k2k near detector analysis
DESCRIPTION
K2K Near Detector Analysis. Outline Introduction Beam line Near detector complex Expected number of SK events Neutrino energy spectrum Conclusions. Kyoto Univ. Hirokazu Maesaka For The K2K Collaboration July 27, 2004. fixed. K2K Experiment. Study n m n x oscillation - PowerPoint PPT PresentationTRANSCRIPT
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
July 27th 2004 K2K Near Detector Analysis 3
• 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
July 27th 2004 K2K Near Detector Analysis 4
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
July 27th 2004 K2K Near Detector Analysis 5
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
July 27th 2004 K2K Near Detector Analysis 6
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
July 27th 2004 K2K Near Detector Analysis 7
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.
July 27th 2004 K2K Near Detector Analysis 8
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
July 27th 2004 K2K Near Detector Analysis 9
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
July 27th 2004 K2K Near Detector Analysis 10
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
July 27th 2004 K2K Near Detector Analysis 11
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
July 27th 2004 K2K Near Detector Analysis 12
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
July 27th 2004 K2K Near Detector Analysis 13
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
July 27th 2004 K2K Near Detector Analysis 14
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)
July 27th 2004 K2K Near Detector Analysis 15
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%
July 27th 2004 K2K Near Detector Analysis 16
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
July 27th 2004 K2K Near Detector Analysis 17
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.
July 27th 2004 K2K Near Detector Analysis 18
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.
July 27th 2004 K2K Near Detector Analysis 19
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.