From new electronics to changes in the PMT configuration, Super-Kamiokande (SK) has undergone several major phases along its history. The latest one, SK-VI, has been the dissolution of 13 tons of gadolinium sulfate octa-hydrate in the hitherto ultra-pure water. The goal of this new phase is to achieve a high neutron efficiency detection. This new capability allows to distinguish different neutrino reactions, enhance signals and remove backgrounds more efficiently. In fact, it has the potential to improve all analyses at SK. This new phase was preceded by the refurbishment of the detector in summer 2018 and then, the dissolution of gadolinium sulfate in summer 2020.

Super-Kamiokande (SK) is a 50 kton water Cherenkov detector located approximately 1 km beneath mount Ikenoyama, Gifu, Japan. While SK can reconstruct charged particle tracks over a wide energy range, the detection efficiency of neutrons is very low. Achieving efficient neutron tagging is useful in all analyses, from the observation of the diffuse supernova neutrino background for the first time, to proton decay studies and oscillation analyses. SK gadolinium (SK-Gd) is the upgrade project to make neutron tagging efficient. After extensive studies, the SK collaboration approved the SK-Gd project on June 27 2015. In the second half of 2018 we refurbished the detector and in the first half of 2020 we added gadolinium to the SK tank for the first time. Here we briefly report the preparations that led to SK-Gd and then, more extensively, the Gd sulfate loading process.

Water Cherenkov detectors are notable for their large masses and their charge particle detection capabilities. These two properties have been exploited in depth in many searches with outstanding results at Super-Kamiokande. On the other hand, neutrons are usually captured on protons and produce a single 2.2 MeV gamma. The Compton scattered electron that is being produced does not yield enough Cherenkov light for the PMT coverage (40%) of Super-Kamiokande to be efficiently detected. However, detecting neutrons would be an important improvement in most of our analyses to either improve our signal event selection (for processes that produce neutrons) or background event rejection (for processes that do not produce any neutron). Gadolinium (Gd) has the largest thermal neutron capture cross section. In this process, it emits a gamma cascade with a total energy of about 8 MeV which would be possible to detect with high efficiency. The EGADS project demonstrated that it is possible to safely add Gd to Super-Kamiokande and the collaboration approved in June 2015 the SuperK-Gd project. The necessary refurbishment of the Super-Kamiokande detector started in June 2018 and finished in early 2019. In this talk, we will report about this work and the project outlook.

From June 2018, the Super-Kamiokande (SK) detector is undergoing a necessary refurbishment to move into its next phase: SuperK-Gd. Dissolving gadolinium (Gd) into the otherwise ultra-pure water will add to SK the ability to efficiently tag neutrons. Gd has the largest thermal neutron capture cross-section emitting a gamma cascade with total energy of 8 MeV. This has to be compared to the single 2.2 MeV gamma produced from the neutron capture on hydrogen. Neutron tagging capabilities will become a new powerful tool both for signals and background reduction in many analyses. The test bench for SuperK-Gd has been EGADS, a R$\&$D project that aimed to demonstrate the feasibility of this idea and that started in 2009. EGADS has shown that Gd sulfate can be easily dissolved and has optimal optical properties to be used in a water Cherenkov detector. At EGADS it has been shown that a very good water quality can be achieved and kept thanks to a novel water purification system specifically designed to keep a good water quality while not removing the dissolved Gd.

Core-collapse supernovae are one of the most energetic events in the universe ($10^{46} J$). When a massive star (M $>$ 8 M$_{\odot}$) ignites its last fusion stage where silicon fusion makes iron, its end is then very close. Basically, the core of the star falls inwardly and the gravitational energy is then released in a supernova explosion. The basic picture of this explosion was confirmed by the few neutrinos detected from the SN1987a supernova at Kamiokande, IMB and Baksan detectors. However, there are many details that are still unknown. Since then, a large detector network has grown with better capabilities. Nowadays, in the case of a supernova explosion in our galaxy, the information that we would acquire would allow us to learn much more about these energetic events and constrain our models. Here, I present a brief summary of this network with special emphasis in SuperK-Gd (the upgraded Super-Kamiokande detector with efficient neutron tagging).

