ice fishing for cosmic neutrinos
Download
Skip this Video
Download Presentation
Ice-fishing for Cosmic Neutrinos

Loading in 2 Seconds...

play fullscreen
1 / 48

Ice-fishing for Cosmic Neutrinos - PowerPoint PPT Presentation


  • 121 Views
  • Uploaded on

Ice-fishing for Cosmic Neutrinos. Subhendu Rakshit TIFR, Mumbai. Goals of neutrino astronomy. Astrophysics: To explore astrophysical objects like AGN or GRBs. Find out sources of high energy cosmic rays. Main aim.. Particle physics:

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'Ice-fishing for Cosmic Neutrinos' - uzuri


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.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
ice fishing for cosmic neutrinos

Ice-fishing for Cosmic Neutrinos

Subhendu Rakshit

TIFR, Mumbai

goals of neutrino astronomy
Goals of neutrino astronomy
  • Astrophysics:

To explore astrophysical objects like AGN or GRBs. Find out sources of high energy cosmic rays. Main aim..

  • Particle physics:

To explore beyond standard model physics options which may affect neutrino nucleon cross-sections at high energy. Other possibilities… Appeared in US particle physics roadmap!

First step: To determine the incoming neutrino flux

astrophysical motivations
Astrophysical motivations
  • Historically looking at the same astrophysical object at different wavelengths revealed many details regarding their internal mechanisms
  • A 3-pronged approach involving conventional photon astronomy, cosmic ray astronomy and neutrino astronomy will yield better results
conventional astronomy with photons
Conventional astronomy with photons
  • Ranges from 104 cm radio-waves to 10-14 cm high energy gamma rays
  • Pros:
      • Photons are neutral particles. So they can point back to their sources
      • photons are easy to detect as they interact electromagnetically with charged particles
  • Cons:
      • Due to the same reason they get absorbed by dust or get obstructed
      • Very high energy photons on its way interact with cosmic microwave background radiation and cannot reach us
cosmic ray astronomy
Cosmic ray astronomy
  • Very high energy cosmic rays (protons, heavy nuclei,..) do reach us from the sky
  • It is difficult to produce such energetic particles in the laboratory
  • It is puzzling where they are produced and how they get accelerated to such energies!!
  • Although they can be detected on Earth, it is not possible to identify the sources as their paths get scrambled in magnetic fields  A serious disadvantage!
  • Only very high energy(>1010 GeV) cosmic rays point back to their sources
neutrino astronomy
Neutrino astronomy
  • The suspected sources of very high energy photons and cosmic rays are believed to be the sources of neutrinos as well
  • Pros: Neutrinos being weakly interacting reaches Earth rather easily
  • Cons: Due to the same reason it also interacts rarely with the detector material ⇒ Large detector size!!
  • Successful neutrino astronomy with the sun and supernova. Now it is time to explore objects like Active Galactic Nuclei or Gamma Ray Bursts
  • Impressive range for future neutrino telescopes:

102 GeV to 1012 GeV!

slide7
Neutrino detectors

Underground

Air shower

Underwater / ice

GeV TeV PeV EeV

1 PeV = 106 GeV

1 EeV = 109 GeV

why a km 3 detector
Why a Km3 detector?
  • Estimations of the expected amount of UHE neutrinos can be made from the observed flux of cosmic rays at high energies. This limits the size of the detector
  • However such estimations are quite difficult as many assumptions go in
  • There can be hidden sources of neutrinos!!
  • So the neutrino flux can always be higher!
slide10
A Km3 detector
  • PMTs detect Cherenkov light emitted by charged particles created by neutrino interactions

IceCube

  • 1KM^3

The Cherenkov cone needs to be reconstructed to determine the energy and direction of the muon

icecube is optimised for detection of muon neutrinos above 1 tev as
IceCube is optimised for detection of muon neutrinos above 1 TeV as:
  • We get better signal to noise ratio
  • Neutrino cross-section and muon range increases with energy. Larger the muon range, the larger is the effective detection volume
  • The mean angle between muon and neutrino decreases with energy like 1/√E, with a pointing accuracy of about 1◦at 1 TeV
  • The energy loss of muons increases with energy. For energies above 1 TeV, this allows us to estimate the muon energy from the larger light emission along the track
slide13
Detection strategy
  • Cosmic rays produce muons in our atmosphere, which can fake a neutrino-induced muon signal  background
  • So we use the Earth to filter them out!
  • Upto PeV neutrinos can cross the Earth to reach IceCube
  • For high energy neutrinos Earth becomes opaque as the probability that the neutrinos will interact becomes higher with  energy
  • So very high energy neutrinos can reach Icecube only from the sky or from horizontal directions!

