Experimental Approaches Working Groups
E1: Working Group on Neutrino Factories and Muon Colliders

Working Group Convenors: Vernon Barger (Wisconsin), Deborah Harris (Fermilab), Yoshi Kuno (Osaka); Michael Zeller (Yale)

If muon colliders can be realized, they offer a path to high-energy lepton collisions for the study of electroweak symmetry breaking and new phenomena. The large Yukawa coupling of the muon to Higgs bosons and similar objects, coupled with the naturally small beam-momentum spread, raises intriguing possibilities for formation experiments. The idea that a millimole of muons might be collected over the course of a year opens new opportunities for neutrino factories based on muon storage rings.


This working group is to consider the physics potential of accelerator complexes that produce very intense muon and neutrino beams. Any such facility will require a very-high-intensity proton source, and could also include conventional neutrino beams, a muon-storage-ring neutrino source or a muon collider. Many of the scientific goals to be explored here overlap with the interests of P2: Flavor Physics, P5: QCD, E3: Linear Colliders, E4: Hadron Colliders, E5: Fixed-Target Experiments, and the underground laboratory aspects of E6: Astro/Cosmo/Particle Experiments. This group will work in close collaboration with working groups M1: Muon Storage Rings and Colliders, and M6: Intense Proton Sources.

A general goal is to describe a roadmap for the development and productive exploitation of intense muon and neutrino sources over the next 20-30 years. Are there synergies between underground neutrino detectors, high-intensity neutrino sources based on pion "superbeams," muon storage rings, and muon colliders? Does a staged construction program for a multi-TeV muon collider promise a strong physics program at each stage? What is the scientific imperative for a lepton collider at tens or hundreds of TeV per beam?

For the different aspects of the physics program:

  1. Neutrino oscillations.

    1. How rich is the program of neutrino oscillation measurements that a neutrino factory would make possible? Will the questions still be interesting when a neutrino factory operates?

    2. What is the optimal machine energy, baseline and flux for measurements of neutrino mixing angles, matter effects, and CP violation? Is more than one baseline necessary?

    3. What results from ongoing experiments might materially change the targets for oscillation studies at a neutrino factory?

    4. What is the role of very low energy experiments that might be done using a neutrino beam created at the Spallation Neutron Source?

    5. How many of the pressing questions could be answered using super-intense muon-neutrino and muon-antineutrino beams generated by pion beams?

    6. Are mixed beams of muon neutrinos and electron antineutrinos (or vice versa) a benefit or a curse? How important is muon polarization?

    7. Can one envisage a practical, large-volume detector that will identify electrons, muons, and taus, and measure their charges? If such a detector could be constructed, what advantages would it bring to experiments?

  2. Nonoscillation neutrino physics. Consider the scientific potential of neutrino beams from muon storage rings and pion superbeams.

    1. What is the potential for conventional neutrino measurements at short baselines at a low-energy neutrino factory or at a high-energy muon storage ring? Specifically, what are the prospects for (i) extracting parton distributions from hydrogen targets? (ii) measuring neutrino cross sections? (iii) determining the weak mixing parameter and the strong coupling constant?

    2. Can a neutrino program based on intense pion beams share detector facilities with a neutrino factory?

    3. What novel experiments could be carried out using polarized targets or silicon targets? What is their scientific importance? Are there other ways to obtain equivalent information?

  3. Intense muon sources. Consider the scientific program that could be developed using intense sources of low-energy muons. How do the requirements on beam properties differ from those appropriate to neutrino factories or muon colliders?

    1. How can intense muon sources advance the study of lepton flavor violation? What are the relative capabilities of muon decay or muon conversion experiments and the study of rare kaon decays?

    2. How could the availability of intense muon sources improve the precision of measurements of fundamental static properties of the muon, including the anomalous magnetic moment and a permanent electric dipole moment?

    3. Are there important applications of copious supplies of low-energy muons beyond particle physics?

  4. Muon colliders. This group should consider the physics potential of muon colliders as Higgs factories, and at center of mass energies of 500 GeV, 1 TeV, and several TeV.

