1 / 16

Is it possible to improve our knowledge of  13 by oscillation experiments at reactors?

Is it possible to improve our knowledge of  13 by oscillation experiments at reactors?. Donato Nicolo` Pisa University & INFN,Pisa NUFACT Working Group, Geneva December 11 2002. Summary. Current status Physics motivations The Chooz result What next?

yoko
Download Presentation

Is it possible to improve our knowledge of  13 by oscillation experiments at reactors?

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Is it possible to improve our knowledge of 13 by oscillation experiments at reactors? Donato Nicolo` Pisa University & INFN,Pisa NUFACT Working Group, Geneva December 11 2002

  2. Summary • Current status • Physics motivations • The Chooz result • What next? • Improvement of statistics and systematics • Potentialities of two-distance tests • The Krasnoyarsk project (Kr2Det) • An alternative experimental frame • Signal and Background • Expected sensitivity • Rate test • Shape test • Outlook and conclusions Donato NICOLO`

  3. Physics motivations • noscillation hypothesis is dominant for atmospheric ’s • but nemmixingcould still be present at a subdominant level • (sin²(213  0.1 at • (limited by Chooz results, also SK at a minor extent) • Implications for measurement ofdCP at LBL accelerator experiments SK data (also confirmed by MACRO) • SK + SNOresults (energy spectra, CC rate, day/night effect) • strongly favour the LMA MSW solution to solar neutrino deficit • The effect might be seen by KamLAND as: • areduction of integral ratevs predictions; • a modulation of the detected energy spectrumforDmsol2 2·10-4eV2 •  a medium baseline reactor experiment is needed • (S. Schönert et al., hep-ex/020313) Donato NICOLO`

  4. The Chooz result R = 1.01  2.8%(stat)  2.7%(syst) M.Apollonio et al., Phys. Lett. B 466 (1999) 415 sin²(213  0.11  |Ue3|  0.03 confirmed by Palo Verde R = 1.01  2.4%(stat)  5.3%(syst) F. Boehm et al., PR D64 (2001) 112001 Sensitivity could be lowered to sin²(213  10-3atneutrino factories (construction to be started in ~2010) Is it possible to reach an intermediate (sin²(213 ~ 10-2) step by reactor experiments? factor 5 improvement  errors must be ~ 0.5% Donato NICOLO`

  5. Possible improvements • systematics • Comparison of neutrino fluxes and spectra at two distances • L1 ~ 100 m, L2 ~ 1 km •  independent of absolute normalisation (spectra, cross section, power, burn-up) • which contributed at 2% to the overall systematic uncertainty at Chooz • Identical detectors (detection technique, geometrical shape)or as • similar as possible minimise differences in efficiencies and calibrations. • statistics • Large volume detectors (target ~50 t)  signal larger by ~10 • to be located underground (300 m.w.e) neutron background suppression • Detector design suited to shield the target from external radioactivity •  accidental background suppression Donato NICOLO`

  6. A possible detector Event signature prompt positron signal (mimicked byn+p n+p) delayed neutronsignal (t = 180 ms) neutron efficiency lower (~50%) than Chooz Mini version of KamLAND (or Borexino) 50 t liquid scintillation target(no Gd-doping) (l ~ 10 m, stable) Mineral oil buffer (~ 1m thick) shield against PMT radioactivity Active cosmic veto Donato NICOLO`

  7. The Kr2Det project • Based on L.V.Mikaelyan’s idea • to be operated by Krasnoyarsk nuclear plant (Russia) • one (over three) reactor still operating,W = 1.6 GWth • L1 = 250 m, L2 = 1100 m • twin detectors (with the possibility to swap their position)  ssyst ~ 0.5% • thick rock overburden (600 m.w.e.) • (neutron flux suppressed by a factor ~3 w.r.t. Chooz) • possibility to measure the background during the reactor stop for refueling • sstat = 0.5 % could be reached in ~ 3y data taking but... plant operating is not guaranteed Russian authorities are strongly demanded to stop reactor operations for safety reasons Donato NICOLO`

