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Neutrino-nucleus cross section measurements at the SNS

Neutrino-nucleus cross section measurements at the SNS. Yu Efremenko. on behalf of the - SNS collaboration. Complimentary to RIB Exotic particle instead of exotic isotopes. Supernovae and neutrinos - SNS overview Potential instruments & physics  reaction cross sections I: liquids

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Neutrino-nucleus cross section measurements at the SNS

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  1. Neutrino-nucleus cross section measurements at the SNS Yu Efremenko on behalf of the -SNS collaboration Complimentary to RIB Exotic particle instead of exotic isotopes • Supernovae and neutrinos • -SNS overview • Potential instruments & physics •  reaction cross sections I: liquids •  reaction cross sections II: solids • A coherent scattering • Backgrounds • Status & Outlook

  2. SN neutrino spectra, 0.1 s post-bounce Core-collapse supernovae • Destruction of massive star initiated by the Fe core collapse • 1053 ergs of energy released • 99% carried by neutrinos • A few happen every century in our Galaxy, but the last one observed was over 300 years ago • Dominant contributor to Galactic nucleosynthesis • Neutrinos and the weak interaction play a crucial role in the mechanism, which is not not well understood SN 1987a Anglo-Australian Observatory

  3.  reactions and nucleosynthesis  opacities Electron capture and core collapse • Prompt supernova mechanism fails • Neutrinos interactions are believed to be crucial in the delayed mechanism • Realistic treatment of  opacities is required for supernova models • Neutrino reactions with nuclei ahead of the shock may alter the entropy & composition of in fall [Bruenn & Haxton (1991)]. • In the outer layers, neutrino reactions may be the dominant source for boron & fluorine [Woosley et al. (1990)] and rare isotopes like 138La and 180Ta [Heger et al. (2005)]. • Neutrino reactions may have an important influence on nucleosynthesis in the r process: setting the neutron-to-proton ratio and altering the abundance pattern [Haxton et al. (1997)]. • Electron capture and the charged-current ne reaction are governed by the same nuclear matrix element: ne + A(Z,N)  A(Z+1,N-1) + e- • New calculations using a hybrid model of SMMC and RPA predict significantly higher rates for N>40 • Supernovae models w/ new rates: shock starts deeper and weaker but less impedance • Many ingredients • Charged-current reactions on free nucleons (and nuclei) • Neutral-current scattering • A coherent scattering • e-e scattering •  scattering •  annihilation Neutrinos and Core Collapse SN The weak interaction plays a crucial role in supernova !!!

  4. ADONIS • An accurate understanding of neutrino cross sections is important for designing and interpreting measurements of neutrinos from supernovae. • Nuclei of interest: 2H, C, O, Pb Supernova n observations • Measurement of the neutrino energy spectra and time distribution from a Galactic supernova would provide a wealth of information on the conditions in supernovae, neutrino oscillations, etc. Bruenn et al. (2004)

  5. So far it is a green field. Only n-C interactions have been accurately studiedexperimentally. There are ~ 40% accurate data for d,Fe,I v-d is well understood theoretically and indirectly has been measured by SNO Neutrinos Nuclei Interactions are: Important for understanding of supernovae mechanism Important for neutrino detection from SN Have a general interest for the nuclear theory It is important to provide accurate v-A measurements for wide range of isotopes

  6. LINAC:  x ~1000  Repeat 60/sec. Accumulator Ring: 1 GeV Similar pulse structure to ISIS  greatly suppressed backgrounds Currently operating at low power 100kW in FY07 Eventual operation > 1 MW (~FY09) ~7x1012p / spill (~10x ISIS)

  7. p  Specific benefits of neutrinos at SNS • Well known neutrino spectra (DAR) • Possibility to separate neutrinos of different flavors by time cut Neutrino production at SNS CAPTURE ~99% e Fragments -   2200 nsec A + DAR e+ ~ 1 GeV +   26 nsec  Fragments

  8. protons 60 m A neutrino facility at theSpallation Neutron Source proposed nSNS site • 20 m2 x 6.5 m (high) • Close to target ~ 20 m • 2x107n/cm2/s • q=165 to protons • lower backgrounds The SNS Target hall

  9. Proton beam (RTBT) n-SNS BL18 ARCS n-SNS facility overview • Total volume = 130 m3 4.5m x 4.5m x 6.5m (high) • Heavily-shielded • 60 m3 steel ~ 470 tons 1 m thick on top 0.5 m thick on sides • Active veto • ~70 m3 instrumentable • Configured to allow 2 simultaneously operating detectors of up to 40 tons A coherent scattering 43 m3 liquid detector Segmented detector for solids Prototypes for SN detectors

