Liquid Hydrogen Target Research Articles

Experimental Study of Cold Dense Nuclear Matter

The fundamental theory of nuclear interactions, Quantum Chromodynamics (QCD), operates in terms of quarks and gluons at higher resolution. At low resolution the relevant degrees of freedom are nucleons. Two-nucleon Short-Range Correlations (SRC) help to interconnect these two descriptions. SRCs are temporary fluctuations of strongly interacting close pairs of nucleons. The distance between the two nucleons is comparable to their radii and their relative momenta are larger than the fermi sea level. According to the electron scattering experiments held in the last decade, SRCs have far-reaching impacts on many-body systems, the nucleon-nucleon interactions, and nuclear substructure. The modern experiments with ion beams and cryogenic liquid hydrogen target make it possible to study properties of the nuclear fragments after quasi-elastic knockout of a single nucleon or an SRC pair. Here we review the status and perspectives of the SRC program in so-called inverse kinematics at JINR (Dubna, Russia). The first SRC experiment at the BM@N spectrometer (2018) with 4 GeV/c/nucleon carbon beam has shown that detection of an intact 11B nucleus after interaction selects out the quasi-elastic knockout reaction with minimal contribution of initial- and final-state interactions. Also, 25 events of SRC-breakups showed agreement in SRC properties as known from electron beam experiments. The analysis of the second measurement of SRC at BM@N held in 2022 with an improved setup is currently ongoing. The SRC project at JINR moved to a new experimental area in 2023, where the next measurement is being planned in terms of experimental setup and physics goals.

Investigation of the Σ0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\mathbf {\\Sigma ^{0}}$$\\end{document} Production Mechanism in p(3.5 GeV)+p Collisions

The production of Σ0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\Sigma ^{0}$$\\end{document} hyperons in proton proton collisions at a beam kinetic energy of 3.5 GeV impinging on a liquid hydrogen target was investigated using data collected with the HADES setup. The total production cross section is found to be σ(pK+Σ0)=17.7±1.7(stat)±1.6(syst)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\sigma (pK^{+}\\Sigma ^{0}) = 17.7 \\pm 1.7 (stat) \\pm 1.6 (syst)}$$\\end{document} µb. Differential cross section distributions of the exclusive channel pp→pK+Σ0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${pp \\rightarrow pK^{+}\\Sigma ^{0}}$$\\end{document} were analyzed in the center-of-mass, Gottfried–Jackson and helicity reference frames for the first time at the excess energy of 556 MeV. The data support the interplay between pion and kaon exchange mechanisms and clearly demonstrate the contribution of interfering nucleon resonances decaying to K+Σ0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ extrm{K}^{+}\\Sigma ^{0}$$\\end{document}. The Bonn–Gatchina partial wave analysis was employed to analyse the data. Due to the limited statistics, it was not possible to obtain an unambiguous determination of the relative contribution of intermediate nucleon resonances to the final state. However nucleon resonances with masses around 1.710 GeV/c2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\ extrm{GeV}/\ extrm{c}^{2}}$$\\end{document} (N∗(1710)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\ extrm{N}^{*}(1710)}$$\\end{document}) and 1.900 GeV/c2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\ extrm{GeV}/\ extrm{c}^{2}}$$\\end{document} (N∗(1900)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\ extrm{N}^{*}(1900)}$$\\end{document} or Δ∗(1900)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\Delta ^{*}(1900)}$$\\end{document}) are preferred by the fit.

Beam spin asymmetry measurements of deeply virtual π0 production with CLAS12

The new experimental measurements of beam spin asymmetry were performed for the deeply virtual exclusive π0 production in a wide kinematic region with the photon virtualities Q2 up to 6.6 GeV2 and the Bjorken scaling variable xB in the valence regime. The data were collected by the CEBAF Large Acceptance Spectrometer (CLAS12) at Jefferson Lab with longitudinally polarized 10.6 GeV electrons scattered on an unpolarized liquid-hydrogen target. Sizable asymmetry values indicate a substantial contribution from transverse virtual photon amplitudes to the polarized structure functions. The interpretation of these measurements in terms of the Generalized Parton Distributions (GPDs) demonstrates their sensitivity to the chiral-odd GPD E¯T, which contains information on quark transverse spin densities in unpolarized and polarized nucleons and provides access to the nucleon's transverse anomalous magnetic moment. Additionally, the data were compared to a theoretical model based on a Regge formalism that was extended to the high photon virtualities.

