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15th Lomonosov Conference on Elementary Particle Physics, 18th-24th August 2011

T2K non-oscillation neutrino physics with near detectors. Michela Ieva. Institut de Fisica d’Altes Energies Barcelona, Spain. on behalf of T2K Collaboration. 15th Lomonosov Conference on Elementary Particle Physics, 18th-24th August 2011. The T2K experiment. J-PARC accelerator

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15th Lomonosov Conference on Elementary Particle Physics, 18th-24th August 2011

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  1. T2K non-oscillation neutrino physics with near detectors Michela Ieva Institut de Fisica d’Altes Energies Barcelona, Spain on behalf of T2K Collaboration 15th Lomonosov Conference on Elementary Particle Physics, 18th-24th August 2011

  2. The T2K experiment J-PARC accelerator complex: 750 Kw of nominal power • Precise measurement of • neutrino oscillation • parameters sin22ϑ23and Δm223 • by νμ→νX disappearance Main Ring Linac • Determination of sin22ϑ13from • the measurement of νμ→νe • appearance Super KAMIOKANDE: 22.5kt–fiducial mass water Cherenkov detector ν beam to Super-K Required accurate knowledge of neutrino beam properties, neutrino cross sections and kinematics before oscillation: The Near Detectors complex: • on-axis detector:INGRID • monitoring stability of beam direction and intensity • off-axisdetectors: ND280 • measurement of ν interactions rate and flavor • before the oscillation

  3. T2K neutrino beam • 30 GeV protons (Main Ring) hit a graphite target • hadrons (π, K) are focused and charge selected by horns • π→ μ +νμdecay tunnel (110 m) • Run I:(January-June 2010) • 3.23x1019p.o.t. (for analysis) • 50 Kw stable beam operation • RUN II:(Nov.2010-March 2011) • 11.08x1019p.o.t. (for analysis) • 145 Kw stable beam operation

  4. The on-axis detector: INGRID • 14 on-axis (vertical and horizontal) modules arranged in a • cross each composed by XY planes of scintillator strips • interleaved with iron • 2 off-axis modules used to study • the symmetry of the beam Proton module: • made of scintillator tracking planes without • iron layers to be able to reconstruct protons in • CCQE ν interactions and used also for cross • sections measurements

  5. Beam profile and stability daily event rate of ν events candidate for the central module Number of events in each horizontal (left) and vertical(right) module clear beam profile 1 mrad Beam (x and y) center as function of time accuracy achieved: better than required 1 mrad (~2% shift of the energy peak @ SK)

  6. The ND280 Detectors Refurbished UA1/NOMAD magnet provides a 0.2T magnetic field. The SMRD (installed inside the air gaps of the magnet return yokes) : scintillator planes to reconstruct large angle μ’s, cosmic rays and beam related event in pit wall and magnet iron. Tracker: 2 FGD: X and Y planes of scintillator bars acting as ν interaction target mass and charged particle tracking. ν beam 3 TPC: 3D tracking, to measure charge, momentum and dE/dx of charged particles. P0D : scintillator planes interleaved with lead/brass and water layers. Active target to measure photons from NC and CCπº interactions. ECAL: Complement the inner detectors with γ/e/μ separation capabilities. 13 independent modules of plastic scintillator/lead XY planes.

  7. The ND280 Detectors

  8. Cosmic ray passing through off-axis detectors ν beam

  9. ND280 Physics Goals As input to T2K neutrino oscillation analyses: Neutrino beam properties Measurements on water and carbon targets • νμmeasurement: interaction rate and energy spectrum • νe beam component measure: intrinsic background to • νe appearance T2K beam energy region • NCπ0 measurement: important background to • νe appearance • Reduce cross-section uncertainties to • oscillation analyses Cross-section measurements Measure neutrino cross-section • P0D water in/out • Water layers in FGD2

  10. Sub-Detectors scintillators and MPPCs POD FGD SMRD • All scintillators detectors use Hamamatsu Multi Pixel Photon • Counter (MPPC) coupled with WLS fibers • The MPPC’s area is 1.3x1.3 mm2 composed by 667 micro-pixels [NIM, A 662 (2010) 567-573] First MPPCs large scale using in a running experiment! All sub-detectors have > 99.5% of their channels fully functional!

