Feb 28 2006 1

MINOS

Antineutrino running

Pedro Ochoa

Caltech

Feb 28 2006 2

MINOS

Generate flux files with inverse horn current(GNUMI v18, -10.0 from nominal, -185kA)

Generate MC files (GMINOS)

Reconstruct MC files(R1.18.2)

1e7 POT of flux generated(used fluka files in

/afs/fnal.gov/files/data/minos/d110 /fluka_hadrons/fluka05_xxx.ntp)

200e20 POT generated

200e20 POT reconstructed

Reverse horn current MC generation

Q: What could we do if we ran in antineutrino mode?

Generated some MC with inverted horn current:

(Special thanks to Alysia M. !!)

Feb 28 2006 3

MINOS

1e20 POT 1e20 POT

NeutrinosAntineutrinos

Energy spectra comparison

NeutrinosAntineutrinos

A B

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 4

MINOS

Negative log likelihood analysis

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:

• 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/cgi-bin/ShowDocument?docid=1422, slide 4.

bins oscosc EEEEL ln!ln)log( expexp

Feb 28 2006 5

MINOS

(q/p)/(σ q/p) forplanes > 25

Antineutrino selection method

NeutrinosAntineutrinos

It was necessary to come up with an antineutrino selection method. Selected antineutrinos that satisfy:

- At least 1 track- Track must intersect 25 planes min.- Track must pass fit- Track must have (q/p)/(σ q/p)>2

The method has an efficiency of 73.6%. The remaining background is 5.6%.

Planes crossed

Background components

e

This method is certainly not optimized, and much work remains to be done in this area !

Feb 28 2006 6

MINOS

The results

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 7

MINOS

1)2(sin

002.02

22

eVm

Input value:Realistic

Ideal

Best possible

1.0e20 of running alone:

1.0e20 POT

1.0e20 POT

Feb 28 2006 8

MINOS

1)2(sin

002.02

22

eVm

Input value:

RealisticIdeal

Best possible

6.0e20 of running alone:

6.0e20 POT

6.0e20 POT

Feb 28 2006 9

MINOS

Realistic

Ideal

Best possible

Combining 1e20 POT of running and 6e20 POT of normal running:

Antineutrino running

Neutrino running

Feb 28 2006 10

MINOS

More results…

1)2(sin

002.02

22

eVm

Input value:

Realistic

Ideal

Best possible

Realistic

IdealBest possible

Realistic

Ideal Best possible

Feb 28 2006 11

MINOS

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.

Summary & Ongoing Work

Antineutrino running:

Feb 28 2006 12

MINOS

A preliminary look at the double ratio method for measuring

transitions

C. Howcroft & P. Ochoa

Caltech

Feb 28 2006 13

MINOS

Basic idea

The basic idea of this method is to compare the ratio of antineutrinos to neutrinos in both detectors to make a measurement of transitions:

1) The carrot MC production in the L010185 configuration was used.

2) The results shown in this talk represent the best possible scenario since:

- Assumed perfect energy resolution- Assumed 100% selection efficiency- No oscillation depletion taken into account- No systematics considered- Assumed 16e20 POT

NDFD

K

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:

K can be determined using MC (or maybe using small fiducial

region in ND)

Feb 28 2006 14

MINOS

Expected (MC) spectra at 16.0e20 POT

These are the histograms of true energy of true (anti)neutrinos in the ND used for the calculations.

ND

ND

Near detector:

Error bars are statistical error based on the MC statistics used and scaled accordingly.

Both plots are scaled to 16.0e20 POT

Only the n140 files were used, i.e. no overlay and fiducial volume interactions only.

Feb 28 2006 15

MINOS

FD

FD

Far detector:

Both plots are scaled to 16.0e20 POT

These are the histograms of true energy of true (anti)neutrinos in the FD used in the calculation.

No oscillation effect was considered.

Feb 28 2006 16

MINOS

Expected (MC) ratio of antineutrinos to neutrinos

From the expected energy spectra we can obtain the expected ratio

in both detectors and compare them to each other:

/

/ ratio

NDFD

ND

FD

/

/

This is the expected (MC) K of slide 12, subsequently referred to as “expected

double ratio”

Feb 28 2006 17

MINOS

Pseudo-experiment generation

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.

The process was repeated 10,000 times.

FDND

3 fluctuations shown 3 fluctuations shown

Feb 28 2006 18

MINOSEach time, the double ratio is calculated and the following histograms filled:

Expected double ratio

Divide by expected double

ratio

Would need to see, at the very least, a ~50% effect in order to claim something is there !!

90% C.L.

98% C.L.

double ratio (double ratio)/(expected double ratio)

Doing the same at 6e20 POT

Feb 28 2006 19

MINOS

Sensitivity to transition probability

E

LmvvP

4sin2sin1)(

222 Neutrinos disappear in usual way:

But now a fraction α of the disappeared neutrinos goes to antineutrinos:

E

LmvvP

4sin2sin)(

222

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:

A negative log likelihood analysis was done, with α as a unique parameter.

It was found that for the input value of α~0.1 and smaller, the transition scenario is indistinguishable from no transitions at all.

Neutrinos:- All (MC)- That transition (MC)- That will appear as antineutrinos

α=0.1-Δlog(L)=2.3

(16e20 POT assumed)

Feb 28 2006 20

MINOSSummary & Ongoing Work

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.

Neutrino-antineutrino transitions:

Feb 28 2006 21

MINOS

Extra: one could deal with fractions instead of ratios. May try this later

FDND