Search results for "PARTICLE PHYSICS"

Search for heavy neutral lepton production in K+ decays

2018

A search for heavy neutral lepton production in $K^+$ decays using a data sample collected with a minimum bias trigger by the NA62 experiment at CERN in 2015 is reported. Upper limits at the $10^{-7}$ to $10^{-6}$ level are established on the elements of the extended neutrino mixing matrix $|U_{\ell 4}|^2$ ($\ell=e,\mu$) for heavy neutral lepton mass in the range $170-448~{\rm MeV}/c^2$. This improves on the results from previous production searches in $K^+$ decays, setting more stringent limits and extending the mass range.

First observation and branching fraction and decay parameter measurements of the weak radiative decay Xi0 -> Lambda e+ e-

2007

The weak radiative decay Xi0 --> Lambda e+e- has been detected for the first time. We find 412 candidates in the signal region, with an estimated background of 15 +/- 5 events. We determine the branching fraction B(Xi0 --> Lambda e+e-) = [7.6 +/- 0.4(stat) +/- 0.4(syst) +/- 0.2(norm)] x 10^{-6}, consistent with an internal bremsstrahlung process, and the decay asymmetry parameter alpha_{XiLambdaee} = -0.8 +/- 0.2, consistent with that of Xi0 --> Lambda gamma. The charge conjugate reaction Xi0_bar --> Lambda_bar e+e- has also been observed.

Numerical exploration of three relativistic particles in a finite volume including two-particle resonances and bound states

2019

In this work, we use an extension of the quantization condition, given in Ref. [1], to numerically explore the finite-volume spectrum of three relativistic particles, in the case that two-particle subsets are either resonant or bound. The original form of the relativistic three-particle quantization condition was derived under a technical assumption on the two-particle K matrix that required the absence of two-particle bound states or narrow two-particle resonances. Here we describe how this restriction can be lifted in a simple way using the freedom in the definition of the K-matrix-like quantity that enters the quantization condition. With this in hand, we extend previous numerical studie…

The COMPASS experiment at CERN

2007

The COMPASS experiment makes use of the CERN SPS high-intensitymuon and hadron beams for the investigation of the nucleon spin structure and the spectroscopy of hadrons. One or more outgoing particles are detected in coincidence with the incoming muon or hadron. A large polarized target inside a superconducting solenoid is used for the measurements with the muon beam. Outgoing particles are detected by a two-stage, large angle and large momentum range spectrometer. The setup is built using several types of tracking detectors, according to the expected incident rate, required space resolution and the solid angle to be covered. Particle identification is achieved using a RICH counter and both…

Probability and statistics

2013

Coherent π0 electroproduction

1993

Abstract We analyze the coherent electroproduction of neutral pions in nuclei. We find that this process does not contribute to the longitudinal response function for spin saturated nuclei and the dependence of the cross section on the azimuthal pion angle is particularly simple and given by 1− ϵ cos 2 o π . This angular dependence could be useful to isolate the coherent contribution in future experiments, offering an advantage over coherent photoproduction. The Δ-peak is considerably moved to lower pion energies and appreciably modified due to medium corrections.

New evidence for a narrow state of mass 2.02 GeV/c2

1993

Abstract We report evidence for the existence of a narrow p p state with a mass of 2.02 GeV/c2 and a width of about 0.02 GeV/c2, produced centrally in π+p(π−p) interactions at 20(12) GeV/c in several final states, proceeding via baryon exchange mechanism, and that could be interpreted as a baryonium candidate. The data come from the analysis of WA56 experiment made at the CERN Ω spectrometer.

Description of πp→Δ(1232)π and πp→Δ(1232)ρ(770) reaction proceeding via baryon exchange mechanism

1991

We analyze the available experimental data on the backward production processes πN→Δπ and πN→ Δπ in the framework of the strong-cut Reggeized absorption model, which is based on the exchange of the baryon Regge trajectoriesNα and Δδ with the associated cuts. The model describes rather well the data on the differential cross sections at incident π momenta ranging from 2.15 to 20 GeV/c. An essential contribution of Δδ exchange even at small energies (Elab of the order of a few GeV) is found. A model-independent analysis of data confirms this fenomena.

The search for dark matter gauge bosons with the Mainz Microtron

2011

Abstract A pilot experiment in the search for light gauge bosons at the spectrometer setup of the A1 collaboration at MAMI is presented. Light gauge bosons arise naturally in a wide range of theoretical approaches beyond the standard model and are in accordance with several pieces of experimental evidence not yet understood in the standard model. A first test measurement at MAMI showed that existing limits on the coupling of such a light gauge boson can be improved by nearly an order of magnitude by fixed target experiments at existing electron accelerators.

Event Excess in the MiniBooNE Search forν¯μ→ν¯eOscillations

2010

The MiniBooNE experiment at Fermilab reports results from a search for {nu}{sub {mu}{yields}{nu}e} oscillations, using a data sample corresponding to 5.66x10{sup 20} protons on target. An excess of 20.9{+-}14.0 events is observed in the energy range 475<E{sub {nu}}{sup QE}<1250 MeV, which, when constrained by the observed {nu}{sub {mu}} events, has a probability for consistency with the background-only hypothesis of 0.5%. On the other hand, fitting for {nu}{sub {mu}{yields}{nu}e} oscillations, the best-fit point has a {chi}{sup 2} probability of 8.7%. The data are consistent with {nu}{sub {mu}{yields}{nu}e} oscillations in the 0.1 to 1.0 eV{sup 2} {Delta}m{sup 2} range and with the evidence…