1. Neutrino interaction measurements in K2K SciBar
RCCN Neutrino Workshop
December 10, 2004, Kashiwa
M.Hasegawa (Kyoto-Univ.)
For the K2K SciBar Group

2. Table of Contents Introduction SciBar Detector
Charged current analysis
Flux fitting 　(σ(nQE)/σ(QE))
Low Q2 deficit
On-going analysis and future prospects
Summary

3. Introduction n K2K near detector
Muon range detector n
Main role is
To measure the neutrino property at production
To study the neutrino interaction
( useful for SK analysis)
SciBar was installed in the summer 2003.

4. SciBar Detector n Preliminary Just constructed in last summer!
Extruded
scintillator
(15t)
Multi-anode
PMT (64 ch)
Wave-length
shifting fiber
EM calorimeter
1.7m 3m
Fine segmented , Full Active
Scintillator-Bar Tracker
Neutrino target is scintillator itself
2.5 x 1.3 x 300 cm3 cell (15000ch)
(Fairly) large volume
(7000 int. / month/10t)
Tracking Threshold : 8cm
(=0.4GeV/c Proton)
Track-finding efficiency
>99% (Single Track)
Preliminary
Excellent p/m(p) using dE/dx
misID(m P) = PEff=90%
High 2-track CC-QE efficiency
Identify ν interaction mode clearly
Just constructed in last summer!

5. SciBar Shot! (1) CCQE candidate CCnQE candidate p m 3 2 1
Area of circle is proportional to ADC.
Hits along the proton track are larger
CCQE candidate
CCnQE candidate p n m 3 2 n 1

6. SciBar Shot! (2) NC p0 candidate ne candidate
Large energy deposit
in Electron Catcher e p
Vertex! p0 e n g
NC elastic scattering cand. p

7. Physics output from SciBar
What can SciBar measure?
To estimate SK number of events and
En spectrum (single ring m-like)
En spectrum at near site from CC-QE (n+nm–+p)
CC-QE form factors
CC resonance production form factors
s(n+pm–+p+p+)/s(CC-QE) as a function of En
s(n+nm–+p+p0)/s(CC-QE) as a function of En
s(n+nm–+n+p+)/s(CC-QE) as a function of En
CC coherent pion production (n+Cm–+C+p+)
CC multi-pion production
NC resonance production (n+Nn+N’+p)
ne/nm flux ratio as a function of En (ne appearance)
 nucleon Ds measurement
s(n+pn+p)/s(CC-QE) as a function of q2

8. Charged current analysis
Main Motivation is to determine En spectrum
near site and σ(nQE)/σ(QE)
CC Quasi elastic
CCQE
1Rm in W-ch
can reconstruct En (pm, qm)
undetected
in W-ch
nonQE
non Quasi elastic
Background for En meas.

9. Flux measurement (strategy)
(F(i) : Flux weight , RnQE/QE : cross section ratio)
En QE (MC) nQE(MC) pm qm
[GeV/c]
[degree]
MC templates
*F(1)
0-0.5 GeV
*F(2)
*F(2)*RnQE/QE
GeV
*F(3)
*F(3)*RnQE/QE
GeV
We change Flux
and nonQE/QE and
search for best combination
by comparing with data.
*F(4)
*F(4)*RnQE/QE
GeV • •

10. Used event for flux fitting
SciBar Dqp QE
nonQE
DATA
CC QE
CC 1p
CC coherent-p
CC multi-p
Dqp
(deg) m
Observed second track
Dqp
Expected proton direction
assuming CCQE
(1) 1 Track ( QE fraction 58%)
(2) 2 Track QE enriched ( QE fraction 72%)
2 Track nonQE enriched (nQE fraction 83%)
We fit these three samples simultaneously.

11. Basic distribution (1track)
q2 is reconstructed w/
assuming CCQE
(dq2 pm
Agreement is well except
for low q2(forward) region.
DATA
CC QE
CC 1p
CC coherent-p
CC multi-p
Used for flux fitting
q2(rec) qm
* MC prediction is normalized by the total number of CC candidate events.

