Neutrino physics with
IceCube DeepCore-PINGU
… and comparison with alternatives
TeVPA 2012
TIFR Mumbai, India
Dec 10-14, 2012
Walter Winter
Universität Würzburg
Contents
 Introduction
 Oscillation physics with Earth matter effects
 Mass hierarchy determination with PINGU
 Neutrino beam to PINGU?
 Atmospheric neutrinos
 Comparison with alternatives, and outlook
 Summary
2
Atmospheric neutrino anomaly
 The rate of neutrinos should
be the same from below and
above
 But: About 50% missing from
below
 Neutrino change their flavor on
the path from production to
detection: Neutrino oscillations
(Super-Kamiokande: “Evidence for oscillations
of atmospheric neutrinos”, 1998)
3
Three flavors: Summary
 Three flavors: 6 params
(3 angles, one phase; 2 x Dm2)
Atmospheric
oscillations:
Amplitude: q23
Frequency: Dm312
Coupling: q13
Suppressed
effect: dCP
Solar
oscillations:
Amplitude: q12
Frequency: Dm212
(Super-K, 1998;
Chooz, 1999;
SNO 2001+2002;
KamLAND 2002;
Daya Bay, RENO
2012)
 Describes solar and atmospheric neutrino
anomalies, as well as reactor antineutrino disapp.!
4
(short baseline)
(also: T2K, Double Chooz, RENO)
5
Consequences of large q13
 q13 to be well
measured by
Daya Bay
 Mass hierarchy:
3s discovery for
up to 40% of all
dCP possible iff
ProjectX, possibly
until 2025
 CP violation
measurement
extremely difficult
Need new
facility!
Huber, Lindner,
Schwetz, Winter, 2009
6
Oscillation physics with
Earth matter effects
Matter profile of the Earth
… as seen by a neutrino
(not to scale)
Inner
core
(PREM: Preliminary Reference Earth Model)
Core
8
Matter effect (MSW)
(Wolfenstein, 1978;
 Ordinary matter:
Mikheyev, Smirnov,
electrons, but no m, t
1985)
 Coherent forward
scattering in matter:
Net effect on electron flavor
 Hamiltonian in matter
(matrix form, flavor space):
Y: electron
fraction ~
0.5
(electrons
per
nucleon)
9
Parameter mapping
… for two flavors
 Oscillation probabilities in
vacuum:
matter:
Matter resonance:
In this case:
- Effective mixing maximal
- Effective osc. frequency
minimal
 MH
Resonance energy:
For nm appearance, Dm312:
- r ~ 4.7 g/cm3 (Earth’s
mantle): Eres ~ 6.4 GeV
- r ~ 10.8 g/cm3 (Earth’s outer
core): Eres ~ 2.8 GeV
10
Mantle-core-mantle profile
(Parametric enhancement: Akhmedov, 1998; Akhmedov, Lipari, Smirnov, 1998; Petcov, 1998)
 Probability for L=11810 km (numerical)
!
Param.
enhancement
Core
resonance
energy
Parametric enhancement
through mantle-core-mantle
profile of the Earth.
Unique physics potential!
Mantle
resonance
energy
Threshold
effects
expected at:
Naive L/E scaling
does not apply!
2 GeV
4-5 GeV
11
Mass hierarchy determination
with PINGU
What is PINGU?
(“Precision IceCube Next Generation Upgrade“)
 Fill in
IceCube/DeepCore
array with additional
strings
 Drive threshold to
lower energies
 LOI in preparation
 Modest cost ~30-50M$
(dep. on no. of strings)
 Two season
deployment anticipated:
2015/2016/2017
(PINGU, 12/2012)
13
PINGU fiducial volume?
 A ~ Mt fiducial mass
for superbeam
produced with
FNAL main injector
protons (120 GeV)
(PINGU, 12/2012)
 Multi-Mt detector for
E > 10 GeV
 atmospheric
neutrinos
 Fid. volume depends
on trigger level
(earlier Veff higher, which is
used for following analyses!)
LBNE-like Atm.
beam neutrinos
14
Mass hierarchy measurement:
statistical significance (illustrated)
Source
(spectrum,
solid angle)
Atmospheric
neutrinos
arXiv:1210.5154
Beams
M. Bishai
x
Osc. effect
(in matter)
x
Detector
mass
x
Cross
section
~E
>2
GeV
> 5 GeV
Core
res.
Measurement at
threshold 
application
rather for future
upgrades:
MICA?
15
Beams to PINGU?
 Labs and potential detector locations (stars) in
“deep underground“ laboratories:
All these baselines cross the Earth‘s outer core!
(Agarwalla, Huber, Tang, Winter, 2010)
FNAL-PINGU: 11620 km
CERN-PINGU: 11810 km
RAL-PINGU: 12020 km
JHF-PINGU: 11370 km
16
Example:
“Low-intensity“ superbeam?
 Here: use most conservative assumption
NuMI beam, 1021 pot (total), neutrinos only
[compare to LBNE: 22+22 1020 pot without Project X ~ factor four higher
exposure than the one considered here]
(FERMILAB-PROPOSAL-0875, NUMI-L-714)
 Low intensity may
allow for shorter decay pipe
 Advantage: Peaks in
exactly the right energy
range for the parametric
enhancement
M. Bishai
 Include all irreducible
backgrounds (intrinsic beam, NC, hadronic
cascades), 20% track mis-ID
17
Event rates
(for Veff 03/2012)
Normal hier. Inv. hierarchy
Signal
1560
54
39
511
59
750
3
4
Neutral currents
2479
2479
Total backgrounds
3032
3292
Total signal+backg.
