P' Grannis: Workshop charge

1
Linear Collider
P. Grannis Workshop charge Chicago,
Jan. 7 9, 2002
Since the Johns Hopkins workshop Mar. 19 21,
2001, a good deal has happened in the Linear
Collider world. From the charge at JHU In the
US, the HEP community has not yet articulated its
support for the LC our chief focus now should
be to make the case for the LC within the physics
community as fairly and as completely as
possible. Only with a recommendation from the
community that the LC is the right next choice
can we address the case with other branches of
science, the government, and international
partners. It will be hard enough even if we
are unanimous! The pressing problems for the LC
community have changed considerably since then.
This workshop is intended to give an overview of
the LC physics and detector issues, and to
provide a forum for discussing the way forward.
2

• I. Milestones
• March 23,24 TESLA Colloquium. The TESLA
  proposal is now under consideration by the German
  Science Council. TESLA TDR
  http//tesla.desy.de/new_pages/TDR_CD/start.html
• July SNOWMASS 2001 N.A. LC group prepared a
  400 page Linear Collider Sourcebook
  http//www.slac.stanford.edu/grp/th/LCBook/
• 1. Introduction
• 2. The Case for a 500 GeV Linear Collider (from
  2000)
• 3. Sourcebook for Linear Collider Physics
• 4. Pathways beyond the Standard Model
• 5. Experimental Program Issues
• 6. Detectors for the Linear Collider
• 7. Suggested Study Questions
• (a big effort by
  many. Thanks particularly to M. Peskin)
• July Snowmass Physics Groups recommendation
• There are fundamental questions concerning
  electroweak symmetry breaking and physics beyond
  the Standard Model that cannot be answered
  without a physics program at a Linear Collider
  overlapping that of the Large Hadron Collider.
  We therefore strongly recommend the expeditious
  construction of a Linear Collider as the next
  major international High Energy Physics project.
  

3

• Milestones, contd
• August ECFA Working Group on Future of
  Accelerator-based Particle Physics in Europe
  recommended
• the realization, in as timely a fashion
  possible, of a world-wide collaboration to
  construct a high-luminosity ee- linear collider
  with an energy range up to at least 400 GeV
• September ACFA statement on the Linear
  Collider
• The ee- LC must start operation when the high
  luminosity run of LHC starts around 2009-2010.
  The center of mass energy of the LC should be
  250-500 GeV where urgent and critical physics is
  expected. Including its energy upgrade to higher
  than 1 TeV, the project as a whole is foreseen to
  evolve for a quarter of a century. ACFA strongly
  endorses the plan to construct such a collider in
  the Asian-Pacific region with Japan as the host,
  and urges KEK to take initiative to investigate
  possible and practical form of globalization for
  the construction, commissioning and operation of
  the collider.
• ACFA/LC Working Group report
  htts//acfahep.kek.jp/ and hep-ph/0109166

4

• Milestones, contd
• October HEPAP subpanel draft statement We
  recommend that the highest priority of the U.S.
  program be a high-energy, high-luminosity,
  electron-positron linear collider, wherever it is
  built in the world
• We recommend that the United States prepare to
  bid to host the linear collider, in a facility
  that is international from the inception, with a
  broad mandate in fundamental physics research and
  accelerator development
• We recommend the formation of a steering
  committee to oversee all linear collider
  activities in the U.S.
• Workshop Plans for near future
• Europe 12 15 April, St. Malo, France
• U.S. May/June, site not yet fixed
• Asia July , Tokyo
• World LC Workshop 26 30 August, Jeju Island,
  Korea

5

• So, the playing field has changed we have a
  strong statement of priority for the LC in all
  regions.
• This does not mean that all physicists in the
  US/elsewhere share the sense of LC as their
  avenue to future experimentation. Many other
  initiatives of merit exist
• Although those in the LC camp argue that the
  physics issues of EWSB are the most ripe for
  fundamental new understanding in the near term,
  we should recognize that these other projects are
  also of fundamental importance.

