Coherent-π production experiments review
Hide-Kazu TANAKAMIT
Outline• Introduction
• Measurements in past
• Recent results at low energy
• K2K, MiniBooNE, SciBooNE
• Future prospect
• Summary
2
Coherent pion production
3
Aνπ
ℓ
• Neutrino interacts with nucleons coherently, producing a pion• No nuclear breakup occurs
Charged Current (CC): νµ+A→µ+A+π+
Neutral Current (NC): νµ+A→νµ+A+π0
ν (ν) µ± (ν / ν)
W± (Z) π±(0)
A
q2
tA
Coherence requires: t = (q - pπ)2 < 1/R2
where R is the size of the nucleus.
From the Rein-Sehgal model:1) σ(CC) = 2 σ(NC)2) σ(A) ~ A1/3
3) σ( ν ) ~ σ( ν )Characterized by a small momentum transfer to the nucleus, forward going π.
Measurements in past• Measurements for ν, ν CC and NC modes
• for various nuclear targets
• High energy region: >7GeV (CC), >2GeV (NC)• R&S model agrees with the high energy results.
4
Experiments CC/NC ν / ν E (GeV) Target<A>
Aachen-Padova NC ν, ν 2 Al<27>
Gargamelle NC ν, ν 2 Freon <30>
CHARM NC ν, ν 20-30 Glass <20.7>
CHARM II CC ν, ν 20-30 Glass <20.7>
BEBC CC ν 5-100 Ne/H2 <20>
SKAT CC, NC ν, ν 3-20 Freon <30>
FNAL 15-ft NC ν 2-100 Ne/H2 <20>
FNAL 15-ft E632 CC ν, ν 10-100 Ne/H2
<20>
Assume:• A1/3 dependence• σ(CC coherent)=2*σ(NC coherent)
Volume 313, number 1,2 PHYSICS LETTERS B 26 August 1993
300
250
o E 200
~b 150
.-~ 100
50
300 ' ' ' ' I ' ~ ' ' I ' ' ' ' I ' ~
Z , i i I i i i i I i i i I I i
0 50 100 150 0
Ev [GeV]
250
•Eo200 ~-~" 150
% 13 ~ 100
5O
- I I I I I I I I I I I I I I I I
B&K
i i i l i i i i I i i i I I i
50 100 150
E ~ [ GeV]
Fig. 5. Visible cross section (En >/ 5 GeV) for coherent single charged plon production for neutrino and antmeutrmo induced
interactions. The predictions of the Rein-Sehgal model (full hne) and of the Bel 'kov-Kopehovlch model (dashed hne) are
indicated
500
400
E o 300
o .?,
~ 200
100
500
i i i I i i i I i ' i ' ' ' ' i i i i i i i i i , i s i
• penment) .I ~ TI x Aachen ~ Padua [1] +Gargamelle[2] 4~"t' " • CHARM.L3].. • SKAT (CC) [4] ./~ ¢, SKAT (NC) [4] • BEBC[7]
, , I , , I , , , I ,O,F~A~-[~],, I , ,qF~/~LI9], I , 20 40 60 80 100 120 140
E v [GeV]
I i I I I I I I i l l I I I I I I l l i I I I i l l I
400 ~ _
300 i ~ :
b 200
J, )~LJT/"1~. ' .L ~ d u a [1] + Gargamelle [2] 100 • CHARM [3] T
i , I i i i I M t , I R M , I r , , I i m r I i i i I i
0 20 40 60 80 100 120 140
E~ [GeV]
Fig. 6. Compilation of experiments on coherent single p]on producUon. Shown are the results from both neutral current
[ 1-4] and charged current [4-9] data, for neutrino and antmeutrmo reduced interactions. The FNAL [8,9 ] values from
combined neutrino and antmeutrmo data have been included m the upper dxagram For this experiment the results for the
visible cross section were corrected for the selecUon of En >/ 5 GeV according to the Bel'kov-Kopellov~ch approach. Data
from other experiments have been scaled, where necessary, to allow comparison The pred]cuons of the Rem-Sehgal model
(full hne) and of the Bel 'kov-Kopeliovlch model (dashed hne) are mdxcated.
