Transcript Conventional Neutrino Beams

Accelerator Neutrino
Oscillation Physics
Lecture I
Deborah Harris
SUSSP
St. Andrews, Scotland
August 15, 2006
What have Accelerator-based
Experiments told us so far?
• No nm→nt mixing at high Dm2
– CHORUS
– NOMAD
• First Accelerator-based ne appearance: LSND
– Still remains to be confirmed or completely refuted
• Confirmation of “Atmospheric Neutrino Anomaly”
and improved precision on Dmatm2 (or Dm132)
– K2K: 1.4GeV, 250km
– MINOS: 3.5GeV, 735km
• Confirmation of limits on q13 from CHOOZ
– K2K
15 August 2006
Deborah Harris, Accelerator Neutrino Oscillation Physics Lecture I
2
What do we want Accelerator
Oscillations Experiments to tell us?
– Are there sterile Neutrinos?
– What is the larger mass splitting (Dm232)
– q13 and CP violation: are they non-zero?
– Neutrino Mass Hierarchy: are n’s like charged fermions?
15 August 2006
Deborah Harris, Accelerator Neutrino Oscillation Physics Lecture I
3
Goals of Long Baseline
Oscillation Measurements
• Measurements of “atmospheric neutrino oscillation
parameters”, Dm23 and sin22q23:
nm disappearance as a function of neutrino energy
P(nm→nm) = 1-sin22q23sin2(Dm232L/4E)
• Verify Oscillation Framework: nt appearance
P(nm→nt) ≈ sin22q23sin2(Dm232L/4E)
• Search for Sterile Neutrinos: Neutral Current
disappearance, looking for three distinct Dm2
• Searches for CP violation and understanding the neutrino
mass hierarchy: P(nm→ne) and P(nm→ ne)
L=Baseline, E=Neutrino Energy
15 August 2006
Deborah Harris, Accelerator Neutrino Oscillation Physics Lecture I
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P(nm→ne) on one slide (3 generations)
P(nm→ne)%
Minakata & Nunokawa JHEP 2001
P(nm→ne)=P1+P2+P3+P4
The ± is n or n
15 August 2006
Deborah Harris, Accelerator Neutrino Oscillation Physics Lecture I
5
Could you simplify please?
Note: this is for Dm122<<Dm232,
and for L/E such that sin2 (Dm232L/4E)=1
15 August 2006
Deborah Harris, Accelerator Neutrino Oscillation Physics Lecture I
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Outline for the rest of this talk
• To reach all of the goals, we will need several acceleratorbased experiments….
• At this point, you could hear a sequence of mini-talks about
the following experiments:
– K2K
– MINOS
– MiniBooNE
– OPERA
– T2K
– NOvA
And I would have earned my trip to Scotland…but that’s not the way I
think about these experiments…so I’ll talk about them all at once, step
by step
15 August 2006
Deborah Harris, Accelerator Neutrino Oscillation Physics Lecture I
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Measuring Oscillation Probabilities
with Accelerator-Based n Beam
N far  n  n x P(n m  n x ) x M far
m
Fnm: Neutrino Flux
(beamline design: lecture I)
• nx: Neutrino Cross Section (McFarland)
• xMfar: Signal efficiency  Detector Mass
(detector design: lecture II)
• How well have we done/can we do? (Lecture III)
•
15 August 2006
Deborah Harris, Accelerator Neutrino Oscillation Physics Lecture I
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Neutrino Beam Fundamentals
Cosmic Ray
• Atmospheric Neutrino Beam:
–
–
–
–
High energy protons strike atmosphere
Pions and kaons are produced
nm
nm
Pions decay before they interact
Muons also decay
p, K
μ
e
ne
• Conventional Neutrino Beam: very similar!
15 August 2006
Deborah Harris, Accelerator Neutrino Oscillation Physics Lecture I
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But we do more than just make pions…
Major Components:
•Proton Beam
•Pion Production Target
•Focusing System
•Decay Region
•Absorber
•Shielding…
15 August 2006
Most nm’s from 2-body decays:
n energy is only
function of
np angle and
p energy
Most ne’s from 3-body decays:
p+→m+nm
K+→m+nm
m+→e+nenm
K+→p0e+ne
Deborah Harris, Accelerator Neutrino Oscillation Physics Lecture I
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Proton Beam
• Rules of Thumb
– number of pions produced is roughly a function of “proton
power” (or total number of protons on target x proton energy)
