Search for Antihelium with the BESS-Polar Spectrometer

Abe, K.; Fuke, H.; Haino, S.; Hams, T.; Hasegawa, M.; Horikoshi, Atsushi; Itazaki, A.; Kim, K. C.; Kumazawa, T.; Kusumoto, A.; Lee, Moo Hyun; Makida, Y.; Matsuda, Shinya; Matsukawa, Yasuhisa; Matsumoto, K.; Mitchell, J. W.; Myers, Z.; Nishimura, Jun; Nozaki, M.; Orito, R.; Ormes, J. F.; Sakai, Kenichi; Sasaki, M.; Seo, E. S.; Shikaze, Y.; Shinoda, R.; Streitmatter, R. E.; Suzuki, Jun–ichi; Takasugi, Y.; Takeuchi, Kei; Tanaka, Kenichi; Thakur, N.; Yamagami, T.; Yamamoto, A.; Yoshida, Tetsuya; Yoshimura, K.

doi:10.1103/physrevlett.108.131301

Cited by 91 publications

(104 citation statements)

References 26 publications

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“…We show in grey the areas currently excluded by the experiments which have looked for a flux of anti-He in cosmic rays: Ams-01 [33], Bess [34] and Pamela [35]. Since all these experimental results are given in terms of He/He ratios, we convert them into anti-He fluxes using the He flux measured by Pamela [36] 2 (Ams-02 has also released preliminary data [37], that we do not use).…”

Section: Jhep08(2014)009mentioning

confidence: 99%

Anti-helium from dark matter annihilations

Cirelli

Fornengo

Taoso

et al. 2014

J. High Energ. Phys.

112

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Galactic Dark Matter (DM) annihilations can produce cosmic-ray anti-nuclei via the nuclear coalescence of the anti-protons and anti-neutrons originated directly from the annihilation process. Since anti-deuterons have been shown to offer a distinctive DM signal, with potentially good prospects for detection in large portions of the DM-particle parameter space, we explore here the production of heavier anti-nuclei, specifically antihelium. Even more than for anti-deuterons, the DM-produced anti-He flux can be mostly prominent over the astrophysical anti-He background at low kinetic energies, typically below 3-5 GeV/n. However, the larger number of anti-nucleons involved in the formation process makes the anti-He flux extremely small. We therefore explore, for a few DM benchmark cases, whether the yield is sufficient to allow for anti-He detection in currentgeneration experiments, such as Ams-02. We account for the uncertainties due to the propagation in the Galaxy and to the uncertain details of the coalescence process, and we consider the constraints already imposed by anti-proton searches. We find that only for very optimistic configurations might it be possible to achieve detection with current generation detectors. We estimate that, in more realistic configurations, an increase in experimental sensitivity at low kinetic energies of about a factor of 500-1000 would allow to start probing DM through the rare cosmic anti-He production.

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Section: Jhep08(2014)009mentioning

confidence: 99%

Anti-helium from dark matter annihilations

Cirelli

Fornengo

Taoso

et al. 2014

J. High Energ. Phys.

112

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“…It led to a new normalisation of the detected antineutrino flux lying some 6% above the detected flux at short distances from reactors [8], triggering the search for sterile neutrinos close to experimental reactors [16]. Meanwhile, the reactor experiments Double Chooz [17], Daya Bay (DB) [18] and Reno [19] have measured the shape of the reactor antineutrino spectrum close to Pressurized Water Reactors (PWR). The comparison between the converted spectra and the measured spectra not only confirmed the reactor anomaly, but also exhibited a large distortion of the data with respect to the model between 5 and 7 MeV in antineutrino energy.…”

