79 research outputs found
Cosmic ray propagation time scales: lessons from radioactive nuclei and positron data
We take a fresh look at high energy radioactive nuclei data reported in the
90's and at the positron data recently reported by PAMELA. Our aim is to study
the model independent implications of these data for the propagation time
scales of cosmic rays in the Galaxy. Considering radioactive nuclei, using
decaying charge to decayed charge ratios -- the only directly relevant data
available at relativistic energies -- we show that a rigidity independent
residence time is consistent with observations. The data for all nuclei can be
described by f_{s,i}=(t_i/100 Myr)^{0.7}, where f_{s,i} is the suppression of
the flux due to decay and t_i is the observer frame lifetime for nucleus specie
i. Considering positron measurements, we argue that the positron flux is
consistent with a secondary origin. Comparing the positron data with
radioactive nuclei at the same energy range, we derive an upper bound on the
mean electromagnetic energy density traversed by the positrons, \bar U_T<1.25
eV/cm^3 at a rigidity of R=40 GV. Charge ratio measurements within easy reach
of the AMS-02 experiment, most notably a determination of the Cl/Ar ratio
extending up to R\sim100 GV, will constrain the energy dependence of the
positron cooling time. Such constraints can be used to distinguish between
different propagation scenarios, as well as to test the secondary origin
hypothesis for the positrons in detail.Comment: 16 pages, 10 figure
Nuclear coalescence from correlation functions
We derive a simple formula relating the cross section for light cluster
production (defined via a coalescence factor) to the two-proton correlation
function measured in heavy-ion collisions. The formula generalises earlier
coalescence-correlation relations found by Scheibl & Heinz and by Mrowczynski
for Gaussian source models. It motivates joint experimental analyses of Hanbury
Brown-Twiss (HBT) and cluster yield measurements in existing and future data
sets.Comment: 10 pages, 4 figures. v2: some clarifications. A missing (2\pi)^3
normalization factor, relating diff cross sec to density matrix traces, is
corrected in Secs.II.A and II.B. It does not affect any of the result
Rapidity dependence of nuclear coalescence: impact on cosmic ray antinuclei
Upcoming studies at the Large Hadron Collider (LHC) aim to extend the
rapidity coverage in measurements of the production cross section of antinuclei
and . We illustrate the impact of such
studies on cosmic ray (CR) flux predictions, important, in turn, for the
interpretation of results from CR experiments. We show that, in terms of the
rapidity effect, covering the range at the LHC should be sufficient
for the astrophysical CR calculation. Important extrapolation remains in other
aspects of the problem, notably .Comment: 6 pages, 3 figure
Cosmic-ray Antimatter
In recent years, space-born experiments have delivered new measurements of
high energy cosmic-ray (CR) and . In addition, unprecedented
sensitivity to CR composite anti-nuclei anti-d and anti-He is expected to be
achieved in the near future. We report on the theoretical interpretation of
these measurements. While CR antimatter is a promising discovery tool for new
physics or exotic astrophysical phenomena, an irreducible background arises
from secondary production by primary CR collisions with interstellar matter.
Understanding this irreducible background or constraining it from first
principles is an interesting challenge. We review the attempt to obtain such
understanding and apply it to CR anti-d and anti-He. Based on
state of the art Galactic cosmic ray measurements, dominated currently by the
AMS-02 experiment, we show that: (i) CR most likely come from CR-gas
collisions; (ii) data is consistent with, and suggestive of the same
secondary astrophysical production mechanism responsible for and
dominated by proton-proton collisions. In addition, based on recent accelerator
analyses we show that the flux of secondary high energy anti-He may be
observable with a few years exposure of AMS-02. We highlight key open
questions, as well as the role played by recent and upcoming space and
accelerator data in clarifying the origins of CR antimatter.Comment: 42 pgs, 18 figs. Invited paper for RM
and production in collisions and the cosmic-ray flux ratio
Secondary astrophysical production of and cosmic rays is
considered. Inclusive , , and production cross sections in
collisions at large are parametrised using recent experimental
data at LHC energies. The astrophysical production rate ratio
is calculated for an input cosmic ray proton flux
consistent with local measurements. At GeV the cosmic ray flux
ratio measured by AMS02 falls below the production rate
ratio by about 50\%, while at high energy GeV the measured flux
ratio coincides with the production rate ratio of the secondary source.Comment: 9 pages, 8 figure
DAMA vs. the annually modulated muon background
We compare the DAMA signal to the muon flux underground, which is annually
modulated due to temperature variations in the stratosphere. We show that the
muon flux at LNGS and the DAMA signal are tightly correlated. Different
mechanisms were proposed in the literature by which muon-induced events may
dominate the signal region in DAMA. We discuss simple statistical constraints
on such mechanisms and show that the DAMA collaboration can falsify the muon
hypothesis, if it is wrong, by reporting their annual baseline count rates.Comment: 12 pages, 6 figure
Neutrino flavour as a test of the explosion mechanism of core-collapse supernovae
We study the ratio of neutrino-proton elastic scattering to inverse beta
decay event counts, measurable in a scintillation detector like JUNO, as a key
observable for identifying the explosion mechanism of a galactic core-collapse
supernova. If the supernova is not powered by the core but rather, e.g., by
collapse-induced thermonuclear explosion, then a prolonged period of
accretion-dominated neutrino luminosity is predicted. Using 1D numerical
simulations, we show that the distinct resulting flavour composition of the
neutrino burst can be tested in JUNO with high significance, overcoming
theoretical uncertainties in the progenitor star profile and equation of state.Comment: 28 pages, 18 figure
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