Fixed Target Experiments Research Articles

Fully Geant4 compatible package for the simulation of Dark Matter in fixed target experiments

We present the package for the simulation of DM (Dark Matter) particles in fixed target experiments. The most convenient way of this simulation (and the only possible way in the case of beam-dump) is to simulate it in the framework of the Monte-Carlo program performing the particle tracing in the experimental setup. The Geant4 toolkit framework was chosen as the most popular and versatile solution nowadays.Specifically, the package includes the codes for the simulation of the processes of DM particles production via electron and muon bremsstrahlung off nuclei, resonant in-flight positron annihilation on atomic electrons and gamma to ALP (axion-like particles) conversion on nuclei. Four types of DM mediator particles are considered: vector, scalar, pseudoscalar and axial vector. The total cross sections of bremsstrahlung processes are calculated numerically at exact tree level (ETL).The code handles both the case of invisible DM decay and of visible decay into e+e− (μ+μ− for Z′, γγ for ALP).The proposed extension implements native Geant4 application programming interfaces (API) designed for these needs and can be unobtrusively embedded into the existing applications.As an example of its usage, we discuss the results obtained from the simulation of a typical active beam-dump experiment. We consider 5×1012 100 GeV electrons impinging on a lead/plastic heterogeneous calorimeter playing a role of an active thick target. The expected sensitivity of the experiment to the four types of DM mediator particles mentioned above is then derived. Program summaryProgram Title: DMG4CPC Library link to program files:https://doi.org/10.17632/6m3yhx4ssw.1Licensing provisions: GNU General Public License 3Programming language: c++Nature of problem: The optimal way to simulate Dark Matter production processes in fixed target experiments in most cases is to do it inside the program for the full simulation of the experimental setup and not separately, in event generators. The code that can be easily embedded in such programs is needed. The code should be able to simulate various DM production processes that happen in a thick target, in particular on nuclei, with maximal accuracy.Solution method: We created a Geant4 compatible DM simulation package for this purpose. The choice of this simulation framework is suggested by its popularity and versatility. The code includes the cross sections precalculated at exact tree level for a wide variety of DM particles.

Characterization of the slow extraction frequency response

The main physics program of the CERN Super Proton Synchrotron (SPS) is dedicated to the fixed target physics experiments hosted in the North experimental Area (NA). Protons are delivered to the NA via third-integer resonant slow extraction over an almost 5 s flattop. In order to maximize the usable intensity delivered to the experiments, the flux of extracted particles should be kept as constant as possible. This is a very general requirement for fixed target experiments served by synchrotrons. Power supply ripples are a well-known issue in resonant slow extraction, affecting the quality of the spill. A long-standing effort is ongoing at CERN to characterize the SPS slow extraction frequency response to its main power supplies. In this paper, beam dynamics simulations are employed to understand and characterize the process, combined with dedicated beam based measurements.

Target Bypass Beam Optics for Future High Intensity Fixed Target Experiments in the CERN North Area

Target Bypass Beam Optics for Future High Intensity Fixed Target Experiments in the CERN North Area

Constraints on light scalars from PS191 results

We argue that the fixed target experiment PS191 operating on a proton beam of 19.2 GeV at CERN in the eighties was sensitive to hypothetical light scalars produced by mesons and decaying to charged particles. The experiment was dedicated to searches for sterile neutrinos produced in weak meson decays and decaying into final states with pairs of charged particles: electrons and muons. Two charged tracks from the same point have been adopted as the signal signature. Exploiting the same signature we use the negative results of searches at PS191 and place new limits on the light scalars coupled to the Standard Model (SM) particles via mixing with the Higgs boson. In particular, previously allowed region of masses 100–150 MeV and mixing above 4×10−4 is disfavored. Our analysis can be extended straightforwardly to models with other patterns of scalar couplings to SM particles.

