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!