Topics of First "N" Papers

1. ``Measurement of hard $\pi^0$ in inclusive, central and peripheral Au+Au collisions---Discovery of QCD Energy loss in Hot Dense Matter.''

   The assumption is that year one running with a full EM calorimeter in a single arm with recorded live integrated luminosity of 20 inverse microbarns should allow measurements of inclusive pizeroes to beyond 6 GeV/c in transverse momentum. Impact parameter dependence as a function of Zcal or E_T should also be posible although the rate for peripheral collisions may be inadequate. It is assumed that no trigger is available for the first year. The main problems are expected to be calibration, efficiency, and combinatoric background. In future years with higher luminosity, triggers using EMcal clusters are possible and desirable.

2. ``Search for prompt photons in inclusive, central and peripheral Au+Au collisions---limits on $\gamma/\pi$ for p_T < 10 GeV/c.''

   Absent any new phenomenon such as a ``flash of photons'' or strong jet quenching in a Quark Gluon plasma, it is unlikely that a prompt photon signal will be able to be significantly extracted from the collossal background of photons from pizero and eta decays. The prompt photon/pizero ratio increases with increasing $p_T$ which means the signal can only be seen at large $p_T$ which usually means high luminosity. This physics is limited both by background and by rate. Non-linearity in the EM calorimeter is also crucial. It is vital, for instance, that two 3 GeV photons have the identical response as one 6 GeV photon. Extensive studies of photon/pizero separation from EM cluster algorithms and combinatoric problems such as false pairing of a candidate photon with a random photon to make a pizero, or loss of a real pizero by the same mechanism are required.

3. ``Measurement of $\pi^+$, $\pi^-$ at large p_T in inclusive, central and peripheral Au+Au Collisions''

   Possibility of other hadrons, flavor tagging of jets a la CCHK ? Should have the same sensitivity as the pizero measurement in year one if the tracking coverage is the same as the EMcal. The issue for tracking is the ability to reconstruct tracks with high resolution at resonable efficiency. Triggers are possible and desirable in later years using pions above the RICH threshold (> 4 GeV/c).

4. ``Measurement of correlations of charged particles/$\pi^0$ with all `hard' probes above in inclusive, central and peripheral Au+Au collisions''

   Di-hadron measurements require full tracking and/or EMcal in both central arms and suffer a reduction in rate of roughly a factor of 6 (not counting p_T cuts) compared to inclusive single particle rates. Here's where we can measure the `acoplanarity' and energy imbalance of `jets', i.e. the ``k_T'' and ``x_E'' distributions.

5. ``Measurement of Shadowing of the Gluon structure function in Au+Au Collisions''

   from the rate of inclusive high p_T muons from heavy quark decay. This requires a single working muon arm and should produce a useful measurement with the year-1 luminosity. Problems are reconstruction efficiency, resolution and background. Evidently, understanding the background has a high priority to prove that the single muons are from heavy quark decay rather than light quark decay or punchthrough.

6. ``Drell-Yan production of di-leptons as a function of centrality in Au+Au collisions''

   This process is rate limited since it is essentially an electromagnetic process produced by hadron constituents. Thus high luminosity and a trigger are required which are not likely in year-1. An interesting issue that can be addressed in PHENIX is the associated multiplicity and $E_T$ (the impact parameter dependence) for drell-yan production. The steeply falling mass spectrum and point-like scaling observed in p-p and p+A collisions also make Drell-Yan pairs a sensitive probe to search for energy loss of quarks and anti-quarks in the initial state of cold nuclear matter.

General Questions for Above Reactions

• What should we expect: $A$ dependence for Central/Peripheral/inclusive with and without Quenching, Cronin Effect, Estimate sensitivity to energy loss vs $\int {\Cal L} dt$
• What can PHENIX do? What beams, lums are needed?
• $k_T$ or $p_T^2$ vs $E_T$ in p+A, A+A: what is known, what do we expect for RHIC, with and without QGP, quenching?
• Based on our present knowledge what measurements can/should we make for p-p, p+A,B+A,Au+Au (vs $\sqrt{s}$) vs $\int {\Cal L} dt$,

Michael J. Tannenbaum 7/28/99 - contact: mjt@bnl.gov