    1. For a Higgs factory, what is the program of measurements a muon collider could accomplish? What luminosity and energy spread are required for incisive studies of the Higgs boson's properties. Other than precise determinations of mass and width, what measurements would establish the nature of the Higgs boson?

    2. For a modest-energy muon collider, can the luminosity be competitive with a linear collider? How great a disadvantage is the less-flexible polarization of the muon beams?

    3. Define a program of experimentation for a 4-TeV muon collider. What are the principal scientific goals? What luminosity is required to carry them out?

    4. Consider the novel experimental environment at a muon collider: evaluate the effects of the different background environment at a muon collider relative to electron and hadron colliders.

    5. For all energies, what compromises must be made for a detector to operate gracefully in the environment? Will detectors at a muon collider need new or different technologies than those at electron or proton machines?

    6. What are the eventual limitations on beam energy and luminosity?

  5. How can full international collaboration on a muon storage ring or muon collider project be realized? Is it feasible to assign full responsibility for design, construction, commissioning, test and operation of major subsystems to different portions of the world community while maintaining effective overall project management?

Organizing Committee Contacts:

E2: Working Group on Electron-positron Colliders below the Z

Working Group Convenors: Ian Shipsey (Purdue), Hitoshi Yamamoto (Hawaii), Gustavo Burdman (Boston); Joel Butler (Fermilab)

Asymmetric electron-positron colliders have become highly productive b factories, and it is natural to consider luminosity improvement programs or new machines with greatly enhanced luminosity. Phi factories offer special conditions for the study of kaon decays, quantum entanglements, and other issues. Tau / charm factories hold promise for detailed measurements at unprecedented sensitivities. The task of this working group is to consider the future of low-energy electron-positron colliders and to evaluate developments needed to make incisive instruments practical.


Electron-positron colliders at energies below the Z mass should be evaluated in terms of the physics potential that they offer and the characteristics required to realize that potential. Specific issues that this group should consider include:

  1. This group should coordinate with the physics issues working groups to help compile the scientific cases for electron-positron colliders as b factories (including "giga-Z" machines as b factories), charm factories, phi factories, and tau factories. What are the outstanding questions that heavy-flavor factories could address? For each physics topic, consider the contributions from existing and potential experiments using other instruments, and give a critical assessment of the competitive advantages and disadvantages of electron-positron colliders. Working group P2: Flavor physics is a natural forum for laying out the comparisons.

  2. What is a reasonable goal for the desired luminosity at the various cm energies? For each kind of instrument, outline a comprehensive experimental program and estimate the integrated luminosity required to carry it out.

  3. Quantify the physics gained at each machine as a function of the beam polarization.

  4. Are there additional energy scales that could yield important results?

  5. What special detector capabilities are required to achieve the scientific goals of each of the machines? Do any detector R&D issues arise?

This group should interact regularly with working group M2: Electron-Positron Circular Colliders, to exchange information on the desirable machine properties and help define accelerator R&D issues for each type of machine.

Organizing Committee Contacts:

E3: Working Group on Linear Colliders

Working Group Convenors: Marco Battaglia (CERN), John Jaros (SLAC), Jim Wells (UC Davis); Ian Hinchliffe (LBNL)

Electron-positron linear colliders (and options using gamma gamma, e-gamma, e-e-) should be evaluated in terms of the physics potential that they offer, and in terms of the accelerator issues that will guide their evolution. This group should work in close collaboration with its counterpart, M3: Linear Colliders, and should examine the impact of a very large circular electron-positron collider discussed in M2: Electron-Positron Circular Colliders.


  1. The eeLC group should coordinate with the physics groups to help compile and critically examine the case for an initial phase of the ee collider at a cm energy of up to about 500 GeV, depending on the results from prior experiments at the Tevatron and LHC. For some representative physics scenarios, what is a reasonable goal for integrated luminosity at various cm energies, beam polarizations and beam particles? is there a compelling initial physics program at a luminosity of a few x 1033 cm-2s-1? Are there particular advantages or challenges to experimentation raised by the different running conditions in the TESLA and NLC/JLC designs?

