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Directional Dark Matter Search with the Newsdm Experiment GRAN SASSO SCIENCE INSTITUTE DOCTORAL THESIS Directional dark matter search with the NEWSdm experiment Author: Supervisors: Valerio GENTILE Prof. Giovanni DE LELLIS Prof. Salvatore CAPOZZIELLO A thesis submitted in fulfillment of the requirements for the degree of Doctor of Philosophy in the Astroparticle Physics January 13, 2019 ii “And no-one showed us to the land And no-one knows the where or whys But something stirs and something tries And starts to climb towards the light” Echoes, Pink Floyd iii Acknowledgements I would like to thank all the people who supported me during my PhD experience. Firstly, I would like to express my gratitude to my Supervisors: Prof. Giovanni De Lel- lis who really taught me what the scientific method is; Prof. Salvatore Capozziello from whom I learnt that there is not a unique way to explain something. I owe a special ac- knowledgment to Prof. Francesco Vissani that I consider to be my first unofficial Supervi- sor and, especially, a friend: you believed in me more than I have ever done. I would like to thank my Referees, Dr. Pierluigi Belli, Dr. Marco Selvi and Prof. Francesco Arneodo, whose comments and suggestions have surely improved the quality of this work. I would also thank Prof. Vitaly Kudryavtsev and Dr. Luciano Pandola for their precious advices on my simulation studies. I would like to thank Antonia who was crucial for my professional growth: you have taught me that no limit is just that and that every effort, sooner or later, will be repaid. I would like to thank my colleagues: Andrey, Asada and Naka-san for their invaluable support throughout the different activities in my PhD work and all the people in Napoli, L’Aquila and Nagoya groups who are part of this scientific adventure. I owe a lot to my closest friends, wherever they are now, and in particular to my new friends met at GSSI: sharing this experience with you made it unique and valuable. I would like to thank my family: my father who has always stressed me the importance of studying (I will never be able to repay you); my mother and my grandmother who have fully and unconditionally supported me; Antonia, Giusy, Domenico, Carmine, Mena, Giuseppe, Eleonora, Alessandra and who is coming up :). You all are my inestimable value. Finally, I would like to thank Prof. Francesco Auletta, who was my teacher at fifth year of high school: if during your first lecture you had not kicked me out of the classroom, most likely I would not be beating my fingers on the keyboard now. iv Contents Acknowledgements iii Introduction 1 1 The dawn of the darkness4 1.1 Early times and first evidences..........................5 1.2 Framework of the modern cosmology......................9 1.3 On the origin and last fate of the Universe: the LCDM model........ 13 1.4 Strong candidates for dark matter: WIMPs................... 17 1.5 WIMPs halo models................................ 19 1.6 An alternative point of view: f(R) theories.................... 21 2 Directional dark matter search 24 2.1 An overview on dark matter search........................ 24 2.2 Direct dark matter search............................. 27 2.3 Results of direct experiments........................... 30 2.3.1 Ionization in high purity Germanium detectors............ 31 2.3.2 Scintillator crystals............................. 32 2.3.3 Cryogenic bolometers........................... 34 2.3.4 Liquid noble-gas detectors........................ 35 2.3.5 Threshold detectors and novel techniques................ 37 2.3.6 WIMP-nucleon exclusion plot....................... 37 2.4 Directional dark matter search........................... 39 3 Nuclear Emulsions for WIMP Search with directional measurement 41 3.1 Nuclear emulsion technique and Nano Imaging Tracker............ 43 3.1.1 NIT emulsion production......................... 44 3.1.2 Chemical treatments and handling.................... 46 v 3.2 Background sources................................. 47 3.2.1 External background sources....................... 48 Environmental gamma source...................... 48 Environmental neutron source...................... 48 Muon-induced neutron and cosmic muons background........ 50 Neutrino diffuse background....................... 51 3.2.2 Internal background sources....................... 53 Electrons induced by 14C......................... 53 Radiogenic Neutrons............................ 56 3.2.3 Instrumental background......................... 56 3.3 The NEWSdm project................................ 58 3.4 Readout strategy.................................. 60 3.4.1 Shape analysis for candidate tracks................... 61 3.4.2 Candidate validation with the resonance effect of polarised light.. 62 3.4.3 Optical microscope for LSPRs analysis.................. 