July 15, 1997

Dr. Gregory Bock
MS 321

Dear Greg,

     Thank you for your presentation at the June PAC meeting on the
prospects for kaon physics with the Main Injector.  The Committee's
comments and recommendations follow:

"    The Committee appreciated the report on the 120 GeV fixed-target
workshop by Greg Bock, which concentrated on the prospects for experiments
using kaons.  Three experiments were discussed, with primary goals
being: a measurement of the decay rate for K0L->pi0 nu nubar (KAMI), a
measurement of the decay rate for K+->pi+ nu nubar (CKM), and a precise 
measurement of the phase of eta+- as a test of CPT invariance (CPT)."

"    In the context of the Standard Model, a measurement of the decay rate for 
K0L->pi0 nu nubar is a direct measurement of Im(Vtd) and has very high physics
justification.  It is as important as the goal of measuring CKM matrix 
elements and CP violation in the many B physics experiments being mounted.
Potential competition in making this measurement comes from a similar 
experiment approved but unfunded at BNL.  Both experiments have technical
requirements beyond the state of the art, mostly in vetoing photons.  This
effort could result in one of the key measurements made at Fermilab in the
next decade."

"    Similarly, The K+ analog experiment measures abs(Vtd) (with corrections 
for c quark contributions).  The theoretical uncertainty in deriving a 
measurement of abs(Vtd) from the decay rate is thought to be of order 10%.
A running BNL experiment expects to detect a few examples of this decay if it
is at the Standard Model level, and could results in a measurement of abs(Vtd)
with a precision of 25%.  The proposed next generation Fermilab experiment
requires a new charged separated beam and is intended to use a novel
spectrometer based upon RICH technology.  It is proposed to measure abs(Vtd) 
with a precision of about 5%."

"    A measurement of the phase of eta+- different from the superweak
prediction is a test of CPT invariance.  The expectation of where (if anywhere)
CPT invariance may be broken is unclear.  The proposed sensitivity of the MI
Fermilab experiment probes dMk/Mk at the level of Mk/Mplank and would
represent an improvement of a factor of 5-10 over the sensitivity expected from
KTeV.  This experiment originally proposed the separated beam discussed 
above, and intends to use apparatus mostly recycled from other experiments."

"    The physics motivation of the experiments to measure K_.pi nu nubar decay
rates is strong; that for the measurement of phi+- less so.  We recommend that
the proponents continue design studies towards the preparation of proposals.
However, resources are limited, there are substantial commitments to
approved experiments, and this program will compete with other proposals.
As a consequence, the threshold for approval will be high."

"    The Committee has the following specific recommendations:"

     KAMI

"    The collaboration is encouraged to test as much of the photon veto
system as possible in the FY99 Tevatron run, if it happens.  Since substantial
funding for a Main Injector experiment is unlikely to be available before 2002,
the collaboration should consider an earlier test run with modest upgrades.
The collaboration is encouraged to provide a document describing the
projected performance of an experiment capable of measuring the decay rate
for  K0L->pi0 nu nubar."

     I note that while I accept the principle of the recommendations, the
funds for the new veto system will have to come from sources other than 
Fermilab funds, and probably a source other than DOE funds.  I will 
communicate my wishes to the KTeV collaboration in a separate letter.

     CKM

"    Both this experiment and the CPT experiment rely on the separated
beam, and the collaboration is encouraged to continue design and R&D for this
beam, especially in the area of superconduction RF cavities.  The Committee 
looks forward to hearing about progress on this beam and the novel 
spectrometer concepts."

     CPT

"    The Committee would like to see more documentation of the proposed
experimental apparatus, and further justification for an improvement of a
factor of 5-10 in the precision of the measurement of phi+- over what is
anticipated from ongoing experiments.  The Committee would also like to see
a comparison with other experiments (for example CHLOE and DAFNE)."

     Please communicate these comments/recommendations to the relevant
participants of the Workshop.

                                           Sincerely,


                                           John Peoples

cc:   K. Stanfield