email sparring by the old guard

Hi,

If you haven't seen the email sparring going on between the old guard,
here it is. (The messages read from the bottom with the latest message
first.)
Mike

==================================================================

Dear Dave, Burt, Adam et al:
I understand very well how treacherous parallels between the lepton sector
and the quark sector can be. In the early days of MSW, the great excitement
was the possibility of amplifying a small neutrino mixing angle into a large
effective one in the sun. Today we know that MSW's role is more subtle than
that.

My point in alluding to B decays is not the last decimal point, but whether
there is evidence for a large source of CPV outside the standard model which
affects quarks and would likely affect leptons too. So far there is none.

You, Burt and everyone else are perfectly correct about first determining
theta 13. If it is too small, then forget about CPV; but if it is
sufficiently large, serious thought will, I expect, be given to a long
baseline experiment comparing nu and nubar. My concern is the question: can
we justify the large effort and the large cost of the proton driver simply
on the basis that there MIGHT be significant CPV in the neutrino sector? Or
do we require more information, experimental or theoretical on that point?

What I have in mind is the original proton decay experiment. A good part of
the argument for doing it was the fact that SU<5>, the simplest grand
unified theory, predicted a lifetime range that was within experimental
reach. Do we have any such attractive theoretical notions today? Or do we
have any experimental hints of CPV in the lepton sector?

Is the case for the proton driver a strong one independent of CPV? Burt
raises a much less expensive alternative to it and I would very much like to
hear about the pro's and con's of that in relation to the issues of neutrino
physics with and without CPV.

I agree with Adam that we should exploit the NuMI beam to the greatest
possible extent. This, however, is not the place to discuss the future of
labs.

Peter
--------------------------
S.Peter Rosen
Sent from my Wireless Handheld

================================================================================

Peter, I'm not used to conducting a discussion where so many may be
getting things they are not really interested in, but this is today's
world, and I hope they are not bored.

I am with Dave Casper on this one. The standard model does not
accommodate many things that have been discovered in the last decade. I
think it is a weak reed to lean on in deciding what not to do. The
critical next neutrino experiment would seem to me to be a reactor theta
1-3 measurement. Such an experiment should be able to get to sin**2
about 0.01. If it is smaller than that it is not likely that any
experiment can measure CP violation in the neutrino sector.

I raised the question about the 8 GeV, 2 MW beam because I think, and
previous FNAL studies seem to have shown, that you can do the neutrino
physics with an upgrade much less costly than an SNS class machine. If
that is still true, the neutrino program can proceed without impacting
the Linear Collider program. If it is not true, the community is going
to have to choose which goes first.

I hope to hear from those who have been working on the question recently.

Burt

Burton Richter
brichter@slac.stanford.edu
phone 650 926 2601
fax 650 926 4500

=======================================================================

I'm not sure what makes a model "plausible" these days, so leave it to the
theorists to address that angle, but from an experimenter's perspective I
just want to point out that there was no a priori expectation of large
lepton mixing, prior to its discovery in the atmospheric and solar sectors,
either.

If one tried to argue on the basis of the quark sector, we would expect
theta_23 to be of order V_cb, while it is actually about 20 times larger.
So we have evidence, at least, that extrapolation from the quark sector to
leptons should be viewed with considerable skepticism.

Given the resources which have been (and continue to be) lavished on nailing
down the last decimal place of the CKM matrix, which you allude to, it would
seem odd to walk away from the lepton sector before we even know the *first*
decimal place for two out of four parameters...

Dave
dcasper@uci.edu

======================================================================
Dear Milind, Stan and Burt:

Thank you for pointing out my mistake. I started thinking about the issueon
the way home on Metro this evening and had a sneaking feeling that I was
missing something. I am glad you caught it.

While I have your attention, let me stir the pot a bit more. Please tell me
if I am making another mistake.

On the subject of CP violation in neutrino physics, I am a bit of a heretic.
In my book, CPV in the neutrino sector is merely a speculation with little
hard evidence to back it up. Leptons certainly communicate with quarks
through the W and Z and must therefore have some induced Standard Model CPV,
but it cannot be very large. If there were large non-SM CPV, would it not
show up in the quark sector as well? At present, we must have about half a
billion BB_bar pairs in the existing B Factories, but I have not heard of
any evidence for large CPV beyond the SM. So, are there PLAUSIBLE models
with large non-SM CPV only in the lepton sector?

Given this heretical view, I am inclined to ask why we should go through the
expense and effort of building another SNS-class machine? Could we not
propose a program using an SNS beam line?

Well chaps, fire away.

Peter

--------------------------
S.Peter Rosen
Sent from my Wireless Handheld
============================================================================

Dear Peter,
  I think your analysis is somewhat oversimplified as far as the scaling
laws go. First of all, your statement that for the same L/E the neutrino
flux drops as 1/E**2 is not correct. That flux does not vary much as a
function of E since the decrease in divergence of the neutrino beam
due to higher E (angle goes as PT/E with PT relatively independent of
energy) just compensates the dilution of intensity due to longer L.
  Regarding scaling, another important fact is that decay probability of
a pion goes in principle as 1/E since as long as the decay pipe
is a fraction of pion decay length (typical in neutrino beams) only a
fraction of pions decay. But that is not rigorously true since in a
typical beam a large fraction of pions hit the decay pipe walls. So energy
dependence will be a strong function of decay pipe radius. In the model
where the cost goes as the volume and PT of the pions after focusing is
energy independent, higher energy will win.
  Target issues may also be important at these high powers. It is
presumably easier to build a target for a low energy, high rep rate beam
than for the same power beam with higher energy and lower rep rate.
  I personally do not believe that these are the dominant issues. In my
mind the important questions extend beyond neutrino physics, ie to what
extent a high power lower energy machine can do significant additional
physics outside the neutrino sector.
     Best regards stan

