GENIE. ! Physics Impact. Hugh Gallagher Tufts University Mar. 11, 2015

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1 GENIE Project started in 2004; >100k line codebase. Simulates neutrino nucleus interactions from 100 MeV TeV on all nuclei, typical usage is as a front end to GEANT simulations. Additional capabilities to support main experimental needs: For use with detailed detector descriptions and neutrino beamline simulations. Out of the box, realistic systematic error estimates based on MINOS/T2K studies. Reweighting interface to evaluate changes in models or model parameters. All data and software used for validation are distributed with the package. Physics Impact Crucial tool for experiments: detector design/optimization, Monte Carlo simulation, systematic error determination. Make possible comparisons between new data and a variety of theoretical models. Key component in the feedback loop between neutrino cross section experiments and the theoretical community. The GENIE Neutrino Monte Carlo Generator. C. Andreopoulos et al., Nucl. Instrum. Meth. A614: (2010)

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3 T H E O R Y Full nuclear-many body theory Relativistic Green s functions Spectral functions Relativistic Fermi Gas nuclear model D A T A Elastic/Quasi-elastic Production of baryon resonances Parton-level inelastic scattering + rare processes (coherent, ΔS=1... ) Resonance decays Empirical fragmentation models PYTHIA (string fragmentation) Formation zones Coherence lengths fundamental scattering mechanism hadronization (in nuclei) optical models intranuclear cascade simulations transport calculations intranuclear rescattering nuclear model primary interaction hadronization intranuclear nuclear model interaction hadronization nuclear modelprimary primary interaction hadronization intranuclear intranuclear nuclear model primary interaction hadronization pion, kaon, intranuclear hadron - nucleus (cross section) hadron (cross section) hadron (cross section) hadron Inclusive electron scattering: Bubble Chambers (ANL, (cross section) hadron transport transport scattering experiments transport hydrogen/deuterium targets (en) BNL, SKAT, BEBC, FNAL), transport nuclear targets (ea) in the quasi-elastic and resonance regions hadron attenuation e/μ : Structure functions e CCFR, NuTEV, MINOS, T2K, NOMAD, MiniBooNE, SciBooNE, ArgoNEUT, MINERvA ν total and reaction cross sections differential distributions of produced particles π

4 In Conclusion: The 4 Challenges Pitt Generator Workshop, May What are the highest priorities and strategy for improving the modeling of nuclear physics in generators? 2. How do we make the latest and greatest theoretical work available to experiments? 3. How do we deal with all of this new data that is arriving increasingly rapidly? 4. How do we assemble the resources and collaborations that we will need to tackle 1-3?

5 Organization Rewritten By- Laws, organization structure to accommodate growth and more community involvement. Significant involvement from FNAL with an emphasis on automated validation framework and supporting the large GENIE user base at the lab. Vision of Fermilab as a hub for GENIE development.

6 Organization Activities organized around working groups Primary Processes (headed by HG) Nuclear Physics (S. Dytman, Pitt) Systematics and Global Tuning (UK/FNAL lead roles) Main decision- making is through Executive Board (HG member)

7 Vision Collaboration Size: Goal is to grow the core collaboration from ~1 FTE spread over several individuals to ~5 FTE spread over roughly 15 individuals. Grow and support the pool of contributors. Schedule: Goal is to have a release schedule with one fully validated physics release a year. Alternating between: - model introduction releases (2.9.0): New physics components are added as optional models, no change to default. - fully tuned release (2.10.0): New model elements are combined in a global tune, including evaluation of systematic errors. FNAL Developer s Workshop (Mar 2014)

8 2014 Developer s Workshop (FNAL) 20 participants from US and Europe. LBNE, T2K, MicroBooNE, MINERvA, IceCuBE involvement. Radiative decays below the pion production threshold (A.Shukraft). Formation zone modelling (A.Hatzikoutelis). Initial thoughts about standardized generator/theory interfaces (S.Mrenna, T.Stainer, H.Gallagher, C.Andreopoulos). Coherence length and associated reweighting method (G.Christodoulou). Extra FSI systematics in GENIE reweighting package (N.Grant and D.Cherdack). Hadronization systematics in GENIE reweighting package - Exact method (A.Norrick, N.Meyer). Hadronization systematics in GENIE reweighting package - Covariance matrix method (C.Andreopoulos). New Np-Nh model implementation (J. Schwehr) High-energy extension for IceCube (K. Hoshina) New inelastic single Kaon production generator (C. Marshall, M. Nirkko)

9 Releases 3 in 2014: Largest was Tufts was release coordinator. Majority of release validation was done here on the Tufts linux research cluster.

