Hadronic Background Research Articles

The SIDDHARTA-2 Veto-2 system for X-ray spectroscopy of kaonic atoms at DAΦNE

The Veto-2 is a fundamental component of a multiple-stage veto system for the SIDDHARTA-2 experiment installed at the DAΦNE collider at INFN-LNF in Italy. It was developed to improve the signal-to-background ratio for the challenging measurement of X-ray transitions to the fundamental level in kaonic deuterium. Its purpose is the suppression of hadronic background in the form of Minimum Ionizing Particles by using the topological correlation between signals in the X-ray and Veto-2 detectors. The Veto-2 system consists of a barrel of plastic scintillators read out by Silicon Photomultipliers. The system performed its first successful test run within the apparatus with a helium-4 target in 2022. The efficiency of the Veto-2 was determined and found to be 0.62 ± 0.01. The Veto-2 improved the signal-to-background ratio for the kaonic helium-4 Lα measurement by ∼ 16%, which is crucial due to the low expected X-ray yield of kaonic deuterium.

Potentialities of CdZnTe Quasi-Hemispherical Detectors for Hard X-ray Spectroscopy of Kaonic Atoms at the DAΦNE Collider.

Kaonic atom X-ray spectroscopy is a consolidated technique for investigations on the physics of strong kaon-nucleus/nucleon interaction. Several experiments have been conducted regarding the measurement of soft X-ray emission (<20 keV) from light kaonic atoms (hydrogen, deuterium, and helium). Currently, there have been new research activities within the framework of the SIDDHARTA-2 experiment and EXCALIBUR proposal focusing on performing precise and accurate measurements of hard X-rays (>20 keV) from intermediate kaonic atoms (carbon, aluminum, and sulfur). In this context, we investigated cadmium-zinc-telluride (CdZnTe or CZT) detectors, which have recently demonstrated high-resolution capabilities for hard X-ray and gamma-ray detection. A demonstrator prototype based on a new cadmium-zinc-telluride quasi-hemispherical detector and custom digital pulse processing electronics was developed. The detector covered a detection area of 1 cm2 with a single readout channel and interesting room-temperature performance with energy resolution of 4.4% (2.6 keV), 3% (3.7 keV), and 1.4% (9.3 keV) FWHM at 59.5, 122.1, and 662 keV, respectively. The results from X-ray measurements at the DAΦNE collider at the INFN National Laboratories of Frascati (Italy) are also presented with particular attention to the effects and rejection of electromagnetic and hadronic background.

Readout Electronics for the Zero Degree Calorimeter at HIRFL-CEE Experiment

The CSR External-target Experiment (CEE) at the Heavy Ion Research Facility at Lanzhou (HIRFL) will be the first GeV large-scale nuclear physics experiment developed independently in China. The primary physics goal of the CEE is to study the nuclear equation of state, hyper nuclei, and radioactive ion beam physics. The Zero Degree Calorimeter (ZDC) of CEE measures the centrality and reaction plane of the nuclear-nuclear collision relative to the hadron background. It consists of 192 roughly trapezoidal Plastic Scintillator (PS) crystal blocks coupled with PMT (Photo Multiplier Tube) to convert charged particles into electrical signals. The readout electronics consists of 12 FEE (Front End Electronics), the sub-trigger module, and the sub-clock module. In addition, one HV (High Voltage) crate provides a high voltage power supply for the PMTs. According to the electrical test on the electronics, the RMS (Root Mean Square) noise is less than 0.4 mV, and the nonlinearity is less than 0.06%. The heavy-ion beam test shows that the ZDC can measure particles up to Z=7, which meets the physics requirements.

Commissioning of the electron identification system for Dilepton measurement in pA collisions at J-PARC

Hadron mass spectra are expected to be modified in nuclear matter due to a partial restoration of chiral symmetry. We perform the J-PARC E16 experiment to measure the spectral modification of vector mesons in nuclei. We detect electron–positron pairs from decays of ϕ mesons, produced in 30 GeV pA reactions. It is a key for our experiment to separate electrons from huge hadronic backgrounds. To identify electrons, we developed two-stage detectors comprising hadron blind detectors (HBDs) and lead-glass electromagnetic calorimeters (LGs). These detectors were constructed and installed at the J-PARC high-momentum beamline in 2020, and commissioning runs were performed in 2020 and 2021. The HBDs and the LGs were stably operated at a high counting rate generated in 10-MHz pA interaction at targets, and successfully detected electrons. In the preliminary results, the pion rejection powers were found to be 97.6 ± 0.6% and 91.2 ± 0.7% for the HBD and LG, respectively, which are consistent with the design performance, at the operation thresholds. Further evaluation of electron efficiency is ongoing.

