Research Report
ICRR Inter-University Research Program 2020
Research Subject: “Data taking, Calibrations, Measurements and Analysis with Super-

Kamiokande and SuperK-Gd”
Principal Investigator:

Luis Labarga

Participating Researchers: Luis Labarga, Lluis Martí, Bryan Zaldivar
Summary of Research Result:

The items listed in the title are fundamental for the collaborative work to get out themost of the Super-Kamiokande experiment, SuperK-Gd, and also the preparation for
the next generation Hyper-Kamiokande.
Calibrations and related
We have evaluated with autoXenon and Ni data the evolution with time of the waterproperties of Super-Kamiokande.
- At the Gd-loading process (beginning of SK-VI) to understand the impact of theGd salt in the water properties and light transmission at different wave lengths.
- Significant information has been obtained from the comparison of autoXenon
and Nickel results based on their different wavelength ranges (autoXenon mostly
above 400 nm , Nickel large fraction below 400 nm)- Further insight has been gathered from the comparison of Xe and Ni results tothose on light transmission at different wavelengths and at different part of thedetectors extracted by the Korean laser system.
- After Gd stabilization, i.e. at the regular data taking period, to monitor the detector
performance and help the water team in the understanding of the observed steadyincrease of Dark Noise, and the preparation of the -already proven successfulcounter measures by the water system.
We have studied the gains of the ID PMTs:- Time evolution of the mean gain during the time interval spanned since thebeginning of SK-V for PMTs grouped into a) Production Year, and b)
Top/Barrel/Bottom detector parts.
- An increase with time, different for those subgroups, is observed. However, in thealready two-year time interval studied, those increases are significantly slower
than then mean in SK-IV (> 2 times). We are studying this effect.

SuperK-Gd: For the search and quantification of critical radioactive contaminations in
the Gd2(SO4)3 to be dissolved in SK-Gd, phase T1.5
- we are screening with high purity Germanium Detectors in the Canfranc
Underground Laboratory samples of different ion exchange resins to be used in
the enlargement of the SK-Gd water purification system needed for T1.5, in whichanother set of ~20 tons of Gadolinium Sulfate will be dissolved in SK water.
- We are starting the preparation at the Canfranc Lab. of the procedures for theintense screening campaign of the produced Gd salt expected for the T1.5 phase.
Physics Analyses:
We are rather involved in the main neutrino oscillation analysis of the experiment.
- Our main works pivot on the use of neutron tagging, for the time being with H, forbetter neutrino-/antineutrino separation, better determination of the incoming
neutrino energy and better discrimination of Neutral Current reactions.
- The most up to date SK oscillation analysis incorporates some of these techniques(so-called Hybrid Analysis) resulting in a significant improvement of thesensitivity of SK atmospheric data to CP violation and mass hierarchy. It has beenpresented officially for the first time in the NEUTRINO 2020 conference.
- We continue working towards a -full data- SK-T2K joint oscillation analyses. The
joint result should improve rather significantly the already very relevant, yet totally
independent results by SK (atmospheric neutrinos) and T2K (beam neutrinos).
We are continuing the research program towards reliable quantitative estimates of theuncertainties in the selection or identification procedures based on Neural Network or,in general, Artificial Intelligence algorithms. I.e. to obtain uncertainties estimates thathave a mathematically correct statistical meaning. These works are intended tosignificantly improve the precision of the systematic error estimates of ourmeasurements.
- The first field of action is on the algorithms for neutron tagging, for the time being
H-tagging, and soon Gd-tagging.
- We foresee next to apply it to accurately include the uncertainty in thediscrimination neutrino / anti-neutrino in the main neutrino oscillation program.
No.