Title: Exploring the physics frontier with nes and nms in MINOS
1Exploring the physics frontier with nes and nms
in MINOS
Pedro Ochoa California Institute of Technology
International School of Subnuclear
Physics Erice, Italy - August 2007
2- The discovery that ns have mass has
revolutionized their place in physics and in our
universe. - However our knowledge of neutrinos remains
incomplete
What is the right mass hierarchy?
Is ?130 or just very small?
(MINOS PRL 97, 191801 2006)
Is q23 exactly p/4?
What is the rest mass of neutrinos?
Are neutrinos their own antiparticles? Are there
more than 3 neutrinos (sterile, heavier than
Z)? Do neutrinos obey CP, CPT?
And also
? Can address some of these questions in the
MINOS experiment !
3The MINOS Experiment
- MINOS (Main Injector Neutrino Oscillation Search)
is a long-baseline neutrino oscillation
experiment
The NuMI nm beam provided by 120 GeV protons from
the Fermilab Main Injector
A Near detector at Fermilab to measure the beam
composition and energy spectrum.
A Far detector at the Soudan Mine in Minnesota to
search for neutrino oscillations.
- Both detectors are magnetized iron-scintillator
sampling calorimeters
4Event topology in MINOS
?e CC Event
NC Event
?µ CC Event
2.3m
3.5m
1.8m
short, with typical EM shower profile
short event, often diffuse
long µ track hadronic activity at vertex
- Challenging to distinguish NC from ne CC.
5ne appearance
- Is q130 or just very small?
- A non-zero q13 could give us a handle on CP
violation and on the mass hierarchy of the
neutrino sector.
- Worlds best limit sin2(2q13) lt 0.12 for
Dm2323x10-3 eV2 (CHOOZ)
? MINOS could make the first non-zero measurement
of q13 !
- MINOS sensitivity will already be comparable to
CHOOZ by the end of 2007.
To be superseded soon
- Ultimate reach of MINOS rests on two pillars
- Signal/background separation
- Background determination
6Nearest neighbors ne selection
- How to make the best selection of ne events?
- Most available selections use multivariate
techniques that rely on reconstructed quantities.
- But in this analysis of reco variables of
hits in event
? Why not perform event ID using strip
information alone?
- Working on a nearest neighbors selection in
collaboration with Cambridge University.
1) Compare each input event to large libraries of
MC ne CC and NC events.
2) Select N best matches
3) Construct discriminant from N best matches
information (e.g. fracCCfraction of N best
matches which are ne CC)
- Approach is, in principle, optimal ! (no loss
raw?reco)
- But need to fully sample phase space (need
50-100M event libraries)
7- How do we determine how well two events match?
Ask the question what is probability the two
events come from same hit pattern at PMTs?
- How does the selection perform?
- fracCC(ylt0.5)fraction of 20 best matches that
were ne with ylt0.5
Library size 5M ne 10M NC
NC ne CC
- Already provides the best significance among
all selections !
Good separation
- Plenty of room for improvement
- Construct more sophisticated discriminant use
larger libraries.
8Beam nes from antineutrinos
- Irreducible background in ne analysis intrinsic
beam nes
- Have developed a method to assess this background
using nms in collaboration with BNL
- About 6 of our beam is
- made of muon anti-neutrinos
- Magnetic field allows us to separate neutrinos
and anti neutrinos on an event by event basis !
1x1020 POT
Far Detector MC
? nms from m give us the number of intrinsic
beam nes
9- How to measure the nms from m decay?
m component in anti-neutrino spectrum is
practically the only one affected when varying
the horn-target separation in the beam.
Most antineutrino parents are p- and K- that go
undeflected through the center of both horns
- Anti-neutrino spectra in three different beam
configurations
pseudo-medium energy (pME) dhorn-target 100cm
pseudo-high energy (pHE) dhorn-target 250cm
Low energy (LE) dhorn-target -10cm
MC
MC
MC
10Technique and status of the measurement
The Technique
(pME-LE)TRUE at 1e18 POT
- Scale pME (or pHE) and LE data to same POT and
take the difference
- Fit with using shapes from the MC
Corrections due to differences in the
antineutrinos from p- and K-
LE
pME
- Have shown that method works with either pME or
pHE data.
- Have 1.6x1019 POT of pHE data taken in 2006 that
we are using. - Result expected very soon !
