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Neutrino interaction studyNeutrino interaction studyin the K2K near detectorsin the K2K near detectors
M. Hasegawa (Kyoto Univ.)for the K2K collaborators
RCNP workshop, Feb. 24, RCNP Osaka
Outline
Introduction - K2K experiment and Near detectors
Current activities- Charged current analysis
for Eν spectrum measurement- Low q2 deficit - Neutral current π0 production- MA measurement
On going analysis and future prospectsSummary
K2K ExperimentKEK to Kamioka –– first accelerator-based
long (>100km) baseline neutrino experiment
KEKν beam lineBeam monitorNear detectors
Super-K (far detector)
L=250km<Eν>~1.3GeV
Goal:Goal:Confirmation of Confirmation of ννµµ→→ννxx oscillationoscillation
reported by Superreported by Super--K K atmatm--ννSearch for Search for ννµµ→→ ννee oscillatonoscillaton
Started in 1999
PRL 93, 051801
Neutrino beam-line
Target/Horn12GeV PS
Decay volume(200m, π+→µ++νµ)
µ monitor
Near Detector
To Kamioka
1.1µs spill/2.2s~5.5x1012 p/spill
Eν (GeV)
νµ energy spectrum @ K2K near detector
<Eν> ~ 1.3GeV
Neutrino interaction ~1GeV
Total (NC+CC)
CC Total
CC quasi-elastic
DISCC single π
NC single π0
Eν(GeV)
σ/E
(10-
38cm
2 /GeV
)
Cross-sectionsNEUT (Nucl.Phys.Proc.112,p171)
Charged current quasi-elastic scattering (CCQE)Neutral current elastic scatteringCC/NC Single π,(η,K ) production via resonancesCC/NC Coherent pion productionsCC/NC Deep inelastic scattering
ν+ n l+ p
ν+ N l + N’ + πν+ N ν + N
(η,K)
ν+ 16O l +16 O + πνµ+ N l + N’ + hadrons
(l : lepton, N,N’ : nucleon, m : integer)
It is possible to investigatevarious neutrino interactionsw/ the K2K near detectors.
(In fact, more precise knowledgeof ν-nucleus interaction is vital to improve the accuracy of (future) oscillation measurements)
K2K Near detectors
Main roleTo measure
- flux- energy spectrum- direction
To study- neutrino interaction
1kt Water Cherencov detector (1kt) Scintillating Fiber Detector (Scifi) Scintillator Bar Detector (SciBar) (2003-) Muon Range Detector (MRD)
inside view
1Kt water cherencov detector (1Kt)
pµ−
νCherenkovlight
• 1000t cylindrical water tank w/ 680 20inch PMTs• Use ring pattern for PID (µ/e)
Flux & low energy (<1GeV) spectrumσ(NCπ0) /σ(total CC)
Physics output
Scintillating Fiber tracker (SciFi)SciScintillating FiFiber sheet / Water
Sandwich detector260cm 173cm
260cm
Spectrum shape (>1GeV)MA measurement
SciBar detector
ν
Extrudedscintillator(15t)
Multi-anodePMT (64 ch)
Wave-lengthshifting fiber
EM calorimeter
1.7m
3m
3m
Neutrino target is scintillator itself2.5 x 1.3 x 300 cm3 cell (15000ch)(Fairly) large volume
(7000 int. / month/10t)
Just constructed in last summer!
Fine segmented , Full ActiveSciScintillator-Bar Bar Tracker
Tracking Threshold : 8cm(=0.4GeV/c Proton)
Track-finding efficiency>99% (Single Track)
Excellent p/µ(π) using dE/dxmisID(µ P) = 1.7% @ PEff=90%
High 2-track CC-QE efficiencyIdentify ν interaction mode clearly
SciBar Shot! (1)
µ
pν
CCQE candidateCCQE candidate
1
23ν
CCnQECCnQE candidatecandidate
Area of circle is proportional to ADC.Hits along the proton track are larger
SciBar Shot! (2)
Large energy deposit in Electron Catcher
e
p
NC π0 candidate νe candidate
Vertex!