274
Plots from Phys.Lett. B313, 267-275 (1993)
ν
ν
Recent resultsat low energy (~1GeV)
5
• <Eν>=1.3 GeV• Target: Scintillator (CH)
• Tracking detector
• Experimental signature:• Two MIP-like (µ+π) tracks • By looking at recoil proton (vertex
activity) isolate coh-π
Coherent π (MC)
Resonant π (MC)
Vertex activity (recoil proton)
πμ
π
μ
• <Eν>=1.1GeV• Target: Mineral oil (CH2)
• Cherenkov detector• Experimental signature:
• Two e-like ring (π0→γγ) events• With pion in forward direction
ν NC coherent π0
MiniBooNE: Phys. Lett. B664, 41 (2008)
ν CC coherent π+
K2K-SciBar: Phys. Rev Lett. 95, 252301 (2005)
Difficulties
This mode is buried beneath a
mountain of CCQE.
The three tracks tend to have
overlapping rings.
!0!
+= CC!
0 three
ring mess....
Sample events purity
total MC 267007 100%
CCQE 168723 63%
CC!0 16504 6%
CC!+ 66268 25%
Data 341272
Data/MC 1.28
Data: 6.3·1020 p.o.t.
MC: 41.1·1020 p.o.t.
Recent resultsat low energy (~1GeV)
6
ν NC coherent π0
MiniBooNE: Phys. Lett. B664, 41 (2008)
ν CC coherent π+
K2K-SciBar: Phys. Rev Lett. 95, 252301 (2005)
= (0.04 ± 0.29 (stat.) +0.32- 0.35 (sys.)) x 10-2
Cross section ratio: σ(CC coh-π) / σ (CC)
No evidence of CC coherent π prod.
CoherentResonant
Background
Coherent fraction in NC-1π0:
Ncoh/(Ncoh + Nres) = (19.5 ± 1.1 (stat.) ± 2.5 (sys.))%
Clear evidence of NC coherent π prod.
More NC-π0 from MiniBooNE
7
C.E. Anderson at NuInt09 • New NC-π0 results for both ν and ν beam modes.
• Demonstrated comparison between data and models
• ν and ν data suggest:
• Clear evidence of non-zero NC coh-π
• Forward angular distribution is sensitive to model predictions
ν
ν
NOTE: MC distributions are absolutely normalized
CC coh-π results from SciBooNE
8
MRD stopped sample<Eν>= 1.1 GeV
MRD penetrated sample<Eν>= 2.2 GeV
No evidence of CC coherent pion produc2on was found.➜ Confirmed K2K results
Phys . Rev. D78 112004, 2008
Upper limit on cross section
9
Measured upper limits on σ(CC coherent π)/σ(CC) raGos are converted to upper limits on absolute cross secGons by using σ(CC) predicted by MC simulaGon.
Rein-Sehgalw/ lepton mass correction(Our default model)
Alvarez-Ruso et al.
Kartavtsev et al.
SciBooNE 90% C.L.
Recently proposed CC coherent π models predict production of CC coherent π events just below our upper limit.
➜ Search for ν CC coherent pion production, since ν data is expected to be more sensitive to look at CC coherent π production than ν data.
New coherent π models:•Singh et al., Phys Rev. Lett. 96:241801 (2006).•Paschos and Kartavtsev, Phys. Rev D74:054007
(2006).•Alvarez-Ruso et al., Phys. Rev C75:05501 (2007).•Nakamura et al. arXiv:0901.2366•Hernandez et al. Phys. ReV D76, 033005 (2007),
D79, 013002 (2009)•...
Upper limit:33% of the prediction
Search for ν CC coherent π at SciBooNE
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ν Coherent-π sample(µ+π w/o activity)
Qrec2 (GeV/c)2
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+: dataWed May 6 17:07:54 2009
! CC coherent "
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(wrong sign)"
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coherent-π
But data suggest non-zero CC coherent π component.