  2. The eeLC group should review the case for and feasibility of special options for LC operations:

    1. Catalogue the physics needs that may require positron polarization, gamma gamma collisions or e-e- collisions. Compare the capabilities of an electron-positron collider and a gamma-gamma collider for making detailed measurements of the properties of Higgs bosons, and for discovering Higgs bosons. What are the R&D issues remaining for each option? What are the requirements on the initial design to allow any of these to be added after the initial phase?

    2. Examine the case for high-luminosity operation at the Z pole. What are the benefits and drawbacks from the design of a special beam delivery system for low energy collisions? Should there be a special detector devoted to operating below 500 GeV?

    3. What special requirements are imposed if a free electron laser program is added to the high energy physics facility? What should the HEP community do to facilitate the potential for a FEL program?

  3. Evaluate the scientific case for an initial-phase "Higgs factory" at an energy of about 300 GeV.

  4. What new physics landmarks come into view as the energy of a linear collider is raised to 1 TeV; to 1.5 TeV; to 2 TeV; to 5 TeV? What luminosity and other performance characteristics would be required to maximize the scientific output?

  5. Are there particular issues that detector R&D must address to guarantee the productivity of a linear collider?

  6. What are the beam physics limits and accelerator limits imposed on LC performance, and what are the primary outstanding R&D issues that are critical to study in the next several years?

  7. The eeLC group should assume that a technical review panel will likely be established within the next year to evaluate the superconducting L-band and warm rf X- or C-band accelerator proposals. That review, conducted under the auspices of some worldwide body, would examine the performance parameters of the machines, the technical risks, needed R&D, comparative costs and upgradability. Without undertaking the work that such a panel would do, the eeLC group should work to sharpen the questions that this review panel should examine, and consider the way in which the panel should operate.

  8. What are the paths for upgrade of an initial LC, both in energy and in luminosity? What extensions in energy using the original TESLA or X-band LC designs are feasible? What R&D issues should be given priority? What is the possibility of upgrading either TESLA or X-band LC using two-beam drive power sources? What are the critical R&D issues? What constraints on the initial phase would ultimate conversion to two-beam drive impose?

  9. How can full international collaboration on a LC project be realized? Is it feasible to assign full responsibility for design, construction, commissioning, test and operation of major subsystems to different portions of the world community while maintaining effective overall project management?

Organizing Committee Contacts:

E4: Working Group on Hadron and Lepton-Hadron Colliders

Working Group Convenors: Ulrich Baur (Buffalo), Raymond Brock (MSU), John Parsons (Columbia); Bill Marciano (BNL)

With the Tevatron and the LHC we anticipate an exciting decade of discovery physics with hadron colliders (ppbar and pp) exploring the energy frontier. The task of this working group is to look beyond these immediate prospects to develop a clear vision of future physics at hadron and lepton-hadron colliders. This group should work in close collaboration with its counterparts, M4: Hadron Colliders, and M5: Lepton-Hadron Colliders.

  1. What is the physics potential for a pp or ppbar collider operating at center-of-mass energies of 100 - 200 TeV? What about 30-40 TeV? Elaborate on possible physics discoveries in this decade which would point the way to specific physics opportunities at a future Very Large Hadron Collider (VLHC). This task should be closely coordinated with working groups P3: Scales Beyond 1 TeV and P1: Electroweak Symmetry Breaking.

  2. Examine the importance of luminosity for a VLHC collider, both for more generic physics measurements, and for specific physics opportunities. Compare pp and ppbar physics potential taking into account the likely differential in luminosity.

  3. Identify the main challenges of building and operating detectors for a VLHC. Identify particular issues that detector R&D must address to guarantee the productivity of a VLHC.

  4. Examine the physics potential of possible energy and luminosity upgrades to the LHC (superLHC). This should include both discovery potential and the role of higher energy in a mature program of detailed measurements of physics at the TeV scale.

  5. Explore the ultimate reach of the mature Tevatron and LHC colliders for B physics. Will we need upgrades or extensions to the BTeV and LHCb experiments in order to maximize their ability to make essential measurements?

