Neutrino oscillation and expected event rate of supernova neutrinos in adiabatic explosion model

We study how the influence of the shock wave appears in neutrino oscillations and the neutrino spectrum using density profile of adiabatic explosion model of a core-collapse supernova which is calculated in an implicit Lagrangian code for general relativistic spherical hydrodynamics. We calculate expected event rates of neutrino detection at SK and SNO for various theta_{13} values and both normal and inverted hierarchies. The predicted event rates of bar{nu}_e and nu_e depend on the mixing angle theta_{13} for the inverted and normal hierarchies, respectively, and the influence of the shock appears for about 2 - 8 s when sin^2 2 theta_{13} is larger than 10^{-3}. These neutrino signals for the shock propagation is decreased by < 30 % for bar{nu}_e in inverted (SK) or by < 15 % for nu_e in normal hierarchy (SNO) compared with the case without shock. The obtained ratio of the total event for high-energy neutrinos (20 MeV < E_{nu} < 60 MeV) to low-energy neutrinos (5 MeV < E_{nu} < 20 MeV) is consistent with the previous studies in schematic semi-analytic or other hydrodynamic models of the shock propagation. The time dependence of the calculated ratio of the event rates of high-energy to low-energy neutrinos is a very useful observable which is sensitive to theta_{13} and hierarchies. Namely, time-dependent ratio shows clearer signal of the shock propagation that exhibits remarkable decrease by at most factor \sim 2 for bar{nu}_e in inverted (SK), whereas it exhibits smaller change by \sim 10 % for nu_e in normal hierarchy (SNO). Observing time-dependent high-energy to low-energy ratio of the neutrino events thus would provide a piece of very useful information to constrain theta_{13} and mass hierarchy, and eventually help understanding the propagation how the shock wave propagates inside the star.Comment: 19 pages, 9 figures, accepted for publication in Physical Review

Hybrid ECAL: Optimization and Related Developments

Hybrid ECAL is a cost-conscious option of electromagnetic calorimeter (ECAL) for particle flow calorimetry to be used in a detector of International Linear Collider (ILC). It is a combination of silicon-tungsten ECAL, which realizes high granularity and robust measurement of electromagnetic shower, and scintillator-tungsten ECAL, which gives affordable cost with similar performance to silicon. Optimization and a data acquisition trial in a test bench for the hybrid ECAL are described in this article.Comment: 7 pages, 4 figures, Talk presented at the International Workshop on Future Linear Colliders (LCWS14), Belgrade, Serbia, 6-10 October 201

Reconstructing particle masses from pairs of decay chains

A method is proposed for determining the masses of the new particles N,X,Y,Z in collider events containing a pair of effectively identical decay chains Z to Y+jet, Y to X+l_1, X to N+l_2, where l_1, l_2 are opposite-sign same-flavour charged leptons and N is invisible. By first determining the upper edge of the dilepton invariant mass spectrum, we reduce the problem to a curve for each event in the 3-dimensional space of mass-squared differences. The region through which most curves pass then determines the unknown masses. A statistical approach is applied to take account of mismeasurement of jet and missing momenta. The method is easily visualized and rather robust against combinatorial ambiguities and finite detector resolution. It can be successful even for small event samples, since it makes full use of the kinematical information from every event.Comment: 12 pages, 5 figure

Polynomials, Riemann surfaces, and reconstructing missing-energy events

We consider the problem of reconstructing energies, momenta, and masses in collider events with missing energy, along with the complications introduced by combinatorial ambiguities and measurement errors. Typically, one reconstructs more than one value and we show how the wrong values may be correlated with the right ones. The problem has a natural formulation in terms of the theory of Riemann surfaces. We discuss examples including top quark decays in the Standard Model (relevant for top quark mass measurements and tests of spin correlation), cascade decays in models of new physics containing dark matter candidates, decays of third-generation leptoquarks in composite models of electroweak symmetry breaking, and Higgs boson decay into two tau leptons.Comment: 28 pages, 6 figures; version accepted for publication, with discussion of Higgs to tau tau deca

Study of the Gauge Mediation Signal with Non-pointing Photons at the CERN LHC

In this paper we study the gauge mediation signal with the ATLAS detector at the CERN LHC. We focus on the case where the NLSP is the long-lived lightest neutralino ($\tilde{\chi}^0_1$) which decays dominantly into a photon ($\gamma$) and a gravitino ($\tilde{G}$). A non-pointing photon from the neutralino decay can be detected with good position and time resolutions by the electormagnetic calorimeter (ECAL), while the photon momentum would be precisely measured if the photon is converted inside the inner tracking detector before reaching the ECAL. A new technique is developed to determine the masses of the slepton ($\tilde{\ell}$) and the neutralino from events with a lepton and a converted non-pointing photon arising from the cascade decay $\tilde{\ell}\to \ell\tilde{\chi}^0_1\to \ell\gamma \tilde{G}$. A Monte Carlo simulation at a sample point shows that the masses would be measured with an error of 3% for $\cal{O}$(100) selected $\ell\gamma$ pairs. Once the sparticle masses are determined by this method, the decay time and momentum of the neutralino are solved using the ECAL data and the lepton momentum only, for all $\ell\gamma$ pairs without the photon conversion. We estimate the sensitivity to the neutralino lifetime for $c\tau=10$ cm to $\cal{O}$(10) m.Comment: 19 page, 7 figures, revte