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Title: Cosmic ray muon charge ratio in the MINOS far detector

Abstract

The MINOS Far Detector is a 5.4 kiloton (5.2 kt steel plus 0.2 kt scintillator plus aluminum skin) magnetized tracking calorimeter located 710 meters underground in the Soudan mine in Northern Minnesota. MINOS is the first large, deep underground detector with a magnetic field and thus capable of making measurements of the momentum and charge of cosmic ray muons. Despite encountering unexpected anomalies in distributions of the charge ratio (N{sub μ +/N μ-) of cosmic muons, a method of canceling systematic errors is proposed and demonstrated. The result is R eff = 1.346 ± 0.002 (stat) ± 0.016 (syst) for the averaged charge ratio, and a result for a rising fit to slant depth of R(X) = 1.300 ± 0.008 (stat) ± 0.016 (syst) + (1.8 ± 0.3) x 10 -5 x X, valid over the range of slant depths from 2000 < X < 6000 MWE. This slant depth range corresponds to minimum surface muon energies between 750 GeV and 5 TeV.

Authors:
 [1]
  1. Univ. of Minnesota, Minneapolis, MN (United States)
Publication Date:
Research Org.:
Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
892438
Report Number(s):
FERMILAB-THESIS-2005-74
TRN: US200704%%419
DOE Contract Number:
AC02-76CH03000
Resource Type:
Thesis/Dissertation
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; 72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; ALUMINIUM; CALORIMETERS; COSMIC MUONS; MAGNETIC FIELDS; MINUS-PLUS RATIO; MUONS; PHOSPHORS; STEELS; Experiment-HEP

Citation Formats

Beall, Erik B. Cosmic ray muon charge ratio in the MINOS far detector. United States: N. p., 2005. Web. doi:10.2172/892438.
Beall, Erik B. Cosmic ray muon charge ratio in the MINOS far detector. United States. doi:10.2172/892438.
Beall, Erik B. Thu . "Cosmic ray muon charge ratio in the MINOS far detector". United States. doi:10.2172/892438. https://www.osti.gov/servlets/purl/892438.
@article{osti_892438,
title = {Cosmic ray muon charge ratio in the MINOS far detector},
author = {Beall, Erik B.},
abstractNote = {The MINOS Far Detector is a 5.4 kiloton (5.2 kt steel plus 0.2 kt scintillator plus aluminum skin) magnetized tracking calorimeter located 710 meters underground in the Soudan mine in Northern Minnesota. MINOS is the first large, deep underground detector with a magnetic field and thus capable of making measurements of the momentum and charge of cosmic ray muons. Despite encountering unexpected anomalies in distributions of the charge ratio (N{sub μ+/Nμ-) of cosmic muons, a method of canceling systematic errors is proposed and demonstrated. The result is Reff = 1.346 ± 0.002 (stat) ± 0.016 (syst) for the averaged charge ratio, and a result for a rising fit to slant depth of R(X) = 1.300 ± 0.008 (stat) ± 0.016 (syst) + (1.8 ± 0.3) x 10-5 x X, valid over the range of slant depths from 2000 < X < 6000 MWE. This slant depth range corresponds to minimum surface muon energies between 750 GeV and 5 TeV.},
doi = {10.2172/892438},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Thu Dec 01 00:00:00 EST 2005},
month = {Thu Dec 01 00:00:00 EST 2005}
}

