NA62 Experiment Research Articles

First search for K+ → π0πμe decays

The first search for the lepton number violating decay K+→π0π−μ+e+ and lepton flavour violating decays K+→π0π+μ−e+, K+→π0π+μ+e− has been performed using a dataset collected by the NA62 experiment at CERN in 2016–2018. Upper limits of 2.9×10−10, 3.1×10−10 and 5.0×10−10, respectively, are obtained at 90% CL for the branching ratios of the three decays on the assumption of uniform phase-space distributions.

Probing hidden leptonic scalar portals using the NA64 experiment at CERN

In this study, we demonstrate the potential of the NA64 experiment at CERN SPS to search for New Physics processes involving e→μ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$e\\rightarrow \\mu $$\\end{document} transitions after the collision of 100 GeV electrons with target nuclei. A new Dark Sector leptonic portal in which a scalar boson φ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\varphi $$\\end{document} could be produced in the lepton-flavor-changing bremsstrahlung-like reaction, eN→μNφ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$eN\\rightarrow \\mu N\\varphi $$\\end{document}, is used as benchmark process. In this work, we develop a realistic Monte Carlo simulation of the NA64 experimental setup implementing the differential and total production cross-section computed at exact tree-level and applying the Weiszäcker–Williams phase space approximation. Using this framework, we investigate the main background sources and calculate the expected sensitivity of the experiment. The results indicate that with minor setup optimization, NA64 can probe a large fraction of the available parameter space compatible with the muon g-2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$g-2$$\\end{document} anomaly and the Dark Matter relic predictions in the context of a new Dark Sector leptonic portal with 1011\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$10^{11}$$\\end{document} EOT. This result paves the way to the exploration of lepton-flavour-changing transitions in NA64.

Recent Results and Plans of the NA64 Experiment at the CERN SPS

Recent Results and Plans of the NA64 Experiment at the CERN SPS

Illuminating the dark: mono-γ signals at NA62

Dipole interactions between dark sector states or between a Standard Model particle and a dark state can efficiently be searched for via high-intensity fixed-target facilities. We propose to look for the associated mono-γ signature at the NA62 experiment running in beam dump mode. Focusing on models of dipole inelastic Dark Matter and active-sterile neutrino dipole interactions, we compute the corresponding expected sensitivities finding promising prospects for discovery already with ~ 1017 proton-on-target, corresponding to the present accumulated dataset.

PID-Based Temperature Stabilization for Silicon Photomultipliers Using Thermoelectric Cooling Devices

In this paper, we present a temperature stabilization system for Silicon Photomultipliers (SiPMs) using thermoelectric cooling devices controlled by a PID (Proportional-Integral-Derivative) controller. Maintaining a stable temperature for SiPMs and their associated front-end electronics is crucial for achieving consistent gain and noise minimization. Our system employs three CP1881-222 thermoelectric coolers per module and is managed by two ATMega1284p microcontrollers. One microcontroller handles the PID control routine, while the other functions as a TCP/IP client. The temperature is monitored using PT100 sensors connected via MAX31865 RTD converters, ensuring precise measurements. The PID algorithm efficiently corrects temperature deviations, maintaining an error margin of approximately ±0.2◦C. The system has been successfully deployed in the HASC subdetector of CERN’s NA62 experiment, where it maintains the SiPM temperature at 20.5◦C, enhancing the subdetector’s performance. The modular design of our PID controller system allows for adaptability to various experimental setups requiring precise temperature control.

Search for Leptonic Decays of Dark Photons at NA62.

The NA62 experiment at CERN, configured in beam-dump mode, has searched for dark photon decays in flight to electron-positron pairs using a sample of 1.4×10^{17} protons on dump collected in 2021. No evidence for a dark photon signal is observed. The combined result for dark photon searches in lepton-antilepton final states is presented and a region of the parameter space is excluded at 90% confidence level, improving on previous experimental limits for dark photon mass values between 50 and 600 MeV/c^{2} and coupling values in the range 10^{-6} to 4×10^{-5}. An interpretation of the e^{+}e^{-} search result in terms of the emission and decay of an axionlike particle is also presented.

Readout studies for the HIKE main electromagnetic calorimeter

The High-Intensity Kaon Experiment (HIKE) is a proposed future kaon experiment designed for the CERN SPS accelerator. To cope with a planned increase of beam intensity by a factor of 4 with respect to the current NA62 experiment, the new Main Electromagnetic Calorimeter (MEC) has to provide a similar improvement in time resolution over the current Liquid Krypton calorimeter, down to ≈100ps for a 40GeV photon, while maintaining a comparable energy and spatial resolution. To achieve these goals, the planned detector consists of a shashlik calorimeter paired with high-resolution analog to digital converter for both energy deposit and arrival time estimates, operating at fast sample rates (∼1GHz).This contribution describes a prototype of the readout system using commercial “off-the-shelf” boards. In particular, we focused on feature extraction and tested it using a pulse generator. We included a data readout logic based on the TCP/IP protocol allows for easy deployment in beam tests.

