External Collaborations

High Energy Physics InstrumentationA number of research projects involving Institute scientists are carried out at other large national and international accelerator facilities in collaboration with groups from other universities and laboratories worldwide. Many of these are directly complementary to the local experimental program but others, as described below, explore other frontiers.

Cyclotron Institute scientists carry out research within the BRAHMS and STAR collaborations at the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory. In collisions of ultra-relativistic heavy-ion beams at center-of-mass energies up to 200 GeV/nucleon pair, ordinary nuclear matter is predicted to undergo a phase transition to a quark-gluon plasma, a new state of matter that existed during the first second after the Big Bang. The BRAHMS group focuses on the study of very high rapidity phenomena, stringently testing theoretical models of the collision. Texas A&M participation in the STAR collaboration focuses on studies of high transverse momentum phenomena in ultra-relativistic nucleon-nucleus and nucleus-nucleus collisions and on studies of the spin of the proton.

The proton has a rich substructure including three valence quarks, the gluons that bind them together, and a “sea” of additional quark-antiquark pairs. Although the naive quark model predicts that the valence quarks provide the spin angular momentum of the proton, detailed experiments have shown that the quarks actually contribute very little. Most of the proton spin must be carried by the gluons or result from orbital angular momentum. To resolve this puzzle, the STAR experiment at RHIC will measure the polarization of gluons within the proton with high precision. TAMU is participating in the STAR spin-physics program and the construction of the STAR Endcap Electromagnetic Calorimeter, which will play a key role in the gluon polarization study.

Institute scientists comprise one of the lead groups in an experiment to measure the Michel parameters in normal muon decay at the TRIUMF “meson factory” in Vancouver, British Columbia. The Michel parameters characterize the shape of the positron spectrum from the muon decay as a function of energy and angle. The Standard Model provides definite predictions for each of the Michel parameters, based on its assumption that the weak interaction is purely left-handed. Any deviation between the measured values and the predictions would be extremely important, since it would require the introduction of right-handed weak currents or other new physics outside the current Standard Model.