Sacha KoppUniversity of Texas at Austin
on behalf of the MINERvA Collaboration
Flux Measurements in the NuMI Beam
What are the challenges?
• Experiments limited by– statistics
– knowledge of flux (E)
You Thought You Wanted…(E)
LE BEAM pME BEAM
What You Really Wanted…(xF,pT)
Pz (GeV/c)
BUT
pHE BEAM
Pz (GeV/c)Pz (GeV/c)
Why Do I say (xF,pT)?! • It is the dominant
uncertainty in predicting the neutrino flux.
• Calculating the (E) requires of
– particle production off the target
– ray tracing through beam optics
• As demo, ab initio flux for NuMI compared to MINOS data. Flux error bars dominated by particle production off the target (calculated prior to tuning to nu data).
“Medium” EnergyBeam Setting
“High” EnergyBeam Setting
“Low” EnergyBeam Setting
MINOS Data
Calculated flux
Compare Hadron Production Models
Model pT
(GeV/c)GFLUKA 0.37
Sanf.-Wang 0.42
CKP 0.44
Malensek 0.50
MARS – v.14 0.38
MARS – v.15 0.39
Fluka 2001 0.43
Fluka 2005 0.36
Fluka2001
Fluka2005
MARS–v.14
MARS–v.15
A perpexing situation for a poor experimentalist…
A Two-Part Proposal to Determine Beam Flux
Hardware (extra targets)
Dedicated RunningFor Special Configurations
The “Two Buddha’s” Near Sensoji Temple, Asakusa, Tokyo
Data Sets for Flux Determination• Special runs to constrain beam energy spectrum
– Vary target position and horn current – 3-5 ton detector fiducial mass– Total ~ 1020 POT before and after “ME Config” for these studies
Hardware Requirements (I)
pre-target beamline target hall hot work cell
target pile re-circulating air cooling system
Move horn 2 to ME setup– Extend the stripline
Switch to ME target– Fixed location upstream – Target doesn’t fit into horn
We want to delay the 2nd part
Target
Drop-shaft from surface
power supply for horns
Hardware Requirements (II)
• After NOvA upgrades target motion will no longer be possible– Required special module -- requires lots of moving parts (deemed risky)– Module experiences too much thermal motion under high heat load.
Allows for 2.5 m of target motion to vary the beam
energy
Baffle
Target
Target/Baffle Carrier• The loss of this module
removes ability to flexibly change E
• MINERvA requests that Lab provides one of these + spare for our studies.
• Could be useful to NOvA too! They need a spare (backup) target!
Hardware Requirements (III)• Target will be re-designed for for NOvA
– Still 6.4mm wide, but not as tall– No longer fits inside horn for LE config
• We therefore request– a fresh LE target to be used for our first set of test runs– a spare LE target to ensure success of test runs after ME switch (could
be used as spare for NOvA, too).
Past Techniques
Used to Wrestle with Beam Flux
High School Sumo ChampionshipsSumo Hall, Ryōgoku, Tokyo, 5 Aug. 2007
• Neutrino data• Muon Monitors• Hadron Production
Experiments
12/25
FNAL NBB
Fluxes came from these
In situ Muon Monitor Flux
• CERN PS• CERN
WANF• IHEP• FNAL
E616• FNAL
NuMI• Typical
~20%
NuMI Mon Flux
• Measurement of of hadron flux using Mon event rates (no error from x-sec)
• L. Loiacono, PhD thesis
• 20% errors
External Production Exp’t
A. Aguilar et al., arXiv:0806.1449
MiniBooNE
• Flux prediction based on HARP.
• As a check: compare the HARP flux to QEL events.
• Scale flux by 1.21!
• What about K2K?! Never see their plot!
… and yet …
• reconciling the MiniBooNE event rate with HARP flux• Consistent within errors• Possible shift?
In situ Flux Using Neutrinos
P. Astier et al., Nucl. Instr. Meth. A 515 (2003) 800.
NOMAD
Also see papers by
• L. Ahrens et al, Phys. Rev. D 34, 75 - 84 (1986)
• K. McFarland, et al., arXiv:hep-ex/9806013
19
NuMI Flux Tuning
• Fit all 7 beam runs.
