Measurement of ^{6}H Ground State Energy in an Electron Scattering Experiment at MAMI-A1

For the first time the neutron-rich hydrogen isotope ^{6}H was produced in an electron scattering experiment in the reaction ^{7}Li(e,e^{'}pπ^{+})^{6}H using the spectrometer facility of the A1 Collaboration at the Mainz Microtron accelerator. By measuring the triple coincidence between the scattered electron, the produced proton, and π^{+}, the missing mass spectrum of ^{6}H was obtained. A clear peak above ^{3}H+n+n+n energy threshold was seen resulting in a ground state energy of ^{6}H at 2.3±0.5(stat.)±0.4(syst.)  MeV with a width of 1.9±1.0(stat.)±0.4(syst.)  MeV. This Letter challenges the understandings of multinucleon interactions and presents a new method to study light neutron-rich nuclei with electron scattering experiments.

First Measurement of A=4 Hypernuclei and Antihypernuclei at the LHC

In this Letter, the first evidence of the _{Λ[over ¯]}^{4}He[over ¯] antihypernucleus is presented, along with the first measurement at the LHC of the production of (anti)hypernuclei with mass number A=4, specifically (anti)_{Λ}^{4}H and (anti)_{Λ}^{4}He. In addition, the antiparticle-to-particle ratios for both hypernuclei (_{Λ[over ¯]}^{4}H[over ¯]/_{Λ}^{4}H and _{Λ[over ¯]}^{4}He[over ¯]/_{Λ}^{4}He) are shown, which are sensitive to the baryochemical potential of the strongly interacting matter created in heavy-ion collisions. The results are obtained from a data sample of central Pb-Pb collisions, collected during the 2018 LHC data taking at a center-of-mass energy per nucleon pair of sqrt[s_{NN}]=5.02  TeV. The yields measured for the average of the charge-conjugated states are found to be [0.78±0.19(stat)±0.17(syst)]×10^{-6} for the (anti)_{Λ}^{4}H and [1.08±0.34(stat)±0.20(syst)]×10^{-6} for the (anti)_{Λ}^{4}He, and the measured antiparticle-to-particle ratios are in agreement with unity. The presence of (anti)_{Λ}^{4}H and (anti)_{Λ}^{4}He excited states is expected to strongly enhance the production yield of these hypernuclei. The yield values exhibit a combined deviation of 3.3σ from the theoretical ground-state-only expectation, while the inclusion of the excited states in the calculations leads to an agreement within 0.6σ with the present measurements. Additionally, the measured (anti)_{Λ}^{4}H and (anti)_{Λ}^{4}He masses are compatible with the world-average values within the uncertainties.

Observation of the antimatter hypernucleus H ¯ Λ ¯ 4

At the origin of the Universe, an asymmetry between the amount of created matter and antimatter led to the matter-dominated Universe as we know it today. The origins of this asymmetry remain unknown so far. High-energy nuclear collisions create conditions similar to the Universe microseconds after the Big Bang, with comparable amounts of matter and antimatter1-6. Much of the created antimatter escapes the rapidly expanding fireball without annihilating, making such collisions an effective experimental tool to create heavy antimatter nuclear objects and to study their properties7-14, hoping to shed some light on the existing questions on the asymmetry between matter and antimatter. Here we report the observation of the antimatter hypernucleusH ¯ Λ ¯ 4 , composed of aΛ ¯ , an antiproton and two antineutrons. The discovery was made through its two-body decay after production in ultrarelativistic heavy-ion collisions by the STAR experiment at the Relativistic Heavy Ion Collider15,16. In total, 15.6 candidateH ¯ Λ ¯ 4 antimatter hypernuclei are obtained with an estimated background count of 6.4. The lifetimes of the antihypernucleiH ¯ Λ ¯ 3 andH ¯ Λ ¯ 4 are measured and compared with the lifetimes of their corresponding hypernuclei, testing the symmetry between matter and antimatter. Various production yield ratios among (anti)hypernuclei (hypernuclei and/or antihypernuclei) and (anti)nuclei (nuclei and/or antinuclei) are also measured and compared with theoretical model predictions, shedding light on their production mechanisms.

