Discussion: Workshop Report and Next Steps

Workshop Report

2

Discussion questions: nucleons to nuclei

what do we know? =============

what do we need to know?===================

What studies can be done at the generator level to quantify the impact of elementary amplitudes? (e.g. with NUISANCE framework)

How can precision scattering data on light nuclei aid the development of nuclear models and computational tools?

Can the uncertainty of nuclear models applied to accelerator neutrino cross sections be quantified?

How can elementary amplitudes and nuclear effects be disentangled in current measurements? How should they be combined in generators?

how will we come to know it? =====================

What is the best configuration for a future elementary target neutrino experiment? (considerations include data quantity and quality, cost, logistics)

What is the potential impact of lattice QCD for the accelerator neutrino program?

Can precise and reliable elementary amplitude measurements be obtained from subtraction techniques in water or hydrocarbon?

What is the potential for non-neutrino experiments to constrain the elementary amplitudes, and which new and better measurements should be performed?

�2

3

discussion and report on elementary amplitudes

• preliminaries

There are many meetings dedicated to the discussion of the broader program of neutrino nucleus interactions

Focus attention here on the question of elementary amplitudes

• important component of the error budget

• necessary to inform and discriminate nuclear models

• well defined quantities

Thanks to all of the speakers and participants !!!

• important, fruitful, interesting intersections (lattice, e-p, muonic atoms, …)

• motivations

�3

discussion and report on elementary amplitudes

• preliminaries

There are many meetings dedicated to the discussion of the broader program of neutrino nucleus interactions

Focus attention here on the question of elementary amplitudes

• important component of the error budget

• necessary to inform and discriminate nuclear models

• well defined quantities

Thanks to all of the speakers and participants !!!

• important, fruitful, interesting intersections (lattice, e-p, muonic atoms, …)

• motivations

�3

4

• definition of elementary amplitude

• FA (too narrow)

• scattering amplitudes at the nucleon level: νN→ℓN, eN→eN, N→Nπ, NN→NN, etc.

• inputs to nuclear modeling

• the initio of ab initio

• any physical quantity that lattice QCD can measure involving one or a few nucleons

• any physical quantity that can be measured in an elementary target (H or D) scattering experiment

�4

(Carlson, Rocco)

5

• the questions

(1) what do we know?

(2) what do we need to know?

(3) how can we come to know it?

All questions are difficult, but after normalization, (1)=(3)=easy, (2)=hard

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6

• the questions

(1) what do we know?

(2) what do we need to know?

(3) how can we come to know it?

Probably not enough, but serious attempts to quantify

(talks of Meyer, Morfin, Ruso, Sato, Wilkinson)

- challenges from low statistics and limited data preservation

- open questions on deuteron corrections

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• the questions

(1) what do we know?

(2) what do we need to know?

(3) how can we come to know it?

New elementary target data (Bross, Kammel)- underground safety raises the bar for making the physics case

Precision lattice QCD (talks of Kronfeld, Lin, Shanahan)

- what can be achieved by subtraction methods using compound targets?

Electron and positron beams (Crawford, Nakamura), muonic atoms (Kammel), …

- FA within sight

- complementary to scattering data

Many elements of the physics case (question 2) are common between these paths. Practitioners have strategic interest in helping make this physics case.

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• the questions

(1) what do we know?

(2) what do we need to know?

(3) how can we come to know it?

Three levels (at least) of answer

(i) regardless of nuclear model, nucleon-level data tests critical elements of oscillation analyses (e.g. disentangling differences in νµ/νe from radiative corrections and detector response) (McFarland)

(ii) propagate elementary input errors through a/the default nuclear model and oscillation analysis. Need those errors to be smaller than the desired precision on fundamental neutrino parameters.

(Ashkenazi, Castillo, Himmel, Mahn, Ruterbories)

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9

• the questions

(1) what do we know?

(2) what do we need to know?

(3) how can we come to know it?

Three levels (at least) of answer

(i) regardless of nuclear model, nucleon-level data tests critical elements of oscillation analyses (e.g. disentangling differences in νµ/νe from radiative corrections and detector response) (McFarland)

(ii) propagate elementary input errors through a/the default nuclear model and oscillation analysis. Need those errors to be smaller than the desired precision on fundamental neutrino parameters.

Studies on impact of alternate form factor • Use as alternate models: “Z expansion”, 3 component fit

and perform T2K analysis with current dipole model (6 fits)

• For T2K 2018 analysis, the (Q2) nuclear model parameters compensate for mis-modeling (no bias)

36

T2K preliminary

T2K preliminary

Will discuss next steps of this in a minute…

(Mahn)

�9

(Ashkenazi, Castillo, Himmel, Mahn, Ruterbories)

10

• the questions

(1) what do we know?

