Results from T2K experiment
1. The T2K experiment. The T2K neutrino beamline and the off-axis method The T2K detectors
2. Oscillation analyses results:
νe appearance results νμ disappearance results
3. Non-oscillation analyses performed at the near detectors of the T2K 4. Summary and conclusions
Magdalena Posiadała-Zezula, University of Warsaw on behalf of the T2K Collaboration Neutrino oscillations
Neutrino oscillations are described by the PMNS matrix with :
3 mixing angles, 2 mass differences, 1 complex CP phase δCP
with Cij (Sij) representing cosθij (sinθij), where θij is the mixing angle between the generations i and j. flavor eigenstates mass eigenstates
−iδ CP ν e 1 0 0 C13 0 S13e C12 S12 0 ν1 0 C S 0 1 0 S C 0 ν µ = 23 23 − 12 12 ν 2 iδ CP ντ 0 −S23 C23 − S13e 0 C13 0 0 1 ν 3
atmospheric and accelerators interference solar and reactors 0 θ ≅ 0 θ ≅ 0 θ23 ≅ 45 13 9 12 34 2 −3 2 δ =? 2 −5 2 Δm32 ≅ 2.4 ×10 eV CP Δm21 ≅ 7.6 ×10 eV € Long baseline accelerator experiments are sensitive to: 2 Atmospheric parameters (θ23, Δ m 32 ) →mainly νμ disappearance € Interference parameters (θ13, δCP) → mainly νe appearance€ Magdalena Posiadała-Zezula, Results from T2K experiment, Miami 2014 University of Warsaw 2 € The T2K experiment
Important goals: - precise measurement of θ23 by νμ - measurement of θ13 by νe appearance: disappearance: 2 0.038 2 0.055 sin 2"13 = 0.140 ± 0.032 (N.H.)at 68% C.L. sin θ23 = 0.514 ± 0.056 (N.H.)at 68% C.L.
! €
Super-Kamiokande ND280 J-PARC
fot. P. Mijakowski
Magdalena Posiadała-Zezula, Results from T2K experiment, Miami 2014 University of Warsaw 3 T2K neutrino beamline in J-PARC
~96m length The J-PARC Main Ring (MR) extracts a 30 GeV proton beam every 2-3 seconds. For each acceleration cycle, a beam is extracted to the T2K neutrino beamline as a 5μs spill. Each spill contains 8 bunches.
Magdalena Posiadała-Zezula, Results from T2K experiment, Miami 2014 University of Warsaw 4 Beam operation history
up to summer 2014
Magdalena Posiadała-Zezula, Results from T2K experiment, Miami 2014 University of Warsaw 5 The off-axis method
The T2K experiment employs the off-axis method, which for the first time has been used in search for neutrino oscillations (BNL-E889 proposal).
The off-axis method uses the fact that the energy,
Eν, of the neutrino emitted at an angle relative to the π (K) direction in a two-body pion (kaon) In T2K, the off-axis angle is set to decay is only weakly dependent on the 2.50 with the neutrino beam energy momentum of the parent meson. at SK peaking at ~0.6 GeV, near the expected first oscillation maximum ( Phys.Rev. D87, 012001, 2013). Magdalena Posiadała-Zezula, Results from T2K experiment, Miami 2014 University of Warsaw 6 The T2K on-axis near detector INGRID
The on-axis detector- INGRID
16 cubic modules. Aim: to monitor the ν beam direction by looking at ν interactions with precision better than 1 mrad on a day-by-day basis.
The INGRID standard module. 1 module is a sandwich of 10 iron and 11 scintillator planes. It is surrounded by veto scintillator planes. arXiv:1407.4256v2, hep-ex
Magdalena Posiadała-Zezula, Results from T2K experiment, Miami 2014 University of Warsaw 7 The T2K off-axis near detector ND280
The ND280 detector is located at 2.5 degrees off axis.
The ND280 is placed inside a 0.2 T magnet previously used by the UA1 and NOMAD experiments.