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ν Coherent π counter sample
(µ+π w/ activity)
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PreliminaryPreliminary
Search for ν CC coherent π at SciBooNE
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Define signal region: Q2<0.1 (GeV/c)2
- 139 events observed- 80 non-coherent π events (BG)
➜ Data - BG: 59±14 (stat)
NEUT (R&S) prediction: 151 (ν:130 ν:21)
➜ Upper limit of ν results 33% of the prediction: 50 (ν+ν)
4σ level “data excess”.
And consistent with ν CC coh-π upper limit within stat error.
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Signal region: Q2<0.1- 87 events observed- 31 non-coherent π events (BG)
➜ Data - BG: 56±11 (stat)NEUT (R&S) prediction: 92 (ν+ν)
Qrec2
Signal region: Q2<0.1- 52 events observed- 49 non-coherent π events (BG)
➜ Data - BG: 2.6±8.5 (stat)
NEUT (R&S) prediction: 59 (ν+ν)
Preliminary & stat. error only
CC coherent π component at small θπ region.
Qrec2
ν CC coherent π
14
θπ < 35 deg θπ > 35 deg
Δφ Δφ
• Similar enhancement in ν data ➜ Pions from CC coh-π production tend to be produced more forward than prediction.
• Important to measure π kinematics.
• In order to describe data, pion kinematics description needs to be improved.
θπ distribution
ν
coherent-π
K. Hiraide at NuInt09
• Hint for CC/NC coherent π puzzle at low energy??• NC coh-π measurement was based on π0-kinematics, CC coh-π
measurement was based on µ-kinematics.
NC-π0 from SciBooNE
15
σ(NC-π0)σ(CC)
= 7.5 ± 0.6(stat.) +0.760.90 (sys.) x 10-2 !
!"#$%&'()*%+,#)-*'.#+/*#012#
!"#3),,# !"#34('&*/(
5677#('.8'#9+4:;<#)&=#94*:'.<#),#4&'#+474.#-4.#>?@
NC-π0 (resonant+coherent)
OtherDirt eventCosmic ray
Preliminary
Reconstructed invariant mass in 2γ system
σ(NC-π0)σ(CC) = 6.8 x 10-2cf. MC prediction:
NC-π0 from SciBooNE
15
σ(NC-π0)σ(CC)
= 7.5 ± 0.6(stat.) +0.760.90 (sys.) x 10-2 !
!"#$%&'()*%+,#)-*'.#+/*#012#
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5677#('.8'#9+4:;<#)&=#94*:'.<#),#4&'#+474.#-4.#>?@
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OtherDirt eventCosmic ray
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Reconstructed invariant mass in 2γ system
! ! "#
!!"#$%&'"(')*'+,",-".'/0"/12)3-$,/2$")/0*&'3-$,/2$")/0*&' 4-$"+-$,/2$")/0*&'
cosθπ
NC-π0 (primary, res+coh)NC-π0 (secondary)
Data/MC prediction are in fairy good agreement.
σ(NC-π0)σ(CC) = 6.8 x 10-2cf. MC prediction:
NC-π0 from SciBooNE
16
σ(NC-π0)σ(CC)
= 7.5 ± 0.6(stat.) +0.760.90 (sys.) x 10-2 !
!"#$%&'()*%+,#)-*'.#+/*#012#
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5677#('.8'#9+4:;<#)&=#94*:'.<#),#4&'#+474.#-4.#>?@
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OtherDirt eventCosmic ray
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Reconstructed invariant mass in 2γ system
σ(NC-π0)σ(CC) = 6.8 x 10-2cf. MC prediction:
: SciBar hit, area∝energy deposit
SciBar EC MRD
γ→e+e
Recoiled proton?
γ→e+e
SciBar has a capability to distinguish NC resonant-π0 and coherent-π0 event-by-event.
ν
Future prospect• MINERvA (NuMI at Fermilab) has an excellent
capability for CC and NC coherent π productions
• Wide energy range: Eν ~2-20 GeV • Several nuclear targets: He, C (and CH), Fe, Pb
• Reconstruct energy of final state hadronic system.
• Data taking starts soon.