• Fit νμ and νμ
spectra• But uses
inclusive events!
• To be replicated by MINERvA using QELs
Phys. Rev. D77, 072002 (2008).
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
Data Upon Which Models are Based
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
24/25
• 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
• Problem mitigated when swapped in new target
figure courtesy M. Dorman
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.
MIPP Data Not Currently Competitive
• MIPP uncertainties were bigger than the 5% uncertainty from the MINOS nu data fit (backgrounds, statistics, etc)
• Must improve by factor 9 in statistics and extend (xF,pT)
J. Paley, NuFact07
Could MIPP Provide a Stronger Measurement?• We would not accept a MIPP-like measurement alone.• MIPP provides a MC input, not a measurement of the nu flux for the experiment!
– MIPP data feeds into our MC, just like the muon lifetime, K BR’s, etc.– It provides no handles that our MC is right (real life variations and uncertainties).
• A cross section experiment like MINERvA must have in situ measurement– Other experiments have all made statements like “Using HARP/MIPP/SHINE, we will
measure to 5%.” These are strong promises!– Past cross section experiments measured fluxes (NBB experiments like CCFR,
CHARM/CDHS). Others are normalized to these.– Biggest uncertainties in cross section measurements from WBB’s are always the flux.
• MIPP and E938 are complex experiments!– Backgrounds to the desired particle species (eg K/pi) are substantial– Kinematic coverage relevant for a neutrino beam has never been achieved.– We demonstrated better coverage of (xF,pT) range in MINOS in situ data
At the very least, we must pursue both in situ and external (MIPP-like) experiments!
The Five Foundations of
Beams
5-story pagoda ofSensoji Temple, Asakusa, Tokyo
Neutrino Beams 101
• Feynman scaling in xF ~ pL/p0
• No scaling for
• ‘Cocconi divergence’
• Tell me what p you want, I’ll tell you what angle to focus.
proton
p0
pTpz
p + A → + X
Neutrino Beams 102
• ‘Cocconi divergence’
• Neutrino divergence
• Reduce divergence ~3, flux goes up by ~ 25
We’ll be sensitive to “edges” where focusing fails.
L. Ahrens et al, Phys. Rev. D 34, 75 - 84 (1986)
Neutrino Beams 103Beam MC
i
i
X i
B
B
Neutrino Beams 104
Focu
sing
pe
ak
figure courtesy Ž. Pavlović
• Focusing errors are fairly small.
• Mostly pile up at edges of focusing system.
figure courtesy Ž. Pavlović
“High”Energy
targetHorn 1
Horn 2
“Low”Energy
protonHorn 1
Horn 2
target
Pions with pT=300 MeV/c and
p=5 GeV/cp=10 GeV/cp=20 GeV/c
Vary beam energy by sliding the target in/out of the 1st horn
Neutrino Beams 105
Opportunity: Flexible Beam Energy
figure courtesy Ž. Pavlović
M. Kostin et al, “Proposal for Continuously- Variable Neutrino Beam Energy,” Fermilab-TM-2353-AD (2002)
in situ Particle Production Off the
Target Measurements using Flexible Beam
Configurations
Sensoji Temple, Asakusa, Tokyo
NuMI Beam Configurations• Can vary
– Horn current (pT kick supplied to ’s)
– Target Position (xF of focused particles)
• Plots show (xF ,pT) of contributing to neutrino flux.
• Similar plots exist for kaons
• Acquired data from 8 beam configurations (here are shown 4)
LE010/185kALE010/0kA
LE100/200kA LE250/200kA
Parameterizing Hadron Production (I)• We tried to
parameterize the Fluka’05 (xF, pT) distributions with an empirical formula.
• In this fit,– A = A(xF)– B = B(xF)– C = C(xF)
• This form is quite similar to BMPT (which has a D(pT)2 term – small??)
• I cannot motivate the (pT)3/2 other than the fact that it fits the Fluka spectrum rather well.