  8. A possible alternative • Chooz2 • Far detector located in the underground site (L2~1000 m, 300 m.w.e.) hosting the previous experiment  S/N ~ 10 • Near detector placed in a new shallow site (L1~100 m, 40 m.w.e.), to be built on purpose • m vertical intensity reduced to only 30% of the surface intensity •  near detector must be smaller (else it would be overwhelmed by cosmic rays!) • systematic error could not be better than 1% • 5t scintillator target size looks like a reasonable compromise • signal: • background: • Rm ~ 2 KHz(2 orders of magnitudes larger than at the underground site) • Nn ~ 3times as low as underground F.Boehm et al. PRD 62 (2000) 092005 • neutron flux n ~ 30 timesas large as underground at full reactor power Donato NICOLO`

  9. Statistical uncertainties reactor 1 • A realistic plant operation frame • reactors operating at full power, • 90% duty cycle • alternated stop (~1month) for refueling • During 3 years data taking one collects: • 800 d with both reactors ON (“ON” period) • 200 d with one reactors OFF (“OFF” period) • R1= (625 ± 2) ev/d • R2 = (63 ± 0.7) ev/d •  sstat = 1.1% • limited by background subtraction reactor 2 time Far detector Donato NICOLO`

  10. A more optimistic scenario • Background measurement could be improved if reactors: • ramp up/down slowly • are both OFF for a while • (both conditions were fulfilled at Chooz) • With 30 d reactor shutdown • R2= (125 ± 0.6) ev/d •  sstat = 0.5% OK • How much does it cost? • 0.05$/kWh  8.5GW 0.3  24 h = 3 M$ • in 1 day •  ~ 100 M$ in 1 month Chooz data Donato NICOLO`

  11. Rate test Based on the comparison of integral rates at two distances = test variable (normalised to 1 in absence of oscillations) statistics systematics Use ² instead of likelihood ratio for statistic test (OK in aGaussian regime) ² = ² - ²min errors added in quadrature • Apply Feldman-Cousins procedure to determine 90% confidence intervals in(sin²(2,dm²)for: • Kr2Det • Chooz2 Donato NICOLO`

  12. Rate sensitivity plot • At dm² = 3x10 ³ eV² • Kr2Det • sin²(2  0.02 • Chooz2 • sin²(2  0.04 • not much encouraging... • Chooz • sin²(2  0.1 Donato NICOLO`

  13. Spectrum test Based on the comparison of positron spectra at two distances Improved sensitivity in the “lobe” regions  more powerful test r 1 month reactors OFF  stat = 0.5% Spectra arranged in 16 bins(DE=0.4 MeV) Build statistic as threshold effects energy scale calibration spectra normalisation (relative efficiencies, target volumes) e+ energy (MeV) FC procedure Donato NICOLO`

  14. Spectrum test sensitivity 1 month reactors OFF 90% sensitivity contours as functions of sa (sgneglected) • At dm² = 3x10 ³ eV² • sa = 0.5% • sin²(2  0.015 • sa = 1.0 % • sin²(2  0.025 • sa = infinite (shape test) • sin²(2  0.04 • Chooz • sin²(2  0.1 Donato NICOLO`

  15. Spectrum test sensitivity (more realistic) reactors ON-OFF 90% sensitivity contours as functions of sa (sgneglected) • At dm² = 3x10 ³ eV² • sa = 0.5% • sin²(2  0.03 • sa = 1.0 % • sin²(2  0.04 • sa = infinite (shape test) • sin²(2  0.1 • Chooz • sin²(2  0.1 Donato NICOLO`

  16. nenx mixing present at subdominant level in the atmospheric n range could influence the solution to the solar ndeficit to be investigated at future neutrino factories down to sin²(2  10 ³ Sensitivity at reactor experiments could be pushed tosin²(2  0.02 if: both detectors were located undergroundsyst = 0.5% background could be measured with reactors OFF stat = 0.5% one reactor plants are preferred, underground if possible Do they exist? Else it is difficult to obtain better than 1% accuracy, both statistics and systematics a factor 23 improvement with respect to Chooz Outlook and conclusions Donato NICOLO`

More Related