• Have been running with the full Tracking Prototype in the ν beam since mid April 2009!
17
CC Coherent Pion Production Cross Section
0
100
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500
0 2.5 5 7.5 10 12.5 15 17.5 20E! (GEV)
" (1
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M2 )/12
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A-Dependence of 5 GeV CC Coherent Cross-Section
0
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2
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0 25 50 75 100 125 150 175 200
A
!(1
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8 c
m2/n
uc
leu
s)
Figure 13: Left: Coherent cross-sections measured by MINER!A compared with existing publishedresults. MINER!A errors here are statistical only. Right: Measurement of the coherent cross-section asa function of atomic number in MINER!AThe shaded band indicates the range of previous measure-ments. Error bars indicate the size of the experimental errors in a single 1-GeV bin. The curve showsthe prediction from the Rein-Seghal model. Crosses are the prediction of the Rein-Seghal model forscattering from carbon, iron, and lead, circles are the predictions of the Paschos-Kartavtsev model.
Applying this set of cuts to our signal sample we find that 7698 signal events pass all cuts, whichgives an overall efficiency of 31%. Applying the factor 0.65 to account for the fact that we have notused fully reconstructed quantities for our kinematic cuts gives us a final event sample of 5004 events.Applying these cuts to the background sample we find that 12 events out of 20k pass all cuts. Nor-malized to the total event rate, this gives an expected background of 4400 events. We note that in thisanalysis other important variables for background rejection, related to associated activity around thevertex, were not used. Figure 13 shows the expected precision of the MINER!A measurement as afunction of neutrino energy. Here we have only included the statistical error on the signal and assumedthat the measured value is that predicted by Rein-Seghal. No attempt has not been made to quantifythe systematic errors on this measuerment other than that resulting from the background subtraction.Previous measurements of the coherent cross-section were statistics limited.
3.3.2 A-dependence of the coherent cross-section
Another task for MINER!A will be comparison of reaction rates for lead and carbon. The expectedyield from lead will be! 1800 charged-current events, assuming the same efficiency. The A-dependenceof the cross-section depends mainly on the model assumed for the hadron–nucleus interaction, andserves as a crucial test for that component of the predictions. No experiment to date has been ableto perform this comparison. For reference, the predicted ratio of carbon to lead neutral-current cross-sections at 10 GeV in the Rein-Sehgal and Paschos models are 0.223 and 0.259, respectively [57].Figure 13 shows the predicted A-dependence according to the model of Rein and Sehgal.
26
A-range of current measurements
Expected MINERvA statistics
A-dependence of CC coh-π
Plots from MINERvA proposal
Summary• Several measurements on coherent pion production.
• ν, ν, CC and NC modes
• Recent results on CC/NC coherent π at low energy, ~1GeV.
• Although good agreement between high energy results and R&S model, not so for low energy results.
• Data suggest: pions from CC coherent π tend to be produced more forward than R&S model prediction.
• A variety of models has been proposed.
• New experimental results will be published shortly.
• Experimental & theoretical studies are in progress.
18
Backup
19
CC-π+ at MiniBooNE
20
J. Nowak at NuInt09
SciBooNE efficiency
21
!!!"#$%&%'(!)*!%++*"*%'",
-.!/!0!"!0!1'2!"#!
!!
3)%'*'4!1'45%/*#'!1'45%/*#'!6#6%'(76
8++*"*%'",
8++*"*%'",!2&#).!1(!!1!.6155
9:;<!2%4&%%.=!#)%'*'4!1'45%
>%(?%%'!67#'!1'2!)*#'
@#!%++*"*%'",!+#&!)*#'!
6#6%'(76!>%5#?!<ABC!D%EF"
8++*"*%'",
8++*"*%'",
The efficiency calculation depends on the model prediction of kinematics
K. Hiraide at NuInt09
Eν, Q2 reconstruction
22
Eν
(Pµ,θµ)
p
µ
CC-QE
Eν, Q2 reconstruction assuming CC-QE (ν+n→µ+p)
Q2rec = 2Erec
! (Eµ ! pµ cos !µ)!m2µ
Erec! =
12
(M2p !m2
µ)! (Mn ! V )2 + 2Eµ(Mn ! V )(Mn ! V )! Eµ + pµ cos !µ
V: nuclear potential (27MeV)
Uses only muon kinematics
!
