Collisions Of Cosmic Rays Research Articles

Review of the safety of LHC collisions

The safety of collisions at the Large Hadron Collider (LHC) was studied in 2003 by the LHC Safety Study Group, who concluded that they presented no danger. Here we review their 2003 analysis in light of additional experimental results and theoretical understanding, which enable us to confirm, update and extend the conclusions of the LHC Safety Study Group. The LHC reproduces in the laboratory, under controlled conditions, collisions at centre-of-mass energies, less than those reached in the atmosphere by some of the cosmic rays that have been bombarding the Earth for billions of years. We recall the rates for the collisions of cosmic rays with the Earth, Sun, neutron stars, white dwarfs and other astronomical bodies at energies higher than the LHC. The stability of astronomical bodies indicates that such collisions cannot be dangerous. Specifically, we study the possible production at the LHC of hypothetical objects such as vacuum bubbles, magnetic monopoles, microscopic black holes and strangelets, and find no associated risks. Any microscopic black holes produced at the LHC are expected to decay by Hawking radiation before they reach the detector walls. If some microscopic black holes were stable, those produced by cosmic rays would be stopped inside the Earth or other astronomical bodies. The stability of astronomical bodies strongly constrains the possible rate of accretion by any such microscopic black holes, so that they present no conceivable danger. In the case of strangelets, the good agreement of measurements of particle production at RHIC with simple thermodynamic models severely constrains the production of strangelets in heavy-ion collisions at the LHC, which also present no danger.

Galactic antiproton spectrum at high energies: Background expectation versus exotic contributions

A new generation of upcoming space-based experiments will soon start to probe the spectrum of cosmic-ray antiparticles with an unprecedented accuracy and, in particular, will open up a window to energies much higher than those accessible so far. It is thus timely to carefully investigate the expected antiparticle fluxes at high energies. Here, we perform such an analysis for the case of antiprotons. We consider both standard sources as the collision of other cosmic rays with interstellar matter, as well as exotic contributions from dark matter annihilations in the galactic halo. Up to energies well above 100 GeV, we find that the background flux in antiprotons is almost uniquely determined by the existing low-energy data on various cosmic-ray species; for even higher energies, however, the uncertainties in the parameters of the underlying propagation model eventually become significant. We also show that if the dark matter is composed of particles with masses at the TeV scale, which is naturally expected in extra-dimensional models as well as in certain parameter regions of supersymmetric models, the annihilation flux can become comparable to---or even dominate---the antiproton background at the high energies considered here.

Creation of X‐Ray Cavities in Galaxy Clusters with Cosmic Rays

We describe how AGN-produced cosmic rays form large X-ray cavities and radio lobes in the hot diffuse gas in galaxy groups and clusters. Cosmic rays are assumed to be produced in a small shocked region near the cavity center, such as at the working surface of a radio jet. The coupled equations for gasdynamics and cosmic ray diffusion are solved with various assumptions about the diffusion coefficient. To form large, long-lived cavities similar to those observed, the diffusion coefficient must not exceed kappa = 10^28 cm^2/s in the hot gas, very similar to values required in models of cosmic ray diffusion in the Milky Way. When kappa does not exceed 10^28, cosmic rays are confined within the cavities for times comparable to the cavity buoyancy time, as implied by observations of X-ray cavities and their radio synchrotron emission. Collisions of proton cosmic rays with thermal plasma nuclei followed by pion decay can result in enhanced gamma ray emission from the cavity walls.

Parallel MOPEX: Computing Mosaics of Large‐Area Spitzer Surveys on a Cluster Computer

The Spitzer Science Center′s MOPEX software is a part of the Spitzer Space Telescope′s operational pipeline that enables detection of cosmic ray collisions with the detector array, masking of the corrupted pixels due to these collisions, subsequent mosaicking of image fields, and extraction of point sources to create catalogs of celestial objects. This paper reports on our experiences in parallelizing the parts of MOPEX related to cosmic ray rejection and mosaicking on a 1,024‐processor cluster computer at NASA′s Jet Propulsion Laboratory. The architecture and performance of the new Parallel MOPEX software are described. This work was done in order to rapidly mosaic the IRAC shallow survey data, covering a region of the sky observed with one of Spitzer′s infrared instruments for the study of galaxy clusters, large‐scale structure, and brown dwarfs.

