Constraining new physics with B to K* mu+ mu- in the early LHC era

TL;DR

This paper identifies key angular observables in B to K* mu+ mu- decays suitable for early LHC measurements, emphasizing the potential of the S5 observable for discovering physics beyond the Standard Model.

Contribution

It introduces a focus on simple, measurable angular observables, especially S5, and assesses their sensitivity to new physics in early LHC data, including a new decay model for simulations.

Findings

S5 observable provides complementary sensitivity to new physics.

Zero-crossing points of Afb and S5 have reduced theoretical uncertainties.

LHCb can measure these observables with high precision in early data.

Abstract

We investigate the observables available in the angular distribution of B to K* mu+ mu- to identify those suitable for measurements in the first few years of LHC data taking. As experimental uncertainties will dominate, we focus on observables that are simple to measure, while maximizing the potential for discovery. There are three observables that may be extracted by counting signal events as a function of one or two decay angles and correspond to large features of the full angular distribution in the Standard Model: Afb, Fl, and S5. Two of these are well known in the experimental community; however, we show that measuring S5 adds complementary sensitivity to physics beyond the Standard model. Like Afb, it features a zero-crossing point with reduced hadronic uncertainties at leading order and in the large recoil limit. We explore the experimental sensitivity to this point at LHCb and show that it may be measured with high precision due to the steepness of the S5 distribution. Current experimental model independent constraints on parameter space are presented and predictions made for the values of the Afb and S5 zero-crossing points. The relative impact of LHCb measurements of Afb, Fl, and S5, with 2 fb^(-1) of integrated luminosity, is assessed. These issues are explored with a new model of the decay that can be used with standard simulation tools such as EVTGEN.