Neutrino masses from new generations

We reconsider the possibility that Majorana masses for the three known neutrinos are generated radiatively by the presence of a fourth generation and one right-handed neutrino with Yukawa couplings and a Majorana mass term. We find that the observed light neutrino mass hierarchy is not compatible with low energy universality bounds in this minimal scenario, but all present data can be accommodated with five generations and two right-handed neutrinos. Within this framework, we explore the parameter space regions which are currently allowed and could lead to observable effects in neutrinoless double beta decay, $\mu - e$ conversion in nuclei and $\mu \rightarrow e \gamma$ experiments. We also discuss the detection prospects at LHC.Comment: 28 pages, 4 figures. Version to be published. Some typos corrected. Improved figures 3 and

Calculations of energy loss and multiple scattering (ELMS) in molecular hydrogen

To show that the principle of ionization cooling will work for muon beams we must be able to simulate energy loss and scattering in media reliably. We have three choices: we can use traditional calculations with their uncertainties; we can make measurements (MUSCAT) or, we can calculate the phenomena more carefully, looking afresh at the phenomena from first principles. In this paper we report on work following this third approach. We derive the double differential cross section for a collision with transverse momentum transfer P-t and longitudinal momentum transfer P-l from a knowledge of the UV and x-ray photoabsorption cross section of the medium, together with the known kinematics and dynamics of the scattering of point charges with screening. Distributions in energy loss and scattering may then be found by Monte Carlo techniques which take into account both correlations in scattering and energy loss, and the true effects of non-Gaussian tails in distributions of interest. Preliminary results are reported for molecular hydrogen. Further work is in progress

Search for nucleon decay with final states l+η0, ν̄η0, and ν̄π+,0 using Soudan 2

We have searched for nucleon decay into five two-body final states using a 4.4 kiloton-year fiducial exposure of the Soudan 2 iron tracking calorimeter. For proton decay into the fully visible final states μ+η0 and e+η0, we observe zero and one event, respectively, that satisfy our search criteria for nucleon decay. The lifetime lower limits (τ/B) thus implied are 89×1030 years and 81×1030 years at 90% confidence level. For neutron decay into ν̄η0, we obtain the lifetime lower limit 71×1030 years. Limits are also reported for neutron decay into ν̄π0, and for proton decay into ν̄π+. ©2000 The American Physical Society

Particle Identification: Time-of-Flight, Cherenkov and Transition Radiation Detectors

Particle identification, PID, is of crucial importance in most experiments. The requirement can range from positive π/K identification in B-physics channels like B$^0_{\mathrm {s}}\rightarrow$D$^\mp _{\mathrm {s}}$K± against a background from B$^0_{\mathrm {s}}\rightarrow$D$^-_{\mathrm {s}}\pi ^+$ which is ∼15 times more abundant, to e/π separation at the level of ∼ 10−2 for momenta > 1 GeV/c in order to effectively suppress a combinatorial background in channels like leptonic decays of heavy vector resonances

Search for nucleon decay into lepton + K0 final states using Soudan-2

A search for nucleon decay into two-body final states containing K^0 mesons has been conducted using the 963 metric ton Soudan 2 iron tracking calorimeter. The topologies, ionizations, and kinematics of contained events recorded in a 5.52 kiloton-year total exposure (4.41 kton-year fiducial volume exposure) are examined for compatibility with nucleon decays in an iron medium. For proton decay into the fully visible final states \mu^+K^0_s and e^+K^0_s, zero and one event candidates are observed respectively. The lifetime lower limits (\tau /B) thus implied are 1.5 \times 10^{32} years and 1.2 \times 10^{32} years, respectively. Lifetime lower limits are also reported for proton decay into l^+K^0_l, and for neutron decay into \nu K^0_s.Comment: 51 pages, including 5 tables and 14 figures; updated text and tables; accepted for publication in Physical Review