Download Higgs Colliquium, U of South Carolina - Physics

The Lonesome Higgs
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Richard Kass
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The Ohio State University
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Outline
ThirdIntroduction
level
to Higgs
LHC
and ATLAS
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Finding the first Higgs particle
Fifth level
Finding the next Higgs particle
Summary
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What is a “Higgs”
A person
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• Second levelPeter Higgs
Professor Emeritus, University of Edinburgh
• Thesis:
Third“Some
level
PhD
problems in the theory of molecular vibrations”
Awards: Nobel Prize, Wolf Prize, Sakurai Prize, Dirac Medal,+++
• Fourth level
A mechanism
A way
to eliminate
• Fifth
levelzero mass scalar particles and give mass to vector
bosons in a theory with a spontaneously broken continuous symmetry.
A field
Its vacuum expectation value is responsible for giving mass to vector
bosons, quarks, & charged leptons.
A particle
(aka “God particle”)
A particle with mass ~125X that of a proton.
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The Standard Model’s Building Blocks
1964
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A brief higgstory of HEP theory
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1950’s-early 1960’s:
Search for a theory that has both massive & massless particles
field theories (other than QED) give unphysical results
field theory Vs S-matrix theory (looks like S-matrix will win….)
Nambu-Goldstone theorem predicts massless scalar particles
• Second
level evidence for massless scalars
But no experimental
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1964:
• Third level
3 papers published in PRL on avoiding massless scalars
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leveland the
“Broken
Symmetries
“Broken Symmetry and the Mass of Gauge Vector Mesons, “ Englert, F. & Brout, R.
PRL 13 (1964) 321-323
PRL 13 (1964) 508-509
Masses of Gauge Bosons ,” Higgs, Peter W.
“Global Conservation Laws and Massless Particles,” G.S. Guralnik, C.R. Hagen,
T.W.B. Kibble, PRL 13 (1964) 585-587
And let’s not forget:
“Plasmons, Gauge Invariance, and Mass,” Anderson, Philip W. Phys. Rev. 130 (1963) 439-442
“Quasi-Particles and Gauge Invariance in the Theory of Superconductivity,” Yoichiro Nambu,
Phys. Rev. 117, (1960) 648
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What did these papers do?
Higgs takes a theory from Goldstone & shows that with a suitable
gauge transformation & a spontaneously broken symmetry the particle
spectrum contains only a massive scalar & a massive vector.
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V(φ)
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-μ/λ
+μ/λ
φ
V(φ)=-½μ2φ2+¼λ2φ4
V’(φ)=0 for φ=0, ± μ/λ
V’’(μ/λ)>0
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Higgs-steria??
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Whatto
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reaction
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All the papers are ignored…..
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Yearly citations for Higgs, PRL 13 (1964) 508
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1964-70: 14 citations!
To date: > 3000 citations.
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Other papers have same
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citation history!
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(including self-cites)
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Higgs-steria??
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What
happened
to make
people take
NOT: “A Model of Leptons,” Weinberg, PRL 19 (1967) 1264 (>9000 cites)
AND
NOT: “Regularization and Renormalization of Gauge Fields,”
Gerard 't Hooft, M.J.G. Veltman Nucl.Phys. B44 (1972) 189-213
• Second
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(> 3300
cites)
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• Third
level (Z) interactions were observed!
Neutral
Current
A new interaction where a neutral spin 1 particle couples to a neutrino.
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No muon produced
by interacting neutrino
V
F J Hasert et al. 1973a Phys. Lett. 46 121.
F J Hasert et al. 1973b Phys. Lett. 46 138.
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Mass Higgs-steria
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>1000 citations
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Nuclear Physics B106 (1976) 292
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Unitarity puts an upper bound on the mass
of the Higgs ≈ 1 TeV
1990
This book has
its own
facebook page*!
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*https://www.facebook.com/pages/The-Higgs-Hunters-Guide/412484908831857
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Standard Model Higgs Predictions
The mass of the Higgs is not predicted in the standard Model.
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it is a free parameter
But how often it is produced in pp collisions Vs Higgs mass is!
