Ebook: Neutrino Physics and Astrophysics

The School “Neutrino Physics and Astrophysics”, held in Varenna (Villa Monastero), from July 26 to August 5, 2011 was a joint event of the International School of Physcics “Enrico Fermi” of the Italian Physical Society (SIF), and of the network International School of AstroParticle Physics (ISAPP).

The “Enrico Fermi” School is a prestigious SIF institution located in VarennaVilla Monastero. It has been active since 1953 and hosts, as teachers, the most distinguished scientists coming from all over the world. The School organizes three-to-four events per year, covering all areas of physics, including physics-based interdisciplinary topics.

The International School of Astro-particle Physics (ISAPP) is a network, born in 2002, whose aim is the build-up of an actual astro-particle community, merging astrophysicists and particle physicists. The organization of Schools and Summer Institutes is one of the activities of the network, which is a net of 33 Institutes in Europe, Russia and Israel.

The ISAPP Schools are true didactic schools at the level of PhD students. The lectures are planned to give both the basic elements and the more recent developments of the central topics of the School. Extended discussions among students and teachers take place in the lecturing hall during the school and at the lunches and dinners, jointly attended by all the participants. In addition, outlines concerning the Standard Model of Elementary Particles and the Cosmology are always given as introductory lectures, to help both the Elementary Particle and Astrophysics communities to reach a common background.

These Proceedings are the written version of the lectures presented at the School and in some cases expanded and upgraded. They do not include the pre-school lectures, which would need a very extended and long text, and a few lectures because they were not translated in a written version by the lecturers (F. Gatti, M. Thomson, C. Peñna-Garay).

The Proceedings contain at the end short communications about the physics results presented in the form of posters by the students during the School. About ten of them have been selected also for an oral presentation.

We hope that this Volume will be useful not only to the participants of the School, but also to other PhD students and young physicists.

We acknowledge the very important support of the Italian Physical Society and the important help of the “Camera di Commercio” of Lecco, the Italian National Institute for Nuclear Research (INFN), the Italian National Institute of Astrophysics (INAF) and the Physics Department of the University of Milan (UNIMI).

G. Bellini and L. Ludhova

To complement the neutrino-physics lectures given at the 2011 International School on Astro Particle Physics devoted to Neutrino Physics and Astrophysics (ISAPP 2011; Varenna, Italy), at the 2011 European School of High Energy Physics (ESHEP 2011; Cheila Gradistei, Romania), and, in modified form, at other summer schools, we present here a written description of the physics of neutrino oscillation. This description is centered on a new way of deriving the oscillation probability. We also provide a brief guide to references relevant to topics other than neutrino oscillation that were covered in the lectures.

The impact in neutrino physics of the recent results on oscillations and the consequent need to measure the value of the neutrino mass are briefly discussed. Different detectors are developed and many experiments are planned to determine this mass, or at least to put an upper limit on it. This can be done by exploring the upper region of the spectrum of low energy β decays or by searching for neutrinoless double-beta decay (DBD). A possible evidence for neutrinoless DBD has been presented by a subset of the Heidelberg-Moscow Collaboration, but experiments of similar sensitivity like CUORICINO and NEMO do not confirm these results. They are however unable to confute it, due to the uncertainties on the calculation of the nuclear matrix elements in the evaluation of the absolute value of the neutrino mass. Various second-generation DBD experiments, of which one (CUORE) is presently in construction, aim to reach the sensitivity on the absolute Majorana neutrino mass predicted by the oscillation experiments under the inverse hierarchy hypothesis.

Neutrinos can play an important role in the evolution of the Universe, modifying some of the cosmological observables. In this contribution we summarize the main aspects of cosmological relic neutrinos and we describe how the precision of present cosmological data can be used to learn about neutrino properties, in particular their mass, providing complementary information to beta decay and neutrinoless double-beta decay experiments. We show how the analysis of current cosmological observations, such as the anisotropies of the cosmic microwave background or the distribution of large-scale structure, provides an upper bound on the sum of neutrino masses of order 1 eV or less, with very good perspectives from future cosmological measurements which are expected to be sensitive to neutrino masses well into the sub-eV range.

