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AMBER -- A Strong-Interaction Facility at CERN

Bernhard Ketzer, Michela Chiosso

TL;DR

AMBER addresses open questions in hadron structure by exploiting high-intensity muon and hadron beams available only at CERN's M2 line. The paper outlines Phase-1 goals—precise antiproton-production cross sections for indirect dark-matter searches, a high-precision proton electric form factor from elastic $\mu$–$p$ scattering, and meson quark-structure studies via $Drell–Yan$ and charmonium production with $\pi^\pm$ and $K^\pm$ beams—with Phase-2 planned for an intense kaon-beam program. It reports 2023–2024 antiproton cross-section measurements and a successful 2025 commissioning of the PRM detector system, paving the way for a 2026 $\mu$–$p$ elastic-scattering run. The experimental strategy relies on a fixed-target setup, a high-precision spectrometer, and a free-streaming DAQ with online high-level triggering to identify complex final states. The anticipated outcomes include reduced uncertainties in cosmic-ray antiproton fluxes, resolution of the proton-radius puzzle, and a comprehensive map of meson structure, contributing to a deeper understanding of QCD.

Abstract

AMBER (NA66) is a fixed-target facility at the M2 beam line of CERN SPS, which performs worldwide unique research on the internal structure and the excitation spectrum of hadrons. The approved first phase of the experiment focuses on three main physics topics: (i) the measurement of the production cross section of antiprotons in $p-\text{He}$ and $p-p/d$ collisions over a wide energy range; (ii) the precise measurement of the electric form factor of protons at small momentum transfers using a high-energy muon beam; (iii) the determination of pion and kaon quark PDFs through Drell-Yan and charmonium production measurements with negative and positive meson beams. Phase-2 will focus on measurements with an intense kaon beam. The high-energy muon, pion and kaon beams required for these measurements are only available at CERN.

AMBER -- A Strong-Interaction Facility at CERN

TL;DR

AMBER addresses open questions in hadron structure by exploiting high-intensity muon and hadron beams available only at CERN's M2 line. The paper outlines Phase-1 goals—precise antiproton-production cross sections for indirect dark-matter searches, a high-precision proton electric form factor from elastic – scattering, and meson quark-structure studies via and charmonium production with and beams—with Phase-2 planned for an intense kaon-beam program. It reports 2023–2024 antiproton cross-section measurements and a successful 2025 commissioning of the PRM detector system, paving the way for a 2026 – elastic-scattering run. The experimental strategy relies on a fixed-target setup, a high-precision spectrometer, and a free-streaming DAQ with online high-level triggering to identify complex final states. The anticipated outcomes include reduced uncertainties in cosmic-ray antiproton fluxes, resolution of the proton-radius puzzle, and a comprehensive map of meson structure, contributing to a deeper understanding of QCD.

Abstract

AMBER (NA66) is a fixed-target facility at the M2 beam line of CERN SPS, which performs worldwide unique research on the internal structure and the excitation spectrum of hadrons. The approved first phase of the experiment focuses on three main physics topics: (i) the measurement of the production cross section of antiprotons in and collisions over a wide energy range; (ii) the precise measurement of the electric form factor of protons at small momentum transfers using a high-energy muon beam; (iii) the determination of pion and kaon quark PDFs through Drell-Yan and charmonium production measurements with negative and positive meson beams. Phase-2 will focus on measurements with an intense kaon beam. The high-energy muon, pion and kaon beams required for these measurements are only available at CERN.
Paper Structure (5 sections, 3 figures)

This paper contains 5 sections, 3 figures.

Table of Contents

  1. Introduction
  2. Antiproton production cross sections for dark matter search
  3. Measuring the proton radius
  4. Investigating the quark structure of mesons
  5. Conclusions and outlook

Figures (3)

  • Figure 1: Statistical uncertainties on the number of antiprotons in different bins in momentum and $p_T$ for the 2023 $p-{\rm He}$ data collected at $\sqrt{s_{{\rm NN}}} = 18.9$ GeV/c.
  • Figure 2: AMBER experimental setup for the PRM programme. (a) Photograph of the target region. (b) (Top) Schematics of the target region with the high-pressure TPC in the centre. (Bottom) Complete spectrometer.
  • Figure 3: (a) Final installation work on the AMBER TPC in the experimental hall, (b) inner view of a Unified Tracking Station (UTS): an SPD plane in the foreground, mounted in front of an SFH station in the background.