K2K and JHF near detectors

NuFact02, July 2002, London K2K and JHF near detectors Takaaki Kajita, ICRR, U.Tokyo For the K2K collab. and JHF-Kamioka WG JHF

Outline • K2K near detector system • Basic idea for JHF near detectors • Summary

K2K experiment @KEK Bird’s Eye Neutrino Beam Line Front (Near) Detector 200m

n flux and direction K2K near detector 300m from the target (SciFi) (1Kton) (MRD) 312 ton (1ev / 20spills) Fid. Vol.: 6 ton 25 ton

Beam direction? (MRD) (0.5GeV < Eμ < 1.0GeV) 1mrad profile center x (cm) profile x (1.0GeV < Eμ < 2.5GeV) ±3-4 mrad. accuracy required. profile center y (cm) profile x June 99 Apr. 01

Role of the SciFi detector μ Max osc. p MRD SciFi Fraction of non-quasi-elastic events must be understood well.

1kton water Cherenkov detector Predict the Super-Kamiokande flux. Overall normalization error on Nsk for Nov99~ KTon: dominated by fid vol error SK: similar to Kton. List of uncertainties: ⇒ energy scale ⇒ FC event selection ⇒ Particle ID ⇒ Ring counting ⇒ Fiducial volume ⇒ Angular resolution ⇒ Threshold ⇒ Events θ > 90 degree.

K2K near detector upgrade Δm2=3×10-3eV2Eν=600MeV. Lower energy ν interactions should be studied. Full Active (solid) Scintillator Tracker • High efficiency for a short (<4cm) track. • Detect a proton down to 350 MeV/c. • PID (p/π) by dE/dx and momentum • Fine segments (1.3×2.5×300cm ). Monte Carlo p 3m μ 3m 45,000 events @3×1019pot 14,400 channels 1.8m

JHF near detectors Second near detector @～2km from the target Target Decay pipe (L=130m) 280m ν First near detector @280m from the target

Discovery of non-zero θ13 Precise measurement of θ23 and Δm . CP violation Required accuracy JHF-Phase I JHF-Phase II (with Hyper-K) 2 Flux prediction @far detector 2% 5% ★Main near detector should be water Ch. ★Near detector pos. must be >1.5km.

Some information on the beam…. Max. osc. (must be predicted accurately) Number of events /100MeV/yr Background (must be understood well) Eν(GeV)

Event rate & Far/near ratio 2 6 /100ton/spill @280m @280m 2 Not a good place…. 1 (φfar / φnear)×(Lfar / Lnear) 0 @2km 0.1 /100ton/spill @2km OK ! 1 Distance from target (km) Water Cherenkov : Impossible @280m (Total mass > 100 tons) 0 0 1 2 3 Eν(GeV)

Near detector @280m • Beam profile monitor • Cannot be water Cherenkov • Detailed study of neutrino interactions @1GeV • No detailed design….., but could be something like: • ・・・・ 0 deg. Super-K 10m ? ※This profile is obsolete… Just to give the idea….

Near detector @2km Muon detector Water Cherenkov detector Fine grained scintillater detector 8m ν beam 4m 8m 8m 15.2m 5m Total mass : 1000ton 9.2m φ Fid. Mass : 100ton Details : not designed yet

Stopping point distribution of muons 4m ν 2m Edge of the fid vol. Measured by muon detector Detector surface

Surface building The detector should look like…. Scintillator detector Water Ch. Muon counter

Summary • Multi component K2K near detector system is essential to understand the neutrino beam and interactions. • In the JHF-Kamioka neutrino project, the near detector system should be similar to the K2K system. • However, in JHF, the distance between the target and the near detector should be > 2km.

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Beam energy stability ? (MRD, 1Kton) MRD 1Kton 2000 2001 Every month Eμ (GeV) Pμ(GeV/c)

K2K and JHF near detectors