– The higher energy n beam you want, the higher energy protons
you need…
Proton Source
Experiment
Proton
Energy
(GeV)
p/yr
Power
(MW)
KEK
K2K
12
11020/4
0.0052 1.4
FNAL Booster
MiniBooNE
8
5 1020
0.05
1
FNAL
Main Injector
MINOS and
NOvA
120
2.51020
0.25
3-17
CNGS
OPERA
400
0.45
1020
0.12
25
J-PARC
T2K
40-50
111020
0.75
0.77
15 August 2006
Neutrino
Energy
(GeV)
Deborah Harris, Accelerator Neutrino Oscillation Physics Lecture I
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Directing Protons is not trivial…
• Example from NuMI: extract
beam from between two other
beamlines, then make it point
down at 3.5o so it comes
through the earth in Soudan
Minnestota, 735km away:
• Example from T2K: Proton
source on prime real estate,
direction to K2K determined,
need to bend HE protons in
small space: “combined
function” magnets (D and Q)
15 August 2006
Deborah Harris, Accelerator Neutrino Oscillation Physics Lecture I
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Integrated proton power vs time…
1.E+14
Beam Dose (Joules)
1.E+13
1.E+12
1.E+11
ANL
FNAL Main Ring
LSND
Nomad/ CNGS
Chorus goal
BNL
CERN PS
CERN SPS
IHEP
LAMPF
KEK
FNAL Booster
FNAL NuMI
MINOS
goal
First MINOS
Restults (1020)
FNAL TeV
1.E+10
K2K
MiniBooNE
1.E+09
2n
flavors
Discovery
of NC’s
1.E+08
1960
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1965
1970
1975
1980
1985
1990
1995
2000
2005
Plot courtesy
Sacha
Year Oscillation
Deborah Harris, Accelerator Neutrino
Physics Lecture
I
2010
Kopp 13
Neutrino Production Targets
• Have to balance many
competing needs:
– The longer the target, the
higher the probability the
protons will interact
– The longer the target, the
more the produced
particles will scatter
– The more the protons
interact, the hotter the
target will get—targeting
above ~1MW not easy!
– Rule of thumb: want target
to be 3 times wider than +1 sigma of proton beam
size
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Target
Material
Shape
Size
(mm)
Length
(cm)
MiniBooNE
Be
cylinder
10
70
K2K
Al
cylinder
30
66
MINOS
graphite
ruler
6.4x20
90
NOvA
graphite
ruler
>6.4
90
CNGS
carbon
ruler
4mm
wide
200
J-PARC
graphite
cylinder
12-15
mm
90
Deborah Harris, Accelerator Neutrino Oscillation Physics Lecture I
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Target Photo Album
MiniBooNE
Image
courtesy of
Bartoszek
Engineering.
Shapes are similar, but cooling methods
vary…some water cooled, some air cooled
CNGS
NuMI
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Deborah Harris, Accelerator Neutrino Oscillation Physics Lecture I
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Focusing Systems
• Want to focus as many particles as possible for
highest neutrino flux
• Typical transverse momentum of secondaries:
approximately LQCD, or about 200MeV
• Minimize material in the way of the pions you’ve just
produced
• What kinds of magnets are there?
– Dipoles—no, they won’t focus
– Quadrupoles
• done with High Energy neutrino beams
• focus in vertical or horizontal, need pairs of them
• they will focus negative and positive pions simultaneously
15 August 2006
Deborah Harris, Accelerator Neutrino Oscillation Physics Lecture I
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What focusing would work best?
• Imagine particles flying out from a target:
– When particle gets to front face of horn, it has transverse
momentum proportional to radius at which it gets to horn
B Field from line source of current is
in the F direction
but has a size proportional to 1/r
How do you get around this? (hint: pt  B l )
15 August 2006
Deborah Harris, Accelerator Neutrino Oscillation Physics Lecture I
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What should the B-Field be?
FROM
TO
• Make the particles at high radius go through a field for
longer than the particles at low radius. (B1/r, but make
dl  r2)
•
•
•
Horn: a 2-layered sheet conductor
No current inside inner conductor, no current outside outer conductor
Between conductors, toroidal field proportional to 1/r
pt
•
em 0 I
r 2l