  6. What is the physics potential for THERA, eRHIC, and other possible next generation lepton-hadron colliders? What is the physics driving a 1 - 1.5 TeV center-of-mass ep collider? What is the physics driving a lower energy e-nucleus collider, or an ep collider with polarization in both beams?

  7. Examine the importance of flexibility in the design and staging of future hadron collider projects, including a moderate-energy electron-positron collider in the big ring. Identify the critical R&D issues whose vigorous pursuit will optimize our ability to respond to a variety of possible new physics discoveries. Are there particular issues that detector R&D must address to guarantee the productivity of a very large hadron collider?

  8. How can full international collaboration on a hadron collider project be realized? Is it feasible to assign full responsibility for design, construction, commissioning, test and operation of major subsystems to different portions of the world community while maintaining effective overall project management?

Organizing Committee Contacts:

E5: Fixed-Target Experiments

Working Group Convenors: Krishna Kumar (UMass), Ron Ray (Fermilab), Paul Reimer (Argonne); Mark Strovink (Berkeley).

Fixed-target experiments offer a great diversity of beams for use in experiments of high sensitivity over a wide range of topics in particle physics. Decay, formation, and scattering experiments (including scattering on polarized or nuclear targets) all hold important potential. The study of subtle effects and rare processes offers a virtual window on very high energy scales. New kinds of experiments may reveal the structure of hadrons at an unprecedented level of detail. The task of this working group is to consider the future of fixed-target experimentation (other than experimentation using muon and neutrino beams, which are the province of working group E1: Neutrino Factories and Muon Colliders). The group should work closely with working groups M6: Intense Proton Sources, and M3: Linear Colliders, and with P2: Flavor Physics, and P4: QCD and Strong Interactions, as well as P1: Electroweak Symmetry Breaking and P3: Scales beyond 1 TeV.


This working group is to consider the scientific opportunities for fixed-target studies in light of the capabilities of existing and planned accelerator complexes. The group should also call attention to the case for beams of novel character that might require research and development to be realized.

  1. Provide an inventory of existing and planned accelerators and the fixed-target beams they supply.

  2. What are the scientific imperatives for the study of rare kaon decays, and what requirements do they place on detectors and accelerators?

  3. What are the needs for the study of charmed particles? Give a critical assessment of the comparative advantages and disadvantages of fixed-target experiments. Working group P2: Flavor Physics is a natural forum for laying out the comparisons with electron-positron colliders discussed in working group E2: Electron-positron Colliders below the Z.

  4. What are the most important issues in hadron spectroscopy, and how can they best be addressed?

  5. What questions drive new experiments using pion, kaon, and proton beams? What beam characteristics do the physics issues demand?

  6. What questions drive new experiments using hyperon beams? What beam characteristics do the physics issues demand?

  7. What questions drive new experiments using electron beams and photon beams such as derived from backscattering lasers from electron beams? What beam characteristics do the physics issues demand?

  8. What opportunities arise from copious sources of antiprotons? What characteristics of the antiproton beams are required for the key applications? What would be the goals and attributes of an "antimatter factory"?

  9. What are the prospects for new studies of neutron properties, including the persistent electric dipole moment, using accelerator sources?

  10. Consider the case of fixed-target beams of higher energy than will be available over the next decade. What are the most compelling scientific goals, and what would it take to address them?

  11. What would be the utility of fixed-target beams derived from a linear collider? What beam characteristics do the physics opportunities demand?

  12. In cooperation with working groups E1 -- E4, survey the needs for test beams over the next decade and beyond and compare those needs with the available inventory.

