FYST11 Lecture 12 BSM II - Particle Physics · 2016. 2. 23. · SUSY cross section versus sparticle...
Transcript of FYST11 Lecture 12 BSM II - Particle Physics · 2016. 2. 23. · SUSY cross section versus sparticle...
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FYST11 Lecture 12 BSM II
Thanks to G. Brooijmans, T. Rizzo, L. Covi
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This week’s topics
• Why go Beyond the SM?
– What are the problems with the SM?
– What direct measurements points to physics BSM
• Some attempts at solutions
– Supersymmetry
– Extended Higgs sector
– Extra dimensions
– A few others
• Searches for DM
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Supersymmetry (SUSY)
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Idea New symmetry fermions bosons
This symmetry is the most general extension of Lorentz invariance
• To create supermultiplets, we need to
add one superpartner to each SM particle
• Superpartners have opposite spin
statistics but otherwise equal quantum
numbers
• Need to introduce an additional Higgs
doublet to the non-SUSY side 5 Higgs
bosons
But where are these partners?! Supersymmetry must be broken (if realized)
SUSY has: Ndof (bosons) = Ndof (fermions) [cf. SM: Ndof (bosons) << Ndof (fermions)]
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Particle spectrum (minimal!)
In reality the new states would mix
Several ideas of how the supersymmetry is broken – intimately connected with EWK symmetry breaking
Since we don’t know the mechanism, have to introduce 𝒪(100) new parameters ….
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SUSY and the hierachy problem
But as m(𝑡 ) m(𝑡) they do not quite cancel, instead just a suppression This still gives a decent result if |m(fermion) – m(boson)| < 𝒪(TeV)
If Supersymmetry not broken we would have perfect cancellation in the loops!
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Once mass spectrum fixed, all cross sections predicted Spin structure of SUSY spectrum: lower s than other BSM models, harder to find !
Gluino & squark
production (examples)
Direct squark pair
production (example)
Direct
gaugino/slepton
pair production (example)
SUSY cross section versus sparticle mass
1000 events produced in 2011
100 events produced in 2011
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Unification of coupling constants with supersymmetry
“minimal
supersymmetric
(extension of) SM”
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Extended Higgs sector
In the Standard Model single Higgs doublet, often
written as 𝜑+
𝜑0 or 0
𝑣2
Extended: Many choices but a few constraints,
for instance suppression of FCNC and 𝑀𝑊
𝑀𝑍= cos 𝜃𝑊
• Most successful: 2 Higgs doublet models (2HDMs)
– Supersymmetry uses this
• See-saw models predict Higgs triplet with 𝜑0, 𝜑+ − , 𝜑++ − −
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5 Higgs bosons! h, H, A, H 16
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Examples of searches for extra Higgs bosons
Singly-charged Doubly-charged
Limits around 𝒪(200 GeV ) 600 GeV
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T. Rizzo, hep-ph/0610104
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Dijets
• SM background obviously much larger
– But single source
– And opens the door to strongly interacting objects
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W’ / e
Another very simple selection: lepton + MET
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Extra Dimensions
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ADD extra dimensions
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ADD signatures
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Warped extra dimensions
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Graviton excitations
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Example The infamous bump is an example of a search for RS gravitons:
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Gauge boson excitations
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(super)Strings
Avoid infinities from point-like particles
Different vibration modes = different particles
One fundamental parameter: string size
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Great idea but we have not yet understood how to test it at current ”low” energies Extra dimensions a must Supersymmetry a plus
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Dark Matter Searches
Lots of models, this is not a unique search!
Typically divided in two ”classes”:
WIMP: weakly interacting massive particle ( elementary particle)
MACHO: Massive Compact Halo Objects (planets, dwarf stars, something large)
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33 or even black holes ~10000 x MSun
(MACHOs) (WIMPS)
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Underground searches (experiments: DAMA, Xenon etc WIMP scatters off nuclei Looking for annual modulation / DM ”wind”
Cross section depends on exchange particle: Z exchange ruled out Now looking for H exchange
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Look for annihilation signals! Measure decay products
Experiments: FERMI, PAMELA, AMS etc
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At the LHC
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No Dark Matter interaction with the detector signature is missing energy Use initial state radiation (ISR) to detect it! (e.g jets, , W, Z, H)
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Summary/outlook
• Many problems with current Standard model
• Many new models to take over
Some important models not mentioned, for instance: – GUT models
– Technicolor
– Hidden valleys
• The LHC energy scale is tuned to be sensitive to many of these, complementary to other current searches
• Several potential signatures requires new ”objects”, ie lepton-jets, long-lived heavy particles, ”quirks” etc
• Several good ideas but Nature decides which (if any) are true!
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