Thesis/Dissertation:
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  • It is now widely accepted that the Standard Model assumption of massless neutrinos is wrong, due primarily to the observation of solar and atmospheric neutrino flavor oscillations by a small number of convincing experiments. The MINOS Far Detector, capable of observing both the outgoing lepton and associated showering products of a neutrino interaction, provides an excellent opportunity to independently search for an oscillation signature in atmospheric neutrinos. To this end, a MINOS data set from an 883 live day, 13.1 kt-yr exposure collected between July, 2003 and April, 2007 has been analyzed. 105 candidate charged current muon neutrino interactions were observed, with 120.5 ± 1.3 (statistical error only) expected in the absence of oscillation. A maximum likelihood analysis of the observed log(L/E) spectrum shows that the null oscillation hypothesis is excluded at over 96% confidence and that the best fit oscillation parameters are sin 223 = 0.95 -0.32 and Δmmore » $$2\atop{23}$$ = 0.93$$+3.94\atop{ -0.44}$$ x 10 -3 eV 2. This measurement of oscillation parameters is consistent with the best fit values from the Super-Kamiokande experiment at 68% confidence.« less
  • The MINOS experiment is a neutrino oscillation baseline experiment intending to use high resolution L/E neutrinos to measure the atmospheric neutrino oscillations parameters to unprecedented precision. Two detectors have been built to realize the measurements, a Near detector, located about 1km downstream from the beam target at the Fermi Laboratory, and a Far detector, located at 736km, at the Soudan Laboratory. The technique relies on the Near detector to measure the un-oscillated neutrino spectrum, while the Far detector measures the neutrino spectrum once oscillated. The comparison between the two measurements is expected to allow MINOS to measure Δm 2 beyondmore » 10% precision level. The Near and Far detectors have been built similarly to minimize possible systematic effects. Both detectors have been endowed with different readout systems, as the beam event rates are very different. The MINOS calibration detector (CalDet), installed at CERN, was instrumented with both readout systems such that they can simultaneously measure and characterize the energy deposition (response and event topology) of incident known particle from test-beams. This thesis presents the investigations to quantify the impact of the performance of both readout systems on the MINOS results using the measurements obtained with CalDet. The relative comparison of the responses of both readout systems have been measured to be consistent with being identical within a systematic uncertainty of 0.6%. The event topologies have been found to be negligibly affected. In addition, the performance of the detector simulations have been thoroughly investigated and validated to be in agreement with data within similar level of uncertainties.« less
  • The phenomenon of flavour oscillations of neutrinos created in the atmosphere was first reported by the Super-Kamiokande collaboration in 1998 and since then has been confirmed by Soudan 2 and MACRO. The MINOS Far Detector is the first magnetized neutrino detector able to study atmospheric neutrino oscillations. Although it was designed to detect neutrinos from the NuMI beam, it provides a unique opportunity to measure the oscillation parameters for neutrinos and anti-neutrinos independently. The MINOS Far Detector was completed in August 2003 and since then has collected 2.52 kton-years of atmospheric data. Atmospheric neutrino interactions contained within the volume of the detector are separated from the dominant background from cosmic ray muons. Thirty seven events are selected with an estimated background contamination of less than 10%. Using the detector's magnetic field, 17 neutrino events and 6 anti-neutrino events are identified, 14 events have ambiguous charge. The neutrino oscillation parameters for v μ andmore » $$\bar{v}$$ μ are studied using a maximum likelihood analysis. The measurement does not place constraining limits on the neutrino oscillation parameters due to the limited statistics of the data set analysed. However, this thesis represents the first observation of charge separated atmospheric neutrino interactions. It also details the techniques developed to perform atmospheric neutrino analyses in the MINOS Far Detector.« less
  • In recent years, neutrino experiments have begun to challenge the Standard Model assumption that neutrinos are massless. There is now firm evidence that neutrinos undergo quantum mechanical oscillations between flavors. This would imply that neutrinos possess mass and that neutrino flavors are mixed by the weak interaction. Atmospheric neutrinos, produced by the interactions of cosmic rays in the earth's atmosphere, can be used to study these oscillations. The MINOS Far Detector has been collecting atmospheric neutrino data since 1st August 2003 using a 5.4 kT steel-scintillator sampling calorimeter located 700 m underground (2100 m water-equivalent) at the Soudan Underground Laboratory, Minnesota. The Far Detector is the first massive underground detector to possess a magnetic field. This makes the separation of atmospheric v μ andmore » $$\bar{v}$$ μ charged current interactions possible for the first time. This thesis presents a study of atmospheric neutrino oscillations in the Far Detector, based on a total detector exposure of 316 days (3.3 kT-Yrs fiducial exposure). The separation of atmospheric neutrinos from the high background of cosmic muons is outlined. A total of 82 candidate events are observed, with an expectation of 109.9 ± 21.4 events in the absence of oscillations. Of the selected events, 40 events have a clearly identified charge, with 27 events tagged as neutrinos and 13 events tagged at anti-neutrinos. This represents the first direct observation of atmospheric v μ and $$\bar{v}$$ μ charged current interactions. A maximum likelihood analysis us used to determine the allowed region for the oscillation parameters Δm$$2\atop{23}$$ and sin 223. This disfavors the null oscillation hypothesis at the 79% confidence level. With the current low statistics, the sensitivity of the analysis is limited. The expected future sensitivity of the atmospheric neutrino analysis is discussed.« less
  • The MINOS Far Detector is a 5400 ton iron calorimeter located at the Soudan state park in Soudan Minnesota. The MINOS far detector can observe atmospheric neutrinos and separate charge current ν μ andmore » $$\bar{v}$$ μ interactions by using a 1.4 T magnetic field to identify the charge of the produced muon. The CPT theorem requires that neutrinos and anti-neutrinos oscillate in the same way. In a fiducial exposure of 5.0 kilo-ton years a total of 41 candidate neutrino events are observed with an expectation of 53.1 ± 7.6(system.) ± 7.2(stat.) unoscillated events or 31.6 ± 4.7(system.) ± 5.6(stat.) events with Δm 2 = 2.4 x 10 -3 eV 2, sin 2(2θ) = 1.0 as oscillation parameters. These include 28 events which can have there charge identified with high confidence. These 28 events consist of 18 events consistent with being produced by ν μ and 10 events being consistent with being produced by $$\bar{v}$$ μ. No evidence of CPT violation is observed.« less