Beam Dump Experiments Research Articles

Bound on the tau neutrino magnetic moment from the BEBC beam dump experiment

We have searched for electrons scattered in the forward direction by neutrinos produced by dumping a 400 GeV/ c proton beam on a copper target. We estimate the number of tau neutrinos produced from the decays of D s mesons in the dump. The data limit the possible magnetic moment of tau neutrinos to be below 5.4×10 −7 ω B. This rules out the suggestion that tau neutrinos of mass O(MeV) constitute the dark matter in the universe.

Investigation of prompt electron-neutrino production in a proton beam dump experiment with the IHEP-JINR ν detector

The production of prompt and ordinary ( ν) e was investigated in a proton beam dump experiment at the 70 GeV Serpukhov accelerator measuring their interactions in the IHEP-JINR neutrino detector. An upper limit of σ charm <2.4 μb/nucleon at 90% CL was obtained near the production threshold.

Limits on neutral light scalar and pseudoscalar particles in a proton beam dump experiment

A search has been performed for weakly interacting neutral light scalar and pseudoscalar particles in a proton beam dump experiment. No positive signal is observed. Limits on the mass and life-time of these particles are set in the frame of the Standard Model and its minimal supersymmetric extension. The Higgs particle of theSU2L×U1 Standard Theory is excluded for masses in the range 1 MeV<mH<80 MeV at 95%CL. Limits on the Peccei-Quinn like axions are derived.

Limits on tau neutrino as dark matter

If the tau neutrino is to constitute the cold dark matter of the galactic halo, as has recently been suggested, it should have a mass between a few MeV and 35 MeV, and a magnetic moment around 10 −6 Bohr magnetons. We investigate the consequences of these neutrino properties for some rare decays and other processes. In particular, we find that such a neutrino could be established or ruled out at a tau-charm factory by studying the decay Ψ(2S) → J/ Ψ+ ππ. Neutral-current processes in beam dump experiments are also a sensitive probe of these neutrinos. Measurements of low-energy cosmic ray positions may also constrain this model once solar wind modulation effects are better understood.

MASS CONSTRAINTS ON A LIGHT HIGGS PRODUCED IN η′ DECAYS

An estimate of the branching ratio BR(η′→ηH) and data from a beam-dump experiment are used to establish limits on the mass of a scalar Higgs boson in the context of the Minimal Standard Model.

An unambiguous search for a light Higgs boson

A search for light Higgs bosons has been performed in an electron beam-dump experiment. No positive signal is observed which allows us to reject at 90% CL the existence of a standard Higgs in the range from 1.2 to 52 MeV. Non-standard Higgs bosons are also excluded in a large range of couplings. This search relies on the well controlled and calculable process of bremsstrahlung from electrons in the Coulomb field of large Z nuclei. Both production and decay are governed by the single coupling constant of Higgs to electrons.

Search for free quarks produced at 800 GeV/c using a new concentration technique.

A high-sensitivity experiment was performed to detect free quarks produced in collisions of 800-GeV/c protons with a heavy target at Fermilab. Two quite different, high-concentration methods were used to obtain a small drop of Hg containing any produced quarks which stopped in a large amount of material. Using a new technique, secondaries were stopped in Hg tanks and the Hg was then distilled to small drops. In a second method, secondaries were stopped in liquid-nitrogen tanks, and charged atoms were collected electrostatically on Au-coated electrodes. The Au coatings were dissolved in Hg. The Hg drops from both techniques were then tested for quarks in the San Francisco State University automated Millikan apparatus. These results show that charged (1/3 quarks are produced below levels of 1.2\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}10}$ at 90% C.L. for both methods. Upper limits are also presented for charged (2/3 quarks. The distillation technique should prove useful in performing high-sensitivity quark searches in future beam-dump experiments.

What can we understand about the muon anomalies in high-energy showers from point sources?

We consider here the muon anomalies which have been claimed to be seen in high-energy air showers arising from point sources. We discuss what type of particle would be required to explain the experimental data and propose a generic class of models which can explain the data. Then we discuss accelerator-experiment limits on the existence of such a particle. In particular, we argue that such a particle need not have been seen yet in either neutrino experiments or in beam-dump experiments. We argue that neutrino experiments at 800 GeV provide perhaps the most sensitive test of our hypothesis in accelerator experiments. We present distinctive features of our model which should be observable in cosmic-ray experiments. Finally we discuss the problem of making an acceptable flux of cygnets at the compact x-ray source.