66 3.5 Sensitivity...................................... 68 4 Background simulation 71 4.1 Input parameters.................................. 71 4.1.1 Neutron sources.............................. 72 4.1.2 Cosmic muons............................... 73 4.1.3 Environmental gammas and electrons from 14C............ 75 4.2 Simulation of NIT response to electrons..................... 78 4.3 Intrinsic neutron and electrons from 14C background............. 81 4.4 Technical test simulation.............................. 83 4.5 Simulation of the pilot experiment........................ 85 4.5.1 Opera emulsion as a veto......................... 87 4.6 Discussion on simulation results......................... 90 5 Resonance effect of polarised light in NIT emulsions 91 5.1 Scanning and analysis processes......................... 91 5.2 Plasmon variables.................................. 93 5.3 Test beam with Carbon ions............................ 95 5.3.1 Simulation of the test beam........................ 98 5.3.2 Scanning of the data............................ 105 5.4 Position accuracy.................................. 105 vi 5.5 Shape analysis.................................... 107 5.6 Plasmon analysis.................................. 109 5.6.1 Microtracks and Npeaks.......................... 111 5.6.2 Isolated grains............................... 111 5.7 Efficiency and track length threshold with plasmon analysis......... 114 5.8 Summary....................................... 118 6 Neutrino studies with NEWSdm detector 122 6.1 Coherent elastic neutrino-nucleus scattering.................. 123 6.2 Neutrino floor for the NEWSdm detector.................... 125 6.3 Supernova neutrinos with the NEWSdm detector............... 128 6.3.1 Supernova neutrino source........................ 129 6.3.2 Supernova neutrino signal......................... 130 6.3.3 Background sources............................ 133 6.3.4 Results.................................... 133 6.4 Neutrinos from nuclear reactors.......................... 137 6.5 Neutrinos from spallation neutron source.................... 138 6.6 Conclusions on neutrino studies......................... 139 Conclusions 141 vii List of Figures 1.4 All-sky WMAP measurement of the CMB radiation temperature [30]. The lowest temperatures are represented by blue regions while the highest by red regions. The small fluctuations shown are of magnitude O(mK) with the average temperature measured to be 2.72548 ± 0.00057 K......... 14 1.5 The CMB power spectrum as a function of angular scale. Red line is the best fit to the model, and the grey band represents the cosmic variance. [31] 15 1.6 (Left): Curvature and expansion of universes containing both matter and a cosmological constant L. The highlighted regions indicate the best fitting values from CMB and galaxy cluster data added to the Supernova Cosmol- ogy Project (SCP) results [37]. (Right): The abundance relative to H of 4He, 2H, 3He and 7Li as a function of baryon density [38]............... 16 1.7 The density as a function of Galactocentric radius for several radial profiles of the DM halo of the Milky Way [50]....................... 21 1.8 Best fit of rotation curves for the galaxies NGC 4455 (left) and NGC 5023 (right). The data are represented by dots, the Newtonian potential by the short dashed line, the correction term by the long dashed line. The total rotation curve vc(R) is represented by the solid line [52]............ 23 1.9 Hubble’s diagram for Type Ia Supernovae. The red line represents the best fit of the theory with the observed data with 1s error bars. The yellow band represents the 1s uncertainty [55]......................... 23 2.1 Diagram of possible dark matter detection channels. The arrows indicate the direction of the reaction [58].......................... 25 2.2 Typical representation of the sensitivity region for dark matter experiment. The black line represents an upper limit reference curve while the colored ones show the variations due to different properties of the detector. The closed curve represents the signal contour in case of an observation [57]... 31 2.3 Direct dark matter techniques [57]......................... 32 viii 2.4 DAMA/LIBRA annual modulation versus the time exposure [76]....... 33 2.5 Schematic representation of the single phase (left) and double phase operation mode [57]....................................... 36 2.6 Signal indications (closed curves) and exclusion limits (open curves) for low (left) and high (right) WIMP mass in the spin-independent case [57, 96]. 38 2.7 Signal indications (closed curves) and exclusion limits (open curves) for low (left) and high (right) WIMP mass in the spin-dependent case [57].... 38 2.8 Schematic representation of the Earth motion through the Milky Way..... 40 2.9 Hammer-Aitoff
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