The ND280 consists of:
1. π0 detector (P0D); 2. three gas-filled TPC’s for momentum and PID measurement; 3. two fine-grained detectors (FGD’s) as active targets; 4. electromagnetic calorimeter (ECal) for energy measurement and PID; 5. muon detectors (SMRD).
Magdalena Posiadała-Zezula, Results from T2K experiment, Miami 2014 University of Warsaw 8 The Super-Kamiokande detector
50 kton water Cherenkov detector (22.5 kton FV)
The geometry of the Super-Kamiokande (SK) detector consists of : an inner and an outer detector. 40 m The inner detector (ID ) is a cylindrical structure with ~11k PMTs
40 m The outer detector (OD) contains ~ 2k PMTs.
Magdalena Posiadała-Zezula, Results from T2K experiment, Miami 2014 University of Warsaw 9 Super Kamiokande detector- detection principle
ν interactions often produce charged particles which may create a cone of Cherenkov photons as they traverse water. When these photons reach the PMTs, they produce a ring-shaped hit pattern which is used to extract information on event vertex position and momenta of particles.
νμ-like – well νe-like – defined cone, scattering of e-, sharp ring. “fuzzy” rings.
Example of reconstructed events in SK. The white line shows reconstructed cone.
Magdalena Posiadała-Zezula, Results from T2K experiment, Miami 2014 University of Warsaw 10 The T2K neutrino flux simulation (Phys.Rev. D87, 012001, 2013).
The prediction of the flux and spectrum of neutrinos at the T2K detectors (INGRID, ND280 and SK) is based on :
1) FLUKA generation – simulation of p+C interactions in the target
2) JNUBEAM simulation- tracking exiting particles from the target. The simulation and its associated uncertainties are driven by: a) primary beam profile measurements, b) measurements of the horns magnetic fields, c) hadron production data and re-weighting, including NA61/SHINE measurements from 2007 run: (Phys.Rev. C85, 035210, 2012, Phys.Rev. C84, 034604, 2011).
Fluxes at INGRID, ND280 and SK
Magdalena Posiadała-Zezula, Results from T2K experiment, Miami 2014 University of Warsaw 11 NA61/SHINE at CERN SPS
Large-acceptance hadron spectrometer.
The main tracking and particle identification devices are large- volume TPCs and ToF.
Two TPCs are located between coils of the two superconducting magnets (1.14 Tm)
Two types of measurements were done for T2K: 31GeV/c protons on:
1). Thin target (4%λint)- studies of primary interactions 2). Replica of the T2K target (1.9λint)- production of all hadrons along the target
Year Thin target Replica target Status registered no of events registered no of events 2007 6.3 x105 used by T2K 2.3x105 Published 2009 4.4x106 2.4x106 Being analyzed 2010 - 1x107 Under Calibration Magdalena Posiadała-Zezula, Results from T2K experiment, Miami 2014 University of Warsaw 12 Possible improvements with 2009 NA61 data with thin target data: with T2K replica target data, better coverage, new hadronic measurements tested on 2007 data
Magdalena Posiadała-Zezula, Results from T2K experiment,Nucl.Instrum.Meth.A701, Miami 2014 2013 University of Warsaw 13 TheT2K predicted ν flux
Flux is mainly composed of νμ
Contamination fromνe is ~1.2%
Total uncertainty on T2K flux is ~10-15% Main uncertainty on flux predictions still comes from hadronic interactions - it will be improved with the 2009 NA61 results
Neutrino Flux prediction : • Hadron production data from SK NA61/SHINE Fit to ND280 data constrains ND280 flux and cross section parameters expected ν sample νμ μ νe (νμ) νe (νμ) sample enhanced in events for candidates enhanced CC event unosc. selected in CC candidates spectra in in DATA events MC in DATA MC
Cross section models: • Interaction generator (NEUT) • External data (MiniBooNE) Extraction of the oscillation parameters