10 Releases v2.9.0 (imminent - original goal was Dec. 2014) Switch to gsl for numerical integration Effective Spectral Function, Transverse Enhancement MEC (Coopersmith & Bodek, Rocherster) *W, Z exchange diagrams for very high E (Hoshina, Wisc, ICECube) Inclusive eta production for transition region (Liu, W&M) Berger-Sehgal, Kuzmin resonance prod, new GA, GV (Nowak, Minnesota/Lancaster) Better A dependence in ha FSI (Geary, Pittsburgh) *Athar Delta S=1 Kaon Prod (Marshall, Roch & Nirkko, Bern) v2.9.2 (spring 2015?) Quasielastic CC Lambda production (Poage, Tufts) Benhar spectral function model (1p1h) Coherent models: Berger-Sehgal & Paschos-Schalla *Valencia MEC Nieves QE z expansion of QE form factors (A. Meyer, Hill) *new K+ FSI (F. de Maria Blaszcyk) v (summer 2015???)

11 Significant recent theoretical work on the impact of scattering mechanisms involving multiple nucleons1,2,3 Multi-Nucleon Correlations Our main conclusion is that MiniBooNE data are fully compatible former determinations of the nucleon axial mass...besides, with we have found that the procedure commonly used to reconstruct the neutrino energy for quasielastic events from the muon angle and energy could be unreliable for a wide region of the phase space, due to the large importance of multinucleon events. Nieves et al, Phys. Lett. B707 (2012) In addition, phenomenological description of the missing strength in electron scattering via empirical enhancements to the magnetic form factor4,5: [1] Martini et al. PRC84 (2011) [2] Nieves et al. Phys Lett. B707 (2012) 72 [3] Amaro et al. PRD84 (2011) [4] Bodek et al. Eur. Phys. J C71 (2011) 1726 [5] S. Dytman et al. private communication

12 Challenge 3 3. How do we deal with all of this new data that is arriving increasingly rapidly? Pitt Generator Workshop, May 2013 D. Schmitz In my opinion this is the hardest problem we face. Understanding correlations in and between data sets. Fundamental limitations in models. Impossibility of fitting the world s data at present. How model-dependent are the corrections needed to prepare data for global fits? Retuning models and evaluating systematic errors requires a lot of effort. ~5-10 years from recent T2K fits (K. Mahn). Requires close collaboration between theorists, experimentalists, and generator authors. Huge volume of data (γa, νa, ea, πa, pa) in principle involved. Collider success (CTEQ,RIVET,...) may be very helpful. Hernandez et al., NuINT12

13 Challenge 4 - Resources and The Global Effort Generators require state-of-the-art theory - theory support. Funding is needed to allow international theory/experimental collaborations to work. Need to work across disciplinary and geographical divides. International: CTEQ-like group - NuSTEC (J. Morfin). Two successful schools in Nuclear theory collaboration (Los Alamos, ANL, ODU, MIT) being formed in response to NP FOA Will include participants from HEP (FNAL) including Tufts. Experimentalist s Theorists Americas Europe Asia

14 Challenge 4 - Resources and The Global Effort 2014 GENIE proposal submitted to DOE and NSF. HG, S. Dytman, McFarlane, Bodek, Mahn, and Wilson. Tufts component identical to what was in our group proposal. Have received feedback on structure of collaboration, proposal, will resubmit in future. Medium term- means increase of 1.5 postdoc FTE on GENIE, possibility of 3 GENIE postdocs based at FNAL (this would be ideal) Europe: Marie Skłodowska-Curie Innovative Training Network (part of Horizon 2020) - C. Andreopoulos Early stage researchers supervised jointly by theorist and experimentalist as a way of crossing the theory/experiment divide. Proposal was ranked in top 5-10%, funding cutoff is 5%. Will resubmit.

