M. Herndon, Illinois HETEP Seminar March Search for FCNC Decays B s(d) → μ  μ - Matthew Herndon, University of Wisconsin Madison University of Illinois HETEP Seminar, March 2010

M. Herndon, Illinois HETEP Seminar March Standard Model predictions validated to high precision, however Colliders will allow us to establish the nature of this new physics in the laboratory and study it in detail Gravity not a part of the SM What is the very high energy behaviour? At the beginning of the universe? Dark Matter? Astronomical observations of indicate that there is more matter than we see Where is the Antimatter? Why is the observed universe mostly matter? Standard Model fails to answer many fundamental questions Many of those questions come from Astrophysics and Cosmology Why Beyond Standard Model

M. Herndon, Illinois HETEP Seminar March How do you search for new physics at a collider? Direct searches for production of new particles Particle-antipartical annihilation: top quark Indirect searches for evidence of new particles Within a complex process new particles can occur virtually Rare Decays present unique opportunity to find and study new physics LHC is now the energy frontier Tevatron is at an intensity frontier billions B and Charm events on tape So much data that we can look for some very unusual processes Where to look Many weak processes involving B hadrons are very low probability Look for contributions from other low probability processes – Non Standard Model Searches For New Physics

M. Herndon, Illinois HETEP Seminar March Look at processes that are suppressed in the SM Excellent place to spot small contributions from non SM contributions Same particles/vertices occur in both B decay diagrams and in dark matter scattering or annihilation diagrams B s(d) → μ + μ - Beyond the SM B s(d) →  μ  μ - SM: No tree level decay GIM, CKM and helicity suppressed BF(B s →  μ  μ - ) = 3.8x10 -9 New Physics: Loop: MSSM: mSugra, Higgs Doublet Rate  tan 6 β/(M A ) 4 3 orders of magnitude enhancement

M. Herndon, Illinois HETEP Seminar March Tevatron and CDF Tevatron: 2TeV pp collider CDF properties Silicon Tracker |η|<2, 90cm long, r L00 = cm Drift Chamber(COT) 96 layers between 44 and 132cm Muon coverage |η|<1.5 Triggered to |η|<1.0 Outer chambers: high purity muons B s(d) → μ + μ - benefits from more data and the excellent CDF detector Results in this talk uses 3.7fb -1 EXCELLENT TRACKING TRIGGERED TO 1.5 GeV/c

M. Herndon, Illinois HETEP Seminar March Primary problem is large background at hadron colliders Analysis selection must effectively reduce the large background around m Bs = 5.37GeV/c 2 to find a possible handful of events Key elements of the analysis: Design an effective discriminant, determine the efficiency for signal and estimating the background level B s → μμ  Experimental Challenge

M. Herndon, Illinois HETEP Seminar March Di-muon CMU-CMU(X)trigger with 5.0 GeV scaler sum p T CMU: p T (μ) > ~2.0 GeV, |η| ~2.2 GeV, 0.6<|η|<1.0 p T cuts: restrict to a well understood trigger region Apply basic quality cuts Drift chamber tracks with hits in 3 silicon layers Likelihood based muon Id and dE/dx to reject hadrons Vertex quality Loose preselection on analysis cuts P T (μ  μ - ) > 4.0 GeV/c, 3D Decay length significance > 2 Loose isolation and pointing (defined later) Sample still background dominated Expect < 20 B s(d) →  μ  μ - events: based on previous limits 460M Events 55K Events Data Sample TRIGGERS ARE CRITICAL Several Billion B and Charm Events on Tape

M. Herndon, Illinois HETEP Seminar March Relative normalization search Measure the rate of B s(d) → μ + μ - decay relative to B +  J/  K +, J/  →μ + μ - Apply same sample selection criteria Systematic uncertainties will cancel out in the ratios of the normalization Example: muon trigger eff same for J/  or B s  s for a given p T 3 X 10 8 B s events B s(d) → μ + μ - Method

M. Herndon, Illinois HETEP Seminar March Estimate all basic selection acceptances and efficiencies. Identify variables that discriminate signal and background Validate modelling using B + Design multivariate discriminant, NN, for background rejection Unbiased optimization based on Pythia signal MC and part of mass sidebands Validate performance on B + data Estimate combinatoric background level from sidebands Separately estimate B→hh Validate background prediction method in control regions designed to be enhanced in expected backgrounds Check low significance signal regions before highest significance region B s(d) → μ + μ - Method

