Using the entire BABAR gamma(4S) dataset, the first two-dimensional unbinned angular analysis of the semileptonic decay (B) over bar -> Dl(-)(v) over bar (l) is performed, employing hadronic reconstruction of the tag-side B meson from gamma(4S) -> B (B) over bar. Here, l denotes the light charged leptons e and mu. Anovel data-driven signal-background separation procedure with minimal dependence on simulation is developed. This procedure preserves all multidimensional correlations present in the data. The expected sin(2) theta(l) dependence of the differential decay rate in the Standard Model is demonstrated, where theta(l) is the lepton helicity angle. Including input from the latest lattice QCD calculations and previously available experimental data, the underlying form factors are extracted using both model-independent (BGL) and dependent (CLN) methods. Comparisons with lattice calculations show flavor SU(3) symmetry to be a good approximation in the B-(s) -> D-(s) sector. Using the BGL results, the CKM matrix element vertical bar V-cb vertical bar = (41.09 +/- 1.16) x 10(-3) and the Standard Model prediction of the lepton-flavor universality violation variable R(D) = 0.300 +/- 0.004, are extracted. The value of vertical bar V-cb vertical bar from (B) over bar -> Dl(-)(v) over bar (l) tends to be higher than that extracted using (B) over bar -> Dl(-)(v) over bar (l). The Standard Model R(D) calculation is at a 1.97 sigma tension with the latest HFLAV experimental average.

Observations with imaging atmospheric Cherenkov telescopes (IACTs) have enhanced our knowledge of nearby supernova (SN) remnants with ages younger than 500 years by establishing Cassiopeia A and the remnant of Tycho's SN as very-high-energy (VHE) gamma-ray sources. The remnant of Kepler's SN, which is the product of the most recent naked-eye supernova in our Galaxy, is comparable in age to the other two, but is significantly more distant. If the gamma-ray luminosities of the remnants of Tycho's and Kepler's SNe are similar, then the latter is expected to be one of the faintest gamma-ray sources within reach of the current generation IACT arrays. Here we report evidence at a statistical level of 4.6 sigma for a VHE signal from the remnant of Kepler's SN based on deep observations by the High Energy Stereoscopic System (H.E.S.S.) with an exposure of 152 hours. The measured integral flux above an energy of 226 GeV is ~0.3% of the flux of the Crab Nebula. The spectral energy distribution (SED) reveals a gamma-ray emitting component connecting the VHE emission observed with H.E.S.S. to the emission observed at GeV energies with Fermi-LAT. The overall SED is similar to that of the remnant of Tycho's SN, possibly indicating the same non-thermal emission processes acting in both these young remnants of thermonuclear SNe.

A decade has passed since high-energy astrophysical neutrinos have been discovered by IceCube, however the corresponding sources have not been fully identified yet. The reported coincidence of the high-energy IceCube-170922A with the gamma-ray blazar TXS 0506+056 is not enough to claim that blazars are the dominant high-energy neutrino emitters in the Universe. In fact, recently IceCube announced a second correlation with NGC 1068, a nearby Seyfert galaxy, which is significantly different from a gamma-emitting blazars. The hunt for counterparts of the IceCube neutrinos using gamma-ray telescopes started in 2012. Nonetheless, these efforts will continue with the next-generation gamma-ray telescopes, such as the CTA Large Size Telescopes (LSTs) and other telescopes, by means of an improved and revised observation strategy. These new observations will allow us to detect enough sources in order to elucidate the mystery of the neutrino emitters. In this contribution, we introduces the efforts made thus far in the search for gamma-ray counterpart of high-energy IceCube events using the current generation IACTs, focusing on alerts made of multiple neutrinos events, and present an idea to improve in the observational strategies with the CTA LSTs that will become operational in the coming decade. We will discuss how to reduce the bias to gamma-ray emitters in order to search for possible neutrino counterparts.

