NOMAD

Home page of the experiment: http://nomadinfo.cern.ch/

1. Goal of the experiment

> The nt appearance in an almost pure nm beam is detected through its CC interactions and subsequent t decay. Nomad is sensitive to about 82% of the t branching ratios. To achieve the needed background rejection power of the order 105 Nomad pioneers a selection tecnique based on kinematic criteria.

> The goal of the experiment is to reach a low and consistently estimated background level while getting an high sensitivity and a robust evaluation of the selection efficiency.

> Due to the naturally suppressed ne component of the beam and to the good lepton identification and reconstruction properties of the detector, Nomad can also perform a nm-ne oscillation search with a sensitivity partially covering the parameter region allowed by the LSND experiment.

2. Physics achievements

> Nomad has collected a sample of 1.3 millions nm CC interactions on the target and has completed the analysis for the nm-nt oscillation search. The robustness and the power of the kinematic selection method has been proven. The large collected statistics of nm CC has been exploited to correct for the systematics of the MC simulation and to obtain a precise description of the backgrounds down to O(10-5) and to check the MC efficiencies. An independent check of the background predictions has been obtained with the analysis of wrong sign candidates. The possible biases due to the study of the data in the region where the signal is expected has been avoided by means of a blind analysis. The exploitation of all the observed t decay channels has allowed to obtain a final sensitivity on P(nm-nt) of 2.6 10-4 (75% of which is due to the low background bins) close to the value of the proposal. No excess has been observed over the expected background so the experiment has established a new 90%CL limit on the P(nm-nt) of 2. 10-4 .