14 July 2004University of Hawaii Physics Seminar New Nu’s from the DONUT Experiment Emily Maher...
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Transcript of 14 July 2004University of Hawaii Physics Seminar New Nu’s from the DONUT Experiment Emily Maher...
14 July 2004 University of Hawaii Physics Seminar
New Nu’s from the DONUT Experiment
Emily Maher
University of Minnesota
University of Hawaii Physics Seminar14 July 2004
DONUT CollaborationAichi Univ. of Education K. Kodama, N. Ushida
Kobe University S. Aoki, T. Hara
Nagoya University N. Hashizume, K. Hoshino, H. Iinuma, K. Ito,
M. Kobayashi, M. Miyanishi, M. Komatsu,M. Nakamura, K. Nakajima, T. Nakano, K. Niwa,
N. Nonaka, K. Okada, T. Yamamori, Takahashi
Univ. of California/Davis P. Yager
Fermilab B.Baller, D.Boehnlein, W.Freeman,B.Lundberg, J.Morfin, R. Rameika
Kansas State Univ. P. Berghaus, M. Kubanstev, N.W. Reay,
R. Sidwell, N. Stanton, S. Yoshida
Univ. of Minnesota D. Ciampa, C. Erickson, K. Heller, R. Rusack,R. Schwienhorst, J. Sielaff, J. Trammell, J. Wilcox
Univ. of Pittsburgh T. Akdogan, V. Paolone
Univ. of South Carolina A. Kulik, C. Rosenfeld
Tufts University T. Kafka, W. Oliver, J. Schneps, T. Patzak
Univ. of Athens C. Andreopoulos, G. Tzanakos, N. Saoulidou
Gyeongsang University J.S. Song, I.G. Park, S.H. Chung
Kon-kuk University J.T. Rhee
E. Maher
University of Hawaii Physics Seminar14 July 2004
Outline
Goals/Motivation/Status Experimental Setup Data Analysis Results (Nu Tau Events & Charm Events) Individual Event Probabilities Cross Section Measurement Conclusion
University of Hawaii Physics Seminar14 July 2004
Goals/Motivation/Status Goals
Directly observe the charged-current interaction of the tau neutrino – previously attempted but never successfully
Answer the question: is the tau neutrino is a standard model particle?
Motivation Check standard model Neutrino oscillation
Status Have observed tau neutrino interaction (Phys. Lett. B 504, 218
(2001)) Upper limit on tau neutrino magnetic moment (Phys. Lett. B 513,
23 (2001)) Paper on technical details of emulsion target (NIM A 493, 41
(2002)) Paper on technical details of spectrometer (NIM A 516, 21
(2003)) Currently working toward cross section measurement for tau
neutrino – is tau neutrino is a standard model particle
University of Hawaii Physics Seminar14 July 2004
directly observe cc interactions of the
+ N + X
SPECTROMETERDs
800GeV
BEAM DUMP
SHIELDING
EMULSION TARGET
~ 3.5 x 1017 protons for ~1000 interactions
~ Expected 5%
p
Experimental Setup – Block Diagram
University of Hawaii Physics Seminar14 July 2004
Shielding- Purify the Neutrino Beam
Primary Target
Emulsion
Target36m
SpectrometerShielding to protect emulsion from the high
flux of muons.
Sweeping Magnets
Max. int. charged particle flux ~105/cm2
~107/ spill @ 10 cm from emulsion edge
~1012 / spill @ 2 m
University of Hawaii Physics Seminar14 July 2004
SpectrometerMuon ID
Calorimeter
Drift Chambers
Magnet ( =225MeV)
5.5m
3.25m
• Trigger • Vertex Location• Momentum Analysis• Electron ID• Muon ID
Veto Wall
EmulsionScintillatingFiber Target
Tp
University of Hawaii Physics Seminar14 July 2004
Emulsion Target Stand
500 Scintillating Fibers
Image Intensifier - CCD Readout.
Lead Shield
260 kg total mass
University of Hawaii Physics Seminar14 July 2004
Emulsion Target Designs
AgBr suspended in a gel (Fuji ET7C ) coated on plastic sheets.
29±2 grains per 100m for minimum ionizing track
95% emulsion 5% emulsion
ResolutionSpatial Resolution: .3m
Emulsion modules consist stacks of sheets made of emulsion, acrylic, and steel. Three configurations were used.
