Neutrino%20Flavor%20Oscillations%20at%20the%20Fermilab%20Main%20Injector

1
Neutrino Flavor Oscillations at the Fermilab Main
Injector
Neutrino News from Fermilab
SMU Physics Department Seminar 22 October 2007
Sacha E. Kopp University of Texas at Austin
2
Quantum Mechanics and Double Slit Experiments

• Particles exhibit wave interference
• Indeterminacy (pattern lost if measure which
  slit)
• One particle vs ensemble
• Interpretation probability waves

e-
?
?
A Tonomura et al., Am. J. of Phys. 57 117-120
(1989)
3
What We Observe at the Screen Lepton Number

• Why must the muon decay weakly?
• Long lifetime result of heavy W
• Lifetime t2ms
• m- ? e- ne nm
• More favorable decay
• m- ? e- g
• Electromagnetic interaction
• Should have lifetime 10-18 sec
• Observed rate lt 1.2 ? 10-11 of all m decays
• (M.L. Brooks et al, Phys. Rev. Lett. 83, 1521
  (1999)

Lm 1 0 0 1 Le
0 1 -1 0
Lepton Number!
Lm 1 0 0 Le 0
1 0
4
ns Have Lepton Number

• Nuclear b decay has e, reactors produce ne
• Reines Cowen expt to observe free ne
• ne p ? e n

Reines Cowan, Science 124, 103 (1956), Phys.
Rev. 113, 273 (1959)

• Contrast to failed experiment by R. Davis
• ne 37Cl ? e- 37Ar

R. Davis, Phys. Rev. 97, 766 (1955)
NOT OBSERVED
5
ns Have Lepton Number (contd)
Saw lots of

• In 1957, Brookhaven AGS and CERN PS first
  accelerators intense enough to make n beam
• p Be ? p X, p ? m n
• 1962 Lederman, Steinberger, Schwartz propose
  experiment to see
• nm N? m- X (Phys.Rev.Lett. 9, 36 (1962))

n
nm N? m- X
Saw none of
n
ne N? e- X
6
Weak Interactions Conserve Lepton Number
m
Lepton Conserved
Lepton Conserved
p
nm
m-
nm
p ? m nm
?
nm N ? m- X

• Many expt confirmations of Lepton number
  conservation (m, t decays, etc)
• Neutrino interactions conserve lepton number too.
• But what happens to the neutrino in between
  creation/annihilation, while in flight?

7
Neutrino Double Slit Experiment

• We create and observe nm? ne ? via weak
  interaction
• But suppose ns have mass ? 0. Can label them by
  
• n1 ? -- the heavier mass state with m m1.
• n2 ? -- the lighter mass state with m m2.
• We do not know in which mass state the neutrino
  propagates (its an unknown slit) must assume
  both ? interference!

n1
nm
nm or ne?
n2
sin21.27Dm2L/En
8
A Mixture of n States

• How can a quantum state produced at tt1 appear
  as a different quantum state at tt2?
• Mass eigenstates need not coincide with
  weak eigenstates (two indep. bases)
• ne? cosq n1? sinq n2?
• nm? - sinq n1? cosq n2?

nm
n2
q
ne
q
n1

• Reminiscent of crossed polarizers.

9
Neutrinos have 3 slits

• The nt discovered ? ?3 lepton flavors must
  exist
• (K. Kodama et al., Phys. Lett. B504 218 (2001)
• Measurements of Z0 boson resonance ? only
  2.983?0.009 lepton flavors participate in weak
  interaction
• S. Eidelman et al., Phys. Lett. B592, 1 (2004)
  
• With 3 n families we expect
• 3 mixing probabilities between flavor i ? j
• 2 distinct mass splittings

10
n Mixing Orthodoxy

• If you believe in flavor mixing, there must be a
  3?3 unitary transformation to mass states

cij ? cosqij
sij ? sinqij

• In the quarks, mixing matrix has phase d?0
  responsible for CP.

But hopefully this picture is wrong or
incomplete! (Peggy Lee Is that all there is?)
11
Two Detector n Experiments
FNAL CCFR experiment, 1982-83
CERN CHARM/CDHS experiments, 1982-83

• Near detector predicts n energy spectrum and rate
  at far detector (asssuming an
  absence of oscillations)
• Greatly reduces systematic uncertainties due to
  calculating beam flux.

12
Interpretation of Oscillation Results
E0 /3 2nd max
E0 /5
E0 1st max
Oscillation Probability
Neutrino Energy

• Oscillations into unknown flavor causes dip in
  obvserved spectrum.