Hard exclusive π0 muoproduction at COMPASS

Hard Exclusive Meson Production (HEMP) and Deeply Virtual Compton Scattering (DVCS) are very promising reactions to access Generalized Parton Distributions (GPDs). Such exclusive measurements were performed at COMPASS in 2016 and 2017 at the M2 beamline of the CERN SPS using the 160 GeV muon beam scattering off a 2.5 m long liquid hydrogen target surrounded by a barrel-shaped time-of-flight system to detect the recoiling target proton. The scattered muons and the produced real photons were detected by the COMPASS spectrometer, which was supplemented by an additional electromagnetic calorimeter for the detection of large-angle photons. Exclusive π0 production is the main source of background for the DVCS measurement, while it provides complementary information for the parametrization of GPDs. We will report on preliminary results of the exclusive π0 production cross section and its dependence on the squared four-momentum transfer |t| and on the azimuthal angle ϕ between the scattering plane and the π0 production plane. The COMPASS data will provide further input to constrain GPDs, in particular chiral-odd (“transversity”) GPDs.

N=16 Magicity Revealed at the Proton Drip Line through the Study of ^{35}Ca.

The last proton bound calcium isotope ^{35}Ca has been studied for the first time, using the ^{37}Ca(p,t)^{35}Ca two neutron transfer reaction. The radioactive ^{37}Ca nuclei, produced by the LISE spectrometer at GANIL, interacted with the protons of the liquid hydrogen target CRYPTA, to produce tritons t that were detected in the MUST2 detector array, in coincidence with the heavy residues Ca or Ar. The atomic mass of ^{35}Ca and the energy of its first 3/2^{+} state are reported. A large N=16 gap of 4.61(11)MeV is deduced from the mass measurement, which together with other measured properties, makes ^{36}Ca a doubly magic nucleus. The N=16 shell gaps in ^{36}Ca and ^{24}O are of similar amplitude, at both edges of the valley of stability. This feature is discussed in terms of nuclear forces involved, within state-of-the-art shell model calculations. Even though the global agreement with data is quite convincing, the calculations underestimate the size of the N=16 gap in ^{36}Ca by 840keV.

Influence of a Magnetic Field on the Gifford-McMahon Cryocooler of the Liquid Hydrogen Target at the BM@N Facility

Influence of a Magnetic Field on the Gifford-McMahon Cryocooler of the Liquid Hydrogen Target at the BM@N Facility

Intruder configurations in 29Ne at the transition into the island of inversion: Detailed structure study of 28Ne

Detailed γ-ray spectroscopy of the exotic neon isotope 28Ne has been performed for the first time using the one-neutron removal reaction from 29Ne on a liquid hydrogen target at 240 MeV/nucleon. Based on an analysis of parallel momentum distributions, a level scheme with spin-parity assignments has been constructed for 28Ne and the negative-parity states are identified for the first time. The measured partial cross sections and momentum distributions reveal a significant intruder p-wave strength providing evidence of the breakdown of the N=20 and N=28 shell gaps. Only a weak, possible f-wave strength was observed to bound final states. Large-scale shell-model calculations with different effective interactions do not reproduce the large p-wave and small f-wave strength observed experimentally, indicating an ongoing challenge for a complete theoretical description of the transition into the island of inversion along the Ne isotopic chain.

STRASSE: a silicon tracker for quasi-free scattering measurements at the RIBF

Silicon Tracker for RAdioactive nuclei Studies at SAMURAI Experiments is a new detection system under construction for quasi-free scattering (QFS) measurements at 200–250 MeV/nucleon at the RIBF facility of the RIKEN Nishina Center. It consists of a charged-particle silicon tracker coupled with a dedicated thick liquid hydrogen target (up to 150-mm long) in a compact geometry to fit inside large scintillator or germanium arrays. Its design was optimized for two types of studies using QFS: missing-mass measurements and in-flight prompt gamma -ray spectroscopy. This article describes (i) the resolution requirements needed to go beyond the sensitivity of existing systems for these two types of measurements, (ii) the conceptual design of the system using detailed simulations of the setup and (iii) its complete technical implementation and challenges. The final tracker aims at a sub-mm reaction vertex resolution and is expected to reach a missing-mass resolution below 2 MeV in sigma for (p, 2p) reactions when combined with the CsI(Na) CATANA array.