Remarks on volume fluctuations in fixed-target heavy-ion experiments

Experimental and theoretical studies of fluctuations in nucleus-nucleus interactions at high energies have started to play a major role in understanding of the concept of strong interactions. The elaborated procedures have been developed to disentangle different processes happening during nucleus-nucleus collisions. The fluctuations caused by a variation of the number of nucleons which participated in a collision are frequently considered the unwanted one. The methods to reduce the impact of these fluctuations in fixed-target experiments are reviewed and tested. They can be of key importance in the following ongoing fixed-target heavy-ion experiments: NA61/SHINE at the CERN SPS, STAR-FXT at the BNL RHIC, BMN at JINR Nuclotron, HADES at the GSI SIS18 and in future experiments such as NA60+ at the CERN SPS, CBM at the FAIR SIS100, JHITS at J-PARC-HI MR.

Invisible decays of axion-like particles: constraints and prospects

Axion-like particles (ALPs) can provide a portal to new states of a dark sector. We study the phenomenology of this portal when the ALP mainly decays invisibly, while its interaction with the standard model sector proceeds essentially via its coupling to electrons and/or photons. We reanalyse existing limits from various collider and beam dump experiments, including in particular ALP production via electron/positron interactions, in addition to the usual production through ALP-photon coupling. We further discuss the interplay between these limits and the intriguing possibility of explaining simultaneously the muon and electron magnetic moment anomalies. Finally, we illustrate the prospects of ALP searches at the LNF positron fixed-target experiment PADME, and the future reach of an upgraded experimental setup.

Dark Photon and Muon g-2 Inspired Inelastic Dark Matter Models at the High-Energy Intensity Frontier.

We study hidden-sector particles at past (CERN-Hamburg-Amsterdam-Rome-Moscow Collaboration and NuCal), present (NA62, SeaQuest, and DarkQuest), and future (LongQuest) experiments at the high-energy intensity frontier. We focus on exploring the minimal vector portal and the next-to-minimal models in which the productions and decays are decoupled. These next-to-minimal models have mostly been devised to explain experimental anomalies while avoiding existing constraints. We demonstrate that proton fixed-target experiments provide one of the most powerful probes for the MeV to few GeV mass range of these models, using inelastic dark matter (iDM) as an example. We consider an iDM model with a small mass splitting that yields the observed dark matter relic abundance, and a scenario with a sizable mass splitting that can also explain the muon g-2 anomaly. We set strong limits based on the CERN-Hamburg-Amsterdam-Rome-Moscow Collaboration and NuCal experiments, which come close to excluding iDM as a full-abundance thermal dark matter candidate in the MeV to GeV mass range. We also make projections based on NA62, SeaQuest, and DarkQuest and update the constraints of the minimal dark photon parameter space. We find that NuCal sets the only existing constraint in ε∼10^{-8}-10^{-4} regime, reaching ∼800 MeV in dark photon mass due to the resonant enhancement of proton bremsstrahlung production. These studies also motivate LongQuest, a three-stage retooling of the SeaQuest experiment with short (≲5 m), medium (∼5 m), and long (≳35 m) baseline tracking stations and detectors as a multipurpose machine to explore new physics.

R -parity violation and light neutralinos at ANUBIS and MAPP

In R-parity-violating supersymmetry the lightest neutralino can be very light, even massless. For masses in the range $500$ MeV$\lesssim m_{\tilde\chi^0_1}\lesssim 4.5$ GeV the neutralino can be produced in hadron collisions from rare meson decays via an R-parity violating coupling, and subsequently decay to a lighter meson and a charged lepton. Due to the small neutralino mass and for small R-parity violating coupling the lightest neutralino is long-lived, leading to displaced vertices at fixed-target and collider experiments. In this work, we study such signatures at the proposed experiments ANUBIS and MAPP at the LHC. We also compare their sensitivity reach in these scenarios with that of other present and proposed experiments at the LHC such as ATLAS, CODEX-b, and MATHUSLA. We find that ANUBIS and MAPP can show complementary or superior sensitivity.

