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Antineutrino running

Investigating antineutrino running at Caltech for oscillation analysis using statistical likelihood, selection methods, and comparative energy spectra analysis. Preliminary step towards understanding CPT violation.

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Antineutrino running

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  1. Antineutrino running Pedro Ochoa Caltech

  2. Reverse horn current MC generation Q: What could we do if we ran in antineutrino mode?  Generated some MC with inverted horn current: 1e7 POT of flux generated(used fluka files in /afs/fnal.gov/files/data/minos/d110 /fluka_hadrons/fluka05_xxx.ntp) Generate flux files with inverse horn current (GNUMI v18, -10.0 from nominal, -185kA) (Special thanks to Alysia M. !!) Generate MC files (GMINOS) 200e20 POT generated Reconstruct MC files (R1.18.2) 200e20 POT reconstructed

  3. Energy spectra comparison 1e20 POT 1e20 POT B A Neutrinos Antineutrinos Neutrinos Antineutrinos A: red Neutrinos in neutrino mode blue  Antineutrinos in antineutrino mode B: red  Neutrinos in antineutrimo mode blue  Antineutrinos in neutrino mode

  4. 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.

  5. Antineutrino selection method Planes crossed • 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%. Background components (q/p)/(σ q/p) for planes > 25 Neutrinos Antineutrinos This method is certainly not optimized, and much work remains to be done in this area !

  6. 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: • A “realistic” contour, in which the selection cuts described in the previous slide are applied and the reconstructed energy is used. • An “ideal” contour, where the selection efficiency is taken to be 100% and no background is considered, but the reconstructed energy is used. • A “best possible” contour, which is obtained like the “ideal” one but using the true energy. This gives the best case scenario.

  7. 1.0e20 of running alone: Input value: 1.0e20 POT 1.0e20 POT Realistic Best possible Ideal

  8. 6.0e20 of running alone: Input value: 6.0e20 POT 6.0e20 POT Ideal Realistic Best possible

  9. Combining 1e20 POT of running and 6e20 POT of normal running: Realistic Ideal Best possible Neutrino running Antineutrino running

  10. Input value: More results… Realistic Realistic Best possible Best possible Ideal Ideal Realistic Ideal Best possible

  11. Summary & Ongoing Work 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.

  12. A preliminary look at the double ratio method for measuring  transitions C. Howcroft & P. Ochoa Caltech

  13. 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: 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. • Assumed perfect energy resolution • Assumed 100% selection efficiency • No oscillation depletion taken into account • No systematics considered • Assumed 16e20 POT 2) The results shown in this talk represent the best possible scenario since:

  14. Expected (MC) spectra at 16.0e20 POT Near detector: ND 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. Only the n140 files were used, i.e. no overlay and fiducial volume interactions only. ND Both plots are scaled to 16.0e20 POT

  15. Far detector: FD 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

  16. From the expected energy spectra we can obtain the expected ratio in both detectors and compare them to each other: ratio Expected (MC) ratio of antineutrinos to neutrinos ND FD This is the expected (MC) K of slide 12, subsequently referred to as “expected double ratio”

  17. 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. ND FD 3 fluctuations shown 3 fluctuations shown The process was repeated 10,000 times.

  18. 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 !!

  19. α=0.1 Neutrinos: - All (MC) - That transition (MC) - That will appear as antineutrinos Sensitivity to transition probability 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: Neutrinos disappear in usual way: But now a fraction α of the disappeared neutrinos goes to antineutrinos: 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. -Δlog(L)=2.3 (16e20 POT assumed)

  20. Summary & Ongoing Work 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.

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

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