  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 Gösgen 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 )<0.2  discovery potential ! „next future“ experiments Strong Support for the EDF power company & local authorities to perform a 2 nd experiment at Chooz Approved in France (2.2 – 2.5 M€,, detector costs 7M€ + civil engineering near site (EDF)) Large expertise available from low energy, low background projects (Chooz, CTF/Borexino, KamLAND) Collaboration : Saclay, APC, Subatech, TUM, MPIK, Tubingen Univ. Hamburg Univ., Kurchatov, Univ. Alabama, Univ. Tennessee, Univ. Lousiana, Univ. Drexel, Argonne, + Italian groups soon …  (maxi-)letter of intent (May 2004)  final proposal end of 2004 Aim for start data taking ~ 2008

Example: beta-n from 8 He (generated by cosmic muon on 12 C in organic liquid scintillator) monitor 8He rate by special beta - alpha delayed coincidence data from other candidates ( 9 Li) available from T. Hagner et al. (muon SPS, CERN), Chooz, CTF, KamLAND Beta - neutron cascades

Spectral information ? Y(‚close‘) - Y(‚far‘) ~ 3.5 years sin 2 2   m 2 = eV 2 very valuable cross- check if one observes an effect in the total rates !

Background studies for Double-Chooz Correlated background events: Monte-Carlo simulation of fast neutrons, generated by cosmic muons first check: simulation of the old Chooz experiment MC - result: 0.8 < bg/day < 4.5 (limited by statistics) Exp. - result: bg = 1.1 / day MC reliable !

Background spectrum Double- Chooz Neutron spectrum - veto offNeutron spectrum - veto on Shielding 100mwe, t = 33.7 h 1 background event preliminary

Sensitivity ? around few for sin 2 2  after ~3 years (20t, 8GW) impact of systematics fairly modest Huber, Lindner, Schwetz & Winter: hep-ph/