We study the processes e+e- -> K+K-a degrees a degrees a degrees y, K degrees SK +/- a -/+ a degrees a degrees y, and K degrees SK +/- a -/+ a+a-y in which an energetic photon is radiated from the initial state. The data were collected with the BABAR detector at the SLAC National Accelerator Laboratory. About 1200, 2600, and 6000 events, respectively, are selected from a data sample corresponding to an integrated luminosity of 469 fb-1. The invariant mass of the hadronic final state defines the effective e+e- center-of-mass energy. The center-of-mass energies range from threshold to 4.5 GeV. From the mass spectra, the first ever measurements of the e+e- -> K+K-a degrees a degrees a degrees, e+e- -> K degrees SK +/- a -/+ a degrees a degrees, and e+e- -> K degrees SK +/- a -/+ a+a- cross sections are performed. The contributions from the intermediate states that include eta, phi, rho, K*(892), and other resonances are presented. We observe the J=psi and psi(2S) in most of these final states and measure the corresponding branching fractions, many of them for the first time.

LMC P3 is a gamma-ray binary comprising of an unconfirmed compact object and an O-star and is located in the Large Magellanic Cloud. Initially discovered in Fermi-LAT data, it shows an orbital period of 10.3 days. H.E.S.S. has reported the detected VHE gamma-ray emission during only 20% of the orbit, between orbital phases 0.2 and 0.4, which roughly corresponds to the inferior conjunction of the compact object. H.E.S.S. has continued the observations of this object since then. Here we will present new results obtained with a much deeper data set. The new data allow a more precise measurement of the location of the VHE gamma-ray peak along the orbit of the system to be made. We will interpret these results with respect to emission and absorption mechanisms in gamma-ray binary systems.

The prototype Large-Sized Telescope (LST-1) of the Cherenkov Telescope Array Observatory (CTAO) is in commissioning phase at the Observatorio del Roque de Los Muchachos at 2200 m a.s.l. in La Palma (Canary Islands, Spain). LST-1 is a 23-m diameter telescope and is the first of four that will compose the LST part of the CTAO Northern array. The LST subarray is optimized to provide the best sensitivity for gamma rays in the 20 GeV - 200 GeV energy range. The MAGIC telescopes, which are located approximately 100 m from the LST-1, is operating as a two 17-m telescope stereoscopic system for more than 14 years. LST-1 and MAGIC routinely perform joint observations of gamma-ray sources to exploit the potential of the three-telescope system. This contribution describes the analysis pipeline and evaluates the performance of the system using Monte Carlo simulations and data on the Crab Nebula. The sensitivity achieved during joint observations with MAGIC and LST-1 is about 30% higher than that of MAGIC alone.

The prototype Large-Sized Telescope (LST-1) of the Cherenkov Telescope Array (CTA) was inaugurated on La Palma, Canary Islands, in 2018. Since then, the telescope is in the commissioning phase and takes regular gamma-ray data on astrophysical sources while waiting for other CTA telescopes in La Palma to be constructed. Here we present the status of the commissioning, lessons learned, the telescope performance, and scientific highlights achieved in the last couple of years. The science results include the detection of active galactic nuclei flares, studies of pulsar wind nebulae and pulsars, the detection of a Nova, and searches for gamma-ray emission from gamma-ray bursts. We also present the status of the construction of the three further LST telescopes (LST-2-4) in La Palma and plans for their commissioning.

The Galactic Centre (GC) region is a highly interesting region for very high energy gamma-ray studies due to its proximity and diverse sources. It is also a unique place for Dark Matter (DM) searches, since we expect a large amount of DM in this region and it is nearby. Currently a new detector is under development to observe the GC region, called the Southern Wide field-of-view Gamma-ray Observatory (SWGO). This instrument will be the first water Cherenkov detector located in the Southern Hemisphere sensitive to >100 GeV gamma rays. In our work, we are going to present a simulation of the GC gamma-ray mission as seen by a SWGO-like observatory. To do so we are using the models published by the Cherenkov Telescope Array (CTA) Collaboration together with simulated Instrument Response Functions (IRFs) for testing purposes. This also allows us to predict the expected sensitivity of SWGO to WIMP DM annihilations using a template based method. A sensitivity study during the design phase of the observatory is important in order to choose the best detector design to get outstanding physics results.

