conventional neutrino beams

Conventional Neutrino Beams

Deborah HarrisNuFact05 Summer Institute

Anacapri, ItalyJune 12-13, 2005

12-13 June 2005 Deborah Harris, Conventional Neutrino Beamlines 2

Fundamentals

• Conventional Neutrino Beam

• Neutrino Factory


Using Pions to make Neutrinos

Major Components:•Proton Beam•Pion Production Target•Focusing System•Decay Region•Absorber•Shielding…

Most ’s from 2-body decays:

→

K+→

Most e’s from 3-body decays:

→ee

K+→ee

energy is onlyfunction of

angle and energy


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 neutrino beam you want, the higher energy protons you have to start with…

• Proton Sources around the world…Name Proton Energy

(GeV)

p/yr Power

(MW)

Neutrino Energy

(GeV)

KEK 12 1e20/4 0.0052 1.4

FNAL Booster 8 5e20 0.05 1

FNAL

Main Injector

120 2.5e20 0.25 3-17

CNGS 400 4.5e19 0.12 25

J-PARC 40-50 1.1e21 0.75 0.77

BNL AGS 28 1.2e21 0.5-1.3 1-2


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 MN:

• 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)


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

Target Material

Shape Size

(mm)

Length (cm)

Mini-BooNE

Be cylinder 10 70

K2K Al cylinder 30 66

MINOS graphite ruler 6.4x20 90

CNGS carbon ruler 4mm wide

200

J-PARC graphite cylinder 12-15 mm

90

BNL AGS

Carbon-carbon

cylinder 6.4mm to 12mm

60cm to 80


Target Photo Album

CNGSImage courtesy of Bartoszek

Engineering.

NuMI

MiniBooNE

Shapes are similar, but cooling methods vary…some water cooled, some air cooled


Focusing Systems

• Want to focus as many particles as possible for highest neutrino flux

• typical transverse momentum of secondaries:

approximately QCD, 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—has been done with High Energy neutrino

beams, but focus in vert. or horiz.


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 direction

but has a size proportional to 1/r

How do you get around this? (hint: pt B l )


What should the B-Field be?

• Make the particles at high radius go through a field for longer than the particles at low radius. (B1/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

• For the record, there are also conical horns—what effect would conical horns have?

FROM TO

tune

outert p

r

lr

cr

Iep

2

20

2


Tuning the Neutrino Beam Energy

• The farther upstream the target is, the higher momentum the horns can “perfectly focus”..see this by considering

( /kt/4e20 p)

CC

evt

s / k

t / 4

e20

p / G

eV

l

Rpp

r

lr

cr

Iep tunetune

outert

2

20

2As l gets longer, then ptune gets higher for the same R


Horn Photo AlbumLength

(m)

Diameter (m)

# in beam

K2K 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

BNL 2.2,1.5 up to .3 2 MiniBooNE

CNGS

K2K

T2K Horn 1

NUMI

Horn World Record (so far): MiniBooNE horn pulsed for 100M pulses before failing


•D

esig

ning

wha

t pro

vide

s th

e 18

0kA

is a

s im

port

ant a

s de

sign

ing

the

horn

itse

lf!


What happens if you have 2 Horns?

• Can pretty much predict components of spectra just from apertures of horns.

~ pT/p = rneck / zhorn.

Overfocused by Horn 1Underfocused by Horn 1Focused by Horn 1, through 2Hits only Horn 2Goes through Horns 1, 2

p

Rneck(cm)

Zhorn(meters)

Max pion momentum

focused (GeV)

Energy

(GeV)

Horn 1 0.9 ~1.0 ~16 6

Horn 2 4.0 10 38 15


Are there ways to change (lower) the neutrino energy?

• Reduce Current in the horns– Yes, but this mostly just gives you fewer neutrinos

in the peak but the same number in the tail

• Move target closer to the horn– Yes, but eventually you hit the inner conductor

• What happens if you move the detector off the main axis of the beamline?

B(in tail)

+ (in peak)p


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 to e oscillation searches,

backgrounds spread over broad energies


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 e 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 50m 1.8m

K2K 200m Up to 3m

MINOS 675m 2m

CNGS 1000m 2.45m

T2K 130m Up to 5.4m

BNL 200m Up to 4m

T2K Decay Region:Can accommodate off axis Angles from 2 to 3 degrees


Decay Pipe Photo Album

CNGST2K

NUMINUMINUMI


Decay Pipe CoolingSlide courtesy C.K.Jung


Beamline Decay Pipe Comparison

Length E(GeV) y y e(theoretical)

MiniBooNE 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%

T2K 130m 9 0.47 0.2% 0.10%

BNL 200m 5 0.72 0.6% 0.3%

cE

cLmy

2

Let y (y) be the number of pion (muon) lifetimes in one decay pipe…


Decay Pipe Effect Summary

05.0

01.0

rms

006.0

rms

Additional RMS

Loss from

Interactions

Filling Decay Pipe with Air: 0.007

1mm Aluminum Window: 0.002

9.01

12

22

Remember, for aFlux ratio of 0.9,


Absorbing Hadrons

• As proton power gets higher and higher, have to think more and more about what will collect all the un-interacted protons!

• MINOS Absorber (1kton):– Water-cooled Al core– Surround with Steel– Surround with concrete

• Note: for 1020 protons on target per year, roughly 1019 per year hit the absorber…

• For scale: NuTeV experiment “pre-oscillation era neutrino experiments” took about 3x1018 protons over entire run


Review of what was covered today

• Targets

• Horns

• Decay Volumes

• Hadron Absorber

Questions to answer tomorrow:

How can you look at what’s happening each time you send protons to the target?

How can you predict precisely how many neutrinos you are making?

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