Muon Collider Physics and Detectors You have heard about the muon collider accelerator initiatives – these need to be informed by the physics needs and detector capabilities. Original studies were done in the 1990’s – largely abandoned in the redirection to ILC Established a baseline for background levels Began design on shielding and background estimates Made plausibility arguments about experimental capabilities But detailed physics studies were lacking Muon collider has re-emerged as a possible option Unless LHC finds new physics soon the initial 500 GeV ILC energy range will become uninteresting CLIC is the primary e + e - alternative, but feasibility is not proven and costs are unknown. Power is known to be high (>500 MW) The Muon Collider option needs to be carefully examined by the HEP community – we need to understand the tradeoffs 1

Landscape in 20 Years We are thinking about a machine which may begin in 20 years – the LHC will have made the basic discoveries, but new physics is likely to be complex and the LHC will have to cope with very low signal/background and as many as 200 interactions/xing – the argument for a precision machine stands Supersymmetry is the best-studied scenario LHC will have limited ability to study the full spectrum LC (CLIC/ILC/Muon Coll) can fill in many of the gaps 2

Luminosity Requirements We need to produce enough events to make meaningful measurements s channel (annihilation) cross sections fall as 1/s For √s > 500 GeV For SM pair production (|θ| > 10°) R = σ/σQED(μ+μ- -> e+e-) ~ flat High luminosity required ⇒ 965 events/unit of R 3 ( Eichten )

Questions 1.Can we build it? - to be answered by the Muon Accelerator Program 2.If we build it what are the physics capabilities? The ILC case has been built over many years – enable precise measurements of new physics uncovered by the LHC, measure higgs branching ratios … For muon collider the central issue is background – muons decay. Can we still claim to make precise measurements in the expected background? Polarization is an important ingredient in ILC measurements – what is lost if muon polarization is not preserved in a collider? The forward region is likely to be obscured – how will this affect physics? 4 KK graviton exchange with jet-charge info  s = 500 GeV,  = 1.5 TeV, 500 fb -1 (Hewett)

Muon Collider Physics Muon collider does not suffer from beam radiation as do e + e - machines Significant advantage in some measurements: Z’ resonance can be measured more accurately Physics which requires beam constraints Measure mass using “edge” method: 5

Fusion Process For s>1 TeV fusion processes become important Large cross sections Increase with s. Important at multi-Tev energies M X 2 < s Backgrounds for SUSY processes t-channel processes sensitive to angular cuts Processes at these energies have not been carefully studied for ILC 6 ( Eichten )

Backgrounds There is a huge background from muon decays in flight. For a 750 x 750 GeV machine with  /bunch: 4.3x10 5  decays/meter 3x10 4 incoherent pairs/crossing The region immediately around the beam is excluded (detectors start at 5-6 cm) The IP is surrounded by a tungsten cone extending 10 deg. from +/- 6 cm away from the IP to absorb halo em energy How does this affect physics reach? Can the cone be instrumented? We have addressed precision physics in a “dirty” environment before – hadron colliders. 7

Backgrounds Reliable background calculations are now available MARS and GEANT (Muons Inc.) versions 8 Ronald Lipton, Fermilab 2/24/2011

Backgrounds II Significant progress has been made in generating unweighted events in MARS Simulation work so far has worked with ~1% of a crossing – limited by computing and disk Need a smarter simulation which can treat background particles optimally, perhaps reducing the flux and increasing interaction probability for neutrals. Need to develop a tool which can use a parameterization of the background to enable less computing-intensive physics simulation. 9 Ronald Lipton, Fermilab 2/24/2011

Detector Simulation 4 th Concept + SiD SiD ILC detector in the muon collider framework 10 Ronald Lipton, Fermilab 2/24/2011 Silicon tracking vertex nose

ILCROOT  -> Z Study ILCROOT based simulation – using “4 th concept design 11 Ronald Lipton, Fermilab 2/24/2011

Energy per tower in central Barrel 12 (V. Di Benedetto - Lecce) 4x4 cm “dual readout cells

Conclusions from early study Jets develop in 16 – 25 towers; mean energy 150 GeV Background in barrel - mean energy 5 GeV, RMS 0.6 GeV Jet energy fluctuation after background pedestal cut 2.5 – 3 GeV Background in endcap > 20 deg - mean energy 5 GeV, RMS 1. GeV Jet energy fluctuation after background pedestal cut 5 – 6 GeV Background in endcap < 20 deg - mean energy 12 GeV RMS 5. GeV Jet energy fluctuation after background pedestal cut 20 – 25 GeV This is a start, but we need to begin to understand the details 13 Ronald Lipton, Fermilab 2/24/2011 (V. Di Benedetto)

14 Ronald Lipton, Fermilab 2/24/2011

Some Comments Background radiation ~.1 x LHC, but crossing 10  s/25 ns – 400x longer implies high occupancies in tracker and calorimeter Most is very soft and much is out of time – can we use correlated layers to reduce backgrounds? Energy resolution in calorimeters set by fluctuations of background energies Worse in endcaps Is particle flow a better choice? How much can timing help? What is the optimal segmentation? Silicon-based tracking should be feasibile But more massive than ILC due to the need to provide a colder environment to avoid radiation damage effects May need to use local correlations Vertex inner radius limited by “nozzles of fire” near beam 15 Ronald Lipton, Fermilab 2/24/2011 CMS track trigger design

A thought Muon collider backgrounds are largely uncorrelated Electromagnetic showers have well-defined shapes Hadronic showers have less well-defined correlations, but they are significantly larger than background Can we design detector layers which have optimal sampling to allow us to use the expected correlations between layers to reject backgrounds and improve signal? How does this effect resolution? Would this be an effective handle for hadrons? Especially neutral hadrons if we use particle flow? 16 Ronald Lipton, Fermilab 2/24/2011

Interesting Problems … Understand the environment Integrate background with candidate detector technologies Find a way to parameterize background to allow less resource-intensive physics studies Understand limitations on detector options due to backgrounds – can the nose be instrumented? Propose detector technologies best suited to the environment Provide a baseline comparison to other options (CLIC) Specific physics studies – hopefully focused by LHC results What is lost by the “nose”? What are the tradeoffs in polarization? What is gained by lower beamstrahlung? In the end we want to be able to compare cost and physics reach to the alternatives – and make an informed decision 17 Ronald Lipton, Fermilab 2/24/2011

Plan for the Future Telluride workshop is a milestone – before the workshop Continue studies using ILCROOT framework Integrate SiD-like detector into muon collider using LCSIM framework – allows direct comparison with CLIC studies Integrate MARS background simulation into LCSIM Detailed background studies Hit rates in various regions of the tracker including event-by-event variations Energy deposit in various regions and depths in the calorimeter including event-by-event variations After the workshop Studies of background parameterization Time dependence, correlations, fluctuations, phi dependence Studies of a few benchmark reactions – with and without background Begin to understand detector design in this environment. Reference detector design ~ Ronald Lipton, Fermilab 2/24/2011