Prompt neutrino production in 400 GeV proton-copper interactions

A new beam-dump experiment has been performed at the CERN Super Proton Synchrotron using the CHARM neutrino detector. The instrumentation and the statistics have been significantly improved with respect to earlier experiments. For a neutrino energy above 20 GeV the asymmetry of the prompt muon-neutrino and electron-neutrino fluxes\([(v_\mu + \bar v_\mu ) - (v_e + \bar v_e )]/[(v_\mu + \bar v_\mu ) + (v_e + \bar v_e )]\) is found to be 0.20±0.10 (stat.)±0.05 (syst.), and the asymmetry of prompt antineutrino and neutrino fluxes for muonneutrinos\((v_\mu - \bar v_\mu )/(v_\mu + \bar v_\mu )\) is 0.02±0.16 (stat.)±0.02 (syst.) in agreement with our previous results. For the cross-section times branching ratio for charm production and semileptonic decay we obtain a value of\(\sigma \times BR\left[ {D(\bar D) \to v_e (\bar v_e ) X} \right] = 1.9 \pm 0.2 \pm 0.2\mu b\) per nucleon. We find no evidence forv τ orv x interactions. The\((v_\tau + \bar v_\tau )\) flux is less than 21% of the total prompt neutrino flux. We derive an improved limit on the branching ratio\(\pi ^0 \to v\bar v\) of 6.5×10−6, and as a verification of the universality of the neutral weak coupling we find\(g_{v_e \bar v_e } /g_{v_\mu \bar v_\mu } = 1.05_{ - 0.18}^{ + 0.15} \).

Neutrino production by 400-GeV/c protons in a beam-dump experiment.

The ${\ensuremath{\nu}}_{e}$ and ${\ensuremath{\nu}}_{\ensuremath{\mu}}$ fluxes from decay of short-lived parents (presumed to be predominantly charmed particles) have been measured in a beam-dump experiment at Fermilab. Novel and important features of the experimental arrangement and procedures are presented and discussed in detail. Details of the analysis of the prompt flux and the backgrounds are presented together with a discussion of the systematic error. The energy and angular distributions of the prompt neutrino flux are presented, and the cross section for charm production is measured to be 57.2\ifmmode\pm\else\textpm\fi{}2.9\ifmmode\pm\else\textpm\fi{}8.5 \ensuremath{\mu}b/nucleon. The dependence of the cross section on atomic weight is measured to be ${\ensuremath{\sigma}}_{c}$\ensuremath{\propto}${A}^{0.75}$. The possibility that charm is produced by a mixture of central and diffractive processes is examined and discussed in the context of these results. The prompt fluxes of ${\ensuremath{\nu}}_{\ensuremath{\mu}}$ and \ensuremath{\nu}${\ifmmode\bar\else\textasciimacron\fi{}}_{\ensuremath{\mu}}$ are roughly equal, as are the prompt fluxes of ${\ensuremath{\nu}}_{\ensuremath{\mu}}$ and ${\ensuremath{\nu}}_{e}$. Quasielastic neutrino interactions were identified and used to provide an independent measurement of the flux which corroborates the energy calibration of the detector. A search for additional sources of prompt neutrinos beyond charm is reported. Negative results were obtained for supersymmetric particles, heavy neutral leptons, and b quarks, subject to the assumption of specific characteristics of the particles and the production mechanisms.

IS THERE A NEW PSEUDOSCALAR PARTICLE?

The decay rate of orthopositronium has recently been measured in a new high precision experiment. The result is 10 standard deviations above the theoretical value. It is shown that a light neutral pseudoscalar R may resolve this discrepancy and still be consistent with the anomalous magnetic moments of the electron and the muon. If the mass mR≤5.7 keV , then the existence of this proposed particle R is consistent with the beam-dump experiments. The lifetime of R is large, τ≥0.14 s.

A new limit for the branching ratio for the decay π0 → νν′ from beam-dump experiments

Abstract If the decay π0 → νν′ exists, it would be a source of prompt neutrinos that would emerge from a beam dump. The data from several beam-dump experiments are examined for evidence of this decay and new upper limits, gG(π 0 → ν e g n e /gG(gpsu0 → all) Γ(π 0 → ν μ g n μ )/Γ(π 0 → all ) −6 and Γ(π 0 → ν τ g n τ /Γ(π 0 → all ) −6 ( all 90% CL ) are derived.

A-dependence of the charm production cross section in 300 GeV/c proton interactions

The A-dependence of the charm production cross section is determined by measuring the yield of prompt single muons in a beam-dump experiment, using a 300 GeV/c proton beam on Al, Fe, and U targets. Assuming that the production cross section varies as Aα, we obtain α(μ+) = 0.79±0.12 and α(μ−) = 0.76±0.13 in the kinematical region xF≳0.1 of the charm.