13
Long Baseline n Oscillation Exps

• Reproduce atmospheric n effect using accelerator
  beam
• L 100s kilometers to match oscillation
  frequency

Near Detector 980 tons
Far Detector 5400 tons
MINOS (Fermilab to Minnesota) L 735 km 2005
K2K (KEK to SuperK) L 250 km Concluded
CNGS (Cern to Gran Sasso, Italy) L 750 km
tested 2006, run 2008
14
The Challenge of Long Baselines
LSND
Nomad/ Chorus
MINOS goal
this analysis
K2K
MiniBooNE
2 n flavors
Discovery of NCs
S. Kopp, Accelerator Neutrino Beams, Physics
Reports 439, 101 (2007), arXivhep-ex/0609129
15
The NuMI Beam
Main Injector Accelerator
Plan View
Extraction magnets
Access Tunnel
Target Hall
Evacuated Decay Volume
n beam
Hadron Absorber
target
Near Detector Hall
focusing horns
Muon Alcoves
Elevation View
Surface Building
Surface Building
Ground Level
Hadron Absorber
Service Shaft
Target Hall
Evacuated Decay Volume
n beam
V118 Bend
Carrier Tunnel
Near Detector Hall
V108 Bend
Muon Alcoves
16
Neutrinos at the Main Injector

• MI ramp time 1.5sec
• MI is fed 1.56ms batches from 8 GeV Booster
• Simultaneous acceleration dual extraction of
  protons for
• Production of p (Tevatron collider)
• Production of neutrinos (NuMI)
• NuMI designed for
• 8.67 ms single turn extraction
• 4?1013ppp _at_ 120 GeV
• Antiproton Production
• Requires bunch rotation (Dt1.5nsec)
• Merges two Booster batches into one batch
  (slip-stacking)

Batch 2
Batch 3
½ Batch (empty)
Main Injector
Batch 1
Batch 4
½ Batch (empty)
Batch 5
Batch 6
Pbar Target
NuMI
17
Bend out of MI
Lambertsons
NuMI Proton Beam Line
Final bend to Soudan
18
Target Hall
Target Hall after Contractor completion
Decay pipe
Target/baffle Module installed
Target Hall shielding installation
19
Focusing Horns
Main horn field between conductors
figure A. Marchionni, J. Hylen
Horn 2 suspended from shielding module being
lowered into shielding pit
Hall probe moving along horn axis
20
MINOS Near Detector
21
MINOS Far Detector
MINOS Far Detector magnetized Fe-scintillator
calorimeter segmented scint for X, Y
tracking 485 planes, 8m diam, 5400 tons
22
Raison dÊtre for a Northern MinnesotaExperiment!
Austin American-Statesman Newspaper, Sunday,
April 18, 2004
23
Neutrino Beams 101
Beam MC
i
X
i
i
24
Consequence Flux Uncertainty
Error (Far/Near)
figure courtesy Ž. Pavlovic
25
Neutrino Beams 102
Low Energy
proton
target
Horn 1
Horn 2
Pions with pT300 MeV/c and p5 GeV/c p10
GeV/c p20 GeV/c
Vary n beam energy by sliding the target in/out
of the 1st horn
figure courtesy Ž. Pavlovic
26
Opportunity Flexible Beam Energy
M. Kostin et al, Proposal for Continuously-
Variable Neutrino Beam Energy,
Fermilab-TM-2353-AD (2002)
figure courtesy Ž. Pavlovic
27
Neutrino Beams 103
p
to far Detector
(stiff)
target
qf
p
qn
(soft)
Decay Pipe
ND

• ND and FD spectra similar, but not identical

Beam MC
Near Detector
LE Beam
figure courtesy M. Kostin
28
Consequence Extrapolating to the FD

• ND and FD spectra are similar, but not identical
• If they were identical, (NuMI approximating a
  point source) could say
• where
• ?FN (Znear/Zfar)2

Far Detector MC Near Detector MC (1.210-6)
29
Extrapolating to the FD (contd)

• The ND sees the NuMI beam as an extended line
  source of neutrinos, while FD

• sees a point source,
• where En ? 0.43 Ep.
• Better than this need a MC to evaluate ?FN.
• Angular correlations in decay
• Pis that interact before decaying

Horn 1 neck
Edge of Decay Pipe
weighted by p lifetime
Horn 2 neck
solid angle
?FN
NuMI Beam MC
30
Blind Analysis Procedure

• Intensive checks of ND data
• neutrino interaction identification in ND FD
• backgrounds, efficiencies, etc.
• beam modeling how well can we extrapolate flux
  measured in ND to the expected flux in the FD??
• Much to be learned from the ND Data
• Not much statistics in the FD
• Not much to learn
• Opportunity to bias ourselves

31
Step 1 Look at ND Data

• Hope no gross disagreements with beam MC
• See if neutrino identification is OK

32
ND Events Observed
First Observed Neutrino Events in Near MINOS
Detector January 21, 2005 nm Fe? m X
33
Neutral Current nm Backgrounds

• Analysis requires an energy spectrum measurement.
• In nmFe?m X interaction, reconstruct
  EnpmEX,
• Cant see full neutrino energy in NC nmFe?nm X
  interactions.

