Antiproton Flux Research Articles

Dark matter after the BESS-Polar II experiment

The BESS-Polar collaboration has recently performed a precise measurement of the local antiproton flux which is consistent with a pure secondary production of antiprotons. We constrain a possible primary component originating from dark matter pair-annihilations. We derive limits on the annihilation cross section which are stronger than or comparable to those from the PAMELA satellite experiment for dark matter masses up to 200 GeV. Especially, we exclude thermal WIMPs with masses in the range 3--20 GeV if they annihilate dominantly into quark pairs unless their cross section is velocity suppressed.

Can a Higgs portal Dark Matter be compatible with the anti-proton cosmic-ray?

Recent direct detection experiments of Dark Matter (DM), CoGeNT and DAMA implicate a light DM of a few GeV. Such a light DM would generate a large amount of anti-proton since suppression for anti-proton flux from DM annihilation is ineffective. We discuss whether a light dark matter with mass of 5–15 GeV, which is especially in favor of the recent experiments reported by CoGeNT, is compatible with the anti-proton no excess in the cosmic-ray. In view of the direct detection of DM and no anti-proton excess in the cosmic-ray both, we show that a Dirac DM is favored than a scalar one since there is no s-wave of the annihilation cross section for the Dirac DM. A large elastic cross section for direct detection can be obtained through the additional light Higgs exchange. We show an allowed region that simultaneously satisfies the DM relic density, the elastic cross section favored by CoGeNT and also the constraint of HLZZ coupling of the light Higgs boson by LEP.

Antiprotons from dark matter annihilation in the Galaxy: Astrophysical uncertainties

The latest years have seen steady progresses in weakly interacting massive particle dark matter (DM) searches, with hints of possible signals suggested both in direct and indirect detection. Antiprotons play a key role in this context, since weakly interacting massive particle annihilations can be a copious source of antiprotons, and the antiproton flux from conventional astrophysical sources is predicted with fair accuracy and matches the measured cosmic ray (CR) spectrum very well. Using the publicly available dragon code, we reconsider antiprotons as a tool to set constraints on DM models; we compare against the most up-to-date $\overline{p}$ measurements, taking also into account the latest spectral information on the $p$ and He CR fluxes. In particular, we probe carefully the uncertainties associated to both standard astrophysical and DM originated antiprotons, by using a variety of distinctively different assumptions for the propagation of CRs and for the DM distribution in the Galaxy. We find that the impact of the astrophysical uncertainties on constraining the DM properties of a wide class of annihilating DM models can be much stronger, up to a factor of $\ensuremath{\sim}50$, than the one due to uncertainties on the DM distribution ($\ensuremath{\sim}2--6$). Remarkably, even reducing the uncertainties on the propagation parameters derived by local observables, nonlocal effects can change our predictions for the constraints even by 50%. Nevertheless, current $\overline{p}$ data can place tight constraints on DM models, excluding some of those suggested in connection with indirect and direct searches. Finally we discuss the impact of upcoming CR spectral data from the AMS-02 instrument on DM model constraints.

Global constraints on effective dark matter interactions: relic density, direct detection, indirect detection, and collider

An effective interaction approach is used to describe the interactions between the spin 0 or spin 1/2 dark matter particle and the degrees of freedom of the standard model. This approach is applicable to those models in which the dark matterparticles do not experience the standard-model interactions, e.g., hidden-sector models. We explore the effects of these effective interaction operators on (i) dark matter relic density, (ii) spin-independent and spin-dependent dark matter-nucleon scattering cross sections, (iii) cosmic antiproton and gamma ray fluxes from the galactic halo due to dark matter annihilation, and (iv) monojet and monophoton production plus missing energy at the Tevatron and the Large Hadron Collider (LHC). We combine the experimental data of relic density from WMAP7, spin-independent cross section from XENON100, spin-dependent cross section from XENON10, ZEPLIN-III, and SIMPLE, cosmic antiproton flux from PAMELA, cosmic gamma-ray flux from Fermi-LAT, and the monojet and monophoton data from the Tevatron and the LHC, to put the most comprehensive limits on each effective operator.

