Λc Physics at BESIII

In 2014 BESIII collected a data sample of 567 [Formula: see text] at [Formula: see text] = 4.6 GeV, which is just above the [Formula: see text] pair production threshold. By analyzing this data sample, we have measured the absolute branching fractions for many decays of [Formula: see text] for the first time. These decays include the semileptonic decays of [Formula: see text], [Formula: see text], the hadronic decays of [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text] and inclusive decay [Formula: see text] + anything. The decays of [Formula: see text], [Formula: see text] and [Formula: see text] are observed for the first time and the others are measured with significantly improved precision. These results are important to benefit the development of the related theories, and provide important inputs for both charmed baryons and [Formula: see text] physics

Search for hidden-strangeness pentaquark in Lambda_c -> p phi pi^0 at BESIII

The search for bound states with structures more complicated than standard mesons and baryons is one of most active fields in high energy physics. Even if most of such states are expected since the first days of the Quark Model, there are no clear indication of their existence. In the past decades several candidates to fill the possible exotic combinations(tetraquarks, pentaquarks, glueballs) were found. More indications are coming, and one of the more vital goals is to try to make connections between these states, in order to realize a new spectroscopy. The hunt for these states is entrusted to the flavour-factories, either at B energies (BELLE and BaBar) or at τ − charm ones (BESIII), and at the hadrons collider (LHCb, and in the future P̄ANDA) and the photoproduction one (GLUEX, CLAS12). The observation of the elusive parts of the Quark Model help to shed more light on the non-perturbative part of the Quantum Chromodynamics (QCD). In fact, our understanding of the strong interaction at its maximum strength relies on the development of more precise effective field theory. The more the experimental spectrum is unveiled, the more these theories can become precise. Among all the exotics, pentaquark candidates seem to be more elusive particles. The only two candidates observed that can fit in the picture of 5 quarks are the ones observed by LHCb Collaboration. LHCb observed two structures in the decay Λ b → pJ/ψK −, in the pJ/ψ invariant mass. One natural step forward in understanding the nature of such states is to search for partners in other flavour sectors. Recently, a model was proposed by R.F. Lebed [2], in which it is shown the possibility to search for hidden-strangeness pentaquark siblings in the decay of Λ c → pφπ0 , with the pentaquark emerging in the pφ pair invariant mass. The aim of this work is to search for exotic hidden-strangeness pentaquarks with BESIII data. BESIII experiments is a central detector optimized for τ and charm physics. In 2014 it has collected a sample of data at the Λ c Λ̄ c baryon threshold thanks to the upgraded center-of-mass energies of the lepton collider BEPCII. The event selection is optimized using MonteCarlo simulation of the detector and of the process. The analysis of the collected data shown a small bump in the pφ invariant mass. The statistical significance of the excess is below 3 sigma, so only the upper limit can be calculated. The resulting upper limit for the branching ratio is found to be UL(Λ c →Ps pi0) < 6.3 10^{-3}. It is also possible calculate the upper limit for the branching ratio of the non resonant process UL( Λ c → pφπ0) < 8.6 10^{-3}. These results are in agreement with the literature. In the next few years, BESIII will collect 3 fb^{-1} in order to improve the measurement and disentangle if the pentaquark P_s exist.La ricerca di stati legati con strutture interne più complesse di quelle dei mesoni e dei barioni convenzionali è uno dei rami più attivi nella fisica delle particelle. Tali strutture risonanti, denominate appunto esotiche, comprendono tetraquark, pentaquark, glueball, ibridi, eccetera. Sebbene predette fin dagli albori del modello a Quark, nella maggior parte dei casi non vi è una chiara prova della loro esistenza. Negli ultimi anni, diversi esperimenti hanno riportato evidenze di stati che difficilmente possono essere interpretati come adroni convenzionali. In attesa di nuove indicazioni sperimentali, l’obbiettivo principale di questo tipo di ricerca è quello di cercare delle connessioni fra queste risonanze e realizzare una vera e propria spettroscopia esotica, in modo da migliorare la comprensione della parte non perturbativa della CromoDinamica Quantistica (QCD). Infatti, al momento, l’unica possibilità per indagare la regione in cui l’interazione forte è al massimo della sua intensità è basata integralmente su teorie effettive di campo sempre più precise. Maggiore è la parte conosciuta dello spettro, maggiore è il potere predittivo di queste teorie. Tale compito è affidato a una nuova generazione di esperimenti: le flavour-factories nel regime dei mesoni B (BELLE, BELLE-II e BaBar), o alle energie del settore tau-charm (BESIII), ai collisionatori adronici (LHCb, e nel futuro PANDA), agli esperimenti di fotoproduzione (CLAS12 e GLUEX). Tra tutti i candidati esotici, i pentaquark sono gli stati più elusivi. Gli unici due candidati osservati che possono essere realisticamente descritti con modelli a 5 quark sono quelli osservati dalla collaborazione LHCb. Infatti, LHCb ha osservato due strutture nel decadimento Lambda_b → p J/psi K-, nello spettro di massa invariante di J/psi p. Al fine di comprendere la natura di queste strutture è naturale cercare stati analoghi in altri sapori. Recentemente, R.F. Lebed ha proposto un modello in un cui è possibile cercare pentaquark detti hidden-strangeness nel decadimento Lambda_c → p phi pi0, nello specifico come risonanze nella masse invariante protone phi. L’obbiettivo di questo lavoro è cercare stati pentaquark esotici con hidden-strangeness con i dati raccolti dall’esperimento BESIII. L’esperimento BESIII è un detector centrale ottimizzato per la fisica del leptone tau e del quark charm. Nel 2014 ha raccolto un set di dati pochi MeV sopra la soglia di produzione di coppie di barioni Lambda_c. La selezione degli eventi è ottimizzata utilizzando una simulazione MonteCarlo. L'analisi degli eventi raccolti mostra un eccesso nella massa invariante pphi. La significatività del segnale è minore di 3 sigma: viene calcolato il limite superiore del rapporto di decadimento Lambda_c -> P_s pi0 è vale BR(Lambda_c -> P_s pi0) p phi pi0) < 8.6*10^{-3}. Questi risultati sono in accordo con le misure in letteratura. BESIII raccoglierà nei prossimi anni 3 fb^{-1}: i nuovi dati serviranno a indagare ulteriormente sull’esistenza del pentaquark P_s

