Presentation on theme: "Jim Olsen Princeton University Princeton Plasma Physics Laboratory Colloquium September 26, 2012 Is it the Higgs Boson?"— Presentation transcript:
Jim Olsen Princeton University Princeton Plasma Physics Laboratory Colloquium September 26, 2012 Is it the Higgs Boson?
Many Princeton undergraduate students have worked on the CMS experiment over the years Pierre Piroué
Searching for the Higgs boson took: Fifty years, thousands of people, and billions of dollars. Why all the fuss?
CMS and ATLAS submitted their papers to Physics Letters on July 31. As of today, each paper has been cited 128 times: Impact Dark Matter Supersymmetry Muon g-2 Vacuum stability Exotic BSM Physics Neutrino Physics The precise nature of this new particle touches on all of these topics, and more. The LHC (and future iterations) may not be sufficient to answer all questions. …
Outline Invention and early Higgs hunting Discovery of a new boson at the LHC Is it the Higgs boson?
One field to rule them all… Standard Model Matter: quarks and leptons Symmetries: U(1) Y, SU(2) L, SU(3) C Local gauge invariance: gauge bosons (force carriers) Higgs field: spontaneous symmetry breaking and the Higgs boson
Whats the problem? Applying local U(1) invariance,, to the Dirac Lagrangian: Free fermionsGauge interactionFree gauge bosons The term is not gauge invariant need massless gauge bosons U(1) EM : photon is the gauge boson electromagnetic interactions SU(2) L : W +, W -, Z 0 are the gauge bosons weak interactions SU(3) C : gluons (8 of them) are the gauge bosons strong interactions Works for the EM and strong interactions, but W and Z bosons are massive (~100 GeV). Need a mechanism to give mass to gauge bosons.
The Higgs* Mechanism * actually, the Nambu-Goldstone-Anderson-Englert-Brout-Higgs-Guralnik-Hagen-Kibble mechanism vev Expand around minimum: Gauge invariance: Gauge boson mass! Mass of a real scalar particle: Higgs boson!
Properties of the SM Higgs boson Mass: Because is not predicted, the Higgs boson mass is a free parameter Interaction: couples to particles according to their mass
Is this the only possibility? NO! Additional Higgs fields i Composite Higgs: top-quark condensate Technicolor: new gauge interactions Extra dimensions Critical to determine if the new particle is the SM Higgs boson
Bounds on the SM Higgs Mass: 1976 and A. Linde, JETP Lett. 23 (1976) 64
Discovery of the Zeta(8.3) with the Crystal Ball detector + X Was not confirmed in later runs. 1984
The Role of the Top Quark The top quark was discovered at Fermilab in 1995 with a mass near 173 GeV, clearly indicating its strong coupling to the Higgs field This result ushered in the modern era of Higgs searches at LEP and FNAL Cabibbo, Maiani, Parisi, Petronzio, Nucl. Phys. B158 (1979) 295
Searching at LEP Operating at CERN from Line shape of the Z 0 boson (number of light s) Search for the Higgs boson
LEP Legacy Search strategy: Produced via Higgs-strahlung
Operating at FNAL from Discovery of the top quark Search for the Higgs boson
At the dawn of the LHC era
Discovery of a new boson at the LHC
Large Hadron Collider proton-proton collider inside the 27km LEP tunnel: Construction: Operation: superconducting dipole magnets with B > 8 Tesla Worlds largest cryogenic plant 2011: 5fb 7 TeV 2012: >10fb 8 TeV
ATLAS and CMS Humans ~3000 scientist, engineers, and students working on each experiment Giant multipurpose particle detectors designed to find or exclude the Higgs boson and signs of physics beyond the SM
Standard CMS Top Cross Sections
Higgs Boson Production at the LHC Gluon FusionVector-Boson Fusion Higgs-strahlung
What does a Higgs boson look mass Narrow! Observed width dominated by detector mass Higgs becomes a broad resonance dominated by natural width Theory input is critical Det. Res. = 1-2% (, ZZ)
How does it Decay (m H = 125 GeV) ? Branching Fractions (%) Cross sections are large Fermion decays (bb+ ) are accessible Natural width is negligible Only region in m H where
Adding*, ZZ, and WW (4+3+2=5) *ASSUMING it is the SM Higgs! > 5
Do CMS and ATLAS agree on the mass?
As a layman, I think we have it. But as a scientist, I have to say, `What do we have? – R. Heuer AP photo
N. Arkani-Hamed (SavasFest 2012)
Impact of a 125 GeV Higgs boson Giudice and Strumia, Nucl. Phys. B858 (2012) 63
Impact of a 125 GeV Higgs boson Vacuum Stability The vacuum is unstable but sufficiently long-lived, compared to the age of the universe. G. Isidori (Higgs Hunting 2012)
Is it the (SM) Higgs boson?
Where do we stand? Are the relative couplings consistent with prediction? Is it spin 0 or 2? Is it a scalar or a pseudoscalar? Does it couple to fermions? Does it decay to exotic final states? Observation in CMS and ATLAS of a new boson with a mass of roughly 125 GeV decaying to vector bosons It is certainly looking and walking like the SM Higgs boson. Does it also quack like the SM Higgs boson? Some questions:
Does it couple to fermions? In the context of the SM Higgs boson phenomenology, we already have strong indirect evidence for a coupling to the top quark via the loop in the dominant production mechanism.
Final results from the Tevatron 2.5 (Global) 2.9 (bb) Is the Tevatron seeing H bb?
Search for and bb at CMS What to watch for in November: Is the SM Higgs boson excluded in ? Is there growing or shrinking evidence in bb? CMS has better sensitivity for H bb than any other experiment
Pattern of couplings Overall, consistent with the SM expectation, but far from excluding other possibilities (and hint of something in )
Is g the same for W and Z?
Does it have the right spin/parity? So far, not enough data to determine spin or parity Difficult to separate 0 and 2, easier to check + vs. - With the data expected by end of the year, maybe
Does it decay to exotic final states? Branching Fractions (%) Until the bb channel is seen, constraints on the full width will be weak.
Is it the SM Higgs boson? Are the relative couplings consistent with prediction? Is it a spin 0 scalar? Does it couple to fermions? Does it decay to exotic final states? Maybe! Would I buy SM Higgs boson stock? Probably!