MINOS Document 8323-v1

Thesis - Measuring neutrino oscillation parameters using &#957;<sub>&#956;</sub> disappearance in MINOS

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Christopher Backhouse
Updated by:
Christopher Backhouse
Document Created:
28 Jun 2011, 14:57
Contents Revised:
28 Jun 2011, 14:57
Metadata Revised:
06 May 2014, 09:39
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MINOS is a long-baseline neutrino oscillation experiment. It consists of two
large steel-scintillator tracking calorimeters. The near detector is situated
at Fermilab, close to the production point of the NuMI muon-neutrino beam. The
far detector is \unit[735]{km} away, \unit[716]{m} underground in the Soudan
mine, Northern Minnesota.

The primary purpose of the MINOS experiment is to make precise measurements of
the ``atmospheric'' neutrino oscillation parameters ($\Dm{\rm atm}$ and
$\sin^22\theta_{\rm atm}$). The oscillation signal consists of an
energy-dependent deficit of $\nu_\mu$ interactions in the far detector. The
near detector is used to characterize the properties of the beam before
oscillations develop. The two-detector design allows many potential sources of
systematic error in the far detector to be mitigated by the near detector

This thesis describes the details of the $\nu_\mu$-disappearance analysis, and
presents a new technique to estimate the hadronic energy of neutrino
interactions. This estimator achieves a significant improvement in the energy
resolution of the neutrino spectrum, and in the sensitivity of the neutrino
oscillation fit. The systematic uncertainty on the hadronic energy scale was
re-evaluated and found to be comparable to that of the energy estimator
previously in use.

The best-fit oscillation parameters of the $\nu_\mu$-disappearance analysis,
incorporating this new estimator were:
$\Dm{}=\unit[2.32^{+0.12}_{-0.08}\times10^{-3}]{eV^2}$, $\sin^22\theta>0.90$
(90\% C.L.). A similar analysis, using data from a period of running where the
NuMI beam was operated in a configuration producing a predominantly
$\bar\nu_\mu$ beam, yielded somewhat different best-fit parameters $\Delta\bar
m^2=\left(3.36^{+0.46}_{-0.40}({\rm stat.})\pm0.06({\rm
syst.})\right)\times10^{-3}\unit{eV^2}$, $\sin^22\bar\theta=0.86^{+0.11}_{-0.12\
stat.})\pm0.01({\rm syst.})$. The tension between these results is intriguing,
and additional antineutrino data is currently being taken in order to further
investigate this apparent discrepancy.

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