(2) what do we need to know?

(3) how can we come to know it?

Three levels (at least) of answer

(iii) the whole shebang

A complete and quantitative answer requires a complete and quantitative nuclear model.

- need to break the circle: improving nuclear models requires better knowledge of the nucleon level amplitudes.

�10

11

• the questions

(1) what do we know?

(2) what do we need to know?

(3) how can we come to know it?

Three levels (at least) of answer

(iii) the whole shebang

A complete and quantitative answer requires a complete and quantitative nuclear model.

- need to break the circle: improving nuclear models requires better knowledge of the nucleon level amplitudes.

z Expansion in GENIEz expansion coded into GENIE - may be turned on with configuration switch

O�cially released in production version 2.12

Uncertainties on free-nucleon cross section as large as data-theory discrepancy=∆ need to improve FA determination to make headway on nuclear e�ects

]2[GeV2Q0 0.5 1 1.5 2

]2/G

eV2

[cm

2/d

Qσd

0

5

10

15

20

-3910×

GENIE RFG z-expansion

GENIE RFG dipole

MINERvA Data

See tutorial: https://indico.fnal.gov/event/12824/ 20 / 25

(Meyer)

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• comments

- It’s a big world - QE, resonance, inelastic processes (Friedland, Morfin). Already at the nucleon level our understanding is rudimentary

- Parameterizations of things we can’t calculate are fine if they contain the true answer and experimental data are available to constrain them.

�12

Saori, Alex and Kendall Discussion

13

Andreas and Aaron Lattice QCD Roadmap: Situation and Plans

14

Physics

• The simplest quantities (fka as “gold plated”) have one hadron in the initial state and zero or one in the final state:

• proton decay matrix elements: 0 current status suffices?

• charges: gV = 1, gA, gS, gT (tensor), … first full error budgets ≲ now

• form factors: F1, F2, FA, FP, FT (tensor), … full error budgets ~ soon

• parton densities, hadron tensor, …, for DIS rapidly developing

• Resonances are a feature of multi-body states, which poses conceptual and

computational challenges: wait (~year) for B → K*(Kπ)lν, then assess realistically.

• Three- and more-body states are a fully open question (need more math).

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15

Resources (needed for planning)• Large fraction of lattice-QCD research (and funding for resources) is driven by excitement

from the experimental program, together with feasibility at any given time:

• CLEO, BaBar, Belle had a huge influence in the past;

• Muon g–2 has a huge influence now;

• in my opinion, the calculations relevant to ν scattering (previous slide) maximize relevance (to HEP), feasibility, and excitement—

• the hard/impossible have a theoretical attraction.

• Unlike earlier hep-ex oriented work, we now have a three parties in the conversation: experimentalists, lattice-QCD practitioners, and nuclear theorists.

• This week I heard the level of interest needed for ν-scattering problems to rise in priority in the next several years.

Andreas and Aaron Lattice QCD Roadmap: Situation and Plans

Gabe’s Proposal – specific deliverable

◆ identify interested parties that can actually do work (very hard to arrange!)◆ set up a plausible lattice deliverable (with uncertainties)◆ have a nuclear theory group help propagate the result into a model and provide

uncertainties (especially propagate the lattice uncertainties in a way we can audit their total impact on the final uncertainties)

◆ code the model into GENIE▼ The last step is highly non-trivial, of course. Maybe we want to code things into a

"toy" model (something like an RFG).▼ working on a model with Saori where the underlying ground state model and form

factors are subsumed into her calculation

◆ Goal 1. something "simple" to try to close the loop and iterate with,◆ Goal 2. something "more correct" involving a calculation like

Saori's - how can we feed this result to her calculation

16

17

Neutrino Scattering Theory Experiment Collaboration (NuSTEC)

http://nustec.fnal.gov

18

NuSTEC: Membership

◆ THEORISTS◆ Luis Alvarez Ruso (co-spokesperson) ◆ Sajjad Athar◆ Maria Barbaro◆ Omar Benhar◆ Richard Hill◆ Patrick Huber◆ Natalie Jachowicz◆ Andreas Kronfeld◆ Marco Martini ◆ Toru Sato ◆ Rocco Schiavilla◆ Jan Sobczyk (nuWRO)

