Jeremy Love & John Butler Boston University...

Technicolor at the LHC

Jeremy Love & John ButlerBoston University

8/15/07

8/15/07 Jeremy Love NEPPSR 2

Standard Model Strengths & weakness What if there is no Higgs?

• Electroweak Symmetry Breaking via QCD

Technicolor Description History and Evolution Straw Man Model

• In Pythia

Experimental Signature ωTC > µµ

Outline


The Standard Model Successful

Predicted the existence of W, Z, and Top Quark before discovery

So far valid to all tests over ~12 orders of magnitude in energy

But unsatisfying What sets the values of the parameters in

the Standard Model? Why three generations of particles in the

Standard Model? What gives rise to the strange structure of

the Standard Model? Does the Higgs exist with the predicted

properties? etc...


The SM Higgs Spontaneously breaks electroweak symmetry giving mass to

fermions and vector bosons The Higgs acquires a Vacuum Expectation Value (VEV) which generates

mass terms for the fields it couples to. Scalar

The only fundamental scalar Not yet observed

• What is the mass?


Imagine A Cold Higgsless World If no Higgs exists QCD would break electroweak symmetry Quarks condense as scalars, pions, getting an expectation value

Coupling of quark condensate gives mass to W and Z breaking electroweak symmetry

Get θWeak, the ratio of W to Z masses, correct MW=g*fπ/2~30MeV fπ= 93MeV

What if we scale up QCD to get W Mass Correct?


Technicolor(Higgsless since 1976!)

New strongly interacting force behaving the same as QCD at a higher energy Add new Techniquarks, and Technigluons

Proposed by S. Weinberg & L. Susskind in 1976 To get θWeak correct And get MW Correct

• FTC=246GeV

Unfortunately, this QCDscaled Technicolor violates precision electroweak measurements

Does not give masses to fermions


Extended Technicolor Technicolor must also give masses to the Standard Model

fermions In ETC a field is added coupling the SM and TC fermions Gives Masses to Quarks and Leptons

Proposed by S. Dimopoulos, L. Susskind, E. Eichten, & K. Lane in 1979

Flavor Changing Neutral Currents work to keep the mass of the heavy quarks light


Walking Technicolor Walking Technicolor imposes restrictions on the coupling constants

Allow heavy quark masses to be larger, without increasing FCNC's WTC still cannot account for the Top Mass Proposed by B. Holdom 1981 Must have a large number of techniquark doublets to have the

coupling constants be low


Topcolor Assisted Technicolor

Another force is added Topcolor This interaction couples to Top and gives the larger mass Many technifermions are needed to break the Topcolor down to SM color

Combined with the previously mentioned extensions to the original Technicolor Model this requires a large number of new technifermions.

Proposed by C.T. Hill in 1995


LowScale Technicolor This model is known as the Technicolor Straw Man Model

• Straw Man (n.) An argument or opponent set up as to be easily refuted or defeated.

An effective theory meant to capture the phenomenology of TC for collider experiments

With a large number of TechniDoublets the condensates form TechniMesons with typical masses of a few hundred GeV The lowest of these mass states are the πTC ρTC ωTC

The ρTC & ωTC are approximately degenerate due to techniisospin

• Predominately decay into WπTC, ZπTC, but occasionally ff.

Proposed by E. Eichten, K. Lane, J. Wormersley 1997 Implemented in Pythia S. Mrenna & K. Lane


Early LHC Data Ideally one would want a signal with:

Interesting• Good Discovery Potential/Exclusion Reach

Large cross section• Should couple to the strong force

Clean decay channel Low background

• Something NonQCD

Technicolor!• ρTC ωTC>µµ


How Do We Study ρTC, ωTC>µµ? Use Pythia to generate signal

events at different invariant mass points for rho, omega 600GeV is shown

Simulate Background DrellYan from 3501300GeV is

shown Simulate detector response

and perform reconstruction Calculate invariant mass


Atlas Discovery Reach


Atlas Sensitivity


Conclusions Technicolor provides an interesting and clean signal to look for in

early LHC data The Atlas experiment should be able to discover Technicolor or

exclude it at 95% confidence over a greater mass range than previous experiments with early

Jeremy Love & John Butler Boston University...

Documents

Transcript of Jeremy Love & John Butler Boston University...