Collisions Of Cosmic Rays Research Articles

The gamma ray north‐south effect

We present theoretical calculations to explain the atmospheric gamma ray north‐south ratios measured by us and other observers. The north‐south effect is caused by the higher cosmic ray flux that strikes the Earth's atmosphere near the poles than near the equator. Primary and secondary cosmic ray integral energy distributions that vary as E−1.65 produce the gamma rays of 1–20 MeV of interest here. Gamma rays from distances north and south of the observer Compton scatter from the atmospheric nitrogen and oxygen into gamma ray telescopes flown on balloons at typical heights of 4 g/cm² residual atmosphere. The gamma rays that originate at the longest distances from the telescopes give the largest north‐south ratios. The north‐south ratios, between zenith angles of 15° and 60°, are greatest for the largest zenith angles and between 1.5 and 20 MeV for the largest gamma ray energies. Comparisons are made to experimental north‐south ratios measured on balloons launched from Palestine, Texas, and from Alice Springs, Australia. Predictions are made for ratios at other geomagnetic latitudes and longitudes. Observers who measure backgrounds for celestial sources 180° in azimuthal angle from the source direction may be misled unless they correct for the north‐south effect. Since neutrons of a few MeV are produced by cosmic ray collisions in the atmosphere in comparable numbers to gamma rays and their scatter path lengths are similar, we expect a neutron north‐south effect comparable to that for gamma rays.

Cosmic-ray induced vacuum decay in the standard model

In the standard model, if the Higgs boson mass, mH, and the top quark mass, mt, satisfy the relationship mt≳95GeV + 0.60 mH, then the vacuum is unstable. However, if the top quark mass is less than 190 GeV, then the lifetime is greater than the age of the universe. There is thus a large region of parameter space in which the vacuum is unstable, but sufficiently long-lived. We examine the possibility that high energy cosmic ray collisions could induce the decay of the vacuum, and show that this region of parameter space can be excluded.

Analysis of one cosmic-ray collision near 107GeV

One giant stratospheric gamma -ray family with square root s=5000 GeV has been observed in an emulsion chamber flown in Concorde at 100 g cm-2. The event displays a large number of photons (ngamma (>500 GeV)=211), an important transverse energy ET=600 GeV and a strong planarity suggesting a clear multijet structure.

ASTROMAG: A particle spectrometer for the space station

The study of the cosmic particle radiation is relevant both to astrophysics and particle physics. One example could be the fact that a direct measurement of the flux of p̄ and of e + is largely inconsistent with the secondary production in the collision of cosmic rays with the interstellar mater. An entirely new possibility of investigation will be offered to the study of the cosmic radiation by the Space Station program. The Space Station will be a permanent manned orbital complex, to be constructed in the 90s for scientific and technological research. Its existence will make possible the implementation outside the Earth's atmosphere, of large and sophisticated instruments, comparable to the ones currently installed at accelerators. ASTROMAG is the acronym for a large superconducting magnet to be installed on the Space Station as an experimental facility, to be equipped with particle detectors of various kinds.

Collisons in space experiments at high energies, laboratory experiments and suggested signatures of quark-gluon plasma: an alternative approach to the analysis of actual observations

In recent times there have been widespread speculations and claims among the cosmic-ray as well as high-energy physicists about the detection of some «signatures» for the formation of what one calls the quark-gluon plasma states in the ultrahigh-energy cosmic-ray collisions involving heavy nuclei. Furthermore, there are reportedly some hints to the detection of such states in laboratory experiments as well. We have collected here what are, in general, believed to be the diagnostics for such quark-gluon plasma states and have also provided alternative explanations for all the relevant observations at laboratory energies and cosmic-ray energies. Thus the obvious conclusion is: the evidences claimed so far are neither unique and decisive nor are very substantial, tenable and conclusive, as one can understand them almost completely from an altogether different theoretical framework.

Transverse momentum spectrum of mesons produced in high energy nucleus-nucleus collisions

The momentum of all charged mesons produced in 19 high energy, high multiplicity nucleus-nucleus collisions of cosmic rays in emulsion have been measured. The transverse momentum distribution differs qualitatively from proton-proton collisions at comparable energies. One possible interpretation is in terms of a transverse explosion with effective temperature T=78 MeV and transverse flow velocity υ=0.61 c.