A new mechanism has been proposed to simultaneously explain the presence of dark matter and the matter-antimatter asymmetry in the universe. This scenario predicts exotic $B$ meson decays into a baryon and a dark sector anti-baryon ($\psi_D$) with branching fractions accessible at $B$ factories. We present a search for $B \rightarrow \Lambda \psi_D$ decays using data collected by the $BABAR$ experiment at SLAC. This reaction is identified by fully reconstructing the accompanying $B$ meson and requiring the presence of a single $\Lambda$ baryon in the remaining particles. No significant signal is observed, and bounds on the $B \rightarrow \Lambda \psi_D$ branching fraction are derived in the range $0.13 - 5.2\times 10^{-5}$ for $1.0 < m_{\psi_D} < 4.2$ GeV/$c^{2}$. These results set strong constraints on the parameter space allowed by the theory.

We study the processes ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}{K}^{+}{K}^{\ensuremath{-}}{\ensuremath{\pi}}^{0}{\ensuremath{\pi}}^{0}{\ensuremath{\pi}}^{0}\ensuremath{\gamma}$, ${K}_{S}^{0}{K}^{\ifmmode\pm\else\textpm\fi{}}{\ensuremath{\pi}}^{\ensuremath{\mp}}{\ensuremath{\pi}}^{0}{\ensuremath{\pi}}^{0}\ensuremath{\gamma}$, and ${K}_{S}^{0}{K}^{\ifmmode\pm\else\textpm\fi{}}{\ensuremath{\pi}}^{\ensuremath{\mp}}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}\ensuremath{\gamma}$ in which an energetic photon is radiated from the initial state. The data were collected with the BABAR detector at the SLAC National Accelerator Laboratory. About 1200, 2600, and 6000 events, respectively, are selected from a data sample corresponding to an integrated luminosity of $469\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$. The invariant mass of the hadronic final state defines the effective ${e}^{+}{e}^{\ensuremath{-}}$ center-of-mass energy. The center-of-mass energies range from threshold to 4.5 GeV. From the mass spectra, the first ever measurements of the ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}{K}^{+}{K}^{\ensuremath{-}}{\ensuremath{\pi}}^{0}{\ensuremath{\pi}}^{0}{\ensuremath{\pi}}^{0}$, ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}{K}_{S}^{0}{K}^{\ifmmode\pm\else\textpm\fi{}}{\ensuremath{\pi}}^{\ensuremath{\mp}}{\ensuremath{\pi}}^{0}{\ensuremath{\pi}}^{0}$, and ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}{K}_{S}^{0}{K}^{\ifmmode\pm\else\textpm\fi{}}{\ensuremath{\pi}}^{\ensuremath{\mp}}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$ cross sections are performed. The contributions from the intermediate states that include $\ensuremath{\eta}$, $\ensuremath{\phi}$, $\ensuremath{\rho}$, ${K}^{*}(892)$, and other resonances are presented. We observe the $J/\ensuremath{\psi}$ and $\ensuremath{\psi}(2S)$ in most of these final states and measure the corresponding branching fractions, many of them for the first time.

Using the entire BaBar Υ(4S) data set, the first two-dimensional unbinned angular analysis of the semileptonic decay B→ D ℓ^- ν_ℓ is performed, employing hadronic reconstruction of the tag-side B meson from Υ(4S)→ BB. Here, ℓ denotes the light charged leptons e and μ. A novel data-driven signal-background separation procedure with minimal dependence on simulation is developed. This procedure preserves all multi-dimensional correlations present in the data. The expected sin^2θ_ℓ dependence of the differential decay rate in the Standard Model is demonstrated, where θ_ℓ is the lepton helicity angle. Including input from the latest lattice QCD calculations and previously available experimental data, the underlying form factors are extracted using both model-independent (BGL) and dependent (CLN) methods. Comparisons with lattice calculations show flavor SU(3) symmetry to be a good approximation in the B_(s)→ D_(s) sector. Using the BGL results, the CKM matrix element |V_cb|=(41.09± 1.16)× 10^-3 and the Standard Model prediction of the lepton-flavor universality violation variable ℛ(D)=0.300± 0.004, are extracted. The value of |V_cb| from B→ D ℓ^- ν_ℓ tends to be higher than that extracted using B→ D ℓ^- ν_ℓ. The Standard Model ℛ(D) calculation is at a 1.97σ tension with the latest HFLAV experimental average.