15 MINERvA 2014 Establishment of MINERvA Generator Group (led by HG, Jan Sobczyk, T. Golan) Analysis software development / validation- event reweighing GENIE validation / external data comparisons Generator-related systematic error evaluation: are there places where the standard GENIE treatment has underestimated important systematic errors? Carry out a program of GENIE-NuWRO comparisons, confirming that GENIE error bands cover the difference between GENIE and NuWRO predictions. Advising / consulting with analyzers on specific systematic errors for their analyses, and establishing a plan of work that is tailored to their analysis.

16 NOvA Similarly to our roles in MINOS and MINERvA, we have provided expert guidance on the use of GENIE and evaluation of generator-related systematic errors for NOvA analyses. NOvA / GENIE event reweighing infrastructure (N. Mayer) Systematics for the nu-mu CC analysis (J. Coelho) As previously mentioned, exploring generator-related explanations to the data/mc discrepancies observed in the NOvA ND. Over the last several years, we ve been bringing expertise on neutrino interactions and GENIE to the benefit of our experimental collaborations. Over the next few years, will see benefits flow to GENIE as data from these experiments are used in our next sets of global tunes and systematic error evaluations.

17 LBNE Atmospheric Neutrinos Mar. Feb. 12, 11, A major push for LBNE in 2013 was to strengthen the physics case for putting the detector underground, and in articulating this case to the international community. As head of the Atmospheric Neutrino Working Group, led up these efforts. Sensitivity studies (A. Blake) include state of the art ingredients: GENIE with Bartol 3D flux, full 3-flavor fitting including ~20 systematic errors. Approximations are in detector response. Event generation and simulation studies were done at Cambridge and Tufts (Gallagher, Coelho, Olson). In particular, studying effect of detector resolution.

18 LBNE Atmospheric Neutrinos Mar. Feb. 12, 11, Results demonstrate the importance of atmospheric neutrinos for LBNE. MH sensitivity comparable to beam neutrinos (for unfavorable delta), and comparable to HyperK. Results presented by Gallagher at ISOUPS (May, Asilomar), written up for the LBNE Scientific Opportunities document and related Snowmass materials. In addition, involvement in the FastMC group and others to fully capture uncertainties in hadronic system modeling in GENIE. Followup studies (Gallagher, Coelho, local HS teachers and students) to evaluate via scan studies assumptions about LAr performance for atmospheric neutrinos. First uses of web-based scan tools. In ELBNF will continue to explore the role of atmospheric neutrino data in the overall program.

19 BACKUP

20 Multinucleon Modeling Theoretical Calculations: Martini et al.1 Nieves et al.2 Amaro et al.3 Carlson et al.4 Relativistic/Non-Relativistic? Which diagrams included? Nuclear Ground State? RPA included? Empirical models: Bodek5 Implementation in Generators: GENIE (S. Dytman) GiBUU NuWRO Summary in: Katori, arxiv: [1] Martini et al. PRC84 (2011) [2] Nieves et al. Phys Lett. B707 (2012) 72 [3] Amaro et al. PRD84 (2011) [5] Bodek et al. Eur. Phys. J C71 (2011) 1726

21 Multinucleon Processes A major topic of discussion in the field right now is the potential importance of multinucleon scattering processes for our understanding of current and future data. R. Subedi et al. Science 320, 1476 (2008); Accumulated experimental evidence (electron and neutrino scattering), and consensus (though not convergence) from the theoretical community on the presence of these effects. Task should be simple - just add it to a generator HG, G. Garvey, G. Zeller, Ann.Rev.Nucl.Part.Sci. 61 (2011)

22 np-nh modeling: so many questions meson exchange currents Hadronic observables? n:p/n:n ratio in initial state? Double counting with existing processes? Short-range correlations, pion absorption? Importance of correct ground state wavefunction? Neutrino vs. anti-neutrino predictions? nucleon-nucleon correlations Alberico et al, Annals Phys. 154 (1984) 356.