Highlights in Astroparticle Physics: Muons, Neutrinos, Hadronic

Highlights in astroparticle physics: muons, radiation from any kind of particle acceleration neutrinos, hadronic interactions, exotic par- (Sect. 5). ticles, and dark matter | Rapporteur Talk HE2 & HE3 • Muons are used in a geophysical application for tomography of a volcano (Sect. 6). J.R. Hörandel • New projects are underway to detect high- energy neutrinos: KM3NeT in the Mediter- ranean Sea, as well as ARA and ARIANNA Department of Astrophysics, IMAPP, Radboud on the Antarctic continent (Sect. 7). University Nijmegen, 6500 GL Nijmegen, The Netherlands | http://particle.astro.ru.nl • First data from the Large Hadron Collider (LHC), in particular from the forward detec- Recent results presented at the International tor LHCf, yield new insight into hadronic in- Cosmic Ray Conference in Beijing will be reviewed. teractions, which are of great importance to de- Topics include HE2: "Muons and Neutrinos" and scribe the development of extensive air showers HE3: "Interactions, Particle Physics Aspects, (Sect. 8). Cosmology". • New upper limits on magnetic monopoles reach sensitivities of the order of keywords: muons, neutrinos, neutrino tele- 10−18 cm−2 s−1 sr−1. Searches for antin- scopes, hadronic interactions, exotic particles, dark uclei indicate that there is less than 1 matter antihelium nucleus per 107 helium nuclei in the Universe (Sect. 9). 1 Introduction • Astrophysical dark matter searches yield upper limits for the velocity-weighted annihi- The 32nd International Cosmic Ray Conference was lation cross section of the order of hσvi < held in August 2011 in Beijing. About 150 pa- 10−24 cm3 s−1 (Sect. 10). pers were presented in the sessions HE2: "Muons and Neutrinos" and HE3: "Interactions, Particle Physics Aspects, Cosmology". Some of the high- 2 HE 2.1 Muon experiments lights presented at the conference will be reviewed. A wide spectrum of (astro-)physical questions is 2.1 Cosmic-ray anisotropy addressed in the papers covered by this rapporteur. The muons registered with GeV energies in under- The common theme seems to be "upper limits and ground muon detectors are produced in air showers bounds". The topics include with TeV energies. Thus, studying the arrival direc- • Underground experiments, measuring the tions of muons in underground facilities provides a muon flux from air showers, find evidence for mean to study the arrival directions of TeV primary anisotropies in the arrival direction of cosmic cosmic rays. rays with TeV energies (Sect. 2). At present, the biggest underground muon detector is IceCube at the South Pole. It is comprised • The sensitivity of neutrino oscillation searches of a 1 km3 water/ice Cerenkovˇ detector at a depth with water/ice Cerenkovˇ detectors has been re- below 1450 m w.e. [1] fBenZvi #306g. 1 The ported. detector is composed of 80 strings, each equipped arXiv:1212.1013v1 [astro-ph.HE] 5 Dec 2012 Supernova searches indicate that the rate of with 60 optical sensor modules. A surface array gravitational stellar collapses in the Galaxy is (IceTop) consists of 81 stations, each composed of less than 0.13 events/year (Sect. 3). 2 Cerenkovˇ detector water ice tanks, read out by • The big neutrino telescopes ANTARES and two optical sensors, respectively. IceCube are fully operational. Limits on the With the more than 32 · 109 events recorded, it diffuse neutrino flux reach sensitivities around is possible to probe the southern sky for per-mille 10−8 GeV cm−2 s−1 sr−1. No point sources 1References in fg refer to the Proceedings of the have (yet) been found (Sect. 4). 32nd International Cosmic Ray Conference, Beijing (2011) and to the slides available on the conference web site • A new method has been introduced, the "end- http://icrc2011.ihep.ac.cn/ f(first) author name #paper point formalism", to calculate electromagnetic numberg. 1 Figure 1: Angular power spectra for the cosmic ray intensity observed by IceCube, see also Fig. 2 [1] fBenZvi #306g. Figure 2: Arrival directions of TeV cosmic rays ob- anisotropy on all angular scales in the arrival direc- served by IceCube and Milagro [1] fBenZvi #306g. tion distribution of cosmic rays. A power spectrum analysis of the relative intensity map of the cosmic- ray flux reveals that the arrival direction distribu- tector with an active mass of about 1.33 kt. The tion is not isotropic, see Fig. 1. Significant struc- measured muon flux as function of time (see Fig. 3) tures are seen on several angular scales: a large- exhibits a seasonal modulation with an amplitude scale structure in the form of a strong dipole and of 1:5%. The muon flux reaches its maximum at a quadrupole, as well as small-scale structure on day 186:2 ± 0:4. scales between 15◦ and 30◦. The skymap exhibits several localized regions of significant excess and It is remarkable that the measured muon phase deficit in cosmic-ray intensity, see Fig. 2. The Ice- almost agrees with