  11. SMRD performances SMRD Beam Event hits Beam events time structure: 6 bunch structure • SMRD activity and reconstructed tracks used to: • Reconstruct high angle μ • veto and background rejection

  12. ECAL performances, PID and Energy • Developed a neural network based on the • shaped and charge distribution of a cluster • to perform track/shower separation 600 MeV Electrons • Distinguish electrons from muons to • measure the νe beam component • Search for isolated shower coming from • interactions producing π0 Sand muons CERN Testbeam Electrons σE 9.8% = E √E • EM energy • proportional to • collected charge: [400 Mev – 2 GeV]

  13. P0D performances Time distribution of interaction vertices • Optimized for the measurement of NCπ0 • interactions: important background to T2K • νe appearance measurement. XY distribution of interaction vertices • Water and carbon target for the • measurement of cross sections on • different materials. Beam center

  14. FGD performances and PID Vertex distribution of selected events Timing resolution FGD1-FGD2 time difference for cosmic ray track: • track direction studies FGD PID: Selected P0D-TPC1-FGD1 tracks stopping in the FGD • using total energy deposited and track range • good separation proton/pion fundamental to • enhance the CCQE purity sample selection

  15. The TPC First large scale application of Micro Pattern Gaseous Detector (MPGD) 3Time Projection Chambers (TPC) • Sensitive volume 180x200x70 cm3 • Gas mixture: Ar/CF4/iC4H10 (95/3/2) • Each TPC endplate is readout by 12 • → 72 modules in total MicroMEGAS modules • each module is divided in 1728 pads, • (36 columnes x 48 rows) → ~120000 channels Horizontal tracks cross 2MM modules → 72 pad columns measurements: • clustering • track pattern recognition • Likelihood fit minimization to obtain track • coordinates, angles, curvature and errors [NIM, A 627 (2011) 25-46

  16. TPC performances: PID [NIM, A 627 (2011) 25-46 The PID is based on the measurement of the ionization energy loss (dE/dx) different for particles with same momentum but different mass • Selected the 70% (truncated mean method) of • low energy clusters to reject high energy tails that • decrease the resolution • 7.8% resolution for MIP better than 10% goal • needed to distinguish electrons from muons at • more than 3σ

  17. [NIM, A 627 (2011) 25-46 TPC spatial and momentum resolution • Estimated by comparing coordinate resulting from global track likelihood fit with a local • single cluster fit • the residual distribution is fitted to a normal distribution providing the values of the spatial • resolution and bias 600 μm of spatial resolution for horizontal tracks • The measured spatial resolution is enough for • a momentum resolution < 10% at 1 GeV • (TPC goal)

  18. Analyses at ND280 tracker TPC+FGD DATA: 2.9x1019 POT MC: 4.9x1020 POT Performed two different analyses with first T2K data (RUN I): • CC inclusive νµselection used in oscillation analyses to normalize the expected flux • at Super-K: NexpSK = Rμ,DataND x NMCSK/Rμ,MCND • measurement of νe beam component: One of the main background to νe appearance dE/dx vs P (before PID) Select ν interaction in the FGD identifying the lepton: • TPC1 veto • At least 1 negative track in TPC2(TPC3) starting • inside FGD1(FGD2) fiducial volume • If there are more than 1 negative track • → selected the most energetic • Use the TPC PID to distinguish between e and μ [δ(i) = (dE/dxmeas - dE/dxexp)(i)/σ(i), i=e,p,μ,π] • PID cut: • νµ selection: |δ(µ)|<2.5, |δ(e)|>2 • νe selection: -1<|δ(e)|<2, |δ(µ)|>2

  19. The νµ selection (RUN I) • Selected a sample of interaction candidates inside the FGD with a 1529 νµ CC purity~ 90% FGD1 X starting point FGD2 X starting point Off-axis configuration visible from the starting point of selected tracks FGD2 Y starting point FGD1 Y starting point Efficiency vs neutrino energy Integrated with the energy spectrum ~ 38%