π0
e
e
νγ
γ NC elastic scattering cand.
p
• What can SciBar measure?To estimate SK number of events andEν spectrum (single ring µ-like)– Eν spectrum at near site from CC-QE (ν+n µ–+p) – CC-QE form factors– CC resonance production form factors
σ(ν+p µ–+p+π+)/σ(CC-QE) as a function of Eνσ(ν+n µ–+p+π0)/σ(CC-QE) as a function of Eνσ(ν+n µ–+n+π+)/σ(CC-QE) as a function of Eν
– CC coherent pion production (ν+C µ–+C+π+)– CC multi-pion production– NC resonance production (ν+N ν+N’+π)
νe/νµ flux ratio as a function of Eν (νe appearance)nucleon ∆s measurement
σ(ν+p ν+p)/σ(CC-QE) as a function of q2
Physics output from SciBar
Main Motivation is to determine Eν spectrum
shape @ near site and σ(nQE)/σ(QE)
CCQE
nonQE
undetected in W-ch
CC Quasi elastic
1Rµ in W-chcan reconstruct Eν (pµ, θµ)
µµµ
µµν θ+−
−=
cospEm2mEm
EN
2Nrec
non Quasi elastic
Background for Eν meas.
charged current analysis
[ ]∑ ∗+= nQEQEnQEQE RiFPData σσθµµ /*)(),(
)1(F×
[ ]∑ ∗+= nQEQEnQEQE RiFPData σσθµµ /*)(),(
0-0.5 GeV
0.5-0.75GeV
Eν QE (MC) nQE(MC)
MC templates*F(1)
*F(2) *F(2)*RnQE/QE
(F(i) : Flux weight , RnQE/QE : cross section ratio)
We change flux weightand nonQE/QE and search for best combinationby comparing with data.
••
••
0.75-1.0GeV
1.0-1.5GeV
*F(3)
*F(4)
*F(3)*RnQE/QE
*F(4)*RnQE/QE
0
20
40
60
0 1 2 3 2550
0500
10001500
pµ
θ µ
[GeV/c]
[degre
e]
Eν spectrum measurement (strategy)
Event sample
Vertex
MRD(Iron plates and drift tubes)SciBar
µ
ν
μ
1kt水チェレンコフ検出器
CC fraction ~ 98%(SB) 100%(Scifi)Event Sample (CCQE candidates)
1kt : 1-Ring μ-like FC eventsScifi , SciBar : MRD matching events
(1Track , 2Track QE,nQE)
QE/nQE
QE nonQE
DATACC QECC 1πCC coherent-πCC multi-π
∆θp
(deg)
(1) 1 Track 60% QE (2) 2 Track QE enriched 60%(SF) / 70%(SB) QE (3) 2 Track nonQE enriched 85% nQE
µ
Expected proton direction assuming CCQE
∆θp
Observed second track
SciBar ∆θp
Use proton track direction to enhanceCCQE / non QE
We fit all samples of near detectors simultaneously.
Low q2 correction
SciBarnon-QE Events
K2K observed forward µ deficit in all ND (KT, SciFi and SciBar).– A source is non-QE events.– For CC-1π,
• Suppression of ~q2/0.1[GeV2] at q2<0.1[GeV2] may exist.
– For CC-coherent π,• The coherent π may not exist.
We do not identify which process causes the effect. The MC CC-1π(coherent π) model is corrected to be consistent with data.
Oscillation analysis is insensitive to the choice.
Study of source ongoing with SciBar.next topics
q2rec
(Data-MC)/MC
DATACC QECC 1πCC coherent-π
Preliminary
q2rec (GeV/c)2
q2rec (GeV/c)2
Φ(Eν) at KEK
Eν
preliminaryχ2=638.1 for 609 d.o.f
– F1 ( En < 500) = 0.03 ± 0.02– F2 ( 500≤ En < 750) = 0.32 ± 0.03– F3 ( 750≤ En <1000) = 0.73 ± 0.04– F4 (1000≤ En <1500) = 1.00 – F5 (1500≤ En <2000) = 0.69 ± 0.03– F6 (2000≤ En <2500) = 0.34 ± 0.02– F7 (2500≤ En <3000) = 0.12 ± 0.02– F8 (3000≤ En ) = 0.05 ± 0.01– nQE/QE = 1.02 ± 0.10
10% error of nonQE/QE is due to lowq2 uncertaintynonQE/QE and low energy spectrum are strongly correlated.
Low q2 problem is key issue for nonQE/QE measurement
small angle cut 0.955CC1π suppression 1.020No coherent π 1.059
7%
3.8%
(Fitting error ~5%)
nonQE/QE (each situation)
Flux fit result (combine all near detectors)
Low q2 (forward µ) deficit
MiniBooNEFrom J. Raaf(NOON04)
(Problem has existed over 3 years)
(GeV2)
Scifi 2track nonQE enriched event
DATACC QECC 1πCC coherent-πCC multi-π
Pure QE sample
Same phenomena is observed by all K2K near detectorsin non-QE sample and other exp. in both QE and non-QE sample.