Antiproton production of propagating cosmic rays under distributed reacceleration

view Abstract Citations (7) References (14) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Antiproton Production of Propagating Cosmic Rays under Distributed Reacceleration Simon, Manfred ; Heinbach, U. ; Koch, Ch. Abstract The available measurements on the cosmic-ray antiproton/proton ratio show an excess of antiprotons above predictions derived in the framework of the standard picture of cosmic-ray origin and propagation. Calculations are performed of the production from collisions of cosmic rays with the interstellar gas under the condition of distributed reacceleration. It could be shown that the calculated antiproton/proton ratio is enhanced compared to that derived from the 'leaky box' model, but it remains difficult to bring it into agreement with the data by reasonable astrophysical assumptions. Publication: The Astrophysical Journal Pub Date: September 1987 DOI: 10.1086/165587 Bibcode: 1987ApJ...320..699S Keywords: Antiprotons; Cosmic Rays; Particle Acceleration; Particle Production; Abundance; Monte Carlo Method; Space Radiation; COSMIC RAYS: ABUNDANCES; COSMIC RAYS: GENERAL; PARTICLE ACCELERATION full text sources ADS |

Adiabatic deceleration of secondary antiprotons in the envelopes of supernova exploding in dense clouds

Antiprotons (\(\bar p\)) in cosmic rays are believed to be secondary particles created by the collisions of cosmic rays with interstellar gas. On the basis of the well-established models of cosmic-ray propagation. the expected flux of\(\bar p\) in the few hundred MeV region is very small compared to the observed flux. In order to explain the observational data, we have examined the possibility of\(\bar p\) being produced in supernova (SN) envelopes during the expansion phase and undergoing the consequent adiabatic deceleration. For this purpose, we have considered in our investigation SN explosion in dense clouds withnH=104 cm−3 to 105 cm−3. Because of this dense medium the SN remnant is decelerated within a few thousand years, and a large amount of\(\bar p\) are produced during this period. We have calculated the\(\bar p\) spectrum from such sources by taking into account all energy-loss processes, and examined its spectral evolution. It is shown that the\(\bar p\) data can be well explained by this model, if about 25% of the cosmic-ray nucleons originate from such sources. The required fraction of SN explosions to occur in dense clouds is about 70%. We have also investigated in detail the influence of various energy-loss processes on the spectral evolution. Furthermore, we have examined the possibility of obtaining\(\bar p\) spectrum with enhanced flux at low energies.

SU(2) × U(1) vacuum and the centauro events

We propose that the “fireballs” invoked to explain the Centauro events are bubbles of a metastable superdense state of nuclear matter, created in high energy ( E ∼ 10 15 eV) cosmic ray collisions at the top of the atmosphere. If these bubbles are created with a Lorentz factor γ ⋍ 10 at their Cm frame, the objections against the origin of these events in cosmic ray interactions are overcome. Assuming further, that the Centauro events are due to the explosive decay of these metastable “bubbles”, a relationship between their lifetime, τ, and the threshold energy for bubble formation, E th, is derived. The minimum lifetime consistent with such an interpretation is τ ∼ 10 −8 s, while the E th appears to be insensitive to the value of τ and always close to E th∼ 10 15 eV. Finally it is speculated that if the available CM energy is thermalized in such collisions, these bubbles might be manifestations of excitations of the SU(2) × U(1) false vacuum. The absence of π 0's in the Centauro events is then explained by the decay modes of these excitations.

Ultra high energy cosmic ray neutrinos

Neutrinos, produced by the collisions of ultra high energy cosmic rays and the 3 K background radiation, require careful treatment of the evolving cosmic ray spectrum. The resulting neutrino differential energy spectrum is flat up to energies of order 10 19eV, thus most events are expected at this energy. The total ν e-flux should be significantly larger than the proton flux at ∼5 × 10 19eV when the recoil proton is correctly treated in photomeson production and when the Bethe-Heitler process (e +e − pair production) is incorporated. Based upon the observed primary proton spectrum we obtain a lower limit on the neutrino flux of ∼5.2/km 2yr sr implying roughly 0.4 detected upward moving events per year in the present Fly's Eye range of sensitivity.