Measurement of the nuclear modification factor for muons from charm and bottom hadrons in Pb+Pb collisions at 5.02 TeV with the ATLAS detector

Heavy-flavour hadron production provides information about the transport properties and microscopic structure of the quark–gluon plasma created in ultra-relativistic heavy-ion collisions. A measurement of the muons from semileptonic decays of charm and bottom hadrons produced in Pb+Pb and pp collisions at a nucleon–nucleon centre-of-mass energy of 5.02 TeV with the ATLAS detector at the Large Hadron Collider is presented. The Pb+Pb data were collected in 2015 and 2018 with sampled integrated luminosities of 208μb−1 and 38μb−1, respectively, and pp data with a sampled integrated luminosity of 1.17pb−1 were collected in 2017. Muons from heavy-flavour semileptonic decays are separated from the light-flavour hadronic background using the momentum imbalance between the inner detector and muon spectrometer measurements, and muons originating from charm and bottom decays are further separated via the muon track's transverse impact parameter. Differential yields in Pb+Pb collisions and differential cross sections in pp collisions for such muons are measured as a function of muon transverse momentum from 4 GeV to 30 GeV in the absolute pseudorapidity interval |η|<2. Nuclear modification factors for charm and bottom muons are presented as a function of muon transverse momentum in intervals of Pb+Pb collision centrality. The bottom muon results are the most precise measurement of b quark nuclear modification at low transverse momentum where reconstruction of B hadrons is challenging. The measured nuclear modification factors quantify a significant suppression of the yields of muons from decays of charm and bottom hadrons, with stronger effects for muons from charm hadron decays.

Potential of CMS as a high-energy neutrino scattering experiment

With its enormous number of produced neutrinos the LHC is a prime facility to study the behaviour of high-energy neutrinos. In this paper we propose a novel search strategy for identifying neutrino scattering via displaced appearing jets in the high granularity calorimeter (HGCAL) of the CMS endcap in the high luminosity run of the LHC. We demonstrate in a cut-and-count based analysis how the enormous hadronic background can be reduced while keeping most of the neutrino signal. This paper serves as a proof-of-principle study to illustrate the feasibility of the first direct observation of high-energetic neutrinos coming from $W$ decays.

A hybrid muon detector design with RPC and plastic scintillator for the experiment at the Super Tau-Charm Facility

The Super Tau-Charm Facility (STCF) is a high-luminosity electron-positron collider project proposed in China. STCF acts as a natural extension of the BEPCII collider. The peak luminosity of STCF is over 50 times higher than that of the BEPCII, greatly benefitting tau-charm physics research. However, it demands a high-performance detector system. To obtain an optimal balance of the μ± identification efficiency and the rejection of charged hadron background, while maintaining a reasonable overall cost, a hybrid muon detector design consisting of three layers of bakelite-RPCs and seven layers of scintillator strips is proposed for the experiment at the STCF. Simulations using the Geant4 package indicate that, in the beam-induced background predicted for the STCF experiment, the identification efficiency for μ± with momenta exceeding 0.8 GeV/c can be higher than 95%, with a 97% π± rejection rate. The identification efficiency for neutrons that are not detected by the electromagnetic calorimeter exceeds 95% for a background rejection rate of 97%. These results demonstrate that the hybrid muon detector design can meet the demands for muon detection in the STCF experiment.

Calibration and performance of the neutron detector onboard of the DAMPE mission

The DArk Matter Particle Explorer (DAMPE), one of the four space-based scientific missions within the framework of the Strategic Pioneer Program on Space Science of the Chinese Academy of Sciences, was successfully launched on 2015 Dec. 17 from Jiuquan launch center. One of the most important scientific goals of DAMPE is to search for evidence of dark matter indirectly by measuring the spectrum of high energy cosmic-ray electrons. The neutron detector, one of the four sub-payloads of DAMPE, is designed to distinguish high energy electrons from hadron background by measuring the secondary neutrons produced in the shower. In this paper, a comprehensive introduction of the neutron detector is presented, including the design, calibration and performance. The analysis with simulated data and flight data indicates a powerful proton rejection capability of the neutron detector, which plays an essential role for TeV electron identification of DAMPE.