Organizing Committee Contacts:

E6: Astro/Cosmo/Particle Experiments

Working Group Convenors: Kevin Lesko (LBNL), Tim McKay (Michigan), Suzanne Staggs (Princeton); Harry Nelson (Santa Barbara)

Experimental research in Astro/Cosmo/Particle Physics is being carried out by detectors underground, undersea, in ice, on the surface of the Earth, and in the sky. In the last decade, remarkable discoveries have been made by instruments of each flavor, including

  1. the evidence for neutrino oscillations from underground atmospheric and solar neutrino experiments,

  2. the detection of cosmic-ray particles above the GZK cutoff by ground-based air shower experiments,

  3. the evidence for the acceleration of the expansion of the universe from supernovae observations made by ground-based telescopes,

  4. the spatial and temporal mapping of the distribution of gamma-ray bursts by satellite instruments, and

  5. the detection of anisotropy in the cosmic microwave background radiation from satellite, balloon, and ground-based detectors

Such results have galvanized interest in astro/cosmo/particle physics, and there has been an explosion of experimental activity. New instruments are now coming on line (including SNO, Fly's Eye, AMS, Chandra, XMM, LIGO, etc.) or are currently under construction (including CDMS-II, Axion, Auger, ICECUBE, ANTARES, NESTOR, INTEGRAL, VERITAS, HESS, MAP, PLANCK, GLAST, LIGO-II, etc.). Even larger and more ambitious experiments are being seriously considered (including UNO, SNAP, DEEP, OWL, LISA, etc.).

The next decade and beyond promise to be very exciting for experimentalists working in these areas. Not only can we expect new and exciting results from experiments that are an order of magnitude (or several orders of magnitude) more sensitive than earlier ones, but the use of new technology and instrumentation in all areas will lead to important breakthroughs in capability. Experiments in astro/cosmo/particle physics have a strong intellectual and technological overlap with those in accelerator-based particle physics and astronomy, and thus it will be important to carry out cohesive development of instrumentation across the various fields. Experimentalists in this area have a broad base of backgrounds including particle physics, nuclear physics, cosmology/astrophysics, and astronomy.

This working group will be most closely connected with working groups P2: Flavor Physics and P4: Astro/Cosmo/Particle Physics. In the area of neutrino oscillations, the group should coordinate its work with working group E1: Neutrino Factories and Muon Colliders. The main goals for this working group are to sketch, in broad terms, the experimental program in astro/cosmo/particle physics, to examine the rationale for future large-scale experiments, and to understand how experimentation in this field will benefit from developments in other fields, and vice-versa. We also need to identify the unique opportunities for experimentation required to move beyond the current generation of detectors.

Along with the new detectors come challenges that also need to be considered by this working group. Among other things, we should consider the issues of coordination between experiments, the need for permanent infrastructure in the field, the mechanisms of project review and funding, and the way in which collected data will be made available to the community at large.


  1. Review the current status of experimentation in the following areas:

    1. nonaccelerator particle physics carried out underground, including solar neutrino, atmospheric neutrino, proton decay, double beta decay, and supernovae neutrino experiments,

    2. high-energy particle (gamma-ray, cosmic rays, and neutrino) detectors,

    3. dark energy and dark matter experiments,

    4. cosmology experiments, and

    5. detectors of gravitational waves.

    The emphasis here should be on existing experiments, or those already under construction.

  2. In the various areas of experimentation, examine the generic detector capabilities needed to carry out the desired scientific program during the next decade and beyond. For example, among other things, how will we be able to:

    1. detect the polarization of the CMBR?

    2. carry out photometric and spectroscopic measurements of many supernovae out to redshifts of 1.5?

    3. detect pp solar neutrinos in real time?

    4. detect WIMPs or axions, or rule them out as interesting dark matter candidates?

    5. make very sensitive wide-field observations of the high energy gamma-ray and neutrino skies?

    6. search for proton decay at sensitivities exceeding 10^35 years?

    7. search for cosmic ray particles with energies exceeding 10^21 eV?

    The future scientific program will reflect strong input from working groups P2 and P4. In conjunction with these generic capabilities, determine what new advances in technology/ instrumentation will be critically needed, and outline the prospects for developing these technologies.

  3. Identify the major new facilities that are being considered. Enumerate their quoted performance (sensitivity, resolutions, etc.) and examine their technical feasibility. What new technologies will be required?

