Exploring the physics frontier with nes and nms in MINOS - PowerPoint PPT Presentation

1 / 21
About This Presentation
Title:

Exploring the physics frontier with nes and nms in MINOS

Description:

Are there more than 3 neutrinos (sterile, heavier than Z)? Do neutrinos obey CP, CPT? ... Search for subdominant ne appearance. Compare n, n oscillations ... – PowerPoint PPT presentation

Number of Views:41
Avg rating:3.0/5.0
Slides: 22
Provided by: juanped
Category:

less

Transcript and Presenter's Notes

Title: Exploring the physics frontier with nes and nms in MINOS


1
Exploring 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 !
3
The 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

4
Event 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.

5
ne 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)
  • At MINOS baseline

? 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To be superseded soon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

6
Nearest 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?
  • Use simple discriminant
  • 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.

8
Beam 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
10
Technique 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 !

11
Other 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)
12
Reversed 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.

13
Summary 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
  • n?n transitions
  • Raised possibility of running in reversed horn
    current mode to measure Dm223
  • ? Situation being considered by collaboration.

14
Backup
15
MINOS 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
  • Test of CPT
  • 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

16
The 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
17
The 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.

18
Systematic 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
19
Oscillation 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)
20
Allowed parameter space
Best fit values
21
Calibration
  • Overall energy scale set by Calibration Detector
    CALDET
  • Mini-MINOS detector at CERN
  • Measured e/m/p/p response
  • In addition,
  • 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
Write a Comment
User Comments (0)
About PowerShow.com