The recurrent symbiotic nova RS Ophiuchi experienced an outburst in August 2021 that was detected at optical and high-energy gamma rays. This triggered follow-up observations of the source at very-high-energy gamma rays with the first Large Size Telescope (LST-1) of the Cherenkov Telescope Array. RS Ophiuchi was observed for several nights after the outburst and it was clearly detected by LST-1. Here we report on the outcomes of this observation campaign of the first nova ever detected at very high energies.

We present a novel approach to the determination of the pointing of Imaging Atmospheric Cherenkov Telescopes (IACTs) using the trajectories of the stars in their camera’s field of view. The method starts with the reconstruction of the star positions from the Cherenkov camera data, taking into account the point spread function of the telescope, to achieve a satisfying reconstruction accuracy of the pointing position. A simultaneous fit of all reconstructed star trajectories is then performed with the orthogonal distance regression (ODR) method. ODR allows us to correctly include the star position uncertainties and use the time as an independent variable. Having the time as an independent variable in the fit makes it better suitable for various star trajectories. This method can be applied to any IACT and requires neither specific hardware nor interface or special data-taking mode. In this paper, we use the Large-Sized Telescope (LST) data to validate it as a useful tool to improve the determination of the pointing direction during regular data taking. The simulation studies show that the accuracy and precision of the method are comparable with the design requirements on the pointing accuracy of the LST (≤14″). With the typical LST event acquisition rate of 10 kHz, the method can achieve up to 50 Hz pointing monitoring rate, compared to 𝒪(1) Hz achievable with standard techniques. The application of the method to the LST prototype (LST-1) commissioning data shows the stable pointing performance of the telescope.

MAGIC is a system of two Imaging Atmospheric Cherenkov Telescopes (IACTs), designed to detect very-high-energy gamma rays, and is operating in stereoscopic mode since 2009 at the Observatorio del Roque de Los Muchachos in La Palma, Spain. In 2018, the prototype IACT of the Large-Sized Telescope (LST-1) for the Cherenkov Telescope Array, a next-generation ground-based gamma-ray observatory, was inaugurated at the same site, at a distance of approximately 100 meters from the MAGIC telescopes. Using joint observations between MAGIC and LST-1, we developed a dedicated analysis pipeline and established the threefold telescope system via software, achieving the highest sensitivity in the northern hemisphere. Based on this enhanced performance, MAGIC and LST-1 have been jointly and regularly observing the Galactic Center, a region of paramount importance and complexity for IACTs. In particular, the gamma-ray emission from the dynamical center of the Milky Way is under debate. Although previous measurements suggested that a supermassive black hole Sagittarius A* plays a primary role, its radiation mechanism remains unclear, mainly due to limited angular resolution and sensitivity. The enhanced sensitivity in our novel approach is thus expected to provide new insights into the question. We here present the current status of the data analysis for the Galactic Center joint MAGIC and LST-1 observations.

A dedicated measurement of additional radiation in e+e- -> mu+mu- gamma and e+e- -> pi+ pi- gamma initial-state radiation events is presented using the full BABAR data sample. For the first time results are presented at next -to-and next-to-next-to-leading order, with one and two additional photons, respectively, for radiation from the initial and final states. Comparison with predictions from PHOKHARA and AFKQED Monte Carlo generators is performed, revealing discrepancies in the one-photon rates and angular distributions for the former. This disagreement has a negligible effect on the BABAR measurement of the e+e- -> pi+ pi-(gamma) cross section, but could affect other measurements significantly. This study sheds a new light on the longstanding discrepancy in this channel that affects the theoretical prediction of hadronic vacuum polarization contributions to the muon magnetic moment anomaly.

The binary system Eta Carinae is a unique laboratory to study particle acceleration up to very high energies (VHE) under a wide range of conditions. Particles are thought to be accelerated at shocks forming in the wind collision region. Eta Carinae has been firmly established as a source of high energy gamma-rays in Fermi-LAT data over several orbits. With its highly eccentric orbit lasting 5.5 years, the periastron passage of the two stars is extremely close. This provides an opportunity to constrain the acceleration and absorption mechanisms of the system. Eta Carinae was detected above 200 GeV by the H.E.S.S. telescopes (H.E.S.S. Collaboration, 2020) based on data before and after the 2014 periastron. Unfortunately the 2014 periastron itself could not be observed by H.E.S.S. due to visibility constraints. Hence the 2020 periastron was the first periastron passage visible for the full 5 telescope H.E.S.S. array and was therefore monitored with an extensive observation campaign spanning the phase range from 0.97 to 1.05. We report the detection of a VHE signal from Eta Carinae during the 2020 periastron and describe its spectral properties together with simultaneous Fermi-LAT data. Together with previous and follow up observations, for the first time a VHE light curve spanning a full orbit is presented.

