Light in the beam dump. Axion-Like Particle production from decay photons in proton beam-dumps

Babette Döbrich,Tommaso Spadaro,Joerg Jaeckel

doi:10.1007/jhep05(2019)213

Abstract

The exploration of long-lived particles in the MeV-GeV region is a formidable task but it may provide us a unique access to dark sectors. Fixed-target facilities with sufficiently energetic and intense proton beams are an ideal tool for this challenge. In this work we show that the production rate of Axion-Like-Particles (ALPs) coupled pre-dominantly to photons receives a significant contribution from daughter-photons of secondary π0 and η mesons created in the proton shower. We carefully compare the PYTHIA simulated spectra of such secondaries to experimental literature, compute the ALP flux from the Primakoff conversion of these photons, and finally revisit existing limits on ALPs and update the prospects for a set of existing and future searches. Our results show that taking this production mechanism into account significantly enhances the sensitivity compared to previous studies based on coherent ALP production in primary proton-nucleus interactions.

Highlights

Mechanism, axion-like particle (ALP) may play a crucial role in electroweak symmetry breaking [18] and in the solution of the hierarchy problem
Our results show that taking this production mechanism into account significantly enhances the sensitivity compared to previous studies based on coherent ALP production in primary proton-nucleus interactions
The main aim of the present paper is to study the production of ALPs in proton beam dumps from decay photons of secondary mesons

Summary

Neutral meson yields in proton beam dumps

The simulation of the production rates of secondary mesons is a challenging task, since the formation of mesons is complicated due to non-perturbative physics. A total of 51.2 ± 3.1 % of the produced π0s stem from the decay of secondary particles (mostly mesons) These figures can be compared with the output of the PYTHIA simulation. First we note our expectation that 400 GeV protons interacting with a fixed proton target do not differ significantly from those of a neutron target, as far as the π0 or η production is concerned This is confirmed by the PYTHIA Monte Carlo both for the scattering distributions and cross sections. Measurements of meson yields from a 400 GeV proton beam on beryllium targets have been performed in [46], and data was taken for four values of the secondary particle momenta (60, 120 and 300 GeV) and two values of transverse-momentum (0 and 500 MeV) at different target lengths. On the right-hand-side of figure 4, for completeness we show the proton and anti-proton inclusive invariant cross sections measured at NA56 compared to the expected output from PYTHIA.

Proton beam energies below 400 GeV

Production of ALPs from meson decay photons

Updated sensitivities for fixed-target experiments

Past experiments

Current and future set-ups

Conclusions