1. Higgs Physics at the Muon Collider
Zhen Liu
Mainly based upon work with Tao Han, arXiv:
and Yuri Alexahin et al., arXiv: , arXiv:
International Symposium on Higgs Physics, IHEP, China, Aug.12-16, 2013

2. What is a Muon Collider?
A Lepton collider, with (relatively) clean environment, and: High beam energy resolution Capability of s-channel resonant production of Higgs boson, High upgradability as Energy Frontier Machine (up to 10 TeV) and lots of challenges
9/19/2018
Zhen Liu U of Pitt ISHP 2013

3. A First Sight of the Muon Collider
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Zhen Liu U of Pitt ISHP 2013

4. 9/19/2018
Zhen Liu U of Pitt ISHP 2013

5. S-channel Higgs Production
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Zhen Liu U of Pitt ISHP 2013

6. Muon Collider as a Higgs Factory
Resonant Production:
At the peak with a perfect energy resolution: 6
About 40,000 events produced per fb-1
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Zhen Liu U of Pitt ISHP 2013

7. SM Higgs is (very) narrow: Must convolute with energy profile:
At mh=126 GeV, Γh = 4.2 MeV
Must convolute with energy profile:
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Zhen Liu U of Pitt ISHP 2013

8. Extreme (good) Case: Recall: Z line shape with ΓZ ≈ 2.5 GeV
Energy Spread much smaller than the physical width:
(Δ = 0.3 MeV, Γh ≈ 4.2 MeV)
Recall: Z line shape with ΓZ ≈ 2.5 GeV
9/19/2018
Zhen Liu U of Pitt ISHP 2013

9. Extreme (bad) Case: Recall: J/ψ scan Γ ≈ 93 keV
Energy Spread much larger than the physical width:
(Δ = 50 MeV, Γh ≈ 4.2 MeV)
Recall: J/ψ scan Γ ≈ 93 keV
9/19/2018
Zhen Liu U of Pitt ISHP 2013

10. “Normal” (ideal) case:
Energy Spread comparable:
(Δ = 5 MeV, Γh ≈ 4.2 MeV)
An optimal fitting would reveal Γh
9/19/2018
Zhen Liu U of Pitt ISHP 2013

11. Remarks on this Method Similar to Z width scanning
However, the challenges/differences are:
Higgs width much narrower than the Z width
(4.2 MeV v.s. 2.5 GeV)
It’s (almost) simple counting. Not much dependence on the final state resolution. While other colliders are with very flat initial state energy distribution, they have to rely on the reconstructed energy of the decay products to see the peak directly.
9/19/2018
Zhen Liu U of Pitt ISHP 2013

12. Leading signals and background rates
The SM Higgs
With a cone angle cut: 10o < θ < 170o
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Zhen Liu U of Pitt ISHP 2013

13. Profile for SM Higgs Leading channels Sig+Bkg Randomize Step choice
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Zhen Liu U of Pitt ISHP 2013

14. Fitting procedure: Minimize χ2 over bins
Three Parameters Fitting
Width
Mass
Cross Section
Minimize χ2 over bins
Estimate standard deviation of fitting via χ2min +1
9/19/2018
Zhen Liu U of Pitt ISHP 2013

15. Fitting the SM Higgs
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Zhen Liu U of Pitt ISHP 2013

16. But First, we need to find the Higgs…
Haven’t we already found the Higgs?
We need to make sure its in a mass window +\ ~30 MeV to performing the scan to map out the SM-like Higgs boson total width.
It’s important to know how much luminosity needed to be investigated to find the Higgs mass peak region.
Study done by A. Conway and H. Wenzel, arxiv:
9/19/2018
Zhen Liu U of Pitt ISHP 2013

17. Pinning down the mass of the Higgs
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Zhen Liu U of Pitt ISHP 2013

18. Pinning down the mass of the Higgs
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Zhen Liu U of Pitt ISHP 2013

19. Remarks for Higgs Factory Muon Collider
Total Width is Important and key to precision Muon collider is good at it (narrow beam spread, high luminosity) Pinning down the peak is non-trivial and costs hundreds of inverse picobarn of integrated luminosity
9/19/2018
Zhen Liu U of Pitt ISHP 2013

20. Muon Collider as Energy Frontier Machine
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Zhen Liu U of Pitt ISHP 2013

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Zhen Liu U of Pitt ISHP 2013

22. S-Channel H/A Production
Again 40,000 times e+ e-
Universal for lepton collider
E. Eichten and A. Martin
Arxiv:
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Zhen Liu U of Pitt ISHP 2013

23. S-Channel H/A Production
E. Eichten and A. Martin
Arxiv:
9/19/2018
Zhen Liu U of Pitt ISHP 2013

24. How About the infamous Wedge?
s-channel
H/A
Pair Production
3 TeV Muon Collider
1.5 TeV
3 TeV
Figure from Snowmass Higgs Group Report
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Zhen Liu U of Pitt ISHP 2013

25. On Vector Boson Scattering (Fusion)
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Zhen Liu U of Pitt ISHP 2013

26. Challenges
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Zhen Liu U of Pitt ISHP 2013

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Zhen Liu U of Pitt ISHP 2013

