John Ellis King’s College London (& CERN) Supersymmetry, Higgs & LHC Physics What we (don’t)...
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Transcript of John Ellis King’s College London (& CERN) Supersymmetry, Higgs & LHC Physics What we (don’t)...
![Page 1: John Ellis King’s College London (& CERN) Supersymmetry, Higgs & LHC Physics What we (don’t) know What else is there? How to discover it?](https://reader037.fdocuments.in/reader037/viewer/2022110400/56649d9e5503460f94a8932b/html5/thumbnails/1.jpg)
John EllisKing’s College London
(& CERN)
Supersymmetry, Higgs & LHC Physics
What we (don’t) know
What else is there?
How to discover it?
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IntroductionStandard Model Particles:
Years from Proposal to Discovery
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The (NG)AEBHGHKMP Mechanism
The only one
who mentioned a
massive scalar boson
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A Phenomenological Profile of the Higgs Boson
• First attempt at systematic survey
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Couplings resemble Higgs of Standard Model
• No indication of any significant deviation from the Standard Model predictions
JE & Tevong You, arXiv:1303.3879
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Does the ‘Higgs’ have Spin Two ?
• Discriminate spin 2 vs spin 0 via angular distribution of decays into γγ JE & Hwang: arXiv:1202.6660
JE, Fok, Hwang, Sanz & You: arXiv:1210.5229
Monte Carlo
simulations
2+ disfavoured @ 99%
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• Pseudoscalar 0- disfavoured at > 99% CL
The ‘Higgs’ is probably a scalar
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Global Analysis of Higgs-like Models
• Rescale couplings: to bosons by a, to fermions by c
• Standard Model: a = c = 1JE & Tevong You, arXiv:1303.3879
b bbarτ τγ γW WZ ZGlobal
No evidence for
deviation from SM
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It Walks and Quacks like a Higgs
• Do couplings scale ~ mass? With scale = v?
• Red line = SM, dashed line = best fitJE & Tevong You, arXiv:1303.3879
Global
fit
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[1] = JE & Tevong You, arXiv:1303.3879
Dixit Swedish Academy
Today we believe that “Beyond any reasonable doubt, it is a Higgs boson.” [1]
http://www.nobelprize.org/nobel_prizes/physics/laureates/2013/advanced-physicsprize2013.pdf
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No BSM? Beware Historical Hubris
• "So many centuries after the Creation, it is unlikely that anyone could find hitherto unknown lands of any value” - Spanish Royal Commission, rejecting Christopher Columbus proposal to sail west, < 1492
• “The more important fundamental laws and facts of physical science have all been discovered” – Albert Michelson, 1894
• "There is nothing new to be discovered in physics now. All that remains is more and more precise measurement" - Lord Kelvin, 1900
• “Is the End in Sight for Theoretical Physics?” – Stephen Hawking, 1980
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• Unstable electroweak vacuum• Dark matter• Baryon asymmetry• Neutrino masses• Inflation• Naturalness problem• Quantum gravity• …
The Standard Model Is Not Enough
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Theoretical Constraints on Higgs Mass
• Large Mh → large self-coupling → blow up at low-energy scale Λ due to renormalization
• Small: renormalization due to t quark drives quartic coupling < 0at some scale Λ→ vacuum unstable
• Vacuum could be stabilized by SupersymmetryDegrassi, Di Vita, Elias-Miro, Giudice, Isodori & Strumia, arXiv:1205.6497
Instability @
1011.1±1.1 GeV
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Vacuum Instability in the Standard Model
• Very sensitive to mt as well as MH
• Instability scale:
• New measurement of mt = 173.34 ± 0.76 GeV
Buttazzo, Degrassi, Giardino, Giudice, Sala, Salvio & Strumia, arXiv:1307.3536
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Instability during Inflation?• Do quantum fluctuations drive us over the hill?
• Then Fokker-Planck evolution• Do AdS regions eat us?
– Disaster if so– If not, OK if more inflation
• Cure with non-ren’ble operator?
Hook, Kearns, Shakya & Zurek: arXiv:1404.5953
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What else is there?
Supersymmetry• Successful prediction for Higgs mass
– Should be < 130 GeV in simple models
• Successful predictions for Higgs couplings– Should be within few % of SM values
• Could explain the dark matter• Naturalness, GUTs, string, … (???)
