K2K Near Detector Analysis

K2K Near Detector AnalysisKyoto Univ. Hirokazu Maesaka

For The K2K Collaboration

July 27, 2004

Outline• Introduction• Beam line• Near detector complex• Expected number of SK events• Neutrino energy spectrum• Conclusions

July 27th 2004 K2K Near Detector Analysis 2

K2K Experiment

• Study x oscillation

– disappearance

• Reduction of the number of events• Energy spectrum distortion (Using CC-QE interaction)

– e appearance

~250km

12GeV<E>=1.3GeV 98%

Super-K50kt watercherencov

fixed

+ n – + p


• Pion monitor– Gas cherenkov detector– To validate beam MC

• Pion production• Far/Near flux ratio

• Muon monitor– Ionization chamber and silicon pad– To monitor muon direction and yield spill by spill.

1.0 2.0

Beam Line

p

SK

Near detectorPion monitorMuon monitor

Target & horns

200m300m 250km

Decay tunnel

E(GeV)

Fa

r/N

ear

Ra

tio


Muon Monitor Profile• Muon center is stable within 1mrad.

+ 1 mrad

– 1 mrad

+ 1 mrad

– 1 mrad

’99 ’04

Pro

file

cent

er Y

Pro

file

cent

er X


Near Detector Complex• 1KT: water cherenkov detector [25t fiducial]• SciFi: scintillating fiber and water target [6t fiducial]• LG: Lead glass calorimeter (removed in 2002)• SciBar: fully-active scintillator detector [10t fiducial]

(installed in 2003)• MRD: Iron absorbers and drift tubes

Muon Range Detector (MRD)

Lead Glass or


Delivered Protons On Target• So far, 8.9 x 1019 POT has been accumulated for

physics analysis.

K2K-I K2K

-IIa

SK Rebuilding

LG r

emov

al

Sci

Bar

inst

alla

tion

Acc

umul

ated

PO

T (

x101

8)

Pro

tons

/Pul

se(x

101

2)

1999 2000 2001 2002 2003 2004

K2K

-IIb

0

5

0

20

40

60

80

100


Analysis Strategy1. The number of SK events: NSK

– All interaction modes are used.– 1KT result is adopted.

• Detector systematics are almost same as SK.

2. Neutrino energy spectrum– CC-QE interaction is used.– 1KT, SciFi, and SciBar data are fitted at the sam

e time.

• Both results are extrapolated to SK by using Far/Near ratio.


NSK (The Expected Number of SK Events)

1KT

SK

1KT

SK

Near

Far1KTSK M

MRNN

EEE

EEER

d)()(

d)()(

1KT

SK

Near

Far

efficiency fiducial mass1KT: 25 tSK: 22,500 t

Far/Near ratio

flux cross section

Period NSK Error . K2K-I (Jun.99 – Jul.01) 79.1 +6.2 –5.4 K2K-II (Jan.03 – Feb.04) 71.8 +5.9 –5.1 All 150.9 +11.6 –10.0


Systematic Errors on NSK

• 1KT origin: +/– 4.7%– Fiducial volume error (4.0%) is dominant.

• Live time correction by POT:K2K-I: +/– 0.6%, K2K-II: +/–0.3%

• SK origin: +/– 3.0%– Fiducial volume error (2%) is dominant.

• Far/Near ratio: +5.6 –7.3%• Spectrum shape: +4.0 –3.6%• Neutrino interaction model:

+0.4 –1.1%

Correlation is taken

into account


Energy Spectrum Determination• Neutrino energy can be reconstructed from p

and for CC-QE event:

V: nuclear potential energy

• Fitting procedure 1. Select charged current events.

2. Fit (p,) 2-dimensional histograms with MC templates, and obtain neutrino energy spectrum and non-QE/QE ratio.

cos)(

22)( 22rec

pEVm

VVmmEVmE

N

NN


Event Selection• 1KT (p<1.5 GeV/c)

– Fully-contained single ring -like

• SciFi and SciBar (p>0.5 GeV/c)

– 1-track– 2-track QE enhanced– 2-track non-QE enhanced

p

p SciBar 2-trackQE non-QE

DATACC QECC resonance CC coherent-CC multi-

degree

Expected proton direction assuming CCQE

pObserved second track


Deficit for forward going muons

• Observed in non-QE enhanced samples– Possible source

1. CC resonance production mode– The best suppression factor: q2

true/0.10[GeV2] (q2true<0.10)

2. CC coherent pionproduction mode– It should be

completely removed.

In both cases, Data and MC

agree well for all sub-samples.

SciBar 2-track non-QE

Reconstructed q2 assuming CC-QE


Strategy of Fitting1. Neutrino energy spectrum is determined by requir

ing > 20deg. for 1KT and > 10deg. for SciFi and SciBar.

2. Non-QE/QE is obtained using entire region with low q2 correction. (E spectrum is fixed.)For oscillation analysis, the corrected MC is used.

20 10 10

1KT

SciFi1-track

SciBar

QE QE QE


1KT data

p (MeV/c)

(

deg.

)Fitting Method

• Detector systematic parametersEnergy scale, Tracking efficiency, Nuclear effects

0-0.5 GeV

0.5-0.75GeV

0.75-1.0GeV

••

••

E QE (MC) nonQE(MC)

MC templates

• flux (E) (8 bins)• interaction (nonQE/QE)


Fit Results2=638.1 for 609 d.o.f

– ( E< 0.50) = 0.78 0.36

– (0.50 E < 0.75) = 1.01 0.09

– (0.75 E < 1.00) = 1.12 0.07

– (1.00 E < 1.50) = 1.00 (fixed)

– (1.50 E < 2.00) = 0.90 0.04

– (2.00 E < 2.50) = 1.07 0.06

– (2.50 E < 3.00) = 1.33 0.17

– (3.00 E ) = 1.04 0.18

– non-QE / QE = 1.02 0.11

Additional nonQE/QE error of 10% is assigned based on the sensitivity of the fitted nonQE/QE value by varying the fit criteria.

• >10(20 ) cut: nonQE/QE =0.95 0.04• CC-1 low q2 corr.: nonQE/QE =1.02 0.03 • No coherent nonQE/QE =1.06 0.0

3

10%


Basic Distributions (1KT)• Statistical error only.

– Fitting errors are not shown.

• Data and MC agree well

1KT

0 20 40 60deg.

1KT p

0 500 1000 1500MeV/c

data

MC

CC-QE

data

MC

CC-QE


Basic Distributions (SciFi)

• K2K-IIa data

• Good agreement

data

MCCC-QE

p1-track

p2-track

QE

p2-tracknon-QE

1-track

2-track

QE

2-tracknon-QE

0

0

0

1

1

1

2

2

2 3

3

3 GeV/c

0

0

0

20

20

20

40

40

40

60

60

60 deg.


Basic Distributions (SciBar)

• Agree well

data

MCCC-QE

0 1 2 3 0 20 40 60

0 1 2 3 0 20 40 60

0 1 2 3 0 20 40 60GeV/c deg.


Conclusions• Neutrino beam profile has been stable.• Both the number of events and a neutrino energy s

pectrum are used for an oscillation analysis.• The number of expected SK events (1KT):

150.9 +11.6 –10.0• Neutrino energy spectrum at KEK has been determ

ined.– Deficit is observed for forward going muons.– Either of CC resonance production mode or CC coherent

mode should be reduced.– The energy spectrum has been determined without small

angle.– Non-QE/QE ratio has been obtained with tuned MC.– The tuned MC is used for an oscillation analysis.

Documents

K2K Near Detector Analysis