Cross-Section Results From
Knossos, Crete – Middle/Late Minoan Tokai, Japan – 21st century
Cross-Section Results from
Mark A. Rayner (Université de Genève) on behalf of the T2K collaboration 3rd International Conference on New Frontiers in Physics Kolymbari, Crete – 6th August 2014 Present and future neutrino oscillation experiments cover a region full of reaction thresholds and sparse data
The cross section per nucleon for all charged current υμ interactions “CC inclusive” Minerva Quasielastic scattering LBNO LBNE NOvA T2K Hyper-Kamiokande
Resonant scattering
Plot: Formaggio and Zeller Rev. Mod. Phys. 84, 1307
Cross-Section Results from T2K – 2 – Interaction models are a key systematic in oscillation analyses
e.g. in the T2K υμ disappearance analysis, Phys. Rev. Lett. 112, 2014
Signal and background cross sections are key in oscillation fits
In particular, model systematics must be reduced to measure δCP Cross-Section Results from T2K – 3 – The T2K experimental setup
The on-axis INGRID detector monitors the beam υμ flux (a.u.) The off-axis near detector ND280 observes υμ and υe on-axis before oscillations The neutrino interaction model is constrained off-axis E The flux model is constrained υ 0 2 GeV 4 GeV 30 GeV ND280 p π μ -mon off-axis υ 295 km
0 m Super 120 m 280 m Kamiokande
See Joanna Zalipska’s talk later in this session for details
Super-Kamiokande then observes υμ disappearance and υe appearance
The narrow band off-axis beam leads to a dramatic υμ disappearance effect The T2K detectors are also used for many cross-section measurements
Cross-Section Results from T2K – 4 – Cross-Section Results from T2K charged current quasielastic neutral current υμ flux (a.u.) CCQE CC (inclusive) CC (inclusive) NC elastic on-axis on CH on CH on CH on water
υμ υμ υe υμ off-axis Eυ
0 2 GeV 4 GeV 30 GeV ND280 p π μ -mon off-axis υ 295 km
0 m Super 120 m 280 m Kamiokande
coherent CCQE CC (inclusive) CC (inclusive) NCQE CC 1π+ on CH on CH on Fe on water on CH υμ υμ υμ υμ υμ
Cross-Section Results from T2K – 5 – a fit model independent and All other cross sections are single
versus Eυ differential in lepton (p, θ) flux-averaged measurements
υμ flux (a.u.) CCQE CC (inclusive) CC (inclusive) NC elastic on-axis on CH on CH on CH on water
υμ υμ υe υμ off-axis Eυ
0 2 GeV 4 GeV 30 GeV ND280 p π μ -mon off-axis υ 295 km
0 m Super 120 m 280 m Kamiokande
coherent CCQE CC (inclusive) CC (inclusive) NCQE CC 1π+ on CH on CH on Fe on water on CH υμ υμ υμ υμ υμ
Cross-Section Results from T2K – 6 – INGRID – on-axis beam monitor
16 standard modules iron target Sandwich of iron and scintillator Measures the flux for a range of angles
Proton The ‘proton module’ carbon target module Single central module of pure scintillator placed Added to facilitate cross-section studies centrally scintillator iron
Event display of a quasielastic scattering
Standard Module
Proton Module
Cross-Section Results from T2K – 7 – Charged current inclusive on CH
SciBooNE observed a higher cross section than predictions see NuInt14 for detailed presentations However our result on CH is consistent with the models on all these analyses Charged current inclusive on Fe
The first result on Fe in the few GeV region The cross section per nucleon is measured to be 5% higher than on CH, in agreement with models [INGRID flux average] Measurements on different nuclei are important for understanding the tricky nuclear model systematics
Cross-Section Results from T2K – 8 – Charged current coherent single π+ production on CH
Select events with muons scattered extremely forward and a pion-like track Momentum transfer of coherent pion production is small
A small signal excess of 1.5σ is observed It agrees well with the prediction by GENIE, but is smaller than NEUT Not incompatible with null results from K2K and SciBooNE Cross-Section Results from T2K – 9 –
The axial-mass puzzle
MiniBooNE and NOMAD results cannot currently be described by a single neutrino interaction model
Could interactions with correlated pairs of nucleons be the answer? “Meson Exchange Currents” or “2p2h”
Cross-Section Results from T2K – 10 – Charged Current Quasielastic on CH
Two measurement using Subdivide further into two energy ranges different event topologies Muons which stop and which penetrate
only a muon track is reconstructed
muon and proton reconstructed Subtracting postulated meson exchange current events and implementing a nuclear spectral function improves but does not yet definitively resolve the low- energy discrepancy between topologies
Cross-Section Results from T2K – 11 – ND280 – off-axis near detector
A suite of targets, tracking detectors and calorimeters in a 0.2 Tesla field υ flux (a.u.) Let’s focus now on the μ ND280 tracker on-axis Fine grained scintillator and water targets off-axis Tracking in 3 TPCs Eυ Calorimetry
0 2 GeV 4 GeV
υμ
υμ neutral current elastic was measured on water in the P0D and found to agree with generators NEUT and GENIE (+ve tracks with p-like dE/dX) PRELIMINARY
Cross-Section Results from T2K – 12 – Differential CC (inclusive) υe cross section on CH
Measuring differences between υμ and υe cross sections is critical for improving the sensitivity of long baseline experiments
The first υe measurement at the GeV scale since the 1978 Gargamelle results Differential in electron momentum, electron angle and Q2 The result can also be converted into a single flux average at the mean energy of the beam for comparison with Gargamelle
