1 / 40

Elastic Neutrino-Nucleon Scattering

Elastic Neutrino-Nucleon Scattering. Argonne, July 2002 C. J. Horowitz. Elastic Neutrino Scattering. Nothing in. Nothing out. Nothing happens. Neutrino Elastic Scattering. Supernovae Introduction Opacity dominated by  -n elastic Detection via  -p and  -A elastic

Download Presentation

Elastic Neutrino-Nucleon Scattering

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. Elastic Neutrino-Nucleon Scattering Argonne, July 2002 C. J. Horowitz

  2. Elastic Neutrino Scattering • Nothing in. • Nothing out. • Nothing happens.

  3. Neutrino Elastic Scattering • Supernovae • Introduction • Opacity dominated by -n elastic • Detection via -p and -A elastic • Strange quark content of nucleon • Parity violating electron scattering • Contributions to nucleon spin • Past -p elastic measurements • Future exp: controlling systematics

  4. Core collapse supernova >8M Star Envelope n July 5, 1054 Shock Crab nebula Hot bubble Proto-neutron star: hot, e rich

  5. Opacity Dominated by -n Elastic • Energy transport mostly by x (´ , ) because twice as many as e and x without charged currents, have longer mean free path. • Opacity of x mostly from -n elastic. • Incorrect elastic cross sec caused Oak Ridge simulation to explode when it did not with correct one. • Uncertainty in -n cross sec from strange quarks very relevant for SN simulations.

  6. Detecting Supernova  • Important to measure total energy radiated in neutrinos. This is binding E of proto-neutron star ~3/5 GM2/R. • Astrophysicists very interested in mass of proto-neutron star. Compactness, M/R, important for SN mechanism,  driven wind and nucleosynthesis. • Benchmark for  osc. measurements. • Most E in x because twice as many as e.

  7. Need to Measure x • 20 anti-e detected from SN1987A via anti- + p ! n + e+. • To measure energy of x need two-body final states: -e, -p or -A elastic. • x-e has small cross sec, swamped by background from e-e. • -p elastic may be possible in Kamland [J. Beacom]. • -A has very large cross section.

  8. Underground Laboratory • Underground lab. will facilitate low background, low threshold, large mass experiments. • Detecting low energy solar n, dark matter, and supernovae via n-A elastic scattering are complimentary. • Backgrounds for SN ¿ solar  or dark matter [Events in known ~10 sec. interval with ~ half in first sec.]

  9. CLEAN (D. McKinsey) • Liquid Ne scintillator (¼ 100 tons) for low energy solar  via -e scattering. • Liquid is self cleaning of radioactive impurities for low backgrounds and thresholds. • Coherent x-Ne cross sec gives yields up to 4 events / ton for SN at 10 kpc (¸ 20 times anti-e+p in H2O). • Should yield large very clean x signal.

  10. Recoil Spectrum

  11. Strange quark content of nucleon • Three form factors • F1s, F2s, Gas • Low Q limits: • F1s(0)=0, dF1s/dQ2  strangeness radius s, • F1s=(s+s) Q2/4M2 for small Q2 • F2s(0)=s strange magnetic moment, • Gas(0)=s, fraction of nucleon spin carried by s

  12. Assume good isospin • Assume strange quarks in proton same as in neutron: s is isoscalar. • Three observables: E+M form factor of proton, neutron and parity violating weak from factor of proton: allows separation of u, d, and s contribution. • Without assuming isospin, can’t separate d from s, even in principle, because they have same E+M and weak charge.

  13. Parity Violating Electron Scattering • Measure asymmetry in cross section of right handed versus left handed electrons. A ¼ 1 ppm • Sensitive to interference between Z0 and  exchange. • Forward angles: F1s, back angles F2s • Little sensitivity to Gas because of small vec. weak coupling of electron (and radiative corrections). PV can’t get s!

  14. Radiative Corrections • Lowest order matrix elem. Squared • Radiative correction e  Z0 p   Some PV

  15. Radiative Corrections • Parity violation admixture in either initial or final wave function. Nucleon need not have good parity. • Parity violating coupling of photon to nucleon (anapole moment).  Example: photon couples to pion loop which has parity violating weak coupling to nucleon 

  16. Sample Results • PV on H and D give both radiative corrections and s. • GMs (or s) consistent with zero put large errors. • Radiative corrections much larger then expected.