4592
Backgrounds:
ne beam
Disapp./track mis-ID
nt appearance
>18s
(stat. only)
3346
18
Mass hierarchy with a beam
All irreducible backgrounds included
(Daya Bay best-fit; current parameter
uncertainties included; based on
Tang, Winter, JHEP 1202 (2012) 028 )
GLoBES 2012
 Very robust mass hierarchy measurement (as long as
either some energy resolution or control of systematics)
19
Atmospheric neutrinos
Akhmedov, Razzaque, Smirnov, 2012
 Neutrino source
available “for free“
 Source not flavorclean  different
channels contribute
and mask effect
 Power law spectrum
arXiv:1210.5154
 Many different
baselines at once,
weighted by solid angle
 Detector:
angular+energy
resolution required!
A. Smirnov
20
Mass hierarchy with
atmospheric neutrinos
 Statistical
significance
depends on
angular and
energy resolution
 About 3-10s likely
for reasonable
values
 Final proof of
principle will
require event
reconstruction
techniques (in
progress)
Akhmedov, Razzaque, Smirnov, 2012
21
Comparison with alternatives
… and outlook
Mass hierarchy
3s
 No “conventional“ atm. neutrino
experiment could be built on a
similar timescale or at a similar
cost
 Bottleneck: Cavern!
Akhmedov, Razzaque, Smirnov, 2012; v5
 PINGU completed by beginning
of 2017?
 3s, Project X and T2K with
proton driver, optimized
neutrino-antineutrino run plan
PINGU
20182020?
Huber, Lindner, Schwetz, Winter, JHEP 11 (2009) 44 23
Probabilities: dCP-dependence
 There is rich dCP-phenomenology:
NH
L=11810 km
24
Upgrade path towards dCP?
 Measurement of dCP
in principle possible,
but challenging
 Wish list:
 Electromagnetic
shower ID
(here: 1% mis-ID)
 Energy resolution
(here: 20% x E)
 Maybe: volume
upgrade
(here: ~ factor two)
 Project X
= LBNE +
Project X!
same beam
to PINGU
 Currently being
discussed in the
context of further
upgrades - MICA;
requires further study
 PINGU as R&D exp.?
Tang, Winter, JHEP 1202 (2012) 028
25
Matter density measurement
Example: LBNE-like Superbeam
 Precision ~ 0.5%
(1s) on core
density
 Complementary
to seismic waves
(seismic shear
waves cannot
propagate in the
liquid core!)
from: Tang, Winter, JHEP 1202 (2012) 028;
see also: Winter, PRD72 (2005) 037302; Gandhi, Winter, PRD75
(2007) 053002; Minakata, Uchinami, PRD 75 (2007) 073013 26
Conclusions: PINGU
 Megaton-size ice detector as upgrade of DeepCore with lower
threshold; very cost-efficient compared to liquid argon, water
 Unique mass hierarchy measurement through MSW effect in
Earth matter
 Atmospheric neutrinos:
 Neutrino source for free, many different baselines
 Requires energy and angular resolution (reconstruction work in progress)
 PINGU to be the first experiment to discover the mass hierarchy at 3-5s?
 Neutrino beam:
 Requires dedicated source, with relatively low intensity
 Proton beams from FNAL main injectior have just right energy to hit mantlecore-mantle parameteric enhancement region
 Even possible as counting experiment, no angular resolution needed
 Beyond PINGU: CPV and matter density measurements
perhaps possible with beam to even denser array (MICA)?
 PINGU as R&D experiment; worth further study!
 Technology also being studied in water  ORCA
27
BACKUP
Possible neutrino sources
There are three possibilities to artificially produce
neutrinos
 Beta decay:
 Example: Nuclear reactors, Beta beams
 Pion decay:
Superbeam
 From accelerators:
Pions
Protons
Target
Selection,
focusing
Muons,
neutrinos
Decay
tunnel
Neutrinos
Absorber
 Muon decay:
 Muons produced by pion decays! Neutrino Factory
29
Detector paramet.: mis-ID
misID:
fraction of events of a
specific channel
mis-identified as signal
1.0?
misIDtracks
<< misID <~ 1 ?
(Tang, Winter, JHEP 1202 (2012) 028)
30
Detector requirements
Want to study ne-nm oscillations with different sources:
 Beta beams:
q13, dCP
 In principle best choice for PINGU (need muon flavor ID only)
 Superbeams:
q13, dCP
 Need (clean) electron flavor sample. Difficult?
 Neutrino factory:
q13, dCP
 Need charge identification of m+ and m- (normally)
31
Detector parameterization
(low intensity superbeam)
 Challenges:
 Electron flavor ID
 Systematics (efficiency, flux normalization  near
detector?)
 Energy resolution
 Make very (?) conservative assumptions here:
 Fraction of mis-identified muon tracks (muon tracks may
be too short to be distinguished from signal) ~ 20%
 Irreducible backgrounds (zeroth order assumption!):
 Intrinsic beam background
 Neutral current cascades
 nm  nt cascades (hadronic and electromagnetic cascades
indistinguishable)
 Systematics uncorrelated between signal and
background
 No energy resolution (total rates only)
(for details on parameterization: Tang, Winter, JHEP 1202 (2012) 028)
32
Measurement of dCP?
 Many proposals
for measuring
CP violation with
a neutrino beam
 Require all a
dedicated (new)
detector + control of
systematics
Coloma, Huber, Kopp, Winter, 2012
33