6 on ?

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6 on ?
An Update on the 2000-2003 Diffuse Muon Neutrino
Analysis Jessica Hodges Friday, December 16th
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6 observed on ? Status The analysis was
unblinded several months ago and 6 events passed
all cuts, including the final energy-dependent
cut, Nchgt100. Background Prediction At the
time of unblinding, the assumed background was
composed of conventional atmospheric neutrinos
using the Lipari weighting scheme. Overall
normalization of 0.887 matched the Monte Carlo to
the data. This led to a background prediction of
9.8 events.
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Consider new neutrino flux predictions instead of
Lipari (which is older and 1-dimensional) Instead
, consider two more recent calculations based on
more up-to-date observations (use the values for
Bartol and Honda from the NeutrinoFlux class
developed by Alessio summer 2005) BARTOL
2004 HKKM 2004
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Differences in the Neutrino Spectrum arise from
different ways to characterize 1 CR flux
from different elements (H, He, heavier
components) 2 hadronic interactions,
particularly kaon flux at high energy
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Four parameters are used to characterize the
cosmic ray flux for each element.
? (Ek) K ( Ek b e -C (Ek)0.5)-?
Honda and Bartol use similar, but not identical,
values for the parameter ? for protons and the
heavier elements. However, the values are so
close that the primary cosmic ray spectra from
Bartol and Honda are identical to within 1.
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HERE YOU CAN SEE THE DIFFERENCES BETWEEN THE
BARTOL AND HONDA PROTON FLUXES
short dashed green line old HKKM
pink solid line HKKM 2004
dashed green line BARTOL 2004
taken from HKKM 2004 paper
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Despite small differences in the individual
element inputs..... For the all-nucleon cosmic
ray spectrum, Bartol and Honda are the same to
within 1.
old Bartol
Bartol 2004
Honda 2004
Since the CR all-nucleon inputs are roughly the
same, any differences in the neutrino flux that
arise between Bartol and Honda are from hadronic
interactions.
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Honda and Bartol are 25 different in their
predicted NEUTRINO flux. Considering both of
these models in my final result should encompass
the range of uncertainty in the hadronic
interaction model.
Consider the red line only. (blue line still
needs to be checked with higher statistics)
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25
plot made by Teresa Montaruli
Bartol 2004 and Honda 2004 are 15 different at
103 GeV 1 TeV
25 different at 104 GeV 10
TeV
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peak energy of atmospheric ? before energy
cut 103 GeV 1 TeV
peak energy of atmospheric ? after energy cut 104
GeV 10 TeV
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my atmospheric neutrinos come from this part of
the CR spectrum
Neutrino energy is roughly a factor of 10 less
than the CR primary energy
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Change the spectral index of the neutrinos.
Reweight events with (Trueen2 )-0.0X
Region of Interest
E? spectrum
log10E?
In my region of interest, the lines are nearly
parallel. Hence, changing the spectral index acts
as a change in overall normalization. This is
because my events are very high energy and I am
pivoting about a very low energy point.
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Thus far, I have explored these ways of changing
my background prediction 1) Changing the flux
model. Bartol and Honda atmospheric neutrinos
have different shapes because they use
different hadronic interaction models. 2)
Changing the neutrino slope and hence the
up/down normalization of the flux. What
other parameters can I study that might alter the
number of events I predict as my background?
Need to check detector effects like OM
sensitivity.
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Assume that every OM has had its absolute
sensitivity modified by - 30. Use 2003
nusim and data files (prepared identically in
Zeuthen). Perform a 2-bin analysis like in
Zeuthen.
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Sensitivity
Vertical Bin
Horizontal Bin
70
100
130
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The data ratio is 1.125. This indicates that at
this cut level, the best fit to the OM
sensitivity must be roughly between 110 and 120.
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Does the optimal sensitivity change with
cuts? Zeuthen followed essentially the same
procedure and found that the best fit sensitivity
for their analysis was 92 /- 10. So, YES,
optimal OM sensitivity varies with the cuts.
---gtgtgt Next, check my different cut levels and
see what OM sensitivity is the best fit.
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Look at the plots of sensitivity vs
ratio. Quickly eyeballing where the best fit OM
sensitivity level 1 75-95 level
2 100-115 level 3 125-135 level
4 135-145 level 5 115-125 level
6 110-120 level 7 110-120 level 8 150?? level
9 105-125
level1
Note that these values are all over the place!
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Is 115 consistent with 92? With this 2-bin
zenith procedure, the value indicated for the OM
sensitivity changes greatly with cut
level. Since Zeuthen's cuts are different than
mine, given what I just told you, it seems
natural that they would measure a best fit to the
OM sensitivity that is different than
mine. Hence, it is difficult (read impossible
with our current knowledge) to pinpoint the OM
sensitivity to one single value that is
independent of any given analysis. The range of
possible OM sensitivities is still wide open.
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How to Proceed 1. Consider ALL of the possible
models across the range of possible OM
sensitivities. 2 hadronic interaction models
(BARTOL, HONDA) 7 neutrino spectrum power
laws (0.4, .02, .01, 0, -.01, -.02,
-.03) 2. Choose a subset of these scenarios as
the best fit or most likely scenarios. 3.
Find out how many events are predicted for
Nchgt100 for these best fit scenarios. Choose
the largest and smallest as the range of possible
background events.
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Consider low energy data Nch lt 100 Data 186
events. The 1 sigma range is 172 to 200 events.
Choose combos which cause the atmospheric
neutrino prediction to fall within 1 sigma of the
measured data value.
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All of these combinations satisfy the condition
that the number of low energy atmospheric
neutrinos predicted falls within 1 sigma of the
measured data value.
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Count the number of events in the best fit
scenarios for Nchgt100. Average these numbers
for table made with the Bartol flux. Repeat for
Honda. These two values will be input as the
high and low range of the atmospheric neutrino
background.
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Next, need a prediction for how the signal
behaves. Is the signal affected differently by
the OM sensitivity? Yes, because higher energy
events are not as affected by threshold effects.
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Threshold effects Dramatically increasing the OM
sensitivity pushes many low energy events into
the survival region.
Ratio of number of events for 130 Lipari / 70
Lipari
Ratio of number of events for 130 Signal / 70
Signal
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Consider the entire range, 70 to 130, and the
number of signal counts. 70 sensitivity 15.7
counts in 2003 100 sensitivity 20.1 counts in
2003 130 sensitivity 25.8 counts in
2003 Hence, suppose that the signal should
fluctuate by 25 in either direction from the
value I predicted for the 4-year analysis. For
2000-2003, I predicted 68.4 signal events after
the energy cut. This could fluctuate to 51.3 or
85.5.
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Final Steps Take the range of predicted signal
and background events and use these to smear out
the confidence belt used to compute the
limit. Find the new limit with systematic
errors. Write a paper. Be happy. -)
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ATIC filled in the gap between 100 and 10000 GeV
The top pink proton fit is the BARTOL proton fit
that you saw on the last page.