Measurements of the lightest hypernucleus (HΛ3): progress and perspective

The hyperon-nucleon (Y-N) interaction is important for the description of the equation-of-state of high baryon density matter. Hypernuclei, the cluster object of nucleons and hyperons, serve as cornerstones of a full understanding of the Y-N interaction. Recent measurements of the lightest known hypernucleus, the hypertriton's (HΛ3) and anti-hypertriton's (H¯Λ¯3) lifetime, mass and Λ separation energy have attracted interests on the subject. Its cross section and collective flow parameters have also been measured in heavy-ion collisions, which have revealed new features on its production mechanism. In this article we summarise recent measurements of HΛ3, focusing on the heavy-ion collisions. We will discuss their implications for the HΛ3 properties and the constrains on the Y-N interaction models.

Search for Λ[over ¯]-Λ Baryon-Number-Violating Oscillations in the Decay J/ψ→pK^{-}Λ[over ¯]+c.c

We report on the first search for Λ[over ¯]-Λ oscillations in the decay J/ψ→pK^{-}Λ[over ¯]+c.c. by analyzing 1.31×10^{9}  J/ψ events accumulated with the BESIII detector at the BEPCII collider. The J/ψ events are produced using e^{+}e^{-} collisions at a center of mass energy sqrt[s]=3.097  GeV. No evidence for hyperon oscillations is observed. The upper limit for the oscillation rate of Λ[over ¯] to Λ hyperons is determined to be P(Λ)=[B(J/ψ→pK^{-}Λ+c.c.)/B(J/ψ→pK^{-}Λ[over ¯]+c.c.)]<4.4×10^{-6} corresponding to an oscillation parameter δm_{ΛΛ[over ¯]} of less than 3.8×10^{-18}  GeV at the 90% confidence level.

Measurement of the Lifetime and Λ Separation Energy of _{Λ}^{3}H

The most precise measurements to date of the _{Λ}^{3}H lifetime τ and Λ separation energy B_{Λ} are obtained using the data sample of Pb-Pb collisions at sqrt[s_{NN}]=5.02  TeV collected by ALICE at the LHC. The _{Λ}^{3}H is reconstructed via its charged two-body mesonic decay channel (_{Λ}^{3}H→^{3}He+π^{-} and the charge-conjugate process). The measured values τ=[253±11(stat)±6(syst)]  ps and B_{Λ}=[102±63(stat)±67(syst)]  keV are compatible with predictions from effective field theories and confirm that the _{Λ}^{3}H structure is consistent with a weakly bound system.

Observation of Directed Flow of Hypernuclei _{Λ}^{3}H and _{Λ}^{4}H in sqrt[s_{NN}]=3 GeV Au+Au Collisions at RHIC

We report here the first observation of directed flow (v_{1}) of the hypernuclei _{Λ}^{3}H and _{Λ}^{4}H in mid-central Au+Au collisions at sqrt[s_{NN}]=3  GeV at RHIC. These data are taken as part of the beam energy scan program carried out by the STAR experiment. From 165×10^{6} events in 5%-40% centrality, about 8400 _{Λ}^{3}H and 5200 _{Λ}^{4}H candidates are reconstructed through two- and three-body decay channels. We observe that these hypernuclei exhibit significant directed flow. Comparing to that of light nuclei, it is found that the midrapidity v_{1} slopes of _{Λ}^{3}H and _{Λ}^{4}H follow baryon number scaling, implying that the coalescence is the dominant mechanism for these hypernuclei production in the 3 GeV Au+Au collisions.