 2
2pcr
router
 ptuneq
There are also conical horns—what effect would conical horns have?
15 August 2006
Deborah Harris, Accelerator Neutrino Oscillation Physics Lecture I
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Tuning the Neutrino Beam Energy
• The farther upstream the target is, the higher momentum pions
the horns can “perfectly focus”..see this by considering
em 0 I r 2 l
R
pt 
 2  ptuneq  ptune
2pcr router
Z
2R
z
As z gets larger, then ptune
gets higher for the same R
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Deborah Harris, Accelerator Neutrino Oscillation Physics Lecture I
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Length
(m)
Diameter
(m)
# in
beam
2.4,2.7
0.6,1.5
2
MBooNE ~1.7
~0.5
1
NuMI
3,3
0.3,0.7
2
CNGS
6.5m
0.7
2
T2K
1.4,2,2.5
.47,.9,1.4
3
K2K
Horn Photo Album
MiniBooNE
K2K
NUMI
T2K Horn 1
15 August 2006
CNGS
Horn World Record (so far):
MiniBooNE horn pulsed for
100M pulses before failing
Deborah Harris, Accelerator Neutrino Oscillation Physics Lecture I
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Horn Question:
• Given two horns that
dpt (GeV )  0.3B(T )l (m)
are each 3m long and
2
16cm diameter, what
m 0I
 7 I ( Am ps)  r 


kind of current would B(T )  2pr  2  10
r (m)  rmax 
you need to give a
200MeV kick to
dpt (GeV ) 2rmax
1
produced secondary I ( Am ps) 
0.3
l 2  107
particles?
1) 2000 Amps
2) 20,000 Amps
3) 200,000 Amps
For pion going through “sweet spot”, assume r/rmax=1/2
For MINOS, for example: (2 horns)
r=0.08m, l=3mx2: so for a 200MeV pt kick, I=180kAmps!
15 August 2006
Deborah Harris, Accelerator Neutrino Oscillation Physics Lecture I
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15 August 2006
Deborah Harris, Accelerator Neutrino Oscillation Physics Lecture I
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Designing what provides the 180kA is almost as
important as designing the horn itself!
What happens if you have 2 Horns?
p
Overfocused by Horn 1
Underfocused by Horn 1
Focused by Horn 1, through 2
Hits only Horn 2
Goes through Horns 1, 2
qp
• Can predict components of
spectra from apertures of horns.
• qp ~ pT/p = rneck / zhorn.
Rneck
(cm)
Zhorn
(meters)
Max pion
momentum
focused (GeV)
um
Energy
(GeV)
Horn 1
0.9
~1.0
~16
6
Horn 2
4.0
10
38
15
15 August 2006
Deborah Harris, Accelerator Neutrino Oscillation Physics Lecture I
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How do these pions (and Kaons) decay?
• In the center of mass of the pion: 2 body means isotropic decay,
neutrino only has one energy
• Now boost to the lab frame: you can show (easily) that
 =boost of pion in lab
q =angle between pion and n
• And furthermore, you can show (slightly less easily) that the
flux of neutrinos at a given location is simply
1
Fn  BR
4pL2
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 2

