters of a 3–4 and 0.5 TeV center-of-mass (COM) energy collider, many studies are now concentrating on a machine near 0.1 TeV (COM) that could be a factory for the s-channel production of Higgs particles. We discuss the research on the various components in such muon colliders, starting from the proton accelerator needed to generate pions from a heavy-Z target and proceeding through the phase rotation and decay (π→μν_μ) channel, muon cooling, acceleration, storage in a collider ring, and the collider detector. We also present theoretical and experimental R&D plans for the next several years that should lead to a better understanding of the design and feasibility issues for all of the components. This report is an update of the progress on the research and development since the feasibility study of muon colliders presented at the Snowmass '96 Workshop [R. B. Palmer, A. Sessler, and A. Tollestrup, Proceedings of the 1996 DPF/DPB Summer Study on High-Energy Physics (Stanford Linear Accelerator Center, Menlo Park, CA, 1997)].

We consider the virtual effects of a general type of anomalous (triple) gauge coupling on various experimental observables in the process of electron-positron annihilation into a final fermion-antifermion state. We show that the use of a recently proposed "Z-peak subtracted" theoretical description of the process allows us to reduce substantially the number of relevant parameters of the model, so that a calculation of observability limits can be performed in a rather simple way. As an illustration of our approach, we discuss the cases of future measurements at the CERN e⁺e^- collider LEP 2 and at a new 500 GeV linear collider.

The ratio R_ν of the neutral- to charged-current cross sections of neutrinos in iron has been measured in an exposure of the CERN-Dortmund-Heidelberg-Saclay neutrino detector to a 160-GeV/c neutrino narrow-band beam at the CERN Super Proton Synchrotron. The result is R_ν=0.3072±0.0025(stat)±0.0020(syst), for hadronic energy greater than 10 GeV. The electroweak mixing parameter is sin²θ_W=0.225±0.005(expt)±0.003(theor)+0.013(m_c-1.5 GeV / c²), where m_c is the charm-quark mass.

Measurements of ψ(3097) and ψ^′(3686) branching fractions for selected hadronic decays are presented. The ratio of ψ^′ to ψ branching fractions for these decays is consistent with the ratio of branching fractions to lepton pairs, with the exception of the decays to pπ and K^*K for which this ratio is substantially smaller.

The total momentum and transverse momentum spectra of electrons in e⁺e^- annihilation at 29 GeV have been measured. The inclusive cross section is determined to be 14.4±1.6±5.2 pb for momenta greater than 2 GeV/c. The average semielectronic branching ratios of charm and bottom quarks are measured to be (6.3±1.2±2.1)% and (11.6±2.1±1.7)%, respectively. The fragmentation function for bottom quarks is determined to be peaked at high z, with 〈z〉_b=0.75±0.05±0.04.

Two-photon interactions have been studied with the SLAC-LBL Mark II magnetic detector at SPEAR. The cross section for η^′ production by the reaction e⁺e^-→e⁺e^-η^′ has been measured at beam energies from 2.0 to 3.7 GeV. The radiative width Γ_γγ(η^′) has been determined to be 5.8±1.1 keV (±20% systematic uncertainty). Upper limits on the radiative widths of the f(1270), A₂(1310), and f^′(1515) tensor mesons have been determined. A search has been made for production of the E(1420) by γγ collisions, but no signal is observed.

The charged-particle multiplicity distribution in τ decays is determined from data collected at the e⁺e^- storage ring PEP. The one-, three-, and five-charged-particle inclusive branching fractions are (86 ± 2)%, (14 ± 2)%, and < 0.5%, respectively.

The Mark II detector at SPEAR has been used to study D-meson production in e⁺e^- annihilation at center-of-mass energies between 3.8 and 6.7 GeV. The neutral and charged D mesons are identified from their K^∓π^± and K^∓π^±π^± decay modes. Measurements of R_D and of the inclusive differential cross section s dσ / dz are presented. The quasi-two-body cross sections σ_DD̅ , σ_D^*D̅ , and σ_{D^*D̅ ^*} are derived from an overall fit to the D recoil spectra. No evidence was found for the associated production of charmed mesons and charmed baryons.

Measurements are presented of the inclusive charged-particle cross sections s dσ / dx for e⁺e^- annihilation at center-of-mass energies of 5.2, 6.5, and 29.0 GeV. Significant scale breaking is observed in these cross sections.

Energy correlations have been measured with the MARK II detector at the PEP storage ring (Stanford Linear Accelerator Center) at c.m. energy of 29 GeV and are compared to first-order QCD predictions. Fragmentation processes are significant and limit the precision with which the first-order strong-coupling constant can be determined.

A search for charged, pointlike, spin-0 particles with large couplings to the τ lepton has been done at the PEP e⁺e^- storage ring (Stanford Linear Accelerator Center). No evidence for such particles is seen, and limits are placed on the branching fraction to τν_τ as a function of mass.

The production of the charmed meson state D^*+ has been observed in e⁺e^- annihilation at 29 GeV. The fragmentation function for charmed quarks appears to be peaked about z=0.5.

The branching fraction for the Cabibbo-suppressed decay τ^-→K^-ν_τ is measured from data obtained with the Mark II detector at SPEAR. Fifteen events containing a K^± in coincidence with a muon or electron of opposite charge are observed. It is determined that B(τ^-→K^-ν_τ)=(1.3±0.5)%.

Searches for 12 neutrinoless decay modes of the τ which violate lepton-number conservation have been made using the reaction e⁺e^-→τ⁺τ^-. No evidence for lepton-number violation is observed, and we have set upper limits (90% C.L.) on the branching ratio for each decay mode. The branching-ratio limits on the radiative decays τ→μγ and τ→eγ are 0.055 and 0.064%, respectively. For the charged lepton decays τ→eee, τ→eμμ, τ→μee, and τ→μμμ, the branching ratio limits are 0.040, 0.033, 0.044, and 0.049%, respectively. Upper limits on the branching ratios for the following charged lepton + neutral hadron decays are τ→eρ⁰ (0.037%), τ→μρ⁰ (0.044%), τ→eK⁰ (0.13%), τ→μK⁰ (0.10%), τ→eπ⁰ (0.21%), and τ→μπ⁰ (0.082%). We also use these data to search for the pair production in e⁺e^- annihilation of some unconventional particles with masses less than about 3 GeV/c².

Direct electrons are observed in baryon events produced in e⁺e^- annihilation at center-of-mass energies above the Λ_cΛ̅ _c threshold. These events are attributed to charmed-baryon pair production and subsequent Λ_c semileptonic decay. Various semileptonic branching ratios of the Λ_c are determined, including B(Λ_c→e⁺X)=(4.5±1.7)%.