Muon Collider Physics and Detector Status Ronald Lipton, Fermilab Outline Physics with a Muon Collider Background rejection Detector tradeoffs Future Plans Ronald Lipton 9/28/2011 1

Muon Collider – Who Ordered That? LHC results will give us a window on the next energy scale. If it is greater than 1 TeV a Muon collider may provide the most affordable option for a precision machine. The Muon Accelerator Program is designed to understand the technical feasibility of a multi-TeV Muon Collider. Such a study needs to be complemented by an understanding of the experimental problems associated with such a machine. Can we do precise measurements in the harsh background environment that accompanies the muon beams? This talk will summarize some of the work of the 2011 Muon Collider Workshop in Telluride last summer Ronald Lipton 8/11/2011 2

Muon Collider Study Motivation Because muons don’t radiate as readily as electrons (m  / m e ~ 207) a muon collider can be circular rather then linear Compact Fits on laboratory site Multi-pass acceleration Cost effective operation & construction Multipass collisions in a ring (~1000 turns) Relaxed emittance requirements & hence relaxed tolerances Ronald Lipton 9/23/ A 4 TeV Muon Collider would fit on the Fermilab Site

Physics Advantages Ronald Lipton 8/11/ (Han) Narrow beam energy spread (0.1%) Precision threshold scans Kinematic constraints S-channel resonance production 2 Detectors are natural  T bunch ~ 10  s Lots of time for readout Backgrounds don’t pile up (m  /m e ) 2 = ~40000 Enhanced s-channel rates for Higgs-like particles Electrons from beam decays provide a precise measurement of beam energy and polarization.

Physics Environment Beam muons decay at rate of ~1.3x10 10 /meter/sec Electrons from beam decays generate a huge background at the IP. Much of our work concerns modeling (Mokhov) this background and studying ways to reject it in the experiment (Raja, Gatto) Ronald Lipton 9/28/ W  = 10 o 6 < z < 600 cm x:z = 1:17 BCH 2 (Mokhov)

Higgs Sector The Muon Collider offers the best chance for s-channel production and study of Higgs. A low energy collider could be used for precision scans of a SM Higgs. Supersymmetic Higgs (H 0,A 0 ) become degenerate as their mass increases. Muon Collider provides the beam resolution to separate A and H to about XXX GeV Masses can be measured in threshold scans at high energy Ronald Lipton 8/11/ ((Barger, Berger,Gunion,Han

WW, ZZ Scattering If there is no light Higgs high energy scattering amplitudes increase with S ww implying new physics to preserve unitarity. To measure effects want S  ~ (3- 5)S ww >4 TeV Underlying physics can be studied by examining various isospin channels May need energies best achieved at  C Ronald Lipton 8/11/ ((Barger, Berger,Gunion,Han Check<-

Supersymmetry Ronald Lipton 9/23/ Slepton decays provide clean mass measurements at ILC, CLIC Accuracy degraded by beamstrahlung Muon Collider could provide better precision but is more susceptible to small angle standard model backgrounds

Slepton Study (Frietas) Ronald Lipton 9/23/ In a muon collider forward angles (~10 o ) are obscured by shielding Rejection of two photon background can be compromised For large  m, can be recovered by energy cuts on one of the FS leptons giving similar resolution to electron collider case With FCAL No forward cal (arXiv:1107:3853v1)

Backgrounds Experiments at the Muon Collider will endure very harsh background environments. The first order of business in evaluating physics capabilities is to understand and simulate the machine backgrounds. A detailed MARS model is available including beam transport and MDI shielding, a similar model is working in G4beamline A central feature of the design is a 10 degree tungsten/borated poly “noise”surrounds the beam pipe to absorb the e-m backgrounds x background reduction. Ronald Lipton 8/11/

It’s About the Background The central question is whether we can do precision physics in the huge muon collider background. Ronald Lipton 9/23/ % of an event (Mazzacane)

Particle Fluxes Ronald Lipton 8/11/ TeV5.8 TeV92 TeV 172 TeV12 TeV (Striganov)

Time Distributions Ronald Lipton 8/11/

Detector Models Ronald Lipton 8/11/ LCSIM Detector ModelILCROOT Detector Model

Background Reduction Much of the background is soft and out of time thus we need Pixelated detectors to reduce occupancy and allow cuts on de/dx such that E mip >> E background Fast detectors to separate hits from particles originating in the IP from backgrounds from the surrounding shielding Energy resolution to implement de/ex cuts Detector systems which can exploit correlations between layers to distinguish signal tracks from uncorrelated backgrounds Ronald Lipton 8/11/

LCSIM Tracker Model Looks like SiD Higher vertex radii Fully pixelated… Models not identical Ronald Lipton 9/23/ ILCROOT LCSIM Results preliminary – LCSIM gives less Rejection than ILCROOT