  20. Detector systematics evaluation TPC1 TPC2 TPC3 • counting missed segments • in data and MC: δRTPCeff = - 2% FGD1 FGD2 • Selected through going • muons • Evaluated changing • TPC-FGD matching • criteria • MC • data δRTPC/FGD = ±2.1% • Pull width difference change the number of selected • event in data and MC. • Used sand muons to compute the efficiency in selecting • muons if |δE(μ)|<2.5 δRpull = +3.0%

  21. νμ CC inclusive measurement (RUN I) Selected events muon momentum Selected events muon direction Results: * (*Flux systematic uncertainties are not included in the errors)

  22. The νe selection (RUN I) Selected events momentum distribution The νeinteractions inside the FGD, electron momentum range 0-2 GeV/c, have been selected applying the same cuts of νµexcept for: • TPC PID to select electrons (instead of muons) • γ conversion rejection (events with a second • e-type tracks and Minv<100 MeV/c) P(MeV/c) Efficiency vs neutrino energy Integrated with the energy spectrum ~ 30% P(MeV/c)

  23. The background to νe selection The background is mainly due to: • Misidentified muons: • Counted how many times a track passes the νe PID • selection in a clean sample of muons (sand or cosmic • muons) : 2.9 events • Electromagnetic background: - electrons from ν interactions in the FGD producingπ0 → γγ→ e+e- - electrons from γ conversion in the FGD coming from outside (magnet, SMRD, ECAL) positive analysis, e+ selection (p< 500 MeV) pair selection (all momenta) analysis Positron candidates: reconstructed momentum Sum of the enery of the pairs

  24. The Likelihood fit and systematics A maximum likelihood fit on the lepton momentum ( 0-2 GeV/c range) was performed to measure the number of νe taking into account the 3 components: • signal (negative analysis) • background: • - e+ (positive analysis) • - pair selection • - misidentified muons Systematic related to νe analysis: - Variation of fraction MISID in the fit: ±0.5 ev - Variation shape νµ component: ±0.5 ev - Data/MC difference in the pull widths: 0.4 ev - PDF for converted photon sample: 1.9 ev Results: 90% CL upper limit νe component < 2.0% νe content is consistent with MC expectation. No anomalous excess of beam νe events is observed at ND280! N N

  25. Future cross section measurements The NC π0 cross-section measurement is of particular interest for T2K: A single π0 at Super-K can mimic an electron from νe interaction NCπ0 cross-section on water Neutrino oscillation analysis background Charged Current: Neutral Current: Specific interest Many different cross-section measurements are under way… • CCQE: Tracker, P0D, INGRID (proton module) • CC1π: Tracker, P0D • CC1π0: Tracker, P0D (carbon/water) • CC coherent π production: Tracker • Δ++ production: Tracker • Others CC DIS, CCNπ:Tracker, P0D • NC elastic:Tracker, P0D • NCπ :Tracker

  26. Conclusions • T2K has collected data during two physics runs (Jan. 2010 to March 2011): • 1.43 x 1020 p.o.t (~ 2% T2K goal). • With 2010 data taking (RUN I) two different analyses have been finalized: • evaluation of νe beam component → no anomalous excess at ND280 • νμ CC inclusivedata/MC ratio → as input to T2K oscillation analysis. • Future cross-section measurements will improve our knowledge of neutrino interacations • at T2K beam energies • At the moment all sub-detectors are completing the recovery from March 11th • earthquake, no major damages. • We plan to restart JPARC accelerator operation in December 2011 and the data taking as soon • as possible.

