The Nella and Leon Benoziyo Center for High Energy Physics


Giora Mikenberg, Director
The Lady Davis Professorial Chair of Experimental Physics

Although the universe in which we live looks very complex, with a large variety of different molecules and forces that binds them together, it is commonly assumed that shortly after the moment of creation the universe was a much simpler place. In particular, it is believed that only a single (unified) force existed. During the expansion of the universe its temperature dropped and the unified force was split into the four forces we know today (gravitation, nuclear, electromagnetic and the weak force which drives the radioactive decay). First viable models of the unification concept were suggested about 25 years ago and were experimentally confirmed some 15 years ago. A major consolidation of this concept was later done at LEP, the Large Electron Positron accelerator situated at CERN. Virtually all of the present knowledge about the fundamental particles and their interaction is included in a model named 'Standard Model'. In spite of its spectacular success and its incredible predictive power, the Standard Model cannot be the ultimate theory of particles and their interactions. Few fundamental measurements are still to be done and few crucial questions are still to be answered. The following projects that are supported by the Benoziyo center, address some of the more fundamental aspects of the Standard Model.

The ATLAS Experiment at the LHC Accelerator

The ATLAS Experiment has been measuring P-P and Pb-Pb collisions since April 2010 at the highest collision energy achieved by mankind. The ATLAS experiment has been performing as planned and coping with the five orders of magnitude increase of the LHC Luminosity, since the beginning of the operations. In particular, the 3,600 Thin-Gap Chamber (TGC) system, which was mainly constructed by the ATLAS-Weizmann group has been fully operational and less than 0.3% of the Weizmann made detectors have shown operational problems. The group has also constructed part of the readout system of the TGC complex. The hardware was commissioned together with the chambers.

The ATLAS group has also actively participated in the analysis of the collected data, in particular, in the understanding of hadronic background and in preparing for future possible discoveries of new particles. In the evaluation of this possible discoveries, a member of the group plays a leading role.

The team is also involved in R&D work required for the adaptation of the TGC technology to the harsh environment of the future Super-LHC (SLHC). At the SLHC the Israeli system will perform two tasks: Triggering on muonic events; and tracking muons which emerged from the interaction point with small angle with respect to the beam direction.

The group has also constructed part of the readout system of the TGC complex. The. hardware was commissioned together with the chambers.

In order to carry out the physics analysis millions of events need to be simulated. The complexity of the ATLAS detector coupled with the high beam energy of the LHC will result in complex events whose simulation require more than 30 minutes per event. The large amount of computing power required can be obtained by large number of closely linked computers within a system called GRID. The Weizmann group has spearheaded the GRID activity in Israel.

Contemporary basic physics is confronting three major issues:

The Weizmann team is focusing on the first two issues. One part of the group (which now has eight students, a postdoc, three technicians, two programmers and six faculty members) working on various aspects of Higgs boson searches. In particular, the group is very active in preparing the statistical tools that will be used for the interpretation of the results. It focuses on the Supersymmetric case in which five Higgs bosons are expected and searches for the charged and lightest Higgs particles through their decay into tau-leptons). The other part of the team focuses on the most popular model that goes well beyond our present knowledge. This model, known as Supersymmetry (SUSY), assumes that each of the known particles has a partner with different spin-statistics. The SUSY partners escape detection, but are expected to be indirectly detected at LHC due to their high mass. Supersymmetry is the first step for the long sought unification of forces. If found, it will solve some major problems in our present models, and will take us a long step toward unification. In particular the group is focusing on inclusive searches, on high jet multiplicity events and, as a first step, on better understanding of jet-energy calibration and resolution and on better identification of high pT b-quark jets.

The Physics of Heavy Ions: the PHENIX and ATLAS Experiment

The main activity of the Heavy Ion group at the Weizmann Institute is centered on the PHENIX Experiment at BNL. The PHENIX Experiment deals mainly with the study of a new state of matter called Quark-Gluon Plasma. This particular state characterizes the Universe a few microseconds after the Big-Bang. The Weizmann Heavy Ion Group is mainly involved in the detection of low mass electron-positron pairs which will follow very interesting results obtained by the group in previous experiments. For this reason, and under the leadership of the Weizmann Group, a new "Hadron Blind Detector" has been developed. This detector has been installed in 2007, fully instrumented with new GEMs. In 2010 PHENIX had a very successful run at RHIC with the HBD fully operational. A large data sample was collected on Au +Au collisions at the top RHIC energy of sqrt{s_NN} = 200 GeV (app. 8 billion minimum bias events). In addition to that, smaller data samples were recorded at 62.4 GeV (700 million events) and at 39 GeV (200 million events). The analysis of this data is being performed in collaboration with groups of Stony Brook University and Tokyo University.

On parallel to this activity, members of the group have played a key role in the analysis of the Heavy Ions data obtained with the ATLAS Experiment at the LHC, and in particular in the first clear observation of jet quenching that has recently been published.