Tuesday, February 16, 2016

Higgs Boson Is Nearly Purely Scalar

A spin-0 boson may be a pure scalar with even parity, like the hypothetical Standard Model Higgs boson, or may be pseudo-scalar with odd parity, such as a pion (a two quark particle of a type of boson called a meson made of first generation quarks bound by gluons).

In principal, a resonance observed experimentally can also be a mix of scalar and pseudo-scalar bosons of the same spin, and many beyond the Standard Model theories assume the existence of a pseudo-scalar Higgs bosons called A, as well as a light and heavy Higgs boson (H and h).

The latest LHC data finds that the Higgs boson we see experimentally is overwhelmingly scalar and not pseudo-scalar, as predicted by the Standard Model. Specifically, there is a 95% probability that that Higgs boson seen experimentally is at least 99.64% scalar and not more than 0.34% pseudo-scalar.  The best fit value is even more strongly scalar and less strongly pseudo-scalar.

The precision may improve in future experiments, but making a conceptual leap to assume the the measured Higgs boson is a scalar spin-0 boson is not unreasonable.

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