What beamline group will supply
for the (day-1) oscillation analysis
A.K.Ichikawa
For T2K beamline group
Note
This is just a starting-point material for day-1
analysis. More discussion among the
beamilne group is necessary.
This note will be modified when
more studies arises,
real data come,
or
statistic increases after day-1.
What beamline group will supply for
the oscillation analysis
• Expected neutrino flux at the near
detectors and far detector.
• Correlation between flux at the near
detectors and that at the far detector, i.e.
far-to-near ratio.
• Systematic errors for above quantities.
For the real data processing, refer
Nakadaira-san’s presentation file at the
last collaboration (pre) meeting.
Systematic errors
to be taken into account for
oscillation analysis
I.
II.
Beam/horn miss-alignment
Horn magnetic field
i.
ii.
III.
IV.
V.
VI.
Absolute field strength
Distortion of the distribution
Primary beam profile
Primary hadron production
Secondary hadron interaction
Something which is not yet forseen.
How to propagate beam systematic
errors for ND/SK spectrum fitting
•
Correction function/vector for spectrum itself
for each systematic errors.
Example: DF(Ei)= Dy*ci
position
•
•
: Dy is proton beam mis-hit
Correlation matrix for systematic errors.
Neutrino spectra itself will be re-weighted and
fitted by near/far detector observations within
the constraints of the systematic error matrix.
Q: Method for evaluating impact of
parameter variation
• Use beam MC
Q: Corresponding available data or measurements,
internal T2K or external, available to constrain
these parameter variations
•
Beam/horn miss-alignment
–
–
•
Survey during the installation
Data from primary beam monitor, MUMON and INGRID
Horn magnetic field
–
Absolute field strength
•
•
–
Distortion of the distribution
•
•
•
Field measurement
Current Transformer at stripilne
Field measurement
Indirectly, MUMON and INGRID
Primary beam profile
–
•
Data from primary beam monitor
Primary hadron production
–
–
–
•
Model comparison and reasonable assumption on the model
discrepancy
NA61 result
ND280 off-axis measurement
Secondary hadron interaction
–
Same as the primary hadron production
Q: is reweighting possible?
• Yes, we will provide neutrino-energyhistogram based weighting for systematic
errors
Q: effect of parameter on numu analysis, on nue
analysis (this may be extracted from the global
analysis)
precision achievable on parameter from the data
• If beamline components including MUMON and INGRID
work as expected, effect on the oscillation analysis from
the beam related systematic errors will be sufficiently
small compared to day-1 statistics and quite controllable
except for the hadron production part.
• For the hadron production part, NA61 results will help a
lot. Further MC study is necessary to evaluate the effect
on the oscillation analysis from hadron production
uncertainty either before NA61 and after NA61. And off
course, ND280 off-axis detector is expected to put
constraint on the numu and nue flux.
Followings are specific questions to
beamline group and answers to them
How will we feedback the data from the muon monitors,
NGRID and even ND280 into the beam monte carlo
(Jnubeam) to either adjust it, evaluate systematic errors,
reweight or include it in a global fit of ND280 (which
depends both on flux and cross-sections)?
• As written in previous pages, the information from
MUMON and INGRID (and primay beam monitor) will be
used to constrain the uncertainty of the beam/horn
misalignment and probably asymmetric distortion of the
horn fields. The correction function of the neutrino
energy spectrum will be made from jnubeam. The actual
correction is a product of a systematic error amplitude
and corresponding correction function. The systematic
error amplitude can be constraint by the information from
MUMON and INGRID etc.
• On the other hand, the data from the ND280 off-axis
detector will be used to put a constraint on the { flux
(neutrino energy spectra) x cross section}. The far
detector {flux x cross section} can be obtained by
extrapolating the ND measurements.
1. how to establish the misalignments
experimentally?
Just as an example: one could think of taking initial
runs with the beam monitors and the NGRID and
operating e.g. no horn, then one horn at a time, etc..
to assess whether one can constrain the alignment
of each of the horns individually (I believe this does
not require high intensity)
• MUMON and INGRID !! (with Horn operation.)
• If horn-off running helps or not is not trivial. I’m
afraid that profile is too broad with horn-off
running to obtain useful information. But yes, we
can and should do study with beam MC.
how will the feedback from the near detector (ND280) be
done? (or what observations are more sensitive to flux and
what are more sensitive to cross-section model?) I think this
will involve some sort of global fit...
• Off-axis method gives numu flux which is rather
independent on the hadron production. So it is expected
that the ND280 off-axis measurement would be sensitive
on the neutrino cross section. NA61 will further strength
this direction.
• More beam MC study is necessary to evaluate how
precisely we can predict the nue flux without NA61 nor
ND280 off-axis measurement. Since the main contributor
to nue at around the peak energy is muon decay, the
uncertainty may be sufficiently small for the quantity
nue/numu. But it is absolutely helpful if either NA61 Kaon
or ND280 measurement (numu high energy tail or nue
itself) is on time for day-1 analysis. (Note that high
precision results are not necessary.)
as a related question to the previous one: how will the nue
flux to SK be determined two methods are possible
-- direct from nue events in ND280
-- indirect from numu events in ND280 constraining the nue
prediction from JNUBEAM
• Yes, both methods seems possible. See
the next slides. It is expected that the nue
from muon has less uncertainty if
nue/numu is used. While the Kaon
uncertainty may be rather large, but this
part may be constraint by numu highenergy tail measurement.
Red : Kaon contribution
Red : Kaon contribution