• Superbeam/long baseline n studies mSR
• Underground/sea/ice labs for p decay, n
  astronomy
• Studies of rare decays of K, B and insights
  into flavor
• Innovative astroparticle experiments SNAP,
  GLAST, LISA, Pierre Auger, CMB
• Very high energy hadron collider

6

• II. The Physics Case for LC
• The broad case for the LC 500 GeV, upgradable
  is now quite clearly delineated (talks by M.
  Peskin, S. Heinemeyer, L. Gibbons, J. Lykken)
• Something playing the role of the SM Higgs
  boson will exist and be accessible at the LC.
  The LHC will not tell us its full character, so
  we will need the LC.
• Some new physics beyond the SM Higgs is
  needed, and its signs should be seen at a 500
  1000 GeV ee- (gg, eg, e-e-) LC
• LHC will give only fragmentary understanding of
  Susy LC will delineate and give understanding
  of Susy-breaking
• LHC and LC both will see evidence for Strong
  Coupling or Extra Dimensions. LHC and LC are
  complementary, with LC offering many unique
  observables.
• There are other physics topics of considerable
  importance QCD studies in new regimes,
  precision EW measurements, new flavor studies in
  the Susy sector, but
• The main rationale for the LC is
  understanding EWSB.

7

• Physics, contd
• There remain many physics studies that are
  critical for filling in areas of the physics
  program (see S. Dawson talk), but the main
  outlines are now there.
• Some of the areas for more physics study
• For representative Susy benchmark points what
  sparticle states are clearly observable ( masses,
  BRs) with realistic luminosity?
• How to measure the cross sections, and with what
  accuracy?
• How accurately can the chargino neutralino
  matrices be experimentally reconstructed?
  (mixings, CP phases etc. in an unconstrained
  MSSM)
• For the tree of Extra dimension models, how
  incisive will LC experiments be? (different
  assumptions of no. and size of extra dimensions,
  the particles that go into the bulk, metric of
  bulk )
• What is the optimum way to delineate the heavy
  Higgs sector in MSSM models? What energy, beam
  particles, polarizations etc. What indirect
  measurements are crucial?

8
Physics, contd Such studies should continue, in
part because they educate us all on the power of
the LC program. But they do not constitute the
dominant need now as we enter the era of
achieving an approved LC. One question that I
still do not feel has had as clear answer as is
needed Why should the 500 GeV LC be started
before the LHC has given physics results? The
bureaucrat with the most meager scientific
understanding can and will ask this of us.
Without a compelling answer, our ship may go dead
in the tortured channels of the Congressional/OMB
deliberation ! I propose a competition for the
best short essay in lay language to answer the
questions Why do we need the LC and
Why start now. (and bear in mind the recent
news articles that declare that the Higgs does
not exist, and CERN wasted 9B on its search ! )
9

• III. Detector Issues
• We need more effort on detector RD and
  simulations.
• Europe and Japan have given more attention to
  this than the US. Although it is too early to
  produced detailed experiment designs (or form
  collaborations), now is the time to develop the
  new ideas that will be needed. (See R. Heuer
  talk.)
• Some may say that a LC detector is not especially
  challenging on the scale of LHC detectors, so can
  rest on proven techniques. But
• We now understand that there is great premium
  on having the best vertex detector one can
  acquire to separate b,c,t, (uds), g cleanly.
• Excellent dE/E for jets is paramount for some
  physics (e.g. Higgs potential). LC detectors are
  free of some of the LHC constraints (radiation
  damage, event pileup). How well can one do?
• Detector integration is different in ee- than
  pp. How to optimize signal handling techniques
  for the lower rates of the LC?
• (see plenary talks by K. Riles, R. Frey, G. Fisk,
  N. Graf for more detail)

10

• Detector Issues, contd
• If we are going to capitalize on new detector
  ideas that expand the LC reach, now is the time
  to do it while the project is going through its
  political approval process, and before detector
  proposals are prepared.
• The US needs an expanded program of detector
  RD.
• The three regions of the world should
  collaborate closely on detector RD projects.
  The issues are the same world-wide, and for any
  type of LC. The financial resources of all
  regions are stretched. Available test beams are
  scattered across the globe.
• Such collaboration is an important precursor to
  the full LC collaboration on both detector and
  accelerator fronts.