2 2
1
+

q




2
Thought question:
What about 3-body decays?
n Energy
n Flux versus Angle
Deborah Harris, Accelerator Neutrino Oscillation Physics Lecture I
24
Besides target location, how else can
you lower the neutrino energy?
• Reduce Current in the horns
– No, this just gives you fewer neutrinos in the peak
p+ (in peak)
p
p+(in tail)
Events (arb)
B
MINOS Far
Detector Spectra
For 3 different
Horn Currents
n Energy (GeV)
15 August 2006
Deborah Harris, Accelerator Neutrino Oscillation Physics Lecture I
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Thought Question
• How much does peak n rate on axis change when
you input half as much current?





1 +  2q 2


N  
2 2
1
+

q




3
200MeV
q ( I  0) 
mp
Events (arb)
 2
Fn  
2 2
1
+

q

2
(Note: 2.53=16, 1.53=3.4)
15 August 2006
N  F
 E
200MeV 
I 
q ( I ) 
1


mp
 I peak 
I=200kA, 100kA, 0kA
At MINOS (735km)
n Energy (GeV)
Deborah Harris, Accelerator Neutrino Oscillation Physics Lecture I
26
Off Axis Strategy
• Trick used by T2K, NOvA (first
proposed by BNL)
– Fewer total number of neutrino events
– More at one narrow region of energy
– For nm to ne oscillation searches,
backgrounds spread over broad energies
Only a consequence of 2-body decay!
15 August 2006
Deborah Harris, Accelerator Neutrino Oscillation Physics Lecture I
27
•
Decay
Regions
How long a decay region you need
(and how wide) depends on what the
energy of the pions you’re trying to
focus.
•
The longer the decay region, the more
muon decays you’ll get (per pion
decay) and the larger ne
contamination you’ll have
•
Again, tradeoffs between evacuating
the decay volume and needing thicker
vacuum windows to hold the vacuum
versus filling the decay volume with
Helium and thin windows, or with air
and no windows…
Length
Diameter
MBoone
K2K
MINOS
CNGS
50m
200m
675m
1000m
1.8m
Up to 3m
2m
2.45m
T2K
130m
Up to
5.4m
T2K Decay Region:
Can accommodate off axis
Angles from 2 to 3 degrees
15 August 2006
Deborah Harris, Accelerator Neutrino Oscillation Physics Lecture I
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Decay Pipe Photo Album
T2K
NUMI
15 August 2006
NUMI (upstream)
CNGS
NUMI (downstream)
Deborah Harris, Accelerator Neutrino Oscillation Physics Lecture I
29
Decay Pipe Cooling
15 August 2006
Slide courtesy
C.K.Jung
Deborah Harris, Accelerator Neutrino Oscillation Physics Lecture I
30
Beamline Decay Pipe Comparison
F(n e ) Lmm c  1
1 
 y


+1
p
F(n m ) Ep t m  e  1
yp 
You can all show that
neglecting things hitting
the side of the decay pipe…
Lmp c 2
yp=the number of pion lifetimes in one decay pipe… yp 
Ep ct p
Length
MiniBooNE
Ep (GeV)
yp
ym
F(ne)/F(nm)
(theoretical)
50m
2.5
0.36
0.3%
0.15%
K2K
200m
3.5
1.0
0.9%
0.5%
MINOS
675m
9
1.3
1.2%
0.8%
CNGS
1000m
50
0.36
0.3%
0.15%
130m
9
0.47
0.2%
0.10%
T2K
15 August 2006
Deborah Harris, Accelerator Neutrino Oscillation Physics Lecture I
31
Neutrino Beam Divergence
• For a perfectly focused monochromatic pion beam,
how wide is the neutrino beam?
1
Fn  BR
4pL2
At what q is Φ(q)= Φ(0)/4?