Magdalena Posiadała-Zezula, Results from T2K experiment, Miami 2014 University of Warsaw 15 Systematic uncertainties- impact of the ND280 measurements Strong reduction of the systematic uncertainties to the event rate at SK, thanks to the ND280 data
Systematic sources νμ νe sample sample [%] [%] ν flux and w/o ND280 meas. 21.8 26.0 cross section w ND280 meas. 2.7 3.1 ν cross sections due to difference 5.0 4.7 of target between near and far detector Final or secondary hadronic 3.0 2.4 interactions Super-K detector 4.0 2.7 Total w/o ND280 meas 23.5 26.8 w/ ND280 meas. 7.7 6.8
Magdalena Posiadała-Zezula, Results from T2K experiment, Miami 2014 University of Warsaw 16 Super-Kamiokande event selection
Fully Contained, 1 ring events inside the fiducial volume of the SK detector
μ–like: e–like: pe > 100 MeV/c pμ > 200 MeV/c NO Michel electron Michel electron less than 2 π0 rejection μ -like PID Erec < 1250 MeV, e-like PID
120 events observed 28 events observed expected 446±23 (syst) expected 4.9±0.6 (syst)
Magdalena Posiadała-Zezula, Results from T2K experiment, Miami 2014 University of Warsaw 17 νe appearance results
Phys.Rev.Lett. 112 (2014) 061802
The neutrino oscillation parameters are
obtained using maximum likelihood fit in (pe, θe)
Results are consistent with independent analysis
based on neutrino reconstructed energy Erec Best fit value : θ ν 2 +0.038 The (pe, e) distribution for e sin 2"13 = 0.140#0.032 for N.H. and $CP = 0 candidate-events with MC predictions.
7.3σ significance to non-zero θ13
! Discovery of νe appearance !!!
T2K has made the first observation of νe in νμ beam
Magdalena Posiadała-Zezula, Results from T2K experiment, Miami 2014 University of Warsaw 18 νμ disappearance analysis
Phys.Rev.Lett. 112 (2014) 181801
World leading measurement for θ23 ! For the first time, the mixing angle θ23 is better constrained by an accelerator experiment than by atmospheric neutrinos.
Fit to data made using 3 flavor framework for oscillations. Maximal mixing is favored 2 +0.055 sin "23 = 0.514#0.056 for N.H.
!
Magdalena Posiadała-Zezula, Results from T2K experiment, Miami 2014 University of Warsaw 19 Joint νμ-νe fit and δCP constrains A joint fit is needed because of the correlations between mixing parameters: θ13, θ23, δCP and others; Two different analyses: Frequentist based on Feldman-Cousins
Bayesian based on Markov Chain MC Both analyses give similar results
Best fit value of δCP ~ -π/2 With additional information from reactor measurements of θ13, we can obtain better limits on δCP
Magdalena Posiadała-Zezula, Results from T2K experiment, Miami 2014 University of Warsaw 20 Other T2K measurements
Non-oscillation analyses with the near detectors:
Measurement of νμ cross section on Fe/CH with the on-axis detector (INGRID)
Measurement of νμ cross-section on C with the off-axis detector (ND280)
Measurement of the beam νe component Inclusive νe cross-section Search for short baseline νe disappearance (reactor and gallium anomalies)
I will only cover some of them.
Magdalena Posiadała-Zezula, Results from T2K experiment, Miami 2014 University of Warsaw 21 Measurement of νµ cross-section on C with the off-axis detector arXiv:1411.6264 [hep-ex] The CCQE interaction: － νl + n → l + p is the dominant CC process at E ∼ 1 GeV.
Magdalena Posiadała-Zezula, Results from T2K experiment, Miami 2014 University of Warsaw 22 Measurement of the intrinsic
νe beam component in ND280 Phys.Rev. D89 (2014) 092003
The main and irreducible background to
the νe appearance signal comes from the presence of νe from the beam, originating from muon and kaon decays.
In T2K, the νe component represents ~1.2% of the total neutrino flux – difficult ! CC0π
A selection of νe CC interactions has been performed using the ND280 sub-detectors with PID capabilities: TPC and ECAL to select electrons and reject muons.