11

• IV. Some remaining LC issues, needing work by
  the combined experimental and accelerator
  communities
• Beam energy calibration how do we achieve
  dE/E of 50 ppm?
• Polarization how to get the needed 0.1
  precision on effective polarization? What is
  the best scheme for positron polarization? How
  well can it be calibrated?
• Is the Low-E / High-E IR strategy really
  optimal?
• What is the physics (and political) rationale
  for 2 IRs vs. 1 IR?
• And, how can we enhance the outreach to other
  sciences by enabling other uses of the LC
  components (linac tunnels, e, e- sources,
  intense g beams, preaccelerators, damping rings,
  spent beams) ?

• X-ray FELs and conventional light sources
• Medical diagnostic/treatment facilities
• Nanoscale instrumentation center
• Laser interferometry projects
• Material /biological science with g beams

12

• Achieving the Linear Collider

• We should never underestimate the difficulty in
  getting the Linear Collider approved.
• The LC project has many extremely challenging
  technical aspects (talks by C. Adolphsen, R.
  Brinkmann, T. Markiewicz) and much remaining RD
  (talks by K. Kubo, S. Holmes) . The
  experimental community needs to participate in
  solving these.
• Cost is well beyond the single project cost for
  basic science in the past. We say it must be
  fundamentally international to afford it, but do
  not yet have a blueprint for this.
• Preoccupation of governments on other issues
• Terrorism and security needs
• Economic recession threats worldwide
• Costs of unification of Germany
• Competition with other science and technology
  projects (bureaucrats dont distinguish laser
  fusion, space experiments, and accelerators).
  Our colleagues in other areas of science must be
  convinced that HEP in general, and the LC in
  particular, makes scientific sense in broad
  terms, and is worth large expenditures.

13
Achieving the Linear Collider, contd
The big steps 1. Get realistic costs for RD,
LC project, infrastructure (the political
process, environmental protection, community
outreach), manpower, contingency,
escalation. The SSC, and now LHC, have been
plagued by unexpected cost overruns. Our
political capital is thereby severely damaged,
and our costing must be correct! 2. Choose the
accelerator technology TESLA vs. NLC/JLC. The
Loew panel will help define the tradeoffs (G.
Loew talk) . We need to start now on a process
to make this decision. We will find it hard to
sell the project to governments until it is made.
If there is clear preference from the ICFA
evaluation process, make the decision! If not,
it does not matter so much! Some of the
communities will have to swallow their pride, but
better sooner than later so we can mount a
collective effort on a common project earlier.
14
Achieving the Linear Collider, contd

• Establish the process for reaching political
  international decisions on
• Shall we convene a working group of
  physicist-statespersons to give these issues a
  draft framework?
• (see paper by G. Trilling on Workshop web page
  talk by M. Tigner, and the panel discussion)
• 4. Articulate the rationale for the LC to
  governments it will not be the last project we
  request! It has to be sold on the basis of
  understanding fundamental makeup of universe
  (structure of space, time, energy and matter)
  and not on spin-offs.

• funding arrangements the shares for host and
  participant nations.
• the way to reach the site decision.
• organizational structure (is it just for LC, or
  envisioned as a structure for future projects?)
• how to retain the health of accelerator/particle
  physics in all regions with a LC in only one.

15
Conclusion
We have done the easier part by coming to
consensus that a Linear Collider is what HEP
should aim for. Now comes the much harder part
in making it occur !