A photogrammetric method for target monitoring inside the MEG II detector.

An automatic target monitoring method based on photographs taken by a CMOS photo-camera has been developed for the MEG II detector. The technique could be adapted for other fixed-target experiments requiring good knowledge of their target position to avoid biases and systematic errors in measuring the trajectories of the outcoming particles. A CMOS-based, high resolution, high radiation tolerant, and high magnetic field resistant photo-camera was mounted inside the MEG II detector at the Paul Scherrer Institute (Switzerland). MEG II is used to search for lepton flavor violation in muon decays. The photogrammetric method's challenges, affecting measurements of low momentum particles' tracks, are the high magnetic field of the spectrometer, high radiation levels, tight space constraints, and the need to limit the material budget in the tracking volume. The camera is focused on the dot pattern drawn on the thin MEG II target, about 1m away from the detector endcaps where the photo-camera is placed. Target movements and deformations are monitored by comparing images of the dots taken at various times during the measurement. The images are acquired with a Raspberry board and analyzed using custom software. Global alignment to the spectrometer is guaranteed by corner cubes placed on the target support. As a result, the target monitoring fulfills the needs of the experiment.

Long-lived sterile neutrinos at the LHC in effective field theory

We study the prospects of a displaced-vertex search of sterile neutrinos at the Large Hadron Collider (LHC) in the framework of the neutrino-extended Standard Model Effective Field Theory (νSMEFT). The production and decay of sterile neutrinos can proceed via the standard active-sterile neutrino mixing in the weak current, as well as through higher-dimensional operators arising from decoupled new physics. If sterile neutrinos are long-lived, their decay can lead to displaced vertices which can be reconstructed. We investigate the search sensitivities for the ATLAS/CMS detector, the future far-detector experiments: AL3X, ANUBIS, CODEX-b, FASER, MATHUSLA, and MoEDAL-MAPP, and at the proposed fixed-target experiment SHiP. We study scenarios where sterile neutrinos are predominantly produced via rare charm and bottom mesons decays through minimal mixing and/or dimension-six operators in the νSMEFT Lagrangian. We perform simulations to determine the potential reach of high-luminosity LHC experiments in probing the EFT operators, finding that these experiments are very competitive with other searches.

Possibilities of Detecting Light Dark Matter Produced via Drell-Yan Channel in a Fixed Target Experiment

This work presents the complete modeling scheme of production and detection of two types of light dark matter (LDM)—Dirac fermionic and scalar particles—in a fixed target experiment using SHiP experiment as an example. The Drell-Yan process was chosen as a channel of LDM production; the deep inelastic scattering on lead nuclei was simulated and analyzed in the detector; the production of secondary particles was modeled with the aid of PYTHIA6 toolkit. Obtained observable parameters of secondary particles produced in events associated with LDM were compared with the background neutrino events that were simulated using GENIE toolkit. The yield of LDM events was calculated with various model parameter values. Using machine learning methods, a classifier that is able to distinguish LDM events from neutrino background events based on the observed parameters with high precision has been developed.

Design of the barrel and endcap DIRC detectors for particle identification in PANDA