The ratio between the observed νe beam component and the prediction:
R(ν e ) =1.01± 0.06(stat.) ± 0.06( flux ⊕ x.sec.) ± 0.05(det .⊕ FSI)
Magdalena Posiadała-Zezula, Results from T2K experiment, Miami 2014 University of Warsaw 23
€ Inclusive νe CC cross-section results arXiv:1407.7389 [hep-ex]
The ND280 used to make the first νe CC differential cross-section measurements at E ∼1 GeV as a function of the electron momentum and scattering angle.
T2K result together with the Gargamelle data.
Magdalena Posiadała-Zezula, Results from T2K experiment, Miami 2014 University of Warsaw 24 Future plans and perspectives
In May 2014, the first anti-neutrino The first event in anti-neutrino beam mode run was started. seen in SK.
The second run is being carried out in this autumn.
Taking anti-neutrino data needs usage of negative horn polarity
Run similar amount of ν and anti-
ν - to have best sensitivity to δCP.
Best measurement of anti-νμ disappearance.
Start searching for anti-νe appearance.
Magdalena Posiadała-Zezula, Results from T2K experiment, Miami 2014 University of Warsaw 25 Summary and conclusions
T2K has performed world leading measurements by taking only 8% of the total expected statistics:
First observation of νe appearance at 7.3 σ. Best measurement of θ23 through νμ disappearance → 3° error.
The near detectors ND280 and INGRID are used for several measurements such as:
νμ and νe cross sections.
This year, the first anti-neutrino run was started. Measure anti-νμ disappearance and anti-νe appearance. Running ~50% anti-ν allow to optimize sensitivity toδCP .
Currently, we are again taking data using anti-neutrino and neutrino run modes.
Magdalena Posiadała-Zezula, Results from T2K experiment, Miami 2014 University of Warsaw 26 appendix
Magdalena Posiadała-Zezula, University of Results from T2K experiment, Miami 2014 Warsaw 27 π0 rejection at Super Kamiokande
2 backgrounds to νe appearance: 0 intrinsic νe component and π → γγ
π 0 → γ+γ if the 2 rings overlap → it might be identified as 1 single ring
The new π0 cut is reducing 70% more of the π0 background than previous methods.
The new algorithm is a maximum-likelihood fit in which charge and time probability density functions (PDFs) are constructed for every PMT hit for a given particle hypothesis. 0 0 0 To separate π events from νe CC events, both the reconstructed π mass (mπ ) and the ratio of the best-fit likelihoods of the π0 and electron fits (Lπ0/Le ) are used. The red line indicates the location of the π0 rejection cut.
Magdalena Posiadała-Zezula, Results from T2K experiment, Miami 2014 University of Warsaw 28 T2K flux predictions for νe
νe flux at ND280 The main and irreducible background
to the νe appearance signal comes from the presence of νe from the beam, originating from muon and kaon decays.
In T2K νe component is expected to represent 1.2% of the total neutrino flux – difficult !
Most of the νe come from:
+ + µ → e + ν µ + ν e
+ 0 + K → π + e + ν e (BR = 5.1%) 0 − + KL → π + e + ν e (BR = 40.5%)
Magdalena Posiadała-Zezula, Results from T2K experiment, Miami 2014 29 University€ of Warsaw Selection of electron neutrino CC events at ND280
1. A good beam spill and good ND280 data quality -all subdetectors were functioning correctly - the reconstructed objects in each spill are split into 8 time bunches. 2. For each bunch the highest momentum negatively charged track is selected in FV of FGD as the lepton candidate 3. The track is rejected if the reconstructed momentum < 200 MeV/c as that region is dominated by background from photon conversions. 4. To select electrons, the TPC and ECal PID capabilities are combined. 5. To ensure good TPC PID performance the selected track needs to have at least 36 reconstructed clusters in the TPC- half of the TPC.
Magdalena Posiadała-Zezula, Results from T2K experiment, Miami 2014 University of Warsaw 30 TPC PID performance
The PID in the TPC is based on the measurement of the ionization produced by charged particles crossing the gas. To perform particle identifcation in the TPC, the ionization in each cluster is corrected for the track length sampled by the pad column. A mean ionization value is calculated and is compared to that expected for particle type “i” at the reconstructed momentum. This comparison is used to form the `pull' i (the difference between the measured mean ionization and the expected one divided by the resolution).
