1. Physics and Detectors for a Muon Collider
Ronald Lipton
Fermilab
January 9, 2014

2. Outline Physics Overview Backgrounds Tools Parametric Studies
Higgs factory
High energy self-coupling
High Energy H/A with full background simulation
Conclusions
January x, 2014

3. Physics Overview
Although the muon collider shares Feynman diagrams with it’s e+e- cousins there are a number of distinct differences which affect the physics reach of a muon-based machine. These considerations are distinct for a Higgs factory where a Muon Collider has x40,000 higher coupling in the s-channel, and a high energy machine, where the same physics processes dominate but the machine characteristics are different.
January x, 2014

4. Higgs Factory
A Muon Collider is uniquely capable of producing Higgs bosons in the s channel with beam energy resolution comparable to it’s width
(mm/me)2 = ~40,000
G(H) ~ 4.2 MeV
DE(beam) ~ few MeV
The beam energy resolution could be comparable to the Higgs width
Direct measurement of width
Precise mass measurement
January x, 2014

5. High Energy Collider
LHC results seem to indicate that any new physics spectrum is likely to be in the multi-TeV range.
This is problematic for e+e- machines due to power lost to radiation.
Muon collider seems to be the only high luminosity lepton collider candidate >3 TeV
January x, 2014

6. Physics Environment Narrow beam energy spread 2 Detectors
Precision scan
Kinematic constraints
2 Detectors
DTbunch ~ 10 ms
(mm/me)2 = ~40,000
Enhanced s-channel rates for Higgs-like particles
Multi-TeV lepton collider cross sections dominated by boson fusion
(Han)
January x, 2014

7. Luminosity Goals L~1034 at 3 TeV provides ~ 965 events/unit R
Much of the yield is in fusion reactions
Need to resolve W, Z jets
Large missing energies
Physics environment similar to CLIC with lower beamstrahlung, higher decay backgrounds, lower polarization and central 10 degrees obscured by shielding
January x, 2014

8. Backgrounds
From the detector side the central issue in a muon collider are backgrounds due to muon beam decays.
For a 0.75-TeV muon beam of 2x1012, 4.28x105 dec/m per bunch crossing, or 1.28x1010 dec/m/s for 2 beams; 0.5 kW/m.
Understanding how to study and mitigate these backgrounds is crucial to the overall validation of the muon collider concept. That has been a primary focus of physics and detector work.
January x, 2014

9. MARS Simulations
MARS – is the framework for simulation of particle transport and interactions in accelerator, detector and shielding components.
Background calculation requires knowledge of machine components and design of integrated shielding throughout the system
Machine must be designed before the background is calculated – may be an iterative process
Completed for 1.5 TeV machine – used in all detector studies; almost completed for Higgs Factory (see N. Mokhov talk)
Background is provided to detector simulation at the surface of MDI.
January x, 2014

10. Machine Detector Interface ModelW
Q = 10o 6 < z < 600 cm x:z = 1:17
BCH2 Q1
N. Mokhov design and MARS simulations
January x, 2014

11. Backgrounds Entering the Detector
Only 4% background
pictured
Hits in the calorimeter
Most of the background is out of time
Timing cut can further reduce the background
Most of the background are low momenta
photons and neutrons
S. Striganov
MARS Simulation
Still a lot of background!!!!! 11
January x, 2014

12. Shielding Cone
A degree tungsten/borated poly “noise”surrounds the beam pipe to absorb the e-m backgrounds resulting in a x background reduction.
Ivan Yakovlevitch … glanced into the roll's middle. To his intense surprise he saw something glimmering there ..   He stuck in his fingers, and pulled out — a nose! .. .A nose! Sure enough a nose! Yes, and one familiar to him, somehow! Oh, horror spread upon his features! - “The Nose” Gogol
January x, 2014

13. Detector Simulation Tools
LCSIM Detector Model
ILCROOT Detector Model
Models derived from the SiD ILC concept
January x, 2014

