We report the first precision measurements of the scaled momentum, the charge multiplicity, and the thrust of hadronic jets in the Breit frame in Deep Inelastic Scattering nu(mu)N and <(nu)over bar(mu)N> charged cur rent events over the Q(2) range from 1 to 100 GeV2. The neutrino data, obtained in the NOMAD experiment at the CERN SPS, extend the Q(2)-evolution of these parameters by two orders of magnitude, and with commensurate precision, when compared to those reported by the ep and e(+)e(-) experiments. (C) 1999 Elsevier Science B.V. All rights reserved.

The NOMAD trigger system is described in the present paper. It is made up of a large area plastic scintillator veto system, two trigger scintillator planes inside a 0.4 T magnetic field and their associated trigger electronics. Special features of the system consist of the use of proximity mesh photomultipliers which allow the trigger scintillators to operate in the magnetic field, and the use of custom-built VME modules which perform the trigger logic decisions, the signal synchronisation and gate generation, event counting and livetime calculations. This paper also includes a description of each of the NOMAD triggers, with their calculated and measured rates, efficiencies and livetimes.

A search was made for a new light gauge boson X which might be produced in pi(0) -->, gamma + X decay from neutral pions generated by 450 GeV protons in the CERN SPS neutrino target. The X's would penetrate the downstream shielding and be observed in the NOMAD detector via the Primakoff effect, in the process of X --> pi(0) conversion in the external Coulomb field of a nucleus. With 1.45 x 10(18) protons on target, 20 candidate events with energy between 8 and 140 GeV were found from the analysis of neutrino data. This number is in agreement with the expectation of 18.1 +/- 2.8 background events from standard neutrino processes. A new 90% C.L. upper limit on the branching ratio Br(pi(0) --> Y + X)< (3.3 to 1.9)X 10(-5) for X masses ranging from 0 to 120 MeV/c(2) is obtained. (C) 1998 Elsevier Science B.V. All rights reserved.

This talk presents the current status of the search for nu(mu) --> nu(tau) oscillations with the NOMAD detector. Significant progress has been made with respect to our published results. The analysis techniques have been improved and a larger data sample, corresponding to the 1995-1997 runs has been used. The search yields no evidence of the presence of oscillations. The updated limit on the neutrino oscillation mixing angle is sin(2) 2 theta(mu tau) < 1.2 x 10(-3), in the limit of large Delta m(2).

The NOMAD experiment is a short base-line search for νμ − ντ oscillations in the CERN neutrino beam. The ντ's are searched for through their charged current interactions followed by the observation of the resulting τ− through its electronic, muonic or hadronic decays. These decays are recognized using kinematical criteria necessitating the use of a light target which enables the reconstruction of individual particles produced in the neutrino interactions. This paper describes the various components of the NOMAD detector: the target and muon drift chambers, the electromagnetic and hadronic calorimeters, the preshower and transition radiation detectors and the veto and trigger scintillation counters. The beam and data acquisition system are also described. The quality of the reconstruction and individual particles is demonstrated through the ability of NOMAD to observe Ks0's, Λ0's and π0's. Finally, the observation of τ− through its electronic decay being one of the most promising channels in the search, the identification of electrons in NOMAD is discussed.

The NOMAD experiment is a short base-line search for νμ → ντ oscillations in the CERN neutrino beam. The ντ ’s are searched for through their charged-current interactions followed by the observation of the resulting τ− through its electronic, muonic or hadronic decays. These decays are recognized using kinematical criteria necessitating the use of a light target which enables the reconstruction of individual particles produced in the neutrino interactions. This paper describes the various components of the NOMAD detector: the target and muon drift chambers, the electromagnetic and hadronic calorimeters, the preshower and transition radiation detectors, and the veto and trigger scintillation counters. The beam and data acquisition system are also described. The quality of the reconstruction of individual particles is demonstrated through the ability of NOMAD to observe Ks ’s, Λ 0’s and π0’s. Finally, the observation of τ− through its electronic decay being one of the most promising channels in the search, the identification of electrons in NOMAD is discussed.

A search was made for a new light gauge boson X which might be produced in p TMgqX decay from neutral pions generated by 450 GeV protons in the CERN SPS neutrino target. The X’s would penetrate the downstream shielding and be observed in the NOMAD detector via the Primakoff effect, in the process of XTMp 0 conversion in the external Coulomb field of a nucleus. With 1.45=10 protons on target, 20 candidate events with energy between 8 and 140 GeV were found from the analysis of neutrino data. This number is in agreement with the expectation of 18.1"2.8 background events from Ž 0 . Ž . y5 standard neutrino processes. A new 90 % C. L. upper limit on the branching ratio Br p TMgqX 3.3 to 1.9 =10 for X masses ranging from 0 to 120 MeVrc is obtained. q 1998 Elsevier Science B.V. All rights reserved.