The
B
_s meson is a meson composed of a bottom antiquark and a strange quark. Its antiparticle is the
B
_s meson, composed of a bottom quark and a strange antiquark.

B–B oscillations

Strange B mesons are noted for their ability to oscillate between matter and antimatter via a box-diagram with Δm_s = 17.77 ± 0.10 (stat) ± 0.07 (syst) ps⁻¹ measured by CDF experiment at Fermilab.^[1] That is, a meson composed of a bottom quark and strange antiquark, the strange
B
meson, can spontaneously change into an bottom antiquark and strange quark pair, the strange
B
meson, and vice versa.

On 25 September 2006, Fermilab announced that they had claimed discovery of previously-only-theorized B_s meson oscillation.^[2] According to Fermilab's press release:

This first major discovery of Run 2 continues the tradition of particle physics discoveries at Fermilab, where the bottom (1977) and top (1995) quarks were discovered. Surprisingly, the bizarre behavior of the B_s (pronounced "B sub s") mesons is actually predicted by the Standard Model of fundamental particles and forces. The discovery of this oscillatory behavior is thus another reinforcement of the Standard Model's durability... CDF physicists have previously measured the rate of the matter-antimatter transitions for the B_s meson, which consists of the heavy bottom quark bound by the strong nuclear interaction to a strange antiquark. Now they have achieved the standard for a discovery in the field of particle physics, where the probability for a false observation must be proven to be less than about 5 in 10 million (5/10,000,000). For CDF's result the probability is even smaller, at 8 in 100 million (8/100,000,000).^[2]

Ronald Kotulak, writing for the Chicago Tribune, called the particle "bizarre" and stated that the meson "may open the door to a new era of physics" with its proven interactions with the "spooky realm of antimatter".^[3]

Better understanding of the meson is one of the main objectives of the LHCb experiment conducted at the Large Hadron Collider.^[4] On 24 April 2013, CERN physicists in the LHCb collaboration announced that they had observed CP violation in the decay of strange
B
mesons for the first time.^[5][6] Scientists found the B_s meson decaying into two muons for the first time, with Large Hadron Collider experiments casting doubt on the scientific theory of supersymmetry.^[7][8]

CERN physicist Tara Shears described the CP violation observations as "verification of the validity of the Standard Model of physics".^[9]

Rare decays

The rare decays of the B_s meson are an important test of the Standard Model. The branching fraction of the strange b-meson to a pair of muons is very precisely predicted with a value of Br(B_s→ µ⁺µ⁻)_SM = (3.66 ± 0.23) × 10⁻⁹. Any variation from this rate would indicate possible physics beyond the Standard Model, such as supersymmetry. The first definitive measurement was made from a combination of LHCb and CMS experiment data:^[10]

${\displaystyle Br(B_{s}\rightarrow \mu ^{+}\mu ^{-})=2.8_{-0.6}^{+0.7}\times 10^{-9))$

This result is compatible with the Standard Model and set limits on possible extensions.