How stable is our vacuum?

It is possible that the vacuum state we live in is not the absolute lowest one. In many spontaneously broken field theories a local minimum of the effective potential, which can be quite stable, can exist for certain parameter values. The Universe, starting at a high temperature, might have supercooled in such a local minimum. If such a metastable minimum is separated by a high enough barrier from the absolute minimum, the tunneling rate from the ‘false’ to the ‘true’ vacuum may be slow enough to not have occurred in one Hubble-spacetime-volume1,2. In that case our vaccum state might suddenly disappear if a bubble of real vacuum formed which was large enough for the bulk energy gain (equal to the product of the volume and the potential drop between false and true vacua) to exceed the surface energy density in its walls (proportional to the barrier potential). Such a bubble would expand at close to the speed of light, with enormous energy release, leaving a large attractive (ρ = −p < 0) cosmological constant in the interior, with a geometry close to anti-deSitter space1. This space-time is singularity-free if a strict vacuum, but any non-zero particle density would cause singularities to develop quickly. Although the persistence of our present vacuum for 1010 yr implies that a spontaneous transition via tunnelling is unlikely, we can ask whether a new generation of elementary particle accelerators might trigger such an unfortunate event. We show here that this chance, fortunately, is completely negligible since the region inside our past light cone has already survived some 105 cosmic ray collisions at centre of mass energies of 1011 GeV and higher.

Neutron oscillation as a source of excess sub-GeV antiprotons in galactic cosmic rays

The recent detection1,2 of an antiproton/proton (p/p) ratio at energies much less than 1 GeV is several orders of magnitude above that predicted for p production from primary cosmic ray collisions. It is well recognized that there is no mechanism to explain this sub-GeV (130–320 MeV) p excess although many suggestions have been made. For example, Eichler3 considers secondary production in high-energy collisions while Kiraly4 et al. suggest black hole evaporation as a p source. Most of these suggestions have inherent difficulties such as the imposition of severe constraints on the sources to suppress excessive γ-ray production. We postulate here that the phenomenon of neutron– antineutron (nn) oscillations as a signature of grand unified theories may operate in neutron-rich astrophysical sources such as supernovae to produce the required low-energy galactic antiproton background.

On the reported detection of sub-GeV antiprotons in galactic cosmic rays

Buffington et al.1 claim to have detected a p/p ratio of 2.2±0.6 × 10−4 at energies between 130 and 320 MeV. This is several orders of magnitude above theoretical predictions2–4 at these lower energies for p fluxes resulting from collisions of primary cosmic rays with the interstellar gas. Measurements at higher energies by Golden et al.5 show a p/p ratio of 5.2±1.5 × 10−4, in excess, by a factor of about 3, of the expected values if ps are of secondary origin in the standard model of galactic cosmic rays. The reported He/He ratio1 is significantly lower than the reported p/p ratio, raising difficulties with some scenarios6 in which the ps are primary cosmic rays from anti-galaxies. Kiraly et al.7 suggest black hole evaporation as a p source. I discuss here scenarios in which the reported sub-GeV p excess might be produced as secondaries in high energy collisions. Such production must take place in compact, optically thick sources.

