Download Lecture 5: Physics Beyond the Standard Model and Supersymmetry

75th Compton Lectures: String Theory in the LHC Era
J. Marsano
Lecture 5: Physics Beyond the Standard Model and
Supersymmetry
Beyond the Standard Model?
• Why do we need physics beyond the Standard Model?
• The Standard Model does not describe
gravity
• Hints of Grand Unification
• Two more issues that we discuss in detail
• Dark Matter
• ’Hierarchy problem’
Dark Matter
• Stars at the edges of galaxies are moving
too fast
• Cannot be explained from gravitational pull of visible matter alone
• Zwicky proposed additional ’dark matter’
that contributes its own gravitational field
• Doesn’t couple to electromagnetism so
we don’t readily see it
• Dark matter can be observed through ’lensing’ effects where its gravitational field
bends the light from distant objects
• The standard model of cosmology requires
about 23% of the energy in the universe to
be comprised of dark matter
Cartoon of Dark Matter Halo
of a spiral galaxy
• Precision tests in Cosmic Microwave
Background observations
75th Compton Lectures: String Theory in the LHC Era
J. Marsano
Detecting Dark Matter
• The abundance of dark matter that we see today
is naturally explained by a simple model where
• Dark matter particle is a WIMP, meaning
– Wearly Interacting Massize Particle
– Couples to W and Z bosons of Weak
Interactions
– Neutral under electromagnetism and
strong interactions
Fermi Satellite
• The dark matter mass ∼ 100-1000 GeV
– mZ ∼ 91 GeV and mW ∼ 80 GeV
→ Dark matter mass ∼ Weak scale
• WIMP Must be stable or have lifetime
longer than the age of the universe (10 billion years)
• No such particle in the Standard Model
• Many ways to see WIMPs
• Production at LHC
– WIMPs may be directly produced in
proton-proton collisions at the LHC
• Indirect Detection
• Direct Detection
• Balloon and satellite experiments look
for dark matter produced by cosmic
rays and signs of dark matter annihilation in space
– Look for dark matter collisions with
heavy nuclei (Ge, I, Xe, etc)
– Some experiments (DAMA, CoGeNT)
reporting a positive signal
– Others (CDMS, Xenon, etc) don’t see
it–no consistent picture yet
– The Fermi satellite may have seen
evidence of dark matter annihilation in the galactic center!
The Hierarchy Problem
• What sets scale of W and Z boson masses?
• Connected to physics of Higgs field and,
more specifically, the dynamics that generates the ’Higgs bath’ that gives masses
to particles
• Where does the scale 100 GeV come from?
Why so different from the fundamental
scale of quantum gravity?
• Why do we even care about this?
75th Compton Lectures: String Theory in the LHC Era
J. Marsano
Infinities in the Standard Model
• Importance of Hierarchy Problem related to
infinities–look closer at those
• The ’Higgs bath’, along with the scale of
W and Z masses, is determined by a dynamically generated potential for the Higgs
field
• This potential is determined by quantum
effects involving interactions of the Higgs
field with Standard Model particles
• When we compute quantum corrections to
Higgs potential, we get infinite answers
• Quantum field theory is smarter than us
• If we get a nonsense answer, we must
have done something wrong
• When we ’sum over histories’, we include
all possible top quark energies/momenta
• Implicitly assumes that we understand
physics at very short distance scales
(very high energies)
• Infinity comes from very high energy
top quarks so it is a sign that this assumption is wrong!
• We do not know the physics at short distance scales so all we can do is parametrize
our ignorance
• Introduce new local interaction to
model unknown short distance physics
• Comes with a parameter that must be
fixed by measurement
75th Compton Lectures: String Theory in the LHC Era
J. Marsano
The Hierarchy Problem Revisited
• The Standard Model is miraculous
• It only depends on unknown short distance
physics through a finite number of parameters (19)
• These parameters are the particle
masses, interaction strengths, etc
• A fundamental description of physics
at all energy scales would determine
the masses and interaction strengths
from first principles. In the Standard
Model these are parameters that reflect our ignorance of physics at short
distance scales
• Once we make a finite number of measurements (19), the Standard Model can make
predictions
• We can now state the Hierarchy problem
more cleanly:
• The W and Z masses depend very sensitively on the parameters that we use
to characterize short distance physics
→ The model is not robust
– As with any model, ultrasensitivity to input parameters is
a sign that essential features are
not properly understood
Why New Physics at the LHC?
• Need something like Higgs below a few TeV
(i.e. few 1000’s of GeV)
• Suggestion of dark matter at 100-1000 GeV
• Evidence already in Fermi data?