The PANDA experiment at the future Facility for Antiproton and Ion Research (FAIR) in Darmstadt/Germany aims to investigate fundamental questions of hadron physics. PANDA is designed as a fixed-target experiment for an antiproton beam with a momentum range of 1.5 GeV/[Formula: see text] to 15 GeV/[Formula: see text]. In order to obtain an excellent particle identification of pions and kaons, two independent DIRC detectors have been developed for two adjacent spatial regions. The Barrel DIRC covers polar angles from [Formula: see text]–[Formula: see text] and performs [Formula: see text] separation with [Formula: see text] or more for momenta from 0.5 to 3.5 GeV/[Formula: see text]. The novel Endcap Disc DIRC (EDD) detector will cover the forward polar angles between [Formula: see text] and [Formula: see text] and will provide a [Formula: see text] separation from 0.5 GeV/[Formula: see text] up to 4 GeV/[Formula: see text] with a separation power at least [Formula: see text]. The design of the Barrel DIRC is based on the successful BaBar DIRC and the SuperB FDIRC R&D with several improvements to optimize the performance for PANDA. Both PANDA DIRC detectors use synthetic fused silica as material for radiators and light guides and lifetime-enhance Microchannel Plate PMTs (MCP-PMTs) as sensors. The Barrel DIRC uses narrow bars as a radiator, a prism-shaped expansion volume and a complex multi-layer spherical lens as focusing system. The Cherenkov radiator for the EDD is a large, 2 cm thick fused silica plate that is divided into four identical quadrants. A combination of bars and cylindrical elements with aluminum coating focus the Cherenkov light on the MCP-PMTs with segmented anode plates. The technical design of the two DIRC detectors and the performance of prototypes, tested in a mixed hadron beam at CERN, will be discussed.

Sub-GeV dark matter production at fixed-target experiments

We analyze the sensitivity of fixed-target experiments to sub-GeV thermal relic dark matter models, accounting for variations in both mediator and dark matter mass, and including dark matter production through both on- and off-shell mediators. It is commonly thought that the sensitivity of such experiments is predicated on the existence of an on-shell mediator that is produced and then decays to dark matter. While accelerators do provide a unique opportunity to probe the mediator directly, our analysis demonstrates that their sensitivity extends beyond this commonly discussed regime. In particular, we provide sensitivity calculations that extend into both the effective field theory regime where the mediator is much heavier than the dark matter and the regime of an off-shell mediator lighter than a dark matter particle-antiparticle pair. Our calculations also elucidate the resonance regime, making it clear that all but a fine-tuned region of thermal freeze-out parameter space for a range of simple models is well covered.

J-PARC heavy ion experiment

J-PARC Heavy Ion project (J-PARC-HI) is a future fixed target experiment to study the properties of the dense matter created by the heavy-ion collisions with 1–12[Formula: see text]AGeV/[Formula: see text] at J-PARC. This project aims to search for the QCD phase boundary and its critical endpoint and to study the equation of state of the dense matter at J-PARC. For this purpose, the high-intensity beam and the precision detector with high-speed DAQ are necessary. J-PARC will be upgraded to produce the world’s highest intensity of heavy-ion beam by adding a new compact heavy-ion linac and a booster ring and utilizing the existing RCS and MR synchrotrons. We will construct the multi-purpose spectrometer with a large acceptance to measure hadrons, dileptons and photons, and their correlations and fluctuations. In these proceedings, we will report the current status of the project, the design of the detector configuration, and detector R&D.

Layouts for fixed-target experiments and dipole moment measurements of short-lived baryons using bent crystals at the LHC

Several studies are on-going at CERN in the framework of the Physics Beyond Collider study group, with main aim of broadening the physics research spectrum using the available accelerator complex and infrastructure. The possibility to design a layout that allows fixed-target experiments in the primary vacuum of the CERN Large Hadron Collider (LHC), without the need of a dedicated extraction line, is part of these studies. The principle of the layouts presented in this paper is to deflect beam halo protons on a fixed-target placed in the LHC primary vacuum, by means of the channeling process in bent crystals. Moreover, the presence of a second bent crystal adjacent to the target opens a unique opportunity for the first direct measurement of electric and magnetic dipole moments of short-lived baryons. Two possible layouts are reported, together with a thorough evaluation on their expected performance and impact on LHC operations.