Features of VBLHEP Liquid-Hydrogen Target Gas System

Features of VBLHEP Liquid-Hydrogen Target Gas System

The Q[formula omitted] high performance LH[formula omitted] target

A high-power liquid hydrogen target was built for the Jefferson Lab Qweak experiment, which measured the tiny parity-violating asymmetry in e→p scattering at an incident energy of 1.16 GeV, and a Q2=0.025 GeV2. To achieve the luminosity of 1.7×1039 cm−2 s−1, a 34.5 cm-long target was used with a beam current of 180 μA. The ionization energy-loss deposited by the beam in the target was 2.1 kW. The target temperature was controlled to within ±0.02 K and the target noise (density fluctuations) near the experiment’s beam helicity-reversal rate of 960 Hz was only 53 ppm. The 58 liquid liter target achieved a differential pressure (head) across the pump of 7.6 kPa (11.4 m) and a mass flow of 1.2 ± 0.3 kg/s (corresponding to a volume flow of 17.4 ± 3.8 l/s) at the nominal 29 Hz rotation frequency of the recirculating centrifugal pump. We describe aspects of the design, operation, and performance of this target, the highest power LH2target ever used in an electron scattering experiment to date.

First measurement of differential cross sections and photon beam asymmetries for photoproduction of the f0(980) meson decaying into π0π0 at Eγ<2.4 GeV

For the first time, differential cross sections and photon beam asymmetries were measured for the reaction γp→f0(980)p→π0π0p by using a linearly polarized photon beam up to 2.4GeV and a liquid hydrogen target. The f0(980) photoproduction signal was clearly observed owing to the absence of contributions from vector-meson photoproduction. The results indicate the t-channel exchange of vector mesons as a mechanism of the f0(980) photoproduction at Eγ≈2.1GeV, putting constraints on the nature of f0(980).Received 17 January 2023Accepted 28 March 2023DOI:https://doi.org/10.1103/PhysRevC.107.L042201©2023 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasPhotonuclear reactionsPolarization phenomenaQuark modelPhysical SystemsHadronsMesonsPropertiesParticle propertiesTechniquesCalorimetersNuclear PhysicsParticles & Fields

A multidimensional study of the structure function ratio [formula omitted] from hard exclusive π+ electro-production off protons in the GPD regime

A multidimensional extraction of the structure function ratio σLT′/σ0 from the hard exclusive e→p→e′nπ+ reaction above the resonance region has been performed. The study was done based on beam-spin asymmetry measurements using a 10.6 GeV incident electron beam on a liquid-hydrogen target and the CLAS12 spectrometer at Jefferson Lab. The measurements focus on the very forward regime (t/Q2 ≪ 1) with a wide kinematic range of xB in the valence regime (0.17 <xB < 0.55), and virtualities Q2 ranging from 1.5 GeV2 up to 6 GeV2. The results and their comparison to theoretical models based on Generalized Parton Distributions demonstrate the sensitivity to chiral-odd GPDs and the directly related tensor charge of the nucleon. In addition, the data is compared to an extension of a Regge formalism at high photon virtualities. It was found that the Regge model provides a better description at low Q2, while the GPD model is more appropriate at high Q2.

Observation of Correlations between Spin and Transverse Momenta in Back-to-Back Dihadron Production at CLAS12.

We report the first measurements of deep inelastic scattering spin-dependent azimuthal asymmetries in back-to-back dihadron electroproduction in the deep inelastic scattering process. In this reaction, two hadrons are produced in opposite hemispheres along the z axis in the virtual photon-target nucleon center-of-mass frame, with the first hadron produced in the current-fragmentation region and the second in the target-fragmentation region. The data were taken with longitudinally polarized electron beams of 10.2 and 10.6GeV incident on an unpolarized liquid-hydrogen target using the CLAS12 spectrometer at Jefferson Lab. Observed nonzero sinΔϕ modulations in ep→e^{'}pπ^{+}X events, where Δϕ is the difference of the azimuthal angles of the proton and pion in the virtual photon and target nucleon center-of-mass frame, indicate that correlations between the spin and transverse momenta of hadrons produced in the target- and current-fragmentation regions may be significant. The measured beam-spin asymmetries provide a first access in dihadron production to a previously unexplored leading-twist spin- and transverse-momentum-dependent fracture function. The fracture functions describe the hadronization of the target remnant after the hard scattering of a virtual photon off a quark in the target particle and provide a new avenue for studying nucleonic structure and hadronization.