• ’Natural’ solution to hierarchy problem requires new physics around 100-1000 GeV
• Many signs point to TeV scale physics!
75th Compton Lectures: String Theory in the LHC Era
J. Marsano
Supersymmetry
• Supersymmetry (SUSY) is a nontrivial extension of space-time symmetries (rotations, etc) that relates particles of different
spin
• If a spin 12 electron e− couples to electromagnetism, there must be a spin 0 particle,
the selectron ẽ− , with exactly the same coupling to electromagnetism
• The Minimal Supersymmetric Standard
Model (MSSM) adds a superpartner like the
selectron for each ordinary particle
• Superpartners not seen (yet) so SUSY not
an exact symmetry of nature
• Can address issues of Standard Model if
SUSY is broken around 100-1000 GeV
Supersymmetry and the Hierarchy Problem
• For each Standard Model contribution to
a computation, one gets additional superpartner contributions
• Superpartners contribute with an opposite
sign relative to Standard Model particles so
bad behavior like infinities cancel between
diagrams
• Removes ultra-sensitivity of Higgs potential on short distance physics
• Not a complete solution because we must
understand why supersymmetry is broken
at 100-1000 GeV
• Nevertheless supersymmetry provides
a possible physical origin of electroweak symmetry breaking and the
electroweak scale
75th Compton Lectures: String Theory in the LHC Era
J. Marsano
Supersymmetry and Dark Matter
• Supersymmetric models often come with a
new symmetry, R-parity, that distinguishes
Standard Model particles from their superpartners
• A superpartner cannot decay to only Standard Model particles. Another superpartner must always be among the decay products
• The Lightest SuperPartner (LSP) has
nothing to decay into – it is stable!
• Natural dark matter candidate!
Supersymmetry and Grand Unification
• Superpartners contribute quantum corrections that determine the strengths of
electromagnetism, weak interactions, and
strong interactions
• Adding superpartners at 100-1000 GeV
substantially improves the unification picture – very suggestive!
Looking for Supersymmetry
• Organize searches based on simplified scenarios for how supersymmetry-breaking is
communicated to the MSSM
MSUGRA/CMSSM : 1-lep + j’s + E T ,miss
L =4.7 fb (2011) [ATLAS-CONF-2012-041]
L =4.7 fb (2011) [ATLAS-CONF-2012-037]
L =4.7 fb (2011) [ATLAS-CONF-2012-033]
GMSB : 1-τ + j’s + E
1
Third generation
-1
940 GeV
L =4.7 fb (2011) [ATLAS-CONF-2012-033]
900 GeV
-1
810 GeV
L =1.0 fb (2011) [ATLAS-CONF-2011-156]
-1
L =2.1 fb (2011) [ATLAS-CONF-2012-002]
-1
-1
T ,miss
T ,miss
∼± χ
∼0 → 3l χ
∼0) : 3-lep + E
Direct gaugino (χ
T ,miss
1 2
1
∼±
AMSB : long-lived χ
1
-1
1
~
∼ ) < 300 GeV)
g mass (m(χ
1
~
∼0
g mass (m(χ1 ) < 150 GeV)
~
∼0 ) < 210 GeV)
g mass (m(χ
900 GeV
-1
L =2.1 fb (2011) [ATLAS-CONF-2012-003]
710 GeV
-1
650 GeV
L =2.1 fb (2011) [ATLAS-CONF-2012-004]
0
1
~
∼0
830 GeV g mass (m ( χ ) < 200 GeV)
1
~
∼0 ) < 60 GeV)
b mass (m(χ
1
~
0
∼
-1
L =2.1 fb (2011) [ATLAS-CONF-2012-036]
310 GeV t mass (115 < m ( χ ) < 230 GeV)
1
~∼ 1
∼±
∼0
∼0
∼±
∼0