After the discovery of Crab, Vela, and Geminga pulsars at Very High Energies, the search for new pulsars at tens of GeV has been gaining huge importance. However, their steep spectra along with the sensitivity of the current generation of Imaging Atmospheric Cherenkov telescopes (IACTs) are limiting the capability to detect more pulsars. The LST-1 is the first prototype of the Large-Sized Telescope of the forthcoming CTA observatory with enhanced sensitivity at tens of GeV. The LST-1 started its commissioning phase in 2018, and since then it has observed the Crab pulsar regularly. Here, we show the first results of the analysis of the Crab and other pulsars taken with the LST-1. The two characteristic emission peaks of the Crab pulsar, P1, and P2, are detected with high significance showing a clear improvement in sensitivity over the previous generation of IACTs. The spectrum is reconstructed up to 450 GeV for P1 and up to 700 GeV for P2. The low energy threshold of LST-1 also allows us to measure the spectrum of the Crab pulsar in the overlapping region with the Fermi-LAT and cross-calibrate both instruments. The results obtained with the first pulsar observations with the LST-1 confirm the excellent potential of LST telescopes to study and discover new pulsars in the near future

A new dark sector antibaryon, denoted ψ_{D}, could be produced in decays of B mesons. This Letter presents a search for B^{+}→ψ_{D}+p (and the charge conjugate) decays in e^{+}e^{-} annihilations at 10.58 GeV, using data collected in the BABAR experiment. Data corresponding to an integrated luminosity of 398  fb^{-1} are analyzed. No evidence for a signal is observed. Branching fraction upper limits in the range from 10^{-7}-10^{-5} are obtained at 90% confidence level for masses of 1.0<m_{ψ_{D}}<4.3  GeV/c^{2}. The result is also reinterpreted to provide the first limits on a supersymmetric model with R-parity violation and a light neutralino.

Since the last H.E.S.S. publication on the stellar cluster Westerlund 2 in 2011, the H.E.S.S. dataset on this region has increased more than three-fold in exposure to $\sim220\,$h of total observation time. By applying a novel approach to correct for atmospheric variations in IACT data, the commonly applied data quality selection criteria can be adapted to exploit as much of this dataset as possible. In combination with current analysis techniques, it is furthermore possible to disentangle and better characterise this complex region of the gamma-ray sky. Applying an extensive 3D fitting procedure, we find three distinct VHE gamma-ray sources in the vicinity of Westerlund 2, adding a new emission region to the previously reported sources HESS J1023$-$575 and HESS~J1026$-$582. Even though the sources partly overlap, their spectral indices differ from one another, providing new clues on the relativistic particle acceleration and propagation in the region around the massive star cluster. The new source component shows an elongated morphology that seems to emerge from the star cluster, following the multi-parsec-scale CO jet cloud initially found in NANTEN data as reported in 2009.

A dedicated measurement of additional radiation in $e^+e^-\to\mu^+\mu^-\gamma$ and $e^+e^-\to\pi^+\pi^-\gamma$ initial-state-radiation events is presented using the full BABAR data sample. For the first time results are presented at next-to- and next-to-next-to-leading order, with one and two additional photons, respectively, for radiation from the initial and final states. Comparison with predictions from Phokhara and AfkQed Monte Carlo generators is performed, revealing discrepancies in the one-photon rates and angular distributions for the former. This disagreement has a negligible effect on the BABAR measurement of the $e^+e^-\to\pi^+\pi^-(\gamma)$ cross section, but could affect other measurements significantly. This study sheds a new light on the longstanding discrepancy in this channel that affects the theoretical prediction of hadronic vacuum polarization contributions to the muon magnetic moment anomaly.