  27. The T2K Collaboration 12 countries, 58 institutions, ~500 members Thank you!

  28. …deep inside…

  29. Neutrino oscillations Mass eigenstates Flavor states …in 2 flavors scheme: • 3 angles (θ12,θ13,θ23) • 1 CP violation phase δ • 2 independent mass • differences Δ2ij=m2i-m2j P (ab) = sin22 sin2(1.27 m2 L/E) constraints imposed by experiments with reactors: Sin2θ13 < 0.13 δ unknown Solar (SNO, KAMLAND, SK): SKI +II, K2K, MINOS

  30. Neutrino interaction models CCQE: Charged Current quasi-elastic • μ in the final state • W exchanged • no meson production NCπ0: Neutral Current single pion • no lepton in the • final state • Z exchanged • 1 π0 in the final • state CC1π: Charged Current single pion • 1 pion in the final state • W exchanged • resonance production dominates • CCπ0, CCπ+- FSI: Final State interactions • particles in the initial nucleus interaction • may not the same that exit

  31. T2K off-axis concept T2K is the first LBL ν experiment using an off-axis beam • Beam is aimed 2.5º off the direction of Super-K • Produced a narrow beam with peak energy (~600 MeV) • tuned to first νe, νµ oscillation maximum • (Δm213L /4Eν~π/2) • Reduction of high energy tail, • reduce background from non-QE and NC • maximizing the event rate the statistical errors are • minimized and thinner energy peak reduce the • systematics due to misreconstruction

  32. ND280 magnet and SMRD • UA1 magnet: • 16 C-shaped elements • each element consists of 18 iron layers • (48mm) • - 17mm air gaps • SMRD modules: • Horizontal (4 counters each) • Vertical (5 counters each) • total of 440 (2008 counters) • SMRD tasks: • measurement of large angle muon • (from ν interactions) momenta and angle • cosmic trigger for calibration • beam monitoring • background rejection

  33. ND280’s ECal The ECAL is a plastic scintillator/lead sampling electromagnetic calorimeter surrounding the ND280’s inner detectors (P0D, TPCs, FGDs) It is composed by 13 independent modules • Downstream ECAL: • 34 layers, 50 scintillator bars 2.04m • long and 1.75mm lead sheet (10.6X0) - 6 Barrel modules: 31 layers 3.84m or 1.52m bars and 1.75mm lead sheets (9.7X0) - 6 P0D ECAL modules: 6 layers, 2.34 bars and 4mm lead sheets (10.6X0) • Analysis goals: • photons detection and their direction and energy measurement • charged particle PID (electron-muon-pion separation) • πº reconstruction

  34. The πº detector (P0D) 7+7 lead/scintillator planes to front and back γ stop (5.7X0) • 17 x 35.5mm co-extruded triangular polystyrene bars with TiO2 reflective layer and central hole • with WLS fiber gives an excellent shower pointing 40 XY brass/scintillator tracking planes interspersed with water cells fiducial mass C/O: 1.8t/0.9t Surrounded by P0DECal γ counter an μ tagger (ε,purity) - Water In/Out running allows inclusive and exclusive π0O16 cross section measurement

  35. J-PARC: Japan Proton Accelerator Research Complex Joint project of KEK and Japan Atomic Energy Agency (JAEA) Located in Tokai village, 60 km from KEK, completed in 2009: • Designed goal 750 Kw • 30 GeV protons to neutrino • beam line • reached 145 Kw with 3 sec pulse • period before earthquake

  36. J-PARC Neutrino beam line

  37. The MicroMegas principle The T2K’s TPCs constituent the first large scale application of Micro Pattern Gaseous Detectors (MPGD) when a charged particles cross the TPC ionizes the gas releasing electron/ions pair along its path a strong (25KV) electric field drifts them to the MicroMegas (readout) plane Once they arrive to the Micromesh a intense (500KV/cm) E field starts the avalanche to the amplification of the signal (typical gain ~1000) the Micromesh also stops the positive ions minimizing the field distortion

  38. The ND280 νe beam component measurement Max oscillation probability @ ~ 0.6 GeV µ+ → e+ + νe + νµ • Positive pions decays create most of νµ in the • oscillation region and low energy νe: π+ → µ+ + νµ • at higer energy kaons (3-body) decays • dominates: K+ → π0 + e+ + νe NA61/SHINE data would help.

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