1

2 2
1
+

q

1
q

15 August 2006
2

1
 
4

 2

2 2
1
+

q




2
Where is Φ(q)= Φ(0)x0.99?

1

2 2
1
+

q

0.07
q
2

  0.99


Deborah Harris, Accelerator Neutrino Oscillation Physics Lecture I
32
Follow Up Question:
• How much additional divergence is added due to
multiple scattering?
13.6 MeV x
rms 
rms 
cp
0.1

– Filling the decay pipe with air?
x=ct=(7.8m) X0=304m
– a 1mm Aluminum window?
x=1mm
15 August 2006
X0=89mm
X0
x
X0
rms 
0.1

rms 
* .06 
0.01
Deborah Harris, Accelerator Neutrino Oscillation Physics Lecture I

33
Additional Question
• How does the loss of neutrinos from divergence compare
to the loss of neutrinos due to pion interactions?
e
 x / lINT
 1
x
l INT
• Filling the decay pipe with Air:
x=ct=(7.8m) lint=692m/0.66 Lose 0.007
• 1mm Aluminum Window
x=1mm lint=390mm/0.66 Lose 0.002
15 August 2006
Deborah Harris, Accelerator Neutrino Oscillation Physics Lecture I
34
Decay Pipe Effect Summary
Additional
RMS (qrms)
Loss from
Interactions
Filling Decay Pipe
with Air:
0.006/sqrt()
0.007
1mm Aluminum
Window:
0.01/
0.002
Where are they =?
3
0.3
Remember, for a
Flux ratio of 0.99,

