January 12, 2007J. Sandweiss Two Important Long Range Programs for RHIC In addition to the many important RHIC research programs that are currently underway or projected. There are two programs which are not so well known but are of high significance and which are not likely to be done at the LHC and, in any case, need to be done at the RHIC energies.

January 12, 2007J. Sandweiss A. Photon-Photon HBT Only direct photons and weakly interacting leptons can be emitted from the quark gluon phase of the collision prior to hadronization. A unique property of the HBT is that only direct photons will display an HBT correlation (due to the “long” life of the π 0 meson). The  -  HBT can be studied as a function of p t, yielding unique information on space time evolution of the early, deconfined, phase.

January 12, 2007J. Sandweiss Feasibility of  -  HBT Our group has studied this, including many increasingly sophisticated simulations, (for the past 3 years). We have concluded that the measurement is both feasible and very informative. It is necessary to use a thin (~.1 rl) converter together with the calorimeter so each detector observes one , and  s that have vanishing momentum difference can be reliably detected.

January 12, 2007J. Sandweiss Challenges of the  -  HBT The π 0 photon flux, while not making an HBT correlation, does lower the size of the signal observed by a large factor (of order 10 3 ). Very careful analysis, which we believe can certainly be done is needed. And Large event samples are needed, event numbers of 1-2 billion. With DAQ1000 this is, however “just” a few weeks of running.

January 12, 2007J. Sandweiss Conclusion To carry out the  -  HBT measurement, long, dedicated runs will be needed along with the commitment of the serious analysis efforts. This is a long range program for RHIC, for example one can anticipate different collision energies, etc. It provides information which cannot be obtained by other means and is one of the strong arguments for a strong continuing RHIC deployment. Some more detailed discussion of the experiment can be found at, a proposal to STAR (not yet acted upon).

January 12, 2007J. Sandweiss B. Violation of P,T by the Strong Interaction There is a good possibility that parity (P) and time reversal symmetry (T) are violated in collisions that produce a “QGP state”. This violation is a spontaneous effect and the P,T effects will be randomly different in each event. This greatly complicates the experimental study of the effect.

January 12, 2007J. Sandweiss References It is not possible here to explain the underlying theory. However this effect deals with the most fundamental aspects of the basic field theory of QCD. Some references are: D. Kharzeev,R.D. Pisarski,& M.H.G.Tytgat Phys. Rev. Lett. 81, 512 (1998) D. Kharzeev, Phys. Lett.B663, (2006) Lattice calculations support the existence of the effect (show a distribution of topological winding numbers).

January 12, 2007J. Sandweiss Experimental Aspects Since the effect (spontaneous symmetry breaking) varies randomly in each event, any P (T) odd observable will average to zero over many events. Thus the effect must be seen in correlations. We have made some estimates (with the help of D. Karzeev) and the effects, e.g. in the observable helicity correlations of Λ pairs (via the parity violating decay of the Λ).

January 12, 2007J. Sandweiss What is needed? Large samples. The Λ-Λ correlation would take several billion STAR events. Other correlations will be similar. Further theoretical as well as experimental work because these correlations do not by themselves prove the effect. They could be caused by “ordinary” strong interactions. The behaviour of the effects must be compared with theoretical estimates of that predicted by the P,T effect and by the “usual” strong interaction.

January 12, 2007J. Sandweiss Summary These two programs offer unique qand fundamental information about the new state of matter produced in high energy heavy ion colissions. They are difficult, but clearly possible. It is my hope that the long range plan will recognize the importance and requirements of these studies.