It is not due to detector systematicsThis discrepancy cannot be explained by the uncertainty of neutrino
spectrum shape. neutrino interaction + nuclear effects
(As for K2K), source is cc1π or coherent π or both.
CC1π vs coherent π
ν µ
ππ∗
t ~ 0
ν µ
πΝ ∗
N
N<< <<<
CC 1π (ν+N µ+N+π) Coherent π
When pi is absorbed inside nucleusor Proton momentum < 400MeV/c,it looks 2track event.
Half of 2nd tracks
in 2track-nonQE sample are proton.
2nd track is completely pion.
We apply PID to 2nd track and makeCC1π enriched/Coherent π enriched samples.
CC Coherent π cross section measurement
Rein-Sehgal
Eν (GEV)
σ(10
-40 C
M2 )/
NU
CL
EO
N
σ(νµCC) = 1.07 x 10-38 cm2/nucleon
Aachen(NC)
GGM(NC)
0123456789
10
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5
K2K (CC)
This measurement is the first experimental resultin a few GeV region for CC int.
providing the test of the theoretical model(σ(Eν), σ(CC)/σ(NC)=2 , σ(A) …)
SciBar can detect the int. with high efficiency (20~30%) and purity (~50%)thanks to the fully activity.
ν µ
ππ∗
t ~ 0
<<<
Coherent π
no activity
Analysis is very close to final stage.release the result in a few months
ν
ν
π0
γ
γ
Data setPeriod : 2000/Jan-Mar. 2001/Jan~Jul. (~ 3x1019 pot)
dataMC
0
100
200
300
400
500
600
700
0 50 100 150 200 250 300Mγγ (MeV/c2)
Nu
mb
er
of
ev
en
ts
Mass peak
(MeV/c2)
data :
147.4MC : 144.1
non-π0 BG very clean π0 sample
Selection Criteria of π0 events 25t fiducial volumeFully-Containednumber of rings = 2both e-like PIDMγγ : 85 ~ 215 MeV/c2
FC 2ring π0 : 2496 events
π0 momentum (FC 2ring π0 sample)#
of F
C 2
ring
π0ev
ents
0
50
100
150
200
250
300
0 200 400 600 800 1000
NC resonant πNC coherent πNC multi πothers
π0 momentum (MeV/c)
( MC is normalizedby area )
large NC fraction ~ 87 %
NFC2Rπ0obs x rpure x corrfid
NNC1π0 =eff
N(NC1π0) : 3.69 ± 0.07 ± 0.37 x 103
stat. sys.
in 25 ton
= 0.065 ± 0.001 ± 0.007stat. sys.
at the K2K beam energy, <Eν>~1.3 GeV
cf. σ(NC1π0) / σ(νµCC) = 0.064 from NEUT
σ(NC1π0)σ(νµCC)
Hep-ex/0408134Submitted to PLB
On going analysis
MA measurement (SciFi, SciBar)
NC π0 , elastic (SciBar)
NC/CC ~20% NC/CC 10~20 %Key : nuclear effect
neutron BG.
Key : Eμ scale
νe measurement (SciBar, 1Kt)
related with K2K νe analysis.
SciFi-MA study (first measurement for water) is almost done.results appear soon.
SciBar-MA analysis is just started.
CC1pi production (SciBar)
Energy dependent cross section (ratio to CCQE)
SummaryThe recent discovery of neutrino oscillation has
renewed interest in the ν-nucleus scattering in thesub to a few GeV region.
In the K2K near detectors, the following topics are studied.- CC coherent pion production (appear soon)- NC pi0 production (submitted in PLB)- MA measurement for water target (appear soon)
On-going analysis-σ(CC1p)/σ(CC) , σ(NC elastic)/σ(QE elastic)- MA (carbon) …..
Many physics results will be released around this summer. Stay tuned!
NEUT: K2K Neutrino interaction MC • CC quasi elastic (CCQE)
– Smith and Moniz with MA=1.1GeV
• CC (resonance) single π(CC-1π)– Rein and Sehgal’s with
MA=1.1GeV• DIS
– GRV94 + JETSET with Bodekand Yang correction.
• CC coherent π– Rein&Sehgal with the cross
section rescale by J. Marteau• NC+ Nuclear Effects
σ/E (10-38cm2/GeV)
Total (NC+CC)
CC Total
CC quasi-elastic
DISCC single π
NC single π0
Eν (GeV)
(Nucl.Phys.Proc.112,p171)