Hyperon Structure and CP tests at BESIII

Hyperons are a powerful diagnostic tool that can shed light on some of the most intriguing questions in contemporary physics. Electromagnetic form factors (EMFFs) are currently the best way to study hyperon structure. In the time-like region the EMFFs can be complex with a relative phase. A non-zero phase polarizes the final state even when the initial state is unpolarized. A dedicated data sample collected by the BESIII experiment allowed for a first complete reconstruction of Λ in the time-like region. The ratio, R and relative phase between the electric and magnetic form factor, ΔΦ are measured to be 0.96±0.14(stat)±0.002(syst) and 37°±12°(stat)±6°(syst), respectively. In addition, the BESIII experiment has collected the world’s largest J/ψ data sample. Due to symmetric excellent detector conditions and low hadronic background, the experiment offers a clean environment for CP-violation tests using . That hyperons can be polarized allows for a simultaneous measurement of angular distributions of hyperons and antihyperons and to test CP symmetry directly. This has been done for the process recently measured by the BESIII experiment. The experimental results showed that the asymmetry decay parameter α(Λ → ππ−) = +0.750±0.009±0.004, is nearly twenty percent larger compared to the old PDG tabulated value. The test on CP symmetry, is the most sensitive test for Λ CP-violation. Preliminary results are presented for the process . The asymmetry decay parameter and −0.015 ± 0.037 ± 0.008 are both measured for the first time.

Identification of boosted Higgs bosons decaying into b-quark pairs with the ATLAS detector at 13\xa0text {TeV}

This paper describes a study of techniques for identifying Higgs bosons at high transverse momenta decaying into bottom-quark pairs, H rightarrow bbar{b}, for proton–proton collision data collected by the ATLAS detector at the Large Hadron Collider at a centre-of-mass energy sqrt{s}=13 text {TeV}. These decays are reconstructed from calorimeter jets found with the anti-k_{t}R = 1.0 jet algorithm. To tag Higgs bosons, a combination of requirements is used: b-tagging of R = 0.2 track-jets matched to the large-R calorimeter jet, and requirements on the jet mass and other jet substructure variables. The Higgs boson tagging efficiency and corresponding multijet and hadronic top-quark background rejections are evaluated using Monte Carlo simulation. Several benchmark tagging selections are defined for different signal efficiency targets. The modelling of the relevant input distributions used to tag Higgs bosons is studied in 36 fb^{-1} of data collected in 2015 and 2016 using grightarrow bbar{b} and Z(rightarrow bbar{b})gamma event selections in data. Both processes are found to be well modelled within the statistical and systematic uncertainties.

A muon-based observable for a photon search at 30–300 PeV

The observation of an ultra-high energy photon component of the cosmic radiation is one of the open problems in Astroparticle Physics. The stringent theoretical and experimental upper limits to the photon flux above 100 TeV make the search of a weak photon signal in the vast hadronic cosmic ray background a challenging task. At these energies, photon primaries entering the atmosphere develop an extensive air shower which is driven by electromagnetic processes with a poor muon component. The muon content of the air showers is one of the most promising observables that could lead to the best possible discrimination between photons and hadronic cosmic rays. In this article, we define a parameter capable of quantifying the muon component while reducing the fluctuations due to the unknown lateral distribution of muons. We explain the different features of this observable using simulated air showers between 30 and 300 PeV. We show that a merit factor of 5 in the separation between photon and proton primaries and a photon signal efficiency of at least ∼ 92% while rejecting 99.97% of the proton-initiated showers can be reached in the mentioned energy range of interest. This separation power can be achieved provided the shower features, specially the primary energy, are reconstructed sufficiently precise and without significant biases.

Gamma/Hadron Separation in Imaging Air Cherenkov Telescopes Using Deep Learning Libraries TensorFlow and PyTorch

In this work we compare two open source machine learning libraries, PyTorch and TensorFlow, as software platforms for rejecting hadron background events detected by imaging air Cherenkov telescopes (IACTs). Monte Carlo simulation for the TAIGA-IACT telescope is used to estimate background rejection quality. A wide variety of neural network algorithms provided by both libraries can easily be tested on various types of data, which is useful for various imaging air Cherenkov experiments. The work is a component of the Astroparticle.online project, which collaborates with the TAIGA and KASCADE experiments and welcomes any astroparticle experiment to join.

