Search for a light Higgs boson in the radiative decays of Y(1S)

The Higgs boson is essential to explain the origin of mass of elementary particles within the
Standard Model (SM) via Higgs mechanism through spontaneous breaking of the
electroweak symmetry. The Large Hadron Collider (LHC) experiment at CERN has recently
found an evidence for a Higgs-like state with a mass of ≈ 126 GeV/c2. However, a light
Higgs boson is also predicted by many extensions of the SM including the Next-to-Minimal
Supersymmetric Standard Model (NMSSM). The Higgs sector of the NMSSM contains a
total of three CP-even, two CP-odd and two charged Higgs bosons. The lightest CP-odd
Higgs boson (A0) could have a mass smaller than twice the mass of b-quark, making it
detectable via radiative Y(nS)→γA0 (n=1,2,3) decays. These Υ(nS) resonances have narrow
width and are produced below the BBbar threshold, providing a clean environment for new
physics searches. We search for di-muon decays of a light Higgs boson in the fully
reconstructed decay chain of Y(2S,3S) → π+π- Y(1S), Y(1S)→γA0, A0→μ+μ- using the
datasets of (92.8 ± 0.8) million Υ(2S) and (116.8 ± 1.0) million Υ(3S) events collected by
BaBar experiment at SLAC, USA. The Y(1S) sample is selected by tagging the pion pair in
the Y(2S,3S) → π+π-Y(1S) transitions. We find no evidence for A0 production in the Y(2S)
and Y(3S) datasets and set 90% C.L. upper limits on the product branching fraction
B(Y(1S)→γA0)×B(A0→μ+μ-) as well as effective Yukawa coupling of b-quark to the A0.