Neutrons and antiprotons in ultrahigh-energy cosmic rays

The neutron fraction in the very high energy cosmic rays near the Greisen-Zatsepin-Kuzmin (GZK) cutoff energy is analyzed by taking into account the time dilation effect of the neutron decays and also the pion photoproduction behaviors above the GZK cutoff. We predict a non-trivial neutron fraction above the GZK cutoff and a negligibly small neutron fraction below. However, there should be a large antiproton fraction in the high energy cosmic rays below the GZK cutoff in several existing models for the observed cosmic-ray events above and near the GZK cutoff. Such a large antiproton fraction can manifest itself by the muon charge ratio $\mu^+/\mu^-$ in the collisions of the primary nucleon cosmic rays with the atmosphere, if there is no neutron contribution. We suggest to use the muon charge ratio as one of the information to detect the composition of the primary cosmic rays near or below the GZK cutoff.

Atmospheric neutrinos

Neutrino oscillation was discovered through the study of atmospheric neutrinos. Atmospheric neutrinos are produced as decay products in hadronic showers resulting from collisions of cosmic rays with nuclei in the atmosphere. Electron neutrinos and muon neutrinos are produced mainly by the decay chain of charged pions to muons and electrons. Depending on the energy of the neutrinos, atmospheric neutrinos are observed as fully contained events, partially contained events and upward-going muon events. The energy range covered by these events is from a few hundred MeV to >1 TeV. Data from various experiments showed zenith angle- and energy-dependent deficit of νμ events, while νe events did not show any such effect. It was also shown that the νμ survival probability obeys the sinusoidal function as predicted by neutrino oscillations. Two-flavour νμ ↔ ντ oscillations, with sin2 2θ > 0.90 and Δm2 in the region of 1.9 × 10−3 to 3.0 × 10−3 eV2, explain all these data. Various detailed studies using high statistics atmospheric neutrino data excluded the alternative hypotheses that were proposed to explain the νμ deficit.

Shower power: isolating the prompt atmospheric neutrino flux using electronneutrinos

At high energies, the very steep decrease of the conventional atmospheric component of theneutrino spectrum should allow the emergence of even small and isotropic components ofthe total spectrum, indicative of new physics, provided that they are less steeplydecreasing, as generically expected. One candidate is the prompt atmosphericneutrino flux, a probe of cosmic ray composition in the region of the knee as well assmall-x QCD, below the reach of collider experiments. A second is the diffuse extragalacticbackground due to distant and unresolved AGNs and GRBs, a key test of the nature of thehighest-energy sources in the universe. Separating these new physics components from theconventional atmospheric neutrino flux, as well as from each other, will be very challenging.We show that the charged-current electron neutrino ‘shower’ channel should be particularlyeffective for isolating the prompt atmospheric neutrino flux, and that it is moregenerally an important complement to the usually considered charged-currentmuon neutrino ‘track’ channel. These conclusions remain true even for the lowprompt atmospheric neutrino flux predicted in a realistic cosmic ray scenariowith heavy and varying composition across the knee (Candia and Roulet, 2003J. Cosmol. Astropart. Phys. JCAP09(2003)005). We also improve the correspondingcalculation of the neutrino flux induced by cosmic ray collisions with the interstellarmedium.

Cosmic-Ray Neutrons on the Ground and in the Atmosphere

AbstractNeutrons from collisions of cosmic rays with the nuclei of atoms in the atmosphere are an irremovable external radiation that causes single-event upsets in microelectronic devices. Predicting soft error rates requires knowledge of the flux and energy distribution of the cosmic-ray-induced neutrons. This article reviews cosmic-ray neutrons in the atmosphere and on the ground, the factors that determine their intensity, and recent calculations and state-of-the-art measurements of neutron spectra covering 12 decades of energy, from the thermal energy range up to 10 GeV.

Peter Meyer

Peter Meyer

Essay: Black Holes in the Lab?

If TeV-scale gravity describes nature, black holes will be produced in particle accelerators, perhaps even with impressive rates at the Large Hadron Collider. Their decays, largely via the Hawking process, will be spectacular. Black holes also would be produced in cosmic ray collisions with our atmosphere, and their showers may be observable. Such a scenario means the end of our quest to understand the world at shorter distances, but may represent the beginning of the exploration of extra dimensions.

