Aspen Workshop April 2007

1. Upper limit on the upward-going electron-neutrino flux from the HiRes Instrument Lauren M. Scott Postdoctoral Research Associate Rutgers, the State University of New Jersey Aspen Workshop April 2007

2. Outline • Motivation for looking at νe (instead of νμ) • The search for upward-going events in the HiRes-II data. • Landau-Pomeranchuk-Migdal effect. • Monte-Carlo technique for modeling HiRes detector • response to νe. • Upper limit on the flux of upward-going νe and ντ • (and comparison with other experiments / theoretical limits). • Uncertainties / assumptions. Aspen Workshop April 2007

3. Why electron-neutrino-induced showers? • At HiRes energies (>1018 eV), interaction cross sections are high. • Earth-skimming events pass through enough material. • σ ≈ 10-32 cm2 (1018 eV), 10-31 cm2 (1021 eV) • Landau-Pomeranchuk-Migdal effect • bremsstrahlung, pair-production cross sections are suppressed • e- (cc) : ELPM = 6 ×1014 eV (rock) • ELPM = 2 ×1018 eV (air, desert floor) • LPM threshold is much higher for νμ and ντ. • Large target volume, interactions occurring deep in the • earth will be detectable at the surface. Aspen Workshop April 2007

4. 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○) Summer 2006 upward-going neutrino search most likely candidates “up/down” cosmic-ray events Aspen Workshop April 2007

5. Modeling the LPM effect • for a full Monte Carlo detector simulation, must model • energy- and depth-dependence of the LPM effect • energy spectrum of particles as a function of depth • LPM effect in air for high-energy events. Stanev, Vankov, Streitmatter, Ellsworth and Bowen, Phys. Rev. D., 1982 Kim, K. PhD Thesis, Univ. of Utah, 2002 Aspen Workshop April 2007

6. 1018, 1019, 1020, 1021 eV Modeling the LPM effect Aspen Workshop April 2007

7. Open circles : Greisen functional form Closed circles : LPM Modeling the LPM effect in rock K. Greisen, Progress in Cosmic Ray Physics vol. 3, 1956 Aspen Workshop April 2007

8. Open circles : Greisen functional form Closed circles : LPM Modeling the LPM effect in air K. Greisen, Progress in Cosmic Ray Physics vol. 3, 1956 Aspen Workshop April 2007

9. 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. Aspen Workshop April 2007

10. εINTER HR-II εTRANS Monte Carlo Technique • Flat distribution of neutrino energies • in log(E). • Isotropic upward-going events. • 70% CC events / 30% NC events • (from ratio of cross sections) • Each event, interpolate depth in rock • that gives Nmax = 107 in air. • CC : superpose LPM airshower • from spectrum at point of exit • from earth • NC : GH profile, unchanged from • rock into air • Calculate εINTERand εINTER. • Force neutrino to interact along • “interaction length.” • Run through full detector trigger • simulation routine (mcru) • Find geometry, plane-fitting for • events that pass trigger (rufpln) Aspen Workshop April 2007

11. Typical MC event Aspen Workshop April 2007

12. 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 Aspen Workshop April 2007

13. HiRes-II νe aperture Aspen Workshop April 2007

14. HiRes-II νe flux limit • 2.3 events over • entire energy range • (90% CL) • livetime = 3638 hours Dotted line: Gelmini et al., 2007. Dashed line: Semikoz & Sigl, 2004. Aspen Workshop April 2007

15. 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 Aspen Workshop April 2007

16. Systematics • Uncertainty associated with cross sections • (this work: pQCD CTEQ5 parameterization) Gazizov & Kowalski, Comp. Phys. Comm, 2005. Aspen Workshop April 2007

17. Systematics • Uncertainty associated with cross sections • (this work: pQCD CTEQ5 parameterization). • LPM threshold in air increases with altitude • (this work: desert floor). • 1018 eV • desert • 5 km • 10 km • 15 km Aspen Workshop April 2007

18. Systematics • Uncertainty associated with cross sections • (this work: pQCD CTEQ5 parameterization). • LPM threshold in air increases with altitude • (this work: desert floor). • 1019 eV • desert • 5 km • 10 km • 15 km Aspen Workshop April 2007

19. Systematics • Uncertainty associated with cross sections • (this work: pQCD CTEQ5 parameterization). • LPM threshold in air increases with altitude • (this work: desert floor). • 1020 eV • desert • 5 km • 10 km • 15 km Aspen Workshop April 2007

20. Systematics • Large systematic uncertainty associated with cross sections • (this work: pQCD CTEQ5 parameterization). • LPM threshold in air increases with altitude • (this work: desert floor). • 1021 eV • desert • 5 km • 10 km • 15 km Adjusting air showers for altitude-dependence of LPM effect will raise the limit somewhat Aspen Workshop April 2007

22. Monte Carlo Technique 1018 eV 1019 eV 1020 eV 1021 eV Aspen Workshop April 2007

23. MC : event by event (earth-skimming) Closed circles : Fraction of CC events whose trajectories pass through the earth. Open circles : Fraction of MC events whose trajectories only pass through the air. Aspen Workshop April 2007

24. MC : event by event (furthest away) Aspen Workshop April 2007

25. Aspen Workshop April 2007