Aspen Workshop

April 2007

Upper limit on the upward-going Upper limit on the upward-going electron-neutrino flux from the HiRes Instrumentelectron-neutrino flux from the HiRes Instrument

Lauren M. ScottLauren M. ScottPostdoctoral Research AssociatePostdoctoral Research Associate

Rutgers, the State University of New JerseyRutgers, the State University of New Jersey

Aspen Workshop

April 2007

• 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.

OutlineOutline

Aspen Workshop

April 2007

Why electron-neutrino-inducedWhy electron-neutrino-inducedshowers?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

Search for upward-going showersSearch 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 searchmost likely candidates “up/down” cosmic-ray events

Aspen Workshop

April 2007

Modeling the LPM effectModeling 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

Modeling the LPM effectModeling the LPM effect

1018, 1019, 1020, 1021 eV

Modeling the LPM effectModeling the LPM effectin rockin rock

Aspen WorkshopApril 2007

0

00

2/10

0

2

3

ln

ln2

31exp

31.0),(

t

ts

E

E

sttEN

C

K. Greisen, Progress in Cosmic Ray Physics vol. 3, 1956

Open circles : Greisen functional formClosed circles : LPM

Aspen Workshop

April 2007

0

00

2/10

0

2

3

ln

ln2

31exp

31.0),(

t

ts

E

E

sttEN

C

Modeling the LPM effectModeling the LPM effectin airin air

K. Greisen, Progress in Cosmic Ray Physics vol. 3, 1956

Open circles : Greisen functional formClosed circles : LPM

Aspen Workshop

April 2007

Modeling the LPM effectModeling the LPM effect

Airshower from a 1020 eVelectron entering air at 50,000 g/cm2 is a super-position of air showers fromNe in each energy bin.

E0 = 1020 eVspectrum @50 kg/cm2

Aspen Workshop

April 2007

Monte Carlo TechniqueMonte 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 εINTER and 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)

εINTER

εTRANS

HR-II

Aspen Workshop

April 2007

Typical MC eventTypical MC event

Aspen Workshop

April 2007

MC : event by eventMC : event by event(deepest)(deepest)

Compare to1018 : 40 m1019 : 100 m1020 : 300 m1021 : 1200 m

Baltrusaitis et al.,Phys. Rev. D 31, 1985

Depth ~ E0.6

Open circles : Fly’s EyeClosed circles : this work

Aspen Workshop

April 2007

HiRes-II HiRes-II ννee aperture aperture

2.1EA

thrown

intertrans

0

accep

i

N

jjj

Ei NAA

ti

Aspen Workshop

April 2007

Dotted line: Gelmini et al., 2007.Dashed line: Semikoz & Sigl, 2004.

HiRes-II HiRes-II ννee flux limit flux limit

2.2 EdE

dN• 2.3 events over entire energy range (90% CL)

• livetime = 3638 hours

Aspen Workshop

April 2007

Dotted line: Gelmini et al., 2007. Red : νe Black : νe + ντ Dashed line: Semikoz & Sigl, 2004. Blue : ντ

Upper limit on the flux of Upper limit on the flux of ννee and and ννττ (C.L. 90%)(C.L. 90%)

Aspen Workshop

April 2007

SystematicsSystematics

• Uncertainty associated with cross sections (this work: pQCD CTEQ5 parameterization)

Gazizov & Kowalski, Comp. Phys. Comm, 2005.

Aspen Workshop

April 2007

SystematicsSystematics

• 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

SystematicsSystematics

1019 eV• desert• 5 km• 10 km• 15 km

• Uncertainty associated with cross sections (this work: pQCD CTEQ5 parameterization).

• LPM threshold in air increases with altitude (this work: desert floor).

Aspen Workshop

April 2007

SystematicsSystematics

1020 eV• desert• 5 km• 10 km• 15 km

• Uncertainty associated with cross sections (this work: pQCD CTEQ5 parameterization).

• LPM threshold in air increases with altitude (this work: desert floor).

Aspen Workshop

April 2007

SystematicsSystematics

• 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 showersfor altitude-dependenceof LPM effect will raisethe limit somewhat

Aspen Workshop

April 2007

Monte Carlo TechniqueMonte Carlo Technique

1018 eV

1019 eV

1020 eV

1021 eV

Aspen Workshop

April 2007

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.

MC : event by eventMC : event by event(earth-skimming)(earth-skimming)

Aspen Workshop

April 2007

MC : event by eventMC : event by event(furthest away)(furthest away)

Aspen Workshop

April 2007