M. Herndon, Illinois HETEP Seminar March ++ -- L 3D primary vertex di-muon vertex P(  ) L 3D primary vertex di-muon vertex ++ -- P(  ) L 3D - Cut on mass, lifetime, p T, how well p points to the vertex and isolation 55K Events Need to discriminate signal from background Reduce background by a factor of ~ Signal characteristics Final state fully reconstructed B s is long lived (cτ = 438 μm) B fragmentation is hard: few additional tracks Background contributions and characteristics Sequential semi-leptonic decay: b → cμ - X → μ + μ - X Double semileptonic decay: bb → μ + μ - X Continuum μ + μ - μ + fake, fake+fake Partially reconstructed, lower p T, short lived, doesn’t point to the primary vertex, and has additional tracks Signal vs. Background

M. Herndon, Illinois HETEP Seminar March primary discriminating variables Mass m  2.5σ  window: σ = 24MeV/c 2 λ=cτ/cτ Bs, λ/  λ,  α : |φ B – φ vtx | in 3D Isolation: p TB /(  trk + p TB ) p TBs, p T  low Combine in NN Discriminating Variables Unbiased optimization based on simulated signal and data sidebands: 2fb -1 optimization Extensively tested for mass bias Set limits using 3NN bins and 5 mass bins

M. Herndon, Illinois HETEP Seminar March Basic Validation Validation vs. published dataset and B + →J/ψK + MC New data ~1.7fb -1 Upgrade: new trigger acceptance muons cross dead region of tracker Effective 2x upgrade Very stable performance with time

M. Herndon, Illinois HETEP Seminar March Detailed Validation Validation vs. published dataset and B + →J/ψK + MC All preselection variables and discriminating variables p T and iso not expected to agree. Reweighed to match B+ and Bs data

M. Herndon, Illinois HETEP Seminar March NN Validation Discriminating variable validation using: B + →J/ψK + MC p T and isolation reweighing applied NN validation Compare performance on B + →J/ψK + data and MC ~4% difference assigned as a systematic uncertainty ~4% uncertainty from pT and iso reweighing Can reliably estimate efficiency of NN

M. Herndon, Illinois HETEP Seminar March Use independent data samples to test background estimates OS-: opposite sign muons, negative lifetime (signal sample is OS+) SS+ and SS-: same sign muons, positive and negative lifetime. No trigger matching ** OS-, SS: Opposite side B hadrons FM: OS- and OS+: fake μ enhanced, one μ fails the muon Id cuts loose vertex cuts ** FM: False muon backgrounds Compare predicted vs. observed # of bg. events: For multiple NN cuts ++  primary vertex Fake di-muon vertex Control Regions

M. Herndon, Illinois HETEP Seminar March Comparison of control with signal region NN input distributions Do not expect perfect agreement Isolation different for events where muons originate from different b hadrons. Test background prediction method by using sidebands to make predictions in extended signal region Extended to maximize statistics Extended signal region: 4σ(m μμ ), < m μμ < GeV Sideband region: 0.5 GeV on either side of the signal region Control Regions

M. Herndon, Illinois HETEP Seminar March Background predictions and observed background in control regions Control Regions Errors based on statistics of sideband region. 24 Independent checks of the background estimation method

M. Herndon, Illinois HETEP Seminar March Expected Sensitivity Efficiencies and acceptances NN efficiencies , 44% We expect substantial signal! NN>0.8, 1.2 events 0.7 events with NN>0.995 Have reached single event sensitivity to the SM

M. Herndon, Illinois HETEP Seminar March Expected Background Combinatoric backgrounds: from linear fit to sidbands. Highest NN bin. Compare to p0 and exponitial fit for systematic uncertainty. B→hh Use Bs(d) → μ+μ efficiencies with analytic model of B→hh mass shape Convolute with muon fake rates measured in D* data

M. Herndon, Illinois HETEP Seminar March Clearly peaks in signal region Sideband estimates not useful Convolute known branching ratios and acceptance with K and  fake rates. All decays observed/measured at CDF N B s Mass Window N B d Mass Window NN> B  hh background small but not negligible B  hh Background Small for Bs Order of magnitude larger for Bd

M. Herndon, Illinois HETEP Seminar March Expected and Observed Data

M. Herndon, Illinois HETEP Seminar March DiMuon Mass vs. NN Mass distributions in three NN bins and vs NN for UU and UX combined Bs NN>0.995, 6 background expected, 7 events observed, signal 0.7

M. Herndon, Illinois HETEP Seminar March B s(d) → μ + μ - Limits Set limits using CLs methodology Systematic uncertainties included Cross check using Bayesian method, consistent at 5% level Limit 4.3x10 -8 (3.3x10 -8 expected) PVAL 23%, sigma D0 expected sensitivity with 5fb -1 : 5.3x10 -8 Previous CDF result with 1.9fb -1 : 5.8x10 -8 (4.8x10 -8 expected) CDF continues to have the world’s best limits Analysis now background limited and reaching a sensitivity where SM signal is substantial!