Cross-Section Results from T2K – 13 – Maximizing model independence
Why not report the cross section versus Eυ as in the Gargamelle analysis? Because such a measurement is entangled with a particular nuclear model and a particular set of cross-section parametrizations
Consider, for example, this track which passes the selection cut for υe
Eυ θ e
pe
Instead we unfold our result to be differential in the lepton’s kinematics Then we need only unfold the detector resolution on the lepton’s momentum
Cross-Section Results from T2K – 14 – Differential CC (inclusive) υμ cross section on CH
A similar measurement with υμ was published last year Phys. Rev. D 87, 092003 (2013)
This is double-differential in (pμ , θμ)
Result consistent with NEUT and GENIE generator predictions
Cross-Section Results from T2K – 15 – Fit versus Eυ to Charged Current Quasielastic (another look at the axial-mass puzzle) Search for single muon-like tracks from the CH target volume and fit the MC
The fitted value of MA slightly favours the MiniBooNE and K2K values rather than the higher energy NOMAD fit, where MA ≈ 1.0 GeV Statistics are too low to make a strong statement yet – watch this space! We will investigate the effect of including Meson Exchange Currents
Cross-Section Results from T2K – 16 – Super-Kamiokande – far detector (off-axis)
A 50 kton water Cherenkov detector The T2K far detector, 295 km from the J-PARC super-beam
The first indication of non-zero θ13
World’s best θ23
Seeking to constrain δCP Other highlights Atmospheric neutrino disappearance Solar neutrino disappearance Proton decay limits And we await a 1987A type Supernova… T2K super-beam cross-section measurements in Super-Kamiokande can now constrain the atmospheric neutrino background to supernovae neutrinos...
Cross-Section Results from T2K – 17 – Neutral Current quasielastic on water
The first measurement of NCQE interactions on oxygen Observation via nuclear de-excitation γ-rays Mainly quasielastic nucleon knockout: υ + 16O → υ + p + 15N* (n + 15O*) Also a few % coherent inelastic scattering: υ + 16O → υ + 16O*
Cross-Section Results from T2K – 18 – arXiv:1403.3140 [hep-ex] Summary New T2K cross-section results include:
CC inclusive cross-section with νe
Theoretical differences are expected between νμ and νe Constraining these with data is critical to reducing systematic uncertainties, as long baseline experiments search for CP violation Quasielastic measurements in ND280 and INGRID First T2K contributions to solving the axial-mass puzzle A first few-GeV cross-section on Fe 1.5σ signal excess on CC coherent 1π+ Neutral current quasielastic cross section on water Useful for the atmospheric background to supernovae υ More cross sections to come from T2K, including: Water cross sections – better near/far cancellation of systematics
Anti-neutrino cross sections – important for δCP Cross-Section Results from T2K – 19 – First ND280 antineutrino candidate recently seen in antineutrino mode Here we need cross-section measurements more than ever!
Minerva LBNO LBNE NOvA T2K Hyper-Kamiokande Thank you for your attention
– 20 –
Backup slides follow
Cross-Section Results from T2K – 21 – CC quasielastic cross section on CH
The low energy one-track / two-track discrepancy is not easily explained Relativistic Fermi Gas Spectral Function Include Meson Exchange currents in the background subtraction
Difficult to make conclusions at this stage A differential measurement is in progress
Cross-Section Results from T2K – 22 – Differential CC (inclusive) υe cross section on CH The Gargamelle result was expressed versus reconstructed neutrino energy To compare we can convert the measurement into a flux average
Largest uncertainties: flux 12.9%, statistics 8.7%, detector 8.4%
Cross-Section Results from T2K – 23 – Neutral current elastic υN→ υN in the P0D
P0D (π0-detector) Select proton-like dE/dx BG: mis-identified CCQE Result is consistent with NEUT and GENIE
Cross-Section Results from T2K – 24 – Why measure neutrino cross-sections?
Neutrino interaction model systematics are large in oscillation fits At Super-Kamiokande they are the dominant source of systematic error
1Rμ in Super-K 1Re in Super-K fractional errors fractional errors on the event on the event distribution distribution
They must be reduced to enable the measurement of δCP
Cross-Section Results from T2K – 25 – 0m 120m 280m 295 km
off-axis p π μ -mon ND280 υ Super Kamiokande
Super Kamiokande Far Detector off-axis
INGRID on-axis ND280 off-axis The T2K beam 30 GeV proton beam injected onto C target 3 magnetic horns focus positive hadrons Pure muon neutrino beam from π+ decays
Cross-Section Results from T2K – 27 – The T2K experiment
Long baseline neutrino oscillation experiment in Japan
Wide collaboration: ~500 people from 59 institutes in 11 countries Measurement of the neutrino oscillation parameters 1. Electron neutrino appearance Phys. Rev. Lett. 112, 061802 (2014) 2. Muon neutrino disappearance arXiv:1403.1532v2 → Open a door for the measurement of CP-violation in a lepton sector!!
Cross-Section Results from T2K – 28 – Differential CC (inclusive) υe cross section on CH Differential in: electron momentum electron angle Q2
Cross-Section Results from T2K – 29 – Formaggio and Zeller
Cross-Section Results from T2K – 30 – Disappearance systematics
Cross-Section Results from T2K – 31 –