Some Introduction Proto-Nubar Meeting 28/Feb/2006 Caius Howcroft 1

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2 At the march meeting I wandered what analysis we might be able to do with the anti-neutrino content of the beam. What I actual was looking for was good thesis topics. Transitions nu->nubar. Beam systematics. Near detector anti-neutrino physics, e.g. x-sections This evolved into the question of what kind of POT of reversed horn running would we need to do interesting anti-neutrino physics.

3 A consistency check that anti-neutrinos are not "appearing" in the far detector. There are some ideas out there that anti-neutrinos might oscillate to neutrinos through majorna mechanisms or other more exotic methods. (for a nice summary see ). However, the scale of the probabilities given here are well below MINOS visibility. It was also pointed out in the "Russian" preprint, that that there is nothing stopping some fraction of the atmospheric nu_mu disaperence being due to nu->nubar oscillations. I would suggest that we want to look at the ratio of fractions as a function of energy, and look for statistically significant deviations from 1.0. Both Pedro and David J. have done a bit of work on this. 3

4 If we know the nu/nubar ratio in the high energy tail we should be able to constrain the hadron productions. There are significant differences in pi+ and pi- in MARS, FLUKA and BMPT. Esp. in neck-to-neck flux, which is where the nubar flux comes from. This was looked at some time ago by Sacha, however at the time the uncertainty on the x-sections was so large that very little could be gained. Currently the uncertainty is <%, so maybe this should be revisted. Results from some studies by Sacha and Bob Z. While these are very out of date, they give us an idea of what level we would need to achieve to be regarded as useful. Numi-768 4

5 The numubar content of the forward current beam comes from the neck-to-neck high energy, unfocus hadrons. Therefore, the numubar content is only high energy. We looked at using the anti-neutrino content of the forward current beam for an oscillation measurement, with predictable results. (See Pedro's Talk) The MC energy distribution for nubar in ND.!"#$%$&$"'(%)*%+"#$%,&+-&$#+"-&). However, when combined with a small sample for reversed horn current these data do become quite useful. v! 3$;4%=>! / :013441;4478 9<01;641;4478 5

6 Charge Identification. The major source of concern will be our understanding of ε -+, the probability of miss-identifying a true ν event as ν. As the make up only % of the beam in the low energy region (the most probable region of interest), any slight mistake here could lead to a signal. Possible handles on this: Cosmic ray muons: Pros: They are plentiful at both detectors Cons: high zenith. The dreaded "mufson effect". 5 forward horn current beam configurations all with the same antineutrino flux but very different neutrino flux. The number of measured n+- events is (ignoring NC) n + = ɛ + N ν + ɛ ++ N ν We should be able to measure from near det data (but can we do it precisely enough) 6

7 Coil off (and reversed coil current) ND data should provide us with insight into the size (and simulation) of multiple scattering and charge reconstruction biases. Re-examine the work done by the atmospheric neutrino guys. They did lots of work on convincing people we understood the charge reconstruction. John Chapman's divided track analysis (cut a track in half and refit each half). Increased statistics: The rock muons have a boosted +/- ratio and we havn't even looked at them yet. 7

8 ) (ev µ+!m - Pedro will show what can be achieved, however, to refresh I show the expected sensitivity for 4 years of data from the atmospheric analysis alone. 90% 68% 99% / ev 3 m!! -3 m -1 - = ev,! m = ev % C.L. 95% C.L. Input Value !m upmu 4 years live time µ- (ev ) FC 4 years live time -! m 3-1 / ev Lucky to get within an order of magnitude. 8

9 Reversing the horn current isn't just a case of throwing the switch. There are two ways it could be done: Reverse the bolt connectors to the horn strip lines. This is quick to do but it also reverse which end of the horn chain is at ground. The problem is that in LE (and possibly LE-) the target (which is at ground) and the high voltage end of the horn are very close to each other. They could instead reverse the voltage. Doing this would probably require purchasing new SCRs at a cost of 5K USD and would take about a week. However, this would then be safe in all beam modes. 9

10 Why might we want to do this? For the same reason that we did the atmospheric neutrino analysis, because its there and can be done relatively easily. Its a measurement of a fundament mass splitting that (as far as I'm aware) has not been measured directly. Lay to reset and CPT theories that are hanging in there. NOvA will have to run in anti-neutrino mode, I'm sure an on axis measurement of the nubar flux will be very useful to them. NOvA may make a better nubar measurement but not until 0 at least, probably more like 013. (construction, offaxis, lower energy) It should give us better insight to the hadron content of the beam and thus help with systematics for the main analysis. Low energy near detector physics measurements, x- sections...

11 But what about the impact on our regular CC analysis? We can make a measurement with less than you think (See pedro's talk). The nubar events/pot is 1/3 that for nus in the forward beam. However, due to the low Y of nubar events and by using nubars in the forward data set we don't need 3e0 to make a measurement comparable to this weekend's result. The required amount of reverse horn data that could be taken in a few months of running. If we were absolutely desperate, the nu comtamination in the reverse horn running could be used. Effectively recovering % of the POTs in reverse mode. 11

12 Nubar contamination We should have enough statistics by the end of this year to produce the nu->nubar result (1st quarter 07) Near detector physics (Jan 07) - Geoff P. High statistics nu->nubar result (late 008) Anti-neutrino running First reverse horn test run next year to get spectrum and do low energy ND physics. Run ~ week Long run sometime late 008? If we don't do it before NOvA turns on we wont do it at all. 1

13 I think its clear that we do definitely want to make a measurement of the nu->nubar analysis. KamLAND has the only result in the area (Jeff H.).The biggest problem here is posing the correct question. May be worth revisiting the idea of using the charge ration to constrain the hadron production model. Near detector physics, x-sections. The case for anti-neutrino running is less clear as it requires: More effort. A modest budget, but not zero A 7-9% hit in the forward horn current data, but will people care about this in 008? 13