Neutrino interaction measurements in K2K SciBar

RCCN Neutrino Workshop December 10, 2004, Kashiwa

M.Hasegawa (Kyoto-Univ.) For the K2K SciBar Group

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

Introduction

Muon range detector

K2K near detector

SciBar was installed in the summer 2003.

Main role is To measure the neutrino property at production To study the neutrino interaction ( useful for SK analysis)

SciBar Detector

Extrudedscintillator(15t)

Multi-anodePMT (64 ch)

Wave-lengthshifting fiber

EM calorim

eter

1.7m

3m

3m

Neutrino target is scintillator itself

2.5 x 1.3 x 300 cm3 cell (15000ch)

(Fairly) large volume

(7000 int. / month/10t)

Just constructed in last summer!

Fine segmented , Full Active SciScintillator-Bar Bar Tracker

Tracking Threshold : 8cm (=0.4GeV/c Proton)Track-finding efficiency >99% (Single Track) Excellent p/using dE/dx misID( P) = 1.7% @ PEff=90%

High 2-track CC-QE efficiency

Identify ν interaction mode clearly

Prelim

inar

y

Prelim

inar

y

SciBar Shot! (1)

p

CCQE candidateCCQE candidate

1

23

CCnQE candidateCCnQE candidate

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 0 candidate e candidate

Vertex!

0

e

e

NC elastic scattering cand.

p

• What can SciBar measure?To estimate SK number of events and

E spectrum (single ring -like) – E spectrum at near site from CC-QE (+n–+p) – CC-QE form factors– CC resonance production form factors (+p–+p++)/(CC-QE) as a function of E

(+n–+p+0)/(CC-QE) as a function of E

(+n–+n++)/(CC-QE) as a function of E

– CC coherent pion production (+C–+C++)– CC multi-pion production– NC resonance production (+N+N’+) e/ flux ratio as a function of Ee appearance

nucleon s measurement (+p+p)/(CC-QE) as a function of q2

Physics output from SciBar

Charged current analysis

Main Motivation is to determine E spectrumshape @ near site and σ(nQE)/σ(QE)

CCQE

nonQE

undetected in W-ch

CC Quasi elastic 1R in W-ch can reconstruct E(p, )

cospEm

2mEmE

N

2Nrec

non Quasi elastic Background for E meas.

Flux measurement (strategy)

nQEQEnQEQE RiFPData /*)(),(

)1(F

nQEQEnQEQE RiFPData /*)(),(

0-0.5 GeV

0.5-0.75GeV

E 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 and 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

p

[GeV/c]

[degre

e]

QE nonQE

DATACC QECC 1CC coherent-CC multi-

p

(deg)(1) 1 Track ( QE fraction 58%) (2) 2 Track QE enriched ( QE fraction 72%) (3) 2 Track nonQE enriched (nQE fraction 83%)

Expected proton direction assuming CCQE

p

Observed second track

SciBar p

We fit these three samples simultaneously.

Used event for flux fitting

p

DATACC QECC 1CC coherent-CC multi-

q2(rec)

Agreement is well exceptfor low q2(forward) region.

Basic distribution (1track)

q2 is reconstructed w/assuming CCQE (q2 ～ 0.01GeV2 @0.10GeV2)

* MC prediction is normalized by the total number of CC candidate events.

Used for flux fitting

Basic distribution (2track QEenriched)

DATACC QECC 1CC coherent-CC multi-

p

Good Agreement(No deficit can be found)

q2(rec)

Basic distribution (2track nQEenriched)

DATACC QECC 1CC coherent-CC multi-

p

Clear deficit can be seen.

q2(rec)

CC1CC coherent

Main source is nonQE

(Next topics)

MC correction in low q2 region

Low q2 suppression in CC-1Q2/0.1 for Q2<0.1(GeV/c)2

No coherent interactions.

We checked the two kinds of correctionsCC1 phenomenological suppressionNo coherent

These correction do not change the flux , but nonQE/QE.

Flux fit result (combined all near detector) (E) at KEK

E

preliminary 2=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 uncertainty nonQE/QE and low energy spectrum are strongly correlated.

LowQ2 problem is key issue for nonQE/QE measurement

small angle cut 0.955 CC1 suppression 1.020 No coherent 1.059

7%

3.8%

(Fitting error ～ 5%)

nonQE/QE (each situation)

SciBar Low q2 study

Low q2(forward ) deficit

MiniBooNEFrom J. Raaf(NOON04)

(Problem has existed over 3 years)

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.

(GeV2)

Scifi 2track nonQE enriched event

DATACC QECC 1CC coherent-CC multi-

(CC1 or coherent or both)

CC1 / coherent

t ~ 0

N

N

<<

<<<

CC 1 (+N+N+) Coherent

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 make CC1 enriched/Coherent enriched samples.

CC1 / coherent

Proton

Pion

Others

Muon Confidence Level (2nd Track : nQE sample)

CC1pi

Others (CC)

Coherent Pi

NCCCQE

CC1pi

Others (CC)

Coherent Pi

NCCCQE

(GeV)2 (GeV)2

Muon-likenonMuon-like

Prelim

inaly

Prelim

inaly

2nd track = Proton like 2nd track = Pion like

Proton Eff. = 85%Purity = 80%

Clear deficit can be seen only in Coherent enriched sample.

CC coherent cross section measurement

Coherent 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.

Analysis stage is very closed to final result.

～ 160 candidate is expected (MC).

20% ～ 30%(stat.+sys.) measurement is expected.

Prelim

inaly

Prelim

inaly

SciBar measurement is not only the firstexperimental result in the few GeV neutrinosfor the charged current production, but alsouse target with ‘A’ less than 20.

K2K

On-going analysisand future prospects

MA measurement

NC π0 , elastic

NC/CC ～ 20% NC/CC 10 ～ 20 %

Key : nuclear effect neutron BG.

～ 10% < 10% ?? Key : Eμ scale

Current situation & goal

e measurement

related with K2K analysis.

NEUT prediction will be more reliable with SciBar data.

Summary

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 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.