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Gluon Fusion Vector-Boson
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Fusion
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Higgs-strahlung
Cross section for pp-> Higgs Vs MHiggs
LHC at 8 TeV CM energy produces ~1000 Higgs/hr
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Standard Model Higgs Predictions
The mass of the Higgs is not predicted in the standard Model.
But how often it decays into quarks, leptons, and vector bosons
as a function of Higgs mass is!
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Higgs Branching fraction vs MHiggs
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MHiggs= 125 GeV
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hardest
detection
easiest
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The Large Hadron Collider
The LHC collides protons
Center of Mass E=14 TeV ~7X Fermilab
Very high luminosity ~100X Fermilab
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LHC is located at CERN
CERN is in France & Switzerland
CERN is located near Geneva
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1232 superconducting dipole magnets B=~8T
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ATLAS
site
9km
main lab
5/29/2012
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SPS
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The ATLAS Experiment
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• Second level
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outside
good momentum, energy, & vertex
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detector
resolution
Identify muons, electrons, photons
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Reconstruct b-jets, taus
flexible triggers
Hermetic detector: can look for
missing energy signatures
inside
detector
Optimized to look for Higgs particles & BSM physics processes12
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pp-> Z->μ+μ-+ other stuff
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Many collisions
within 50 ns.
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Discovering the Standard Model at the LHC
Before you can discover new physics must discover the old physics.
Standard Model has many predictions for cross sections.
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Excellent test of how well the ATLAS detector works.
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cross section
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Measurements & predictions agree over ~ 12 orders of magnitude
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Higgs->γγ Candidate
To “find” a particle calculate the invariant mass of its decay products
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2 energetic
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gammas
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Invariant Mass of two particles:
m2=(E1+E2)2-(P1+P2)2
For photons:
m2=Eγ1Eγ2(1-cosθ)
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Higgs Particle Discovery Modes
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H->ZZ*->4 leptons
H->γγ
(e+e-e+e- /μ+μ-μ+μ- /e+e-μ+μ-)
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Also observed: H->WW*, H->bb, and H->τ+τHiggs decay into dibosons, quarks, and leptons
All decay channels consistent with mass=125 GeV
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The standard model is “complete”
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Beyond the standard model
Many important issues remain!
The Standard model is incomplete:
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Cannot predict the mass of the Higgs or how many Higgs particles.
The minimum is one, but there can be more!
Does not contain dark matter or dark energy.
Magnitude of CP violation for baryon asymmetry (CKM CPV too small)
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No
gravity
Neutrino mass ?
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Why
generations
• three
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levelof quarks and leptons & >19 parameters?
The “Hierarchy” problem:
Why
is the Higgs
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levelso light compared to the Planck scale: 102 Vs 1019 GeV
Technical problems:
Quantum corrections to the Higgs mass are larger than 125 GeV.
Corrections must cancel at an amazing level: implies fine tuning to 1 part in ~1030
Muv~Mplanck~1019 GeV
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Going Beyond the Standard Model
Supersymmetry is a popular BSM with an extended Higgs sector
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SUSY is a theory with symmetry between fermions & bosons.
For every SM particle there is a SUSY particle with spin that differs by ½.
Eliminates hierarchy problem
SUSY compatible with string theory & SM
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Natural extension to grand unified theories
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Lightest SUSY particle may be stable and might be dark matter
SUSY may contain a new conserved quantum number, R
• ThirdB=baryon
level#, L=lepton #, S=spin, R=1 for SM, -1 for SUSY particles
R=(-1)
If R is conserved, SUSY particles must be produced in pairs.
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BUT SUSY has ~ 100 free parameters!
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Many possible models to consider, masses of SUSY particles unspecified.
