Accelerator Neutrinos

Abstract:

We report on a search for the flavor-changing neutral current decay D ⁰→µ⁺µ^- in pp^- collisions at √s = 1.96 TeV using 65 pb^-1 of data collected by the CDF II experiment at the Fermilab Tevatron Collider. A displaced-track trigger selects long-lived D⁰ candidates in the D⁰→µ ⁺µ^- search channel, the kinematically similar D ⁰→П⁺p^- channel used for normalization, the Cabibbo-favored D⁰K^-П^- channel used to optimize the selection criteria in an unbiased manner, and their charge conjugates. Finding no signal events in the D⁰→µ⁺µ^- search window, we set an upper limit on the branching fraction B(D⁰→µ⁺µ^-)≤2.5×10^-6 (3.3×10^-6) at the 90% (95%) confidence level.

Abstract:

With the evidence for massive neutrinos from recent ν-oscillation experiments, one of the most fundamental tasks of particle physics over the next years will be the determination of the absolute mass scale of neutrinos, which has crucial implications for cosmology, astrophysics and particle physics. The KArlsruhe TRItium Neutrino (KATRIN) experiment is the next-generation direct neutrino mass experiment with a sensitivity to sub-eV ν-masses. It combines an ultra-luminous molecular windowless gaseous tritium source with a high resolution electrostatic retarding spectrometer (MAC-E filter) to measure the spectral shape of β-decay electrons close to the endpoint at 18.6 keV with unprecedented precision. If no neutrino mass signal is found, the KATRIN sensitivity after 3 years of measurements is mν < 0.2 eV/c2 (90 % CL.); a ν-mass signal of mν = 0.35 (0.30) eV/c2 can be measured with 5 (3) σ evidence.