  4. An important infrastructure issue concerns a national underground laboratory. Taking as a starting point the Underground Science (Bahcall) report, consider the scientific programs that motivate an underground laboratory and enumerate the desirable characteristics of an underground laboratory. Are the requirements of different experiments compatible with a single site? Taking into account underground laboratory space around the world, consider whether the U.S. needs such a facility. What advantages and challenge would the creation of a new national underground laboratory entail?

  5. The development of experiments in this area has proceeded in a somewhat random fashion. Instrumentation development has not been supported vigorously enough, there has been insufficient communication between the experimental groups, and duplication of experiments with similar scientific goals. How can some of these issues be better handled in the next decade? What mechanisms can be used to coordinate worldwide experimental effort in this field?

  6. Experiments in astro/cosmo/particle physics are being built by people with a variety of backgrounds (nuclear physics, particle physics, astrophysics/astronomy, etc.). Funding comes from a variety of agencies (including NSF, DOE, NASA, Smithsonian, and private sources). Often, cultural differences lead to problems that should be avoidable in obtaining funding or developing efficiently organized collaborations. For example, the astronomical and particle physics communities have different outlooks on the public availability of gathered data. Another example is the project review and funding procedures. Different agencies have different procedures, and this often leads to a lengthy funding process. Examine some of these cultural differences, seeking community and agency input. What mechanisms are working and what are not? How can the community and the agencies work together more effectively?

Organizing Committee Contacts:

E7: Working Group on Particle Physics and Technology

Working Group Convenors: Stephan Lammel (Fermilab), Wesley Smith (Wisconsin), …, …

Particle physics has often been the driver of progress in technologies that are the key to advances in other scientific fields, in industry and eventually commerce. Examples of past decades range from cryogenic vacuum systems and superconducting wire and magnet technology to the invention of the World Wide Web. At other times, although not directly the generator of new technologies, our field has sparked progress by pushing new technologies to meet the needs of our next-generation experiments or numerically intensive theoretical investigations. Recent examples include high-precision radiation-tolerant particle detectors like silicon pixels that are now finding applications in the field of medical imaging as fast, low-exposure alternatives to x-ray films; compact high-speed electronics capable of acquiring and processing vast floods of data; high-gradient linear accelerators for electron-positron colliders that may form the basis for the future development of x-ray free electron lasers of super-high instantaneous brilliance; petabyte-scale analysis challenges of current and next generation collider experiments and the plans to meet these needs through the development of "Data Grids." Astrophysics has joined particle physics in this role through new programs such as large-scale sky surveys, precise measurements of cosmological parameters, and simulation of astrophysical processes. The scale, complexity and duration of ongoing and future programs have forced new approaches to the development of software by large and distributed collaborations, and have benefitted from the application of new statistical and algorithmic approaches from applied mathematics. These changes have resulted in the adoption of new programming models and tools and have led to a major role by computing professionals (software engineers) in experiments and advanced computation.


This working group should review leading-edge technologies recently developed (or in need of development) for new experiments and theoretical or computational investigations. Developments related to particle detectors, accelerators, online data acquisition systems, offline data analysis systems and networked "Grid" systems, or other areas, should be examined for their impact on experimental, theoretical, and computational investigations in particle physics. Technologies developed, or to be developed, within particle physics should be examined for their potential impact on society. The group should also review the demands for computer science expertise and software engineering in the current and future programs. It should comment on:

  1. The technology advances developed or enhanced by research in particle physics over the past 20 -- 30 years.

  2. Key problems and areas in particle detection technology, accelerator technology, information technology, and advanced algorithms for further developments that are vital for progress in our field.

  3. Areas of opportunity in the above fields where particle physics may play a principal role in fostering progress in key technologies important to scientific research and/or society at large.

  4. Areas where new developments in other fields may directly benefit particle physics over the next several years.

  5. Promising areas for common developments among experiments, and between particle physics and other fields, that could be of great mutual benefit.

  6. The changing role of computing professionals in our field and the need of physicists to enhance their knowledge of modern computing approaches and tools.

The working group should aim at formulating a plan for further development and improved exploitation of such technologies, to the mutual benefit of our field and society at large. It should estimate the scope, structure, manpower and other resources that will be required to make such a plan effective.

Organizing Committee Contacts: