Physics Studies for Future Facilities

1. P. Grannis, Stony Brook UEC Meeting, July 7, 1999 Physics Studies for Future Facilities We have heard much on the issues related to the future of Fermilab, to the U.S. and the world HEP communities -- from wise directors, sagacious government officials, and the machine experts. What can the great unwashed user-on-the-street add to all of this? The basic answer is that the ‘users’ need to engage the physics and accelerator issues squarely and open-mindedly. The case for any new facility will only be made convincingly when there is a clear consensus on its worth from the community. Arguing on a parochial basis will get us exactly nowhere.

2. The Physics Landscape The minimal Standard Model reigns supreme Experimentally : No confirmed measurement outside the SM, apart from the news that n’s seem to have mass and thus may imply something about very high scales. A very weak indication that the SM requires a Higgs of mass in a region now partly excluded (but consistent with Susy) MSSM Tevatron SM Higgs A few oddball events (but there are always events on the fringe of the zoo) Theoretical prejudices suggest Physics beyond the Standard Model : Desire for unification, not present in SM Ugliness of the fine tuning of the Higgs mass Hopes to connect to a theory including gravity The bewildering array of arbitrary parameters

3. What Could We Learn in the Next Five Years? At LEP2:Expect to see the SM Higgs up to mH = 105 GeV; MSSM higgs up to mh,A ~ 90 GeV. At Tevatron:Could rule out SM Higgs up to 180 GeV; discover in much of that region. Either LEP or Tevatroncould sense the existence of Supersymmetry. And either LEP or Tevatron could find something completely new ... But we could know very little new about Beyond the SM before LHC gets fully operational.

4. The Contenders The potential new facilities are well known to us all : A TeV scale linear e+e- collider (0.5, 1.0, 1.5, 3.0 TeV??) A m+m-colliding beam storage ring (up to 3 TeV, with potential use as bright neutrino source) A very high energy hadron collider, VLHC (e.g 100 TeV in the cm.) At this time, the only facility that seems technically understood well enough to consider for the near term is the ee linear collider at the TeV scale. Current cost estimates are large ! We need to work hard to refine its scope, cost and physics benefit. All of these assume that the relevant question is the origin of EW Symmetry Breaking -- and indeed today it is. Will it still be the most pressing issue in 2010? Do we know that the physics of EWSB will not be understood reasonably by 2010? Are we confident that the flavor sector will not be ripe for exploration then?

5. Reading the Tea Leaves If we want to start on a new facility before the LHC program becomes mature, we will have to understand the possible physics scenarios. Be realistic about what the LHC experiments will do ! The LHC claims an ironclad case for finding a SM Higgs, and for discovering Susy and exploring the Susy spectrum of particles. Within several representative minimal Sugra models, LHC can determine the Susy parameters. Experiments with real data can find ways to exceed our expectations ! “ The Tevatron won’t find top if it’s heavier than 130 GeV ” (174 GeV!) “ The precision for the W mass at the Tevatron will be about 150 MeV, and for top mass, about 10 - 15 GeV ” (65 MeV, 5 GeV !) “ Cannot do precision B physics at a hadron collider -- its too dirty ” (BC , t B , sin2b !) “ Single photon detection at high pT in a hadron collider is tough! (contamination from p0) ”

6. Scenarios In the absence of full knowledge of EWSB mechanisms, planning for new facilities will have to proceed using a set of possible scenarios. What is the right new facility beyond LHC in each sensible scenario? e.g. LEP/Tevatron find low mass Higgs (or low mass Susy, anomalous top production or couplings). LHC is assured of detailed exploration. No discoveries at LEP/Tevatron; LHC finds evidence for Susy that conforms to minimal Sugra. LHC finds Higgs with mass > 150 GeV and nothing else (no Susy). No Higgs OR Susy at LEP/Tevatron/LHC -- we are in the strong coupling soup. B-factories, B/K/n experiments find non-closure of the unitarity triangle, or other dramatic departures from SM predictions.

7. What should We be doing? The Fermilab community -- theorists, experimentalists and accelerator physicists -- need to become strongly engaged in studies to illuminate the physics issues and to find optimal techniques for the accelerator components. Work to establish the right machine by studying the physics signatures within the various scenarios; What type of machine is best? What energy and luminosity are required? How can we improve the accelerator techniques to make it achievable? A new facility may or may not be built at Fermilab -- but that is not now the relevant question. We need to establish the case for making the best physics progress, working with our colleagues across the U.S. and world-wide. Only with this consensus can we hope to convince those with funds!

8. Some steps 1. Start to confront the physics issues : Build on the models of the very successful series of Tunnel Visions talks on accelerator facilities, and the Tevatron Run II Physics Workshops held in the past year at Fermilab: A series of extended talks on physics issues and capabilities at different possible facilities -- and to help guide defining scenarios. Circle Line Tours 2 hr talks; Expert speakers; designated interrogators, with questions beforehand to the speaker -- time for extensive interaction and questions. e.g. LHC capabilities for Higgs/Susy Higgs Linear e+e- collider capability for Higgs/Susy Higgs Muon Collider capability for Higgs/Susy Higgs LHC Susy capabilities Lepton Collider Susy capabilities Strong Coupling physics What flavor physics advances could influence our future?

9. Steps ... 2. Do some real work Plan a Lepton Collider Workshop at Fermilab, following the series. From those talks, we should have a clearer picture of the critical physics questions and the scenarios that we should focus on. In a workshop (November ‘99?), would focus on simulations of physics for lepton colliders. Some general questions, and specific detailed studies. e.g. Some general issues: Can lepton colliders fully determine the character and parameters of the Susy sector beyond the LHC capability? How well can lepton colliders determine JPC, couplings, branching ratios for Susy particles? What energy and luminosity is required to do this? What can lepton colliders do on Higgs/Susy Higgs beyond LHC? Can one gain understanding of the Susy hidden sector -- what machine parameters are needed for this? What is needed for a lepton collider to make incisive measurements on strong coupling? Can lepton colliders extend understanding of the flavor sector?

10. Steps ... … and some specific questions Study moderate mass Higgs for mass optimization, determination of cc, bb couplings in an e+e- linear collider. How well can one determine its quantum numbers and total width? Show that Susy signatures with a SU(2) neutralino as LSP (and near degeneracy of the c10 and c1+) can be detected and identified in a lepton collider. Optimize a study to discover and measure scalar leptoquark branching ratios for a mass 300 - 500 GeV, decaying into bt, tt, bn, or tn. etc. , etc. The results of these studies would be the basis for talks and discussion at: The U.S. NLC Workshop in LBL (early 2000) The sequel to the Shelter Island mmCollider workshop The International Linear Collider workshop to be held at Fermilab in October 2000

11. A Couple of other points One of the largest problems before us is finding ways to improve the reach of future accelerator facilities -- e.g. good ideas on detailed questions such as rf delivery, beam emittance control, cooling, etc. The User community can and should participate in this ( does your University train accelerator physicists ??) Getting worldwide agreement on what to propose is the physicists responsibility. Getting workable cooperation amongst regions and governments to jointly participate requires enlightened leadership by the scientific agencies, and the elected representatives.

12. Circle Line Tours Conclusions It’s time for the Fermilab community to engage strongly in mapping the future The key is understanding the directions that physics will take us & Lepton Collider Workshop at Fermilab to focus our attention on these questions