IceCube

sources of neutrinos
Sources of neutrinos
  • Signal: The neutrinos from astrophysical sources: AGN or GRBs for example
  • Background: Atmospheric neutrinos. They are produced from cosmic ray interactions with the atmosphere  A guaranteed flux well measured in AMANDA. Agrees with expectations.

As the ATM  flux falls rather rapidly(∝ E-3) with energy, at higher energy we can observe the ‘signal’ neutrinos from AGN or GRBs free of these background neutrinos

slide15
Neutrino spectra

Note: At higher energies the flux is smaller. But higher energy neutrinos also have higher cross-section. So detection probability is also higher!

another background
Another background
  • Cosmogenic or GZK neutrinos:

UHE cosmic ray protons interact with CMBR photons to produce these neutrinos via charged pion decay

However at IceCube the rate would be quite small

eliminating backgrounds
Eliminating backgrounds
  • Energy cuts
  • Directional cuts
  • Directional signals
  • Temporal considerations
slide19
Production at astrophysical sources:

Initial flavour ratio

  • Propagation through space:

Massive neutrinos undergo quantum mechanical oscillations. So neutrinos reach Earth with a flavour

ratio

  • Propagation through the Earth:

Neutrinos while propagating may interact with the Earth. CC or NC interactions. τpropagation is more elaborate:τ→τ→τ→τ...

  • Detection at IceCube:

Muon neutrinos produce muons via CC interactions. All neutrinos produce showers through NC interactions. A CC interaction by a τmay produce spectacular signatures!

production at astrophysical sources
Production at astrophysical sources:

A proton gets accelerated and hits another proton or a photon. They produce neutron, π+andπ0.Their decay produces cosmic rays, neutrinos and photons respectively

p +  → π+ + n

p +  → π0 + p

slide21
Propagation through space:
  • For massive neutrinos flavour and mass eigenstates are different. This implies that a neutrino of a given flavour can change its flavour after propagating for sometime! For example: µ ↔ e Neutrino oscillation

At time t=0, we produce a e

After sometime t, the mass eigenstates evolve differently

So the probability of detecting another flavour is nonzero

slide22
At source
  • Now remember the initial flavour ratio at source was
  • Recent neutrino experiments have established that neutrino flavour states µ and τmix maximally
  • Hence it is of no wonder that after traversing a long distance these two states will arrive at equal proportions
  • Note that although there were no tau neutrinos at the source, we receive them on Earth!

On Earth

slide23
Propagation through the Earth:
  • While traversing through the Earth, neutrinos can undergo
      • a charged current(CC) interaction with matter. The neutrino disappears producing e or mu or tau. The dominant effect
      • or a neutral current interaction(NC) with matter. The neutrino produces another neutrino of same flavour with lower energy
  • As a consequence, the number of neutrinos decrease as they propagate through the Earth.
  • This depends on the energy of the neutrino. Higher energy neutrinos get absorbed more, their mean free path is smaller
detection
µdetection
  • Muons range: few Kms at TeV and tens of Km at EeV
  • The geometry of the lightpool surrounding the muon track is a Km-long cone with gradually decreasing radius
  • Initial size of the cone for a 100TeV muon is 130m. At the end of its range it reduces to 10m.
  • The kinematic angle of µ wrt the neutrino is µ is 1◦/√(E/1TeV)and thereconstruction error on the muon direction is on the order of 1◦
  • Better energy determination for contained events. More contained events at lower energy
slide26
~ Km long muon tracks from µ

