Muon Collider Physics and Detectors

1. 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

2. 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-studiedscenario • LHC will have limited ability to study the full spectrum • LC (CLIC/ILC/Muon Coll) can fill in many of the gaps

3. Luminosity Requirements • We need to produce enough eventsto 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 (Eichten)

4. Questions • Can we build it? - to be answered by the Muon Accelerator Program • 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? KK graviton exchange with jet-charge info s = 500 GeV,  = 1.5 TeV, 500 fb-1 (Hewett)

5. 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:

6. Fusion Process For s>1 TeV fusion processes become important • Large cross sections • Increase with s. • Important at multi-Tev energies • MX2 < s • Backgrounds for SUSY processes • t-channel processes sensitive to angular cuts Processes at these energies have not been carefully studied for ILC (Eichten)

7. Backgrounds • There is a huge background from muon decays in flight. For a 750 x 750 GeV machine with 1012m/bunch: • 4.3x105m decays/meter • 3x104 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.

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

9. 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. Ronald Lipton, Fermilab 2/24/2011

10. Detector Simulation4th Concept + SiD • SiD ILC detector in the muon collider framework Silicon tracking vertex nose Ronald Lipton, Fermilab 2/24/2011

11. ILCROOT mm -> nnZ Study • ILCROOT based simulation – using “4th concept design Ronald Lipton, Fermilab 2/24/2011

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

13. 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 (V. Di Benedetto) Ronald Lipton, Fermilab 2/24/2011

14. Ronald Lipton, Fermilab 2/24/2011

15. Some Comments • Background radiation ~ .1 x LHC, but crossing 10ms/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 CMS track trigger design Ronald Lipton, Fermilab 2/24/2011

16. 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? Ronald Lipton, Fermilab 2/24/2011

17. 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 Ronald Lipton, Fermilab 2/24/2011

18. 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 ~2012 Ronald Lipton, Fermilab 2/24/2011