M. Herndon, Illinois HETEP Seminar March History and Future

M. Herndon, Illinois HETEP Seminar March Strongly limits specific SUSY models: SUSY SO(10) models Allows for massive neutrino Incorporates dark matter results BF(B s   +  - ) < 4.3x10 -8 at 95% CL BF(B s   +  - ) = 1.0x10 -7 BF(B s   +  - ) = 5x10 -8 Dark matter constraints L. Roszkowski et al. JHEP Excluded! Typical example of SUSY Constraints However, large amount of recent work specifically on dark matter B s → μ + μ -  Physics Reach A previous result circa 2005

M. Herndon, Illinois HETEP Seminar March S. Baek, D.G. Cerdeno Y.G. Kim, P. Ko, C. Munoz, JHEP , 2005 B s → μ + μ -  and Dark Matter Excluded by new B s →  μ  μ - tan  =50 B s →  μ  μ - correlated to dark matter searches CMSSM supergravity model B s →  μ  μ - and neutralino scattering cross sections are both a strong function of tanβ In focus point region, high tanβ(50), positive μ, favoured in CDM allowed fits Current bounds on B s →  μ  μ - exclude parts of the dark matter parameter space

M. Herndon, Illinois HETEP Seminar March Best B s and B d results: well ahead of D0 and the B factories Limit excludes allowed parameter space of SO(10) models Expanding sensitivity to interesting areas of MSSM parameter space Results correlated with some of the other most interesting topics in physics such as Higgs searches and dark matter! B (s,d) →  μ + μ -  results BF(B s   +  - ) < 4.3x10 -8 at 95% CL BF(B d   +  - ) < 7.6x10 -9 at 95% CL Worlds Best Limits! Conclusions

M. Herndon, Illinois HETEP Seminar March Backup

M. Herndon, Illinois HETEP Seminar March B Physics constraints impact dark matter in two ways Dark matter annihilation rates Interesting for indirect detection experiments Annihilation of neutralinos Dark matter scattering cross sections Interesting for direct detection experiments Nucleon neutralino scattering cross sections Models are (n,c)MSSM models with constraints to simplify the parameter space: Key parameters are tanβ and M A as in the flavour sector along with m 1/2 Two typical programs of analysis are performed Calculation of a specific property: Nucleon neutralino scattering cross sections Constraints from B s(d) →  μ  μ - and b  s  as well as g-2, lower bounds on the Higgs mass, precision electroweak data, and the measured dark matter density. General scan of allowed SUSY parameter gives ranges of allowed values Results can then be compared to experimental sensitivities B Physics and Dark Matter

M. Herndon, Illinois HETEP Seminar March Informs you about what types of dark matter Interactions are interesting H. Baer et. al. What’s consistent with the constraints? There are various areas of SUSY parameter space that are allowed by flavour, precision electroweak, WMAP Stau co-annihilation Funnel Bulk Region Low m 0 and m 1/2, good for LHC Focus Point Large m 0 neutralino becomes higgsino like Enhanced Higgs exchange scattering diagrams Disfavoured by g-2, but g-2 data is controversial TeV SUSY and Dark Matter

M. Herndon, Illinois HETEP Seminar March An analysis uses all available flavour constraints B s →  μ  μ -, b  s ,B s Oscillations, B   CMSSM - constrained so that SUSY scalers and the Higgs and the gauginos have a common mass at the GUT scale: m 0 and m 1/2 respectively J. Ellis, S. Heinemeyer, K. Olive, A.M Weber and G. Weiglein hep-ph/ Focus Point Stau co-annihilation Definite preferred neutralino masses ~ This region favoured because of g-2 Flavour Constraints on m 

M. Herndon, Illinois HETEP Seminar March Putting everything together including most recent theory work on b  s  R. Austri, R. Trotta, L. Roszkowski, hep-ph/ Current experiments starting to probe interesting regions Analysis shows a preference for the Focus Point region, g-2 deweighted Higgsino component of Neutralino is enhanced. Enhances dominant Higgs exchange scattering diagrams Interesting relative to light Higgs searches at Tevatron and LHC Probability in some regions has gone down However… S. Baek, et.al.JHEP , 2005 B Physics and Dark Matter

M. Herndon, Illinois HETEP Seminar March S. Baek, D.G. Cerdeno Y.G. Kim, P. Ko, C. Munoz, JHEP , 2005 B s → μ + μ -  and Dark Matter Excluded by new B s →  μ  μ - tan  =50 B s →  μ  μ - correlated to dark matter searches CMSSM supergravity model B s →  μ  μ - and neutralino scattering cross sections are both a strong function of tanβ In focus point region, high tanβ(50), positive μ, CDM allowed Current bounds on B s →  μ  μ - exclude parts of the dark matter parameter space