Transcript Slide 1

MINOS
Antineutrino running
Pedro Ochoa
Caltech
Feb 28 2006
1
Reverse horn current MC generation
Q: What could we do if we ran in antineutrino mode?
MINOS
 Generated some MC with inverted horn current:
Generate flux files with inverse horn current
(GNUMI v18, -10.0 from nominal, -185kA)
Generate MC files
(GMINOS)
Reconstruct MC files
(R1.18.2)
Feb 28 2006
1e7 POT of flux generated
(used fluka files in
/afs/fnal.gov/files/data/minos/d110
/fluka_hadrons/fluka05_xxx.ntp)
(Special thanks to Alysia M. !!)
200e20 POT
generated
200e20 POT
reconstructed
2
Energy spectra comparison
MINOS
A
1e20 POT
Neutrinos
Antineutrinos
B
1e20 POT
Neutrinos
Antineutrinos
A: red  Neutrinos in neutrino mode
blue  Antineutrinos in antineutrino mode
B: red  Neutrinos in antineutrimo mode
blue  Antineutrinos in neutrino mode
Feb 28 2006
3
Negative log likelihood analysis
MINOS
In order to get an idea of how well we could do an antineutrino oscillation
analysis (and thus a CPT violation measurement) with this data I performed a
negative log likelihood analysis with the following basics:
• For a given input parameter (typically m2=0.002 and sin2(2θ)=1) an
expected energy spectrum is obtained and then fluctuated statistically by a
Poisson. 800 pseudo-experiments are obtained in this fashion.
• Each pseudo-experiment spectrum is compared to the different spectra
generated for various combinations of m2,sin2(2θ) by the means of a negative
log likelihood:
 log(L)  bins ln Eexp! Eexp ln Eosc  Eosc 
• The average –log(L) is then obtained for each combination of m2,sin2(2θ)
and the minimum is substracted. The 2.3 contour gives an approximate ~90%
confidence limit.
• A complete “recipe” can be found at http://minos-docdb.fnal.gov:8080/cgibin/ShowDocument?docid=1422, slide 4.
Feb 28 2006
4
Antineutrino selection method
It was necessary to come up with an
antineutrino selection method. Selected
antineutrinos that satisfy:
Planes crossed
- At least 1 track
- Track must intersect 25 planes min.
- Track must pass fit
- Track must have (q/p)/(σ q/p)>2

MINOS

The method has an efficiency of 73.6%. The
remaining background is 5.6%.
Background
components


Feb 28 2006

(q/p)/(σ q/p) for
planes > 25
Neutrinos
Antineutrinos
e
This method is certainly not optimized, and much work
remains to be done in this area !
5
The results
MINOS
The results show a high dependence on the effectiveness of the selection cuts.
Therefore, for completeness purposes and in order to separate the effects that
the selection, the energy resolution and the statistics have, the results in the
following pages have three different contours:
1) A “realistic” contour, in which the selection cuts described in the previous
slide are applied and the reconstructed energy is used.
2) An “ideal” contour, where the selection efficiency is taken to be 100% and no
background is considered, but the reconstructed energy is used.
3) A “best possible” contour, which is obtained like the “ideal” one but using the
true energy. This gives the best case scenario.
Feb 28 2006
6
1.0e20 of  running alone:
MINOS
1.0e20 POT
1.0e20 POT
Realistic
Input value:
Best possible
m2  0.002eV 2
sin 2 (2 )  1
Ideal
Feb 28 2006
7
6.0e20 of  running alone:
MINOS
6.0e20 POT
6.0e20 POT
Ideal
Best possible
Realistic
Input value:
m2  0.002eV 2
sin 2 (2 )  1
Feb 28 2006
8
Combining 1e20 POT of  running and
6e20 POT of normal  running:
MINOS
Neutrino
running
Antineutrino
running
Realistic
Ideal
Best possible
Feb 28 2006
9
More results…
MINOS
Realistic
Realistic
Best possible
Ideal
Best possible
Ideal
Input value:
m2  0.002eV 2
Realistic
Ideal
Best possible
sin 2 (2 )  1
Feb 28 2006
10
Summary & Ongoing Work
MINOS
Antineutrino running:
 200e20 POT of carrot-equivalent reversed horn current data was
produced and analyzed. The possibility of running in antineutrino mode
is worth of consideration, as its combination with antineutrinos from
normal running may provide a reasonable calculation of Δm2(bar)
 Next step to a fuller treatment of antineutrino running is to include
systematics. This may not be very easy due to the different contributions
from neutrino running and antineutrino running.
Feb 28 2006
11
MINOS
A preliminary look at the double
ratio method for measuring
     transitions
C. Howcroft & P. Ochoa
Caltech
Feb 28 2006
12
Basic idea
MINOS
The basic idea of this method is to compare the ratio of antineutrinos to
neutrinos in both detectors to make a measurement of      transitions:
  