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confidence: 99%

Updated Summation Model: An Improved Agreement with the Daya Bay Antineutrino Fluxes

et al. 2019

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A new summation method model of the reactor antineutrino energy spectrum is presented. It is updated with the most recent evaluated decay databases and with our Total Absorption Gammaray Spectroscopy measurements performed during the last decade. For the first time the spectral measurements from the Daya Bay experiment are compared with the detected antineutrino energy spectrum computed with the updated summation method without any renormalisation. The results exhibit a better agreement than is obtained with the Huber-Mueller model in the 2 to 5 MeV range, the region which dominates the detected flux. An unexpected systematic trend is found that the detected antineutrino flux computed with the summation model decreases with the inclusion of more Pandemonium free data. The detected flux obtained now lies only 1.9% above that detected in the Daya Bay experiment, a value that may be reduced with forthcoming new Pandemonium free data leaving less and less room to the reactor anomaly. Eventually, the new predictions of individual antineutrino spectra for the 235 U, 239 Pu, 241 Pu and 238 U are used to compute the dependence of the reactor antineutrino spectral shape on the fission fractions.

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“…No single event of observation of anti-helium or any heavier antinuclei was reported. The best up-to-date limit on the anti-helium flux was reported by BESS [5] and it is:He/He < 7×10 −8 . Potentially PAMELA and AMS might improve this limit by an order and two orders of magnitude respectively.…”

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confidence: 99%

How to see an antistar

2014

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Polarization of photons emitted in weak decays occuring at distant star allows to determine whether this star is made from antimatter. Even more promissing is the observation of neutrinos (antineutrinos) produced at neutronization (antineutronization) reactions at the beginning of SN (SN ) explosion.According to the Standard Cosmological Model (SCM) no primordial antimatter remains in the Universe. Let us shortly remind the arguments which lead to this conclusion. When in the course of the post Big Bang expansion the universe cooled down below the QCD phase transition at T QCD = 100 − 200 MeV, baryon-antibaryon pairs started to annihilate. If the baryon number of the Universe at these temperatures was locally zero, then the remaining frozen concentration of baryons would be (see e.g. ref.[1]):where n B is the number density of baryons, by assumption equal to that of antibaryons, and n γ is the number density of photons in CMB. This result is by factor 10 11 smaller than the presently observed baryon concentration, which can be e.g. deduced from the recent Planck data [2], as:with the precision at the per cent level. Here it is implicitly assumed that the amount of antibaryons is negligibly small, nB ≪ n B . In order to avoid conclusion (1) we have either to assume that at the era of baryon-antibaryon annihilation the universe was predominantly and homogeneously populated by baryons, or that the universe has domain structure with spatially separated domains of matter and antimatter. In the last case it might be even not excluded that the total baryonic number of the universe is zero.In the frameworks of the SCM the first option is accepted, which has a strong support from the baryogenesis theory, whose basic principles have been formulated by Sakharov almost half a century ago [3]. In all known scenarios of baryogenesis an excess of baryons over antibaryons was generated at very (or rather) high temperatures, while at the subsequent cosmological expansion and cooling down the baryon-to-photon ratio (2) stayed approximately constant, up to the entropy release by the massive particle annihilation.In the universe with an excess of baryons a chance for antibaryons to survive was negligibly small, though in the early universe there were almost equal number densities of baryons and antibaryons, (n B − nB)/n B ≈ η ≪ 1 . The temperature at which the "massacre" of antibaryons by dominant baryons stopped is fixed by the annihilation freezing which is determined by the time when the annihilation rate became equal to the cosmological expansion rate:where σv ≈ 1/m 2 π is the cross-section of pp → nπ reaction times the proton velocity in c.m. system, m p is the proton mass, M p is the Planck mass and n is the number of pions produced in pp annihilation.That is why the remaining antiproton concentration being proportional tois unobservably small: there is not a single primordial antiproton in all presently visible part of our Universe. This bound is evidently too strong. Statistical fluctuations of the antibaryonic density coul...

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Search for Antihelium with the BESS-Polar Spectrometer

Cited by 91 publications

References 26 publications

Anti-helium from dark matter annihilations

Anti-helium from dark matter annihilations

Updated Summation Model: An Improved Agreement with the Daya Bay Antineutrino Fluxes

How to see an antistar

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