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K2K NC p 0 production. Shoei NAKAYAMA (ICRR, Univ. of Tokyo) for the K2K Collaboration July 28, 2004 @ NuFact04. Outline. Introduction Motivation for p 0 analyses K2K neutrino beam, 1kt water Cherenkov detector Selecting p 0 events and data/MC comparison FC 2ring p 0 sample

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k2k nc p 0 production

K2K NC p0 production

Shoei NAKAYAMA (ICRR, Univ. of Tokyo)

for the K2K Collaboration

July 28, 2004 @ NuFact04

outline
Outline
  • Introduction
    • Motivation for p0 analyses
    • K2K neutrino beam, 1kt water Cherenkov detector
  • Selecting p0 events and data/MC comparison
    • FC 2ring p0 sample
    • data / MC comparison
  • Relative cross section measurement
    • efficiency corrected N(NC1p0)
    • taking ratio to N(nmCC)
  • Summary
motivation for p 0 analyses
Motivation for p0 analyses
  • Main background to nm ne search

p0  gg can mimic an electron

      • asymmetric decay
      • ring overlap
  • Usable to distinguish nm  nt from nm  ns in atmospheric nm oscillation

single p0 events : good NC sample

(see Nakayama’s talk @ICRC2003)

g

g

g

g

nm nt

nm ns

no osc.

nmCC

NC

no change

attenuated

need to know accurately p0 production cross section, p0 momentum and angular distribution

k2k experiment
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 University

KOREA: Chonnam National University / Dongshin University / Korea University /

Seoul National University

U.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 Seattle

POLAND: Warsaw University / Solton Institute

Since 2002

JAPAN: Hiroshima University / Osaka University

CANADA: TRIUMF / University of British Columbia

EUROPE: Rome / Saclay / Barcelona /

Valencia / Geneva

RUSSIA: INR-Moscow

k2k neutrino beam

En (GeV)

K2K neutrino beam
  • almost pure nm beam (~98%)
  • En ~ 1 GeV

Aluminum target

nm energy spectrum

@ front detector site

x1010

Front detector

200m decay tunnel

p+ m+ + nm

Nn / cm2 / 0.1GeV / 1020 pot

p

12GeV PS

1kt water cherenkov detector
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

2m

n beam

4m

25t fiducial volume

data set and selection criteria
Data set and selection criteria

p0 events

  • single-event spill
  • Fully-Contained
  • number of rings = 2
  • both e-like PID
  • Mgg : 85 ~ 215 MeV/c2

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

nring and pid cuts

data

MC

data

MC

Nring and PID cuts

Nring

PID

Preliminary

Preliminary

m-like

e-like

1st ring

m-like

e-like

2nd ring

( MC is normalized by area )

hatch = NC where single p0 and no other mesons get out of 16O nucleus

p 0 mass distribution

data

MC

p0 mass distribution

Preliminary

( MC is normalized by area )

the number of events after each cut

Mass peak (MeV/c2)

data : 147.4 ± 0.5

MC : 144.1 ± 0.3

Preliminary

non-p0 BG

FC 2ring p0 : 2496 events

very clean p0 sample

neutrino interaction mc neut version4 5
(quasi-) elastic

n N  ℓ N’ ( ℓ: lepton )

MA = 1.1 GeV/c2

resonant meson production

n N  ℓ N’ p (h, K)

based on Rein&Sehgal

MA = 1.1 GeV/c2

coherent p production

n16O  ℓ16O p

Rein&Sehgal

J.Marteau et al., NIM A451(2000) cross section rescaled by ~0.7

Neutrino interaction MC ( “NEUT” version4.5 )

n interaction vertex

nuclear effects

  • p and p rescattering in 16O nucleus
    • absorption
    • inelastic scattering
    • charge exchange
  • Pauli blocking
  • Fermi motion
  • nuclear potential
  • deep inelastic scattering
    • n N  ℓ N’ ppp…
    • GRV94 + JETSET
    • A.Bodek et al., hep-ex/0203009 rescaled by q2/(q2+0.188)
the fraction of each interaction channel
The fraction of each interaction channel

CC multi p production

4.1 %

CC resonant meson production

8.8 %

NC resonant meson production

60.4 %

NC elastic scattering

5.0 %

NC multi p production

10.8 %

FC 2ring p0 sample

NC coherent p0 production

10.4 %

large NC fraction ~ 87 %

p 0 momentum distribution

data

MC

p0 momentum distribution

100 MeV/c bin

25 MeV/c bin

Preliminary

Preliminary

stat. error only

# of FC 2ring p0 events

# of FC 2ring p0 events

( MC is normalized

by area )

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

p 0 production angle distribution

data

MC

p0 production angle distribution

10 bins

40 bins

Preliminary

Preliminary

backward

forward

# of FC 2ring p0 events

# of FC 2ring p0 events

stat. error only

( MC is normalized by area )

Agreement between data and neutrino MC is good.

what can be measured
What can be measured ?

p0’s from 16O are largely modified by nuclear effects.

