Reactor Working Group Report Future reactor experiments to

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Reactor Working Group Report • Future reactor experiments to measure sin 22 13 •

Reactor Working Group Report • Future reactor experiments to measure sin 22 13 • What do we learn by combining reactor and accelerator measurements? • Beyond 13 • Conclusions and Recommendations Erin Abouzaid, Kelby Anderson, Gabriela Barenboim, Bruce Berger, Ed Blucher, Tim Bolton, Janet Conrad, Joe Formaggio, Stuart Freedman, Dave Finley, Peter Fisher, Moshe Gai, Maury Goodman, Andre de Gouvea, Nick Hadley, Dick Hahn, Karsten Heeger, Boris Kayser, Josh Klein, John Learned, Manfred Lindner, Jon Link, Bob Mc. Keown, Irina Mocioiu, Rabi Mohapatra, Donna Naples, Jen-chieh Peng, Serguey Petcov, Jim Pilcher, Petros Rapidis, David Reyna, Mike Shaevitz, Robert Shrock, Noel Stanton, Ray Stefanski, Richard Yamamoto 29 June 2004 APS Neutrino Study

Neutrino physics at nuclear reactors : The key parameter for next generation of neutrino

Neutrino physics at nuclear reactors : The key parameter for next generation of neutrino oscillation experiments. Its value sets scale of experiments needed to study CP violation, mass hierarchy. The reactor experiment offers only way to measure this mixing angle free of degeneracies. In combination with accelerator measurements, can resolve 2 degeneracy, and provide early information about CP violation, mass hierarchy. Strong consensus in working group that experiment with sensitivity of sin 22 13=0. 01 should be our goal. Beyond : sin 2 W, neutrino magnetic moment, m 122 and 12, sterile neutrinos, SN physics, CPT tests + worldwide reactor monitoring, searching for a reactor at the center of the earth?

Methods to measure sin 22 13 • Accelerators: Appearance ( e) Use fairly pure,

Methods to measure sin 22 13 • Accelerators: Appearance ( e) Use fairly pure, accelerator produced beam with a detector a long distance from the source and look for the appearance of e events T 2 K: <E > = 0. 7 Ge. V, L = 295 km NO A: <E > = 2. 3 Ge. V, L = 810 km • Reactors: Disappearance ( e e) Use reactors as a source of e (<E >~3. 5 Me. V) with a detector 1 -2 kms away and look for non-1/r 2 behavior of the e rate Reactor experiments provide the only clean measurement of sin 22 : no matter effects, no CP violation, almost no correlation with other parameters.

Reactor Measurements of 13: Search for small oscillations at 1 -2 km distance (corresponding

Reactor Measurements of 13: Search for small oscillations at 1 -2 km distance (corresponding to Pee Past measurements: Distance to reactor (m)

Chooz: Current Best Experiment P=8. 4 GWth CHOOZ Systematic errors Reactor flux 2% Detect.

Chooz: Current Best Experiment P=8. 4 GWth CHOOZ Systematic errors Reactor flux 2% Detect. Acceptance 1. 5% Total 2. 7% L=1. 05 km D=300 mwe m = 5 tons, Gd-loaded liquid scintillator Neutrino detection by sin 22 < 0. 2 for m 2=2 10 3 e. V 2

How can Chooz measurement be improved? Add near detector: eliminate dependence on reactor flux

How can Chooz measurement be improved? Add near detector: eliminate dependence on reactor flux calculation; need to understand relative acceptance of two detectors rather than absolute acceptance of a single detector + optimize baseline, larger detectors, reduce backgrounds ~200 m ~1500 m Issues affecting precision of experiment: • Relative uncertainty on acceptance • Relative uncertainty on energy scale and linearity • Background (depth) • Detector size • Baseline • Reactor power

Detectors and analysis strategy designed to minimize relative acceptance differences Identical near and far

Detectors and analysis strategy designed to minimize relative acceptance differences Identical near and far detectors Shielding 6 meters To reduce backgrounds: depth + active and passive shielding Central zone with Gd-loaded scintillator surrounded by buffer regions; fiducial mass determined by volume of Gd-loaded scintillator Events selected based on coincidence of e+ signal (Evis>0. 5 Me. V) and s released from n+Gd capture (Evis>6 Me. V). No position reconstruction; little sensitivity to E requirements.

Study has focused on three scales of experiments: • Small sin 22 13 ~

Study has focused on three scales of experiments: • Small sin 22 13 ~ 0. 03 (e. g. , Double-Chooz, KASKA) • Medium sin 22 13 ~ 0. 01 (e. g. , Braidwood, Diablo Canyon, Daya Bay) • Large sin 22 13 ~ 0. 005 (e. g. , Angra) (sensitivities at 90% confidence level) For each scenario, understand scale of experiment required and physics impact.