Measurements of _{Λ}^{3}H and _{Λ}^{4}H Lifetimes and Yields in Au+Au Collisions in the High Baryon Density Region

We report precision measurements of hypernuclei _{Λ}^{3}H and _{Λ}^{4}H lifetimes obtained from Au+Au collisions at sqrt[s_{NN}]=3.0  GeV and 7.2 GeV collected by the STAR experiment at the Relativistic Heavy Ion Collider, and the first measurement of _{Λ}^{3}H and _{Λ}^{4}H midrapidity yields in Au+Au collisions at sqrt[s_{NN}]=3.0  GeV. _{Λ}^{3}H and _{Λ}^{4}H, being the two simplest bound states composed of hyperons and nucleons, are cornerstones in the field of hypernuclear physics. Their lifetimes are measured to be 221±15(stat)±19(syst)  ps for _{Λ}^{3}H and 218±6(stat)±13(syst)  ps for _{Λ}^{4}H. The p_{T}-integrated yields of _{Λ}^{3}H and _{Λ}^{4}H are presented in different centrality and rapidity intervals. It is observed that the shape of the rapidity distribution of _{Λ}^{4}H is different for 0%-10% and 10%-50% centrality collisions. Thermal model calculations, using the canonical ensemble for strangeness, describes the _{Λ}^{3}H yield well, while underestimating the _{Λ}^{4}H yield. Transport models, combining baryonic mean-field and coalescence (jam) or utilizing dynamical cluster formation via baryonic interactions (phqmd) for light nuclei and hypernuclei production, approximately describe the measured _{Λ}^{3}H and _{Λ}^{4}H yields. Our measurements provide means to precisely assess our understanding of the fundamental baryonic interactions with strange quarks, which can impact our understanding of more complicated systems involving hyperons, such as the interior of neutron stars or exotic hypernuclei.

Studies of hypernuclei with heavy-ion beams, nuclear emulsions and machine learning

The lightest hypernucleus, the hypertriton, has been a benchmark in the field of hypernuclear physics. However, some of recent experiments employing energetic heavy-ion beams have revealed that the hypertriton lifetime is significantly shorter than 263 ps which is expected by considering the known weakly binding nature of the hypertriton. The STAR collaboration has also measured the hypertriton binding energy, and the deduced value is contradicting to its formerly known small binding energy. These measurements have indicated that the fundamental physics quantities of the hypertriton such as its lifetime and binding energy have not been understood, therefore, they have to be measured very precisely. Furthermore, an unprecedented Λnn bound state observed by the HypHI collaboration has to be studied in order to draw a conclusion whether or not such a bound state exists. These three-body hypernuclear states are studied by the heavy-ion beam data in theWASA-FRS experiment and by analysing J-PARC E07 nuclear emulsion data with machine learning.

The effect of postoperative vaginal progesterone in ultrasound-indicated cerclage to prevent preterm birth

OBJECTIVES

To compare pregnancy outcomes according to the use of postoperative vaginal progesterone in patients who underwent ultrasound-indicated cerclage.

METHODS

This was a retrospective cohort study of 86 consecutive asymptomatic singleton pregnancies who had undergone cerclage because of incidentally found short cervical length under 20 mm through transvaginal ultrasound between 16°^/7 and 24^6/7 weeks' gestational age. Outcomes were compared according to the use of vaginal progesterone after cerclage. Primary outcome measure was preterm delivery < 34 weeks of gestation.

RESULTS

(1) The frequency of preterm delivery < 34 weeks of gestation was significantly lower in patients with postoperative vaginal progesterone than those without (2.2 versus 18.4%, p = .021); (2) the median gestational age at delivery in the postoperative vaginal progesterone group was significantly longer than the control group (38.3 weeks (interquartile range, 37.5-39.1 weeks) versus 37.3 weeks (interquartile range 33.9-38.6 weeks), p = .020); (3) Multivariable logistic regression analysis demonstrated the use of vaginal progesterone after cerclage was found to be independently associated with decrease in preterm delivery before 34 weeks (Odds ratio 0.10; 95% confidence interval, 0.01-0.93) and 37 weeks (Odds ratio 0.24; 95% confidence interval, 0.07-0.85).