~ 10m long cascades from e, τ

e detection
edetection
  • In a CC interaction, a edeposits 0.5-0.8% of their energy in an EM shower initiated by the electron. Then a shower initiated by the fragments of the target
  • The Cherenkov light generated by shower particles spreads over a vol of radius 130m at 10TeV and 460m at 10EeV. Radius grows by ~50m per decade in energy
  • Energy measurement is good. The shower energy underestimates the neutrino energy by a factor ~3 at 1 TeV to ~4 at 1 EeV
  • Angle determination poor! Elongated in the direction of e so thatthe direction can be reconstructed but precise to ~10◦
slide28
τ detection
  • The propagation mechanism of a tau neutrino is different, as tau may decay during propagation
  • As a result the tau neutrino never disappears. For each incoming τanotherτof lower energy reaches the detector
  • The Earth effectively remains transparent even for high energy tau neutrinos
  • Tau decays produce secondary flux of e and µ

τ

τ

τ

τ

slide29
Double bang events: CC interaction of τfollowed by tau decay
  • Lollipop events: second of the two double bang showers with reconstructed tau track
  • Inverted lollipop events: first of the two double bang showers with reconstructed tau track. Often confused with a hadronic event in which a ~100GeV muon is produced!
  • For Eτ< 106 GeV, in double bang events showers are indistinguishable. For Eτ~ 106 GeV, tau range is a few hundred meters and the showers can be separated.

For 107 GeV < Eτ< 107.5 GeV, the tau decay length is comparable to the instrumented detector vol. lollipop

Eτ> 107.5 GeV tau tracks can be confusing

slide34
Without energy loss

Including energy loss

slide37
Expected muon event rate per year at IceCube

µ induced

µ+ τinduced

slide40
Production at astrophysical sources:

Initial flavour ratio ?

  • Propagation through space:

Massive neutrinos undergo quantum mechanical oscillations. So neutrinos reach Earth with a flavour

ratio ??

  • Propagation through the Earth:

Neutrinos while propagating may interact with the Earth. CC or NC interactions. τpropagation is more elaborate:τ→τ→τ→τ...

  • Detection at IceCube:

Muon neutrinos produce muons via CC interactions. All neutrinos produce showers through NC interactions. A CC interaction by a τmay produce spectacular signatures!

N xsection sensitive

slide41
Detection of atm µs will enable us to probe CPTV, LIV,VEP which change the standard 1/E energy dependence of osc length. Due to high threshold of IceCube, osc of these high energy atm neutrinos is less
  • N xsection can get enhanced in XtraDim models
  • N xsection can get reduced at high energies in color glass condensate models
  • Visible changes in muon rates, shower rates
  • For xtradim upgoing neutrinos get absorbed at some energy and also downgoing for higher energies
  • For lower N xsection models angular dependence and energy dependence for upgoing events are more important
slide42
Crude neutrino flux determination from up/down events
  • OK for fixed power flux, but otherwise contained muon events are better. But poorer statistics
  • Auger is better for UHE neutrinos. New physics effects will be more dramatic
  • IceCube can probe neutrino spectrum better as Xsection uncertainties are only at high energies where the flux is smaller
  • Flavour ratio determination possible at IceCube as different flavours have distinctive signatures.
other possibilities
Other possibilities
  • DM detection: Neutrinos from solar core
  • SUSY search: look for charged sleptons
  • RPV, Leptoquarks
  • Part of supernova early detection system!
  • New physics interactions at the detector
  • New physics during propagation
summary
Summary
  • UHE neutrinos: particle physics opportunities for the future
  • IceCube is a discovery expt.
  • Determining neutrino spectrum independent of new physics poses a challenge
  • Even crude measurements at IceCube may provide some clue about drastically different new physics scenarios at high energies
  • Some success with IceCube will lead to bigger detectors
  • At present we just need to detect an UHE neutrino event at IceCube!
particle physics motivations
Particle physics motivations

LHC CM energy ECM = 14 TeV

⇒ LHC: E=108 GeV Tevatron: E=106 GeV

Here we talk about neutrino flux of 1012 GeV!

⇒ ECM = 14 ×100 TeV

n cross sections
N cross-sections
  • We need PDF’s for x < 10-5 for E>108 GeV
  • Several options but not much discrepancy!
  • GRV and CTEQ cross-sections differ at the most by 20%
slide47
Beacom et al, PRD 68,093005(2003)

e shower(CC+NC)

For downgoing μ

Horizontal μcreating a detectable μ track

τlollipop

τdouble bang

ad