Supersymmetry at HERA

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Supersymmetry at HERA
DESY Student Seminar, 14.Nov.2005 Claus Horn
Motivation for SUSY Basic SUSY facts Different
SUSY models Current limits Sparticle creation at
HERA SUSY analyses at ZEUS Future prospects
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Shortcomings of the Standard Model
SM is only low energy approximation, In a
fundamental theory all interactions should be
unified GUT gravity What is the origin of
mass, Introduction of Higgs boson runs into
problems. Cosmological problems 21 parameters
too many! Why three generations ? Why Qel
Qp ? ...
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Motivation for Supersymmetry

• Coleman-Mandula theorem
• Unification of the forces
• Solution of the Hierarchy problem
• Candidates for dark matter
• Necessary for quantum-gravity

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Coleman-Mandula Theorem
In a theory with non-trivial scattering in more
than 11 dimensions, the only possible conserved
quantities that transform as tensors under the
Lorentz group are the generators of the Poincare
group and scalar quantum numbers.
Graded Lie-algebras super algebra
Tensors fulfill comutation relations Add
anti-commutators
Pm Energy-momentum operator Q Supercharge
SUSY is the only possibel extension of the
Poincare group.
Our last chance to discover a fundamental
space-time symmetry!
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Unification of the Forces
Renormalisation Group Equations describe running
of the coupling constants due to screening /
antiscreening
Example
Slope depends on number and masses of
particles in the model
Miracle!
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Solution of the Hierarchy Problem
Corrections to the Higgs mass
SM
Cancelation requires fine tuning to 17 orders of
magnitude!
MSSM
Contributions of particles are canceled by
contribution of their superpartners.
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For unbroken SUSY No quantum correction to the
Higgs mass (DmH0).
Broken SUSY running Higgs mass
mh
No SUSY
SUSY Higgs sector very restricted mh lt 150
GeV
SUSY exact
mH
Q²
Q2
SUSY particles
superpartners have to be lighter than 1 TeV
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Basic Facts about SUSY
Symmetry between fermions and bosons
Qbosongt fermiongt Qfermiongt bosongt
No superpartners with same masses are observed.
SUSY is a borken symmetry.
Spontaneous SUSY breaking in SM sector not
possible supertrace theorem sum rules
between particle and sparticle masses, e.g.
excluded!
Hidden sector models
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Supermultiplets
Chiral supermultiplets (fermion,sfermion)
(spin ½, spin 0) Vectorial supermultiplet
(gauge boson, gauginos) (spin 1, spin ½)
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Sparticles of the MSSM
Charged gauginos mix to form two charginos.
Neutral gauginos mix to form four neutralinos.
M depends on M2, tan(b) and m.
BRs of c0 and c?
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Parameters of the MSSM

• mA pseudoscalar Higgs boson mass
• tan(b) ratio of VEV of two Higgs doublets
• m Higgs mixing parameter
• M1, M2, M3 gaugino mass terms
• All sfermion masses
• Ai all mixing parameters of squark and slepton
  sector

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SUSY Breaking
MSSM does not explain origin of SUSY
breaking soft breaking terms are introduced by
hand
more than 100 free parameters
Hidden sector models mSUGRA, GMSB
Flavour problem solved in GMSB model.
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minimal SUperGRavity (mSUGRA)
Constraints

• Unified masses at the GUT scale
• m0 common scalar mass
• m1/2 common gaugino mass
• Unified trilinear couplings A0
• Radiative EW symmetry breaking

Parameter m0, m1/2, A0, tan(b), sign(m)
M(G) ? 1 TeV (in AMSB ? 10 TeV)
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Gauge Mediated SUSY Breaking (GMSB)
LSP (in not-yet excluded parameter space) is
always gravitino
Gravitino can be very light
Possible NLSPs neutralino, stau
Distinct event signature photon/tau missing
energy
Gravitino might be candidate for dark matter even
in RPV models.
Parameter L, sqrt(F), Mmess, N, tan(b), sign(m)
Very predictive mass spectrum, easy to
distinguish from SUGRA.
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Typical Mass Spectra
Neutralino1 is light(est) Next right-handed
slepton (stau) chargino1 Squarks are relatively
heavy
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R-parity
1 for SM particles -1 for sparticles
Multiplicative discrete symmetry RP(-1)3BL2S
RPC sparticles pair-produced, LSP stable
Most general Lagrangian contains additional
trilinear terms in superpotential which violate
RP
HERA is the ideal place to look for l !
(Proton decay only if l and l are ?0 at the
same time.)
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Overview of current best Limits

• Neutralinos / Charginos
• RPC and RPV
• Sleptons
• RPC and RPV
• Squarks
• RPC and RPV

