Signals in the Co-annihilation Region of Supersymmetry at the LHC

1. Signals in the Co-annihilation Region of Supersymmetry at the LHC- Supersymmetry and Dark Matter - 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* Masters Defense Texas A&M University

2. Outline • Supersymmetry (SUSY) and Cosmology • Dark matter • Supersymmetric particles • How to measure a small mass difference (DM) and mass ( ) • Counting methods • Invariant mass methods • Results • Conclusions Masters Defense Texas A&M University

3. 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. Masters Defense Texas A&M University

4. 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. Masters Defense Texas A&M University

5. 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). Masters Defense Texas A&M University

6. 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. Masters Defense Texas A&M University

7. 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. Masters Defense Texas A&M University

8. g t 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 DM. time Co-annihilation diagram Masters Defense Texas A&M University

9. 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 DM and . • To do this, we need an accelerator with a large center of mass energy and high luminosity. Masters Defense Texas A&M University

10. 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. Masters Defense Texas A&M University

11. 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! Masters Defense Texas A&M University

12. 3t Final State Provides Unique Signal of Co-annihilation DM is small , so this t is low energy. escapes undetected. missing energy • Produce SUSY events in pp collisions at LHC. • Look at SUSY particle production and decay. • Look for 3 t : 2 high energy and 1 low energy. t p t Look at the mass of this pair high energy t p another high energy t or Masters Defense Texas A&M University

13. ET Spectrum of Third t • DM tells us how much energy is available to produce the low energy t. Large DM large t energy lots of events pass threshold Small DM small t energy few events pass threshold Masters Defense Texas A&M University

14. Counting vs. DM • At constant , the probability that the third t has energy> 20 GeV depends on DM. • For DM > 5 GeV, the number of counts increases nearly linearly. • For DM < 5 GeV, there is primarily background due to single top quarks produced in gluino and squark decay. Masters Defense Texas A&M University

15. 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 Masters Defense Texas A&M University

16. tt Invariant Mass Mtt Background easy to subtract off Large DM: Many events Large mass Small DM: Few events Small mass Masters Defense Texas A&M University

17. tt Invariant Mass vs. DM • The invariant mass distribution depends directly on DM. Masters Defense Texas A&M University

18. tt 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 DM and . Masters Defense Texas A&M University

19. Gluino Mass vs. DM : Simulataneous Measurement • Counts and mass have inverse relationships. • Use this to indirectly measure both the gluino mass and DM. Masters Defense Texas A&M University

20. 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. Masters Defense Texas A&M University

21. Conclusions • For cosmological reasons, the co-annihilation region of supersymmetry is an important place to study. • Our methods may help us measure DM 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 Masters Defense Texas A&M University

22. END OF TALK Back-up Slides Masters Defense Texas A&M University

23. Results: Fixed Gluino Mass • If a measurement of is available, we can use our methods to make a more precise measurement of DM. • We assume a 5% uncertainty on . • This dominates the uncertainty. Masters Defense Texas A&M University

24. Cuts Provide Nearly Background Free Region • Assume: • 50% tau efficiency • 1% fake rate • Cuts: • 2t > 40 GeV • 1t > 20 GeV • Jet 1 > 100 GeV • MET > 100 GeV • Jet 1 + MET > 400 GeV • Mtt < 100 GeV Masters Defense Texas A&M University

25. DMMeasurement • Systematic uncertainty based on 5% variation in gluino mass • We assume a 1% fake rate with 20% uncertainty • For all luminosities with significance > 3s, we are systematic dominated Masters Defense Texas A&M University

26. DM Measurement (MM) • Like the counting method, we are always in a systematic dominated region. Masters Defense Texas A&M University