From: Paul Grannis and Charlie Baltay
As you may have heard, the two of us (Paul Grannis and
Charlie Baltay) have agreed to work together to
coordinate the US Study of Physics and Detectors of
Future e+ e- Linear Colliders. The motivation for this
is a desire to bring a wider community of US physicists
into these studies. If a linear collider is to be in our
future, it will require a strong and broad consensus that
it is the optimal facility for extending our
understanding of basic physics issues. The directors
designate of Fermilab and SLAC have blessed this
arrangement.
We have been discussing future directions for the study
following the successful international e+e- meeting at
Sitges, and have the following suggestions:
1. Evolution of Detector Designs
The US studies presented at Sitges concentrated mostly on
common designs for a small and large detector, which were
labelled S1 and L1. How will these designs evolve, and
how frequently should we update or modify the designs?
In discussion with various people we arrived at the
suggestion that twice a year is about right for the next
few years. We therefore propose that we do the next
round of modifications by August 1999. We urge everyone
involved to start thinking now about what modifications
they would want to see. You can find the current designs
on the worldwide web at the following address:
http://hepwww.physics.yale.edu/lc/graphics.html
We are not prejudging at this time whether these
modifications should be minor or major. We also ask the
Detector Working Groups to have discussions with their
membership about what changes make sense at this time.
There is a meeting scheduled at SLAC on August 4, 1999 to
discuss the proposed changes and arrive at a consensus on
what designs S2 and L2 should look like. We imagine that
the next set of design iterations after August would be
at the "Sequel to KEYSTONE" meeting that's planned for
early 2000.
2. Evolution of the Physics Studies
Up to the Sitges meeting the focus of the physics studies
have been to evaluate the capabilities of the e+ e-
collider and how the physics affects the detector
designs. This kind of study clearly should continue. In
addition, however, we have to keep in mind that a project
of this magnitude requires that the case for a superb
scientific pay-off be nearly foolproof, and that there be
a clear and strong consensus within the community on the
appropriateness of this facility as our next step. This
has to be done in the context of the LHC, which is likely
to start its physics program years before the next e+e-
linear collider. Thus the physics goals and capabilities
of the e+e- collider must be evaluated as a comparison
with the capabilities of the LHC. Our suggestion on how
to get started on this is to make up several scenarios
of that the LHC is likely to find and ask how the e+e-
collider will contribute to further our understanding
beyond what we learned from the LHC. For instance:
2.1 Let us assume that SUSY exists at the expected
mass scale (many states below 1 Tev)
* What are the realistic estimates of the LHC
experiments' ability to unravel this
spectroscopy? Recent LHC physics studies
make a case that the mass spectrum for
gauginos, squarks/gluinos and sometimes
sleptons will be established to reasonable
precision; that some branching ratios will
also be determined. In this scenario, what
are the essential advances that will be made
at the Linear Collider beyond LHC? (To what
extent are better mass measurements, detailed
branching ratios and couplings, quantum
numbers critical to our understanding of
Nature's choice of the low mass Susy
phenomenology?)
* Are there significant regions of Susy
parameter space in which one could expect LHC
to fail to disentangle the basic particle
content, but for which LC could do so? How
dependent is this on LC energy?
* Most LHC studies have been done in relatively
constricting Susy models: minimal SUGRA or
gauge mediated Susy. To what extent can the
Linear Collider experiments understand more
complex supersymmetry sectors? For example,
for what model assumptions could one
determine that there are more than two Higgs
doublets? or more than five Susy unification
parameters? or failure to achieve gauge
coupling unification?
* What information can be gained from NLC
experiments on the supersymmetry hidden
sector scale and its symmetry properties?
* An ambitious program is outlined for LC
experiments to do precision Susy and Susy
Higgs measurements, together with studies of
salient Standard Model processes. Given a
reasonable assumption of LC luminosity growth
to design value, what is the length of
running time to accomplish this program?
* With what precision can LC determine the J CP
composition of a Higgs boson candidate at 130
GeV? at 500 GeV? at 1000 GeV?
2.2 Let us assume that the LEP/Tevatron/LHC uncover
no evidence for TeV scale supersymmetry or a
Susy Higgs sector.
* If there is a SM Higgs, what is the outline
of the linear collider program to extend our
knowledge of it beyond the LHC?
* If there is no SM Higgs up to the LHC reach,
what is the program of the NLC? Can one make
a convincing case that the linear collider
extends the search for strong coupling beyond
that possible at LHC?
2.3 Should a 500 GeV limited energy linear collider
become available somewhere in the world, what is
the physics case for construction of a second
facility at 1 TeV? 1.5 TeV? 3 TeV?
2.4 What are the physics cases beyond the issues of
Electroweak Symmetry breaking?
* For TeV scale compactification and millimeter
scale gravity, or other indications of
physics of more than 4 dimensions.
* New insights into hot dark matter.
* What if the CKM triangle fails to describe
Nature; is there any role for a linear
collider to play?
* What insights into Yukawa coupling
unification, or the origin of flavors?
We realize that the answer to some of these questions are
implicit in the studies that have been carried out so far
and these answers just have to be pulled together in the
context of an LHC comparison. Some of the other
questions need a fresh approach.
We would like to get everyone's suggestions about how to
do all this and how to get the Physics Groups started so
that by the "Sequel to KEYSTONE" meeting we could start
serious discussions along these lines.
3. Future Meetings
August 4-5, 1999 at SLAC to discuss evolution of
the detector designs (August 4) followed by a
simulation meeting (August 5).
Sequel to KEYSTONE - probably at Berkeley,
February-March 2000 or so.
The next international meeting, Sequel to Sitges,
will be at Fermilab, September-October 2000.
Please let us know your comments and suggestions on all
of this.
With best regards,
Paul and Charlie
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