!"#$%&'"(%)*+,"-./0"12$)3
Pµ
!
!"#$%&'"(%)*+,"-./0"12$)3
θµ
!"
!"#$%&'()#'"*+,!, +-2+.&&)/0%1+22-,+30%"/.'0#&4+
!"#$%&'(!"!#$%&'()!#*+$,! #-$.'!/0
&)&*+,-./&01-23&45$16,%5-7
5!,67879:
!; 1/!23'4567/
Eνrec
!
!"#$%&'"(%)*+,"-./0"12$)3Q2rec
SciBooNE 1-trk sample
Preliminary
Preliminary
CC-QECC-resonant πCC-coherent πNCBkg (EC/MRD)
Data
rec
Q2 resolution forCC coherent π
23
41
Q2 resolution of CC-coherent ! events
Mean: -0.024 (GeV/c)2
Sigma: 0.016 (GeV/c)2
Q2 resolution of CC-coherent ! sample
Q2 resolution of CC-coherent πevents
Mean: -0.024 (GeV/c)2 Sigma: 0.016 (GeV/c)2
ν Coherent pion production
• Neutrino interacts with nucleons coherently, producing a pion• No nuclear breakup occurs
Charged Current (CC): νµ+A→µ+A+π+
Neutral Current (NC): νµ+A→νµ+A+π0
Several measurements in past (‘80-’90).
Volume 313, number 1,2 PHYSICS LETTERS B 26 August 1993
300
250
o E 200
~b 150
.-~ 100
50
300 ' ' ' ' I ' ~ ' ' I ' ' ' ' I ' ~
Z , i i I i i i i I i i i I I i
0 50 100 150 0
Ev [GeV]
250
•Eo200 ~-~" 150
% 13 ~ 100
5O
- I I I I I I I I I I I I I I I I
B&K
i i i l i i i i I i i i I I i
50 100 150
E ~ [ GeV]
Fig. 5. Visible cross section (En >/ 5 GeV) for coherent single charged plon production for neutrino and antmeutrmo induced
interactions. The predictions of the Rein-Sehgal model (full hne) and of the Bel 'kov-Kopehovlch model (dashed hne) are
indicated
500
400
E o 300
o .?,
~ 200
100
500
i i i I i i i I i ' i ' ' ' ' i i i i i i i i i , i s i
• penment) .I ~ TI x Aachen ~ Padua [1] +Gargamelle[2] 4~"t' " • CHARM.L3].. • SKAT (CC) [4] ./~ ¢, SKAT (NC) [4] • BEBC[7]
, , I , , I , , , I ,O,F~A~-[~],, I , ,qF~/~LI9], I , 20 40 60 80 100 120 140
E v [GeV]
I i I I I I I I i l l I I I I I I l l i I I I i l l I
400 ~ _
300 i ~ :
b 200
J, )~LJT/"1~. ' .L ~ d u a [1] + Gargamelle [2] 100 • CHARM [3] T
i , I i i i I M t , I R M , I r , , I i m r I i i i I i
0 20 40 60 80 100 120 140
E~ [GeV]
Fig. 6. Compilation of experiments on coherent single p]on producUon. Shown are the results from both neutral current
[ 1-4] and charged current [4-9] data, for neutrino and antmeutrmo reduced interactions. The FNAL [8,9 ] values from
combined neutrino and antmeutrmo data have been included m the upper dxagram For this experiment the results for the
visible cross section were corrected for the selecUon of En >/ 5 GeV according to the Bel'kov-Kopellov~ch approach. Data
from other experiments have been scaled, where necessary, to allow comparison The pred]cuons of the Rem-Sehgal model
(full hne) and of the Bel 'kov-Kopeliovlch model (dashed hne) are mdxcated.
