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July 22, 2003

Prof. Douglas Michael

Department of Physics

California Institute of Technology

Pasadena, California 91125

Prof. Stanley Wojcicki

SLAC, Bin 63

2575 Sand Hill Road

Menlo Park CA 94025

Dear Doug and Stan,

We would like to thank you and your colleagues for submitting your
proposed run plan for MINOS. In conjunction with presentations by Dave
Finley on the work of the Proton Committee, it provided the basis of
considerable discussion at the Aspen meeting of the Physics Advisory
Committee (PAC).

We have included below the section of the written report from the PAC
which pertains to neutrinos. Some of this appears in the publicly-posted
recommendations, however, you will note some questions directed at
MINOS.

You will recognize from the words that the PAC considers MINOS to be a
very high priority experiment, which will assuredly make measurements
which will advance our knowledge and understanding of neutrino flavor
transitions. We would like to join with them in congratulating you and
the NuMI project on some phenomenal progress during the past year. The
fact that you are already operating the complete far detector is
extremely impressive.

The thrust of the questions from the PAC is such as to explore the
correct strategy for the experiment. It is important for us to
understand its strengths and limitations. We and the Committee hope that
these questions can be helpful as you prepare your verbal presentation
to the Committee, an opportunity that you have not yet enjoyed. We look
forward to this happening at the December meeting.

Sincerely,

Michael Witherell

cc: K. Stanfield

H. Montgomery

S. Holmes

J. Appel

**B. *[Neutrino Opportunities]{.underline}***

#  1. [Health of the Near-Term Program]{.underline}

Neutrino physics has produced a great amount of excitement in the field
during the past five years, first with the evidence for oscillation in
atmospheric neutrinos from SuperKamiokande, next with the resolution of
the solar neutrino problem by SNO, and most recently with the reactor
anti-neutrino experiment KamLAND. An accelerator-based neutrino
oscillation experiment, K2K, has also been collecting data that is
consistent with the neutrino oscillation hypothesis, albeit with limited
statistics. In view of the rich physics opportunities opened up by these
recent discoveries and the existing neutrino program at the Laboratory,
the Laboratory is in a position to address important questions.

##  2. [MiniBooNE]{.underline}

MiniBooNE is an important neutrino experiment that should be in a
position to definitively verify or refute the neutrino oscillation
signal suggested by the LSND experiment.

The Committee commends the collaboration for timely construction of the
detector, and for working closely with the Laboratory and its Booster
team to successfully bring the proton intensity up quickly during the
last eight months. The collaboration is poised to produce first physics
results. The installation of the collimator and other improvements this
summer is expected to reduce effects of the beam losses and will allow
even higher intensity, potentially up to 510^20^ pot/year. The Committee
urges the Directorate to continue to work on improvement in the
performance and reliability in the Booster that provides beams to the
entire accelerator program at the Laboratory. The Committee also
anticipates a further discussion in the fall of progress and plans from
the experiment.

##  3. [MINOS]{.underline}

MINOS is a crucial neutrino experiment that will put the evidence for
oscillation in atmospheric neutrinos on completely solid ground. Its
goals are:

a)  Verify oscillation in muon neutrinos, by observing the "dip,"
    excluding decay or decoherence hypotheses.

b)  Measure *m*^2^ accurately. This is a fundamental physics parameter,
    and in addition it is potentially important for optimizing the
    location/energy of an off-axis neutrino experiment.

c)  Search for *~e~* appearance to a level of 1/2 to 1/3 of the CHOOZ
    limit.

d)  Test possible CPT violation between neutrino and anti-neutrino
    oscillations in atmospheric neutrinos.

The Committee congratulates the collaboration for completing the
construction of the far detector and for its successful initial study of
atmospheric neutrino-induced events. The Committee also notes that the
MINOS collaboration has worked closely with the Beams Division to ensure
the success of NuMI.

MINOS is currently scheduled to run for four years with an expectation
of initially achieving 2.510^20^ pot/year. The Committee thanks the
collaboration for their proposed run plan and detailed studies on
sensitivities in oscillation parameter measurements, limits on
alternative hypotheses, and a *~e~* appearance search, with various
numbers of protons, 7.410^20^, 1610^20^, and 2510^20^. From the
presented studies, it is clear that MINOS can take advantage of
increased proton intensity to improve accuracy in measurements, and
reach in a *~e~* appearance search. On the other hand, the need for
improvement is sensitive to the actual value of *m*^2^ and hence cannot
be assessed rigorously at this moment.

