Evaluating the charged background rejection requirement in an experiment to measure $\rm BR(K_L \to \pi^0 \nu \bar{\nu})$ at the CERN SPS

TL;DR

This paper assesses the necessary charged background rejection level for an experiment measuring the rare decay $K_L o \pi^0 u ar{ u}$ at CERN, aiming to distinguish true signals from background noise with high precision.

Contribution

It provides a detailed evaluation of the charged background rejection requirement, quantifying the reduction factor needed to achieve the desired signal-to-background ratio.

Findings

Charged background must be reduced by a factor of 1/(3×10^9).

Achieving this reduction is crucial for the experiment's success.

The study informs detector design and background suppression strategies.

Abstract

Measuring the rate at which the long-lived, neutral kaon decays into a neutral pion, neutrino, and anti-neutrino allows physicists an opportunity to test precise predictions made by the Standard Model. Differences between theoretical predictions and experimental measurements may point to new physics. Not only does the Standard Model predict a very low probability at approximately 3 $K_L \to \pi^0 \nu \bar{\nu}$ decays in 100 billion $K_L$ decays, but many of the common decays leave false signals in the detector that look the same as the true signal. Charged decays have been studied to determine the required detection efficiency necessary to eliminate them. The conclusion of these studies is that a reduction by a factor of $1/(3\times10^9)$ will be required to achieve the 10:1 signal to charged background ratio necessary for the experiment.