Accelerator Neutrino Beamsas used in

cross sectionexperiments

Sacha E. Kopp

University of Texas

at Austin

The Big Picture

• Many come to this business from osc. expt

• Previous dedicated cross section experiment was in 1980’s.

• Let us agree that

• Oscillation experiments optimized differently. What is (E) ± (E)?

A Little Historical Foundation

G.T. Danby et al, Physical Review Letters 9 36 (1962)

Modern Beam

• Same physics principle

• But add focusing

• And add instrumentation

TargetHorns

Decay PipeAbsorber

Muon Monitors

Rock

μ+

π+

10 m 30 m675 m

5 m 12 m 18 m

figure courtesy Ž. Pavlović

Hadron Monitor

νμ

Many Neutrino Beams!

S. Kopp, “Accelerator Neutrino Beams,” Phys. Rep. 439, 101 (2007)

Many old Horror Stories

• And several dramatic failures of targets– H. White, Fermilab-TM-662, 1976– A. Mann, Neutrino Interactions With Electrons and Protons: An Account of an

Experimental Program in Particle Physics in the 1980s, AIP Press

NAL Team & Neutrino Horn Cone, 1974several dramatic horn failures

CERN PS beamasymmetry in horn field

J.C. Dusseux et al, CERN-72-11, 1972CERN WANF misalignment

L. Cassagrande, CERN-96-06

adventure

Ah, so things are better today!

• primary beam intensity ±2%, position ±90m• horn geometry (shape) < 0.5mm• horn alignment ±0.5mm• horn field to ±0.5%

Why focus anyway?

• Feynman scaling in xF ~ pL/p0

• No scaling for

• ‘Cocconi divergence’

proton

p0

pTpz

p + A → + X

Why focus anyway?

• ‘Cocconi divergence’

• Neutrino divergence

• Reduce divergence ~3, flux goes up by ~ 25

L. Ahrens et al, Phys. Rev. D 34, 75 - 84 (1986)

Horns ‘O Plenty

• On axis

beam energy tune is selected by

NuMI Low Energy Beam

Era of Precision-Focused Beams

• Mechanical tolerances on horns improved

• Near-analytic calculations or error conditions

• Errors large at ‘edge’ of focusing

Z. Pavlovic, “A Measurement of Muon Neutrino Disappearance in the NuMI Beam,” PhD Thesis, UT Austin 2008

NuMI Variable Energy Beam

targetHorn 1

Horn 2

Pions with pT=300 MeV/c and

p=5 GeV/cp=10 GeV/cp=20 GeV/c

Slide the target in/out of the 1st horn

M. Kostin et al, “Proposal for Continuously-Variable Neutrino Beam Energy,” Fermilab-TM-2353-AD (2001).

10 cm

100 cm

250 cm

The Call of the Mermaid

“I’ll just let [Harp/NA69/NA49/MIPP/SPY] solve my

problems”-- Hans Christian Anderson

Does any one recall the fate of the person that answers the mermaid’s call?

Atherton400 GeV/c p-Be

Barton100 GeV/c p-C

SPY450 GeV/c p-Be

You Really Wanted (E)(xF,pT)

NuMI HE BeamNuMI HE Beam

NuMI LE BeamNuMI LE Beam

p (GeV/c)

p T (

GeV

/c)

Modern Data Sets are $%#&! Good!

• Modern data sets better than original ‘beam surveys’– single particle detection– particle ID– large acceptance

• So can’t we just use this to map (xF,pT)??

pT (GeV/c)

d/d

p T (

mb/

GeV

/c)

eg: C. Alt et al, Eur.Phys.J.C49:897-917,2007

No! (1) Thick Target Effects

• Most ptcle production exp’ts on thin targets

• Nu production target ~ 2int

• Reinteractions!

• 20-30% effect

Min

iBoo

NE

NuMI

CNGS

J-PARC

figure courtesy Z. Pavlovic

No! (2) In-beam variations

18/25

• Temperature in NuMI target hall varies by 8°C as beam power cycles.

• Causes change in horn current ~1 kA

• Observe direct variation in beam flux (Mons)

• Thermal variations in your beam MC?

NuMI-only

figure courtesy L. Loiacono

NuMI-Collider Combined mode

No! (3) Beam Degradations?

Each data point is one

month’s data

Neutrino Energy (GeV)

Eve

nts

/ 10

16P

OT

/ G

eV • Started after installation of new target.

