# Presentation: 014177

## Charged current single pion to quasi-elastic cross section ratio in MiniBooNE

- Steven Linden
- DNP ’08

## Charged Current Single π+ (CCπ+ ) Events in MiniBooNE

- CCπ+  Resonant

- CCπ+  Coherent

- In MiniBooNE we don’t have the ability to distinguish resonant and coherent channels on an event by event basis.  We thus use a (semi-)inclusive CCπ+  sample.
- Coherent CCπ+  events are expected to constitute less than 10% of CCπ+  events. (Limits from K2K (1))
- In MiniBooNE, we have over 46,000 events in our CCπ+  sample.

- Charged Current Single π+ (CCπ+ ) Events in MiniBooNE

- (1) K2K Collaboration: M. Hasegawa et al., arXiv:hep-ex/0506008v2

## Why do we care about CCπ+ ?

- From a neutrino physics perspective:
- 	CCπ+  events are very abundant at energies used in oscillation experiments.
- 	In many detectors CCπ+  events can look like CCQE.
- 	Thus CCπ+  is a major background in many oscillation studies (e.g., in	MiniBooNE).
- From a nuclear/hadronic physics perspective:
- 	CCπ+  interactions can offer insight into the mechanisms of both resonant 	and coherent pion production.
- 	For example, using CCπ+  data in MiniBooNE we have compared various 	parameterisations the axial and vector form factors (see J. Nowak’s     	talk later today).
- 	Cross section results can help to test our modelling of intra-nuclear final 	state interactions.

## How do we perform the CCπ+ /CCQE measurement?

- We perform a measurement of the CCπ+  to CCQE cross section ratio rather than the absolute CCπ+  cross section in order to eliminate flux uncertainties.
- Our method is to use Monte Carlo to predict the cut efficiency and signal fraction as a function of energy for each sample and use these to correct the raw numbers of events passing cuts.
- f = signal fraction = (signal events passing cuts)/(events passing cuts)
- ε = cut efficiency = (signal events passing cuts)/(signal events)
- U = Energy unsmearing matrix (I’ll discuss this in a moment)

## Event Samples

- Our event selection is quite simple.
- CCπ+  events are identified by:
- 	1. The outgoing muon
- 	2. The decay electron at the end of the muon’s track
- 	3. The decay positron at the end of the pion’s track
- CCQE events are identified by:
- 	1. The outgoing muon
- 	2. The decay electron at the end of the muon’s track
- These simple cuts are very effective at selecting the event samples.
- Additional cuts are used to improve purity.

- CCπ+: 	12% efficiency
- 	46,649 events
- CCQE:	26% efficiency
- 	195,482 events

- CCπ+ event

## Event Samples

- CCQE

| CCQE (red) | 72.0 % |
| --- | --- |
| CCπ+  resonant (blue) | 18.3 % |
| CCπ+  coherent (green) | 1.1 % |
| NCπ0 (dark purple) | 2.0 % |
| Multi-pion (light purple) | 0.5 % |
| Other | 6.1 % |

| CCπ+  total | 86.8% |
| --- | --- |
| CCπ+  resonant (red) | 80.9% |
| CCπ+  coherent (dark blue) | 5.9 % |
| CCQE (dark green) | 5.2 % |
| Multi-pion (light purple) | 3.8 % |
| CCπ0 (light green) | 1.5 % |
| DIS (light blue) | 1.0 % |
| Other | 1.6 % |

- CCπ+

- Reconstructed E_nu

- Reconstructed E_nu

## Energy Unsmearing

- Migration Matrix (CCQE)

- Unsmearing Matrix (CCQE)

- Bin events by E_rec and E_true

- Normalize each E_rec bin

- Avoids the problems of matrix inversion (which for this analysis was not viable).
- Introduces bias from MC true energy distributions - net effect is increased systematic uncertainty.

- Our neutrino energy reconstruction is not perfect - we must use Monte Carlo to find a mapping back to true neutrino energy.

## Results

- On the left: Our measured CCPiP/CCQE cross section ratio (black) compared with our Monte Carlo prediction based on Rein-Sehgal and Smith-Moniz (red).
- On the right: A comparison of our result (black) with measurements from ANL (1) (red) and K2K (2) (blue).
- Here the MiniBooNE and K2K ratios have been corrected for an isoscalar target (ANL’s measurement was already on an isoscalar target).

- (1) G.M. Radecky et al., Phys. Rev. D 25, 1161 (1982)
- (2) K2K Collaboration: A. Rodriguez et al., arXiv:0805.0186

## Effective Ratio Measurement

- We can also measure the ratio of events with CCπ+ -like final state particles to those with CCQE-like final state particles.
- Another way to think of this is as the cross section ratio before corrections for nuclear effects.
- This provides a ratio measurement that is independent of the way we model intra-nuclear processes.

- The effective ratio is smaller than the true ratio because there is a significant number of CCQE-like CCπ+  events due to pion absorption.

- Red: Effective measurement
- Black: True measurement

## Conclusion

- Our measurement is consistent with previous results as well as predictions from the Rein-Sehgal and Smith-Moniz models.
- A paper will be submitted soon.
- We’re entering the age of high-precision CCπ+  cross section measurements.
- These measurements will provide valuable input both in future neutrino experiments and in hadronic and nuclear modelling.