A liquid hydrogen target to fully characterize the new MEG II liquid xenon calorimeter

The MEG II experiment aims to improve the sensitivity to μ+→e+γ down to 6×10−14, surpassing the 4.2×10−13 UL by MEG. To achieve this sensitivity the detector performances need to be assessed and monitored via dedicated calibrations. To calibrate the Liquid Xenon Calorimeter near the signal energy (52.8 MeV), photons are produced through the Charge EXchange (CEX) process π−p→nπ0(→γγ). Here we present the liquid Hydrogen target used for the CEX run 2021, during the first MEG II physics run.

Spin Density Matrix Elements in exclusive vector meson muoproduction at COMPASS

We present results on Spin Density Matrix Elements (SDMEs) measured in hard exclusive muoproduction of [Formula: see text] and [Formula: see text] mesons on the proton at COMPASS using 160 GeV/[Formula: see text] polarized [Formula: see text] and [Formula: see text] beams scattering off a liquid hydrogen target. The measurements cover the range 5 GeV/[Formula: see text] [Formula: see text] 17 GeV/[Formula: see text], 1.0 (GeV/[Formula: see text])2 [Formula: see text] 10.0 (GeV/[Formula: see text])2 and 0.01 (GeV/[Formula: see text])2 [Formula: see text] 0.5 (GeV/[Formula: see text])2. Here, [Formula: see text] denotes the virtuality of the exchanged photon, [Formula: see text] the mass of the final hadronic system and [Formula: see text] the transverse momentum of the vector meson with respect to the virtual-photon direction. The measured non-zero SDMEs for transitions of transversely polarized virtual photons to longitudinally polarized vector mesons ([Formula: see text]) indicate a violation of [Formula: see text]-channel helicity conservation. Additionally, for [Formula: see text] production we observe a dominant contribution of natural-parity-exchange transitions and a small contribution of unnatural-parity-exchange transitions. On the contrary, the contribution of unnatural-parity-exchange for [Formula: see text] production is significant and it decreases with increasing [Formula: see text], being still non-negligible at the largest [Formula: see text] values accessible at COMPASS. The results provide an important input for modeling Generalized Parton Distribution (GPDs).

Commissioning of liquid xenon gamma-ray detector for MEG II experiment

The liquid xenon (LXe) gamma-ray detector in the MEG II experiment measures the energy, position and timing of the gamma-ray from μ+→e+γ, and it is the key to the unprecedented sensitivity of the experiment. All the photo sensors of 4092 VUV MPPCs and 668 PMTs were read out for the first time and a physics data collection started in 2021. The detector response was monitored all through the beam time, and the LXe detector operated stably. The timing and energy resolution were measured using the gamma-rays from the π0 decays after charge exchange reaction of charged pions in a liquid hydrogen target. The detector has been successfully commissioned and is ready for the long physics run.

Structure of ^{36}Ca under the Coulomb Magnifying Glass.

Detailed spectroscopy of the neutron-deficient nucleus ^{36}Ca was obtained up to 9MeV using the ^{37}Ca(p,d)^{36}Ca and the ^{38}Ca(p,t)^{36}Ca transfer reactions. The radioactive nuclei, produced by the LISE spectrometer at GANIL, interacted with the protons of the liquid hydrogen target CRYPTA, to produce light ejectiles (the deuteron d or triton t) that were detected in the MUST2 detector array, in coincidence with the heavy residues identified by a zero-degree detection system. Our main findings are (i)a similar shift in energy for the 1_{1}^{+} and 2_{1}^{+} states by about -250 keV, as compared with the mirror nucleus ^{36}S; (ii)the discovery of an intruder 0_{2}^{+} state at 2.83(13)MeV, which appears below the first 2^{+} state, in contradiction with the situation in ^{36}S; and (iii)a tentative 0_{3}^{+} state at 4.83(17)MeV, proposed to exhibit a bubble structure with two neutron vacancies in the 2s_{1/2} orbit. The inversion between the 0_{2}^{+} and 2_{1}^{+} states is due to the large mirror energy difference (MED) of -516(130) keV for the former. This feature is reproduced by shell model calculations, using the sd-pf valence space, predicting an almost pure intruder nature for the 0_{2}^{+} state, with two protons (neutrons) being excited across the Z=20 magic closure in ^{36}Ca (^{36}S). This mirror system has the largest MEDs ever observed, if one excludes the few cases induced by the effect of the continuum.

