SLAC Particle Theory Overview

circa 2007

Group Members Faculty & Staff: Stan Brodsky Michael

Peskin

Lance Dixon Tom Rizzo

JoAnne Hewett Eva Silverstein

Stefan Höche Jay Wacker

Shamit Kachru Marvin Weinstein

Professor Professor

Professor

Professor Professor – ½ campus

Senior Staff

Associate Staff

Professor – ½ campus

Assistant Professor

Permanent Staff

Particle Theory Program: at a Glance

QCD

Heavy Flavors

BSM Pheno

Model Building

Astro Interface

Formal Theory

Experimental Programs

QCD Highlights• Leading effort in development of AdS/QCD framework• 1st computation of W/Z+3/4 jet production @ NLO• Prediction of left-handed W polarization at large pT

– now observed by ATLAS/CMS• Development of BlackHat: general code for efficient NLO

calculation of multi-jet processes – providing theoretical uncertainties on ATLAS/CMS data-driven

estimations of SUSY MET+jets backgrounds• Sherpa event generator development and maintenance

– only multi-purpose event generator maintained by US National Lab HEP theory staff member

Direct connections of QCD research:SLAC program: ATLAS, BaBar, Super-BBroader program: CDF, D0, CMS, GSI, H1, Jlab, RHIC

Brodsky, Dixon, Höche, Peskin

Heavy Flavor Highlights

• Development of algorithms for tagging top-quarks via boosted jets

• Define and study top-quark forward-central charge asymmetry at LHC

• Development of axigluon models that account for At

FB observed @ Tevatron

• Study of relating Bs →μμ to Bs Mixing in models with new physics

Direct connections of Heavy Flavor research:SLAC program: ATLAS, BaBar, LC, SuperBBroader program: CDF, D0, CMS, LHCb

Brodsky, Hewett, Rizzo, Wacker

BSM Phenomenology Highlights

• Generation of large pMSSM data sample – used by ATLAS/CMS

• Development of Simplified Model approach to new physics searches - adopted by ATLAS/CMS

• Leading effort on SUSY MET-based collider search techniques – collaboration with ATLAS/CMS

• Novel Higgs signatures in 4GMSSM – new searches @CMS

• Development of techniques to distinguish DM models at colliders

Direct connections of BSM Pheno research:SLAC program: ATLAS, LCBroader program: CDF, D0, CMS

Hewett, Peskin, Rizzo, Wacker

BSM Model Building Highlights

• 1st construction of Supersymmetric Atoms • Development of dynamical SUSY Breaking

models• Scattering states in AdS/CFT • Microscopic theory of gauge mediated SUSY

breaking• Construction and study of composite DM

models

Direct connections of BSM Model Building research:

SLAC program: ATLAS, BaBar, CDMS, Fermi, LC, SuperB

Broader program: CDF, D0, CMS, LHCb, DM direct

dectection

Hewett, Kachru, Peskin, Rizzo, Silverstein, Wacker

Cosmology/Astro-Interface Highlights

• Comprehensive study of signatures of dark forces and construction and running of related experiment

• DM searches in faint dwarf galaxies – in collaboration with Fermi

• Construction of DM density profiles based on ΛCDM – in collaboration with KIPAC theory

• Comprehensive study of pMSSM DM signatures• Development of natural and UV-complete large-field

inflation, with signatures including gravitational waves• Complete analysis of redshifted slow roll brane inflation• Development of inflationary mechanisms and bottom-up

systematics of non-Gaussianity – in collaboration with KIPAC theory

Direct connections of Cosmo/Astro-interface research:SLAC program: BaBar, BICEP/SPUD, CDMS, Fermi, KIPAC theory,

Super-BBroader program: CMB Pol, DM direct detection, Jlab, Kloe,

PAMELA/HESS, Planck

Hewett, Kachru, Peskin, Rizzo, Silverstein, Wacker

Formal Theory Highlights• Studied uplifting of AdS/CFT to Cosmology and

behind black hole horizons• Controlled QFTs with Lifshitz scaling symmetry:

applications to phase transitions and transport • Showed N=4 super-Yang-Mills theory is solvable

analog for QCD scattering• Demonstrated finiteness of N=8 supergravity

through 4 loopsDirect connections of Formal theory research:SLAC program: ATLAS, KIPAC theory,

Phenomenological thrust, Photon ScienceBroader program: CDF, D0, CMS, Cosmology ,

Pheno

Dixon, Kachru, Silverstein, Weinstein

The Large Hadron Collider: CERN, Geneva, Switzerland

The LHC era has begun!