2/3
)( TCpT
T
eBpAdp
dN
Fluka ‘05
Parameterizing Hadron Production (II)
FFF xbxx 11
• Both A(xF) and B(xF) fit reasonably well to following shape
• All this says, of course, is that Fluka’05 is roughly consistent with BMPT• The values of the exponents are not in agreement with BMPT’s paper, but this
is a thick target parameterization, and they quoted invariant cross section.
Parameterizing Hadron Production (III)• Used empirical form
similar to BMPT to parameterize Fluka2005:
• Fit was to a MC of our thick-target yield estimated by Fluka2005.
• Tune parameters of the fit to match ND data.
ND Spectra After Reweighting (I)
ND Spectra After Reweighting (II)
ND Spectra After Reweighting (III)
ND Spectra After Reweighting (IV)
ND Spectra After Reweighting (V)
ND Spectra After Reweighting (VI)
ND Spectra After Reweighting (VII)
ND Spectra After Reweighting (VIII)
(xF,pT) weights
• Result of the fit is set of weights in (xF,pT) plane that should be applied to /K yields
• Data prefers more low pT pi’s
weightsweights
Region of LE beam focusingRegion of
insignificant focusing
Constraint of fit on ratio
• Anti-nu’s tune the flux off the target
• Out put of fit agrees well with recent NA49 data
Constraint of fit on K/ ratio• Recent
data from FNAL E907 to which we can compare
Improvement in Flux Uncert.Before
use this line
use this line
After
• We obtain greater precision than MIPP or E938 proposal.
What To Take Away From MINOS• Proof of principle that can
disentagle underlying (xF,pT) from focusing effects.
• Precision is ~5% in neutrino flux.
• If we use a “known” or “standard candle” channel, this could be turned into a flux.
• Not possible with MINOS data, but possible with MINERvA QELs!
• Gives a flux shape, can be normalized at E>25 GeV.
(Fluka2005)
Question: Why Repeat this in MINERvA?
• MINOS data is shown here as a proof of principle that neutrino data in a flexible beam is sensitive to underlying hadron production.
• Since MINOS used inclusive events, it should not be interpreted as a measurement, however. We never cared if there was an overall scale factor in flux or cross section (just wanted to predict far detector!)
• MINERvA will use QELs, for which the shape of the cross section is reasonably flat and known to ~10%.
• If we use the inclusive events >30GeV to normalize the flux, then this analysis in MINERvA, repeated with QELs, can give the flux shape.
But Time is Of the Essence!
(could we make due with less beam?)
• Our revised request is for o 4e20 POT in the LE beamo 0.9e20 POT for special runs
in the LE configurationo 0.9e20 POT for special runs
after the ME conversion
• This is a bit less than our original request submitted to Program Planning
the eleventh hour
We revised to 70% of POT• I took #POT from
MINOS and x10
• For MINERvA we want to do this study with only QELs
• In LE configuration, much of x-sec is QEL, so we’re OK.
• At high energy configurations, more events, but these are Res+DIS, so don’t want to take credit for this.
Revise 4 3 target positions?
• Must make sure to map out full (xF,pT) space
• Error reported here is MINUIT float. Not reflected is how well model agrees with data
• Some of these go down, reflecting that those configurations were in tension with the others.
• Could probably combine LE100+150---> LE125?
Must we repeat in ME configuration?
• Yes.
• The flux derived in the LE configuration of horns will be valid only in LE configuration
• New horn configuration leads to new focusing uncertainties
• New passive material will be different in beam line; this component will need to be measured.
Performing Measurements in ME Configuration
• Spectra have lots of rich structure – a good thing!
Performing Measurements in ME Configration
• We can vary (xF,pT) just as well as in the LE configuration
LE010/200kA LE100/200kA
ME010/185kA
ME010/0kA ME010/185kA
ME250/200kA
ME150/200kA
ME100/200kA
Summary of Our Philosophy
• Accuracy of measurement is 5-10%– 5% from the flux fit– 10% from normalization mode– Better than any other technique.
• We are requesting resources from the Lab to do this– extra moveable LE target + carrier– Special running of 0.9e20POT in LE and ME configurations
• Analysis emphasizes direct measurements to measure flux in situ.– There are always uncertainties in using
external production experiments– Must ensure what’s happening during
MINERva experiment!