A measurement of the cosmic-ray antiproton flux and a search for antihelium

A balloon-borne instrument has measured the cosmic-ray antiproton flux between 130 and 320 MeV and searched for antihelium between 130 and 370 MeV per nuclear. These particles were selected from the background of normal-matter cosmic rays by combining a selective trigger with a detailed spark chamber visualization of each recorded event. Antiprotons are identified by their characteristic annihilation radiation. Residue from background processes meeting the selection criteria is small. The observed 14 antiprotons yield a measured differential flux of 1.7±0.5X 10^(-4) antiprotons m^(-2) sr(-1) s^(-1)i Mev^(-1) at the top of the atmosphere. The corresponding antiproton/pro-ton ratio is 2.2±0.6X10^(-4), only slightly smaller than the ratio observed by other experiments at higher energies. Thus the antiprotons have a spectral shape similar to the protons, at least down to about 100 MeV. The expected flux of these particles can be calculated under the assumption that they were created by collisions of high-energy cosmic rays with the interstellar gas. Calculations using the standard leaky box model for propagation in the Galaxy predict a flux two orders of magnitude smaller than that observed. A small low-energy flux is predicted due to a kinematic suppression of the production of low-energy antiprotons. The discrepancy between calculations and experiment may be evidence that cosmic-ray protons have passed through substantially more than 5 g cm^(-2) of material during their lifetime. In addition, the combined results from this experiment and previous ones may be evidence for stochastic, energy-changing processes in interstellar space which act upon the secondary antiprotons after their creation. The search for cosmic-ray antihelium sets a 95% confidence level upper limit on the He /He ratio of 2.2 X 10^(-5).

Anti-matter in the primary cosmic radiation

Anti-matter in the cosmic radiation incident on the Earth can be of two types: antiparticles from distant antigalaxies and secondary particles generated by collisions of cosmic rays with nuclei of the interstellar medium (ISM) either in our Galaxy or in other galaxies. Insofar as the 2.7 K relict radiation inhibits the former for positrons (with energy above some tens of MeV) and the expected ratio of extragalactic particles to galactic particles is very small for protons (and thus antiprotons) it is conventional to assume that collisions in the ISM are the source of the e+ and p detected. We consider here the manner in which cosmic rays are propagated in the Galaxy by studying the fluxes of these antiparticles.

Energy estimates of cosmic-ray events

We propose new methods for estimating the energy of the incident particles in high-energy cosmic-ray collisions. We demonstrate their validity in accelerator experiments.

Particle production in cosmic ray collisions

We show that the large multiplicities and narrow rapidity distributions of particles produced in high energy central collisions of cosmic ray nuclei are well predicted by the collective tube model. We anticipate a faster increase with energy of average multiplicities in particle collisions at energies above 1 TeV and a cross-over of the pp and πp average multiplicities.

On the hydrodynamic expansion of a relativistic gas

An exact solution to the one-dimensional relativistic Euler equations is presented which is not of a self-similar nature and which satisfies certain initial conditions found to be appropriate in describing high-energy cosmic-ray collisions and models of radio galaxies. A full numerical analysis is performed to demonstrate the temporal behavior of all relevant thermodynamic quantities at any given point in the expansion. The results indicate that the motion is self-similar at the very beginning of free expansion, that this description ceases to be valid when the entire bulk of fluid is in motion, and that with the passage of time, the nonsimilar solution prevails over more and more of the fluid except for a small region near the leading edge where the fluid borders on the vacuum. The very bulk of the expansion is shown to become nonsimilar because the leading edge of the self-similar solution moves into the vacuum at the speed of light while that of the nonsimilar solution approaches c only asymptotically. The relativistic expansion of a gaseous disk is analyzed as an example.

Eleven-Year Variation in Polar Ozone and Stratospheric-Ion Chemistry

A mechanism for producing an 11-year oscillation in ozone over the polar caps is the modulation of galactic cosmic rays by the solar wind. This mechanism has been shown to give the observed phase in ozone oscillations and the correct qualitative dependence on latitude. However, the production of nitrogen atoms from cosmic-ray collisions seems inadequate to account for the ozone amplitude. Negative ions are also produced as a result of cosmic-ray ionization, and negative-ion chemistry may be of importance in the stratosphere. Specifically, NO(x)(-) may go through a catalytic cycle in much the same fashion as NO(x), but with the important distinction that it does not depend on oxygen atoms to complete the cycle. Estimates of the relevant rates of reaction suggest that negative ions may be especially important over the winter polar cap.

Fluxes of -rays, antiprotons and deuterons in cosmic rays

Calculations are presented on the fluxes of secondary particles with energies greater than 10 GeV arising from the collisions of primary cosmic rays with interstellar matter. The calculations are based on the parametrization of the accelerator data on production cross sections of pi +or-, p and deuterons in proton-proton collisions up to 1500 GeV as a function of rapidity variable for different transverse momenta of the particle produced.