TMD observables in unpolarised Semi-Inclusive DIS at COMPASS

In 2016 and 2017, the COMPASS Collaboration at CERN collected a large sample of DIS events with a longitudinally polarised 160 GeV/c muon beam scattering off a liquid hydrogen target. Part of the collected data has been analysed to extract preliminary results for the amplitudes of the modulations in the azimuthal angle of the charged hadrons and for their transverse-momentum distributions. These observables give relevant information for the study of the transverse momentum and spin structure of the nucleon. Similarly to the results obtained in COMPASS with a deuteron target, the azimuthal asymmetries exhibit interesting kinematic dependences, while the squared-transverse-momentum distributions can be described by the sum of two exponential functions.

Spin Density Matrix Elements for Exclusive $\rho^{0}$ Meson Muoproduction at COMPASS

Spin density matrix elements were extracted from COMPASS data for exclusive \rho^{0}ρ0 meson muoproduction on a liquid hydrogen target. The measurement cover the kinematic range of 1.0 (GeV/cc)^22&lt; Q^{2} &lt;&lt;Q2&lt; 10.0 (GeV/cc)^22, 5.0 GeV/c^2c2&lt; W &lt;&lt;W&lt; 17.0 GeV/c^2c2 and 0.01 (GeV/cc)^22&lt;p^{2}_{T}&lt;&lt;pT2&lt; 0.5 (GeV/cc)^22. Here, WW denotes the mass of the final hadronic system, Q^{2}Q2 the virtuality of the exchanged photon and p_{T}pT the transverse momentum of the \rho^{0}ρ0 meson with respect to the virtual-photon direction. We observe a violation of s-channel helicity conservation for the transition \gamma^{*}_{T} \to \rho^{0}_{L}γT*→ρL0. Additionally, we find a dominant contribution of the natural-parity-exchange transitions.

Target dependence of isotopic cross sections in the spallation reactions 238U + p, d and 9Be at 1 AGeV * *Supported by the National Natural Science Foundation of China (11875328, 12075327)

The spallation of 238U is an important way to produce rare isotopes. This work aims at studying the cross sections of isotopes produced in 238U + p, d and 9Be reactions at 1 A GeV and their target dependence. (1) A physical model dependent (Bayesian neural network) BNN, which includes the details of IQMD-GEMINI++ model and BNN, was developed for a more accurate evaluation of production cross sections. The isospin-dependent quantum molecular dynamics (IQMD) model is used to study the non-equilibrium thermalization of the 238U nuclei and fragmentation of the hot system. The subsequent decay of the pre-fragments is simulated by the GEMINI++ model. The BNN algorithm is used to improve the prediction accuracy after learning the residual error between experimental data and calculations by the IQMD-GEMINI++ model. It is shown that the IQMD-GEMINI++ model can reproduce the available experimental data (3282 points) within 1.5 orders of magnitude. After being fine tuned by the BNN algorithm, the deviation between calculations and experimental data were reduced to within 0.4 order of magnitude. (2) Based on the predictions by the IQMD-GEMINI++-BNN framework, the target dependence of isotopic cross sections was studied. The cross sections to produce the rare isotopes by the 238U + p, d and 9Be reactions at 1 A GeV are compared. For the generation of neutron-rich fission products, the cross sections for the 238U + 9Be are the largest. For the generation of neutron-deficient nuclei in the region of A = 200–220, the cross sections for 238U + p reaction are the largest. Considering the largest cross sections and the atomic density, the beryllium target is recommended to produce the neutron-rich fission products by the 238U beam at 1 A GeV, while the liquid-hydrogen target is suggested to produce the neutron-deficient nuclei in the region of A = 200–220.