3(B-L)+2S
Minimal Supersymmetric Model (MSSM)
5 Higgs particles:
3 neutral scalars (2 CP even, 1 CP odd), 2 charged scalars, H±
Next-to-Minimal Supersymmetric Model (NMSSM)
7 Higgs particles
5 neutral scalars (3 CP even, 2 CP odd), 2 charged scalars, H±
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Many BSMs with Higgs Particles
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Minimal Composite Higgs Model (MCHM)
(1 Higgs)
Higgs boson = composite (pseudo-Nambu-Goldstone boson)
strong interaction to the rescue => no hierarchy problem
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Single additional electroweak singlet
simplest
extension,
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level two CP-even Higgs bosons
Two Higgs Doublet Models (2HDM)
(5 Higgs)
• Third level
additional
doublet h0, H0 (CP-even), A0 (CP-odd), H±
=> fixeslevel
hierarchy problem
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4 types based on coupling structure (Type II = MSSM)
• Fifth level SUSY (NMSSM)
Next-to-Minimal
(7 Higgs)
MSSM + complex singlet(S): H1, H2, H3, A1, A2, H±
=>generates MSSM μ-term through S spontaneous symmetry breaking
Higgs Triplet Model
h0, H0 (CP-even), A0 (CP-odd), H±, H±±
=> generates neutrino masses/mixings
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Which Higgs have we found?
Is the 125 GeV Higgs consistent with the standard model?
Detailed studies show quantum numbers are consistent with JPC=0++
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scalar Vs pseudoscalar
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Can rule out spin 1, 2,
mixtures, etc.
• Second level
• Third level
Couplings & branching fractions to fermions & vector bosons are SM.
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Higgs Coupling Vs mass
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All production & decay measurements are consistent with SM!
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Direct Higgs Searches
Search
Higgs/scalar
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Generic searches looking for H->γγ, ZZ(*), WW(*), bb, tt, etc
for more massive versions of H(125)
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Charged Scalars H ->ZW , cs, τν, etc
by SUSY
& other BSMs
•predicted
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Scalars that decay into other scalars
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can
happen if
m >2*(125 GeV)
Scalars
that level
violate lepton number (e.g. H-> τμ)
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possible in SUSY and Randall Sundrum models
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Scalars
that
decay into undetectable particles
Since Higgs couples to mass decays into neutrinos highly suppressed
Unaccounted for “missing” energy in the detector
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Higgs Decay to γγ/ZZ*/WW*
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H->γγ
No evidence up to ~600 GeV
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• Second level
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(*) → 4leptons
H→
ZZ
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No evidence up to ~900 GeV
ATLAS-CONF-2013-013
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ATLAS: arXiv:1407.6583 [hep-ex]
CMS-PAG-HIG-14-006
CMS: Phys. Rev D 89. 092007
H->WW(*)
No evidence up to ~1000 GeV
ATLAS-CONF-2013-067 CMS-HIG-13-023
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Search for charged Higgs, H±
Search for Charged H± →W± Z
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No signal, set model dependent limits
Many other searches for more Higgs particles: h0, H± & H±±
No signals, set limits that depend on mass and x-section
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What is next?
The LHC is preparing to operate at 13/14 TeV CM energy
Higher CM energy = 1.75X more H(125)’s
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Higgs production modes
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Higgs cross section
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LHC luminosity to increase 2X + more days taking data
>10X increase in H(125) sample in ~ 3 years
LHC has a plan to take data that goes until 2035!
Will increase sensitivity to finding additional Higgses by >100X
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Summary
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We have found the scalar particle predicted by Higgs.
Its mass is 125 GeV
Englert & Higgs
-->
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All particles of the standard model are now accounted for.
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We need “new” physics to explain why the SM works so well.
We•need
“new”
physics to explain the physics not in the SM.
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The most popular NP models contain additional Higgs Bosons.
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Despite intense efforts by ATLAS and CMS there is no evidence for any
additional
scalar
particles with m> 100 GeV and < ~ 1 TeV
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More
results
https://twiki.cern.ch/twiki/bin/view/CMSPublic/PhysicsResultsHIG
https://twiki.cern.ch/twiki/bin/view/AtlasPublic/HiggsPublicResults
The next chapter in the hunt for more Higgs bosons begins in a few months
when ATLAS & CMS start collecting 13 TeV CM energy data.
How much longer will the Higgs be lonesome?
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Extra Slides
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