Axion creation in high-energy scattering of electrons on atoms.

The creation of axions in high-energy collisions of electrons on atoms is calculated. The fact that the axion spectrum is strongly peaked at high axion energies may make it possible to detect high-energy axions created in a thin target, if the axions exist. Such an experiment may supplement current beam-dump experiments.

Limits on axions from nuclear decays

Recent heavy ion experiments at GSI have releaved anomalous electron-positron coincidences. The anomalous events seem to come from something that decays into a two-body final state. It has been proposed that a 1.8 MeV axion could explain the data. However, both conventional axion theory and more recent variants are inconsistent with existing measurements of electron-positron angular correlations in nuclei. Beam dump experiments also exclude the axion theories. We discuss the old data and new measurements in terms of the axion theory and a more general particle explanation for the GSI result.

Limits on millicharged matter from beam-dump experiments.

It has been proposed by Goldberg and Hall that the dark matter in galactic halos may be a type of shadow matter which interacts electromagnetically with ordinary matter (via a mixing effect) with effective charge \ensuremath{\Vert}Q\ensuremath{\Vert}=2\ensuremath{\epsilon}e where \ensuremath{\epsilon}\ensuremath{\ll}1. We put constraints on the mass (${m}_{s}$) and effective charge (i.e., \ensuremath{\epsilon}) of such particles by examining their possible production and detection in high-statistics proton beam-dump experiments. We find, for example, that \ensuremath{\epsilon}\ensuremath{\lesssim}2\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}2}$ for 1\ensuremath{\lesssim}${m}_{s}$\ensuremath{\lesssim}200 MeV.

Search for tau-neutrino interactions in the BEBC beam dump experiment

A novel and efficient kinematic method is used to estimate the number of ν τ charged current interactions with E ν > 20 GeV in the BEBC beam dump experiment. The result, −14±12 ν τ events, is consistent with zero. The ratio of D s to D meson production in 400 GeV proton interactions in copper is estimated to be below 0.65 at 90% c.l. The oscillation probability P( ν e→ ν τ ) averaged over the electron-(anti)neutrino spectrum is found to be below 18%. The hypothesis that ν e and ν τ are identical is excluded by about 6 standard deviations. A remarkable event is described: it contains a muon, a high p T photon and a high p T hadron.

E+e- peaks at 1.8 MeV: Phenomenological constraints on nuclear transitions, axions, and the particle interpretation.

We investigate phenomenological constraints on a variety of possible explanations of the e/sup +/e/sup -/ peaks observed by the EPOS Collaboration at GSI. We first review problems with a variety of proposed nuclear-related production mechanisms. Next we investigate constraints on the axion interpretation of the observed events. New non-accelerator-related constraints come from considerations of shifts in the hyperfine splitting in positronium, and an analysis of the decays K..--> pi..e/sup +/e/sup -/ and ..pi -->..e/sup +/e/sup -/e/sup +/..nu.., which are relevant for a proposed short-lived axion variant. We then demonstrate that present and past beam-dump experiments are, in a model-independent way, sensitive to a new 1.8-MeV particle coupling to electrons. Our estimates suggest that if the particle does not interact in the target one should see very high event rates for all allowed lifetimes from 10/sup -14/--10/sup -10/ sec at high-energy facilities and lifetimes greater than 10/sup -10/ sec at low-energy dumps.

Search for axion-like particles in electron bremsstrahlung

A search for weakly interacting particles with short lifetime has been performed in an electron beam-dump experiment. Comparing the rate of produced positrons behind a dump of variable geometry, limits are placed or a large range of lifetime. A 1.8 MeV particle, as hinted from recent results using heavy ion collisions, is ruled out for lifetimes between 6 × 10 −4 and 9 × 10 −11 s. These results, those previously published for longer lifetimes and the g - 2 agreement with QED rule out a simple particle interpretation of the heavy ion effect.

Characteristics of charm production by 400-GeV protons.

In a beam-dump experiment at Fermilab the cross section for charm-particle production has been deduced from a measurement of the prompt neutrino flux. The reaction cross section, if we assume only DD-bar and the dependence on atomic weight A/sup 0.75/, is 57.2 +- 2.9 +- 8.5 ..mu..b/nucleon and the dependence on Feynman x and transverse momentum is E/sub D/ d/sup 3/sigma/sub pD//sup 3/proportional(1-x)/sup 3.2/e/sup -1/ .5p/sub perpendicular/ (p/sub perpendicular/ in GeV/c). The data are consistent with as much as 40% diffractive production of ..lambda../sub c/D-bar.