Probability of each p0-16O interaction in NEUT MC

 We measure the p0 production cross section after nuclear effects.

nc1 p 0 definition
“ NC1p0 “ definition

n

NC

only one p0 and no other mesons get out of

a 16O nucleus via NC interactions.

(after nuclear re-scatterings)

?

p0

BG interactions

CC

NC

NC or CC

invisible m

n, invisible m

Recoil p

p0

p0

p0

invisible

p+

p0 w/ invisible m

p0 w/ invisible p,m

p0 produced outside nuclei

nc1 p 0 estimation
NC1p0 estimation

sys.

true/rec = 1.03 ± 0.02

rec  true

fiducial correction

non-NC1p0

subtraction

FC 2ring p0 mom.

NFC2Rp0obs x rpure x corrfid

NNC1p0 =

eff

Preliminary

detection and reconstruction

efficiency

raw NC1p0 mom.

non nc1 p 0 bg subtraction
non-NC1p0 BG subtraction

fraction

NC1p0fraction curve

estimated by neutrino MC

NC 1p071 %

CC w/ invisible p, m

3 %

CC w/ invisible m

6 %

Preliminary

m

m

BG

p0

p0

p

NC1p0

NC w/ invisible p

7 %

p0 produced outside

the nuclei 10 %

inner : stat.

outer : stat.+sys.

n

nor m

p0

p0

p

systematic error on bg subtraction
systematic error on BG subtraction

total: 6.9 %

  • n cross section 6.3 %
  • MA(QE) 1.11.0 && MA(1p) 1.11.0 0.2 %
  • QE cross section +-10% <<1 %
  • 1p cross section +-10% 0.9 %
  • DIS cross section +-5% 0.5 %
  • w/o Bodek reweighting(DIS) 5.1 %
  • w/o Marteau reweighting(coherent p) 1.6 %
  • CC/NC +-20% 3.2 %
  • nuclear rescattering 1.6 %

absorption probability +-30% 1.5 %

inelastic scattering probability +-30% 0.7 %

p0 from nucleon(or p) interaction 2.3 %

in water (2nd interaction)

total interaction probability +-20% 2.3 %

estimated by

reweighting

estimated from

different MC sets

generated with

varied cross section

efficiency correction
efficiency correction

FADC peak cut

(effectively

1000p.e. cut)

p0 detection efficiency curve

estimated by MC

FC cut

Preliminary

Preliminary

Nring = 2

1st ring is e-like

2nd ring is e-like

invariant mass cut

systematic errors for overall efficiency

ring counting 5.4 %

PID 3.9 %

escale(+-3%) 0.3 %

total 6.8 %

inner : stat.

outer : stat.+sys.

overall efficiency : ~46%

nc1 p 0 production in true 25t eff corrected
NC1p0 production in true 25t (eff corrected)

Preliminary

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

MC true

(inner: MC stat,

outer: MC stat + sys error on shape

from our MC model

uncertainties)

# of NC1p0 interactions

stat. sys.

N(NC1p0) : 3.69 ± 0.07 ± 0.37 x 103

Preliminary

in 25 ton

normalized by the number of all events in 25t fiducial

n m cc interactions as a normalization
nmCC interactions as a normalization

nmCC enriched sample :

FC single-ring m-like + FC multi-ring m-like + PC

m

m

m

FC single-ring m-like

FC multi-ring m-like

PC

nmCC fraction 96.5 % 91.2 % 98.5 %

High nmCC fraction, High efficiency

n n m cc estimation
N(nmCC) estimation

N(nmCC)

= N(FCm+PC)25tobs x (1 – BGnon-n) 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

Nobs

FC1Rm 22612

FCmRm 12386

PC 15228

in 25 ton

Preliminary

Preliminary

systematic error on N(nmCC)

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 %

results
Results

Preliminary

stat. sys.

s(NC1p0) / s(nmCC) = 0.065 ± 0.001 ± 0.007

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

cf. s(NC1p0) / s(nmCC) = 0.064 from NEUT

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

(K2K beam spectrum averaged)

<En> ~ 1.3 GeV

summary
Summary
  • 2496 FC 2ring p0 events are observed.
  • Our neutrino MC reproduces data quite well. (p0 momentum, p0 direction)
  • Efficiency corrected number of NC1p0 interactions and their momentum distribution are measured.
  • s(NC1p0) / s(nmCC) = 0.065 ± 0.001 ± 0.007 at the K2K beam energy.
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