Gamma-ray observations and massive stars

Gamma-rays from astrophysical sources testify energetic processes such as nucleosynthesis and cosmic ray collisions. Gamma-rays are observable from throughout the Galaxy, unattenuated by interstellar matter, provided their intensity exceeds the current instrumental sensitivity level (∼ 10−5ph cm−2s−1 at 1 MeV). Massive stars are at the origin of relevant sources: The all-sky image in the 1.809 MeV γ-ray line from radioactive 26Al traces nucleosynthesis throughout the Galaxy. The structure of this emission along the plane of the Galaxy suggests massive stars as dominating sources of this radioactivity. Discrimination of the contribution from core collapse supernova against that from WR-wind ejected hydrostatic nucleosynthesis products may be obtained from 60Fe γ-ray line observations, or from spatial-profile consequences of the metallicity dependence of 26Al production in theories for both source sites. As a single source, the nearest WR star in the γ2 Vel system is found to eject less 26Al into interstellar space than current theories predict. However, a more adequate comparison must be based on a time-dependent 26Al light-curve of the system. Furthermore, continuum γ-ray production in WR binaries through wind-wind interaction, and constraints on the low-energy cosmic ray origin in WR winds through characteristic nuclear deexcitation line studies are targets of research. Studies stimulated by COMPTEL'S 3–7 MeV excess report from the Orion region indicate that the γ-ray line measurements could separate the origins from supernova ejecta and wind material. The COMPTEL Orion result is now attributed chiefly to an instrumental artifact, and has been withdrawn. Nevertheless, the search for MeV emission from massive star clusters, as well as from interacting binaries such as WR 140, promises a unique test of particle acceleration scenarios related to the source mechanism for cosmic ray production.

Simulation of atmospheric cascade including vacuum excitation and Higgs production

We consider here a new mechanism for multiparticle production in the simulation of a cosmic ray cascade in the atmosphere. The mechanism is the decay of Higgs particles that are produced through vacuum excitation in a cosmic ray collision. We develop a model of hadronic interaction based on the GENCL code of the UA5 experiment, incorporating a fraction of energy transfer to bubble formation by phase transition due to vacuum excitation and subsequent multiparticle production via conversion of Higgs particles to heavy fermion pairs. Such events are expected to have high multiplicity and excess muons. We compare the muon multiplicity distribution with and without this effect for different fractions of energy transfer going to Higgs boson production. Our results show that signatures of Higgs boson production may be seen above the primary energy ${10}^{17}\mathrm{eV},$ with an increasing fraction of energy transfer as we go to higher energies.

US and Japan Plan to Create Cross-Country Neutrino Beams

Deep inside the Kamioka zinc mine, in the mountains west of Tokyo, the just-completed Super Kamiokande proton-decay and neutrino detector is now being filled with 50 000 tons of highly purified water. (Fifty thousand tons is the displacement of a large battleship.) Super Kamiokande is a Japan-US collaboration. In a few months this newest, and largest by far, of the water-Cerenkov detectors will be recording neutrinos from the Sun and from collisions of cosmic rays in the atmosphere. It will also be keeping its 11 200 photomultiplier eyes peeled for neutrino bursts from distant supernova explosions and for evidence that one of the detector's 1034 nucleons has decayed. (See the photograph on this page).

Quasielastic neutrino scattering from oxygen and the atmospheric neutrino problem.

We examine several phenomena beyond the scope of Fermi-gas models that affect the quasielastic scattering (from oxygen) of neutrinos in the 0.1 -- 3.0 GeV range. These include Coulomb interactions of outgoing protons and leptons, a realistic finite-volume mean field, and the residual nucleon-nucleon interaction. None of these effects are accurately represented in the Monte Carlo simulations used to predict event rates due to $\mu$ and $e$ neutrinos from cosmic-ray collisions in the atmosphere. We nevertheless conclude that the neglected physics cannot account for the anomalous $\mu$ to $e$ ratio observed at Kamiokande and IMB, and is unlikely to change absolute event rates by more than 10--15\%. We briefly mention other phenomena, still to be investigated in detail, that may produce larger changes.

