“Rare/other” processes working group summary Motto: “100% uncertainties sound conservative, but...” Jeremy Wolcott Tufts University “Nu-Print” Neutrino Cross Section Strategy Workshop March 14, 2018
What are we considering? ● Any reactions not covered by the other working groups – NC – ν e , ν τ CC – Strange production (K, Λ, Σ, ...) – Truly “rare” things: ● Coherent/diffractive processes ● ν+e elastic scattering ● Exotic stuff (e.g. “explanations” for MiniBooNE excess) ● Corrections/subdominant channels to more common processes – Final-state radiation in CC reactions – Processes with radiative delta resonance decays (Δ + →p γ, etc.) 2
What are the physics needs? ● Backgrounds for oscillation physics – NC π channels (π ± for ν μ disapp., π 0 for ν e app.) – Single-photon- or π 0 -producing CC reactions (ν e app.) ● Signals for oscillation physics – ν e appearance – NC inelastic processes for sterile searches – Rare subprocesses of ν μ CC (e.g. ν → Λ CCQE) ● Backgrounds for BSM physics searches – Strange production (particularly kaons) ● Beam characterization – ν+e elastic, CC coherent? 3
Evaluating the prospects Model quality Are models available? Are there known flaws? Is there active work underway? Constraint quality Are there measurements? Of what quality/applicability? If not, are measurements plausible? [All opinions the author's, discussion members may (will?) disagree] 4
Evaluating the prospects How much should we be panicking? Are our models for some important process poor or missing? Do we have data constraints? 5 [All opinions the author's, discussion members may (will?) disagree]
ν e CC (lepton non-universality) Good quality models 0π form factors : ● Detailed phenom. investigation of possible univ. violation exists ● Several measurements (MINERvA, T2K; NOvA ongoing), but no prospects of stringent non- universality constraints 1π form factors : Good quality measurements ● No theory work. Could maybe treat analogously to 0π?? DIS/SIS form factors : ● NOvA measurement in progress ● No theory work?? ● Challenging to measure (bknds). NOvA measurement in progress should probe SIS Radiative effects : ● Theory tractable for real radiation; virtual radiation 6 challenging but not impossible? ● All measurements challenging
ν e CC (lepton non-universality) ● Panic level: elevated – Critical, major oscillation signal channel – Phenom. work (Day-McF) suggests form factor differences under control for CCQE (~few % unc.); currently no guidance for higher W – Real radiation possible signal confusion for T2K (less worry for calo. style detectors) – Virtual radiation (box diagrams) challenging to calculate, ~few % effects for ν e app. – Impossible to produce stringent data constraints without extremely well characterized ν e flux (i.e. muon source) One instance of a “McFarland Bicycle Diagram” for virtual (internal) photon radiation in CCQE 7
ν e CC (lepton non-universality) ● Panic level: elevated – Critical, major oscillation signal channel – Phenom. work (Day-McF) suggests form factor differences under control for CCQE (~few % unc.); currently no guidance for higher W – Real radiation possible signal confusion for T2K (less worry for calo. style detectors) – Virtual radiation (box diagrams) challenging to calculate, ~few % effects for ν e app. – Impossible to produce stringent data constraints without extremely well characterized ν e flux (i.e. muon source) 8
Neutral current Good quality models NC 1π : ● currently using Rein-Sehgal :-\ ● T2K (π ± ), NOvA (π 0 ) NC DIS/SIS : measurements in progress; ● formalism “should” work? MiniBooNE (π 0 ) (but shadowing, EMC...) ● M. Kabirnezhad model improvements ● no modern measurements Good quality measurements NC 0π : ● Simplistic generator models. No npnh. (Better available? → ab initio work) ● T2K measurement. (2-body??) MiniBooNE attempt? 9
Neutral current ● Panic level: high – Important backgrounds for CC ν oscillation – Important signal for NC ν oscillation – Generator models very basic, little (no) current effort to improve? – Some effort from model-building side (e.g.: Lovato et al ., 1711.02047) – Measurements in progress (T2K, NOvA) 10
Strange production Associated strange production : ● Models available. FSI critical. Good quality models ● Multiple MINERvA measurements (CC, NC) Single kaon production : ● Good quality model (Athar) ● Hard to measure (narrow energy region where dominates) Good quality measurements ν → Λ CCQE: ● Model exists, almost in GENIE ● Challenging to measure. 11
Strange production ● Panic level: guarded – Kaon measurements indicate models ~ok for now. Further measurements challenging – Lambda CCQE modeled but hard to measure, but unclear how important 12
“Standard candle” processes ν + e elastic : ● Tree level prediction exact. Good quality models Radiative corrections improvable. ● MINERvA measurement. NOvA in progress Coherent pion : ● Microscopic model only works at low E ν , PCAC otherwise ● MINERvA & T2K measurements on multiple targets (CC), NOvA (NC) Good quality measurements 13
“Standard candle” processes ● Panic level: low – Detailed COH measurements. Rate is low. – DFR on H probably not important bknd for osc. (can reject) – ν + e path forward understood 14
Other photon production ● Panic level: unsure – Potential backgrounds for ν e appearance – Disparate models, generally no generator implementations (radiative Δ decay an exception) – Unclear to what degree current ν e ID techniques are susceptible – Difficult to measure (photon backgrounds from “conventional” sources – π 0 s, etc.) – “The #!$@ everywhere is also the problem” --anonymous ? ? ? ? 15
Summary of this summary talk ● Fairly wide gulf between theory, generator implementation, and measurements in many respects ● Most important (?) priorities for current and near- future measurements: – Neutral current (esp. inelastic channels) – Radiative effects in CC reactions (where possible) ● Serious thought on possible photon backgrounds (and work on generator implementations) desirable 16
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