Probing Lepton Flavour Violation with NA64 Experiment

Probing Lepton Flavour Violation with NA64 Experiment

First Results in the Search for Dark Sectors at NA64 with the CERN SPS High Energy Muon Beam

We report the first search for dark sectors performed at the NA64 experiment employing a high energy muon beam and a missing energy-momentum technique. Muons from the M2 beamline at the CERN Super Proton Synchrotron with a momentum of 160 GeV/c are directed to an active target. The signal signature consists of a single scattered muon with momentum <80 GeV/c in the final state, accompanied by missing energy, i.e., no detectable activity in the downstream calorimeters. For a total dataset of (1.98±0.02)×1010 muons on target, no event is observed in the expected signal region. This allows us to set new limits on the remaining (mZ′,gZ′) parameter space of a new Z′ (Lμ−Lτ) vector boson which could explain the muon (g−2)μ anomaly. Additionally, our study excludes part of the parameter space suggested by the thermal dark matter relic abundance. Our results pave the way to explore dark sectors and light dark matter with muon beams in a unique and complementary way to other experiments. Published by the American Physical Society 2024

Development of a new CEDAR for kaon identification at the NA62 experiment at CERN

The NA62 experiment at CERN utilises a differential Cherenkov counter with achromatic ring focus (CEDAR) for tagging kaons within an unseparated monochromatic beam of charged hadrons. The CEDAR-H detector was developed to minimise the amount of material in the path of the beam by using hydrogen gas as the radiator medium. The detector was shown to satisfy the kaon tagging requirements in a test-beam before installation and commissioning at the experiment. The CEDAR-H performance was measured using NA62 data collected in 2023.

A new hydrogen-filled Cherenkov detector for Kaon tagging at the NA62 experiment at CERN

The precision measurement of K + → π + νν̅ at the NA62 experiment requires a kaon identification detector to have a time resolution better than 100 ps, at least 95 % kaon identification efficiency, and a pion misidentification probability of less than 10-4. Since the start of NA62 data taking in 2016, kaon identification has been performed by a differential Cherenkov with achromatic ring focus (CEDAR) detector with a nitrogen gas radiator. A new CEDAR using hydrogen (CEDAR-H) as a radiator gas has been developed to reduce the material in the beamline, reducing the beam particle scattering within the detector.CEDAR-H was validated during a two-week test beam at CERN in 2022 and was approved by the NA62 collaboration for use in data taking from 2023. The test beam results, installation and commissioning in the NA62 beamline are reported.

Test of the vector portal with dark fermions in the charge-exchange reactions in the NA64 experiment at CERN SPS

We consider an experiment to search for dark sector particles in invisible (or semi-invisible) decays of neutral mesons M0=π0, η, η′, ω, f2(1270), which produced the charge-exchange reactions π−+(A,Z)→M0+(A,Z−1);M0→ of high-energy pions (or kaons) on a nuclei target in the NA64 experiment at the CERN SPS. This reaction chain would lead to a striking signature of the signal event—the complete disappearance of the beam energy in the setup []. Using data obtained from the measurements at IHEP (Protvino) and Fermilab (Batavia) we show that the integral cross sections σ for the production of the M0 s slightly deviate from the phenomenological formula σ∼Z2/3, where Z is the nuclei charge. In particular, we present the formulas for the differential and integral cross sections that explicitly depend on the Mandelstam and Z variables. Derived formulas are used to predict the M0 yield as a function of beam energy for several target nuclei, and to estimate the projection sensitivity for the proposed search in the dark vector portal model. Sensitivity to different decay modes of M0s is explored. Published by the American Physical Society 2024

Constant Fraction Discriminator for NA62 experiment at CERN

A new Constant Fraction Discriminator with additionalTime over Threshold measurement capabilities will be presented.It operates in a wide dynamic range of 1:150, with an excellent timeresolution of better than 70 psover one order of magnitude of the input signals.It is highly customizable for different signal shapes and thresholds,using remotely-programmableparameters for Detector Control System commands.Two outputs, each in the Nuclear Instrumentation Module and Low VoltageDifferentialSignaling standards,provide a precise signal arrival time and Time over Thresholdinformation with programmable thresholds.The technical specification and performance measured with cosmic rays and in thehigh-intensity NA62 experiment will be reported.