RELIC DENSITY AND PAMELA EVENTS IN A HEAVY WINO DARK MATTER MODEL WITH SOMMERFELD EFFECT

In a wino LSP scenario the annihilation cross-section of winos gravitationally bound in galaxies can be boosted by a Sommerfeld enhancement factor which arises due to the ladder of exchanged W bosons between the initial states. The boost factor obtained can be in the range S ≃104 if the mass is close to the resonance value of M ≃4 TeV . In this paper we show that if one takes into account the Sommerfeld enhancement in the relic abundance calculation then the correct relic density is obtained for 4 TeV wino mass due to the enhanced annihilation after their kinetic decoupling. At the same time the Sommerfeld enhancement in the χχ→W+ W- annihilation channel is sufficient to explain the positron flux seen in PAMELA data without significantly exceeding the observed antiproton signal. We also show that (e-+e+) and γ-ray signals are broadly compatible with the Fermi-LAT observations. In conclusion we show that a 4 TeV wino DM can explain the positron and antiproton fluxes observed by PAMELA and at the same time give a thermal relic abundance of CDM consistent with WMAP observations.

Indirect dark matter searches as a probe of degenerate particle spectra

We consider the possibility that the cosmological dark matter consists of particles very close in mass to new colored particles below the TeV scale. While such a scenario is inherently difficult to directly confirm at colliders, we find that indirect dark matter searches may be a powerful alternative. In particular, we show that in this case dark matter annihilation to q¯qg final states can give rise to significant antiproton (but also gamma-ray) fluxes, and compare the resulting constraints to bounds from direct searches at LEP, the Tevatron and the LHC. For supersymmetric neutralinos degenerate with squarks, e.g., antiprotons can give rise to more stringent constraints for masses below around 45–80 GeV.

Main results from the PAMELA space experiment after five years in flight

After five years of data taking in space, the experiment PAMELA is showing very interesting features in cosmic rays, namely in the fluxes of protons, heliums, electrons, that might change our basic vision of the mechanisms of production, acceleration and propagation of cosmic rays in the galaxy. In addition, PAMELA measurements of cosmic antiproton and positron fluxes are setting strong constraints to the nature of dark matter. PAMELA is also measuring the radiation environment around the Earth, and has recently discovered an antiproton radiation belt. In this paper PAMELA main results will be reviewed.

Radio data and synchrotron emission in consistent cosmic ray models

It is well established that phenomenological two-zone diffusion models of the galactic halo can very well reproduce cosmic-ray nuclear data and the observed antiproton flux. Here, we consider lepton propagation in such models and compute the expected galactic population of electrons, as well as the diffuse synchrotron emission that results from their interaction with galactic magnetic fields. We find models in agreement not only with cosmic ray data but also with radio surveys at essentially all frequencies. Requiring such a globally consistent description strongly disfavors very large (L≳15 kpc) and, even stronger, small (L≲1 kpc) effective diffusive halo sizes. This has profound implications for, e.g., indirect dark matter searches.

Cosmic-ray antiproton constraints on light singlino-like dark matter candidates

The CoGeNT experiment, dedicated to direct detection of dark matter, has recently released excess events that could be interpreted as elastic collisions of ∼ 10 GeV dark matter particles, which might simultaneously explain the still mysterious DAMA/LIBRA modulation signals, while in conflict with results from other experiments such as CDMS, XENON-100 and SIMPLE. It was shown that 5–15 GeV singlino-like dark matter candidates arising in singlet extensions of minimal supersymmetric scenarios can fit these data; annihilation then mostly proceeds into light singlet-dominated Higgs (pseudo-)scalar fields. We develop an effective Lagrangian approach to confront these models with the existing data on cosmic-ray antiprotons, including the latest PAMELA data. Focusing on a parameter space consistent with the CoGeNT region, we show that the predicted antiproton flux is generically in tension with the data whenever the produced (pseudo-)scalars can decay into quarks energetic enough to produce antiprotons, provided the annihilation S-wave is significant at freeze out in the early universe. In this regime, a bound on the singlino annihilation cross section is obtained, 〈 σ v 〉 ≲ 10 − 26 cm 3 / s , assuming a dynamically constrained halo density profile with a local value of ρ ⊙ = 0.4 GeV / cm 3 . Finally, we provide indications on how PAMELA or AMS-02 could further constrain or detect those configurations producing antiprotons which are not yet excluded.

Influence of microscopic particle interaction models on the flux of atmospheric antiprotons

We study the effect of particle interaction models on the theoretical estimates of atmospheric antiproton flux by comparing the BESS observations of antiproton spectra with the spectra obtained by means of a full three dimensional Monte Carlo simulation program. For such a purpose, we use two popular microscopic interaction models, namely FLUKA and UrQMD, to simulate antiproton spectra at multiple observation levels. In this article, we further compare the atmospheric antiproton fluxes predicted by a few popular microscopic high energy particle interaction models with each other to get an idea about the influence of such models at energies beyond the BESS upper cutoff up to about 100 GeV. We find that the simulated antiproton flux has strong dependence on the choice of interaction models. The present analysis seems to further indicate that the theoretical prediction of galactic antiproton spectrum may be uncertain by an appreciable amount due to our limited knowledge of particle interaction characteristics.