 
   K  
 
 
   FD
   ND
K can be determined using
MC (or maybe using small
fiducial region in ND)
Purpose of this work was to be a first step towards a fuller analysis by:
● determining how we expect K to be given the most recent MC.
● getting an idea of how statistically limited we are.
Please note that:
1) The carrot MC production in the L010185 configuration was used.
2) The results shown in this
talk represent the best
possible scenario since:
Feb 28 2006
- Assumed perfect energy resolution
- Assumed 100% selection efficiency
- No oscillation depletion taken into account
- No systematics considered
- Assumed 16e20 POT
13
Expected (MC) spectra at 16.0e20 POT
MINOS
ND

Near detector:
These are the histograms of true
energy of true (anti)neutrinos in the
ND used for the calculations.
Error bars are statistical error
based on the MC statistics used and
scaled accordingly.
ND

Only the n140 files were used, i.e. no
overlay and fiducial volume
interactions only.
Both plots are scaled to 16.0e20 POT
Feb 28 2006
14
MINOS
FD

Far detector:
These are the histograms of true
energy of true (anti)neutrinos in the
FD used in the calculation.
No oscillation effect was considered.
Both plots are scaled to 16.0e20 POT
FD
Feb 28 2006

15
Expected (MC) ratio of
antineutrinos to neutrinos
From the expected energy spectra we can obtain the expected
  / 
MINOS
ratio
in both detectors and compare them to each other:
  / 

ratio

/  FD


/  ND
ND
FD
This is the expected (MC) K of
slide 12, subsequently referred
to as “expected double ratio”
Feb 28 2006
16
Pseudo-experiment generation
MINOS
Need to be able to determine how much deviation can be expected from
the expected double ratio due to statistics.
In order to do that, took the 4 expected (anti)neutrino spectra
(neutrinos in the FD and ND, and antineutrinos in the FD and ND), and
fluctuated them statistically with a Poisson distribution.

ND
3 fluctuations shown

FD
3 fluctuations shown
The process was repeated 10,000 times.
Feb 28 2006
17
MINOS
Each time, the double ratio is calculated and the following histograms filled:
double ratio
(double ratio)/(expected double ratio)
Divide by
expected
double
ratio
90% C.L.
Expected double ratio
98% C.L.
Doing the same
at 6e20 POT
Would need to see, at the very least, a ~50% effect in order to claim
something is there !!
Feb 28 2006
18
Sensitivity to transition probability
MINOS
Also tried to roughly determine up to what percentage of transitioned
neutrinos we could have a sensitivity to in MINOS. For that invented a toy
model:
 m2 L 

P(v  v )  1  sin 2 sin 
Neutrinos disappear in usual way:
4
E


2
But now a fraction α of the disappeared
2
2  m L 

P(v  v )   sin 2 sin 
neutrinos goes to antineutrinos:
4
E


2
2
A negative log likelihood analysis was done, with α
as a unique parameter.
α=0.1
-Δlog(L)=2.3
Neutrinos:
- All (MC)
- That transition (MC)
- That will appear as antineutrinos
It was found that for the input value of α~0.1 and
smaller, the transition scenario is
indistinguishable
from no transitions at all.
Feb 28 2006
(16e20 POT assumed)
19
Summary & Ongoing Work
MINOS
Neutrino-antineutrino transitions:
 Using a toy model it was found that MINOS should be able to see if ~10%
(or more) of the neutrinos that disappear in the usual way transition to
antineutrinos.
 The MC expectation value of the double ratio (antineutrinos to neutrinos
was quantified with the latest version of the MC.
 Just based on statistics, it seems we would need to see a variation of
more than ~50% in the double ratio in order to claim new physics at
16e20 POT. Will work on adding other things to the calculation (selection
efficiencies, backgrounds, systematics…).
 Also have to work on a good antineutrino selection method.
Feb 28 2006
20
MINOS
Extra: one could deal with fractions instead of ratios. May try
this later
ND

   
Feb 28 2006
FD

   
21