NA62

NA62 is a fixed-target particle physics experiment at CERN’s Super Proton Synchrotron (SPS) designed to study rare decays of charged kaons (K+). Its primary goal is to measure the branching ratio of the ultra-rare decay K+ → π+ ν ν̄ with high precision, providing a stringent test of the Standard Model and sensitivity to new physics. The program also includes searches for other rare kaon decays and precision tests of fundamental symmetries.

Experimentally, NA62 uses a high-intensity K+ beam produced by 400 GeV protons hitting a target, delivering kaons with a momentum around 75 GeV/c. Kaons in the beam are identified by the KTAG Cherenkov detector, and their momenta are measured by the GTK silicon pixel spectrometer placed upstream of the decay region. Kaon decays occur in a long, evacuated fiducial volume. Downstream, a comprehensive detector suite provides tracking, particle identification, and veto capabilities: a magnetic spectrometer with straw-tube tracking, a Ring Imaging Cherenkov (RICH) detector for pion–muon separation, and the Liquid Krypton (LKr) electromagnetic calorimeter for photons and electrons. A system of photon and charged-particle vetoes, including the large-angle veto (LAV) and other veto detectors, suppresses backgrounds. A dedicated muon veto (MUV) completes the coverage. CHANTI counters near the beam line help veto inelastic interactions.

The K+ → π+ ν ν̄ decay is highly suppressed in the Standard Model, with a clean theoretical prediction and small hadronic uncertainties. Measuring its branching ratio tests the CKM framework and constrains possible new physics contributions. NA62 also explores related rare decays and precision kaon measurements. The collaboration comprises institutions across Europe and beyond and continues data-taking and analysis to achieve its stated precision goals.