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30 th ICRC – 2007 Merida, Mexico

Upper limit on the electron-neutrino flux from the HiRes Instrument Lauren M. Scott Rutgers, the State University of New Jersey. 30 th ICRC – 2007 Merida, Mexico. Outline. Motivation – why ν e (instead of ν μ )? Landau-Pomeranchuk-Migdal (LPM) effect.

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30 th ICRC – 2007 Merida, Mexico

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  1. Upper limit on the electron-neutrino flux from the HiRes Instrument Lauren M. Scott Rutgers, the State University of New Jersey 30th ICRC – 2007 Merida, Mexico

  2. Outline • Motivation – why νe (instead of νμ)? • Landau-Pomeranchuk-Migdal (LPM) effect. • Search for upward-going neutrino events in the HiRes-II data. • Monte-Carlo technique for modeling HiRes detector • response to νe. • Upper limit on the flux of νe and ντ • (and comparison with other experiments / theoretical limits). • Conclusions 30th ICRC – 2007 Merida, Mexico

  3. Why electron-neutrino-induced showers? • At HiRes energies (>1018 eV), ν-N interaction cross sections are high. • Earth-skimming events pass through enough material to interact. • σ ≈ 10-32 cm2 (1018 eV), 10-31 cm2 (1021 eV) • LPM effect • bremsstrahlung, pair-production cross sections are suppressed • in a dense medium. • LPM threshold ~ 1/γ2 – much higher for electrons (charged-current) • e- (cc) : ELPM = 6 ×1014 eV (rock) • ELPM = 2 ×1018 eV (air, desert floor) • Large target volume, interactions occurring deep in the • earth will emerge from the ground with enough high-energy • charged particles to create a detectable air shower. • Upward-going events with E > ELPM in air will have long shower • profiles making them detectable at greater distances than • hadronic showers. 30th ICRC – 2007 Merida, Mexico

  4. Modeling the LPM effect • for a full Monte Carlo detector simulation, • must model • energy- and depth-dependence of the LPM effect in rock shower profiles • energy spectrum of particles as a function of depth in rock • energy- and altitude-dependence of the LPM effect in air shower profiles Stanev, Vankov, Streitmatter, Ellsworth and Bowen, Phys. Rev. D., 1982 Kim, K. PhD Thesis, Univ. of Utah, 2002 30th ICRC – 2007 Merida, Mexico

  5. Modeling the LPM effect LPM showers in rock ELPM = 6 ×1014 eV 1018, 1019, 1020, 1021 eV 30th ICRC – 2007 Merida, Mexico

  6. Modeling the LPM effect E0 = 1020 eV spectrum @ 50 kg/cm2 Airshower from a 1020 eV electron entering air at 50,000 g/cm2 is a super- position of air showers from Ne in each energy bin. 30th ICRC – 2007 Merida, Mexico

  7. Modeling the LPM effect LPM showers in air (1.4 km above sea level) ELPM = 2 ×1018 eV 1018, 1019, 1020, 1021 eV 30th ICRC – 2007 Merida, Mexico

  8. Modeling the LPM effect LPM showers in air (15 km above sea level) ELPM = 2 ×1019 eV 1018, 1019, 1020, 1021 eV 30th ICRC – 2007 Merida, Mexico

  9. Search for upward-going showers • Expect events to • have small elevation angles • have long tracks • be detected mostly in the HiRes-II • lower-ring mirrors (elevation from 3○ to 17○) • No evidence of any neutrinos in the HiRes-II data 30th ICRC – 2007 Merida, Mexico

  10. εINTER HR-II εTRANS Monte Carlo Technique • Flat distribution of neutrino • energies in log(E). • Isotropic upward-going • events. • Calculate εINTER and • εTRANS. • Force neutrino to interact • along “interaction length.” • Run through full detector • trigger simulation routine 30th ICRC – 2007 Merida, Mexico

  11. Typical MC event 30th ICRC – 2007 Merida, Mexico

  12. HiRes-II νe aperture 30th ICRC – 2007 Merida, Mexico

  13. Upper limit on the flux of νe and ντ(C.L. 90%) Dotted line: Gelmini et al., 2007. Red : νeBlack :νe + ντ Dashed line: Semikoz & Sigl, 2004. Blue : ντ 30th ICRC – 2007 Merida, Mexico

  14. Conclusions • No conclusive evidence of an upward-going neutrino in the • HiRes-II data. • νe limit about ~2.5 orders of magnitude better than the Fly’s Eye. • Largest uncertainty - neutrino cross section models. • (different CTEQ models change the limits by 20 to 50%) • HiRes is a good high-energy neutrino detector despite being • optimized for cosmic ray detection. 30th ICRC – 2007 Merida, Mexico

  15. HiRes-II νe flux limit Dotted line: Gelmini et al., 2007. Dashed line: Semikoz & Sigl, 2004. 30th ICRC – 2007 Merida, Mexico

  16. Open circles : Fly’s Eye Closed circles : this work MC : event by event (deepest) Depth ~ E0.6 Compare to 1018 : 40 m 1019 : 100 m 1020 : 300 m 1021 : 1200 m Baltrusaitis et al., Phys. Rev. D31, 1985 30th ICRC – 2007 Merida, Mexico

  17. Systematics • Uncertainty associated with cross sections • (this work: pQCD CTEQ5 parameterization) Gazizov & Kowalski, Comp. Phys. Comm, 2005. 30th ICRC – 2007 Merida, Mexico

  18. Open circles : Greisen functional form Closed circles : LPM Modeling the LPM effect in rock K. Greisen, Progress in Cosmic Ray Physics vol. 3, 1956 30th ICRC – 2007 Merida, Mexico

  19. Open circles : Greisen functional form Closed circles : LPM Modeling the LPM effect in air K. Greisen, Progress in Cosmic Ray Physics vol. 3, 1956 30th ICRC – 2007 Merida, Mexico

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