Sensitivity Using Rate and Energy Spectrum (Huber et al. hep-ph/0303232) Sh ape on ly

Sensitivity Using Rate and Energy Spectrum (Huber et al. hep-ph/0303232) Sh ape on ly no rm = Sta tist ics on norm= 0. 8% ly no m 2 = 3× 10 -3 e. V 2 rm = 0

Sensitivity Using Rate and Energy Spectrum (Huber et al. hep-ph/0303232) Sh ape on ly

Sensitivity Using Rate and Energy Spectrum (Huber et al. hep-ph/0303232) Sh ape on ly no rm = Sta tist ics on norm= 0. 8% ly no Small m 2 = 3× 10 -3 e. V 2 Medium rm = Large 0

Different Scales of Experiments Small: sin 22 13 ~ 0. 03 (e. g. ,

Different Scales of Experiments Small: sin 22 13 ~ 0. 03 (e. g. , Double-Chooz, KASKA) Double-Chooz: 10 ton detector at L-1. 05 km. Rate only, non-optimal baseline, shallow near detector, few cross checks Cost: ~$20 M; start datataking in 2008 Medium: sin 22 13 ~ 0. 01 (e. g. , Braidwood, Diablo Canyon, Daya Bay) 50 -100 ton detectors, optimized baseline, optimized depths, rate and shape info, perhaps movable detectors to check calibration, multiple far detector modules for additional cross checks Cost: ~$50 M (for US sites); start datataking in 2009 Large: sin 22 13 ~ 0. 005 (e. g. , Angra) ~500 ton fiducial mass; sensitivity mainly through E spectrum distortion

Reactor Sensitivity Studies: Comparing and Combining with Offaxis Measurements (M. Shaevitz) • Experimental Inputs

Reactor Sensitivity Studies: Comparing and Combining with Offaxis Measurements (M. Shaevitz) • Experimental Inputs JPARC to Super. K (T 2 K) • : 102 signal / 25 bkgnd 5 yrs; : 39 signal / 14 bkgnd 5 yrs • plus upgrade 5 rate for sin 22 =0. 1 Offaxis Nu. MI (Nova) • : 175 signal / 38 bkgnd 5 yrs : 66 signal / 22 bkgnd 5 yrs • plus Proton Driver upgrade 5 rate • Oscillation parameters for sin 22 =0. 1

Setting Limit on sin 22 13 × 5 beam rate large medium small reactor

Setting Limit on sin 22 13 × 5 beam rate large medium small reactor T 2 K combine with med. reactor NOνA 90% CL upper limits for an underlying sin 22θ 13 of zero A medium scale reactor experiment sets a more stringent limit on sin 22θ 13 than offaxis, even with proton driver like statistics (× 5 beam rate). combine with med. reactor Green: Offaxis exp. Only Blue: Combined Reactor plus Offaxis White: Offaxis Only (x 5 rate)

Determining Value of sin 22 13 Chooz-like, small scale Braidwood-like medium scale T 2

Determining Value of sin 22 13 Chooz-like, small scale Braidwood-like medium scale T 2 K NOνA 90% CL regions for sin 22θ 13 = 0. 05, δCP=0 and Δm 2 = 2. 5× 10 -3 e. V 2 In the case of an observation, even a small -scale reactor measurement makes a better determination of sin 22θ 13 than off-axis experiments Green: Offaxis exp. Only Blue: Combined Medium Reactor plus Offaxis Red: Combined Small Reactor plus Offaxis

Importance of Multiple Measurements The reactor measurement may not agree with the results of

Importance of Multiple Measurements The reactor measurement may not agree with the results of the offaxis experiments. With a 1% LSND-like oscillation For example: The reactor experiment is blind to an LSND-like oscillation, but it shows up in off-axis as an unexpectedly large νe appearance. The combination of the two experiments can resolve the effect. δCP = 180º sin 22θ 13 = 0. 02

Resolving the 23 Degeneracy • If 23 45 , disappearance experiments, which measure sin

Resolving the 23 Degeneracy • If 23 45 , disappearance experiments, which measure sin 22 23, leave a 2 -fold degeneracy in 23 – it can be resolved by combination of a reactor and e appearance experiment. Green: Offaxis exp. Only Blue: Combined Medium Reactor plus offaxis experiment

Resolving the 23 Degeneracy • If 23 45 , disappearance experiments, which measure sin

Resolving the 23 Degeneracy • If 23 45 , disappearance experiments, which measure sin 22 23, leave a 2 -fold degeneracy in 23 – it can be resolved by combination of a reactor and e appearance experiment. • The Double-Chooz sensitivity is insufficient to resolve degeneracy Green: Offaxis exp. Only Blue: Combined Medium Reactor plus offaxis experiment Red: Double-Chooz plus offaxis

Constraining the CP Phase • Oscillation probability vs CP ( m 2 = 2.

