on behalf of the NUCLEON collaboration Cosmic ray secondary nuclei in the NUCLEON space experiment after two years of data acquisition Kovalev Igor, SINP MSU on behalf of the NUCLEON collaboration ICRC 2017 Good evening. Today on behalf of the NUCLEON collaboration I would like to present to you secondary nuclei spectra measurements conducted by our experiment.

Why measure secondary nuclei ratios? Secondary nuclei in CR are mainly produced in interactions between primary nuclei and interstellar medium Thus, the secondary to primary nuclei ratio and its energy dependence allows to observe main features of CR propagation through the ISM Why should we even try to measure secondary nuclei spectra? These spectra contain a lot of information about cosmic ray propagation through the interstellar medium. The main source of the secondary nuclei is from interaction of primary (heavier) nuclei with interstellar gas and other objects. Therefore by measuring the ratios between respective secondary and primary nuclei spectra we can conclude different aspects of their propagation throughout the galaxy. ICRC 2017

The NUCLEON apparatus ICRC 2017 ChMS (1) 450 um Pads, ~16x16 mm ~50x50 cm2 4 planes Carbon target (2), ~0.25 nuclear interaction length KLEM (4) Strips, pitch ~0,5 mm ~50х50 cm2 6 planes Tungsten converter (4), ~0,5 rad. interaction length on each plane IC (5) 300 um Strips, pitch ~1 mm ~25х25 cm2 Tungsten absorber (5), ~2 rad. interaction lengths on each plane So, the NUCLEON apparatus was built to measure energy spectra of all nuclei from protons to iron in a wide energy range from several hundreds GeV up to 1 PeV. The scheme of the apparatus is shown here. As can be seen, it consists of the following parts: Charge measurement system, 4 silicon pad planes, a carbon target with an interaction length of 1/4, Energy measurement system, 6 silicon strip planes with tungsten layers 1/2 radiation length each, the tungsten-silicon calorimeter. 6 smaller-sized silicon strip planes with tungsten layers 2 radiation lengths each, and the scintillator trigger system. The geometrical factor is 0.24 meters squared times steradian for the KLEM system and 0.06 meters squared times steradian for the calorimeter. Geometrical factor: KLEM 0.24 m2sr, IC 0.06 m2sr ICRC 2017

Energy measurement Two different energy measurement methods are used: 1. The kinematic method KLEM (Kinematic Lightweight Energy Meter) for the first time 2. The calorimetric method usual and well studied Two energy measurement methods are used in the NUCLEON apparatus: the kinematic lightweight energy meter, or KLEM, which is used for the first time, and a conventional small-aperture calorimeter. ICRC 2017

KLEM Energy reconstruction from spatial distribution of secondary particles S-estimator: S = Σ ln2 (2H/Xi) Ni So how exactly does the KLEM method work? Basically, the KLEM method is an old kinematic method used in nuclear emulsion experiments, but with a twist. The difference is in the thin tungsten layers positioned near the detectors. They allow to convert some of the gamma rays to measurable electrons. To measure energy, we determine spatial distribution of secondary particles after the first interaction in the carbon target. From that distribution we build an S-estimator, the formula for which is shown here, and the value of this S-estimator is proportional to the energy of the primary particle. ICRC 2017

Energy measurement correlation Here is a correlation graph between the KLEM method and the calorimeter in terms of model-independent parameters. It shows that the KLEM method gives a reasonable estimate of the particle energy and can be used for energy reconstruction. ICRC 2017

The NUCLEON apparatus placement Onboard the Resurs-P satellite as an additional payload Orbit: sun-synchronous, average altitude 475 km, inclination 97 degrees Weight: 375 kg Power: 180 W Telemetry: 10 GB/day Application of the KLEM method allowed us to build a lightweight apparatus (only 375 kg) with a rather high aperture, which allowed it to be installed as an additional payload on a regular satellite Resurs-P, thus significantly reducing the cost of the experiment. The satellite is placed in a low-Earth sun-synchronous orbit with average altitude of 475 kilometres and an inclination of 97 degrees. The power consumption of the NUCLEON apparatus is 180 watts, and daily telemetry volume is 10 GB. ICRC 2017

Charge reconstruction The NUCLEON apparatus gives charge resolution of approximately 0.2. It allows us to clearly separate low abundance secondary nuclei from high abundance primary ones. ICRC 2017

Energy reconstruction The energy resolution of the NUCLEON apparatus was measured during the test beams at SPS in CERN. The KLEM method energy resolution turned out to be approximately 60 % for pions (better for heavier nuclei), and for the calorimeter - roughly 50 %. ICRC 2017

I would like to emphasise that all of the following data are very preliminary, and that no systematical error estimation was made at this point. All of the presented errors are purely statistical.  Here is the Boron to Carbon ratio as measured by the KLEM method. For the calorimeter, statistics are still too low to be presented. Currently the NUCLEON apparatus gives a significant improvement in the measured energies, while being in a reasonable agreement with data from other experiments. As can be seen, there is an indication of flattening of the ratio, although statistical significance is rather small at this point.  ICRC 2017

In Nitrogen to Oxygen ratio an indication of similar behaviour can be seen, although statistical significance of it is even smaller. ICRC 2017

E. G. Berezhko, L. T. Ksenofontov, V. S. Ptuskin, V. N. Zirakashvili, H. J. Voelk. Astron.Astrophys. 410 (2003) 189-198 (arXiv:astro-ph/0308199v1). One of the possible explanations is a model proposed by Berezhko et al. in 2003. In this model, secondary nuclei are reaccelerated in the supernova remnants, leading to the flattening of secondary to primary ratios up to the complete independence of the ratios from energy.  ICRC 2017

SubFe (Z=16-24) to Fe ratio ICRC 2017 In recent years, the ATIC experiment has shown a rise in the subIron to Iron ratio, although with rather low statistical significance. The NUCLEON apparatus also shows that there is an indication of the rising of the ratio. But the statistics in this energy region are also pretty low. ICRC 2017

Strange HEAO-3-C3 results, 1985-1988 The HEAO-3-C3 experiment has seen a rise in the heavy nuclei ratios (Binns et al., 1988), although it was concluded that it was a systematic error and decided not to publish this result. ICRC 2017

Conclusions The 2 years preliminary analysis of the NUCLEON space experiment data gives multiple indications of the existence of several features in the energy spectra of cosmic ray secondary nuclei at energies around few TeV per nucleon A number of question are posed which may be clarified with better statistics NUCLEON space experiment is continuing... No more than 1/3 expected data were collected In conclusion: the NUCLEON experiment has collected approximately a third of its planned data volume. The secondary to primary nuclei ratios show several new features, but right now statistical significance of them is low. So we hope that with the increased data set these features will be confirmed. ICRC 2017