Magdalena Posiadała-Zezula, Results from T2K experiment, Miami 2014 University of Warsaw 31 Control of the backgrounds
in νe CC interactions
The selection of νe CC interactions is designed to reject two large backgrounds: 1. muons produced in CC interactions that are the dominant component of the T2K beam -rejected using the PID capabilities of ND280 2. the conversions of photons in the FGD producing electrons in the TPC and it cannot be rejected using PID algorithms.
1. Those electrons mostly come from νμ interactions which occur inside or outside FGD producing π0 which decay into two photons. 2. One of the two photons then converts inside the FGD producing an e+ + e- pair. 3. If the positron is not reconstructed in the TPC the event is topologically
equivalent to a νe CC interaction. 4. This background may be reduced when information on both: electrons and positrons reconstructed in TPC is available.
Magdalena Posiadała-Zezula, Results from T2K experiment, Miami 2014 University of Warsaw 32 Charge hadron measurements from thin target data-NA61
We developed three analyses Positive particles Negative particles techniques: !+ !- protons antiprotons 2.5 K+ 2.5 K- 2 1). dE/dx+ToF –particles identified e+ e- 10 102 via time-of-flight and dE/dx deuterons antideuterons
2 dE/dx [mip] 2 measurements in the ToF and TPCs. dE/dx [mip] 10 ± + 10 π , K ,p with p≥1GeV/c- 2007 data 1.5 1.5 and in addition K- with 2009 data- 1 status of 2009 : finished with total 1 1 1 0.1 1 10 0.1 1 10 error values. p [GeV/c] p [GeV/c] 2). dE/dx analysis at low momentum, π+ (π-) with p≤1 (3)GeV/c- status of 2009: released central values up to 1 GeV/c, systematic in progress. 3). h- analysis via measurements of negatively charged particles; spectra of π- in broad momentum range- status of 2009: work in progress.
Magdalena Posiadała-Zezula, University of Results from T2K experiment, Miami 2014 Warsaw 33 Charge hadron measurements from thin target data-NA61
π+ multiplicities in p+C at 31 GeV/c from dE/dx +ToF analysis from 2009 data compared to 2007 results. Total error plotted. Improved statistical precision with 2009 data.
Results for K±,p, π- in the appendix
Magdalena Posiadała-Zezula, University of Results from T2K experiment, Miami 2014 Warsaw 34 Fractional flux error
(Phys.Rev. D87, 012001, 2013) Used π±, K+ measurements from 2007 run of NA61
peak at EV~0.6GeV Magdalena Posiadała-Zezula, University of Results from T2K experiment, Miami 2014 Warsaw 35 Importance of the T2K replica target analysis-NA61 Neutrinos are coming from hadrons produced by primary interaction and from other various interactions which can occur in the long target (~90 cm length) as well as in the surrounding target material present in the beamline (Nucl. Instrum. Meth. A701, 99-114, 2013).
νμ νe
60% 60%
30% 30%
The contribution of parents originating from the target sums up to 90 %, among which 60% are due to primary interactions, and 30% are due to re-interactions in the target. The remaining 10% are interactions outside the target. We used limited in statistics 2007 T2K replica target data to test the method of tuning T2K flux. Magdalena Posiadała-Zezula, University of 2009 T2K replica target analysis isResults almost from T2Kfinished, experiment, pion Miami spectra 2014 will be used to tune T2K Warsaw 36 simulation. The T2K replica target re-weighting
At least two different approaches based on the NA61 replica target data can be used to in T2K simulation:
absolute yields, we use the NA61 measured yields at the surface of the target corrected for various efficiencies like detector geometrical acceptance, particle losses. In this case weights are defined the same way as for thin target data, and re-weighting is done within T2K simulation
raw yields, we use NA61 measured yields at the surface of the target without any corrections. We need also the reconstructed yields obtained from the NA61 simulation based on the model used in T2K. Re-weighting is done within NA61 simulation- model dependent.
Magdalena Posiadała-Zezula, University of Results from T2K experiment, Miami 2014 Warsaw 37