Signatures of cosmic-ray interactions on the solar surface

view Abstract Citations (125) References (35) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Signatures of Cosmic-Ray Interactions on the Solar Surface Seckel, D. ; Stanev, Todor ; Gaisser, T. K. Abstract The fluxes of neutrinos, gamma rays, antiprotons, neutrons, and antineutrons that result from collisions of high-energy Galactic cosmic rays with the solar atmosphere are estimated. The results are sensitive to assumptions about cosmic-ray transport in the magnetic fields of the inner solar system. The high-energy photon flux should be observable by the Gamma Ray Observatory. The neutrino flux should produce less than one event per year in the next generation of neutrino telescopes. The antiproton flux is unobservable against the Galactic background. The neutron and antineutron fluxes are detectable only if neutrons produced in terrestrial cosmic-ray events may be discriminated against. Publication: The Astrophysical Journal Pub Date: December 1991 DOI: 10.1086/170753 Bibcode: 1991ApJ...382..652S Keywords: Galactic Cosmic Rays; Solar Atmosphere; Antiprotons; Interplanetary Magnetic Fields; Neutrinos; Neutrons; Solar Magnetic Field; Solar System; Space Radiation; COSMIC RAYS: GENERAL; GAMMA RAYS: GENERAL; NEUTRINOS; SUN: ACTIVITY full text sources ADS |

Higgs-particle production through vacuum excitations.

We consider here a nonperturbative mechanism for the production of Higgs particles through vacuum excitations. It appears that it could already have been seen in ``chiron'' events, ``halo'' events, and some other signals in high-energy cosmic-ray collisions.

Vacuum stability, wormholes, cosmic rays and the cosmological bounds on mt and mH

In the standard model, if the top quark mass m t is larger than some critical value depending on the Higgs mass m H, then we live in an unstable vacuum state corresponding to a local minimum of the effective potential. An experimental discovery of the top quark with m t above this critical value would invalidate the standard version of the wormhole theory, according to which the vacuum energy should be zero at the absolute minimum of the effective potential. However, unless the top quark is much heavier than this, the lifetime is much heavier than this, the lifetime of the unstable vacuum state is greater than the age of our part of the universe. In this paper we develop a stochastic approach to tunneling and apply it to examine the possibility that cosmic ray collisions may trigger vacuum decay and derive improved cosmological bounds on m H and m t.

Coplanar jets.

We argue that the observation of multiple cores in very-high-energy cosmic-ray collisions is expected in models where jet production becomes a feature of all interactions above ${10}^{4}$ TeV. The most striking feature of such events is the collinearity of cores in emulsion experiments. We argue that the observed alignment of three cores is a consequence of transverse-momentum conservation about the beam in a boosted two-jet event. We predict a certain degree of alignment in events with four cores which reflects a dynamical correlation in three-jet events given by QCD. Such correlations have already been observed in collider experiments. Additional four-core events must be observed in emulsion experiments before the alignment hypothesis is tested for cosmic-ray interactions.

Can the electroweak vacuum be unstable?

The electroweak vacuum need not be absolutely stable. For certain top-quark and Higgs-boson masses in the minimal standard model, our vacuum is instead metastable with a lifetime exceeding the present age of the Universe. It has been suggested that a metastable vacuum is generally ruled out because high-energy cosmic-ray collisions would have long ago induced its decay. I argue that the reasoning for this conclusion is erroneous. As a consequence, upper bounds on the top-quark mass derived from stability arguments are relaxed. Also presented is an analytic method for accurately approximating the lifetime of the vacuum from the effective potential without solving for the 0(4) bounce solution numerically.

The cosmic-ray antiproton spectrum from dark matter annihilation and its astrophysical implications - A new look

The spectrum of antiprotons from dark matter annihilation are calculated using the Lund Monte Carlo program, and simple analytic expressions for the spectrum and low-energy antiproton/proton ratio are derived. Comparing the results with recent upper limits on low energy antiprotons, it is concluded that the reported 4-13 GeV antiproton flux cannot be accounted for by dark matter annihilation. The new upper limits do not provide useful constraints on dark matter particles. They restrict the annihilation rate and imply that annihilation gamma ray and e(+) fluxes would be far below the fluxes produced by cosmic-ray collisions. It may be possible to look for a dark matter halo annihilation signal at antiprotons energies below 0.5 GeV, where the flux from cosmic-ray collisions is expected to be negligible.