The Super-Kamiokande experiment performs a large variety of studies, many of them in the neutrino sector. The archetypes are atmospheric neutrino (recently awarded with the Nobel prize for Mr. T. Kajita) and the solar neutrinos analyses. In these proceedings we report our latest results and present updates to indirect dark matter searches, our solar neutrino analysis and discuss the future upgrade of Super-Kamiokande by loading gadolinium into our ultra-pure water.

The detection of the diffuse supernova neutrino background (DSNB) for the very first time and its difficulty due to the large irreducible backgrounds originally motivated the idea of adding gadolinium (Gd) into the ultra-pure water of Super-Kamiokande (SK). Since the main mode to detect the DSNB is through inverse beta decay, these backgrounds could be greatly reduced if neutrons could be detected with high efficiency. Today, this is not currently possible. Adding Gd was proposed by GADZOOKS! about 10 years ago and since then much research has been done towards achieving this goal. Given the many advantages that adding Gd means, the EGADS project was set in 2009 to Evaluate the Gadolinium’s Action on Detector Systems. Soon we will be able to demonstrate that this technique is possible, feasible at reasonable costs and safe making possible the advantages of reducing backgrounds in several analyses at SK or in future experiments like Hyper-Kamiokande.

The Super-Kamiokande (SK) experiment has been developing an extensive R&D program to develop a technique that would allow tagging of antineutrinos at SK. This technique is based on the simple idea of adding Gadolinium (Gd) to water, a solute with exceptional properties. A 200 ton tank facility is now under construction in a new hall near SK. It simulates the conditions at SK in order to further develop this technique and serve as a ground field to test it. It will have its own water filtration system, photo-multipliers, data acquisition system (DAQ) and other ancillary equipment.

Inclusive charm and beauty cross sections are measured in e − p and e + p neutral current collisions at HERA in the kinematic region of photon virtuality 5≤Q 2≤2000 GeV2 and Bjorken scaling variable 0.0002≤x≤0.05. The data were collected with the H1 detector in the years 2006 and 2007 corresponding to an integrated luminosity of 189 pb−1. The numbers of charm and beauty events are determined using variables reconstructed by the H1 vertex detector including the impact parameter of tracks to the primary vertex and the position of the secondary vertex. The measurements are combined with previous data and compared to QCD predictions.

We present a summary of the activities of the Multi-Jet final states and energy flowsWorking Group of theHERA and the LHC workshop , 2007-2008. Among the more specific topics considered were th e status of and recent progress in higher order calculations, bot h in fixed perturbative expansions and in resummed approaches, recen t progress in the description of jets, including the description of for wa d jets, new calculations performed using kT -factorization and new determinations of unintegrated parton densities.

The process of charm quark fragmentation is studied using D * ± meson production in deep-inelastic scattering as measured by the H1 detector at HERA. The parameters of fragmentation functions are extracted for QCD models based on leading order matrix elements and DGLAP or CCFM evolution of partons together with string fragmentation and particle decays. Additionally, they are determined for a next-to-leading order QCD calculation in the fixed flavour number scheme using the independent fragmentation of charm quarks to D * ± mesons. Two different regions of phase space are investigated defined by the presence or absence of a jet containing the D * ± meson in the event. The fragmentation parameters extracted for the two phase space regions are found to be different.

The process of charm quark fragmentation is studied using D * ± meson production in deep-inelastic scattering as measured by the H1 detector at HERA. The parameters of fragmentation functions are extracted for QCD models based on leading order matrix elements and DGLAP or CCFM evolution of partons together with string fragmentation and particle decays. Additionally, they are determined for a next-to-leading order QCD calculation in the fixed flavour number scheme using the independent fragmentation of charm quarks to D * ± mesons. Two different regions of phase space are investigated defined by the presence or absence of a jet containing the D * ± meson in the event. The fragmentation parameters extracted for the two phase space regions are found to be different. Eur. Phys. J. C (2009) 59: 589–606 DOI 10.1140/epjc/s10052-008-0792-2 Regular Article Experimental Physics Study of charm fragmentation into D∗± mesons in deep-inelastic scattering at HERA