Timing A 1 ns + de/ex cut can reduce the background hit density by nnn Such a cut with IP cuts can reduce the number of background tracks to <10 in a typical event. (Gatto, Mazzacane, Terentev) Ronald Lipton 8/11/ TT TT Background Single Muon  T +/- 5 ns  E/  X  T +/- 5 ns  E/  X 17

System Dependence (LCSIM) Ronald Lipton 9/23/ Arrival time (ns) Mostly neutrons Mostly photons

Hit Occupancy (ILCROOT) Ronald Lipton 9/23/ Need to cross check With LCSIM model

Correlated Layers 20th Century Muon Collider studies assumed 300  m square pixels ILC studies now assume ~ 20  m square pixels x 225 less occupancy/pixel S. Geer suggested a stacked layer design to reduce occupancy based on inter-layer correlations for the muon collider in 1998 This technology looks very much like what we are developing for the CMS upgrade Ronald Lipton 8/11/  Col Track correlation module (Geer)

Double Layer Hit Window Ronald Lipton 9/23/

Tracker Data Flow Readout – triggered or all events Is data load acceptable? Is power acceptable? How do we trigger, given the large backgrounds? Optical links – current technology 10 pj/bit 10 Gbit/sec per interconnect Data can be move with little power penalty if rad hard encoders are available Ronald Lipton 9/23/ Silicon Tracker Data Load hits/event 10 cluster factor 30 bits/hit 1.00E+05 crossings/sec 1.50E+12 bits/sec Optical Readout 1.00E-11 j/bit 1.50E+01 Watts 1.00E+10 bits/channel x sec 1.50E+02 encoders

Calorimetery Issues EM showers have well defined development we can exploit fast timing and can fit to shower shape Can we use fast timing for hadron calorimetry? How does hadron shower propagation time affect background rejection? Segmented crystal calorimeter? Sampling “imaging” calorimeter? Can we use layer correlations? Can we reject the soft photons in the first layers without compromising EM resolution? Ronald Lipton 8/11/

LCSIM Calorimeter Model q Ronald Lipton 9/23/

ECal: Tungsten, 10 x 1cm layers 1x1x1cm cells Background 1ns timing cut EM calorimeter in LCSIM Reduction: EM – 23% of energy survives a 1 ns timing cut 6% of that energy is beyond 1 st EM cell Ronald Lipton 9/23/ No timing Cut EM cal layer

Hadron showers LCSIM study of “generic” calorimeter 10 GeV pions – vary time cut Ronald Lipton 9/23/ (Alex Conway)

Time Development Ronald Lipton 9/23/ Hadron shower time development for background and 10 GeV pion showers Background 10 GeV pion

Hadron Calorimetry Adriano dual readout calorimeter studied by Lecce group (Gatto) Fast timing imaging calorimeter proposed by Raja It will be crucial to explore the time evolution of hadron showers in detail What can ns level time stamping do? What is the material dependence? Optimal sampling and pixel size? Can layer correlations be used? Use initial 1 ns signals to “gate” regions for full reconstruction PFA in the time dimension! Ronald Lipton 9/23/ GeV pion in calorimeter Hadrons—red Electrons-cyan Muons- green Out of time hits - yellow Raja

Time Resolution The basic formula is: For silicon detectors the rise time due to signal formation in the silicon is 5-10 ns (collect electrons) and will probably dominate. The mobility is voltage dependent – so we want to overbias. The intrinsic signal/noise is set by the detector capacitance, thickness, and front-end power. Typically 15-20:1 – backgrounds also add “noise” which is improved by segmentation. Rise time and noise depend on front-end transistor transductance (gm) ~ transistor current – the basic tradeoff Time resolutions of 200ps – 1 ns are reasonable with proper time walk compensation and signal processing There will be tails due to straggling, delta rays and overlaps with out of time background. Transistor bandwidth in weak inversion ~gm ~ Id power Power need not be excessive – but pixels more complex Ronald Lipton 9/23/

Radiation The overall non-ionizing flux is similar to s-LHC We know what is needed to operate silicon in this environment Low temperatures (-10 deg C) – also helps mobility Thin sensors – also helps collection time, but lower s/n hurts time resolution Single sided n-on-p preferred Ionizing radiation causes positive charge in IC insulating layers Density tends to saturate In deep submicron technologies these charges tunnel out of the thin oxide layers – naturally radiation hard Future generations of electronics should be OK unless there are significant changes in the technology Ronald Lipton 9/23/

Conclusions and Comments Muon Accelerator Project is up and running – making substantial progress We are beginning a renewed physics and detector program to study the TeV Muon Collider environment We have a strong foundation – reliable MARS simulation of backgrounds integrated into GEANT-based detector models. As a field we need to be in a position to make an informed decision about the tradeoffs of alternate approaches. We need to understand the options if physics points to a multi- TeV lepton collider. CLIC is a strong possibility, but not a “no brainer”, especially as the required energy increases. There are strong overlaps of interest of Muon Collider with CLIC in physics, fast timing, detector design, and simulation. Ronald Lipton 9/23/