the phase of a dark matter sig- Cube observations complement measurements from nal, claimed by the DAMA experiment at the same other detectors in the northern hemisphere, such location [2]. The maximum of the dark matter sig- as the Milagro experiment. The origin of this nal is observed on June 2nd (day 152). This correla- anisotropy is still unknown. tion has also been pointed out in a recent paper [3], Another detector in the northern hemisphere is using muon flux measurements from the LVD detec- the MINOS neutrino oscillation experiment fde tor. It remains unclear if the seasonal modulation Jong #1185g. It is comprised of a near and a far of the underground muon flux significantly influ- detector, two steel-scintillator sampling calorime- ences the observed dark matter signal, after taking ters, installed at 100 m and 700 m underground, re- into account various measures to reduce the muon- spectively. Muon data from the near detector have related background. been used to investigate the arrival direction of cosmic rays. A sky map of the significances indicates anisotropies which are compatible with observations by ARGO-YBJ. A projection of the arrival directions on the right ascension axis yields a relative 2.3 Solar modulation anisotropy amplitude on the order of 0.1%. Solar modulation of Galactic cosmic rays is inves- 2.2 Annual modulation tigated with GRAND fPoirier #1292g. This is an array of 64 proportional wire chamber stations Annual variations in the (average) temperature pro- dispersed in an area of 100 m × 100 m. It contin- file of the atmosphere alter the air density and, thus, uously monitors the muon flux recorded for about influence the development of air showers. This af- 20 years. The muon data extend the energy range fects in particular the decay of pions into muons covered by the world-wide neutron monitor network and yields to a seasonal modulation of the observed to higher energies. An example is the Forbush de- muon flux. crease on October 29th, 2003, when GRAND reg- The BOREXINO solar neutrino detector is lo- istered a sudden intensity drop of 8%. In addition, cated at Gran Sasso National Laboratory below a the direction of the incoming muons is recorded, rock coverage corresponding to about 3800 m w.e. giving hints of the disturbances in the structure of fd'Angelo #510g. It is a liquid scintillation de- the heliosphere during a Forbush decrease. 2 Figure 3: Cosmic-ray induced muon flux observed by BOREXINO as function of time fd'Angelo #510g. 2.4 Muon interactions mum resolvable pT = 8 GeV for a 1 TeV muon. A data sample of slightly more than 100 days, taken When a high-energy muon traverses matter, such as during the construction phase of the detector has Antarctic ice, catastrophic energy losses occasion- been analyzed. No high pT muon has been found. ally occur fBerghaus #85g. With IceCube the longitudinal profile of such events is reconstructed. This provides a calorimetric measurement of the 2.5 Muon charge ratio cascades with TeV energies. The technique is used Recent measurements of the atmospheric muon to extend the measured atmospheric muon spec- charge ratio for momenta around 1 GeV/c are trum to higher energies up to 500 TeV. in agreement with expectations from calculations A similar method is applied in the ANTARES fBrancus #400g fAbdolahi #749g. neutrino telescope to reconstruct the energy of electromagnetic showers induced by muons in water fMangano #158g. The cascades are in- 3 HE 2.2 Solar, atmospheric, duced by TeV muons via pair production and bremsstrahlung. Muons with energies up to and related neutrino exper- 100 TeV have been reconstructed. iments In extensive air showers muons with high trans- verse momentum pT are occasionally produced In present experiments, neutrinos are measured fGerhardt #323g. The dominant production over a wide energy range. An overview on sev- processes are the semileptonic decay of heavy eral detectors and their energy range is given in quarks and the decay of high pT kaons and pions Fig. 4. Astrophysical neutrinos are expected from in jets. High pT muons manifest themselves in the MeV energies (solar neutrinos) up to the EeV range data as single muons separated a few hundred me- (presumably extragalactic sources). The properties ters from the shower core. IceCube with its surface of neutrinos are investigated using neutrinos gener- detector IceTop is well suited to study such effects. ated in nuclear reactors (MeV regime) and acceler- High pT muons can be reconstructed with a mini- ators (GeV regime). Recent results on neutrino os- 3 Figure 4: Energy range of various neutrino detectors, after fHa #324g. cillation measurements are discussed in Sect. 3 and the detection of high-energy neutrinos in Sect. 4. Neutrino oscillations are commonly described in terms of the L=E dependence, where E is the neutrino energy and L its oscillation path length [4].

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