# Presentation: 008363

## NC π0 Production in the MiniBooNE Antineutrino Data

- Van NguyenColumbia University
- for the MiniBooNE collaborationNuFact07
- August 8th, 2007

## MiniBooNE detector
NC π0 production
Objective and method of current analysis
MC/Data comparisons
Summary

- NC π0 production
- Objective and method of current analysis
- MC/Data comparisons
- Summary

- Outline

## The MiniBooNE Detector

- 12-meter diameter spherical tank
- 1280 PMT in inner region
- 240 PMT in outer veto region
- 800 tons pure mineral oil

## MiniBooNE Antineutrino Running

- In **antineutrino mode**, neutrinos are ~30% of the total events (as opposed to neutrino mode where** **antineutrinos are ~2% of the total events)

- G. Zeller

## NC π0 Production

- NC π0's can be created through resonant and coherent
- production:
- Resonant NC π0 production:
**Coherent NC π****0** production:
- 	(Signature: π0 which is
- 	highly forward-going)

## NC π0 Production cont’d

- A π0 decays promptly into two photons
- (τπ0 ~ 8x10-17 s).

- This event can be misidentified if there are not two resolvable tracks.

- Understanding of these
- events is crucial!

- p

- NC π0 Production cont’d

- _MiniBooNE event signatures_

- μ+

- e+

## Present Antineutrino NC π0 Data

- Present Antineutrino NC π0 Data

- Only one published measurement of the absolute rate of antineutrino NC π0 production; this measurement was reported with 25% uncertainty at 2 GeV.
- Current theoretical models on coherent π0 cross sections can vary by up to an order of magnitude in their predictions at low energy, the region most relevant for     oscillation experiments.

## Objective

- To measure the rate of π0 production and use it to constrain this background in an oscillation search.
- Specifically, we aim for a measurement of the total π0 production in bins of true π0 momentum.

## Cosθ and Coherent π0 Production

- Coherent and resonant production are distinguishable by cosθπ, which is the cosine of the lab angle of the outgoing π0 wrt to the beam direction.

- We can use this fact to extract a measure of the coherent fraction.

- J. Link

## Study Coherent π0's in Terms of Eπ(1-cosθπ)

- In coherent events, Eπ(1-cosθπ) has a more regular shape, as a function of momentum, than cosθπ alone, so we’ll fit for the coherent content as a function of this energy weighted angular distribution.

- J. Link

- Eπ(1-cosθπ)

- Pπ<200 MeV

- Eπ(1-cosθπ)

- Eπ(1-cosθπ)

- Eπ(1-cosθπ)

- cosθπ

- cosθπ

- cosθπ

- cosθπ

- 200 MeV<Pπ<300 MeV

- 300 MeV<Pπ<500 MeV

- Pπ>500 MeV

- Pπ>500 MeV

- 300 MeV<Pπ<500 MeV

- 200 MeV<Pπ<300 MeV

- Pπ<200 MeV

- Eπ(1-cosθπ)

- Eπ(1-cosθπ)

## Study Coherent π0's in terms of  Eπ(1-cosθπ)

- Study Coherent π0's in terms of  Eπ(1-cosθπ)

- J. Link

- Eπ(1-cosθπ)

- Eπ(1-cosθπ)

- Eπ(1-cosθπ)

- Eπ(1-cosθπ)

- Pπ<200 MeV

- 200 MeV<Pπ<300 MeV

- 300 MeV<Pπ<500 MeV

- Pπ>500 MeV

## Coherent NC π0's in ν vs.    Running

- νμ coh π0

- νμ res π0

- G. Zeller

## Pre-cuts:
 	Only one sub-event (no decaying μ, NC)
	Veto hits < 6 (eliminates cosmic rays)
	Tank hits > 200 (above Michel endpoint)
 	Event radius < 500 cm (fiducial cut)
NC π0 analysis cuts:
	eμ likelihood prefers e hypothesis (EM-like)
 	eπ likelihood prefers π0 hypothesis (2ring)
	80 MeV/c2<m γγ <200 MeV/c2 (mass window)

-  	Only one sub-event (no decaying μ, NC)
- 	Veto hits < 6 (eliminates cosmic rays)
- 	Tank hits > 200 (above Michel endpoint)
-  	Event radius < 500 cm (fiducial cut)
**NC π****0**** analysis cuts:**
- 	eμ likelihood prefers e hypothesis (EM-like)
-  	eπ likelihood prefers π0 hypothesis (2ring)
- 	80 MeV/c2<m γγ <200 MeV/c2 (mass window)

- Event Selection

- MiniBooNE π0 candidate

## Data/MC Comparison for Variables We Cut On

- Note: Plots are relatively normalized with statistical errors only.

## Note: Plots are relatively normalized with statistical errors only.

## π0 Kinematics

- mγγ(MeV)

- Note: Plots is  relatively normalized with statistical errors only.

## Note: Plots are relatively normalized with statistical errors only.

## No COH contribution

- _

- Suggestive of antineutrino
- NC coherent π0 production

- Note: Plots are relatively normalized with statistical errors only.

## Left: mγγ with 0<Eπ(1-cosθπ)<50 MeV  

- Left: mγγ with 0<Eπ(1-cosθπ)<50 MeV
- Right: mγγ with 50<Eπ(1-cosθπ)<700 MeV

- mγγ(MeV)

- mγγ(MeV)

- Note: Plots are relatively normalized with statistical errors only.

## K2K CC Coherent π+ Results

- (PRL **95**, 252301 (2005))

- Saw no evidence for coherent CC π+ production
- Models need to explain both MiniBooNE and K2K coherent NC π0 results along with K2K CC π+ results

## Summary

- There is good agreement between data and MC for π0's in the MiniBooNE antineutrino data
- The data suggests antineutrino NC coherent π0 production
- Next step: fit for an exact coherent fraction in the nubar data (been done for the neutrino sample) with systematic errors

## Acknowledgments

- I would like to give many thanks to:
- Janet Conrad
- Sam Zeller
- Richard Van de Water
- Hirohisa Tanaka
- Kendall Mahn
- Alexis Aguilar
- Jon Link
- Heather Ray
- and the NSF