Search for tau neutrinos with the MAGIC telescopes: improving selection criteria*

MAGIC, a system of two Cherenkov telescopes located at the Roque de los Muchachos Observatory (2200 a.s.l.) in the Canary Island of La Palma, has lately been engaged in an unconventional task: the search for a signature of particle showers induced by earth-skimming cosmic tau neutrinos arising from the ocean, in the PeV to EeV energy range. When pointing at the sea, the MAGIC telescopes can collect data in a range of about 5 deg in zenith and 80 deg in azimuth: the analysis of the shower images from ~30 hours of data, together with the simulations of upward-going tau neutrino showers, shows that the air showers induced by tau neutrinos can be discriminated from the hadronic background coming from a similar direction. We have calculated the point source acceptance and the expected event rates, assuming an incoming v flux consistent with IceCube measurements, and for a sample of generic neutrino fluxes from photohadronic interactions in AGNs and GRBs. A 90% C.L. upper limit on the tau-neutrino point source flux of 2.0 × 10–4 GeV cm–2 s–1 has been obtained. The presented results can also be important for future Cherenkov experiments such as the Cherenkov Telescope Array. This next generation ground-based observatory can have a much better possibility to detect v, given its larger FOV and much larger effective area.

The TAIGA Experiment: From Cosmic Ray Physics to Gamma Astronomy in the Tunka Valley

The article presents the relevance and advantages of the new gamma observatory TAIGA (Tunka Advanced Instrument for cosmic ray physics and Gamma Astronomy), which is being constructed in the Tunka Valley 50 km from Lake Baikal. Various detectors of the six TAIGA gamma observatory arrays register the Cherenkov and radio radiation, as well as the electron and muon components of EAS. The primary objective of the TAIGA gamma observatory is to study the high-energy part of the gamma-ray spectrum, in particular, in order to search for Galactic PeVatrons. The energy, direction, and position of the EAS axis are reconstructed in the observatory based on the data of the wide-angle Cherenkov detectors of the TAIGA-HiSCORE experiment. Taking into account this information, the gamma quanta are distinguished from the hadron background using the data obtained by the muon detectors and telescopes that register the EAS image in the Cherenkov light. In this hybrid mode of operation, the atmospheric Cherenkov telescopes can operate in the mono-mode, and the distance between them can be increased to 800–1000 m, which makes it possible to construct an array with an area of 5 km2 and more at relatively low cost and in a short time. By 2019, the first stage of the gamma observatory with an area of 1 km2 will be constructed; its expected integral sensitivity for detecting the gamma radiation with an energy of 100 TeV at observation of the source for 300 hours will be approximately $$2 \times 5$$ 10–13 TeV cm–2s–1.

Applicability of transverse mass scaling in hadronic collisions at energies available at the CERN Large Hadron Collider

We present a study on the applicability of transverse mass scaling for identified particle spectra in proton-proton collisions at $\sqrt{s}=7$ TeV based on data taken by the ALICE experiment at the LHC. The measured yields are parametrized and compared to estimates obtained from a generalized transverse mass scaling approach applied to different reference particle spectra. It is found that generalized transverse mass scaling is not able to describe the measured spectra over the full range in transverse momentum. At low $p_{\rm T}$, deviations of $20$% or more are obtained, in particular if pions are used as reference particles. A better scaling performance is obtained, when kaons are used as reference particles. At high $p_{\rm T}$ all tested spectra with the possible exception of the charged kaons exhibit a scaling behavior. Investigating the feed-down contributions from resonance decays to the charged pion yields reveals, that using them as reference a general scaling may not be achievable. Our findings imply that for precision measurements of direct photon and di-electron spectra at low transverse momentum one should measure the relevant hadronic background, instead of relying on $m_{\rm T}$ scaling for its estimate.

Muon study for gamma/hadron air-shower discrimination in the HAWC observatory

The High-Altitude Water Cherenkov observatory is a ground-based array designed to study energetic gamma-rays. Experiments with this purpose have to face a huge rate of undesired hadronic background. Motivated by the fact that muon content is quite different in gamma-induced (poor in muons) and hadronic-induced (rich in muons) air-showers, we study the idea of formulating a new variable for background reduction related with counting the number of muons candidates present in such showers. Therefore, in this work we used the time differences between photomultipliers tubes to identify the signature of muons inside the water Cherenkov detectors. Showers with a high presence of muons typically must produce a characteristic time difference around 5 ns among the central detector (PMT_C) and each one of the laterals (PMT: A, B, D).

