Results from the PolarquEEEst missions

The PolarquEEEst scientific programme consists in a series of measurements of the cosmic ray flux up to the highest latitudes. It started in Summer 2018, when three telescopes made out of scintillators readout by SiPMs were built and installed in Italy, Norway and on a sailboat leaving from North Island, to circumnavigate the Svalbard archipelago and land in Tromsø. They collected data on a latitude range from 44° N up to 82° N, with a dense sampling of the Northernmost interval. The PolarquEEEst mission continued afterwards with a series of measurements in Italy, Southward reaching Lampedusa, and in Germany. In May 2019 the PolarquEEEst collaboration accomplished another important result, installing a cosmic ray observatory for the detection of secondary cosmic muons at Ny Alesund, at 79° N, made of three independent identical detectors positioned a few hundred meters from each other, and synchronized in order to operate together as a network. The configuration used will allow high precision measurements never performed before at these latitudes on a long term, also interesting for their connection with environmental phenomena. The network will also complement the existing stations for the detection of cosmic neutrons at the Svalbard archipelago, enlarging by far the physics scope that is possible to pursue in this field at this peculiar location. Here the various missions are presented, and some preliminary results from the measurements performed are shown.

a sailboat leaving from North Island, to circumnavigate the Svalbard archipelago and land in Tromsø. They collected data on a latitude range from 44 • N up to 82 • N, with a dense sampling of the Northernmost interval. The PolarquEEEst mission continued afterwards with a series of measurements in Italy, Southward reaching Lampedusa, and in Germany.
In May 2019 the PolarquEEEst collaboration accomplished another important result, installing a cosmic ray observatory for the detection of secondary cosmic muons at Ny Alesund, at 79 • N, made of three independent identical detectors positioned a few hundred meters from each other, and synchronized in order to operate together as a network. The conguration used will allow high precision measurements never performed before at these latitudes on a long term, also interesting for their connection with environmental phenomena. The network will also complement the existing stations for the detection of cosmic neutrons at the Svalbard archipelago, enlarging by far the physics scope that is possible to pursue in this eld at this peculiar location.
Here the various missions are presented, and some preliminary results from the measurements performed are shown.

Introduction
At the beginning of the last century it was believed that cosmic rays were high-energy neutral particles (i.e. gamma rays), and therefore no eects of the Earth's magnetic eld on cosmic ray ux was expected.
Later on, the observation of the dependence of the cosmic ray ux on latitude led to the conclusion that cosmic rays are mainly constituted of charged particles. In fact, the geomagnetic eld, roughly dipolar, swipes away low energy charged cosmic rays with an energy threshold depending on latitude, preventing them to reach the ground.
In 1933 A. H. Compton compiled a set of data collected by various groups at dierent locations, sometimes on the ground, sometimes on boats [1]. These data clearly showed an increase of the cosmic particles rates with latitude, roughly 20% in magnitude when passing from the Equator to about 50 degrees latitude. Above that value a attening in the dependence of the cosmic rays intensity measured at sea level vs. latitude was observed. This behaviour had also been predicted with a model, by G.Lemaitre and M.S.Vallarta, published almost at the same time as Compton's paper [2].
The observed dependence of the cosmic rays intensity at sea level with latitude was veried multiple times in the second half of the twentieth century, using compilations of data from experiments located at various sites on the ground, or from smaller devices hosted on board of ships cruising the Oceans. Nevertheless, very scarce measurement are available above the Arctic Circle, even today, particularly concerning the charged components of the cosmic rays, and more data, possibly on a long time scale, are therefore needed.
The PolarquEEEst experiment was designed to ll in this gap. Its basic unit is a small, portable device, based on scintillators coupled to Silicon PhotoMultipliers (SiPMs), and equipped with custom trigger and read out electronics, able to measure the charged component of the cosmic rays impinging onto it. Four identical units were built, conventionally called POLA-01, POLA-02, POLA-03 and POLA-04, and used for multiple purposes in various occasions, in the framework of a scientic programme mainly devoted to the study of cosmic rays at extreme Northern latitudes. This paper rst describes the detector layout and characteristics. Then the various missions when the POLA detectors were used are discussed, and some preliminary results from the analysis currently undergoing are presented. Finally some considerations about the perspectives of the PolarquEEEst scientic programme are drawn.

The PolarquEEEst detector
Sensitive elements of the PolarquEEEst detectors are 1 cm thick planes of BC400 Saint-Gobain plastic scintillators, each made out of four tiles 20 ×30 cm 2 in dimensions, as shown in Figure 1.
Each tile is read out by means of two AdvanSid ASD-NUV4S-P-40 Silicon PhotoMultipliers (SiPMs). Each POLA detector comprises two scintillator planes, separated by 11 cm, enclosed in a light-tight box.
The SiPMs are readout by Front End electronics (FE) custom cards, each able to independently process the analog signals from two SiPMs. Each card includes two input preampliers, and discriminators, whose thresholds can be remotely adjusted. Output from the FE card are low-voltage dierential signals, fed to a custom Trigger and Read-out Board (TRB). The DAQ is performed by a Raspberry Pi 3 B+ board (RPi3), controlling the TRB through a I2C connection and via a custom software, and receiving data from it and storing them on a SD device. The Raspberry Pi is also used for readout of several sensors, including three temperature, pressure and humidity sensors, an accelerometer, a 3 D gyroscope (both used to monitor the device orientation) and a magnetometer (see Figure 2).