The anticipation has fueled many ideas

November 2007

CMS

ATLAS

pp e+e- + anything at the LHC

Yellow = SM background as a function of the binned invariant mass of the two leptons showing statistical fluctuations

Signals for a possible new Z’

Clearly the red case is very visible while the blue one is not..a small change in background might obscure it…so knowing the background very precisely would be very important in this case.

gg H W+ W- e ± ± + neutrinos (=ME) at the Tevatron

Lots of SM reactions can conspire to look like a Higgs boson which is only a tiny addition to the ordinary SM rate at the Tevatron. Unless the rates for all these processes are very well understood it will be impossible to claim that a Higgs boson has been found in this reaction…

10x Higgscontribution

Thus it is generally extremely important to be able to make precise calculations of SM processes in order to find new physics which may be hiding in the background.

This effort in the SLAC Theory group is headed by Lance Dixon, Stefan Hoeche

Most calculations in the SM are performed using ‘Perturbation Theory’ which is an expansion of cross sections in a small parameter, e.g., the fine-structure constant in QED, using Feynman diagrams. These are pictorial representations of complex mathematical expressions which are determined by the interactions in a specific theory.

e+

e-

QED

-

+

2 particles in and 2 particles out

22

The complexity of these calculations depends upon the number of particles in the final state , e.g., 22 is easy involving at most a few graphs, while 2 8-10 may involve hundred or thousands of graphs & is VERY hard even at leading order(LO)

The complexity ALSO depends on the order of the calculation, e.g. , 22 at NLO may involve hundreds of graphs depending on the identities of the particles! This is an enormous but important effort..

This is the same process in QED but at NLO (with a single loop).. it is STILL 22

‘loops’ occur at NLO

LO

LO

NLO

NNLO

2n

This is an important background for Higgs searches as well as for Supersymmetry, one possible new physics scenario

The Hierarchy ProblemEnergy (GeV)

1019

1016

103

10-18Solar SystemGravity

Weak

GUT

Planckde

sert

Future Collider Energies

All of known physics

mH2 ~ ~ MPl

2

Quantum Corrections:

Virtual Effects dragWeak Scale to MPl

A Cellar of New Ideas’67 The Standard Model’77 Vin de Technicolor

’70’s Supersymmetry: MSSM

’90’s SUSY Beyond MSSM

’90’s CP Violating Higgs

’98 Extra Dimensions

’02 Little Higgs

’03 Fat Higgs’03 Higgsless’04 Split Supersymmetry’05 Twin Higgs

a classic!aged to perfection

better drink now

mature, balanced, welldeveloped - the Wino’s choice

complex structure

sleeper of the vintagewhat a surprise!

svinters blend

all upfront, no finishlacks symmetry

young, still tannicneeds to develop

bold, peppery, spicyuncertain terrior

J. Hewett

finely-tuned

double the taste

21

The Hierarchy Problem: SupersymmetryEnergy (GeV)

1019

1016

103

10-18Solar SystemGravity

Weak

GUT

Planckde

sert

Future Collider Energies

All of known physics

mH2 ~ ~ MPl

2

Quantum Corrections:

Virtual Effects dragWeak Scale to MPl

mH2 ~ ~ - MPl

2

boson

fermion

Large virtual effects cancel order by order in perturbation theory

Two MSSM Model Frameworks

• The constrained MSSM (CMSSM)– Based on mSUGRA – gravity mediated– Common masses & couplings at the GUT scale– m0, m1/2, A0, tanβ = v2/v1, sign

• The phenomenological MSSM (pMSSM) – 19 real, weak-scale parameters scalars:

mQ1, mQ3

, mu1, md1

, mu3, md3

, mL1, mL3

, me1, me3

gauginos: M1, M2, M3

tri-linear couplings: Ab, At, Aτ

Higgs/Higgsino: μ, MA, tanβ

• The most general, CP-conserving MSSM w/ R-parity conservation

• Minimal Flavor Violation at the TeV scale • The first two sfermion generations are degenerate & have negligible Yukawa couplings

• The lightest neutralino is the LSP & a thermal relic

What is the pMSSM ???Berger, Conley, Cotta, Cowley, Gainer, Hewett, Ismail, Le, Rizzo

pMSSM

Model Generation

LHC & LC

Fermi/Pamela Indirect Detection

CDMS/XENON Direct DetectionICE3

???

Red=20%, green=50%, blue=100% indicate background systematic errors

Solid=4j, dash=3j, dot=2j final states FLAT

Coverage in the all 3 channels depends quite sensitivelyon how well the backgrounds are understood

How many models fail to have even one channel with S > some fixed value with L=10 fb-1 and B=20%?

FLAT

These models willbe hard to find no matter what the lumi is…

Benchmark Models?

We are working with both ATLAS & CMSSUSY groups in studying these low-Smodels in detail

Please come to the theory open house this afternoon!

2:00 Madrone Rm