◆ EXPERIMENTALISTS◆ Sara Bolognesi◆ (Steve Brice) ◆ Raquel Castillo

◆ Dan Cherdack◆ Steve Dytman (GENIE) ◆ Andy Furmanski◆ Yoshinari Hayato (NEUT) ◆ Teppei Katori◆ Kendall Mahn◆ Camillo Mariani◆ Jorge G. Morfín (co-spokesperson) ◆ (Ornella Palamara) ◆ Jon Paley◆ Roberto Petti ◆ Gabe Perdue (GENIE) ◆ Federico Sanchez ◆ (Sam Zeller)

( ) indicates advisor

19

NuSTEC Projects

◆ Two expanded (9 day) and three shorter (5 day) schools on neutrino nucleus scattering physics.

◆ Input to the present workshop via Richard Hill a co-organizer◆ The NuSTEC Workshop on Shallow-and-Deep Inelastic Scattering.◆ Multiple collaborative projects between the NuSTEC members

reflecting both theory and experimental needs.

20

DRAFT

NuSTEC White Paper: Status and Challenges of Neutrino-Nucleus

Scattering

L. Alvarez-Ruso,1 M. Sajjad Athar,2 M.B. Barbaro,3 D. Cherdack,4 M.E.Christy,5 P. Coloma,6

T.W. Donnelly,7 S. Dytman,8 R. J. Hill,9, 10, 6 P. Huber,11 N. Jachowicz,12 T. Katori,13

A. S. Kronfeld,6 K. Mahn,14 M. Martini,15 J. G. Morfın,6 J. Nieves,16 G. Perdue,6

R. Petti,17 D. G. Richards,18 F. Sanchez,19 T. Sato,20 J. T. Sobczyk,21 and G. P. Zeller6

1Instituto de Fısica Corpuscular (IFIC)2Department of Physics, Aligarh Muslim University Aligarh-202 002, India

3Dipartimento di Fisica, Universita di Torino and INFN,Sezione di Torino, Via P. Giuria 1, 10125 Torino, Italy

4Colorado State University, Department of Physics, Fort Collins, CO 80523, USA5Department of Physics, Hampton University, Hampton, Virginia, 23668 USA

6Fermi National Accelerator Laboratory, Batavia, IL 60510, USA7Center for Theoretical Physics, Laboratory for Nuclear Science and Department of Physics,

Massachusetts Institute of Technology, Cambridge, MA 02139, USA8University of Pittsburgh, Department of Physics and Astronomy, Pittsburgh PA 15260, USA

9Perimeter Institute for Theoretical Physics, Waterloo, ON, N2L 2Y5 Canada10TRIUMF, Vancouver, BC, V6T 2A3 Canada

11Center of Neutrino Physics, Virginia Tech, Blacksburg, VA 24061, USA12Ghent University, Department of Physics and Astronomy,

Proeftuinstraat 86, B-9000 Gent, Belgium13Queen Mary University of London, London, UK

14Michigan State University, Department of Physics and Astronomy, East Lansing, MI 48824, USA15IRFU Saclay, Saclay, Paris, France

16Instituto de Fisica Corpuscular (IFIC),Centro Mixto Universidad de Valencia-CSIC,

Institutos de Investigacion de Paterna, E-46071 Valencia, Spain17Department of Physics and Astronomy,

University of South Carolina, Columbia SC 29208, USA18Je↵erson Laboratory, 12000 Je↵erson Avenue, Newport News, VA 23606, USA

19IFAE Barcelona Institute Science and Technology, Barcelona, Spain20Department of Physics, Osaka University,

Toyonaka, Osaka 560-0043, Japan; kJ-PARC Branch,KEK Theory Center, KEK, Tokai, 319-1106, Japan

21Institute of Theoretical Physics, University of Wroclaw,pl. M. Borna 9, 50-204, Wroclaw, Poland

(Dated: March 3, 2017)

CONTENTS1

I. Executive Summary 42

II. Overview of the Current Challenges in the Theoretical and Experimental Studies of3

Neutrino Nucleon/Nucleus Interaction Physics 44

A. Introduction - General Challenges 45

B. The Measurement of Neutrino Oscillation Parameters and Neutrino Nucleus6

Interaction Physics 67

C. Quasielastic Peak Region 68

D. Delta Resonance Peak Region. Contribution from Heavier Resonances 79

E. Shallow and Deep-Inelastic Scattering Region VIII 810

F. Coherent Meson Production IX 911

G. Generators 912

III. The Impact of Neutrino Nucleus Interaction Physics on Oscillation Physics Analyses 1113