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This report outlines findings from the Directional Sensitivity workshop held on March 23, 2007, in Heidelberg, focusing on neutrino direction measurements within the Double Chooz experiment. Key topics include analyses of CHOOZ measurements with varied reactor separations, the significance of reactor power monitoring, and estimates utilizing maximum likelihood analyses. The proceedings highlight the challenges involved in distinguishing the signals from two reactors due to small separation angles, emphasizing the need for extensive event data and the impact of non-Gaussian behavior on results.
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Directional Sensitivity in Double Chooz LAUNCH Workshop Heidelberg 23.3.2007 Kathrin A. Hochmuth Max-Planck-Institut für Physik
Outline • Neutrino Direction Measurements • CHOOZ measurements • Two Reactors - separation of sources? - monitoring power output? • analytical estimates and maximum likelihood analysis - for Double Chooz setup with 30° separation - for hypothetical setup with 90° separation in collaboration with M. Lindner and G. Raffelt
Neutrino Direction = average displacement for reactor energies ~ 1.9 cm Note: uncertainty of locating the positron annihilation and neutron absorption points is large! Uncertainty of displacement
Setup CHOOZ determined each of the angles with s ~ 12° with 2,500 events Double Chooz near detector: 160,000 events per year
One Reactor CHOOZ event rate (2,500); true values q f
One Reactor CHOOZ event rate (2,500); true values q f Double Chooz event rate (160,000)
Two Reactors ??? 160,000 events Single Reactor Double Chooz 30° separation Hypothetical setup 90° separation
Probability Distribution Function tilt angle w.r.t x-y plane; relative strength of the reactors, where (assume for now: ) displacement: 1.9 cm uncertainty of the displacement: 20 cm Separation angle Central angle For Double Chooz
Important Points y-axis distribution gives information on the angular separation x-distribution gives only information on the center of the distribution No distinction from a single Gauss; >10 Mio events needed
Important Points y-axis distribution gives information on the angular separation x-distribution gives only information on the center of the distribution No distinction from a single Gauss; >10 Mio events needed
Non-Gaussianity Good resolution Bad resolution No clear distinction because cosf1~1
Angular Separation of 2 Sources 160,000 events Non-Gaussian behavior No distinction from 0° Reactor 1 Separation angle Central angle well determinded x-distribution behaves like a single Gaussian
7 years Double Chooz Reactor 1 Separation angle 3 s distinction possible after 7 years
Hypothetical 90° separation for 160,000 events: Clear separation of the angles f1,f2 with s1~3.2° central angle: sc~2.3° • separation angle: s~4.6° Note:
Reactor Strength Reactor strength 1 year Double Chooz: 160,000 events: 5 years: f1=45° after 1 year: True value: b1=b2=0.5 after 1 month
Conclusions • Separation of the two Double Chooz reactors challenging, because of small separation angle and • 3 s separation of the two Double Chooz reactors after 7 years • Separation Potential increases with increasing angles=> clear distinction for 90° separation after 1 year • Possible to monitor the strength of each individual reactor; for 1 year Double Chooz with
References M. Apollonio et al.(CHOOZ Collaboration), Phys.Rev.D 61 (2000) 012001 [hep-ex/9906011]. M. Apollonio et al. Eur.Phys.J. C 27 (2003) 331 [hep-ex/0301017] F. Ardellier et al.(Double Chooz Collaboration) hep-ex/0606025v4 (26 October 2006). P. Vogel and J. F. Beacom, Phys. Rev. D 60 (1999) 053003 H. O. Back et al. (Borexino Collaboration),physics/0408032. P. H. Frampton and P. Vogel, Phys.Rept. 82 (1982) 339. K. A. Hochmuth et al, Earth Moon Planets 99:253-264,2006 ,[hep-ph/0610048]. K. A. Hochmuth et al, Astropart.Phys.27:21-29,2007 ,[hep-ph/0509136].
Thank you! N U L A C H
