Transcript S2_upmu

Soudan 2
Peter Litchfield
Minnesota University
For the Soudan 2 collaboration
Analysis of all contained and most partially contained events published
last year (PR D68 (2003) 113004)
New data on uncontained single muons has been extracted.
A preliminary oscillation fit including the new data has been performed
Reduced 90% allowed region, still in good agreement with Super-K
Probability of no oscillations now 6∙10-5
Soudan 2
Fine granularity
detector, originally built
to study proton decay
Low threshold
Good particle ID and
two track resolution
Surrounded by an
efficient veto shield to
tag non-neutrino events
produced by neutrals
from cosmic ray muon
interactions
Previous data
Data taking stopped in June 2001
with a fiducial exposure of 5.9 ktonyears
Analysis of contained and most
partially contained events was
published last year
Soudan 2 can observe and
reconstruct individual particles at the
production vertex, including protons in
quasi-elastic interactions. Much
improved resolution on L/E over just
detecting the lepton.
Data divided into 6 sub-sets
depending on topology and resolution.
The “high resolution” sample showed
clear evidence of oscillations in the L/E
distribution
Previous results
Bin-free Likelihood analysis of contained and
partially contained events using the FeldmanCousins prescription.
No oscillation hypothesis probability 5.8∙10-4
Partially contained 
Last summer’s analysis did not include events with a single  with its upper
end contained and lower end exiting the detector
Mixture of upward going  (upmu) from  interactions below the detector and
downward going  (downmu) from  interactions in the detector
The fine granularity of Soudan 2 allows these to be separated.
Downward , scattering increases
downwards, proton recoil at top
Upward , scattering increases
upwards, decay at top
Data reduction
The standard Soudan 2 analysis chain, program filter, physicist scan and
interactive graphics event reconstruction, was used.
The physicist scan included an estimate of the track direction (up or down)
MC events for  interacting in the detector were already included in the data
as originally processed.
New MC events for  interacting in the rock below the detector and with a 
stopping in the detector were generated and processed though the analysis
chain.
Soudan 2 has no fast timing, throughgoing upward  and  produced in the
detector which leave the top of the detector and have little or no hadronic
shower cannot be distinguished from the overwhelming background of
downward cosmic 
Because of the flat overburden at
Soudan the number of incoming,
stopping upgoing cosmic ray muons
was estimated to be negligible.
Events
Backgrounds
Data
Upward going tracks in the detector
can arise from cosmic ray muon
interactions in the rock producing
upward going pions.
We expect the veto shield to register
extra hits from other particles
produced in the interactions.
MC
Number of veto shield hits
Backgrounds
We expect hadronic tracks to
have a maximum range before they
interact
Veto shield hits
Data
Apply cuts:
MC
Range > 260 g/cm2
Range (g/cm2)
All veto shield hits are
associated with the muon track
After cuts
After cuts data and MC agree
Estimate negligible background
remaining
Veto shield hits
Data
MC
Range g/cm2
Check, hadronic events
Some events have obvious hadronic scatters
Cos(zenith)
Shaded events only have veto shield hits
associated with the track
Most have downward zeniths
None pass cuts
Background of non-scattering hadrons is
small
Veto shield hits
Range g/cm2
Range g/cm2
Event numbers
Scanned
No oscillation MC truth
Data
downmu
upmu
downmu
13.31.4
0.70.2
17
upmu
1.90.5
58.41.9
26
ambiguous
0.90.4
3.60.5
2
MC error is the error due to the MC statistics
A small number of events did not have a distinguishable direction and were
labeled ambiguous.
The separation of up and down going muons is good
The data and MC agree on the number of downmu. These come from
downward going neutrinos which the previous analysis has shown are largely
unoscillated
The data has only 50% of the expected MC rate for the upmus. These come
from upward going neutrinos from the other side of the earth which the
previous analysis has shown to be suppressed by oscillations.
Downmu
Energy of outgoing muon is
estimated from the multiple
scattering, shown in the previous
analysis of partially contained events
to be a reasonable estimator
Can calculate L/E, shown in plot
Shaded events are MC events
assigned the wrong direction
Data agrees well with the MC with
no oscillations.
In the fit to be described these
events are added to the partially
contained events already included in
the previous fit.
Upmu
Only observable is zenith angle or
equivalently distance traveled L
Upward going muons
Events/0.1
Tracks are at the end of their range, no
information on the hadron shower, no
measurement of  energy
Upward events suppressed, some
evidence for reduced suppression near
horizontal
Azimuthal angle is flat
Cos(zenith)
A new analysis incorporating
the new data has been carried
out using the same formalism as
that published in PR D68
Bin-free maximum likelihood
analysis using the FeldmanCousins prescription
Likelihood is calculated on a
15x80 grid of sin22θ23 x log10m2
Likelihood difference with the
best likelihood point obtained.
Best fit point in the grid square
centered at m2=0.0052 eV2 and
sin22θ23=0.97 but the Super-K
best fit point is not much worse.
L
New Oscillation Analysis
Comparison with data
2/data points
PCE
UPMU
All data
No oscillations
5.0/5
9.4/5
62.2/30
Best fit
4.1/5
0.9/4
32.5/30
Saturated oscillations
18.2/5
0.8/4
59.9/30
Best fit
No oscillations
Saturated oscillations
(high m2,sin22θ23)
Limits calculation
If all errors were statistical the 90% confidence region would be defined by a
likelihood rise of 2.3 from the minimum
BUT errors are NOT statistical
Effects of physical boundaries (sin22θ23<1.0)
Errors on L/E are not gaussian
Flux normalisation and background subtraction introduces nuisance
parameters
Systematic errors on calibrations, fluxes and cross-sections
Calculate confidence regions using the Feldman-Cousins prescription
Confidence level contours are calculated by performing MC experiments at
each grid square, including experimental statistical and systematic variations, and
calculating the likelihood difference between that square and the best likelihood.
90% confidence contours defined by the likelihood difference that contains 90%
of the MC experiments
Confidence limits
MC90
90% likelihood surface
Comparisons
Effect of new data
Old analysis
This analysis
Comparison with Super-K and MACRO
Probability of no oscillations
To calculate the probability of no
oscillations MC experiments are
generated in the lowest m2,
sin22θ23 grid square
100,000 experiments generated,
including all statistical and
systematic effects
Difference between the lowest
negative log likelihood and that in
this square (LMC) plotted
6 MC experiments had a LMC
greater than the data likelihood
(16.02)
Probability of no oscillations 6∙10-5
Conclusions
The new uncontained single muon data confirm the oscillation picture
first found by Super-K and confirmed by previous Soudan 2 analyses.
Small, if any, oscillation supression of downward  interactions
Large supression of upward  interactions
The bin-free likelihood analysis confirms and reduces the allowed
region obtained earlier.
The probability of no oscillations is 6∙10-5
All Soudan 2 data is well fitted by oscillations with parameters that
agree with those found by Super-K
This is THE END for Soudan 2 oscillation physics, all available data
has been analysed.