Can a supernova be located by its neutrinos?

A future core-collapse supernova in our Galaxy will be detected by several neutrino detectors around the world. The neutrinos escape from the supernova core over several seconds from the time of collapse, unlike the electromagnetic radiation, emitted from the envelope, which is delayed by a time of order hours. In addition, the electromagnetic radiation can be obscured by dust in the intervening interstellar space. The question therefore arises whether a supernova can be located by its neutrinos alone. The early warning of a supernova and its location might allow greatly improved astronomical observations. The theme of the present work is a careful and realistic assessment of this question, taking into account the statistical significance of the various neutrino signals. Not surprisingly, neutrino-electron forward scattering leads to a good determination of the supernova direction, even in the presence of the large and nearly isotropic background from other reactions. Even with the most pessimistic background assumptions, SuperKamiokande (SK) and the Sudbury Neutrino Observatory (SNO) can restrict the supernova direction to be within circles of radius $5^\circ$ and $20^\circ$, respectively. Other reactions with more events but weaker angular dependence are much less useful for locating the supernova. Finally, there is the oft-discussed possibility of triangulation, i.e., determination of the supernova direction based on an arrival time delay between different detectors. Given the expected statistics we show that, contrary to previous estimates, this technique does not allow a good determination of the supernova direction.Comment: 11 pages including 2 figures. Revised version corrects typos, adds some brief comment

Neutrino mass from cosmology: Impact of high-accuracy measurement of the Hubble constant

Non-zero neutrino mass would affect the evolution of the Universe in observable ways, and a strong constraint on the mass can be achieved using combinations of cosmological data sets. We focus on the power spectrum of cosmic microwave background (CMB) anisotropies, the Hubble constant H_0, and the length scale for baryon acoustic oscillations (BAO) to investigate the constraint on the neutrino mass, m_nu. We analyze data from multiple existing CMB studies (WMAP5, ACBAR, CBI, BOOMERANG, and QUAD), recent measurement of H_0 (SHOES), with about two times lower uncertainty (5%) than previous estimates, and recent treatments of BAO from the Sloan Digital Sky Survey (SDSS). We obtained an upper limit of m_nu < 0.2eV (95% C.L.), for a flat LambdaCDM model. This is a 40% reduction in the limit derived from previous H_0 estimates and one-third lower than can be achieved with extant CMB and BAO data. We also analyze the impact of smaller uncertainty on measurements of H_0 as may be anticipated in the near term, in combination with CMB data from the Planck mission, and BAO data from the SDSS/BOSS program. We demonstrate the possibility of a 5 sigma detection for a fiducial neutrino mass of 0.1eV or a 95% upper limit of 0.04eV for a fiducial of m_nu = 0eV. These constraints are about 50% better than those achieved without external constraint. We further investigate the impact on modeling where the dark-energy equation of state is constant but not necessarily -1, or where a non-flat universe is allowed. In these cases, the next-generation accuracies of Planck, BOSS, and 1% measurement of H_0 would all be required to obtain the limit m_nu < 0.05 - 0.06eV (95% C.L.) for the fiducial of m_nu = 0eV. The independence of systematics argues for pursuit of both BAO and H_0 measurements.Comment: 22 pages, 6 figures, 12 table

The angular distribution of the reaction νˉe+p→e++n\bar{\nu}_e + p \to e^+ + n

The reaction $\bar{\nu}_e + p \to e^+ + n$ is very important for low-energy ($E_\nu \lesssim 60$ MeV) antineutrino experiments. In this paper we calculate the positron angular distribution, which at low energies is slightly backward. We show that weak magnetism and recoil corrections have a large effect on the angular distribution, making it isotropic at about 15 MeV and slightly forward at higher energies. We also show that the behavior of the cross section and the angular distribution can be well-understood analytically for $E_\nu \lesssim 60$ MeV by calculating to ${\cal O}(1/M)$, where $M$ is the nucleon mass. The correct angular distribution is useful for separating $\bar{\nu}_e + p \to e^+ + n$ events from other reactions and detector backgrounds, as well as for possible localization of the source (e.g., a supernova) direction. We comment on how similar corrections appear for the lepton angular distributions in the deuteron breakup reactions $\bar{\nu}_e + d \to e^+ + n + n$ and $\nu_e + d \to e^- + p + p$. Finally, in the reaction $\bar{\nu}_e + p \to e^+ + n$, the angular distribution of the outgoing neutrons is strongly forward-peaked, leading to a measurable separation in positron and neutron detection points, also potentially useful for rejecting backgrounds or locating the source direction.Comment: 10 pages, including 5 figure

