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SLAC Particle Theory Overview
circa 2007
Group Members
Faculty & Staff:
Stan Brodsky
Michael Peskin
Professor
Professor
Lance Dixon
Tom Rizzo
Professor
Senior Staff
JoAnne Hewett
Eva Silverstein
Professor
Professor – ½ campus
Stefan Höche
Jay Wacker
Associate Staff
Assistant Professor
Shamit Kachru
Marvin Weinstein
Professor – ½ campus
Permanent Staff
Particle Theory Program: at a Glance
QCD
Heavy Flavors
Formal Theory
Experimental Programs
BSM Pheno
Astro Interface
Model Building
QCD Highlights
Brodsky, Dixon, Höche, Peskin
• 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-B
Broader program: CDF, D0, CMS, GSI, H1, Jlab, RHIC
Heavy Flavor Highlights
Brodsky, Hewett, Rizzo, Wacker
• 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 AtFB
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, SuperB
Broader program: CDF, D0, CMS, LHCb
BSM Phenomenology Highlights
Hewett, Peskin, Rizzo, Wacker
• 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, LC
Broader program: CDF, D0, CMS
BSM Model Building Highlights
Hewett, Kachru, Peskin, Rizzo, Silverstein, Wacker
• 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
Cosmology/Astro-Interface Highlights
Hewett, Kachru, Peskin, Rizzo, Silverstein, Wacker
• 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-B
Broader program: CMB Pol, DM direct detection, Jlab, Kloe, PAMELA/HESS,
Planck
Formal Theory Highlights
Dixon, Kachru, Silverstein, Weinstein
• 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
loops
Direct connections of Formal theory research:
SLAC program: ATLAS, KIPAC theory, Phenomenological
thrust, Photon Science
Broader program: CDF, D0, CMS, Cosmology , Pheno
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
Signals for a possible
new Z’
Yellow = SM background as a function of the binned invariant
mass of the two leptons showing statistical fluctuations
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
10x Higgs
contribution
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…
 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+
QED
2 particles in and
 2 particles out

22
e-
+
The complexity of these calculations depends upon the number of
particles in the final state , e.g., 22 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. , 22
at NLO may involve hundreds of graphs depending on the identities of
the particles! This is an enormous but important effort..
‘loops’ occur at NLO
This is the same process
in QED but at NLO (with
a single loop).. it is STILL
22
2n
NNLO
NLO
LO
LO
This is an important background for Higgs searches as well
as for Supersymmetry, one possible new physics scenario
The Hierarchy Problem
Energy (GeV)
Planck
Quantum Corrections:
1016
GUT
Virtual Effects drag
Weak Scale to MPl
desert
1019
Future
Collider
Energies
103
Weak
All of
known
physics
10-18
Solar System
Gravity
mH2 ~
~ MPl2
A Cellar of New Ideas
’67
’77
The Standard Model
Vin de Technicolor
’70’s
Supersymmetry: MSSM
’90’s
SUSY Beyond MSSM
’90’s
CP Violating Higgs
’98
Extra Dimensions
’02
Little Higgs
’03
’03
’04
’05
Fat Higgs
Higgsless
Split Supersymmetry
Twin Higgs
a classic!
aged to perfection
better drink now
mature, balanced, well
developed - the Wino’s choice
svinters blend
all upfront, no finish
lacks symmetry
bold, peppery, spicy
uncertain terrior
complex structure
young, still tannic
needs to develop
sleeper of the vintage
what a surprise!
finely-tuned
double the taste
J. Hewett
21
The Hierarchy Problem: Supersymmetry
Energy (GeV)
Planck
Quantum Corrections:
1016
GUT
Virtual Effects drag
Weak Scale to MPl
desert
1019
Future
Collider
Energies
boson
103
Weak
mH2 ~
~ MPl2
fermion
mH2 ~
All of
known
physics
10-18
Solar System
Gravity
~ - MPl2
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
What is the pMSSM ???
Berger, Conley, Cotta, Cowley, Gainer, Hewett, Ismail, Le, Rizzo
• 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
pMSSM
LHC & LC
Model
Generation
Fermi/Pamela
Indirect Detection
CDMS/XENON
ICE3
Direct Detection
???
FLAT
Solid=4j, dash=3j, dot=2j final states
Red=20%, green=50%, blue=100%
indicate background systematic errors
Coverage in the all 3 channels depends quite sensitively
on 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%?
Benchmark
Models?
These models will
be hard to find no
matter what the
lumi is…
We are working with
both ATLAS & CMS
SUSY groups in
studying these low-S
models in detail
FLAT
Please come to the theory
open house this afternoon!
2:00 Madrone Rm
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