The role of neutrinos in stars is introduced for students with little prior astrophysical exposure. We begin with neutrinos as an energy-loss channel in ordinary stars and conversely, how stars provide information on neutrinos and possible other low-mass particles. Next we turn to the Sun as a measurable source of neutrinos and other particles. Finally we discuss supernova (SN) neutrinos, the SN 1987A measurements, and the quest for a high-statistics neutrino measurement from the next nearby SN. We also touch on the subject of neutrino oscillations in the high-density SN context.

This is a summary of a series of lectures on the current experimental and theoretical status of our understanding of origin and nature of cosmic radiation. Specific focus is put on ultrahigh energy cosmic radiation above ~ 10¹⁷ eV, including secondary neutral particles and in particular neutrinos. The most important open questions are related to the chemical composition and sky distributions of these particles as well as on the location and nature of their sources. High energy neutrinos at GeV energies and above from extra-terrestrial sources have not yet been detected and experimental upper limits start to put strong contraints on the sources and the acceleration mechanism of very high energy cosmic rays.

Low-energy neutrino physics and astrophysics has been one of the most active fields of particle physics research over the past two decades, achieving important and sometimes unexpected results, which have paved the way for a bright future of further exciting studies. The methods, the techniques and the technologies employed for the construction of the many experiments which acted as important players in this area of investigation have been crucial elements to reach the many accumulated physics successes. The topic covered in this review is, thus, the description of the main features of the set of methodologies at the basis of the design, construction and operation of low-energy neutrino detectors.

Gigantic neutrino telescopes are primarily designed to search for very high energy neutrino radiation from the cosmos. Neutrinos travel unhindered over cosmological distances and therefore carry unique undistorted information about their production sites: the most powerful accelerators of hadrons in nature. In these lectures, we present the relevant physics motivations and their specifics. We review methodological aspects of neutrino telescopes: the experimental technique, some of the faced problems and the capabilities in terms of discovery potential, effective area, isolation of a signal from atmospheric backgrounds, etc. Instruments and their operation in various media are described. We also mention the instrumental birth and provide an outlook of the detection technique toward very low and ultrahigh energies.

Within the last two decades major progress was achieved in experimental neutrino physics. This was only possible due to the constant development of new technologies in this field. Today a very broad progress of technologies can be observed, making possible neutrino experiments at very low energies (i.e. in the sub-MeV regime) until extreme high energies. In this lecture I will try to describe two examples, how new technologies developed within the last years. Both are mainly dealing with low energy neutrinos (i.e. below ≈ 1 GeV), however we will see how this technology may also be expanded to search for proton decays. This contribution will begin with a brief description of neutrino oscillations and the experimental status quo, followed by a short discussion about open questions in neutrino physics. Then the new technology developed for the search of θ₁₃ with the three reactor neutrino experiments will be presented, which started data taking in 2011. Finally I will discuss some aspects of a future project utilizing a very large, homogeneous liquid-scintillator volume.

Underground laboratories provide the low radioactive background environment necessary to explore the highest energy scales that cannot be reached with accelerators, by searching for extremely rare phenomena. Experiments range from the direct search of the dark matter particles that constitute the largest fraction of matter in the Universe, to the exploration of the properties of the neutrinos, the most elusive of the known particles and which might be particle and antiparticle at the same time, to the investigation on why our universe contains only matter and almost no antimatter, and much more. After an introduction, I will recall a few historical facts and then summarise the ongoing research topics. I will then focus on two frontier challenges: neutrino physics and dark matter search.

Borexino is a low background liquid-scintillator detector acquiring solar neutrino data at the LNGS underground laboratory in Italy. Borexino is the only experiment capable to perform spectrally resolved measurements of the low-energy ⁷Be solar neutrinos. Using three years of data since the start of data taking in 2007, Borexino has performed the first direct measurement of the ⁷Be solar neutrino rate with accuracy better than 5%. The absence of day-night asymmetry of the ⁷Be solar neutrino rate was measured with a total uncertainty of 1%. Borexino results alone reject the LOW region of solar neutrino oscillation parameters at more than 8.5σ CL. Combined with the other solar neutrino data, Borexino measurements isolate the MSW-LMA solution of neutrino oscillations without assuming CPT invariance in the neutrino sector.

