The Higgs Boson as a Probe of New Physics Ian Lewis University of - - PowerPoint PPT Presentation

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The Higgs Boson as a Probe of New Physics Ian Lewis University of - - PowerPoint PPT Presentation

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The Higgs Boson as a Probe of New Physics Ian Lewis University of Kansas March 17, 2016 Ian Lewis (University of Kansas) 1 July 4, 2012 ATLAS and CMS announce discovery of a new particle. Consistent with long sought-after Higgs

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March 17, 2016 Ian Lewis (University of Kansas) 1

The Higgs Boson as a Probe of New Physics

Ian Lewis University of Kansas

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March 17, 2016 Ian Lewis (University of Kansas) 2

July 4, 2012

  • ATLAS and CMS announce discovery of a new

particle.

– Consistent with long sought-after Higgs boson.

"We have reached a milestone in our understanding of Nature".

  • -- CERN Director General Rolf Heuer
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March 17, 2016 Ian Lewis (University of Kansas) 3

Long Search

  • 50+ years of work by theorists.
  • 25+ years of work by thousands of experimentalists.
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March 17, 2016 Ian Lewis (University of Kansas) 4

  • as
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March 17, 2016 Ian Lewis (University of Kansas) 5

Standard Model Complete

Quarks: charge +2/3 (up type) and -1/3 (down type) Leptons: charge -1 and 0

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March 17, 2016 Ian Lewis (University of Kansas) 6

Role of the Higgs

  • Higgs is the source
  • f fundamental

mass in the Standard Model.

– Important for

understanding fundamental laws of nature.

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March 17, 2016 Ian Lewis (University of Kansas) 7

Masses

  • Many massive

particles in Standard Model

  • Massive Gauge

bosons.

– W/Z.

  • Photon and gluon

are massless.

  • What is the matter

with mass?

  • Natural units
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March 17, 2016 Ian Lewis (University of Kansas) 8

What's the matter with mass?

  • Maxwell's equations:
  • Invariant under the transformation:
  • Add mass, break gauge invariance:
  • Why photon is massless.
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March 17, 2016 Ian Lewis (University of Kansas) 9

The Need to Explain Masses

  • Have masses for gauge bosons.
  • What is source of gauge invariance breaking?
  • Explicit breaking:

– Equations of theory explicitly break an invariance.

  • Spontaneous breaking:

– Lowest lying energy state (vacuum) of theory

breaks invariance.

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March 17, 2016 Ian Lewis (University of Kansas) 10

Ferromagnetism

  • Before magnetization:
  • After magnetization:
  • Spontaneous

symmetry breaking.

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March 17, 2016 Ian Lewis (University of Kansas) 11

Higgs Mechanism

  • Introduce a Higgs.
  • Write fundamental equations (with Higgs) invariant

under all transformations.

  • Vacuum breaks gauge invariance.

– Higgs obtains a nonzero value throughout space.

  • Vacuum expectation value,

– Particles interact with Higgs vacuum, gaining mass.

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March 17, 2016 Ian Lewis (University of Kansas) 12

Standard Model Higgs Boson

  • Introduce complex Higgs with four degrees of

freedom.

  • Three degrees of freedom absorbed into weak

force carriers ( ) giving them masses.

  • One degree of freedom left, the physical Higgs

boson, h.

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March 17, 2016 Ian Lewis (University of Kansas) 13

Large Hadron Collider (LHC) Overview

  • 17 mile ring outside

Geneva, Switzerland.

  • Colliding protons at a

center of mass energy

  • f 7-14 TeV.

– ~10 mph less than

speed of light.

– ~1 GJ of energy stored

at 14 TeV (Aircraft carrier traveling ~20 mph)

  • Purpose is to discover

new physics at the TeV scale.

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Hadron Collider

  • Hadrons (like a proton) are made of quarks and gluons.
  • LHC collides two protons at very high energy (7-14 TeV).
  • Constituents of proton annihilate at a typical energy of

~ 1 TeV:

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March 17, 2016 Ian Lewis (University of Kansas) 15

LHC

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March 17, 2016 Ian Lewis (University of Kansas) 16

Compact Muon Solenoid (CMS)

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March 17, 2016 Ian Lewis (University of Kansas) 17

Detecting Final State

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March 17, 2016 Ian Lewis (University of Kansas) 18

Amount of Data Produced

  • Over 600 million collisions per second per

experiment.

– Amount of data produced is 1 petabyte per second – Could fill ~200,0000 DVDs per second – Comparable to total amount of digital data produced

worldwide.

  • Experiments store and analyze less.

– Around 30 petabytes per year. – ~6,000,000 DVDs per year stored to be analyzed

  • Very successful!
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March 17, 2016 Ian Lewis (University of Kansas) 19

Higgs Discovery!

  • July 4, 2012 (mass of Tin atom)
  • Created around 650,000 Higgs through 2015.
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March 17, 2016 Ian Lewis (University of Kansas) 20

Higgs production rate is small

Higgs rate is small, need to dig signal out of all the other Standard Model processes.