New constraints from PAMELA anti-proton data on annihilating and decaying dark matter

Recently the PAMELA experiment has released its updated anti-proton flux and anti-proton to proton flux ratio data up to energies of ≈ 200GeV. With no clear excess of cosmic ray anti-protons at high energies, one can extend constraints on the production of anti-protons from dark matter. In this letter, we consider both the cases of dark matter annihilating and decaying into standard model particles that produce significant numbers of anti-protons. We provide two sets of constraints on the annihilation cross-sections/decay lifetimes. In the one set of constraints we ignore any source of anti-protons other than dark matter, which give the highest allowed cross-sections/inverse lifetimes. In the other set we include also anti-protons produced in collisions of cosmic rays with interstellar medium nuclei, getting tighter but more realistic constraints on the annihilation cross-sections/decay lifetimes.

Froggatt-Nielsen model for leptophilic scalar dark matter decay

We construct a model of decaying, TeV-scale scalar dark matter motivated by data from the PAMELA and Fermi-LAT experiments. By introducing an appropriate Abelian discrete symmetry and an intermediate scale of vector-like states that are responsible for generating lepton Yukawa couplings, we show that Planck-suppressed corrections may lead to decaying dark matter that is leptophilic and has the desired lifetime. The dark matter candidate decays primarily to lepton/anti-lepton pairs, and at a subleading rate to final states with a lepton, anti-lepton and standard model Higgs boson. We show that the model can reproduce the observed positron flux and positron fraction while remaining consistent with the bounds on the cosmic ray antiproton flux.

THE DISCOVERY OF GEOMAGNETICALLY TRAPPED COSMIC-RAY ANTIPROTONS

The existence of a significant flux of antiprotons confined to Earth's magnetosphere has been considered in several theoretical works. These antiparticles are produced in nuclear interactions of energetic cosmic rays with the terrestrial atmosphere and accumulate in the geomagnetic field at altitudes of several hundred kilometers. A contribution from the decay of albedo antineutrons has been hypothesized in analogy to proton production by neutron decay, which constitutes the main source of trapped protons at energies above some tens of MeV. This Letter reports the discovery of an antiproton radiation belt around the Earth. The trapped antiproton energy spectrum in the South Atlantic Anomaly (SAA) region has been measured by the PAMELA experiment for the kinetic energy range 60-750 MeV. A measurement of the atmospheric sub-cutoff antiproton spectrum outside the radiation belts is also reported. PAMELA data show that the magnetospheric antiproton flux in the SAA exceeds the cosmic-ray antiproton flux by three orders of magnitude at the present solar minimum, and exceeds the sub-cutoff antiproton flux outside radiation belts by four orders of magnitude, constituting the most abundant source of antiprotons near the Earth.

Measurements of cosmic-ray antiprotons with PAMELA

The PAMELA experiment is a satellite-borne apparatus designed to study charged particles, and espe- cially antiparticles, in the cosmic radiation. The apparatus is mounted on the Resurs DK1 satellite which was launched on 15 June 2006. PAMELA has been traveling around the earth along an elliptical and semi-polar orbit for almost five years. It mainly consists of a permanent magnetic spectrom- eter, a time of flight system and an electromagnetic imag- ing calorimeter, which allows antiprotons to be identified from a dominating cosmic-ray background. New measure- ments of the cosmic-ray antiproton flux and the antiproton- to-proton flux ratio between 60 MeV and 180 GeV are pre- sented, employing data collected between June 2006 and De- cember 2008. Compared to previous experiments, PAMELA extends the energy range of antiproton measurements and provides significantly higher statistics. The derived antipro- ton flux and antiproton-to-proton flux ratio indicates that the main source of cosmic-ray antiprotons is considered to be secondary production and no primary contribution has to be invoked.