  10. Homogeneous detector • 3.5m x 3.5m x 3.5m steel vessel (43 m3) • 600 PMT’s (8” Hamamatsu R5912)  Fiducial volume 15.5 m3 w/ 41% coverage • Robust well-understood design • dE/E ~ 6% • dx ~ 15-20 cm • dq ~ 5 - 7 • Neutron discrimination ? • Layout and coverage ? • More compact photosensors 60% of mass lost to fiducial cut • First experiments: • 1300 events/yr ne+12C12N+e- (mineral oil) • 450 events/yr ne+16O 16F+e- (water) • 1000 events/yr nx+2H  p+n+ nx (heavy water)

  11. Standard model tests e + 12C  e- + 12N g.s. • Shape of the e spectrum from  decay is sensitive to scalar and tensor components of the weak interaction SNS expected 1-yr operation L=0.11 KARMEN upper limit Armbruster et al., PRL81 (1998) • We should substantially improve the limit on L with only 1 year of data L=0

  12. Segmented detector corrugated metal target • Target - thin corrugated metal sheet (e.g. 0.75 mm-thick iron) Total mass ~14 tons, 10 tons fiducial Other good metal targets: Al, Ta, Pb • Detector 1.4x104 gas proportional counters (strawtube) 3m long x 16mm diameter • 3D position by Cell ID & charge division • PID and Energy by track reconstruction • Expected Statistic 1100 events/yr ne+FeCo+e- 1100 events/yr ne+AlSi+e- 4900 events/yr ne+Pb Bi+e- strawtube 16 mm anode wire

  13. Slow charge collection e broad timing problematic narrow time (ms) Strawtube R&D • Currently testing prototypes Diameters between 10-16 mm Lengths ranging up to 2 m Gases (Ar-CO2, Isobutane, CF4) • Measure resolution with cosmic muons Energy, position, time • How much can time resolution be improved using pulse shape information? • Simulations to improve the fast neutron discrimination.

  14. Never measured Only observable is low energy (~10keV) nuclear recoil A Important for supernova dynamics (neutrino opacity) Z0 A D.Z. Freedman PRD 9 (1974) Straight-forward to calculate Huge cross section > 10-39 cm2 Can be detected with Dark Matter search technique Neutrinos Coherent Scattering

  15. Backgrounds • Uncorrelated • Cosmic rays • Muons  neutrons • Neutrons • Cosmogenic activity • SNS activation • Natural radioactivity • Correlated prompt • Beam loses in RTBT • From the SNS target • Neighboring instruments • Multiply-scattered neutrons Reduced by ~ 6x10-4 (60 Hz * 10 s)

  16. wave-length shifting fibers read out by multi-anode PMT Bunker 1.5 cm iron extruded scintillator 1 cm x 10 cm x 4.5 m • Efficiencies • muons ~99% muons • gamma = 0.005% • neutron =0.07% Cosmic ray veto Sensitive to cosmic muons Blind for neutrons, gammas

  17. Segmented Performance: e+FeCo+e- Total rate t<10ms & no veto (98%) Events/year (1 MW) Fiducial cut (DE/cell)ave < 10 keV 57% n efficiency cosmics eliminated Neutrons little reduced

  18. clean time window Time cut • Negligible fast neutron background expected after ~ 1 s (Net events)/year (Events/ms)(Spills/yr) (1 MW) Crucial to understand neutron background, especially for t=1-10s

  19. Desk/PC rack Open for prototype testing • 60 tons of steel installed • 2 stacks of shield block • 52”x 52” x 60” high • 4 Detector stations • 5” liquid scintillator • 3He counters Background Studies Layout

  20. Installation n/ separation • Block installation complete • Detectors and data acquisition system ready • Taking data as we speak PuBe

  21. n-SNS Collaboration http://www.phy.ornl.gov/nusns • Active, diverse collaboration • 20 institutions

  22. August 2004 “First green light” from SNS August 2005 Proposal submitted Likely withdrawn FY07 NSAC LRP Timeline March 2004 Study report completed Letter of Intent to SNS Project Cost October 2004 Neutrino Matrix FY 2010-FY2011 Construction

  23. Summary & Outlook • Neutrino scattering and reactions are important for understanding supernovae • Influence core collapse • Affect shock dynamics • Modify the distribution of iron-peak elements • May be the dominant source of B, F, 138La, 180Ta • Affect r process nucleosynthesis • The combination of high flux and favorable time structure at the SNS can allow a diverse program of measurements • High statistics in less than 1 year of operation • We have a strong collaboration of experimentalists and theorists • We welcome new ideas and participation • See http://www.phy.ornl.gov/nusns

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