The COBRA experiment is searching for neutrinoless double beta decay using CdZnTe semiconductor detectors. The main focus is on Cd-116, with a decay energy of 2814 keV well above the highest naturally occurring gamma lines. Furthermore, Te-130, with a high natural abundance, and Cd-106, a double β⁺ emitter, are under investigation. Advantageous is the possibility to operate the detectors at room temperature. Besides coplanar grid detectors, pixelised detectors are considered. The latter ones would allow for particle discrimination, therefore providing efficient background reduction. The current status of the experiment is described, including the upgrade of the R&D set-up in spring 2011 at the LNGS underground laboratory, the different detector concepts and the latest half-life limits. Furthermore, studies on the use of liquid scintillator for background suppression and Monte Carlo simulations are presented.

The GERmanium Detector Array (GERDA) is a neutrinoless double beta decay experiment in the Laboratori Nazionali del Gran Sasso (LNGS) and directly addresses the question of the Dirac or Majorana nature of neutrinos and their absolute mass scale. GERDA is specifically designed to test the currently pending claim of the Heidelberg Moscow Collaboration within its first phase of data taking which is soon to commence. The commissioning phase which started in July 2010 already reached a background level better than Heidelberg-Moscow, but remains by the time of April 2011 above the design goal. Initially, an unexpectedly large background contribution from ⁴²K was discovered, which became the major subject of investigation during the commissioning.

We consider the possibility of several mechanisms contributing to the ββ0ν decay amplitude in the general case of CP non-conservation: light Majorana neutrino exchange, heavy left-handed (LH) and right-handed (RH) Majorana neutrino exchanges, lepton charge non-conserving coupling in SUSY theories with R_p breaking. We study the cases of two “non-interfering” and two “interfering” mechanisms and we show how the lepton-number-violating parameters characterizing each of the considered mechanisms can be determined from data on the ββ0ν decay half-lives of two or three nuclear isotopes, respectively. This method can be generalized to the case of more than two ββ0ν decay mechanisms and allows to treat the cases of CP-conserving and CP–non-conserving couplings generating the ββ0ν decay in a unique way.

The Askar'yan Radio Array (ARA), a neutrino detector to be situated at the South Pole, will be sensitive to ultrahigh-energy cosmic neutrinos above 0.1 EeV and will have the greatest sensitivity within the favoured energy range 0.1 EeV up to 10 EeV. Neutrinos of this energy are guaranteed by the current observations of the GZK-cutoff by the HiRes and the Pierre Auger Observatories. The detection method is based on Cherenkov emission by a neutrino-induced cascade in the ice, coherent at radio wavelengths, which was predicted by Askar'yan in 1962 and verified in beam tests at SLAC in 2001. The detector is planned to consist of 37 stations with 16 antennas each, deployed at depth of up to 200 m under the ice surface. During the last polar season (2010–2011), a prototype station was successfully deployed and is taking data relevant to future analyses: ambient noise background studies and data for characterization of the South Pole ice sheet. The IIHE, as part of a worldwide collaboration of institutions in the USA, Asia, Oceania, and Europe, is contributing to the construction of the detector array, focusing on data acquisition methods. This talk will give a short report on the status of the ARA detector.

We carry out a detailed analysis of the supernova (SN) neutrino flavor evolution during the early time accretion phase (post-bounce times t_pb≤ 500 ms), characterizing the ν signal by recent SN hydrodynamics simulations. We find that trajectory-dependent “multi-angle” effects associated with the dense ordinary matter suppress collective oscillations induced by the ν−ν interaction in the deepest SN regions.