Expected performance of the ASTRI mini-array in the framework of the Cherenkov Telescope Array

The Cherenkov Telescope Array (CTA) Observatory is a world-wide project for the ground-based study of the sources of the highest energy photons. By adopting telescopes of three different size categories it will cover the wide energy range from tens of GeV up to hundreds of TeV, limited only by the source physical properties and the gamma absorption by the extragalactic background light. The full sky coverage will be assured by two arrays, one in each hemisphere. An array of small size telescopes (SSTs), covering the highest energy region (3-100 TeV), the region most flux limited for current imaging atmospheric Cherenkov telescopes, is planned to be deployed at the southern CTA site in the first phase of the CTA project. The ASTRI collaboration has developed a prototype of a dual mirror SST equipped with a SiPM-based focal plane (ASTRI SST-2M) and has proposed to install a mini-array of nine of such telescopes at the CTA southern site (the ASTRI mini-array). In order to study the expected performance and the scientific capabilities of different telescope configurations, full Monte Carlo (MC) simulations of the shower development in the atmosphere for both gammas and hadronic background have been performed, followed by detailed simulations of the telescopes. In this work the expected performance of the ASTRI mini-array in terms of sensitivity, angular and energy resolution are presented and discussed.

Electron/proton separation and analysis techniques used in the AMS-02 (e+ + e−) flux measurement

AMS-02 is a large acceptance cosmic ray detector which has been installed on the International Space Station (ISS) in May 2011, where it is collecting cosmic rays up to TeV energies. The search for Dark Matter indirect signatures in the rare components of the cosmic ray fluxes is among the main objectives of the experiment. AMS-02 is providing cosmic electrons and positrons data with an unprecedented precision. This is achieved by means to the excellent hadron/electron separation power obtained combining the independent measurements from the Transition Radiation Detector, electromagnetic Calorimeter and Tracker detectors. In this contribution we will detail the analysis techniques used to distinguish electrons from the hadronic background and show the in-flight performances of these detectors relevant for the electron/positron measurements.

Light-flavor squark reconstruction at CLIC

We present a simulation study of the prospects for the mass measurement of TeV-scale light-flavored right-handed squarks at a 3 TeV e+e- collider based on CLIC technology. In the considered model, these particles decay into their standard-model counterparts and the lightest neutralino, resulting in a signature of two jets plus missing energy. The analysis is based on full GEANT4 simulations of the CLIC_ILD detector concept, including Standard Model physics backgrounds and beam-induced hadronic backgrounds from two-photon processes. The analysis serves as a generic benchmark for the reconstruction of highly energetic jets in events with substantial missing energy. Several jet finding algorithms were evaluated, with the longitudinally invariant kt algorithm showing a high degree of robustness towards beam-induced background while preserving the features typically found in algorithms developed for e+e- collisions. The presented study of the reconstruction of light-flavored squarks shows that for TeV-scale squark masses, sub-percent accuracy on the mass measurement can be achieved at CLIC.

Dilepton production and reaction dynamics in heavy-ion collisions at SIS energies from coarse-grained transport simulations

Dilepton invariant-mass spectra for heavy-ion collisions at SIS 18 and BEVALAC energies are calculated using a coarse-grained time evolution from the Ultra-relativistic Quantum Molecular Dynamics (UrQMD) model. The coarse-graining of the microscopic simulations enables to calculate thermal dilepton emission rates by application of in-medium spectral functions from equilibrium quantum-field theoretical calculations. The results show that extremely high baryon chemical potentials dominate the evolution of the created hot and dense fireball. Consequently, a significant modification of the $\rho$ spectral shape becomes visible in the dilepton invariant-mass spectrum, resulting in an enhancement in the low-mass region $M_{ee} = 200$ to 600 MeV/$c^{2}$. This enhancement, mainly caused by baryonic effects on the $\rho$ spectral shape, can fully describe the experimentally observed excess above the hadronic cocktail contributions in Ar+KCl ($E_{\mathrm{lab}}=1.76$ $A$GeV) reactions as measured by the HADES collaboration and also gives a good explanation of the older DLS Ca+Ca ($E_{\mathrm{lab}}=1.04$ $A$GeV) data. For the larger Au+Au ($E_{\mathrm{lab}}=1.23$ $A$GeV) system, we predict an even stronger excess from our calculations. A systematic comparison of the results for different system sizes from C+C to Au+Au shows that the thermal dilepton yield increases stronger ($\propto A^{4/3}$) than the hadronic background contributions, which scale with $A$, due to its sensitivity on the time evolution of the reaction. We stress that the findings of the present work are consistent with our previous coarse-graining results for the NA60 measurements at top SPS energy. We argue that it is possible to describe the dilepton results from SIS 18 up to SPS energies by considering the modifications of the $\rho$ spectral function inside a hot and dense medium within the same model.