1

2 2
1+  q
0.07

2

  0.99


Ep (GeV) p (peak)
Moral of this story:
Different p energies imply
very different decay pipe
choices
15 August 2006
choice
MiniBooNE
2.5
18
air
K2K
3.5
26
He
MINOS
9
66
vacuum
CNGS
50
370
vacuum
T2K
9
67
He
Deborah Harris, Accelerator Neutrino Oscillation Physics Lecture I
35
Absorbing Hadrons
• As proton power gets higher and
higher, have to think more and more
about what will collect all the uninteracted protons!
• MINOS Absorber (1kton):
– Water-cooled Al core
– Surround with Steel
– Surround with concrete
MINOS
• CNGS Absorber
– Graphite core + Al cooling modules
– Surround with cast iron
– Surrounded by rock
• Note: for 1020 protons on target per
year, roughly 1019 per year hit the
absorber…
15 August 2006
CNGS
Deborah Harris, Accelerator Neutrino Oscillation Physics Lecture I
36
How can you measure the beam
performance?
protons
Pions+…
Muons+…
Neutrinos
• Remnant Proton Measurements
– Tales from the front line: NuMI and the target leak
• Muon Measurements
– 7o muon spectrometer (MiniBooNE)
– “Range stack” Muon Monitor system (MINOS)
15 August 2006
Deborah Harris, Accelerator Neutrino Oscillation Physics Lecture I
37
Neutrino Beamline Instrumentation
• Proton Beam
–
–
–
–
Number of Protons on Target
Position and angle
Spot size of beam on target
Proton Losses before target
• Target
– Position and angle
– Is it intact?
– Temperature
• Horns
–
–
–
–
Position and angle
Current
Is it intact?
Temperature
• Absorber
– Temperature
15 August 2006
Deborah Harris, Accelerator Neutrino Oscillation Physics Lecture I
38
What about seeing the Protons at the
end of the decay pipe?
• Proton spot size at end of pipe is large: cannot just put
in a new secondary position monitor
• Proton rates are now very intense: can use ionization
chambers, but they must be very resistant to radiation
damage, and can be low gain
• Question: what else makes it
down to the end of the
decay pipe?
– Muons from pion decay
– Undecayed pions
– Secondary shower particles
15 August 2006
Deborah Harris, Accelerator Neutrino Oscillation Physics Lecture I
39
Seeing protons at end of pipe
No target in the way
Target in the way
For most beamlines, this
“hadron monitor” is really a
proton monitor: it tells you
about the protons and the
target, but not about how well
you are making neutrinos
15 August 2006
Deborah Harris, Accelerator Neutrino Oscillation Physics Lecture I
40
Lesson Learned: be prepared for disasters…
Look at what is
between target
and baffle by
shooting protons
there!
• Leaky Target at NuMI
– the target has pipes around it that carry water to cool it
– March 2005, discovered a leak: speculate the target surrounded by water…
– Use Hadron Monitor to verify that water was there, and to check that it hasn’t
reappeared since we solved the problem…
15 August 2006
Deborah Harris, Accelerator Neutrino Oscillation Physics Lecture I
41
Monitors to Study n Beam (MINOS)
m+
nm
m+
m+
p
p+
Hadron Monitor: sees uninteracted protons after decay pipe
Muon Monitors: 3 different depths means three different muon
momentum spectra
15 August 2006
Deborah Harris, Accelerator Neutrino Oscillation Physics Lecture I
42
Getting to Neutrino Spectrum from
Muon Spectrum (MINOS)
• As you get to higher muon energies, you are
looking at higher pion energies…which in turn
mean higher neutrino energies…
15 August 2006
Deborah Harris, Accelerator Neutrino Oscillation Physics Lecture I
43
Muon Monitors in Different Energy
Neutrino Beams
•
•
Graphs courtesy S. Kopp
•
By looking at the rates in the three different muon
detectors, can see how the energy distributions of
the muons changes
Can study neutrino fluxes by moving the target and
seeing how you make more high energy neutrinos
the farther back you move the target
Can study fluxes by changing the horn current and
see how you make more low energy neutrinos as
you increaste the horn current.
15 August 2006
Deborah Harris, Accelerator Neutrino Oscillation Physics Lecture I
44
Oscillation Experiments: Beams
past, present, and near future…
Exp’t
n Energy
(GeV)
MiniBooNE
1.2
K2K
1.4
MINOS
2-6
OPERA
15-25
T2K
0.7
NOvA
2
MiniBooNE
OPERA
T2K
K2K
15 August 2006
Deborah Harris, Accelerator Neutrino Oscillation Physics Lecture I
MINOS
NOvA
45
Conventional Neutrino Beam Summary
Major Components:
•Proton Beam
•Production Target
•Focusing System
•Decay Region
•Shielding
•Monitoring
15 August 2006
Ways to Understand n Flux:
Hadron Production
Proton Beam measurements
Pion Measurements
Muon Measurements
at angles vs momentum
at 0o versus shielding
Deborah Harris, Accelerator Neutrino Oscillation Physics Lecture I
46
What else you can do with muons:
Measure K/p ratio in Beam
 ne’s from muon decay constrained by nm spectrum (since they are part
of the same channel)
• Kaons have no such constraint
• Remember problem set: to get the ne /nm
Ratio you would also need to know the K/p production ratio (and focusing
differences)
Any way this can be measured in the beam? Beam too hot to add Cerenkov
counters to get track/track information
Decay
Maximum pt
Think 2-body decay kinematics:
Center of Mass
15 August 2006
p+→m+nm
30MeV
K+ → m+nm
236MeV
KL→ pmnm
216MeV
Lab Frame
Deborah Harris, Accelerator Neutrino Oscillation Physics Lecture I
47
Example from MiniBooNE
Backgrounds from muons
that scatter in the dirt/collimator
• By adding collimator and spectrometer at 7o, they will
measure
 p/K ratio from difference in peaks
 K/KL ratio from m+ versus m-
15 August 2006
Deborah Harris, Accelerator Neutrino Oscillation Physics Lecture I
48
Measuring p angular distribution in real
beamline
• K2K Gas Cerenkov counter: measures angular
distribution of Pions as function of momentum
• Located right
after horns
• Works for pions
above 2GeV
15 August 2006
Deborah Harris, Accelerator Neutrino Oscillation Physics Lecture I
49
Measuring p angular distribution in real
beamline
15 August 2006
Deborah Harris, Accelerator Neutrino Oscillation Physics Lecture I
50