Towards a test of the Born rule in high-energy collisions

TL;DR

This paper explores how to experimentally test the Born rule in high-energy particle collisions, focusing on spin and polarization probabilities, and discusses the challenges in repurposing existing collider experiments for such tests.

Contribution

It proposes a framework for testing the Born rule at short timescales in high-energy collisions using spin and polarization measurements, highlighting potential experimental approaches.

Findings

Identification of collider experiments suitable for Born rule tests

Proposal of nonlinear expectation values as indicators of violations

Discussion of challenges in experimental implementation

Abstract

We consider how the Born rule, a fundamental principle of quantum mechanics, can be tested for particles created on the shortest timescales ($\sim10^{-25}\,\mathrm{s}$) currently accessible at high-energy colliders. We focus on targeted tests of the Born rule for spin or polarisation probabilities, which offer a particularly clean experimental signal, and which can be described by a simple hidden-variables model of two-state systems proposed by Bell. These probabilities test a remarkable feature of the quantum formalism, whereby expectation values for incompatible experiments are linearly related. Born-rule violations can be parameterised by nonlinear expectation values for quantum measurements of spin or polarisation, together with anomalies in ensemble averages, which may then be constrained by experiment. Notable experiments considered here include the recent detection of single photons from top-quark decay, and the indirect measurement of tau-lepton polarisation. Repurposing these experiments as tests of the Born rule, however, presents several challenges, which are discussed in this paper.