12. Basic distribution (2track QEenriched)pm
Good Agreement
(No deficit can be found)
DATA
CC QE
CC 1p
CC coherent-p
CC multi-p qm
q2(rec)

13. Basic distribution (2track nQEenriched)
Clear deficit can be seen. pm
 Main source is nonQE
CC1p ?
CC coherent p ?
(Next topics)
DATA
CC QE
CC 1p
CC coherent-p
CC multi-p qm
q2(rec)

14. MC correction in low q2 region
Low q2 suppression in CC-1p
{Q2/0.1 for Q2<0.1(GeV/c)2}
No coherent p interactions.
We checked the two kinds of corrections
CC1p phenomenological suppression
No coherent p
These correction do not change the flux , but nonQE/QE.

15. Flux fit result (combined all near detector)
F(En) at KEK
c2=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
preliminary
small angle cut
CC1p suppression
No coherent p 7%
3.8%
(Fitting error ～5%)
nonQE/QE (each situation) En
10% error of nonQE/QE is due to lowQ2 uncertainty
nonQE/QE and low energy spectrum are strongly correlated.
LowQ2 problem is key issue
for nonQE/QE measurement

16. SciBar Low q2 study

17. Low q2(forward m) deficit
(Problem has existed over 3 years)
Scifi 2track nonQE enriched event
DATA
CC QE
CC 1p
CC coherent-p
CC multi-p
MiniBooNE
From J. Raaf
(NOON04)
(GeV2)
Same phenomena is observed by other detectors.
 It is not due to the detector systematics.
This discrepancy cannot be explained by uncertainty of
the neutrino spectrum shape.  Neutrino interaction
From K2K (SciBar/Scifi) data , source is nonQE int.
(CC1p or coherent p or both)

18. CC1p / coherent p n m n m p* p p t ~ 0 CC 1p (n+Nm+N+p) Coherent p
< p*
<
<
N *
<
< p p N
t ~ 0 N
When pi is absorbed inside nucleus
or 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 make
CC1p enriched/Coherent p enriched samples.

19. CC1p / coherent p Preliminaly
Muon Confidence Level (2nd Track : nQE sample)
Proton
Proton Eff. = 85%
Purity = 80%
Pion
Others
non
Muon-like
Muon-like
Preliminaly
2nd track = Proton like
2nd track = Pion like
Coherent Pi
Coherent Pi
CC1pi
CC1pi
Others (CC)
Others (CC) NC NC
CCQE
CCQE
(GeV)2
(GeV)2
Clear deficit can be seen only in Coherent p enriched sample.

20. CC coherent p cross section measurement
SciBar measurement is not only the first
experimental result in the few GeV neutrinos
for the charged current production, but also
use target with ‘A’ less than 20.
K2K
Coherent p is most suspicious mode of low q2 deficit.
Scibar can select this mode with(fairly)
high efficiency (20～30%) and purity (>～50%)
by using info. of activity around vertex region.
～160 candidate
is expected (MC).
20%～30%(stat.+sys.)
measurement is expected.
Preliminaly
Analysis stage
is very closed to
final result.

21. On-going analysis and future prospects

22. Current situation & goal
NC π0 , elastic
NC/CC ～20%  NC/CC 10～20 %
Key : nuclear effect
neutron BG.
MA measurement
～10%  < 10% ??
Key : Eμ scale
ne measurement
related with K2K analysis.
NEUT prediction will be more reliable with SciBar data.

23. Summary First physics result will be released
A brand new neutrino detector ‘SciBar’ was installed
in K2K near detector and took ～ 20k neutrino data.
Basic distributions for muon agree with MC prediction
well except for lowq2 region.
We confirmed a main cause of lowq2 deficit was
nonQE int, especially coherent p is suspicious with
observed data.
We already started the following analysis,
nonQE/QE and MA /NC pi0 / .....
First physics result will be released
in the begging of next year.