Neutrino-nucleus cross-section measurements at T2K Callum Wilkinson - PowerPoint PPT Presentation

Neutrino-nucleus cross-section measurements at T2K Callum Wilkinson On behalf of the T2K collaboration

Why neutrino cross sections? ● Event rate; Neutrino flux; Cross section; Detector smearing; Oscillation probability ● Near/far ratios don’t fully cancel systematics: ● Dramatic E ν change ● ND is ν μ dominated. Use to infer ν e ● σ( E ν , x ) relates observables x to E ν Require few % cross-section systematics to fulfill design goals of future OA experiments 2

Why neutrino cross sections? Ann. Rev. Nucl. Part. Sci., 68, 2018 Broad neutrino fluxes, must understand the entire nuclear response... … but no consistent theoretical description Nuclei Nucleons Quarks Integrate! Energy transfer 3

The plot thickens (E.g. 2p2h) Final state particles do not correspond to initial interaction type (or energy transfer)! 4

The T2K experiment ● Long-baseline accelerator neutrino oscillation experiment ● Near detectors: ● Constrain flux and cross-section model before oscillation ● Cross-section measurements in unoscillated beam ● Far detector: oscillation analyses 5

Near detector complex ND280 (2.5º) INGRID (0º) 6 WAGASCI (1.5º)

Near detector complex ● Fluxes: ● On axis ● 1.5° off-axis ● 2.5° off-axis ● ν (FHC) and ν (RHC) enhanced modes Phys. Rev. D88, 032002 (2013) ● ND280 (2.5° off-axis): ● Plastic scintillator (C 8 H 8 ) and water targets ● High resolution tracking + magnet for sign and momentum ● WAGASCI (1.5° off-axis): water and C 8 H 8 ● INGRID (on-axis): water, iron and C 8 H 8 targets 7

T2K cross-section strategy Build selections of interaction topologies by adding restrictions on outgoing hadrons: ● No model-dependent corrections ● Increasing N π ≈ increasing energy transfer l ± p l ( ) ν l θ l Initially measure lepton kinematics Benefit from different fluxes/targets Hadrons Add hadron kinematics over time 8

ND280 CC0π ν μ & ν μ ● Measure CC0π on C 8 H 8 by selecting muon, allowing protons, and vetoing pions ● Control samples for CC1π & CCNπ backgrounds T2K PRELIMINARY T2K PRELIMINARY 9 Paper in preparation

ND280 CC0π ν μ & ν μ Simultaneous fit to measure cross section in 58 p μ ,cosθ μ bins for each mode, including correlations between the samples T2K PRELIMINARY ν μ P a p e r i n p r e p a r a t i o n 10

ND280 CC0π ν μ & ν μ ● Correlations between measurements can be used to uncover model differences ● Adds significantly more power for model-building T2K PRELIMINARY T2K PRELIMINARY T2K PRELIMINARY 11 Paper in preparation

ND280 ν μ -CC0π C 8 H 8 & H 2 O ● Combined FGD1 (C 8 H 8 ) and FGD2 (C 8 H 8 + H 2 O) analysis ● Difficult to reconstruct vertices from passive water layers, so a T2K PRELIMINARY joint fit is essential! P a p e r i n p r e p a r a t i o n T2K PRELIMINARY FGD2 12

ND280 ν μ -CC0π C 8 H 8 & H 2 O T2K PRELIMINARY (105.7) P a (145.9) p e r i n p r e p a r a t i o n ● Fully correlated C 8 H 8 and water measurements also produced ● Next step is a fully correlated ν μ /ν μ , C 8 H 8 /water analysis 13

INGRID CC-inclusive ● On-axis E ν spectrum ● Limited phase space due to detector design: 1μ - : p μ ≥ 0.4 GeV, θ μ ≤ 45° ● Use pure C 8 H 8 , water+C 8 H 8 and iron+C 8 H 8 targets → A-scaling 14 arXiv:1904.09611

WAGASCI ν μ -CC0π0p ● Water+C 8 H 8 detector 1.5˚ off axis ● Limited phase space due to detector design: ● 1μ ± : p μ ≥ 0.4 GeV, θ μ ≤ 45° ● 0π: p π ≥ 0.2 GeV, θ π ≤ 70° ● 0p: p p ≥ 0.6 GeV, θ p ≤ 70° ● Unma gnetized, so main result is ν μ + ν μ to avoid model dependence H 2 O+C 8 H 8 C 8 H 8 (Tracking) target target 15

WAGASCI ν μ -CC0π0p C 8 H 8 H 2 O T2K PRELIMINARY P a p T2K PRELIMINARY e r i n p r e p a r a t i o n ● Results including correlations between C 8 H 8 and H 2 O measurements ● Future work will produce correlated INGRID (0º), WAGASCI (1.5º), and ND280 (2.5º) measurements, to maximize model constraining power 16

ND280 electron neutrinos (ν e ) T2K PRELIMINARY RHC ν e FHC ν e P a p e r i n p ● Important to understand intrinsic T2K PRELIMINARY r e p backgrounds for OA experiments a r a t i ● Also important to control o n potential ν e /ν μ differences RHC ν e ● Challenge to characterize and constrain γ-backgrounds 17

ND280 NC1γ ● Rare SM process, background for ν e -appearance in Cherenkov detectors ● Enhancements suggested as a possibility to explain low energy excess in MiniBooNE ● Search for e + e - pairs with low invariant mass ● Backgrounds from π 0 producing processes 18 J. Phys. G 46, 08LT01 (2019)

Conclusions ● Neutrino cross-section measurements are critical for current and future oscillation experiments ● T2K focuses on making unbiased, model-independent cross-section measurements: ● Variety of nuclear targets ● Different fluxes ● Different observable channels ● Aim to provide high quality data to constrain various cross-section models 19

Backup 20

Nuclear targets ● Free nucleon: the interaction level cross section, including hadronization at high energy transfer ● Initial nuclear state: how nucleons behave inside the nucleus. E.g., Relativistic Fermi Gas. ● Nuclear effects: additional effects due to the presence of multiple nucleons. E.g. np-nh interactions. ● Final State Interactions: subsequent interactions before interaction products exit the nucleus. 21

Free nucleon response QE DIS RES 22

Nuclear response QE DIS 2p2h RES Interactions with more than one nucleon contribute 23

Nuclear response QE DIS 2p2h RES Can’t reconstruct ω, so no way to avoid poorly modelled regions! Integrate! 24

ν-A cross section data ● Can only measure for outgoing particle kinematics, as a function of topology , not interaction channel ● Integrated over a broad neutrino flux ● Post-FSI, integrate out all degrees of freedom other than y : ● Direct theory comparisons to data are difficult ● Require Monte Carlo generator to do integrals numerically 25

Electron neutrinos (ν e ) P a p e r i n T2K PRELIMINARY p r e p a r a t i o n ● Forthcoming publication to add to the extremely spartan literature ● Future work on ν e -CC0π sample 26