CONCLUSIONS

The use of vaginal progesterone was associated with lower rates of preterm birth before 34 and 37 weeks of gestation in women who underwent ultrasound-indicated cerclage placement.

Exotic hypernuclear systems and heavy ion collisions

We discuss perspectives in hypernuclear studies opened by their integration with heavy ion physics. Particularly, neutron–rich Λ hypernuclei and double–Λ hypernucleican be produced, which are hardly attainable by traditional reactions and can enrich our knowledge on hadronic interactions.

Open Questions in the Understanding of Strangeness Production in HIC – Experiment Perspective

Open questions concerning strangeness production in heavy-ion collisions are discussed with a focus on the experimental aspects. The open points are presented in the context of recent measurements.

Processes of hypernuclei formation in relativistic ion collisions

The study of hypernuclei in relativistic ion collisions open new opportunities for nuclear and particle physics. The main processes leading to the production of hypernuclei in these reactions are the disintegration of large excited hyper-residues (target- and projectile-like), and the coalescence of hyperons with other baryons into light clusters. We use the transport, coalescence and statistical models to describe the whole reaction, and demonstrate the effectiveness of this approach: These reactions lead to the abundant production of multi-strange nuclei and new hypernuclear states. A broad distribution of predicted hypernuclei in masses and isospin allows for investigating properties of exotic hypernuclei, as well as the hypermatter both at high and low temperatures. There is a saturation of the hypernuclei production at high energies, therefore, the optimal way to pursue this experimental research is to use the accelerator facilities of intermediate energies, like FAIR (Darmstadt) and NICA (Dubna).

Experimental review of hypernuclear physics: recent achievements and future perspectives

Since the shutdown of several old proton synchrotrons, which played a fundamental role in the second generation experiments in hypernuclear physics performed in Europe, USA and Japan, some new experimental setups aiming to achieve sub-MeV energy resolution have been operating for a long time. Over the last decade the hypernuclear physics community has been committed to carrying out several third generation experiments by exploiting the potential offered by new accelerators, such as a continuous electron beam machine and a ϕ-factory. Large data samples were collected on specific items thanks to dedicated facilities and experimental apparatuses. The attention was mainly focused on both high-resolution spectroscopy and the decay mode study of single Λ-hypernuclei. Nowadays this phase is over but, until recently, important and, to some extent, unexpected results were achieved. An updated review of selected experimental results is presented, as well as a survey of perspectives for future studies.

Is there a flavor hierarchy in the deconfinement transition of QCD?

We present possible indications for flavor separation during the QCD crossover transition based on continuum extrapolated lattice QCD calculations of higher order susceptibilities. We base our findings on flavor-specific quantities in the light and strange quark sector. We propose a possible experimental verification of our prediction, based on the measurement of higher order moments of identified particle multiplicities. Since all our calculations are performed at zero baryochemical potential, these results are of particular relevance for the heavy-ion program at the LHC.

Identifying multiquark hadrons from heavy ion collisions

Identifying hadronic molecular states and/or hadrons with multiquark components either with or without exotic quantum numbers is a long-standing challenge in hadronic physics. We suggest that studying the production of these hadrons in relativistic heavy ion collisions offers a promising resolution to this problem as yields of exotic hadrons are expected to be strongly affected by their structures. Using the coalescence model for hadron production, we find that, compared to the case of a nonexotic hadron with normal quark numbers, the yield of an exotic hadron is typically an order of magnitude smaller when it is a compact multiquark state and a factor of 2 or more larger when it is a loosely bound hadronic molecule. We further find that some of the newly proposed heavy exotic states could be produced and realistically measured in these experiments.

Physics. Fishing antihypernuclei out of a quark-gluon soup

Rare antimatter hypernuclei can form when an ultrahigh-energy plasma of quarks and gluons cools down.