CERN Accélérateur de science

Université de Genève

École de physique - Département de physique nucléaire et corpusculaire
24, quai Ernest-Ansermet
1211 GENÈVE 4
Tél: (022) 379 62 73 - Fax: (022) 379 69 92


The leading baryon remnants in high energy proton-proton and nuclear collisions carry a great deal of information. In the ATLAS experiment a new device for high energy pp collider physics - the Zero Degree Calorimeter (ZDC) - has been providing information from this kinematic region and ATLAS triggers since LHC startup.
Previous high energy collider experiments have measured leading protons, albeit in a miniscule range of Feynman x, and this has led to the very productive field of hard diffraction. ATLAS ZDC measurements, instead, cover neutral leading baryon and photon production over the range 0.2<xF<1.0 and provide a wealth of information about correlations between the forward baryon sector and the central region. These data are of interest, particularly, for new topics, which become interesting at the very high energies accessed by the LHC. For example, due to the shrinking of the diffractive peak and the growth of the hard component in pp collisions at the LHC, there is growing interest in characterizing these collisions in terms of collision impact parameter as suggested by Bjorken and by Frankfurt et al. The ultimate aim is to be able to trigger on very central collisions with the highest overlapping gluon density of the colliding nucleons.
Triggering on centrality is more challenging in pp scattering than in the Heavy Ion collider case where it is well known.
The information about forward production is critical also for understanding the dynamics of the interaction of the highest energy cosmic rays in the atmosphere.
Planned measurements of diffractive and non-diffractive photonuclear interactions during the upcoming ATLAS Heavy Ion run by the Univeristy of Geneva group will employ the ZDC for triggering and data analysis. This measurement will allow for the first time to study photon nucleus interactions at s1/2 up to 1 TeV.
The ATLAS ZDC addresses a number of interesting technical challenges. Not least of these is the 200 Watts of continuous beam energy (5 Gigarad/year) which the LHC dumps into each detector at design luminosity. The ZDC has far exceeded the time of flight performance of all other ATLAS detector subsystems. I will discuss the techniques used to obtain this high performance from sparsely sampled waveforms.
The style of this talk will be at the level of graduate physics and engineering students

The T2K neutrino oscillation experiment has been taking data since the beginning of the year, and several neutrino beam events have been observed in the Super-K detector, 295 km from the J-Parc accelerator and the ND280 detector.
The main goals of the experiment are to measure the disappearance of muon neutrinos and the appearance of electron neutrinos, as well as precise measurements of neutrino-nucleon interactions. A positive appearance signal would make it possible to search for neutrino CP-violation. The expected sensitivity to oscillation parameters are presented in the context of the many unanswered questions that prevail in the neutrino sector of the standard model.

Information : http://dpnc.unige.ch/seminaire/annonce.html
Organizer : G. Pasztor