Status of the GEM/CSC tracking system of the BM@N experiment

Baryonic Matter at Nuclotron (BM@N) is a fixed target experiment at the NICA accelerator complex (JINR) aiming at studies of nuclear matter in relativistic heavy ion collisions. Triple-GEM (Gas electron multiplier) detectors have been identified as suitable for the BM@N central tracking system, which is located inside the analyzing magnet. A cathode strip chamber (CSC) is mounted outside the magnet to improve the momentum resolution of the experimental setup. Seven GEM detectors and one CSC are integrated into the BM@N experimental setup and data acquisition system. The structure of the BM@N GEM and CSC detectors and the results of the study of their characteristics are presented. The full configuration of the GEM/CSC tracking system is shortly reviewed.

Methods for centrality determination in nucleus-nucleus collisions with forward hadron calorimeters at the BM@N experiment

The BM@N (Baryonic Matter at Nuclotron) is the fixed target experiment at the Nuclotron (JINR, Dubna, Russia) accelerator complex. The main goal of the BM@N experiment is studying properties of dense nuclear matter produced in the ion-ion collisions at beam energies up to 4.5 AGeV. First experiments were done for carbon, argon and krypton ions beams with C, Al, Cu and Pb targets. The methods of central events selection on event-by-event base with ZDC (Zero Degree Calorimeter) for these reactions are presented. The new Forward Hadron Calorimeter (FHCal) with transverse and longitudinal segmentation will be used to measure the collision centrality in heavy ion experiments after the BM@N upgrade. The FHCal has the beam hole in the center due to expected high beam intensities. New forward quartz hodoscope is been developed to be placed in the beam hole to measure the charge of fragments. New methods of centrality determination with the FHCal and forward quartz hodoscope are discussed.

MPGD-based photon detectors for the upgrade of COMPASS RICH-1 and beyond

COMPASS is a fixed target experiment at CERN SPS aimed to study hadron structure and spectroscopy. Hadron identification in the momentum range between 3 and 55 GeV/c is provided by a large gaseous Ring Imaging Cherenkov Counter, RICH-1. To cope with the challenges imposed by the new physics program of COMPASS, RICH-1 has been upgraded by replacing four MWPC-based photon detectors with newly developed MPGD-based photon detectors. The architecture of the novel detectors is a hybrid combination of two layers of THGEMs and a Micromegas. The top of the first THGEM is coated with CsI acting as a reflective photo-cathode. The anode is segmented in pads capacitively coupled to the APV-25 based readout. The new hybrid detectors have been commissioned during the 2016 COMPASS data taking and stably operated during the 2017 run. In this paper design, construction, operation and performance aspects of the novel photon detectors for COMPASS RICH-1 are discussed.

Measurements of {Xi }{^-} and overline{Xi }{^+} production in proton\u2013proton interactions at sqrt{s_{NN}} = 17.3\xa0hbox {Ge}hbox {V} in the NA61/SHINE\xa0experiment

The production of Xi (1321)^{-} and overline{Xi }(1321)^{+} hyperons in inelastic p+p interactions is studied in a fixed target experiment at a beam momentum of 158 hbox {Ge}hbox {V}!/!c. Double differential distributions in rapidity {y} and transverse momentum p_{T} are obtained from a sample of 33M inelastic events. They allow to extrapolate the spectra to full phase space and to determine the mean multiplicity of both {Xi }{^-} and overline{Xi }{^+} . The rapidity and transverse momentum spectra are compared to transport model predictions. The {Xi }{^-} mean multiplicity in inelastic p+p interactions at 158 hbox {Ge}hbox {V}!/!c is used to quantify the strangeness enhancement in A+A collisions at the same centre-of-mass energy per nucleon pair.

LSND constraints on the Higgs portal

High-luminosity fixed target experiments provide impressive sensitivity to new light weakly coupled degrees of freedom. We revisit the minimal case of a scalar singlet $S$ coupled to the Standard Model through the Higgs portal, that decays visibly to leptons for scalar masses below the di-pion threshold. The dataset from the LSND experiment is found to impose the leading constraints within two mass windows between $m_S \sim 100$ and 350 MeV. In the process, we analyze a number of scalar production channels in the target, finding that proton bremsstrahlung provides the dominant channel at LSND beam energies.