28. Simulation Studies Underway
Detector and beam transport
Muon Collider-based detector model
Initial generator level simulation - Conway and Wenzel (arXiv: ) – more conservative assumptions
Cuts on forward shielding cone (15 deg)
Cuts to reject Z*/g background
Studies of width measurement and BR sensitivity
Full simulation becoming available
Study timing cuts on background and signal
Optimize background shielding and beam transport
Decay Backgrounds
9/19/2018
Zhen Liu U of Pitt ISHP 2013

29. Muon Collider Higgs factory Whitepaper
Detector and beam transport
Covers the topics of:
Physics
Collider environment
Detector design
Detector simulations
9/19/2018
Zhen Liu U of Pitt ISHP 2013

30. MAP Timeline Mark Palmer 2010 ~2020 ~2030 Muon Accelerator R&D Phase
Proton Driver Implementation – Project FNAL
Intensity Frontier
Energy Frontier
MAP Feasibility Assessment
Advanced Systems R&D
Muon Ionization Cooling Experiment (MICE)
IDS-NF RDR
Proposed Muon Storage Ring Facility (nSTORM)
Evolution of Long Baseline n Factory
Collider Conceptual  Technical Design
Collider Construction  Physics Program
Pr X Stage I
Pr X Stage II
Pr X Stage III & IV
Indicates a date when an informed decision should be possible
At Fermilab, critical physics production could build on Stage II of Project X 30
Opportunities with High Intensity Accelerators Beyond the Current Era
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Zhen Liu U of Pitt ISHP 2013
Aug 4, 2013

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Zhen Liu U of Pitt ISHP 2013

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Zhen Liu U of Pitt ISHP 2013

33. Summary
Muon Collider is an exiting candidate for future colliders, especially for its two distinguished features of s-channel Higgs production and serve as a Energy Frontier Machine. Lots of interesting physics Lots of challenges
9/19/2018
Zhen Liu U of Pitt ISHP 2013

34. Thank you!
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Zhen Liu U of Pitt ISHP 2013

35. Back Up
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Zhen Liu U of Pitt ISHP 2013

36. 9/19/2018
Zhen Liu U of Pitt ISHP 2013

37. Background
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Zhen Liu U of Pitt ISHP 2013

38. Background
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Zhen Liu U of Pitt ISHP 2013

39. Total Width at LHC and ILC
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Zhen Liu U of Pitt ISHP 2013

40. What Can be Measured?
Model-independent lower bound on total width is achivable.
9/19/2018
Zhen Liu U of Pitt ISHP 2013

41. On the total width determinations
LHC
Assumption on invisible/undetectable
SM-like:
No invisible, undetectable
Dominated by σ(bb)[1,2]
Invisible from measurement,
no undetectable
The above+Br(Inv)
~25% [2,3]
Assumption on upper bound
gHWW/gHZZ=SM
gHVV≤gHVVSM
σ(gg,VV), σ(gg,γγ),
σ(VBF,γγ), ~18%*- [4]
[1] M. Duhrssen, hep-ph/
[2] V. Barger+M.Inshida+W. Keung, ;
[3] B.Yang+P.Drapper+J.Shelton, arXiv: ; M. Peskin, arXiv: ;
[4] Dobrescu+Lykken, arXiv:
9/19/2018
Zhen Liu U of Pitt ISHP 2013

42. 9/19/2018
Zhen Liu U of Pitt ISHP 2013

43. On the total width determinations
LHC
Assumption on invisible/undetectable
SM-like:
No invisible, undetectable
Dominated by σ(bb)[1,2]
Invisible from measurement,
no undetectable
The above+Br(Inv)
~25% [2,3]
Assumption on upper bound
gHWW/gHZZ=SM
gHVV≤gHVVSM
σ(gg,VV), σ(gg,γγ),
σ(VBF,γγ), ~18%*- [4]
[1] M. Duhrssen, hep-ph/
[2] V. Barger+M.Inshida+W. Keung, ;
[3] B.Yang+P.Drapper+J.Shelton, arXiv: ; M. Peskin, arXiv: ;
[4] Dobrescu+Lykken, arXiv:
9/19/2018
Zhen Liu U of Pitt ISHP 2013

44. On the total width determinations
“recoil mass technique”:
No additional assumption
9/19/2018
Zhen Liu U of Pitt ISHP 2013

45. + other individual channels
ILC
Inclusive σ(ZH)
+ other individual channels
250 fb-1
σ(ZH) +
σ(ZH,bb),
σ(vvH,bb),
σ(ZH,WW),
~10%*[1]
500 fb-1
σ(vvH,WW)+
σ(ZH),
~6%+[2]
*at 68% C.L., PRELIMINARY
[1] C. F. Duerig, Master thesishttp://lhc-ilc.physik.uni-bonn.de/thesis/
Masterarbeitduerig.pdf;
[2] H. Baer et al., ILC DBD report.
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Zhen Liu U of Pitt ISHP 2013

46. Total Width at Muon Collider
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Zhen Liu U of Pitt ISHP 2013

47. Realistic studies: * TH and Z. Liu, arXiv: 1210.7803. 9/19/2018
Zhen Liu U of Pitt ISHP 2013