The PolarquEEEst2018 mission
The Connections to the sensors used can be seen.
Polarquest2018 was a six weeks cruise of the eco-friendly 60 feet sailboat Nanuq which, on   However, in order to draw reliable conclusions about a possible dependence of the observed rate of cosmic particle on the latitude, all local eects which can aect such measurement have to be taken into consideration. One important factor to be taken into account for POLA-01 is its variable inclination with respect to the vertical direction, due to the fact that it was mounted on a sailing boat which stayed inclined for long periods of time because of the sea conditions or the sailing pace.
Also a correction to the measured raw rates of all three POLA detectors, associated to the instantaneous atmospheric pressure, has to be applied. An increase in pressure, in fact, causes a reduction of the observed rate because cosmic secondary particles have to traverse more material from their production high up in the atmosphere before reaching the ground.  average value amount to about ± 0.26 Hz, namely less than 1 %. In the same Figure 5 also the geographical latitude where the POLA-01 detector was located is shown.
A map of the cruise performed by the sailboat Nanuq with on-board the POLA-01 detector, is shown in Figure 6, with, superimposed, the cosmic particle rate measured, expressed in colour code. From the Figure,   The rate of cosmic particles measured by POLA-01 as a function of the geographic latitude, divide by it average value, is shown in Figure 7. The same rate, but plotted as a function of the geomagnetic latitude, which, in these regions, can signicantly dier from the geographic one, is shown in Figure 8. In both cases, the rates stay more or less constant around their average values, with uctuations generally contained in the ± 1 % range already cited, and no clear trend can be seen which could suggest a possible dependency of the cosmic particle rate on the latitude where it was measured.
All these considerations strongly support the hypothesis of a basically at behaviour of the ux of cosmic rays at sea level in the range of latitudes explored, in agreement with the measurements and the model previously cited.

The PolarquEEEst journey in Italy and Germany
In Fall 2018, after the dismounting of the POLA-01 detector from its location on-board the sailboat Nanuq, a new campaign of measurements with the PolarquEEEst experiment was started. Goal of this campaign was to explore a range of latitudes where the cosmic ray ux at sea level is expected to have an important dependence on latitude and to evaluate the amount of such a dependence. For this purpose, the POLA-01 detector was mounted onto a car, and transported across Italy and Germany, taking data on programmed stops during the trip. The detector did not receive any modication with respect to the conguration adopted for the previous data taking campaign, except that its power system was modied in order to be powered up with a standard 220V AC current.
POLA-01 collected data on multiple occasions, in a variety of conditions. Locations, periods of data taking and the corresponding geographic latitudes are listed in Table 1  Analysis of the data taken by the three detectors to identify the expected dependence of the measured rate with latitude are ongoing, and will be published in a forthcoming paper. Some preliminary results, which demonstrate an increase of the cosmic particle rate with latitude, are reported in [5].
In May 2018, POLA-03 was dismounted from its location at Bra and brought to CERN. In the meanwhile another detector, identical to the others and labelled POLA-04, was manufactured and moved to CERN as well. POLA-01, POLA-03 and POLA-04 underwent careful tests and calibrations, and also a software upgrade, before being used for the following data taking campaign, described in detail in the next Section.    Figure 11, where a histogram lled with the time dierences of events detected by POLA-01 and POLA-04 between June and September 2019 is shown. A peak of events characterized by a time dierence close to zero, namely impinging almost at the same time onto the two detectors, can be clearly seen above the background of accidentals. As it can be seen from the map, POLA-01 and POLA-04 is the pair of closest stations of the network, selecting therefore EAS with a relatively low energy. The detection of coincidences among POLA-01 and POLA-03 or POLA-04 and POLA-03, or among the three POLA detector, would select EAS of progressively higher energy, giving the possibility to indirectly measuring the cosmic rays energy spectrum. The proposed measurement would last longer than one year, ideally for many, in order to appreciate the cosmic rays seasonal variations and to monitor part of the eleven-year solar cycle, particularly interesting since we are now close to its nal part and the beginning of the next. This kind of study, in addition to being an absolute rstling at latitudes around 80 N, would perfectly insert in the framework of measurements on cosmic rays which is currently being performed worldwide, lling a gap in the presently available observations.

Conclusions
The PolarquEEEst experiment has undergone three campaigns of data taking. The rst, whose goal was to measure the cosmic particle ux at the Northernmost latitudes, where very few measurements are available, allowed to demonstrate that, in the range explored, no appreciable dependence on the geographical latitude has been found, in agreement with the theoretical expectations.
The second campaign was aimed at assessing such a dependence, performing measurements from 35 • N and Northbound, where eects are expected to be appreciable by the PolarquEEEst instrumentation. Even if analysis is still ongoing, preliminary results show that such a measurement was successful.
The third campaign is continuing now, and will be for several years, and its goal is to perform accurate measurements at 79 • N of both Extensive Air Showers and of the local cosmic particle ux, opening new interesting perspectives in this research eld.