Measurement of the K+ → π+γγ decay

A sample of 3984 candidates of the K+→π+γγ decay, with an estimated background of 291±14 events, was collected by the NA62 experiment at CERN during 2017–2018. In order to describe the observed di-photon mass spectrum, the next-to-leading order contribution in chiral perturbation theory was found to be necessary. The decay branching ratio in the full kinematic range is measured to be (9.61±0.17)×10−7. The first search for production and prompt decay of an axion-like particle with gluon coupling in the process K+→π+a, a→γγ is also reported.

Light dilaton in rare meson decays and extraction of its CP property

The dilaton ϕ is a pseudo-Nambu-Goldstone boson associated with the spontaneous breaking of scale invariance in a nearly conformal theory, and couples to the trace of the stress-energy tensor. We analyze experimental constraints on a light dilaton with mass in the MeV–GeV range from rare meson decays. New model-independent inclusive bounds for the b → sϕ transition largely exclude the parameter space of a light dilaton that could explain the muon g − 2 anomaly. Despite similarities between a dilaton and a Higgs-portal scalar, the dilaton-photon coupling is enhanced compared to the Higgs-portal scalar due to contributions from loops of the conformal sector. Consequently, the shortened lifetime of the dilaton relaxes bounds from K → π + invisible searches at the NA62 experiment and constraints from the Big Bang Nucleosynthesis. We utilize this fact to search for the dilaton signature at a lepton collider such as the ongoing Belle II experiment. Further, we demonstrate how to extract the CP property of the dilaton using the variation of the differential cross-section of e+e− → e+e−ϕ with the azimuthal angle between the outgoing leptons.

ψ(2S) Suppression in Pb-Pb Collisions at the LHC

The production of the ψ(2S) charmonium state was measured with ALICE in Pb-Pb collisions at sNN=5.02 TeV, in the dimuon decay channel. A significant signal was observed for the first time at LHC energies down to zero transverse momentum, at forward rapidity (2.5<y<4). The measurement of the ratio of the inclusive production cross sections of the ψ(2S) and J/ψ resonances is reported as a function of the centrality of the collisions and of transverse momentum, in the region pT<12 GeV/c. The results are compared with the corresponding measurements in pp collisions, by forming the double ratio [σψ(2S)/σJ/ψ]Pb−Pb/[σψ(2S)/σJ/ψ]pp. It is found that in Pb-Pb collisions the ψ(2S) is suppressed by a factor of ∼2 with respect to the J/ψ. The ψ(2S) nuclear modification factor RAA was also obtained as a function of both centrality and pT. The results show that the ψ(2S) resonance yield is strongly suppressed in Pb-Pb collisions, by a factor of up to ∼3 with respect to pp. Comparisons of cross section ratios with previous Super Proton Synchrotron findings by the NA50 experiment and of RAA with higher-pT results at LHC energy are also reported. These results and the corresponding comparisons with calculations of transport and statistical models address questions on the presence and properties of charmonium states in the quark-gluon plasma formed in nuclear collisions at the LHC. © 2024 CERN, for the ALICE Collaboration 2024 CERN

Physics Beyond the Standard Model with the NA62 Experiment at CERN

Physics Beyond the Standard Model with the NA62 Experiment at CERN

Precision measurements with Kaon decays at CERN

The NA62 experiment at CERN collected the world’s largest dataset of charged kaon decays in 2016–2018, leading to the first measurement of the branching ratio of the ultra-rare K+ → π+vv− decay, based on 20 candidates. Recent results from analyses of K+ → π0e+vγ, K+ → π+µ+µ− and K+ → π+γγ decays, using a data sample recorded in 2017-2018, are reported. Preliminary results of the first observation and analysis of the K± → π0π0µ±v decay, based on the NA48/2 data collected in 2003-2004, are also shown.

Probing invisible vector meson decay mode with the hadronic beam in the NA64 experiment at SPS CERN

Probing invisible vector meson decay mode with the hadronic beam in the NA64 experiment at SPS CERN

Physics beyond the Standard Model with NA62

The NA62 experiment at CERN took data in 2016–2018 with the main goal of measuring the K + → νν̅ decay. The NA62 dataset is also exploited to search for light feebly interacting particles produced in kaon decays. Searches for K + → e + N and K + → μ + N decays, where N is a massive invisible particle, are performed. The N particle is assumed to be a heavy neutral lepton, and the results are expressed as upper limits of 𝒪(10-8) the neutrino mixing parameter |U14|2, where l = e,μ. Dedicated trigger lines were employed to collect di-lepton final states, which allowed stringent upper limits to be established for the rates lepton flavor and lepton number violating kaon decays. Upper limits on the rates of several K + decays violating lepton flavour and lepton number conservation, obtained by analysing this dataset, are presented here.