Spring Plates as a Valid Additional Fixation in Comminuted Posterior Wall Acetabular Fractures: A Retrospective Multicenter Study

Background: The posterior wall fracture is the most frequent pattern of acetabular fractures. Many techniques of fixation have been described in the literature and involve plates, screws, or a combination of both. This study aims to investigate the clinical and radiological outcomes of spring plates in the treatment of comminuted posterior wall acetabular fractures. (2) Methods: A retrospective multicenter (four level I trauma centers) observational study was performed. Patients with a comminuted posterior wall acetabular fracture treated with a spring plate (DePuy Synthes, West Chester, PA) were included. Diagnosis was made according to the Judet and Letournel classification. Diagnosis was confirmed with plain radiographs in an antero-posterior view and Judet views, iliac and obturator oblique views, and thin-slice CT with multiplanar reconstructions. (3) Results: Forty-six patients (34 males and 12 females) with a mean age of 51.7 years (range 19–73) were included. The most common mechanism of injury was motor vehicle accident (34 cases). In all cases, spring plates were placed under an overlapping reconstruction plate. The mean follow-up was 33.4 months (range 24–48). The mean period without weight-bearing was 4.9 weeks (range 4–7), and full weight-bearing was allowed at an average of 8.2 weeks (range 7–11) after surgery. (4) Conclusions: According to the present data, spring plates can be considered a viable additional fixation of the posterior wall acetabular fractures

New G-parity violating amplitude in the J/Psi decay?

The J/ψ meson has negative G parity so that, in the limit of isospin conservation, its decay into π+π- should be purely electromagnetic. However, the measured branching fraction B(J/ψ→π+π-) exceeds by more than 4.5 standard deviations the expectation computed according to BABAR data on the e+e-→π+π- cross section. The possibility that the two-gluon plus one-photon decay mechanism is not suppressed by G-parity conservation is discussed, even by considering other multipion decay channels. As also obtained by phenomenological computation, such a decay mechanism could be responsible for the observed discrepancy. Finally, we notice that the BESIII experiment, having the potential to perform an accurate measurement of the e+e-→π+π- cross section in the J/ψ mass energy region, can definitely prove or disprove this strong G-parity-violating mechanism by confirming or confuting the BABAR data

A Fit to the Available <i>e</i>⁺<i>e</i>⁻ → <inline-formula><math display="inline"><semantics><mrow><msubsup><mi mathvariant="sans-serif">Λ</mi><mi>c</mi><mo>+</mo></msubsup><msubsup><mover accent="true"><mi mathvariant="sans-serif">Λ</mi><mo>¯</mo></mover><mi>c</mi><mo>−</mo></msubsup></mrow></semantics></math></inline-formula> Cross Section Data Nearby Production Threshold by Means of a Strong Correction to the Coulomb Enhancement Factor

There are two available sets of data on the e+e−→Λc+Λ¯c− cross section at energies close to the production threshold, collected by the Belle and by the BESIII Collaborations. The measurement of the former, performed by means of the initial state radiation technique, is compatible with the presence of a resonance, called ψ(4660), observed also in other final states. On the contrary, the latter is measured an almost flat and hence non-resonant cross section in the energy region just above the production threshold, but the data stop before the possible rise in the cross section for the resonant production. We propose an effective model to describe the behavior of the data near this threshold, which is based on a Coulomb-like enhancement factor due to the strong interaction among the final state particles. In the framework of this model, it is possible to describe both datasets

Operation of the CGEM Detector

A ten years extension of the data taking of BESIII experiment, recently approved, motivated an upgrade program both for the leptonic collider BEPCII and for some of the sub-detectors of the spectrometer. BESIII is a multipurpose spectrometer optimized for physics in the charm-τ energy region. In particular, the current inner drift chamber is suffering from aging and the proposal is to replace it with a detector based on Cylindrical Gas Electron Multiplier (CGEM) technology to improve both the secondary vertex reconstruction and the radiation tolerance. The CGEM Inner Tracker will be composed of three coaxial layers of cylindrical triple GEMs, operating in an Ar + iC4H10 (90:10) gas mixture with field and gain optimized to maximize the spatial resolution. The new detector is readout with innovative TIGER electronics produced in 110 nm CMOS technology. A cosmic telescope instrumented with two out of three layers is in operation in Beijing since January 2020, remotely controlled by Italian groups due to the pandemic situation. A dedicated readout chain was developed for data acquisition. In this paper, the general status of the project will be presented with a particular focus on the preliminary results from the cosmic data taking and future plans

The new CGEM Inner Tracker and the new TIGER ASIC for the BES III Experiment

A new detector exploiting the technology of Gas Electron Multipliers is under construction to replace the innermost drift chamber of BESIII experiment, since its efficiency is compromised owing the high luminosity of Beijing Electron Positron Collider. The new inner tracker with a cylindrical shape will deploy several new features. The analogue readout and two complementary algorithms to reconstruct the position will allow achieving a spatial resolution of 130 µm in a 1 T magnetic field. For this purpose, TIGER, a new custom 64-channel ASIC, providing time and charge measurements, has been developed. Here, a summary of the most recent results on detector and electronics prototypes is given