Shell-model calculations of neutrino scattering from 12C

Neutrino reaction cross-sections, $(\nu_\mu,\mu^-)$, $(\nu_e,e^-)$, $\mu$-capture and photoabsorption rates on $^{12}$C are computed within a large-basis shell-model framework, which included excitations up to $4\hbar\omega$. When ground-state correlations are included with an open $p$-shell the predictions of the calculations are in reasonable agreement with most of the experimental results for these reactions. Woods-Saxon radial wave functions are used, with their asymptotic forms matched to the experimental separation energies for bound states, and matched to a binding energy of 0.01 MeV for unbound states. For comparison purposes, some results are given for harmonic oscillator radial functions. Closest agreement between theory and experiment is achieved with unrestricted shell-model configurations and Woods-Saxon radial functions. We obtain for the neutrino-absorption inclusive cross sections: $\bar{\sigma} = 13.8 \times 10^{-40}$ cm$^2$ for the $(\nu_{\mu},\mu^{-})$ decay-in-flight flux in agreement with the LSND datum of $(12.4 \pm 1.8) \times 10^{-40}$ cm$^2$; and $\bar{\sigma} = 12.5 \times 10^{-42}$ cm$^2$ for the $(\nu_{e},e^{-})$ decay-at-rest flux, less than the experimental result of $(14.4 \pm 1.2) \times 10^{-42}$ cm$^2$.Comment: 19 pages. ReVTeX. No figure

What can we learn from neutrinoless double beta decay experiments?

We assess how well next generation neutrinoless double beta decay and normal neutrino beta decay experiments can answer four fundamental questions. 1) If neutrinoless double beta decay searches do not detect a signal, and if the spectrum is known to be inverted hierarchy, can we conclude that neutrinos are Dirac particles? 2) If neutrinoless double beta decay searches are negative and a next generation ordinary beta decay experiment detects the neutrino mass scale, can we conclude that neutrinos are Dirac particles? 3) If neutrinoless double beta decay is observed with a large neutrino mass element, what is the total mass in neutrinos? 4) If neutrinoless double beta decay is observed but next generation beta decay searches for a neutrino mass only set a mass upper limit, can we establish whether the mass hierarchy is normal or inverted? We base our answers on the expected performance of next generation neutrinoless double beta decay experiments and on simulations of the accuracy of calculations of nuclear matrix elements.Comment: Added reference

Neutrinoless double beta decay within Self-consistent Renormalized Quasiparticle Random Phase Approximation and inclusion of induced nucleon currents

The first, to our knowledge, calculation of neutrinoless double beta decay ($0\nu\beta\beta$-decay) matrix elements within the self-consistent renormalised Quasiparticle Random Phase Approximation (SRQRPA) is presented. The contribution from the momentum-dependent induced nucleon currents to $0\nu\beta\beta$-decay amplitude is taken into account. A detailed nuclear structure study includes the discussion of the sensitivity of the obtained SRQRPA results for $0\nu\beta\beta$-decay of $^{76}$Ge to the parameters of nuclear Hamiltonian, two-nucleon short-range correlations and the truncation of the model space. A comparision with the standard and renormalized QRPA is presented. We have found a considerable reduction of the SRQRPA nuclear matrix elements, resulting in less stringent limits for the effective neutrino mass.Comment: 13 pages, 3 figures, 1 tabl

Fully-Renormalized QRPA fulfills Ikeda sum rule exactly

The renormalized quasiparticle-RPA is reformulated for even-even nuclei using restrictions imposed by the commutativity of the phonon creation operator with the total particle number operator. This new version, Fully-Renormalized QRPA (FR-QRPA), is free from the spurious low-energy solutions. Analytical proof is given that the Ikeda sum rule is fullfiled within the FR-QRPA.Comment: 9 page

Capture of Solar and Higher-Energy Neutrinos by Iodine 127

We discuss and improve a recent treatment of the absorption of solar neutrinos by ${}^{127}$I, in connection with a proposed solar neutrino detector. With standard-solar-model fluxes and an in-medium value of -1.0 for the axial-vector coupling constant $g_A$, we obtain a ${}^8$B-neutrino cross section of 3.3$\times 10^{-42}$, about 50\% larger than in our previous work, and a ${}^7$Be cross section that is less certain but nevertheless also larger than before. We then apply the improved techniques to higher incoming energies that obtain at the LAMPF beam dump, where an experiment is underway to finalize a calibration of the ${}^{127}$I with electron neutrinos from muon decay. We find that forbidden operators, which play no role in solar-neutrino absorption, contribute nonnegligibly to the LAMPF cross section, and that the preliminary LAMPF mean value is significantly larger than our prediction.Comment: 13 pages + 3 postscript figures (attached), in RevTex 3 , submitted to Phys. Rev.