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Rare Decays at D0

Rare Decays at D0. Rare Decays at D0 D. Buchholz – Northwestern University For the D0 Collaboration. Flavor Changing Neutral Currents. Standard Model and data agree remarkably well Standard Model forbids FCNC at tree level Look for deviations from SM

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Rare Decays at D0

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  1. Rare Decays at D0 • Rare Decays at D0 • D. Buchholz – Northwestern University • For the D0 Collaboration D. Buchholz, Rare Decays at D0, ICHEP 2008

  2. Flavor Changing Neutral Currents • Standard Model and data agree remarkably well • Standard Model forbids FCNC at tree level • Look for deviations from SM • One place to search for new physics is in FCNC decays • FNAL’s Tevatron has large c and b cross sections • Challenge- how to select c and b decays from much larger inelastic total σ • Trigger on single μ from semileptonic or leptonic decays D. Buchholz, Rare Decays at D0, ICHEP 2008

  3. D+(s)→π+μ+μ- Example of beyond tree level diagram in SM for D+→π+μ+μ- • Look in the up quark sector c→ u μμ • Expect long distance resonance production, e.g. c→ u , which is not a test of FCNC • BR =1.9X10-6 • Short range continuum production , test of FCNC • Modification to SM- e.g. • Fajfer et al, PRD 73, 054026 (2006) – effect of light Higgs • Burdman et al., PRD 66 014009, (2002) – RPV in up sector but not in down sector D. Buchholz, Rare Decays at D0, ICHEP 2008

  4. Resonant D+(s) Decays • Resonant production • Select  region for m(μμ) • N(Ds+)=254±36 • N(D+) = 115±31 • Statistical Significance • 8σ for combined Ds+ and D+ • 4.1 σ for D+ • First observation for Ds+ • First evidence for D+ • Measure BR(D+→ π+→μ+μ-π+) • (1.8±0.5±0.6)x10-6 D. Buchholz, Rare Decays at D0, ICHEP 2008

  5. Continuum D+(s) Decays • Remove resonant  →μ+μ- mass region and then look in m(μ+μ-π+) • leaves 19 candidates in D+ window • Background expect from sidebands 25.8±4.6 • Normalize to D+→ π+ • BR(D+→ μ+μ-π+) • <3.9x10-6 @90%CL • PRL 100, 101801 (2008) D. Buchholz, Rare Decays at D0, ICHEP 2008

  6. Purely Leptonic B decays • Look for B0→ℓ+ℓ-, either from B0d or B0s • Helicity suppressed FCNC • SM predicts Buras- Phys Lett B566, 115 (2003) • BR(B0s→μ+μ-) =(3.4 ± 0.54)x10-9 • BR(B0d→μ+μ-) =(1.0 ± 0.14)10-9; suppressed by |Vtd/Vts|2 ~ 0.04 • Depends on one SM operator in effective Hamiltonian with small hadronic uncertainties • To reach SM limit for B0→ℓ+ℓ- • Current limits B0s→ μ+μ- is closest D. Buchholz, Rare Decays at D0, ICHEP 2008

  7. Analysis Process for B0(s)→μ+μ- • Dimuon trigger • Select broad mass range • Optimize selection- • use likelihood ratio method based on 6 exp variables - LHR • Blind analysis in B mass region • Normalize to B±→J/ΨK±, J/Ψ→μ+μ- • to get a branching ratio D. Buchholz, Rare Decays at D0, ICHEP 2008

  8. Look for B0(s)→μ+ μ- decays • Separate data into Run IIa and IIb • Plot Invariant μ+ μ-mass vs. LHR • Cut on LHR to get final number of μ+ μ- in B0 region and sidebands • 1 event in Run IIa • 2 events in Run IIb • Consistent with background • Preliminary result • BR(B0s→ μ+μ-)<7.3 x10-8 • D0 Conf. Note 5344 D. Buchholz, Rare Decays at D0, ICHEP 2008

  9. CPV and Bs→Ds(*)Ds(*) Partial width difference between CP even and CP odd Bs decays ≈ saturated by the Bs→Ds(*)Ds(*) branching fraction No CPV Also traces out contour in DG/fs plane with CPV See poster session- SungWoo Youn from D0 for Bs→Ds(*) Ds(*) details Projection from J/yf Projection from Ds(*)Ds(*) Not used in constraints b/c theory error uncontrolled Odd fraction of Ds(*)Ds D. Buchholz, Rare Decays at D0, ICHEP 2008

  10. Finding Bs→Ds(*)Ds(*) Extracted using one semileptonic Ds decay and normalized to Bs→Dsmn Use Likelihood ratio method for analysis Signal extracted from 2-D unbinned log-likelihood fit to m(Ds)-m(f) plane p m(KKp) g K Bs K DsDs K K g m n m(KK) D. Buchholz, Rare Decays at D0, ICHEP 2008

  11. Extract Background from Bs→Ds(*)Ds(*) ~10% Residual backgrounds from Bu,d and Bs semileptonic decay subtracted by looking in 2-D m(fm)-m(Dsfm) plane B→DsDsKX Bs→Dsfmn D. Buchholz, Rare Decays at D0, ICHEP 2008

  12. Bs→Ds(*)Ds(*) preliminary results Statistics at 2.8 fb-1 Accelerator division will reduce this Sys dominated by input Bs and Ds BFs Need help from CLEO-c and Belle ϒ(5S) Consistent with standard model- see poster of SungWoo Youn D. Buchholz, Rare Decays at D0, ICHEP 2008

  13. Conclusions • D0 very active in decay studies of FCNC • B0s→ μ+μ- • D+→μ+μ-π+ • Adding information on existing puzzles • CPV from fswithDs(*)Ds(*) • Tevatron contributing to rare heavy quark decays • Rare bottom and ultra rare charm • More statistics to come D. Buchholz, Rare Decays at D0, ICHEP 2008

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