22 December 2006Masters Defense Texas A&M University1 Adam Aurisano In Collaboration with Richard Arnowitt, Bhaskar Dutta, Teruki Kamon, Nikolay Kolev*, Paul Simeon, David Toback & Peter Wagner Texas A&M University Regina University* Signals in the Co-annihilation Region of Supersymmetry at the LHC - Supersymmetry and Dark Matter -

22 December 2006Masters Defense Texas A&M University2 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

22 December 2006Masters Defense Texas A&M University3 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.

22 December 2006Masters Defense Texas A&M University4 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.

22 December 2006Masters Defense Texas A&M University5 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).

22 December 2006Masters Defense Texas A&M University6 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.

22 December 2006Masters Defense Texas A&M University7 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 m 0 and all gauginos (super partners of gauge bosons) have mass m 1/2. Only three other parameters are required to determine all particle masses and couplings.

22 December 2006Masters Defense Texas A&M University8 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.  Co-annihilation diagram time

22 December 2006Masters Defense Texas A&M University9 Goal  If SUSY is correct, and we are in the co- annhilation region, we want to measure the parameters m 0 and m 1/2, or indirectly, we can measure  M and.  To do this, we need an accelerator with a large center of mass energy and high luminosity.

22 December 2006Masters Defense Texas A&M University10 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.

22 December 2006Masters Defense Texas A&M University11 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!

22 December 2006Masters Defense Texas A&M University12 3  Final 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   high energy   is small, so this  is low energy. another high energy  Look at the mass of this pair or escapes undetected.  missing energy

22 December 2006Masters Defense Texas A&M University13 E T 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

22 December 2006Masters Defense Texas A&M University14 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.

22 December 2006Masters Defense Texas A&M University15 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

22 December 2006Masters Defense Texas A&M University16  Invariant Mass Small  M: Few events Small mass Large  M: Many events Large mass Background easy to subtract off M 

22 December 2006Masters Defense Texas A&M University17  Invariant Mass vs.  M The invariant mass distribution depends directly on  M.

22 December 2006Masters Defense Texas A&M University18  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 m 1/2. Because the invariant mass has the opposite trend of counting, we can combine these methods to simultaneously measure  and.

22 December 2006Masters Defense Texas A&M University19 Gluino Mass vs.  M : Simulataneous Measurement Counts and mass have inverse relationships. Use this to indirectly measure both the gluino mass and  M.

22 December 2006Masters Defense Texas A&M University20 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.

22 December 2006Masters Defense Texas A&M University21 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/

22 December 2006Masters Defense Texas A&M University22 END OF TALK Back-up Slides

22 December 2006Masters Defense Texas A&M University23 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.

22 December 2006Masters Defense Texas A&M University24 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

22 December 2006Masters Defense Texas A&M University25  M  Measurement 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

22 December 2006Masters Defense Texas A&M University26  M Measurement (MM) Like the counting method, we are always in a systematic dominated region.