22 december 2006masters defense texas a&m university1 adam aurisano in collaboration with...

22 December 2006 Masters Defense Texas A&M University 1

Adam AurisanoIn Collaboration with

Richard Arnowitt, Bhaskar Dutta,Teruki Kamon, Nikolay Kolev*, Paul Simeon,

David Toback & Peter Wagner

Texas A&M UniversityRegina University*

Signals in the Co-annihilation Region of Supersymmetry at the

LHC- Supersymmetry and Dark

Matter -


Outline

Supersymmetry (SUSY) and Cosmology Dark matter Supersymmetric particles

How to measure a small mass difference (M) and mass ( ) Counting methods Invariant mass methods

Results Conclusions

g~0

1~~

gM ~


Introduction

Current cosmology data indicates that ~24% of universe’s energy content is cold dark matter.

There are many candidates for dark matter. Supersymmetry provides a model for the Grand

Unification of forces new Supersymmetric particles.

The lightest SUSY particle provides one of the best motivated dark matter candidates.


Cold Dark Matter Cosmologists have observed that

there is not enough “normal” matter in our universe to account for its features

Rotation of galaxies Bullet galaxies Cosmic Microwave Background

anisotropies Dark matter candidates must heavy,

have no charge, be non-baryonic, and likely be “cold” (non-relativistic) for galaxy formation.

This excludes all known Standard Model particles.

Neutrinos fail the “cold” criterion.


Why SUSY?

Supersymmetry (SUSY) is a theory that postulates a symmetry between fermions and bosons.

The minimal version roughly doubles the particle count of the Standard Model.

In models with “R-parity”, the lightest SUSY particle is stable: this provides an excellent dark matter candidate, the .

SUSY allows for model building up to the GUT scale by reducing the Higgs mass divergence from quadratic to logarithmic.

SUSY solves the “hierarchy problem” by dynamically generating the Electro-weak symmetry breaking scale.

However: SUSY must be a broken symmetry (superpartners are heavier than their SM counterparts).

01

~


Minimal Supersymmetric Standard Model

The MSSM is the minimal possible supersymmetric extension of the Standard Model.

Does not explain the symmetry breaking, so masses are determined ad-hoc.

This leads to over 100 new parameters.


mSUGRA

Minimal Supergravity postulates that symmetry breaking is mediated by the gravity sector.

In addition, it assumes that at the unification scale all sfermions (super partners of fermions) have mass m0 and all gauginos (super partners of gauge bosons) have mass m1/2.

Only three other parameters are required to determine all particle masses and couplings.


Co-annihilation Region

There are three parameter space regions where the predicted mSUGRA dark matter abundances are consistent with observation.

With the additional observational constraint that we believe that the results of the g-2 collaboration will continue to show deviations from the Standard Model, only the co-annihilation region remains.

Co-annihilation, along with annihilation, controls the dark matter relic density.

This is governed by M.

01

~~ MMM

~01~

Co-annihilation diagram

tim

e


Goal

If SUSY is correct, and we are in the co-annhilation region, we want to measure the parameters m0 and m1/2, or indirectly, we can measure M and .

To do this, we need an accelerator with a large center of mass energy and high luminosity.

gM ~


Large Hadron Collider

pp collider After turn on, the

LHC will be the high energy frontier with a center of mass energy = 14 TeV!

This is 7 times the current highest energy collider.


Compact Muon Solenoid

One of the two general detectors at the LHC will be CMS.

The detector surrounds a collision point and records the energy and momentum of the produced particles.

If we are lucky, we will see new physics!


3Final State Provides Unique Signal of Co-annihilation

Produce SUSY events in pp collisions at LHC.

Look at SUSY particle production and decay.

Look for 3 2 high energy and 1 low energy.

p

p

~

q~g~

g~

q

qg

high energy

is small ,so this is low energy.

02

~ 01

~

another high energy

Look at the mass of this pairq~or

escapes undetected.missing energy

01

~


ET Spectrum of Third M tells us how

much energy is available to produce the low energy .

Large M large energy lots of events pass threshold

Small M small energy few events pass threshold


Counting vs. M

At constant , the probability that the third has energy> 20 GeV depends on M.

For M > 5 GeV, the number of counts increases nearly linearly.

For M < 5 GeV, there is primarily background due to single top quarks produced in gluino and squark decay.

gM ~


Counting vs. Gluino Mass

The number of counts depends on almost entirely through gluino production. Low mass = high

production cross-section

High mass = low production cross-section

gM ~


Invariant Mass 01

02

~~

~~

Small M:

Few events

Small mass

Large M:

Many events

Large mass

Background easy to subtract off

M


Invariant Mass vs. M

The invariant mass distribution depends directly on M.

gMMM ~


Invariant Mass vs. Gluino Mass

The invariant mass distribution only depends on indirectly.

In mSUGRA, all gaugino masses are related through the renormalization group equations to the parameter m1/2.

Because the invariant mass has the opposite trend of counting, we can combine these methods to simultaneously measure and .

gM ~

gM ~


Gluino Mass vs. M : Simulataneous Measurement

Counts and mass have inverse relationships.

Use this to indirectly measure both the gluino mass and M.


Results

Our gluino mass measurement is indirect, but it may be the only one possible at low luminosities.

When direct measurements become available, a comparison would be an excellent check for mSUGRA.

Previous methods to determine assume not in the co-annihilation region.

gM ~


Conclusions

For cosmological reasons, the co-annihilation region of supersymmetry is an important place to study.

Our methods may help us measure M and well at the LHC. Our indirect measurement of may be the only

one available at low luminosity. With optimization of cuts, we may be able to

make a better measurement. Submitted to Phys. Lett. B,

arXiv:hep-ph/0608193

gM ~

gM ~


END OF TALK

Back-up Slides


Results: Fixed Gluino Mass

If a measurement of

is available, we can use our methods to make a more precise measurement of M.

We assume a 5% uncertainty on .

This dominates the uncertainty.

gM ~

gM ~


Cuts Provide Nearly Background Free Region

Assume: 50% tau efficiency 1% fake rate

Cuts: 2 > 40 GeV 1> 20 GeV Jet 1 > 100 GeV MET > 100 GeV Jet 1 + MET > 400 GeV

M < 100 GeV


MMeasurement

Systematic uncertainty based on 5% variation in gluino mass

We assume a 1% fake rate with 20% uncertainty

For all luminosities with significance > 3, we are systematic dominated


M Measurement (MM)

Like the counting method, we are always in a systematic dominated region.

22 december 2006masters defense texas a&m university1 adam aurisano in collaboration with...

Documents

universitygoalif susy

universitywhy susy

lightest susy particle

dark matter relic density

normal matter

mass m0

mass m12

known standard model