The Committee understands that the envisaged proton intensity of
2.510^20^ pot/year can be provided after currently planned improvements
in the Booster. The Committee, however, cannot endorse the proposed run
plan for 2510^20^ pot without knowing the costs associated with
increasing the proton intensity beyond this point. The Committee will
discuss the detailed run plan after seeing the improvement in Booster
performance, development in information from other experiments, as well
as initial data from MINOS itself.

In the next presentation to the PAC, the Committee asks the MINOS
collaboration to address the following questions:

a)  In the recent run plan submitted to the Committee, the errors on
    *m*^2^~23~, sin^2^2~23~ and the upper limit on sin^2^2~13~ decrease
    only slowly beyond the level of 1010^20^ pot. What physics justifies
    additional running, up to the level of 2510^20^ pot?

b)  In the scenarios considered in the run plan, the error on *m*^2^~23~
    comes close to the asymptotic value with a relatively small number
    of protons. What, then, is the optimal run plan, including the
    possibility of using NuMI beams at different energies, to minimize
    the error on sin^2^2~23~?

c)  Similarly, what is the optimal run plan to minimize the upper limit
    on sin^2^2~13~?

##  4. [Proton Economics]{.underline}

The Committee is grateful for the presentation at this meeting by the
Chairman of the Proton Committee. Proton economics is a very serious
issue for the Laboratory. The Committee anxiously awaits the written
report.

The Committee understands from the presentation that

a)  The current performance of the Booster provides 310^20^ pot/year for
    MiniBooNE and 4.210^19^ protons/year needed for slip stacking in the
    Main Injector.

b)  The improvements in the Booster that are now being implemented can
    provide beams to MiniBooNE at 510^20^ pot/year level until NuMI
    comes online.

c)  The Booster will be able to provide a baseline of 2.510^20^pot/year
    to NuMI concurrent with the slip stacking, while leaving an option
    for additional protons up to 4.510^20^/year coming directly from the
    Booster. With further improvements of the Main Injector, these
    additional protons might alternatively be sent to NuMI.

d)  Beyond the scheduled four years running of NuMI, the requested
    number of protons (mostly for BTeV and CKM) drops off. However, the
    Committee anticipates a further request for protons for NuMI, at an
    even higher level.

The Committee urges the Laboratory to follow up to make sure that
MiniBooNE will get at least 510^20^ protons in total, and NuMI will be a
success, in addition to Run II as the highest priority project. An
off-axis NuMI experiment may require still higher proton intensity. The
plans to extend the capability of the accelerator complex beyond 2005
need further study and the costs associated with the improvements should
be clarified.

#  5. [Future]{.underline}

As discussed at the June 2002 PAC meeting, the important targets of the
accelerator-based neutrino physics are the measurement of ~13~, the
determination of the mass hierarchy, and eventually the observation of
any CP violation. The Committee is pleased to learn of the process by
which the user community is exploring detector options for an off-axis
NuMI experiment, and to see a sample of the progress that is being made.
The Committee looks forward to seeing the results of this work,
including the response to the questions the Committee posed at the June
2002 PAC meeting.

Given that the J-PARC based neutrino beam is likely to be built,
possibly in 2008, there will be competition. From the presentation by
the Deputy Director based on the constant level of effort, there will
not be room for new initiatives from Fermilab base funding until FY2008.

The relationship between the developing program in Japan based on J-PARC
and that associated with the NuMI beam will depend on the pace of
development of the off-axis experiment within the limited resources. It
is anticipated that the two initiatives could be complementary because
the sensitivities to the matter effect in the *~e~* appearance
probabilities are different between the two initiatives. The extent to
which the comparison of the *~e~* appearance probabilities from the two
experiments can yield a determination of the mass hierarchy may well be
limited by statistics.

Both from the point of view of the competition with J-PARC and the
discrimination of the mass hierarchy, a high proton intensity is called
for. The current discussions on the off-axis experiment assume
410^20^/year for five years on a 50kT target, which is already beyond
the NuMI baseline of 2.510^20^/year. Extending the capability of the
existing accelerator complex is highly desirable in this respect. The
Committee urges the Directorate to keep working on proton economics and
to identify paths to incrementally increase the available number of
protons, possibly beyond 1010^20^/year.