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March 17, 2016 Ian Lewis (University of Kansas) 21

Higgs Production

  • Masses in Standard Model come from Higgs

mechanism.

– Completely predictive. – Vacuum expectation value

  • Protons made mostly of light quarks and

gluons.

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March 17, 2016 Ian Lewis (University of Kansas) 22

Quantum Effects to the Rescue

  • Top quark can mediate coupling to gluon.
  • Dominant production mode at the LHC.
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March 17, 2016 Ian Lewis (University of Kansas) 23

Higgs Production Rates

Other subdominant processes depend on W/Z and top quark couplings. What about decay?

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March 17, 2016 Ian Lewis (University of Kansas) 24

  • WW and ZZ probes gauge boson mass generating mechanism.
  • Decays to di-photon at 0.2% of the time
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March 17, 2016 Ian Lewis (University of Kansas) 25

Di-Photon

  • Higgs discovered using quantum production

and decay modes!

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March 17, 2016 Ian Lewis (University of Kansas) 26

Masses and Higgs Couplings

  • Remarkably Standard

Model like.

  • Have measured Higgs

rates to 20-40%.

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March 17, 2016 Ian Lewis (University of Kansas) 27

  • 2023 : 10 times current data
  • 2030s: 100 times current data

13 TeV LHC started in 2015

  • M. Lamont, Moriond 2015
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March 17, 2016 Ian Lewis (University of Kansas) 28

Future Higgs Boson Measurements

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March 17, 2016 Ian Lewis (University of Kansas) 29

What do Higgs Measurements Tell Us?

  • Consider very massive new physics.

– Standard Model leading order in a power expansion of

energies.

– Precision measurements bound next order in

expansion:

  • Then measuring rates to ~5% give new physics

scale at the TeV scale.

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March 17, 2016 Ian Lewis (University of Kansas) 30

Higgs is Central

  • Production and decay modes quantum effects.

– Sensitive to new physics

  • Expect new physics to be related to Higgs boson

properties.

– Source of fundamental mass just starting to be

probed.

– Standard Model is simplest realization of mechanism

  • Explains mass, but where does the Higgs

vacuum expectation value come from?

– Consider a simple harmonic oscillator.

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March 17, 2016 Ian Lewis (University of Kansas) 31

Harmonic Oscillator Example

  • Stored Potential energy:

– Invariant under

  • Force equation:
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March 17, 2016 Ian Lewis (University of Kansas) 32

Deformed Harmonic Oscillator

  • Stored Potential energy:

– Invariant under

  • Shift to a minimum:

– Invariance not manifest at

minimum:

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March 17, 2016 Ian Lewis (University of Kansas) 33

Higgs Potential

  • Higgs potential:
  • Have minimum:
  • Expand about vacuum:
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March 17, 2016 Ian Lewis (University of Kansas) 34

Higgs Self-Interactions

  • Higgs Potential:
  • Potential has two parameters, everything determined:
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March 17, 2016 Ian Lewis (University of Kansas) 35

  • Need to measure potential to test Standard Model
  • Double Higgs production sensitive to trilinear coupling:
  • Probing Higgs potential, source of mass.
  • All couplings known in Standard Model.

Measuring Higgs Potential

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March 17, 2016 Ian Lewis (University of Kansas) 36

Future Measurements of Potential

  • Measurement at LHC with 3000 ab-1 (2030s)

– ATLAS: observe at 1.3 σ significance

  • Bound

– CMS: Observe at 1.9 σ significance

  • Small rate, may be sensitive to new physics.
  • Particularly new physics that alters Higgs

potential.

ATL-PHYS-PUB-2014-019 CMS PAS FTR-15-002

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March 17, 2016 Ian Lewis (University of Kansas) 37

Extended Scalar Sector

  • Standard Model Higgs source of all fundamental

mass.

– Can have multiple sources of gauge invariance breaking. – Two Higgses are possible, sometimes required.

  • New source of new gauge invariance breaking

contribute to W/Z masses.

– Alter Higgs couplings to W/Z

  • What about scalar bosons that don't contribute to

gauge invariance breaking?

– Can even probe new scalars unrelated to gauge

invariance breaking.

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March 17, 2016 Ian Lewis (University of Kansas) 38

New Scalar

  • Consider a new scalar with no Standard Model

charges

  • After gauge invariance breaking, the Higgs

boson has no charge.

  • The two can mix quantum mechanically.
  • Changes Higgs couplings
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March 17, 2016 Ian Lewis (University of Kansas) 39

Higgs Couplings

  • Write equations in gauge invariant way.
  • Rotate into mass eigenstate basis
  • Original particles are superpositions of mass

eigenstates.

  • Higgs precision measurements: ATLAS, JHEP11(2015)206
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March 17, 2016 Ian Lewis (University of Kansas) 40

New Scalar Potential

  • Any new scalar will alter potential

– S has no couplings to anything else in Standard Model

  • New potential

– Interaction terms: – Expansion about vacuum – New Higgs Interactions.

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March 17, 2016 Ian Lewis (University of Kansas) 41

Higgs and Scalar Interactions

  • Comes from:
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March 17, 2016 Ian Lewis (University of Kansas) 42

Double Higgs Resonance

  • New Double Higgs

production process.