∼0
∼0
-1
L =1.0 fb (2011) [1110.6189]
170 GeV χ mass (( m ( χ ) < 40 GeV,χ , m ( χ ) = m ( χ ), m ( l,ν ) = ( m ( χ ) + m ( χ )))
1
1
1
1
2
1
2
2
∼±
∼0
-1
L =2.1 fb (2011) [ATLAS-CONF-2012-023] 250 GeV χ mass (m ( χ ) < 170 GeV, and as above)
1
1
118 GeV ∼±
±
∼
-1
χ mass (1 < τ(χ ) < 2 ns, 90 GeV limit in [0.2,90] ns)
L =4.7 fb (2011) [CF-2012-034]
-1
L =4.7 fb (2011) [ATLAS-CONF-2012-037]
-1
L =2.1 fb (2011) [1112.3832]
390 GeV
1
L =34 pb (2010) [1103.1984]
SMP : R-hadrons
L =34 pb (2010) [1103.1984]
1
-1
562 GeV
-1
294 GeV
-1
309 GeV
L =34 pb (2010) [1103.1984]
-1
-1
L =37 pb (2010) [1106.4495]
L =1.1 fb (2011) [1109.3089]
Bilinear RPV : 1-lep + j’s + E T ,miss
L =1.0 fb (2011) [1109.6606]
136 GeV
~
g mass
~
b mass
~
t mass
810 GeV
L =2.1 fb (2011) [ATLAS-CONF-2012-022]
RPV : high-mass eµ
Hypercolour scalar gluons : 4 jets, m ij ≈ m kl
~
∼0 ) > 50 GeV)
g mass (m(χ
805 GeV
L =1.1 fb (2011) [1111.4116]
L =2.1 fb (2011) [ATLAS-CONF-2012-003]
Stable massive particles (SMP) : R-hadrons
SMP : R-hadrons
SMP : R-hadrons (Pixel det. only)
GMSB : stable ∼τ
1
~
∼0
∼±
∼0
~
g mass (m(χ1 ) < 200 GeV,m(χ ) = 1(m(χ )+m(g))
2
~
g mass (tanβ < 35)
~
920 GeV g mass (tanβ > 20)
~
990 GeV g mass (tanβ > 20)
-1
L =4.7 fb (2011) [ATLAS-CONF-2012-041]
L =2.1 fb (2011) [ATLAS-CONF-2012-005]
MSUGRA/CMSSM - BC1 RPV : 4-lepton + E T ,miss
• Too early to ’rule out’ TeV scale SUSY
-1
T ,miss
~
∼0) : 0-lep + b-j’s + E
Gluino med. b (~
g→bbχ
T ,miss
1
~
∼0) : 1-lep + b-j’s + E
Gluino med. t (~
g→t t χ
T ,miss
1
~
∼0) : 2-lep (SS) + j’s + E
Gluino med. t (~
g→t t χ
T ,miss
~1
∼0) : multi-j’s + E
Gluino med. t (~
g→t t χ
T ,miss
1
~~ ~
∼0) : 2 b-jets + E
Direct bb (b1→ bχ
T ,miss
1
~~
Direct t t (GMSB) : Z(→ll) + b-jet + E
T ,miss
∼± χ
∼0 → 3l χ
∼0) : 2-lep SS + E
Direct gaugino (χ
1 2
1.20 TeV
-1
T ,miss
∫
1.40 TeV
-1
Pheno model : 0-lep + j’s + E T ,miss
Pheno model : 0-lep + j’s + E T ,miss
∼± (~
∼± ) : 1-lep + j’s + E
Gluino med. χ
g→ qqχ
T ,miss
GMSB : 2-lep OSSF + E T ,miss
~ ~
q = g mass
Ldt = (0.03 - 4.7) fb-1
~ ~
q = g mass
~
s = 7 TeV
850 GeV g mass (large m 0 )
~
~
∼0
1.38 TeV q mass (m ( g) < 2 TeV, light χ )
ATLAS
1
0
~
~
∼
Preliminary
g mass (m(q) < 2 TeV, light χ )
-1
MSUGRA/CMSSM : multijets + E T ,miss
GGM : γ γ + E
DG
• Collider signatures vary significantly
across the parameter space – systematic searches difficult
L =4.7 fb (2011) [ATLAS-CONF-2012-033]
GMSB : 2-τ + j’s + E
Long-lived particles
• Many fixed by current observation but
complicated parameter space remains
RPV
• The MSSM has ∼ 125 new parameters
Inclusive searches
ATLAS SUSY Searches* - 95% CL Lower Limits (Status: March 2012)
MSUGRA/CMSSM : 0-lep + j’s + E T ,miss
∼τ mass
-1
760 GeV
-1
-1
∼ mass (λ =0.10, λ =0.05)
ν
τ
311
312
~ ~
q = g mass (cτLSP < 15 mm)
~
1.77 TeV g mass
1.32 TeV
L =2.1 fb (2011) [ATLAS-CONF-2012-035]
L =34 pb (2010) [1110.2693]
~
g mass
,
-1
185 GeV
10-1
sgluon mass (excl: msg < 100 GeV, msg ≈ 140 ± 3 GeV)
1
10
*Only a selection of the available mass limits on new states or phenomena shown
Summary of ATLAS SUSY searches
Mass scale [TeV]