Nailing Electroweak Physics (aka Higgs Hunting)

with the Next Linear Collider

Bob WilsonHigh Energy Physics Group

CSU Physics Research EveningNovember 7, 2002

Outline

• Complementary to CSU HEP BaBar research (Toki)

• Electroweak unification and the origin of mass

• What is the Next Linear Collider?

• Other physics at the NLC

Electromagnetism and Radioactivity

• Maxwell unified Electricity and Magnetism with his famous equations (1873)

• Matter spontaneously emits penetrating radiation– Becquerel uranium

emissions in 1896

Could this new interaction (the weak force) be related to E&M?

– The Curies find radium emissions by 1898

Fast Forward to Electroweak Unification

• Weinberg (1967) realized that the vector field responsible for the EM force – (the photon)

and the vector fields responsible for the Weak force – (then undiscovered W+ and W-)

could be unified if another vector field, mediated by a heavy neutral boson (Z), were to exist

• This same notion occurred to Salam

tan W = g’/g

sin2W=g’2/(g’2+g2)

e = g sin W = g’ cos

W

Electroweak Symmetry Breaking

• The weak nuclear force and the electromagnetic force are unified into a single description by the symmetry group SU(2) x U(1)Y

• But this underlying symmetry is broken to produce the observed particles (,Z0). How? Why?

• The answer appears to lead to a deep understanding of fundamental physics– the origin of mass– supersymmetry and possibly the origin of dark matter– additional unification (strong force, gravity) and possibly hidden

space-time dimensions

A primary goal of the next generation of high energy accelerators will be to elucidate the origin of Electroweak Symmetry Breaking

Electroweak Measurements

Confirmation from many independent measurements related to parameters of the theory.

But…

The Higgs Boson

• Why is the underlying SU(2)xU(1) symmetry broken?

• Theoretical conjecture is the Higgs Mechanism

A non-zero vacuum expectation value of a scalar field, gives mass to W and Z and leaves photon massless

• There is a particle (or particles) associated with this field – the Higgs boson

(SM) Mhiggs < 195 GeV at 95% CL. LEP2 limit Mhiggs > 114.1 GeV. Tevatron can discover up to 180 GeV

W mass ( 33 MeV) and top mass ( 5 GeV) agree with precision measures and indicate low SM Higgs mass

LEP Higgs search – Maximum Likelihood for Higgs signal at mH = 115.6 GeV with overall significance (4 experiments) ~ 2

Experimental indications for a Light Standard Model-like Higgs

Linear Colliders

• Acceleration of electrons in a circular accelerator is plagued by Nature’s resistance to acceleration– Synchrotron radiation– E = 4/3 (e234 / R) per turn (recall = E/m, so E ~ E4/m4)– eg. LEP2 E = 4 GeV Power ~ 20 MW

electrons positrons

• For this reason, at very high energy it is preferable to accelerate electrons in a linear accelerator, rather than a circular accelerator

The First Linear Collider

• This concept was demonstrated at SLAC in a linear electron-positron collider prototype operating at ~91 GeV called the SLC

• Operated 1989-98– precision Z0 measurements– established LC concepts

• CSU base for many years– PhD students usually spend

an extended period there

electrons positrons

The Next Linear Collider?

• A plan for a high-energy, high-luminosity, electron-positron collider (international project)– Ecm = 500 - 1000 GeV– Length ~25 km ~15 miles

• Beam size at collision– 245 nanometers x 3

nanometers(really!)

• Construction could begin around 2005-6 and operation around 2011-12

not to scale

Linear Collider Detectors

•Many similarities to detectors the CSU group has helped to design and build in the past… but many interesting new challenges

•Particularly interested in Particle Identification methods -How do we distinguish between e, , , K, p?

•Computer simulation codes

•Helping to coordinate an international collaboration to do R&D

•New funding from the US Dept. of Energy

Other physics to explore

• Supersymmetry– all particles matched by super-partners– inspired by string theory (or vice versa)– could play role in dark matter problem– many new particles (details only at NLC)

• Extra Dimensions– string theory prediction

– solves hierarchy (Mplanck > MEW) problem if extra dimensions are large (or why gravity is so weak)

– large extra dimensions could be observable at NLC (see Physics Today, February 2002)

The Linear Collider will be a powerful tool for studying the Higgs Mechanism and Electroweak Symmetry Breaking.

This physics follows a century of unraveling the theory of the electroweak interaction.

We can expect these studies to further our knowledge of fundamental physics in unanticipated ways.

You could be in on the ground floor!

Conclusion