• Have ruled out horns (swapped)

• Have ruled out He leak in decay volume

• Consistent with density variation at shower max

figure courtesy M. Dorman

No! (4) Downstream Interactions

Near Decay Pipe

• Wrong sign neutrinos have huge contribution

• What if you run a nubar beam?! X3 worse effect!

• Not covered by particle production experiments!figure courtesy A. Himmel

CNGS: Earth B Field?!

NeutrinoFocus +

Anti-neutrino

Focus

They See shift of 6.4 cm (consistent with 0.3 Gauss)

figure courtesy E. Geschwendtner

A Cautionary Tale

• CERN PS team did particle prod @ IHEPJ.V. Allaby, et al., Phys. Lett. 29B 48 (1969)

• In-situ flux using Mons suggested X2 off?!D. Bloess, et al, CERN-69-28 (1969),

Nucl. Inst. Meth. 91 (1971) 605.

• Particle production round two – ok to 15%J.V. Allaby, et al., CERN-70-12.

The light at the end of the

Tunnel!

• Just need an in situ measure of (xF,pT)

• No extrapolation to ‘real experiment’

• Averages over effects in beam

In situ Muon Monitor Flux• CERN

PS• CERN

WANF• IHEP• FNAL

E616• Typical

~20%

• also FNAL NuMI (L. Loiacono, this workshop)

In situ Flux Using Neutrinos

A. Aguilar et al., arXiv:0806.1449

MiniBooNE

• Compare HARP flux to QEL events.

• Scale flux by 1.21!• What about K2K?!

P. Astier et al., Nucl. Instr. Meth. A 515 (2003) 800.

NOMAD • L. Ahrens et al, Phys. Rev. D 34, 75 - 84 (1986)

• K. McFarland, et al., arXiv:hep-ex/9806013

26

NuMI Flux Tuning

• Fit all 7 beam runs.

• Fit νμ and νμ

spectra• But uses

inclusive events!

• To be replicated by MINERvA using QELs• MINOS: also low- events (see M. Kordosky’s talk)

Phys. Rev. D77, 072002 (2008).

NuMI Mon Flux

• Similar to tuning by MINOS, but uses Mon event rates (no error from x-sec)

• L. Loiacono, poster at this workshop

• 20-30% errors

Summary• Flux needs for oscillation experience far

less stringent than for cross section exp’t.

• Ab initio measurements don’t replicate in situ effects – especially in intense beams!

• How can we design for cross section measurements and checks UP FRONT?!

• In situ measurements must be independent of the cross sections to be measured – use QELs or elastic scatters?

References

• Proc. of Int. Workshop on Neutrino Beams and Instrumentation (NBI)

– http://proj-cngs.web.cern.ch/proj-cngs/NBI2006/NBI2006.html

– http://www.hep.utexas.edu/nbi2005/

– http://www-ps.kek.jp/nbi2003/

– http://proj-cngs.web.cern.ch/proj-cngs/2002_workshop/announce_1.html

• Proc. Informal Workshops on Neutrino Beams– CERN-63-37, CERN-65-32, CERN-69-28

• S. Kopp, “Accelerator Neutrino Beams,” Phys. Rep. 439, 101 (2007)

Grandfather of All “Beams”*

* G.T. Danby et al, Observation of high-energy neutrino reactions and the exisitence of two kinds of neutrinos,” Phys. Rev. Lett. 9 36 (1962)

p p,K,

31/25

FNAL NBB

NB: Apparently Mon not used because of backgrounds

Fluxes came from these

A Cautionary Tale (2)

• ANL did particle production experiment on “actual” target: R.A. Lundy, et al., Phys. Rev. Lett. 14 (1965) 504.

• Motivated by bad fit to Sanford-Wang, did second round with limited points J.G. Asbury, et al., Phys. Rev. 178 (1969) 2086.

G.J. Marmer, et al.,Phys. Rev. 179 (1969) 1294.

• Finally had to do “round three” Y. Cho, et al., Phys. Rev. D 4 (1971) 1967.

D. Bloess, et al., Determination of the spectrum in the CERN 1967 neutrino

experiment, Nucl. Inst. Meth. 91 (1971) 605.

35/25

Comparison to Alcove 1 DataGNuMI Monte Carlo Muon Monitor Data

36/25

Simultaneous fit to Antineutrinos• Antineutrinos come from off the target• Our simultaneous and anti- fit came surprisingly close to

new p+C data available from CERN NA49 experiment!