14. Attacking the Background
It is clear that timing and energy discrimination will be crucial in limiting the background in a Muon Collider
We have concentrated on understanding the time resolution required and how it may affect the detector mass and resolution for physics objects
The R&D is synergistic with CLIC, which requires ns level resolutions, LHC which is looking at fast timing for background reduction, and intensity frontier experiments, which may require 100’s of ps resolutions
Studies have proceeded with several tools – ILCROOT, LCSIM and GEANT
January x, 2014

15. Timing Is The Key Timing for MARS background particles
- MARS background (on a surface of the shielding cone)
up to ~1000 ns of TOF (time of flight w.r.t. BX)
Timing of ILCRoot MARS background hits in VXD and Tracker
- TOF for neutron hits has long tale up to a few ms (due to “neutron gas”)
Time gate width of 4 ns can provide a factor of background rejection keeping efficiency of hits from IP particles higher than 99% at hit time resolution σ=0.5 ns.
N. Terentiev
January x, 2014

16. Tracking Backgrounds Neutrons
Time of energy deposit with respect to TOF from IP
dE/dx
Path in detector
electrons
electrons
positrons
Compton
High energy
conversions
soft
conversions 16
January x, 2014

17. Timing Is Also The Key For Calorimetry
Background
Front Section
V. Di Benedetto
Rear Section
Signal
Sci signal is developed in sci fibers
with 2.4 ns decay time
Cerenkov is read directly on LeadGlass
Time bin of 25 ps
Sci signal is developed in sci fibers
Cerenkov is read by WLS
Both with 2.4 ns decay time
Time bin of 25 ps
A. Mazzacane (Fermilab)
CSS 2013 — July 29- August 6, 2013 17
January x, 2014

18. Parametric Studies
We have explored capabilities for both a Higgs factory muon collider and Higgs self-coupling measurements at a possible high energy (6 TeV) machine. These were based on parametric studies assuming backgrounds in these machines could be controlled, but the detectors were limited by a degree cone.
January x, 2014

19. Higgs Factory
The s-channel Higgs production affords the most precise measurement of a second generation fermion Higgs-Yukawa coupling constant, the muon coupling, gμ, to a precision δgμ/gμ ~ (few)%.
The s-channel Higgs production affords the best mass measurement of the Higgs boson to a precision of ~(few) x10−6 with a luminosity of 1032 cm−2s−1.
It affords the best direct measurement of the Higgs boson width to a precision of a few%
January x, 2014

20. Higgs Factory S/B
Higgs production in an S-channel factory still has significant SM background.
cross sections are calculated as the peak value of the peak Breit-Wigner convoluted with a Gaussian of width 3.54 MeV to simulate the effect of beam smearing. The inclusion of initial state radiation effects and full one loop corrections further reduces the cross sections for Higgs production by a factor of 0.53; resulting in
a total Higgs cross section of 13.6 pb.
January x, 2014

21. Higgs Factory Physics Background reduction
Use Event shape and energy cuts to reduce Z decay backgrounds under the Higgs peak
January x, 2014

22. Higgs Mass and Width
336000
Fitted values of Higgs decay width, mass and branching ratio from simulated data. Mass values are the difference between the measured mass and the true mass of 126 GeV. Total integrated luminosity was 4.2 fb−1
143000
Accuracy of fitted parameters
January x, 2014

23. Higgs Self-Coupling
Measurement of the Higgs trilinear self-coupling is a direct probe of the shape of the Higgs potential and a crucial test of the Standard Model.
All future high energy accelerators are likely to address this measurement.
A high energy Muon collider would have the advantage of higher luminosity and cross section
CLIC will have larger acceptance
Study the tradeoffs …
Variation of
s with l provides the sensitivity
January x, 2014

24. Self-coupling Analysis
For now we take the CLIC analysis and scale the results to the event yield correcting for events lost to the cone
January x, 2014

