MINOS Document 5229-v1

Astroparticle Physics with the MINOS Far Detector- Dissertation

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Eric Grashorn
Updated by:
Eric Grashorn
Document Created:
10 Oct 2008, 13:45
Contents Revised:
10 Oct 2008, 13:45
Metadata Revised:
08 May 2009, 16:34
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Since August 2003, the MINOS Far Detector
collected over 67~million underground muons at Soudan MN, USA.
As the temperature of the atmosphere changes, the
interaction height of incident cosmic rays changes, which affects the
production of muons that are seen underground.
A four percent
peak-to-peak seasonal fluctuation was seen over a period of four years, which
was highly correlated to the measured temperature variations of the upper
atmosphere over the same period. The coefficient relating changes in
the muon rate to changes changes in atmospheric temperature, $\alpha_T$,
was found to be: $\alpha_T = 0.877\pm0.010$~(stat.)~$\pm
0.017$~(syst.). A new model was developed to describe the observed
effect, and is the first to include the contribution from kaons. This
model predicts $\alpha_T = 0.865 \pm 0.015$.
The first
measurements of charge separated seasonal variations were reported:
$\alpha_T(\mu^+) = 0.782 \pm 0.056$~(stat.)$~\pm0.02$~(syst.),
$\alpha_T(\mu^-) = 0.788 \pm 0.066$~(stat.)$~\pm0.02$~(syst.).
The observed difference between the pion-only temperature coefficient
and the kaon-inclusive temperature coefficient allowed a measurement of the atmospheric K/$\pi$ ratio = $0.21\pm0.08$.

A high significance observation of two muon signals, the shadow of the
sun and moon, have been seen. The shadow of the moon was observed at
the \unit[5]{$\sigma$} level, and the shadow of the sun was observed at the \unit[4.3]{$\sigma$} level.
The angular resolution of the detector was found to be $0.62^{\circ}$
using dimuons, and the two
dimensional shadowing distribution was used to quantify the absolute
pointing of the detector $0.15\pm0.10^{\circ}$.

A cosmic ray point source search was performed, and no statistically significant source was found. In the
absence of a source, 95\% flux limits were placed on cosmic ray
sources. The minimum flux limit was $\unit[2.7\times 10^{-16}]{cm^{-2}s^{-1}}$, which is comparable to
the previous best limit set by MACRO~\cite{Habig:1996,Dekhissi:2000mu}.
Using the 239 Gamma Ray Bursts (GRBs) of the first Swift catalog a search for
space-time coincidence between neutrino induced muons and GRBs was
performed. In the absence of a statistically significant coincidence,
90\% flux limits were placed on neutrino production in GRBs.
Assuming a Waxman-Bahcall neutrino spectrum~\cite{Waxman:1997ti}, the
average 90\% flux limit
was found to be $\unit[1.7\times 10^{-8}]{GeV cm^{-2}s^{-1}}$. This new
limit is slightly better than the MACRO~\cite{Ambrosio:2000yx} and AMANDA~\cite{Achterberg:2007nx} limits as
well as the theoretical limit set by cosmic
rays~\cite{Waxman:1998yy,Bahcall:1999yr}, but does not constrain the model.

Files in Document:
Referenced by:
  • MINOS-doc-5941: Blessing package for Seasonal Effect/KPi Ratio in ICRC Proceedings
  • MINOS-doc-5940: Moon/Sun Shadows blessing package for ICRC proceedings
  • MINOS-doc-5939: Blessing package for Astroparticle Physics ICRC Proceedings
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