K2K NC 0 production

Shoei NAKAYAMA (ICRR, Univ. of Tokyo)for the K2K Collaboration

July 28, 2004 @ NuFact04

Outline

• Introduction– Motivation for 0 analyses– K2K neutrino beam, 1kt water Cherenkov detector

• Selecting 0 events and data/MC comparison– FC 2ring 0 sample– data / MC comparison

• Relative cross section measurement– efficiency corrected N(NC10)

– taking ratio to N(CC)

• Summary

Introduction

Motivation for 0 analyses

• Main background to e search

0 can mimic an electron• asymmetric decay• ring overlap

• Usable to distinguish from s in atmospheric oscillation

single 0 events : good NC sample

(see Nakayama’s talk @ICRC2003)

s

CC NC

no change

attenuatedneed to know accurately 0 production cross section, 0 momentum and angular distribution

no osc.

K2K experiment

JAPAN: High Energy Accelerator Research Organization (KEK) /Institute for Cosmic Ray Research (ICRR), Univ. of Tokyo / Kobe University / Kyoto University /Niigata University / Okayama University / Tokyo University of Science / Tohoku UniversityKOREA: Chonnam National University / Dongshin University / Korea University /Seoul National UniversityU.S.A.: Boston University / University of California, Irvine / University of Hawaii, Manoa /Massachusetts Institute of Technology / State University of New York at Stony Brook /University of Washington at SeattlePOLAND: Warsaw University / Solton Institute

Since 2002JAPAN: Hiroshima University / Osaka UniversityCANADA: TRIUMF / University of British ColumbiaEUROPE: Rome / Saclay / Barcelona /Valencia / Geneva RUSSIA: INR-Moscow

K2K neutrino beam

E (GeV)

• almost pure beam (~98%)

• E ~ 1 GeV

N

/ cm

2 /

0.1G

eV /

1020

pot

energy spectrum@ front detector sitex1010

12GeV PS

p

Aluminum target

Front detector

200m decay tunnel

+ + +

1kt water Cherenkov detector

• 1000t cylindrical water tank• a smaller version of Super-Kamiokande (~1/50 volume)• 680 20inch PMTs with 70cm spacing (same as SK)• the same detection mechanism, analysis algorithms

and interaction MC as SK

beam

25t fiducial volume

2m

4m

Selecting 0 events and data/MC comparison

Data set and selection criteria

Observed data : 2000/1~3, 2001/1~7 (~ 3x1019 pot)

0 events

single-event spill Fully-Contained number of rings = 2 both e-like PID M : 85 ~ 215 MeV/c

2

Nring and PID cuts

Nring PIDe-like -like

e-like -like

1st ring

2nd ring

hatch = NC where single 0 and no other mesons get out of 16O nucleus

dataMC

dataMC

( MC is normalized by area )

PreliminaryPreliminary

0 mass distribution

very clean 0 sample

( MC is normalized by area )dataMC

FC 2ring 0 : 2496 events

the number of events after each cut

non-0 BG

Mass peak (MeV/c2)

data : 147.4 ± 0.5 MC : 144.1 ± 0.3

Preliminary

Preliminary

Neutrino interaction MC ( “NEUT” version4.5 )

• (quasi-) elastic– N ℓ N’ ( ℓ : lepton )

– MA = 1.1 GeV/c2

• resonant meson production– N ℓ N’ (, K)

– based on Rein&Sehgal

– MA = 1.1 GeV/c2

• coherent production– 16O ℓ 16O – Rein&Sehgal – J.Marteau et al., NIM A451(2000)

cross section rescaled by ~0.7

• and p rescattering in 16O nucleus– absorption– inelastic scattering– charge exchange

• Pauli blocking• Fermi motion• nuclear potential

• deep inelastic scattering

– N ℓ N’ …

– GRV94 + JETSET– A.Bodek et al., hep-ex/0203009 rescaled by q2/(q2+0.188)

interaction vertex nuclear effects

The fraction of each interaction channel

NC resonant meson production60.4 %

NC coherent 0 production10.4 %

NC multi production10.8 %

NC elastic scattering5.0 %

CC resonant meson production8.8 %

CC multi production4.1 %

large NC fraction ~ 87 %

FC 2ring 0 sample

0 momentum distribution

100 MeV/c bin 25 MeV/c bin

stat. error onlydataMC

The observed data is reproduced fairly well by our neutrino MC.

# o

f F

C 2

rin

g

0 ev

ents

# o

f F

C 2

rin

g

0 ev

ents

PreliminaryPreliminary

( MC is normalizedby area )

0 production angle distribution

10 bins 40 bins

stat. error only

dataMC

Agreement between data and neutrino MC is good.

backward forward

Preliminary

# o

f F

C 2

rin

g

0 ev

ents

# o

f F

C 2

rin

g

0 ev

ents

( MC is normalized by area )

Preliminary

Relative cross section measurement(NC10) / (CC)

What can be measured ?

