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Search for coherent charged pion production in neutrino-carbon interactions

Search for coherent charged pion production in neutrino-carbon interactions. F.Sánchez for the K2K collaboration UAB/IFAE. K2K Experiment. n m disappearance Energy spectrum distortion. 250 km. K2K near detectors. 1kt Water Čerenkov detector (1kt)

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Search for coherent charged pion production in neutrino-carbon interactions

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  1. Search for coherent charged pion production in neutrino-carbon interactions F.Sánchez for the K2K collaboration UAB/IFAE

  2. K2K Experiment • nmdisappearance • Energy spectrum distortion 250km

  3. K2K near detectors • 1kt Water Čerenkov detector (1kt) • Scintillating Fiber Detector (Scifi) • Scintillator Bar Detector (SciBar) (from 2003) • Muon Range Detector (MRD)

  4. SciBar Detector • Extruded Scintillator Bar • WLS fiber readout. • Active target. • 2.5 x 1.3 x 300 cm3cell. • Order of 15000 channels. • Light yield ~8 p.e./MeV. • Detect 10 cm track. • Distinguish protons from pby using dE/dx. Miss ID < 5% (<1GeV/c proton). Extruded scintillator (15t) EM calorimeter 3m n 3m 1.7m

  5. m pm nm qm n proton Motivation of SciBar • Assuming Charged Current Quasi-Elastic interaction the energy is reconstructed • Also q2 can be computed the same way. • CC-nonQE interactions are backgrounds for En measurement • Neutrino flux at <1GeV and neutrino interactions around 1GeV are important since the oscillation maximum at K2K is around 600 MeV. CC-QE Interaction m nm N p nucleon CC-nonQE Interaction

  6. Detector Components VME board 64 ch MA-PMT Frontend board

  7. Scintillating Fibers and Lead Plates 262 cm n Beam Readout Cell 8 cm 4 cm n Electron Catcher • Energy tail catcher. • Measure electron neutrino flux. • Study p0 production. • “spaghetti” calorimeter re-used from CHORUS. • 1mm diameter scintillating fibers in the grooves of lead foils. • 4x4cm2 cell is read out from both ends. • 2 planes with a total of 11X0 Horizontal: 30 modules Vertical : 32 modules • Expected resolution 14%√E.

  8. m m Vertex MRD (Iron plates and drift tubes) Vertex SciBar CC Event Selection • SciBar MRD 3D track matching (3D) • ~35% of all n interactions. CC-QE fraction is ~55% (MC) • MRD 1st layer stopping (1L) • ~9% of all n interactions. CC-QE fraction is ~31% (MC) • Momentum of m is computed from its range in SciBar, EC and MRD. 3D matching (3D) 1st layer stopping (1L)

  9. Particle Id. Muon C.L. Total deposit energy vs. Range m sample DATA Energy (mips) Proton-like(purity 90%) Mu-like(purity ~ 99.6%) protonsample Range (cm) Excellent p/m(p) using dE/dx For 90% proton efficiency we get 1.7% of m miss-ID probability. Proton Efficiency Muon mis-ID m-Like Proton like

  10. p n m 3 2 n 1 SciBar Event examples CCQE candidate CCnQE candidate

  11. Total (NC+CC) CC Total CC quasi-elastic DIS CC single p NC single p0 NEUT: K2K Neutrino interaction MC s/E (10-38cm2/GeV) • CC quasi elastic (CCQE) • Smith and Moniz with MA=1.1GeV • CC (resonance) single p(CC-1p) • Rein and Sehgal’s with MA=1.1GeV • DIS • GRV94 + JETSET with Bodek and Yang correction at low q2. • CC coherent p • Rein&Sehgal model based on PCAC. • NC • + Nuclear Effects En (GeV)

  12. Coherent p+ production • K2K and MiniBoone has reported in the past a deficit of events at low q2: nuclear effects?, coherent production?,… K2K MiniBoone

  13. m m proton n n p p Coherent p+ signature • In the coherent p+ production the neutrino scatters off the entire nucleus with small energy transfer. • Rein&Sehgal based on the Partially Conserved Vector Current (PCAC) model has been tested at higher energies. • The coherent p+ signature consists on: • a m- and a p+ in the final state. • No activity in the area of the vertex beyond the outgoing tracks.

  14. Coherent p+ analysis 1 track MRD sample This selection gives 5 independent samples: • 1 track, 2 tracks QE, 2 tracks nQE proton and 2 tracks nQE pion are used to characterize the background. • The coherent sample is used to set the measurement. • The overall CC sample is used to define the normalization: QE 2 tracks Proton like non QE Pion like Coherent sample

  15. m Dqp QE enriched sample Dqp < 25deg nQE enriched sample Dqp > 25deg nQE/QE selection QE Non QE CCQE CC1p Coherent Pi Dqpis the angle between the second track and the predicted proton direction in CCQE reactions. Multi Pi Others (deg) QE Efficiency QE Purity 80% Efficiency 70% Purity (deg)

  16. Proton-p Id Muon Confidence Level (2nd Track : nQE sample) Proton enriched Proton p enriched Pion Others Proton efficiency Proton Purity 85% Efficiency 80% Purity Muon confidence level

  17. Constrain of MC uncertainties • Control samples are fitted simultaneously for q2>0.10(GeV/c)2 to constrain MC uncertainties. 1 track 2 tracks QE 2 tracks NQE p like 2 tracks NQE proton-like • Simultaneously the MRD momentum scale and the MC true ratio between NQE and QE are fitted.

  18. Constrain of MC uncertainties • These values are used to re-weight the MC. • Errors are propagated to the final sample.

  19. Selected samples after the fit No evidence for Coherent events Deficit of events q2<0.10(Gev/c)2 c2/d.o.f = 73.2 / 80 for q2 > 0.10 (Gev/c)2

  20. Vertex activity • Highest energy deposited among cells close to the vertex. • The CC-QE is used as a control sample. Coherent selection cut. CC-QE

  21. Final coherent enriched sample cut @ q2=0.10 (Gev/c)2

  22. Reduction summary

  23. Final efficiency <En> ~ 1.3GeV MRD sample shifts the distributions to high energies due to an effective threshold of 450 GeV/c.

  24. Results N (nmCC) N (coherent p)

  25. Systematic Errors • Nuclear effects:p and proton cross-section is varied by 30%. • Interaction model for CCQE and CC1p cross-section is changed varying the axial mass by 10%. In deep Inelastic we vary the Bodek-Yang correction by 30%. • CC1p suppression is estimated from the 20% deficit for q2<0.10 (GeV/c)2 observed in the non-QE proton sample. • Event selection is dominated by the 2nd track efficiency. • Detector response is dominated by scintillator quenching. • Energy spectrum error comes from the uncertainties in the K2K near detector flux shape.

  26. Results ~30% of MC expectation

  27. Rein&Sehgal s(nm CC) = 1.07 x 1032 cm2/nucleon GGM(NC) s(1040 cm2/nucleon) Aachen(NC) Comparison with other results • No data available for CC-Coherent. • To compare with NC with should do two assumptions: s(NC) ~ 2s(CC) A1/3 nuclear dependency.

  28. Conclusions • We have reported the search for CC coherent p production by nmwith a mean energy of 1.3 GeV. • The data corresponds to 1.7x1019pot recorded with the new SciBar detector at K2K neutrino beam line. • No evidence for this channel has been found and an upper limit on the cross-section has been derived: • s(CC-Coh)/s(CC) < 0.6 10-2 @ 90 % C.L. • This is the first experimental measurement of this channel in the region around 1.3 GeV.

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