CC (no osc.)
MINOS MC
Hypothetical MINOS Data
CC (with osc.)
NC Background
Visible Neutrino Energy (GeV)
34
Coping with High Intensity

• 10-20 events/spill in the ND (cf 10-4/spill in
  the FD!)

In one spill (5?1012 ppp)
Time (msec)
35
Beam is Stable
36
ND Compared to Beam MC

• These plots show the beam spectrum as dead
  reckoned by Fluka2005 our tracking MC through
  the beam line.
• Errors bars from the beam systematics (dominated
  by p/K production in the target).
• Some real apparent contradictions? MC is low in
  the LE beam, but high in the ME beam.

High Energy Beam Setting
Medium Energy Beam Setting
Low Energy Beam Setting
MINOS Data
Calculated n flux
figure courtesy P. Vahle
37
ND Spectra After Tuning
figure courtesy Ž. Pavlovic, P. Vahle
38
Step 2 Decide How to Extrapolate ND ? FD

• FD Spectrum (F/N ratio) ? ND Spectrum
• NEn Number of events at given energy of
  neutrino in ND or FD
• i particular energy bin
• Tests on mock data to ensure no biases,
  understand systematics

39
Alternative ExtrapolationMatrix Method

• A. Para M. Szleper, arXivhep-ex/0110032

40
Checks of the Fitting

• MC Mock data sets
• 100 experiments
• each 1020 POT exposure
• Studies of
• biases
• statistical precision

figures courtesy D. Petyt
Best Fit c2
Best Fit sin2(2q)
Best Fit Dm2 (eV2)
41
Systematic Uncertainties
Uncertainty Shift in ?m2 (10-3 eV2) Shift in sin2(2?)
Near/Far norm. (livetime, fid vol) ?4 0.065 lt0.005
Absolute hadronic energy scale ?10 0.075 lt0.005
NC contamination ?50 0.010 0.008
All other systematic uncertainties 0.041 lt0.005
Total systematic (summed in quadrature) 0.11 0.008
Statistical error (data) 0.17 0.080
42
Step 3 Peek at the Far Detector Data( Box is
still closed)

• In 2006 analysis, question was Do ns
  disappear?
• unknown blinding function to hide most of the
  data
• Collaborators given free access to open data
  set
• Only got to see full data set once box was open
• In 2007 analysis, want unbiased Dm2, sin2(2q)
  measurement
• Access to all the data, but complete blinding of
  all rates
• Did not look at energy spectrum, so couldnt bias
  Dm2

43
Checks on the FD Data
Track Vertex in X (m)
Track Vertex in Y (m)
Track Vertex in Z (m)

• These are all CC neutrino events
• Rates blinded we dont know the normalization
• MC has been scaled to agree with data

44
Calibration
region used for calibration
figure courtesy N. Tagg

• Calibratrions based on stopping cosmic ray ms.
• Study ionization for 20-plane window upstream of
  stopping m location.

45
Example Events (I)

• These events taken from the open data sample in
  the FD (which we are permitted to look at in
  detail).
• En 3.0 GeV
• y Ehad/En0.3

46
Example Events (II)

• These events taken from the open data sample in
  the FD (which we are permitted to look at in
  detail).
• En 24.4 GeV
• y Ehad/En0.4

47
Example Events (III)

• These events taken from the open data sample in
  the FD (which we are permitted to look at in
  detail).
• En 10.0 GeV
• y Ehad/En0.3

48
Example Events (IV)

• These events taken from the open data sample in
  the FD (which we are permitted to look at in
  detail).
• En 2.1 GeV
• y Ehad/En0.1 (quasi-elastic?)

49
Example Events (V)

• These events taken from the open data sample in
  the FD (which we are permitted to look at in
  detail).
• En 18.7 GeV
• y Ehad/En0.9

50
Example Events (VI)

• These events taken from the open data sample in
  the FD (which we are permitted to look at in
  detail).
• En 3.3 GeV
• y Ehad/En0.6

51
Example Events (VII)

• These events taken from the open data sample in
  the FD (which we are permitted to look at in
  detail).
• En 25 GeV
• y Ehad/En0.6

52
Step 4 Look at All EventsOpen the Box
53
FD Events are In time and Uniform
Time Relative to Spill (msec)
54
Neutrino Energy Spectrum
Null Oscillation Hypothesis c2 /n.d.f 139.2/36
3.9
55
Oscillation Hypothesis Fit
c2/n.d.f 41.2/341.2
P(c2,n.d.f)0.18
56
Fair and Balanced
57
Fitting into the Unphysical Region
58
Compare 1.3 2.5 ?1020POT Datasets