274
Plots from Phys.Lett. B313, 267-275 (1993)
ν
ν
40
40
Eν (GeV)
Eν (GeV)
x 10-38 cm2
2
2High energy results and the model suggest: cross sections of coherent π prod. for ν and ν are similar size.σ(νCC-coh) ~ σ(ν CC-coh)
Solid line: Rein-Sehgal modelDotted line: Bel’kov-Kopeliovich
Measurements are at high energy region.Rein-Sehgal model well describes the data.
➜ ν data is expected to be more sensitive to look at CC coherent π production than ν data. ∵ σ(ν CC) > σ(ν CC)
24
Reconstructing π0
25
π0 vertexγ→e+e-
SciBar
Z (beam direction)z=0
Reconstructed π0 vertex position
Dirt events
SciBar detectorPreliminary
! ! !"
!"!#$%&'()#*%)+&'!,-.!0 #$%&'()#*%)$/!01((! !0 #$%&'()#*%)$/!0&0$')*0!
2#&0!3$#$!451'6!"!+(!($71#1)$/!+')&!45!"!1'/!458'/!"!
Reconstructed invariant massfor 2γ system
Preliminary
Data: ~550 eventsMC: ~60% NCπ0 purity
ex. Dirt event
Y. Kurimoto
ν contamination in ν beam mode
26
ν (wrong sign) ~30%background in MRD stopped sample
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+: data
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1.8
2
~90% ν purity( ν CC-QE: 80%)
1-track w/o activity sample
Preliminary
Eν (GeV)
ν (wrong sign)
Right
SignWron
g
SignSciBooNE
Neutrino cross section(NEUT prediction)
27
• QE• Llewellyn Smith, Smith-Moniz• MA=1.2GeV/c2
• PF=217MeV/c, EB=27MeV(for Carbon)
• Resonant π• Rein-Sehgal (2007)• MA=1.2 GeV/c2
• Coherent π• Rein-Sehgal (2006)• MA=1.0 GeV/c2
• DIS• GRV98 PDF• Bodek-Yang correction
• Intra-nucleus interactions
MINOS, MINERvA, NuMIK2K, NOvA
MiniBooNE, T2K, SciBooNE
Super-K atmospheric ν
Carbon target
Normalization for MC sample
• Use “fractional” normalization for MC sample, which is defined by CC event selection.
• For example...
28
Define normalization:Start with the same # of events
Data MC
CC selection(SciBar-MRD matching) 30,337 30,337
# of track(2-track selection) 5,939 5898
PID(µ+π selection) 2,255 2,388
Vertex activity (isolate coh-π) 425 661
at SciBooNE
NC-1π0 meas. by K2K-1KT• 1KT detector: K2K near detector
• 1,000 ton water Cherenkov
• Neutrino energy: 1.3 GeV
• 1st meas. of NC-1π0 prod. in H2O
• 2,496 NC-π0 sample• NC-1π0 purity (in 1π0 sample): 71%
• Resonance: 52%• Coherent: 10%• Final state interaction: 7%
• σ(NC1π0)/σ(CC) = (6.4 ± 0.1 ± 0.7)%
• NEUT prediction: 6.5%• Good agreement with expectations
• Momentum distribution disagrees
Physics Letters B619, 255 (2005)
NC-1π0 meas. at MiniBooNE • MiniBooNE detector at FNAL• 800 ton mineral oil (CH2) Cherenkov
• Neutrino energy: 0.7GeV (peak)
• 1st measurement of NC coherent-π0 below 2GeV
• 28,000 NC-1π0 events• S/N~30
• Coherent fraction in NC-1π0; Ncoh/(Ncoh + Nres) = (19.5±1.1± 2.5)%
• Model predicted (Rein-Sehgal) 30% fraction.
• 1.5 times lower than default prediction.
• Higher production rate wrt predictions at low π0 momentum.
Phys. Lett. B664, 41 (2008)
• MiniBooNE anti-neutrino data also suggested coherent π contribution. V. T. Nguyen, AIP Conf.Proc.967:285-288,2007. (NuInt07)
Comparison
31
Other measurements athigher neutrino energy
assuming• A2/3 dependence• σ(CC coherent)=2*σ(NC coherent)
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