Huge multidimensional parameter spaces
Results only valid under restricted conditions.
Comparison between different analysis difficult.
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Current best Limits
Parameter region
Neutralinos / Charginos
LEP m(c0) gt 92 GeV
RPC MSSM m(c) gt 103 GeV
tan(b)2, m-200
LEP m(c0) gt 40 GeV
RPV MSSM m(c) gt 103 GeV
tan(b)1.5
D0 m(c0) gt 84 GeV
RPV mSUGRA m(c) gt 160 GeV
tan(b)1.5
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Current best Limits - sleptons
selectronR gt 100 GeV smuonR gt 95 GeV stauR gt 86
GeV
RPC MSSM m -200 tan(b) 1.5
LEP
RPV MSSM l?0 m -200 tan(b) 1.5
LEP
selectronR gt 100 GeV smuonR gt 98 GeV stauR gt 97
GeV
D0 m(n) gt 460 GeV l1320.05
l3110.16
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Current best Limits - squarks
RPC
D0 m(q) gt 320 GeV

mSUGRA m0 25 GeV
D0 m(g) gt 232 GeV

mSUGRA m0 500 GeV
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Current best Limits - squarks
RPV
CDF m(t) gt 155 GeV
l333?0
HERA m(t) gt 275 GeV
l1j10.3
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Sparticle Creation at HERA
Systematic approach needed to filter all
interesting channels.
Approach
Particles are produced on-shell (same for all
SUSY models). Decay depends on sparticle spectra
of SUSY model.

HERA topologies Abstract notation
SUSY-flow graphs Fundamental vertices
Abstract diagrams
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HERA Topologies

• All topologically distinct graphs
• with up to three outgoing (s)particle lines
• Initial state is fixed to electronquark
• (g and g from proton are only considered with 2
  outgoing lines)

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SUSY-flow Graphs
Choos RPV vertices Mark sparticle lines with a
. In the case of RPC C-like loops result.
F, RPC
Number of SUSY propagators Number of SUSY
particles
discarded
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Abstract Notation Fundamental Vertices
Physics description on an abstract level to
reduce complexity.
All vertices of the MSSM ! (neglecting pure
bosonic SM vertices)
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Restrictions

• diagrams with gt 3 on-shell produced (s)particles
  are neglected
• diagrams with outgoing g, g, Z0 are not
  discussed
• diagrams with initial g/g and 3 outgoing
  particles are discarded
• u-channel diagrams are not stated expicetly
• diagrams with gt 1 sparticle propagator are
  discarded
• interactions of Higgs bosons are not considered
• vertices with only SM bosons are neglected
• diagrams with three RPV vertices are discarded

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Example Application to type C Diagrams
RPC
RPV
SUSY-flow graphs
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Possible abstract diagrams
C3 disfavoured due to high limits on squark
masses C7 - C6 lepto-quark search /
contact interaction C5 beeing analysed at the
moment !
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Sparticle Decays
Neutralino
RPC MSSM RPV MSSM
GMSB
Stable LSP
missing energy
Chargino
RPC RPV
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Sparticle Decays
Sleptons
RPC
RPV
RPC MSSM missing E, e / m / t RPV MSSM 2 jets /
2 l / 2jets2l GMSB l g G
Squarks decay in the same way.
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Results
Diagrams with squarks are neglected.
Characteristic signatures for different models!
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Results
With two outgoing lines C5 With three outgoing
lines and one sparticle F4-2 With three outgoing
lines and two sparticles D1
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Interesting SUSY Diagram D1

• Only SM propagators
• Production of two sparticles
• with m?100 GeV each

Highest expected cross section for
Signature RPC MSSM E e- RPC GMSB e-2(gG)

• G g
• Low Q2 (PhP)

Calculated cross section 20 pb for
mcme120 GeV (no warrenty!)
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Interesting SUSY Diagram F4-2

• Only SM propagators
• Only one sparticle
• Slepton production
• (first time at HERA)

Signature RPV MSSM 2jets / 2jets2l RPV GMSB
lG / lgG
Highest expected cross section for resolved
PhP
Cross section to be determined
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Current Analyses at ZEUS
Production via C5
Decay in MSSM Gaugino analysis
NC-like channel
e- jets
CC-like channel
Decay in GMSB Gravitino analysis
n jets
Signature
jet g missing energy
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Gravitino Analysis
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Discriminant Method
Multidimensional cuts generally result in a
better S/B ratio, than one dimensional cuts.
Improvement variable box size
events /box (box_size)d
All events get classified. Less statistics
needed. Faster calculation. More accurate
results. Generally better S/B seperation.
Box size
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Gravitino Analysis
No events in signal region
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Limits Gravitino Analysis
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Limits Gaugino Analysis
Extended LEP limits in M2 - m plane
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Future LHC and ILC
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Future Prospects - LHC
SUSY gauge couplings are the same as in SM. Cross
sections only surpressed by mass terms. At high
energies production rates should be similar to SM!
Discovery is no problem. (reonstruct Meff)
SUSY signal and SM bkg. for tt- decay (m01TeV,
m1/2500 GeV)
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SUSY at LHC
LHC 5s discovery curves
But
Complicated decay channels g -gt qq -gt cqq -gt
llqq -gt cllqq
Problem is to seperate different SUSY channels.
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Future Prospects - ILC
Higher luminosity at similar energy
Precision measurements of SUSY parameters!
LHC
ILC
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Future
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Summary

• SUSY is a very interesting and promising theory.
• It is challenging, but
• there are SUSY channels were HERA is favoured
• compared to LEP and the Tevatron.
• If we do not find it before, then
• the LHC will give the final answer
• Be prepared to discover a new world !