25. Self-coupling results
Results obtained by scaling CLIC results – note that the values can be improved by utilizing polarization
HL-LHC – evidence
ILC (20yr) – 13%
3 TeV CLIC (polarization) – 10%
January x, 2014

26. Physics analysis with background
Heavy Neutral Higgses (H/A) and charged Higgses (H±) are a simple possibility of New Physics beyond the Standard Model.
H/A are likely to be difficult to find at the LHC and at e+e- colliders are produced in association with other particles, such as Z, since the electron Yukawa coupling is too small for s-channel production.
H and A can be produced as s-channel resonances at a Muon Collider (Eichten and Martin arXiv: ).
Pseudo-data (in black) along with the fit result in the bb channel.
Tthe peak signal is more than an order of magnitude larger than the physics background.
H/A production in the Natural Supersymmetry model compared with Z0h, Z0H and heavy Higgs pair production.
January x, 2014

27. Full Simulation
Fully simulated with track and calorimeter reconstruction in ILCroot framework H/A events generated by Pythia at √s = 1550 GeV with a Gaussian beam energy smearing (R=0.001) (A. Martin)
In these preliminary studies, considered the bb̅ decay of the H/A which is the channel with the largest BR (64%).
Applied a perfect b-tagging (using information from MonteCarlo truth).
Reconstructed 2 jets applying PFA-like jet reconstruction developed for ILC benchmark studies.
NO machine background
ILCroot Event Display
NO Time Gate NO Background
Dijet mass distribution including
neutrino contribution
Significant neutrino component
A. Mazzacane (Fermilab)
CSS 2013 — July 29- August 6, 2013 27
ILCroot Simulation
January x, 2014

28. Background Rejection In The Calorimeter
Tiime gate for each section
Front Section
Rear Section
Scint
Cer
Front readout
6.3 ns
1.5 ns
12.8 ns
10.3 ns
Back readout
5.7 ns
0.8 ns
8.5 ns
7.0 ns
Signal efficiency
83%
76%
BG suppression
98.5%
97.3%
Scint/Cer back readout
Calorimeter tower readout scheme
Rear Section 160 cm
Scint/Cer front readout
BG energy
Front Section
Rear Section
Total
228 TeV
155 TeV
After time cut
3 TeV
4 TeV
V. Di Benedetto
Front Section 20 cm
Scint/Cer readout back
Scint/Cer readout front
Approach to reject machine background.
Apply time cut.
Individuate Region of Interest (RoI), i.e. regions where the energy is 2.5σ above the background level in that region.
In the RoI apply soft energy subtraction, i.e. subtract the mean value of the background in that region.
In the other regions apply hard energy cut, i.e. subtract 4σ of the background.
Preliminary
A. Mazzacane (Fermilab)
CSS 2013 — July 29- August 6, 2013 28
January x, 2014

29. Result with Background
YES Time Gate NO Background
Applied 3 ns layer dependent time gate in the tracking system and the time gate in the calorimeter.
YES Time Gate YES Background
Fully simulated signal and beam background Applied 3ns time gate and energy cut theta dependent to further reject the background
ILCroot Simulation
A. Mazzacane (Fermilab) 29
January x, 2014

30. Future Plans We are completely constrained by manpower
<2 FTE available
FNAL guest scientists + undergrads
Computing support at FNAL no longer available through detector R&D
We will complete and document Snowmass studies
Further work will depend on manpower and physics interest
Higgs factory studies with full background simulation
Study a less optimal supersymmetric signals with a detector fully optimized for background rejection
Timing used in silicon tracking fits
High speed, segmented crystal calorimeter
January x, 2014

31. Conclusions
We have used the ILCROOT and LCSIM frameworks to study physics capabilities and background rejection
Timing is key for both calorimetry and tracking
We have produced the first physics simulation with full muon collider backgrounds and demonstrated acceptable performance.
We have studied capabilities for Higgs physics
Future program will depend on manpower available
January x, 2014