Measurement with Double Chooz IDM chasing the missing mixing angle e x Disappearance ~ sin 2 (2 ik )sin 2 ( m 2 ik L/4E) m1m1 m2m2 m3m3 m solar m atm e mixes via small mass difference m solar and large mixing angle to other flavors does it also mix via large mass difference (~ m atm ) mixing angle must be small (CHOOZ), but is it zero or not? KAMLAND CHOOZ e x Why reactors? The actual best limit is coming from a reactor experiment ! Chooz, Paolo Verde sin 2 2 m 2 = eV 2 Experimental method Nuclear reactors are a powerful source of low energy (up to ~ 8 MeV) electron anti-neutrinos Detection via inverse beta decay: Q-value ~ 1.8 MeV E e ~ E - Q ( spectroscopy) suppress background via delayed coincidence method How to improve the sensitivity? The problem: Reactor exp. = Disappearance exp. compare total flux (and spectrum) with the no- oscillation hypothesis one depends on systematic uncertainties, like: absolute source strength, cross section, detection efficiency, fuel development over time... The basic idea: Use 2 identical detectors oscillation frequency basically known L/2 ~ 1.0 km km choose the right distance for the signal with the far detector m 2 = ( ) eV 2 osc.length L monitor the reactor with the close detector (100m) (cancels also uncertainties like cross section, efficiencies etc.) Improve sensitivity on sin 2 (2 13 ) to 0.02 0.03 Statistics N(far) ~ energy uncertainty (E) < 1% normalization uncertainty rel < 1% number of target protons efficiencies (positron, neutron) rel excellent calibrations required... Additional uncertainties: shape (~ 2%) cross section (~ 1.9%) should cancel ! fuel composition ( 235 U, 238 U, 239 Pu, 241 Pu) should cancel ! Bugey; comparison with spectrum deconvoluted from exp. determined beta spetra Feilitzsch, Schreckenbach; used for analysis of the Gsgen experiment Approach towards an experiment... 3 workshops on Future Low Energy -Experiments spring 2003 Alabama, USA fall 2003 Munich, Germany spring 2004 Niigata, Japan White paper thanks to Maury Goodman. paper available hep-ex/ (or Daya Bay Requirements on the Site for the Experiment: Strong power plant Shielding (300m.w.e. or better) for at least the far detector Only one (or two) cores (=sources) preferred Support from the power plant company CHOOZ Site Chooz (site of far detector) d~1.05 km P~8.4 GW 300mwe far detector no excavation for far detector Detector design, Double-Chooz -target Gd- scintillator -catcher, scintillator buffer, non- scintillating Muon Veto, scintillator 2.4m 3.6m 5.5m 6.7m ) ) ) ) ) ) PMs 2.8m Sensitivity ? sensitivity between 0.02 and 0.03 for sin 2 2 after ~3 years (for m 2 = eV 2 ) P. Huber et al. hep-ph/ Comparison to LBL-projects? P. Huber et al. hep-ph/ uncertainty in 13 for LBL projects - MSW effects in the earth - CP phase Background? accidental background single rate, radio purity experiences from CTF, Chooz, KamLAND not critical, determine online correlated background (muon induced) fast neutrons beta - neutron cascades in Chooz signal/background ~ 25 -> 100 (aim) larger target (12m 3 ), better muon veto, Background Double-Chooz Correlated background events: Monte-Carlo simulation of fast neutrons, generated by cosmic muons expected rate far detector (300mwe) ~ 0.15 / day (lower than 0.3 / day at 90% cl) signal / background far det. > 100 expected rate close detector (60mwe) ~ 2 / day signal / background close det. > 500 (if distance is ~ 150m) spectral shape of background quite flat (unequal to signal spectrum) Conclusions Search for 13 with a new reactor experiment is very promising Double-CHOOZ sensitivity: sin 2 (2 13 )< , 90% C.L. ( m 2 = eV2) Current limit: CHOOZ : sin 2 (2 13 )