  17. HAPPEX • Forward angle exp. at Jefferson Lab Hall A, Q2=0.5 Gev2. • Errors: stat., syst. and E+M form factors • SAMPLE:

  18. Other PV Experiments • G0 will measure PV from H and D at front and back angles over large Q2 range. • A4 in Germany, PV from H at intermediate angles. • HAPPEX II: PV from H at more forward angle Q2=0.1 GeV2. • Low Q24He experiment isolates F1s • Elastic PV from Pb will measure neutron radius. [Weak chage of n À p]. • Qweak PV from H at low Q2 as standard model test. Also PV e-e exp. at SLAC.

  19. Bring Me the Head of a Strange Quark • Can one measure s with accuracy much better than §0.3 ? • Can one find a significantly nonzero strange quark signal with PV?? • It may be very hard to improve significantly on the systematic errors of SAMPLE and G0.

  20. Neutrino-Nucleon Elastic Scattering • Measure both s and s • Radiative corrections small. • Past experiments (BNL, LSND) • Present (BOONE) • Future ratio experiments very promising.

  21. BNL Exp. With 170 ton detector in wide band beam (1986)

  22. BNL cross sections Energy of recoil gives Q2, this + angle gives E

  23. s=-1.26

  24. CJH+S. Pollock, PRC48(’93)3078 Rel. Mean Field Calculations compared to BNL data. s or  strongly correlated with MA.

  25. Sensitivity to Parameters

  26. E=150 MeV

  27. Ratio of p/n sensitive to s

  28. Garvey, Kolbe, Langanke and Krewald • Continuum RPA calculation averaged over LSND’s decay in flight  beam. • Ratio very sensitive to s, some sensitivity to s.

  29. Low E Sensitivity to Parameters

  30. LSND had background problems Rex Tayloe

  31. Mini Boone • In <E>¼ 800 MeV beamline. • Large tank of mineral oil (Both Cerenkov and scint. Light). • Will try and measure ratio of neutral to charged current. • However lack of segmentation will limit precision.

  32. A Future -p Elastic Experiment • Physics goals are compelling: • Gas(Q2) and s. • F2s or s independent of PV radiative correcections. • Very attractive  fluxes at beam lines for long baseline -osc. experiments (NUMI, BOONE, KeK…)

  33. Need to control systematic errors! • Beam flux and spectrum (measure a ratio) • Theory errors from: • MA (lower Q2, measure MA, look at a ratio), • s (lower Q2, also measure with anti-). • Detector efficiencies, backgrounds. • Inelastic contributions: Pions! (good particle id, segmented detector, lower beam energy) • Nuclear structure (Q2¸ 0.5 Gev2) • Two-body contributions to rxn. Mechanism.

  34. Possible ratio measurements • Ratio of ejected neutrons to protons • Very sensitive to s. • Insensitive to beam flux. • Insensitive to “isoscalar” distortions. • Worry about neutron detection efficiency and two-body corrections to reaction mechanism. • At high Q2, neutron detection hard.

  35. Ratio of Neutral to Charged Currents • Ratio of protons from:  + p ! + p to protons from:  + n !- + p. • Note, both are quasielastic scattering from an N=Z nucleus such as 12C. • Very simple observable: ratio of protons of a given E without muons to those with muons.  p p

  36. Example: E=0.8 GeV, Q2=0.5 • R ¼ 0.14 • Assume Gas=s/(1+Q2/MA2)2 • Error in extracted s • 5% measurement of R 0.04 • §0.03 GeV uncer. in MA 0.01 • §0.3 uncer. in s 0.07 • §2 uncer. in s 0.002 • 5% ratio sensitive to s at §0.04 • Determine one combination of s and s from  and another from anti-.

  37. Experimental Considerations • Many systematics, such as absolute flux, cancel in ratio. • Need to know spectrum but ratio only weakly depends on E. • Need to identify pions to separate elastic from inelastic events. [This may require a segmented detector.] • Want large acceptance for muons.

  38. Ratio of Nucleon to Nucleus Elasitc • Consider a CH2 target. • -C elastic cross section is large and accurately known. Makes very good beam monitor. • Measure ratio of -p to -C elastic events. • Need to see low energy C recoils.

  39. Measurement of Axial Form Factor • Needed to control systematic errors for extraction of s. • Accurate determination of MA possible with charged current quasielastic events. • Search for non dipole behavior? Look at large Q2 range: 0.5-2+GeV2. How to control systematic errors??

  40. A Future -p Elastic Experiment • Physics goals are compelling: • Gas(Q2) and s. • F2s independent of PV radiative correc. • Ga(Q2) and Axial mass MA. • Very attractive  fluxes at beam lines for long baseline -oscillation exp. • Measuring ratio of neutral to charged currents is simple and controls many systematic errors.

More Related