*************************************************************************************
Stan Wojcicki
Department of Physics SLAC Phone:
                                                650-723-2924(Campus)
Varian, Room 170 MS 63 650-926-2806(SLAC)
382 Via Pueblo Mall 2575 Sand Hill Rd FAX: 650-926-4001
Stanford University Menlo Park, CA 94025
Stanford, CA 94305 E-mail: sgweg@slac.stanford.edu
************************************************************************************

On Mon, 30 Aug 2004, Rosen, Peter wrote:Dear Burt:
How about the following naive and over-simplified argument? Suppose you want
to study oscillations for a particular range of L/E, dictated, of course by
the value of Delta m2. If you increase the proton energy by a factor x,
then the average neutrino energy increases by a factor y, which is
calulable. For fixed L/E, L must also increase by y, and so the beam
intensity dereases by 1/y2 and the total neutrino cross section, being
proportional to neutrino energy increases by y. Overall then, for the same
neutrino intensity, the event rate goes down by 1/y.

Now what about the intensity as you increase energy keeping the power
constant?
Obviously the number of protons goes down by x, but the production of
neutrinos will increase by a factor xprime, which must either be well-known,
or calulable. Thus the event rate changes by xprime/xy. Depending on these
factors, then, you can figure out the optimal energy for a given beam power.
Surely this has been done in various studies.

As for neutrino-nucleus cross-sections, the most interesting one,
physicswise and astrophysicswise, tend to be at lower energies.

How are you doing these days? Perhaps we can talk on one of your trips to
town,

Peter
--------------------------
S.Peter Rosen
Sent from my Wireless Handheld
============================================================================

An important issue that needs to be addressed in the study is the
physicscase for a 2 MW, 8 GeV driver. Such a facility is much more
costly thata 2 MW, 120 GeV facility simply because the higher energy
means that a factor of 15 less current is required. While some have
argued that the lower energy facility has a dual use as a prototype for
other machines, that is an issue that has to stand on its own or as a
supplement to the science case for a given energy. I have not yet seen
the case for the lower energy, more costly facility.

Burton Richter
brichter@slac.stanford.edu
phone: 650 926 2601
fax: 650 926 4500

-----Original Message-----
From: owner-neutrino_superbeams@LISTSERV.FNAL.GOV [mailto:owner-neutrino_superbeams@LISTSERV.FNAL.GOV] On Behalf Of Jorge_G_Morfin
Sent: Monday, August 30, 2004 8:58 AM
To: minerva@fnal.gov; minos_all@fnal.gov; boone@fnal.gov; off-axis@fnal.gov; neutrino_superbeams@fnal.gov
Cc: Ron Ransome
Subject: Proton Driver Physics Study: Neutrino Scattering Physics

Dear Colleagues,

There is a physics study underway to develop the mission need (CD0) for
a Proton Driver at Fermilab that will provide 2 MW of 8 GeV protons with
a new Linac and 2 MW of up to 150 GeV protons with the Main Injector.
Although the proton requirements of neutrino oscillation experiments are
the primary motivation for the Driver, an ambitious neutrino scattering
physics program should also be an important part of the mission. To
formulate this program, a Neutrino Scattering Physics working group is
being formed to address the questions of physics topics to be studied as
well asbeams and detectors to be designed to take advantage of the
increased proton intensity.
At the recent International Workshop on Neutrino Factories and
Superbeams (NuFact04) the conclusion of the neutrino scattering working
group was that after the completion of K2K, MiniBooNe, MINERvA and
JPARC-1, low-energy neutrino-nucleus interactions would be reasonably
well studied. Consequently, the emphasis for a superbeam (such as the
Fermilab Proton Driver neutrino beam) should be placed on physics using
anti-neutrinos on nuclear targets, neutrino and anti-neutrino beams on
hydrogen and deuterium targets and (very) narrow-band beams for detailed
neutral current studies. The goal of our Proton Driver working group
will be to continue thephysics studies started at NuFact04 and to start
addressing the specificfacility design challenges of a high-purity
anti-neutrino beam, a narrow-band beam and fine-grained detectors
incorporating LH2 and LD2 targets. This both for 8 GeV and up to the
maximum Fermilab Main Injector energy of 150 GeV protons on target,
The final report is due in December. A workshop is being organized at
Fermilab, to be held October 6-9, to bring the working groups together.
At this workshop the Neutrino Scattering Physics working group will
emphasize discussion and problem-solving with a minimum of formal
presentations. The workshop information can be found at

http://www-td.fnal.gov/projects/PD/PhysicsIncludes/Workshop/index.html

Please let us know if you are interested in getting involved in the
physics, beamline and/or detector questions we must address.

                                           Best regards,

                                   Jorge G. Morfin (morfin@fnal.gov)
                               Ron Ransome (ransome@physics.rutgers.edu)

                               Co-conveners: Neutrino Scattering Physics
                                               working group

-- 
Mike Shaevitz
Columbia University Office:  212-854-3305
Nevis Laboratories Office:   914-591-2806
http://www.nevis.columbia.edu/~shaevitz/