We carried out a model-independent search for light scalar or pseudoscalar particles
a's (an example of which is the axion) that couple to two photons by using a photon-regeneration method at high ...energies allowing a substantial increase in the sensitivity to eV masses. The experimental set-up is based on elements of the CERN West Area Neutrino Facility (WANF) beam line and the NOMAD neutrino detector. The new particles, if they exist, could be produced through the Primakoff effect in interactions of high energy photons, generated by the 450 GeV protons in the CERN SPS neutrino target, with virtual photons from the WANF horn magnetic field. The particles would penetrate the downstream shielding and would be observed in the NOMAD neutrino detector through their re-conversion into real high energy photons by interacting with the virtual photons from the magnetic field of the NOMAD dipole magnet.
From the analysis of the data collected during the 1996 run with 1.08×10
19 protons on target, 312 candidate events with energy between 5 and 140 GeV were found. This number is in general agreement with the expectation of 272±18 background events from standard neutrino processes. A 90
%
CL
upper limit on the
aγγ-coupling
g
aγγ
< 1.5
×10
−4
GeV
−1
for
a masses up to 40 eV is obtained.
The ATLAS Muon Trigger Slice Biglietti, M.; Carlino, G.; Conventi, F. ...
2006 IEEE Nuclear Science Symposium Conference Record,
2006-Oct., Letnik:
2
Conference Proceeding
At LHC the 40 MHz bunch crossing rate dictates a high selectivity of the ATLAS trigger, which has to keep the full physics potential of the experiment with a limited DAQ and storage capability. A ...three-level trigger has been designed to reduce the input rate to about 100 Hz. The capability to select events with muons at an early stage of the trigger system is crucial to cope with the expected rates. In this paper we will describe the trigger of the muon system (muon vertical slice). The first level of trigger, implemented in a custom hardware, will use measurements from the trigger chambers of the muon spectrometer to reduce the initial rate to 100 kHz. It selects muons with transverse momentum above programmable thresholds with a coarse evaluation of the muon position (regions of interest, RoIs). The RoIs are passed to the second trigger level in which fast algorithms reconstruct muons with high transverse momentum combining full granularity information from trigger and precision chambers of the muon spectrometer. A third trigger level, the event filter will access the full event to further reduce the rate to about 100 Hz. To accomplish this, components of physics analysis traditionally deferred to offline physics analysis, are embedded within the on-line trigger system. Along with the muon vertical slice implementation and description we will also present the expected performance relative to signal efficiencies, background rejection and execution time.
We report on a direct search in NOMAD for a new 33.9 MeV/c2 neutral particle (X) produced in pion decay in flight, π→μX followed by the decay X→νe+e−. Both decays are postulated to occur to explain ...the time anomaly observed by the KARMEN experiment. From the analysis of the data collected during the 1996–1998 runs with 4.1×1019 protons on target, a single candidate event consistent with background expectations was found. The search is sensitive to a pion branching ratio BR(π→μX)>3.7×10−15, significantly smaller than previous experimental limits.
A study of strange particle production in $\nu_\mu$ charged current interactions has been performed using the data from the NOMAD experiment. Yields of neutral strange particles ($\ko$, $\lam$, ...$\alam$) have been measured. Mean multiplicities are reported as a function of the event kinematic variables $E_\nu$, $W^2$ and $Q^2$ as well as of the variables describing particle behaviour within a hadronic jet: $x_F$, $z$ and $p_T^2$. Decays of resonances and heavy hyperons with identified $\ko$ and $\lam$ in the final state have been analyzed. Clear signals corresponding to $\rm {K^\star}^\pm$ $\rm {\Sigma^\star}^\pm$, $\rm \Xi^-$ and $\rm \Sigma^0$ have been observed.
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