Three- and four-jet production is measured in deep-inelastic ep scattering at low x and Q 2 with the H1 detector using an integrated luminosity of 44.2 pb -1 . Several phase space regions are selected for the three-jet analysis in order to study the underlying parton dynamics from global topologies to the more restrictive regions of forward jets close to the proton direction. The measurements of cross sections for events with at least three jets are compared to fixed order QCD predictions of 𝒪(α_s^2) and 𝒪(α_s^3) and with Monte Carlo simulation programs where higher order effects are approximated by parton showers. A good overall description is provided by the 𝒪(α_s^3) calculation. Too few events are predicted at the lowest x∼10 -4 , especially for topologies with two forward jets. This hints to large contributions at low x from initial state radiation of gluons close to the proton direction and unordered in transverse momentum. The Monte Carlo program in which gluon radiation is generated by the colour dipole model gives a good description of both the three- and the four-jet data in absolute normalisation and shape.

The production of dijets in diffractive deep inelastic scattering has been measured with the ZEUS detector at HERA using an integrated luminosity of 61 pb-1. The dijet cross section has been measured for virtualities of the exchanged virtual photon, 5 < Q2 < 100 GeV2, and γ*p centre-of-mass energies, 100 < W < 250 GeV. The jets, identified using the inclusive kT algorithm in the γ*p frame, were required to have a transverse energy E* T,jet > 4 GeV and the jet with the highest transverse energy was required to have E* T,jet > 5 GeV. All jets were required to be in the pseudorapidity range -3.5<η* jet<0. The differential cross sections are compared to leading-order predictions and next-to-leading-order QCD calculations based on recent diffractive parton densities extracted from inclusive diffractive deep inelastic scattering data.

Measurements are presented of diffractive open charm production at HERA. The event topology is given by ep→eXY where the system X contains at least one charmed hadron and is well separated by a large rapidity gap from a leading low-mass proton remnant system Y. Two analysis techniques are used for the cross section measurements. In the first, the charm quark is tagged by the reconstruction of a D*±(2010) meson. This technique is used in deep-inelastic scattering (DIS) and photoproduction (γp). In the second, a method based on the displacement of tracks from the primary vertex is used to measure the open charm contribution to the inclusive diffractive cross section in DIS. The measurements are compared with next-to-leading order QCD predictions based on diffractive parton density functions previously obtained from a QCD analysis of the inclusive diffractive cross section at H1. A good agreement is observed in the full kinematic regime, which supports the validity of QCD factorization for open charm production in diffractive DIS and γp.

A search for second and third generation scalar and vector leptoquarks produced in ep collisions via the lepton flavour violating processes ep to mu-X and ep to tau-X is performed by the H1 Collaboration at HERA. The full H1 ep data sample taken at a centre-of-mass energy of 319 GeV is used for the analysis, corresponding to an integrated luminosity of 411 pb^-1. No evidence for the production of such leptoquarks is observed in the H1 data. Leptoquarks produced in ep collisions with a coupling strength of lambda=0.3 and decaying with the same coupling strength to a muon-quark pair or a tau-quark pair are excluded at 95% confidence level up to leptoquark masses of 712 GeV and 479 GeV, respectively.

Inclusive D *± production is measured in deep-inelastic ep scattering at HERA with the H1 detector. In addition, the production of dijets in events with a D *± meson is investigated. The analysis covers values of photon virtuality 2 ≤ Q 2 ≤ 100 GeV 2 and of inelasticity 0.05≤y≤0.7. Differential cross sections are measured as a function of Q 2 and x and of various D *± meson and jet observables. Within the experimental and theoretical uncertainties all measured cross sections are found to be adequately described by next-to-leading order (NLO) QCD calculations, based on the photon–gluon fusion process and DGLAP evolution, without the need for an additional resolved component of the photon beyond what is included at NLO. A reasonable description of the data is also achieved by a prediction based on the CCFM evolution of partons involving the k T -unintegrated gluon distribution of the proton.