  • Resonant production and

decay of scalar S.

– Enhance rate.

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March 17, 2016 Ian Lewis (University of Kansas) 43

Large Enhancements

  • Ratio of double

Higgs rate with S included to double Higgs rate in Standard Model

  • Dashed lines

excluded due to theoretical constraints.

Chen, Dawson, IL PRD91 (2015) 074012

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March 17, 2016 Ian Lewis (University of Kansas) 44

Altering the Higgs potential

  • Implications of new scalars:

– Many more minima in the potential.

  • One Higgs: Minimize with respect to Higgs.
  • Multiple scalars: Minimize with respect to all scalars
  • Global minimum must have correct gauge invariance

breaking.

– Scalar S cannot give masses to W and Z. – Higgs vacuum expectation value has to be the same as in

Standard Model.

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March 17, 2016 Ian Lewis (University of Kansas) 45

Double Higgs Resonance

  • Require minimum with

Standard Model Higgs vacuum expectation value is global minimum.

– Places constraints on

parameters in the scalar potential,

– Affect S-h-h coupling

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March 17, 2016 Ian Lewis (University of Kansas) 46

Large Enhancements

Chen, Dawson, IL PRD91 (2015) 074012

  • Ratio of double

Higgs rate with S included to double Higgs rate in Standard Model

  • Dashed lines

have incorrect vacuum expectation value for Higgs.

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March 17, 2016 Ian Lewis (University of Kansas) 47

Bounds With Current Data

  • Ratio of double

Higgs rate with S to Standard Model prediction.

– Area within

green and magenta curves are theoretical bounds.

  • Current bounds

not enough

Chen, Dawson, IL PRD91 (2015) 074012

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March 17, 2016 Ian Lewis (University of Kansas) 48

Extrapolated bounds

  • Ratio of double

Higgs rate with S to Standard Model prediction.

– Area within

green and magenta curves are theoretical bounds.

  • Need 2023 data
  • Scenario where

scalar only has couplings through Higgs.

Chen, Dawson, IL PRD91 (2015) 074012

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March 17, 2016 Ian Lewis (University of Kansas) 49

Higher Order Corrections

  • Everything previous was at LO in coupling constant perturbation theory.

– SM double Higgs production very large corrections at higher order in

perturbation theory.

– Similar size of corrections for model with new scalar.

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March 17, 2016 Ian Lewis (University of Kansas) 50

Higher Order Corrections

  • Ratio of rates largely do not depend on if those

rates are calculated at higher orders.

Dawson, IL PRD92 (2015) 094023

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March 17, 2016 Ian Lewis (University of Kansas) 51

New Physics

  • We know there has to be new physics.
  • Energy budget of the universe:
  • Dark matter may be a secluded sector
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March 17, 2016 Ian Lewis (University of Kansas) 52

Higgs and Dark Matter Sector

  • Particles that do not couple with Standard

Model are strongly motivated.

  • Higgs is possible probe into these scenarios.

– If dark matter sector have Scalars, can write

couplings to Higgs.

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March 17, 2016 Ian Lewis (University of Kansas) 53

Dark Forces

  • Dark matter sector may not be simple.

– Possible for dark matter to have dark forces.

  • Z, photon, and dark force mediator may have

same quantum number:

– is the dark force messenger particle. – Obtains couplings to Standard Model

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March 17, 2016 Ian Lewis (University of Kansas) 54

Connection to Higgs

  • New physics can also give rise to Higgs

coupling:

  • Exotic Higgs decay to four leptons:
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March 17, 2016 Ian Lewis (University of Kansas) 55

LHC Search

  • With 300 fb
  • 1:

– Exclusion: – Discovery:

  • Stronger than current bounds.
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March 17, 2016 Ian Lewis (University of Kansas) 56

Search for

  • Complementary to low energy searches look up to

masses ~1 GeV.

  • Observable within next decade.

Davoudiasl, Lee, IL, Marciano Phys. Rev. D88 (2013) 015022

Mass of Dark Z 2 σ (Exclusion) 3 σ (Observation) 5 σ (Discovery) 5 GeV 78 fb

  • 1

180 fb

  • 1

490 fb

  • 1

10 GeV 100 fb

  • 1

230 fb

  • 1

640 fb

  • 1
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March 17, 2016 Ian Lewis (University of Kansas) 57

Conclusions

  • LHC had a very successful first run.

– Culminated in discovery of a Higgs boson

  • Higgs boson discovery helps us to begin to understand the origin of

fundamental mass in the Standard Model.

  • LHC has turned back on at higher energies.

– Still expect new physics, and have some hints. – Strong motivation this new physics is related to Higgs physics.

  • Higgs measurements sensitive to new physics.

– Test the origin of the fundamental masses of particles. – Help us search for new sources or changes in the breaking of gauge

invariance.

– Search for sector decoupled from rest of the Standard Model. – Can use as a complementary search for a light dark sector. – Interesting new physics scenarios probed in next run.

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March 17, 2016 Ian Lewis (University of Kansas) 58

Thank You