The Many Uses of Upwardgoing Muons in SuperK

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The Many Uses of Upward-going Muons in Super-K

• Muons traveling up into Super-K from high-energy
  nm reactions in the rock below provide a
  high-energy insight into many different problems.

Alec Habig, Univ. of Minnesota Duluth for the
Super-K Collaboration
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Upward-going m

• High energy nm can interact in rock some distance
  away and still produce a m seen by detector
• Higher energy particles, more range, more
  effective volume!
• Increasing target mass at high E offsets falling
  nm spectra
• Down-going entering cosmic ray muons restrict
  this technique to upward-going entering muons

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Up-ms in Super-K

• For SK-I
• 4/96 to 7/01
• 1678 live-days up-thru (1657 up-stop)
• More than other SK analyses, this one is
  insensitive to poor detector conditions
• For gt7m path (gt1.6 GeV)
• 1878 thru-m
• 456 stop-m

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Atmospheric nm

• Up-m flux is presented as a function of cosq and
  thus baseline
• cosq-1 (Up) have L10,000 km
• cosq0 (Horizontal) have L500 km
• Lower E, longer L ns oscillate more
• The data match the oscillated MC far better than
  the non-oscillated MC
• sin22q1.0, Dm22.7x10-3

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Energy Lever Arm

• For nm seen as up-m
• Typical En 10 GeV for stop-m, 100 GeV for
  thru-m
• Compare to contained event energies GeV
• From the soft atmospheric n spectrum. A harder n
  spectrum would produce a larger fraction of high
  energy parent n
• Disadvantage for any single event, the parent n
  energy is known only to be larger than the
  observed m energy

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nm, nt Oscillation

• Even with comparatively small statistics and
  lousy energy resolution, the observation of nm
  disappearance at higher energies further refines
  the oscillation fit
• Left 90 C.L. contours with and without up-m
  data
• Best fit (physical region)
• sin22q 1.0
• Dm2 2.5x10-3

90 C.L. FC,PC Alone With up-m
(absolute best fit slightly unphysical at
sin22q1.03)
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nm to nsterile?

• High energy n experience matter effects which
  suppress oscillations to sterile n
• Matter effects not seen in up-m or high-energy PC
  data
• Reduction in neutral current interactions also
  not seen
• constrains ns component of nm disappearance
  oscillations
• Pure nm-ns disfavored
• ns fraction lt 20 at 90 c.l.

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Unusual Models

• Alternative ways to make nm disappear without
  invoking standard nm,nt flavor oscillations
  include
• Lorentz invariance violation
• Neutrino decay, decoherence
• Fits using all available SK n data
  (FCPCNCmultiring up-m, 190 d.o.f.) strongly
  constrains many such models
• Hard for a model to get a good fit over 5 orders
  of magnitude in energy and 4 in baseline
• Long t nm decay and nm decoherence disfavored but
  not eliminated

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Galactic Atmospherics?

• Cosmic rays interact with interstellar medium as
  well as our atmosphere
• Would also produce n
• ISM most dense at low galactic latitudes
• Do we see excess n in the galactic plane?
• A search for these n does not see this weak signal

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Astrophysical n

• A hard n spectrum more likely a n signal will be
  seen as up-m
• n space-time coincidences with GRBs not seen at
  any energy in SK
• AGNs or other astrophysical sources would produce
  point sources of high-energy n
• All sky searches for such point-sources are
  negative
• Unbinned searches for unusual clustering of up-m
  also negative

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Pick a Source, Any Source

• To test your favorite model of n production at
  some high energy astrophysical source
• Up-m near sources counted, a sampling shown here
• Expected count from atm.n background calculated
• No excess seen, flux limits computed

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WIMP Detection

• WIMPs could be seen indirectly via their
  annihilation products (eventually nm) if they are
  captured in a gravitational well
• WIMPs of larger mass would produce a tighter n
  beam
• Differently sized angular windows allow searches
  to be optimized for different mass WIMPs

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WIMP Results

• The Sun, Earth, and Galactic center are potential
  WIMP traps
• No excess of n are seen in any angular cone about
  them
• Upper limit of WIMP-induced n calculated
• Varies as a function of possible WIMP mass
• Lower limits for higher masses are due to the
  better S/N in smaller angular search windows

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Probing for WIMPs

• Most model dependence in indirect searches lies
  in the cross-section
• Most conservative limits are taken for other
  uncertainties
• Direct-detection experiments also do not know
  cross-sections
• Comparisons can be made between direct and
  indirect searches
• Both spin-dependent (left) and spin-independent
  (right) WIMP-nucleon interactions can be probed
  (a la Kamionkowski, Ullio, et al)

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Summary

• The high-energy end of the nm spectrum observed
  by Super-K is seen as up-going m
• The extra lever arm in energy contributes to
  oscillation parameter estimation out of
  proportion to the small statistics and poor
  energy resolution of the sample
• The high parent n energies allow probes of
  unusual areas of physics and astrophysics
• Nothing unexpected seen, unfortunately

The presenter gratefully acknowledges support for
this poster from the National Science Foundation
via its RUI grant 0098579, and from The Research
Corporations Cottrell College Science Award