• Reconstruction and selection method
• Changes number of events
• 2s change in ?m2
• Shower modeling
• ?m2 systematic decrease 0.0610-3eV2
• New data set fluctuates down

59
Our Long-term Goal
.
For Dm2 0.0020 eV2, sin2 2q23 1.0
Oscillated/unoscillated ratio of number of nm CC
events in far detector vs Eobserved
Expectation if Dm20.001eV2 Expectation if n
Decay Expectation if Extra Dimensions
Hypothetical MINOS Data
figure courtesy D. Petyt
60
Off-Axis Beam from NuMI

• Possible to measure rates P(nm?ne)? P(nm?ne) due
  to
• CP violation
• ns propagating through matter
• Fermilab P929 (NOnA)

ATLAS
D?
NOnA
61
Competition in Japan
62
1st Demonstration of Off-Axis Beam
MiniBooNE
q
p, K
p beam
Decay Pipe

• NuMI ns sprayed in all directions.
• K?mn and p?mn decays lead to lower En at large
  decay angle

Total Calculated NuMI Beam flux
Calculated n flux from p Decays
110mrad to MiniBooNE
Calculated n from K Decays

• Opportunity to double-check our beam flux
  calculations using mature neutrino detector

figure courtesy Alexis Aguilar-Arévalo
Visible Neutrino Energy (GeV)
63
The Fermilab Neutrino Program

• Many ideas are now being discussed/proposed/built
• MINOS Precision oscillation parameters
• NOvA first observation of nm?ne, matter
  effects?
• MINErVA precision scattering cross sections
• MicroBooNE Liquid Argon TPC RD
• NuSOnG weak mixing angle
• FNAL-DUSEL CP Violation in neutrinos?
• Project X accelerator would enable diverse program

Workshop on Physics Opportunities with the
Project X Accelerator Fermilab, Nov 16-17,
2007
64
The path forward is crystal clear
SMU student Yurii Maravin, Summer 1994
but very fragile indeed.
Prof. Thomas Coan, Fall 1993
65
The Blind Leading the Blind?
accelerator
double-beta
direct mn
Knowing in part may make a fine tale, but wisdom
comes from seeing the whole.
It Remains a World-Wide Effort to Interpret
Neutrino Disappearance and the Possibilities of
Neutrino Mass
atmospheric
LSND/MiniBooNE
reactor
solar
66
Conclusions

• MINOS rapidly progressing
• Construction complete after 6 years
• 3.5?1020 POT delivered
• First result confirms ns disappear
• Under oscillation hypothesis,
• Rich program of physics ahead
• Results on oscillations vs other new physics
• Search for rare osc. phenomena, like nm?ne, nm?ns
• Is nm?nt mixing maximal?
• Future experiments CP violation

67
Backup Slides
68
Alternatives for nm Disappearance
SuperK effect is combination of Dm2(solar) and
Dm2(LSND) Barenboim et al., hep-ph/0009247
Neutrinos propagating in Extra
Dimensions Barbieri et al., hep-ph/9907421
Neutrinos actually decay to lighter
states Barger et al., hep-ph/9907421
NuMI low energy beam
No osc.
oscillations
Barenboim
NuMI high energy beam

• Most think nm?nt looks like a good explanation of
  the atmospheric n depletion, but one must be open
  to other possibilities given
• The 3 Dm2 problem
• Naturalness, attraction of a nsterile GUTs
• Due skepticism of jumping to conclusions in hard
  experiments

69
Charged Current nm Selection
MINOS MC
MINOS MC
MINOS MC
Track length (planes)
Track length beyond Shower
Track Charge
Track Curvature/Resolution
Track Pulse Height / Plane
Y 1 pm/En

• Charged current events distinguished by
• muon track
• long event length
• Probability distribution function to reduce
  nm-NC bckgd to nm-CC sample.

70
Charged Current nm Selection (contd)
CC-like
Near Detector Data
rejected as NC like
Event Classification Parameter

• In LE beam, expect 89 efficiency, 98 CC purity

71
Tuning the Beam Spectra in (xF, pT)
LE10/170kA
LE10/185kA
LE10/0kA
Vary the horn current
LE10/200kA
LE100/200kA
LE250/200kA
Vary the targets location
72
F/N Ratio After Tuning

• Several tunings of the (xF, pT) spectra were
  attempted.
• All can accommodate the ND neutrino spectra.
• All yield similar tuned F/N ratio (within 2)

73
Charged Current nm Selection Variables
Track length (planes)
Track length beyond Shower
Curvature/Resolution
Track Pulse Height / Plane
Y 1 pm/En
Classification Parameter
74
Comparison with Unblinded MC
c2 /n.d.f 30.8/20 1.5
Reconstructed y?Ehad/En
No Osc. Osc. (Dm20.0024 eV2) MINOS Data