The aim of the Karlsruhe Tritium Neutrino experiment (KATRIN) is the direct (model-independent) measurement of the neutrino mass. For that purpose a windowless gaseous tritium source is used, with a tritium throughput of 40 g/day. In order to reach the design sensitivity of 0.2 eV/c² (90% C.L.) the key parameters of the tritium source, i.e. the gas inlet rate and the gas composition, have to be stabilized and monitored at the 0.1% level (1σ). Any small change of the tritium gas composition will manifest itself in non-negligible effects on the KATRIN measurements; therefore, Laser Raman spectroscopy (LARA) is the method of choice for the monitoring of the gas composition because it is a non-invasive and fast in-line measurement technique. In this paper, the requirements of KATRIN for statistical and systematical uncertainties of this method are discussed. An overview of the current performance of the LARA system with respect to precision will be given. In addition, two complementary approaches of intensity calibration are presented.

Stellar evolution is sensitive to the existence of low-mass particles with very weak couplings to matter. They can be abundantly produced in stellar interiors, escape without further interaction, and thus contribute directly to the stellar energy losses. Neutrinos are a prime example, but hypothetical particles predicted in extensions of the standard model of particle physics could also play a role. The comparison of detailed astronomical observations with detailed stellar evolution calculations has been widely used to constrain the existence of axions, millicharged particles, Kaluza-Klein gravitons and so forth, and to test novel couplings of neutrinos such as dipole moments. Our goal is to re-examine the impact of novel low-mass particles in the evolution of globular cluster stars in light of the most recent astronomical and physical data.

We study the impact of the inverse seesaw mechanism on several leptonic and hadronic low-energy flavour-violating observables in the context of the Minimal Supersymmetric Standard Model. Indeed, the contributions of the light right-handed sneutrinos from the inverse seesaw significantly enhance the Higgs-mediated penguin diagrams. We find that this can increase the different branching ratios by as much as two orders of magnitude.

A part from the 11 y solar cycle, another relevant time scale of solar activity variability are the quasi-biennal oscillations (QBOs). Through Empirical Mode Decomposition, we have isolated from Homestake and SAGE solar neutrino data QBOs which show significant correlation with that isolated from solar activity indices.

The Double Chooz experiment consists of two identical detectors, studying the coming from Chooz nuclear reactors. The goal is to measure the unknown leptonic parameter θ₁₃. The far detector, sensitive to θ₁₃, has already been taking data since April 2011. The near one, aiming at monitoring the reactor flux, will be installed in 2012. We present the concept, detection method, estimated sensitivity and discovery potential of the experiment as well as its first results on θ₁₃.

The NUCIFER project aims to test a small electron-antineutrino detector to be installed a few 10 meters from a reactor core for monitoring its thermal power and for testing the sensitivity to the plutonium content, in order to apply this technology to non-proliferation. Moreover, recent re-analysis of previous reactor neutrino experiments shows a significant discrepancy between measured and expected neutrino count rates. Among the various hypotheses a new phenomenon as the existence of a fourth sterile neutrino can explain this anomaly and NUCIFER will be able to address this hypothesis. The detector is now almost finished and we will test it at the French OSIRIS research reactor for the next months.

Low energy electrons created in the hull of the spectrometer vessel are a main background source in the KATRIN experiment, requiring efficient electrostatic and magnetic shielding. This shielding efficiency was measured with photoelectrons created by a pulsed UV-Laser shooting on the inner vessel surface of the KATRIN pre-spectrometer. The obtained results agree with simulations.

The IceCube Neutrino Observatory, situated at the geographic South Pole, was completed in December 2010. A lattice of 5160 photomultiplier tubes monitors one cubic kilometer of deep Antarctic ice in order to detect neutrinos via Cherenkov photons emitted by charged by-products of their interaction in matter. We report on IceCube's response to MeV neutrinos generated by core-collapse supernova explosions of nearby massive stars. This unique telescope was designed to detect energies greater than 100 GeV. Due to subfreezing ice temperatures, the photomultipliers' dark noise rates are particularly low. Therefore IceCube can also detect large numbers of MeV neutrinos by observing a collective rise in all photomultiplier rates on top of the dark noise. In the case of a supernova at the galactic center, IceCube's sensitivity matches that of a background free megaton-scale supernova search experiment and decreases to 20 and 6 standard deviations for star explosions at the galactic edge (30 kpc) and the Large Magellanic Cloud (50 kpc), respectively.