Prof Subir Sarkar: Publications

IceCube

IceCube at Oxford

I am a member since 2004 of the IceCube collaboration which discovered cosmic high energy neutrinos and identified some of their astrophysical sources.

IceCube @ Oxford

Mixed dark matter from technicolor

(2010)

Authors:

Alexander Belyaev, Mads T Frandsen, Francesco Sannino, Subir Sarkar

Cosmogenic photons as a test of ultra-high energy cosmic ray composition

(2010)

Authors:

Dan Hooper, Andrew M Taylor, Subir Sarkar

Asymmetric dark matter and the sun.

Phys Rev Lett 105:1 (2010) 011301

Authors:

Mads T Frandsen, Subir Sarkar

Abstract:

Cold dark matter particles with an intrinsic matter-antimatter asymmetry do not annihilate after gravitational capture by the Sun and can affect its interior structure. The rate of capture is exponentially enhanced when such particles have self-interactions of the right order to explain structure formation on galactic scales. A "dark baryon" of mass 5 GeV is a natural candidate and has the required relic abundance if its asymmetry is similar to that of ordinary baryons. We show that such particles can solve the "solar composition problem." The predicted small decrease in the low energy neutrino fluxes may be measurable by the Borexino and SNO+ experiments.

Non-gaussianity from violation of slow-roll in multiple inflation

Journal of Cosmology and Astroparticle Physics 2010:5 (2010)

Authors:

S Hotchkiss, S Sarkar

Abstract:

Multiple inflation is a model based on N=1 supergravity wherein there are sudden changes in the mass of the inflaton because it couples to 'flat direction' scalar fields which undergo symmetry breaking phase transitions as the universe cools. The resulting brief violations of slow-roll evolution generate a non-gaussian signal which we find to be oscillatory and yielding fNL ∼ 5-20. This is potentially detectable by e.g. Planck but would require new bispectrum estimators to do so. We also derive a model-independent result relating the period of oscillations of a phase transition during inflation to the period of oscillations in the primordial curvature perturbations generated by the inflaton. © 2010 IOP Publishing Ltd and SISSA.

Calibration and characterization of the IceCube photomultiplier tube

Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 618:1-3 (2010) 139-152

Authors:

R Abbasi, Y Abdou, T Abu-Zayyad, J Adams, JA Aguilar, M Ahlers, K Andeen, J Auffenberg, X Bai, M Baker, SW Barwick, R Bay, JL Bazo Alba, K Beattie, JJ Beatty, S Bechet, JK Becker, KH Becker, ML Benabderrahmane, J Berdermann, P Berghaus, D Berley, E Bernardini, D Bertrand, DZ Besson, M Bissok, E Blaufuss, DJ Boersma, C Bohm, O Botner, L Bradley, J Braun, S Buitink, M Carson, D Chirkin, B Christy, J Clem, S Cohen, C Colnard, DF Cowen, MV D'Agostino, M Danninger, C De Clercq, L Demirörs, O Depaepe, F Descamps, P Desiati, G De Vries-Uiterweerd, T DeYoung, JC Díaz-Vélez, J Dreyer, JP Dumm, MR Duvoort, R Ehrlich, J Eisch, RW Ellsworth, O Engdegård, S Euler, PA Evenson, O Fadiran, AR Fazely, T Feusels, K Filimonov, C Finley, MM Foerster, BD Fox, A Franckowiak, R Franke, TK Gaisser, J Gallagher, R Ganugapati, M Geisler, L Gerhardt, L Gladstone, A Goldschmidt, JA Goodman, D Grant, T Griesel, A Groß, S Grullon, RM Gunasingha, M Gurtner, C Ha, A Hallgren, F Halzen, K Han, K Hanson, Y Hasegawa, J Haugen, K Helbing, P Herquet, S Hickford, GC Hill, KD Hoffman, A Homeier, K Hoshina, D Hubert, W Huelsnitz, JP Hülß, PO Hulth

Abstract:

Over 5000 PMTs are being deployed at the South Pole to compose the IceCube neutrino observatory. Many are placed deep in the ice to detect Cherenkov light emitted by the products of high-energy neutrino interactions, and others are frozen into tanks on the surface to detect particles from atmospheric cosmic ray showers. IceCube is using the 10-in. diameter R7081-02 made by Hamamatsu Photonics. This paper describes the laboratory characterization and calibration of these PMTs before deployment. PMTs were illuminated with pulses ranging from single photons to saturation level. Parameterizations are given for the single photoelectron charge spectrum and the saturation behavior. Time resolution, late pulses and afterpulses are characterized. Because the PMTs are relatively large, the cathode sensitivity uniformity was measured. The absolute photon detection efficiency was calibrated using Rayleigh-scattered photons from a nitrogen laser. Measured characteristics are discussed in the context of their relevance to IceCube event reconstruction and simulation efforts. © 2010 Elsevier B.V.

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