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Search for light CP-odd Higgs decay with a charm tag at BABAR

This study presents the search for a light CP-odd Higgs (A0) decaying into charm quarks using the BABAR detector. The analysis utilizes data taken at the Y(2S) resonance and excludes the mass range 8.95-9.1 GeV/c2.

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Search for light CP-odd Higgs decay with a charm tag at BABAR

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  1. Search for light CP-odd Higgs decay with a charm tag at BABAR Richard Kass Ohio State University On behalf of the BABAR Collaboration Phys. Rev. D. 91, 071102 (2015) Richard Kass

  2. Search Motivation Many extensions of the Standard Model (SM) include a CP-odd Higgs boson If light enough a CP-odd Higgs (A0) can be produced via bottomonium decays: ϒ→γA0 The region mA0 < 2mb not constrained by LEP results Good region for B-factories Many previous A0 BaBar searches Richard Kass

  3. Light CP-odd Higgs In next-to-MSSM there are 7 scalar fields including a CP odd Higgs: A0 = cosθAAMSSM+sinθAAs Branching fraction can be “large”: BR(Y->γA0) =>10-7 - 10-4 For small values of tanβ& mA0 > 2mcBR(A0->cc) can be large: 0.1-1 R. Dermisek et al. PRD 76, 051105 (2007) R. Dermisek et al. PRD 81, 075003 (2010) BR(A0 ->cc) BR(Y->γA0) BR(A0 ->cc) mA0 GeV Also predictions for τ+τ-, μ+μ-, gg, ss A0 ●mA0<2mτ ●2mτ<mA0<7.5 GeV ●7.5 GeV<mA0<8.8 GeV ●8.8 GeV<mA0<9.2GeV Richard Kass

  4. BaBar Detector 1.5 T Solenoid Electromagnetic Calorimeter (EMC) Detector of Internally Recflected Cherenkov Light (DIRC) e+ (3.1 GeV) e- (9 GeV) Drift Chamber (DCH) Instrumented Flux Return (IFR) Silicon Vertex Tracker (SVT) SVT, DCH: charged particle tracking: vertex & mom. resolution, K0s/Λ EMC: electromagnetic calorimeter: g/e/π0/η DIRC, IFR, DCH: charged particle ID:π/μ/K/p Highly efficient trigger for B,c meson, qq, tau events NIM A479, 1 (2002) NIM A729, 615 (2013) Richard Kass Richard Kass 4

  5. BaBar Data Set Took data 1999-2008 at PEP-II asymmetric e+e- collider: This analysis uses data taken at Y(2S) 98x106 events, 13.6fb−1 on peak, 1.4fb−1 off peak CUSB Richard Kass

  6. Selection of Events-I Get a clean sample of Υ(1S) decays: Tag Υ(2S) -> Υ(1S) π+π- Gives a cleaner sample of events than using Υ(2S) -> gA0 Recoiling mass (mR) against dipions consistent with Υ(1S) |mΥ(1S) –mR|< 10 MeV/c2 Search for Υ(1S) -> γ A0 A0 -> ccwith a reconstructed charm meson (“tag”) Charm tags: D0->K-π+ /D0->K-π+ π+π-/D0->Ksπ+π- D+->K-π+ π+/D*+->π+D0 [D0->K-π+π0] Richard Kass

  7. Selection of Events-II Use a Boosted Decision Tree (BDT) to separate signal & background 24 variables input into BDT: 2 event variables 10 kinematic variables (main power) e.g. D0 mass, g energy… 3 vertex variables 3 event shape 6 CM opening angle variables e.g. angle between D&g…. Divide data into low & high mass Off resonance data (pts) Vs e+e-->qq MC (hist.) High mass Low mass Low mass: 4.00 ≤ mX ≤ 8.00 GeV/c2 High mass: 7.50 ≤ mX ≤ 9.25 GeV/c2 Richard Kass

  8. Analysis Details-I Low mass: 4.00 ≤ mX ≤ 8.00 GeV/c2 Search for a narrow peak in the low and high mX regions low mass 9.8k candidates high mass 7.4M candidates Exclude 8.95 ≤ mX ≤ 9.1 GeV/c2 to avoid Y(2S)->χB->Y(1S) NO obvious peaks…. High mass: 7.50 ≤ mX ≤ 9.25 GeV/c2 χBremoved Richard Kass

  9. Analysis Details-II A0 signal mX is modeled with a crystal ball (CB) function Width of Gaussian component of CB functions varies with mX Natural A0 width is expected to be small compared to detector resolution Mass resolution improves with increasing (decreasing) mX (Eγ). Reconstruction efficiency varies with mX: 4%@ 4.00 GeV/c2, 2.6% %@ 9.25 GeV/c2 Includes: cc hadronization, BFs, detector acceptance, BDT selection Systematic error is dominated by cc hadronization ~10% Also: signal PDF shape, D mass PDF, dipion BF & pdf, MC stats, γeff., NY(2S) Richard Kass

  10. Results from fits Perform binned extended maximum likelihood fits in the low & high mX regions: 10 MeV steps for low mX 2 MeV steps for high mX Signal PDF: Crystal Ball (fixed) Bkgd PDF: 2nd order polynomial (float) Output of fit: Nsig, Nbkg 3 polynomial parameters NO significant signal Largest “signal”: 2.3σ (low mass region) local significance. Low mass: 4.00 ≤ mX ≤ 8.00 GeV/c2 2.3σ 4.145 GeV/c2 High mass: 7.50≤mX≤9.25 GeV/c2 2.0σ 8.411 GeV/c2 Richard Kass

  11. A0->cc Search Results Produce 90% CL upper limits for B(Υ(1S) -> γ A0)xB(A0->cc) 90% CL upper limits range from 7.4x10-5 to 2.4x10-3 Richard Kass

  12. Summary Significant constraints on new physics from B-factories Many BaBar searches for low mass CP-odd Higgs, A0 Latest search: No evidence for A0->cc via Y(1S) decay Details in: Phys. Rev. D. 91, 071102 (2015) Richard Kass

  13. Extra Slides Richard Kass

  14. A0 branching fractions Dermisek & Gunion, Phys. Rev. D 81, 075003 (2010) Richard Kass

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