Constraining the CP Phase • Oscillation probability vs CP ( m 2 = 2. 5 x 10 -3 e. V 2 , sin 22 13 = 0. 05) • Reactor measurement defines allowed bands:

Reactor Role in Determining CP For δCP = 270º the reactor measurement eliminates some

Reactor Role in Determining CP For δCP = 270º the reactor measurement eliminates some of the range in CP phase when combined with off-axis ν only running. Off-axis anti-neutrino running resolves the CP phase on its own, after an additional 3 to 5 years. Green: Offaxis exp. Only Blue: Combined Medium Reactor plus Offaxis Red: Combined Small Reactor plus Offaxis

 CP Constraints from Off-Axis + Reactor Dashed – without Reactor Solid – with

CP Constraints from Off-Axis + Reactor Dashed – without Reactor Solid – with medium scale Reactor large medium small reactor To the right of the curve, this value of may be excluded by at least two sigma large medium small reactor Reactor measurement does not add much to CP reach of + offaxis, Nominal Beam Rates but a sin 22 limit from reactor can largely rule out the possibility of a CP measurement at Nova or T 2 K. × 5 Nominal Beam Rates m 2 = 2. 5× 10 -3 e. V 2

Resolving the Mass Hierarchy Reactor (+/- 0. 01) normal CP inverted NO A (5

Resolving the Mass Hierarchy Reactor (+/- 0. 01) normal CP inverted NO A (5 yr ) m 2=2. 5 x 10 -3 e. V 2

Resolving the Mass Hierarchy Dashed – without Reactor Solid – with medium scale Reactor

Resolving the Mass Hierarchy Dashed – without Reactor Solid – with medium scale Reactor large medium small reactor Nominal Beam Rates × 5 Nominal Beam Rates To the right of the curve, mass hierarchy is resolved by at least two sigma large medium small reactor Reactor measurement does not contribute much to resolving the mass hierarchy … but a sin 22 limit from even a small reactor experiment can largely rule out the possibility of determining sign( m 232) at Nova and T 2 K. m 2 = 2. 5× 10 -3 e. V 2

Beyond 13: Weak Mixing Angle Studies indicate that a measurement of sin 2 W

Beyond 13: Weak Mixing Angle Studies indicate that a measurement of sin 2 W with precision comparable to Nu. Te. V could be performed using e – e scattering (normalized with inverse decay). (Conrad, Link, Shaevitz, hep-ex/0403048)

Beyond 13 (cont. ) CPT tests: comparing measurements at reactor experiments with solar neutrinos

Beyond 13 (cont. ) CPT tests: comparing measurements at reactor experiments with solar neutrinos and accelerator neutrinos SN Physics: Like all scintillator experiments, a reactor experiment will detect SN neutrinos of all flavors (with -p elastic scattering), providing a test of SN models. Solar parameters: A detector 70 km from an isolated reactor complex will allow improved measurements of the solar Parameters.

Conclusions • The worldwide program to understand oscillations and determine the mixing parameters, CP

Conclusions • The worldwide program to understand oscillations and determine the mixing parameters, CP violating effects, and mass hierarchy will require a broad range of measurements. • Our group believes that a key element of this program is a two-detector reactor experiment (with baselines of 200 m and 1. 7 km) with sensitivity of 0. 01 for sin 22 13. • It will provide a measurement of free of ambiguities and with better precision than any proposed experiment, or will set limits indicating the scale required for future experiments. • In combination with accelerator experiments, it can resolve the degeneracy in 23, and may give early indications of CP violation and the mass hierarchy. • It can also provide interesting measurements of the weak mixing angle, as well as neutrino magnetic moments, CPT tests, and supernova physics.

Highest priority recommendation We recommend the rapid construction of a two-detector reactor experiment with

Highest priority recommendation We recommend the rapid construction of a two-detector reactor experiment with a sensitivity of 0. 01 for sin 22 .

Other recommendations: • To help accomplish our highest priority recommendation, we recommend R&D support

Other recommendations: • To help accomplish our highest priority recommendation, we recommend R&D support necessary to prepare a full proposal. • We recommend continued support for the KAMLAND experiment. KAMLAND has made the best determination of m 122 to date, and will provide the best measurement of m 122 for the foreseeable future. As the deepest running reactor experiment, it also provides critical information about cosmic-ray related backgrounds for future experiments. • We recommend the exploration of potential sites for a next-generation experiment at a distance of 70 km from an isolated reactor complex to make high precision measurements of 12 and m 122. • We recommend support for development of future large-scale reactor 13 experiments that fully exploit energy spectrum information.