0’s from 16O are largely modified by nuclear effects.

Probability of each 0-16O interaction in NEUT MC

We measure the 0 production cross section after nuclear effects.

“ NC10 “ definition

0

NC

?

only one 0 and no other mesons get out ofa 16O nucleus via NC interactions.(after nuclear re-scatterings)

0

invisible CC

0

, invisible NC or CC

+invisible 0

NC

Recoil p

BG interactions

0 w/ invisible 0 w/ invisible , 0 produced outside nuclei

NC10 estimation

NFC2R0obs x rpure x corrfid

NNC10 = eff

non-NC10

subtraction

rec truefiducial correction

detection and reconstructionefficiency

FC 2ring 0 mom.

raw NC10 mom.

true/rec = 1.03 ± 0.02

sys.

Preliminary

non-NC10 BG subtraction

NC10 fraction curveestimated by neutrino MC

NC10

BG

inner : stat.outer : stat.+sys.

NC 10 71 %

fraction

0

0

0

0

or

CC w/ invisible 6 %

CC w/ invisible , 3 %

NC w/ invisible 7 %

0 produced outside the nuclei 10 %

Preliminary

systematic error on BG subtraction

cross section 6.3 %MA(QE) 1.11.0 && MA(1) 1.11.0 0.2 %QE cross section +-10% <<1 %1 cross section +-10% 0.9 %DIS cross section +-5% 0.5 %w/o Bodek reweighting(DIS) 5.1 %w/o Marteau reweighting(coherent ) 1.6 %CC/NC +-20% 3.2 %

nuclear rescattering 1.6 %absorption probability +-30% 1.5 %inelastic scattering probability +-30% 0.7 %

0 from nucleon(or interaction 2.3 %in water (2nd interaction)

total interaction probability +-20% 2.3 %

estimated fromdifferent MC setsgenerated withvaried cross section

total: 6.9 %

estimated byreweighting

efficiency correction

0 detection efficiency curveestimated by MC

inner : stat.outer : stat.+sys.

overall efficiency : ~46%

FADC peak cut(effectively 1000p.e. cut)

FC cut

Nring = 2

1st ring is e-like

2nd ring is e-likeinvariant mass cut

systematic errors for overall efficiency

ring counting 5.4 %PID 3.9 %escale(+-3%) 0.3 %

total 6.8 %

Preliminary Preliminary

NC10 production in true 25t (eff corrected)

N(NC10) : 3.69 ± 0.07 ± 0.37

x 103

stat. sys.

data (inner: stat, outer: stat+sys)

MC true

(inner: MC stat,

outer: MC stat + sys error on shape

from our MC model

uncertainties)

normalized by the number of all events in 25t fiducial

in 25 ton

# o

f N

C1

0 in

tera

ctio

ns

Preliminary

Preliminary

CC interactions as a normalization

CC enriched sample :FC single-ring -like + FC multi-ring -like + PC

FC single-ring -like FC multi-ring -like PC

High CC fraction, High efficiency

CC fraction 96.5 % 91.2 % 98.5 %

N(CC) estimation

N(CC)

= N(FC+PC)25tobs x (1 – BGnon-) x purity x corrfid / eff

= 50226 x (1 – 0.015) x 0.960 x 1.02 / 0.854

stat. sys.

= 5.65 ± 0.03 ± 0.26 x 104

BG: NC inefficiency: multi-ring PID FADC cut

eff energy scale 1.2 %PID 1 %

(1/eff) x rpure E spec. 0.5 %cross section 1.1 %

corrfid fiducial volume 4 % total 4.6 %

Nobs

FC1R 22612FCmR 12386PC 15228

systematic error on N(CC)

in 25 ton

Preliminary

Preliminary

Results

(NC10) / (CC) = 0.065 ± 0.001 ± 0.007

cf. (NC10) / (CC) = 0.064 from NEUT

cf. (CC) ~ 1.1 x 10-38 cm2 / nucleon from NEUT

(K2K beam spectrum averaged)

stat. sys.

<E> ~ 1.3 GeV

at the K2K beam energy, <E>~1.3 GeV

Preliminary

Summary

• 2496 FC 2ring 0 events are observed.

• Our neutrino MC reproduces data quite well.(0 momentum, 0 direction)

• Efficiency corrected number of NC10 interactions and their momentum distribution are measured.

• (NC10) / (CC) = 0.065 ± 0.001 ± 0.007 at the

K2K beam energy.