NUMERICAL SIMULATIONS OF THE MAGNETIC RAYLEIGH-TAYLOR INSTABILITY IN THE KIPPENHAHN-SCHLÜTER PROMINENCE MODEL

The existence of a significant flux of antiprotons confined to Earth's magnetosphere has been considered in several theoretical works. These antiparticles are produced in nuclear interactions of energetic cosmic rays with the terrestrial atmosphere and accumulate in the geomagnetic field at altitudes of several hundred kilometers. A contribution from the decay of albedo antineutrons has been hypothesized in analogy to proton production by neutron decay, which constitutes the main source of trapped protons at energies above some tens of MeV. This Letter reports the discovery of an antiproton radiation belt around the Earth. The trapped antiproton energy spectrum in the South Atlantic Anomaly (SAA) region has been measured by the PAMELA experiment for the kinetic energy range 60--750 MeV. A measurement of the atmospheric sub-cutoff antiproton spectrum outside the radiation belts is also reported. PAMELA data show that the magnetospheric antiproton flux in the SAA exceeds the cosmic-ray antiproton flux by three orders of magnitude at the present solar minimum, and exceeds the sub-cutoff antiproton flux outside radiation belts by four orders of magnitude, constituting the most abundant source of antiprotons near the Earth.

Antiprotons from dark matter: Effects of a position-dependent diffusion coefficient

Energetic antiprotons in cosmic rays can serve as an important indirect signature of dark matter. Conventionally, the antiproton flux from dark matter decays or annihilations is calculated by solving the transport equation with a space-independent diffusion coefficient within the diffusion zone of the galaxy, and assuming free propagation outside this zone. Antiproton sources outside of the diffusion zone are ignored. In reality, it is far more likely that the diffusion coefficient increases smoothly with distance from the disk, and the outlying part of the dark matter halo ignored in the conventional approach can be significant, containing as much as 90% of the galactic dark matter by mass in some models. We extend the conventional approach to address these issues. We obtain analytic approximations and numerical solutions for antiproton flux assuming that the diffusion coefficient increases exponentially with the distance from the disk, and including contributions from dark matter annihilations/decays in essentially the full dark matter halo. We find that the antiproton flux predicted in this model deviates from the conventional calculation for the same dark matter parameters by up to about 25%.

Higgsino dark matter model consistent with galactic cosmic ray data and possibility of discovery at LHC-7

A solution to the PAMELA positron excess with Higgsino dark matter within extended supergravity grand unified (SUGRA) models is proposed. The models are compliant with the photon constraints recently set by Fermi-LAT and produce positron as well as antiproton fluxes consistent with the PAMELA experiment. The SUGRA models considered have an extended hidden sector with extra degrees of freedom which allow for a satisfaction of relic density consistent with WMAP. The Higgsino models are also consistent with the CDMS-II and XENON100 data and are discoverable at LHC-7 with 1 fb^(-1) of luminosity. The models are testable on several fronts.

Study of slow and fast extraction for the ultralow energy storage ring (USR)

The Facility for Antiproton and Ion Research (FAIR, GSI) will not only provide future users with high fluxes of antiprotons in the high-energy range, but it is also intended to include a dedicated program for low-energy antiproton research in the keV regime, realized with the FLAIR project. The deceleration of antiprotons with an initial energy of 30 MeV down to ultralow energies of 20 keV will be realized in two steps. First, the beam is cooled and slowed down to an energy of 300 keV in a conventional magnetic ring, the Low energy Storage Ring (LSR) before being transferred into the electrostatic Ultralow energy Storage Ring (USR). In this synchrotron the deceleration to a final energy of 20 keV will be realized. This paper describes the ion-beam optical and mechanical layout of the beam extraction from the USR and summarizes the expected beam qualities of extracted beams.

Cosmic antiproton constraints on effective interactions of the dark matter

Using an effective interaction approach to describe the interactions between the dark matter particle and the light degrees of freedom of the standard model,we calculate the antiproton flux due to the annihilation of thedark matter in the Galactic Halo and compare to the most recent antiproton spectrum of the PAMELA experiment. We obtain useful constraints on the sizeof the effective interactions that are comparable to those deduced from colliderand gamma-ray experiments.

Modeling of the Near-Earth Low-Energy Antiproton Fluxes

The local interstellar antiproton spectrum is simulated taking into account antineutron decay, (He,p) interaction, secondary and tertiary antiproton production, and the solar modulation in the “force field” approximation. Inclusive invariant cross-sections were obtained through a Monte Carlo procedure using the Multistage Dynamical Model code simulating various processes of the particle production. The results of the simulations provided flux values of to and to antiprotons/( s sr GeV) at energies of 0.2 and 1 GeV, respectively, for the solar maximum and minimum epochs. Simulated flux of the trapped antiprotons in the inner magnetosphere due to galactic cosmic ray (GCR) interactions with the atmospheric constituents exceeds the galactic antiproton flux up to several orders. These simulation results considering the assumptions with the attendant limitations are in comprehensive agreement with the experimental data including the PAMELA ones.