11Other anti-neutrino physics
- Other very interesting physics can be done with
anti-neutrinos
1) n?n transitions have never been looked for
before in atmos sector.
- Some models beyond the SM predict them (i.e.
Langacker and Wang, Phys. Rev. D 58 093004). - Could fully explain the atmospheric neutrino
results (Alexeyev and Volkova, hep
ex/0504282)
2) Anti-neutrino oscillation analysis large CPT
violating region for Dm232 remains unexplored
68, 90, 99 C.L. CPT violating regions still
allowed by global fit (except LSND)
A. Strumia and F. Vissani, Implications of
neutrino data circa 2005, Nucl. Phys. B726 (2005)
12Reversed horn current running?
- Anti-neutrino spectrum peaks at higher energies
- ?Have studied the possibility of running with
reverse horn current
1x1020 POT
1x1020 POT
Reversed horn current (RHC)
Forward horn current (FHC)
Peak reduction due primarily to cross-section
difference
- In such case negative particles are focused by
the horns thus yielding an anti-neutrino beam.
- Not a lot of RHC running needed to make a nice
measurement of Dm223 - ?Possibility currently being studied by
collaboration.
13Summary Ongoing work
- MINOS could make the first observation of a
non-zero q13
- Developing a nearest neighbors ne selection which
already has the best performance. - ? Plenty of room for further improvement !
- Measuring the intrinsic beam ne background with
anti-neutrinos.
- Very interesting anti-neutrino physics can be
done in MINOS
- Raised possibility of running in reversed horn
current mode to measure Dm223 - ? Situation being considered by collaboration.
14Backup
15MINOS Physics Goals
- Test the nm disappearance hypothesis
- Measure Dm232 sin2(2q23) precisely
- PRL 97, 191801 (2006)
- Provide high statistics discrimination against
other disappearance models (neutrino decay etc).
- Search for subdominant ne appearance
- Compare n, n oscillations
- Neutrino/nucleon interaction physics
- Atmospheric neutrino oscillations
- PRD 75, 092003 (2007)
- PRD 73, 072002 (2006)
At MINOS baseline
- Cosmic ray physics
- hep-ex/0705.3815
16The NuMI Beam
Parabolic horn system designed at IHEP-Protvino
- Moveable target relative to horn 1 allows for
different beam configurations. - Designed for 1.867s cycle time, 4x1013
protons/pulse and 0.4MW.
Number of expected CC interactions at the FD (no
oscillations)
Beam
Target z position (cm)
FD Events per 1e20 pot
LE-10
-10
390
pME
-100
970
pHE
-250
1340
17The MINOS detectors
NEAR DETECTOR
FAR DETECTOR
veto shield
coil
coil
5.4 kton mass 484 scintillator/steel planes
1 kton mass 282 steel and 182 scintillator planes
- Functionally identical detectors
- Iron-scintillator sampling calorimeters.
- Magnetized steel planes B ? 1.2T
beam
- GPS time stamping to synchronize FD with ND/beam.
18Systematic uncertainties
- Systematic uncertainties obtained by generating
MC with the following systematic shifts and using
it as fake data, with standard oscillation
parameters. - The three largest uncertainties were included as
nuisance parameters in the oscillation fit.
Uncertainty
?m2 (10-3 eV2)
sin2(2q23)
Near/far normalisation (4)
0.065
lt0.005
Abs. shower energy scale (10)
0.075
lt0.005
NC normalisation (50)
0.010
0.008
All other
0.040
lt0.005
Total sys. (quad. sum)
0.11
0.008
Statistical
0.17
0.080
19Oscillation Fit
Data sample
Observed
Expected (no osc.)
Observed /expected
nm (all E)
563
738 30
0.74 (4.4s)
496 20
nm (lt10 GeV)
310
0.62 (6.2s)
350 14
nm (lt5 GeV)
198
0.57 (6.5s)
20Allowed parameter space
Best fit values
21Calibration
- Overall energy scale set by Calibration Detector
CALDET
- Mini-MINOS detector at CERN
- Measured e/m/p/p response
- Light injection system (PMT gain)
- Cosmic rays (strip to strip and inter-detector)
Energy resolution (E in GeV) Hadrons 56 /
vE ? 2 Electrons 21 / vE ? 4 / E