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Search with ~ 20/fb @ 8 TeV
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Data
• Electroweak precision observables
• Flavour physics observables
• gμ - 2
• Higgs mass• Dark matter• LHC
MasterCode: O.Buchmueller, JE et al.
Deviation from Standard Model:
Supersymmetry at low scale, or …?
MH = 125.6 ± 0.3 ± 1.5 GeV
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O. Buchmueller, R. Cavanaugh, M. Citron, A. De Roeck, M.J. Dolan, J.E., H. Flacher, S. Heinemeyer, G. Isidori,
J. Marrouche, D. Martinez Santos, S. Nakach, K.A. Olive, S. Rogerson, F.J. Ronga, K.J. de Vries, G. Weiglein
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p-value of simple models ~ 5% (also SM)
2012 20/fb
Scan of CMSSM
Buchmueller, JE et al: arXiv:1312.5250
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51 20/fb2012
Squark mass
CMSSM
Favoured values of squark mass also significantly
above pre-LHC, > 1.6 TeV
Buchmueller, JE et al: arXiv:1312.5250
Reach of LHC at
High luminosity
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51 20/fb2012
CMSSM
Favoured values of gluino mass significantly
above pre-LHC, > 1.8 TeV
Buchmueller, JE et al: arXiv:1312.5250
Gluino mass
CMSSM
Reach of LHC at
High luminosity
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Confronted with likelihood analysis of CMSSM
LHC Reach for Supersymmetry
K. De Vries
(MasterCode)
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Where May SUSY be Hiding?
Excluded by
b s γ, Bs μ+μ-
Relic density constraint,
assuming
neutralino LSP
JE, Olive & Zheng: arXiv:1404.5571
Stop
coannihilation
strip
Stau
coannihilation
strip
Excluded by ATLAS
Jest + MET search
Excluded because
stau or stop LSP
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Exploring the Stau Coannihilation Strip
• Disappearing tracks, missing-energy + jets, massive metastable charged particles
Desai, JE, Luo & Marrouche: arXiv:1404.5061
Present
sensitivity
Present
sensitivity
LHC Run II should explore robustly
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Exploring the Stop Coannihilation Strip
• Extends close to boundary of stop LSP wedge
• Extends to masses far beyond current limitsJE, Olive & Zheng: arXiv:1404.5571 Prospective sensitivity of LHC Run II
Present
bounds
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Exploring the Stop Coannihilation Strip
• Extended by Sommerfeld effects on annihilations
• Compatible with LHC measurement of mh
• May extend to mχ = mstop ~ 6500 GeVJE, Olive & Zheng: arXiv:1404.5571
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Exploring the Stop Coannihilation Strip
• Present limits extend to mstop ~250 GeV
• Future LHC runs should reach mχ=mstop~500 GeV
• Unfinished business for FCC-hh?JE, Olive & Zheng: arXiv:1404.5571
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What Next: A Higgs Factory?
To study the ‘Higgs’ in detail:• The LHC
– Consider LHC upgrades in this perspective• A linear collider?
– ILC up to 500 GeV– CLIC up to 3 TeV
(Larger cross section at higher energies)
• A circular e+e- collider?• An ep collider?• A γγ collider? A muon collider?• Wait for results from LHC @ 13/14 TeV
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Possible Future Higgs Measurements
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• Predictions of current best fits in simple SUSY models
• Current uncertainties in SM calculations [LHC Higgs WG]
• Comparisons with– LHC– HL-LHC– ILC– TLEP (= FCC-ee)(Able to distinguish from SM)
Impact of Higgs Measurements
K. De Vries
(MasterCode)
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Future Circular e+e- Collider?
Not just Higgs physics:
Also Tera-Z, Oku-W, Mega-t
M = 246.0 ± 0.8 GeV, ε = 0.0000+0.0015-0.0010
•
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TLEP:Part of a Vision for the Future
Exploration of the 10 TeV scale
Direct (VHE-LHC) + Indirect (TLEP)
Need major effort to develop the physics case
Work together
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Theoretical Confusion
• High mortality rate among theories• (MH, Mt) close to stability bound
• Split SUSY? High-scale SUSY? • Modify/abandon naturalness? Does Nature care?• String landscape? • SUSY anywhere better than nowhere• SUSY could not explain the hierarchy• New ideas needed!