BULK Sampling 800 Sampling 200
0.32 mm0.08 mm
1.0 mm
0.10 mm0.80 mm
1.0 mm
0.10 mm0.20 mm
Stainless Steel
EmulsionAcrylic
University of Hawaii Physics Seminar14 July 2004
• Predict interaction point in emulsion from spectrometer tracks (software + humans)
• Define a volume in emulsion around predicted interaction point. Digitize all track segments in emulsion volume (hardware processor at Nagoya University)
• Search digitized emulsion data for interaction (software pattern recognition)
•Use spectrometer and emulsion to characterize event ( , )• Use emulsion data to locate kinks, tridents (software pattern recognition)
8 hrs/event
Overview of Analysis
All in mm
e
NETSCAN
University of Hawaii Physics Seminar14 July 2004
Locating Vertices in Emulsion Data
Segment detection efficiency >98%
University of Hawaii Physics Seminar14 July 2004
Event must have:• No e, from primary vertex• Decay with one or three charged products
85% of decays are single charge
CriteriaFinding Interactions
Tau parent must have: • Short decay lengthlength < 10 mm (mean 2.5 mm)
• At least one segment on parent 76% tau’s have visible track
• Small production angle angle < 200 mr (mean 40 mr)
Single prong events must have:• Minimum pt - pt > 250 MeV/c
WXN
0.8 mmacrylic
100 microns emulsion
Single Prong
University of Hawaii Physics Seminar14 July 2004
Components for Finding Interactions Lepton ID
Muon ID – must have 4 out of 6 hits in -ID system in spectrometer
Electron ID – combination of three techniques Identify for electron pairs in emulsion Identify electromagnetic showers in scintillating
fibers Identify electrons using EMCAL
Momentum MeasurementUse spectrometer (analysis magnet and drift
chambers) Use multiple scattering in emulsion data to
measure momentum
University of Hawaii Physics Seminar14 July 2004
WXN
Spectrometer
Fiber tracker Emulsion
Results Charged Current Interaction
University of Hawaii Physics Seminar14 July 2004
From spectrometer
From emulsion
Emulsion tracks to spectrometer
Results Charged Current Interactione
University of Hawaii Physics Seminar14 July 2004
Data Analysis Status
1026 predicted vertices from spectrometer
867 within fiducial volume
655 digitized emulsion data exists
433 vertex found
433 systematic decay search
6.6106 triggers
655 emulsion vertex location attempted
6 candidates
charm candidates7
66 %
Location efficiency
417 events
University of Hawaii Physics Seminar14 July 2004
How Many Events Do We Expect?
How many events do we expect? (calculated using MC)Expect 14.6 tau neutrino charged current interactions
85% will be single prong - expect 12.4 single prong events15% will be tridents events – expect 2.2 trident events
Probability of passing the selection cuts is 0.52 for single prong Expect 6.4 events Observe 4 events
Probability of passing selection cuts is 0.90 for trident events Expect 2 events Observe 2 events
How many background events do we expect? (calculated using MC)Expect 0.8 single prong eventsExpect 2 trident events
University of Hawaii Physics Seminar14 July 2004
What is the Probability all Events are Background?
A signal of 4 single prong events with an expected background of 0.8 events
A signal of 2 trident events with an expected background of 2.0 events
1. The Poisson probability of all signal events being background
Single Prong Events Trident Events
!):(
N
eNf
N
))|(1(_ iPPi
bkgall
01.0!
)8.0:4(
N
ef
N 30.0
!)2:2(
N
ef
N
2. The above method is based on applying cuts to the data set. If we could use a different analysis which uses the events’ topologies, the analysis would contain more information, so it would be more accurate. This analysis will give a relative probability of each candidate being a tau neutrino event, which can be used to calculate a probability that all of the events are background. Since each event is independent, the probability that all events are background is calculated using the following equation:
Two Methods: Individual Event Analysis and Neural Net Analysis
University of Hawaii Physics Seminar14 July 2004
Parameters
Parameters Track production angle Event angular
symmetry Track decay length L Daughter momentum Daughter decay angle Sum of daughter IP = Lsin
Use 4-parameter or 5-parameter analysis to assign probabilities to
event interpretation. pt
View perpendicular to direction
hadrons
hadrons
e
L
Vector sum of all hadrons
p
e
IP
University of Hawaii Physics Seminar14 July 2004
P = The probability of a set of parameters, x, being a result of eventi , where .
Two inputs for each event type:
1. Ai prior probability:
Knowledge of the likelihood of each event i
Relative Normalization (aka Nsignal, Ncharm bkg, Nint.
bkg),
2. PDFi(x): probability density function
Probability of finding event in (x, x+x)
where x is a 4- (for trident events) or 5- (for single prong events) tuple of parameters specific to the individual event
Individual Event Analysis - Bayesian Analysis
jjj
iii
xPDFA
xPDFAxP
)(
)(event|
n}interactio hadronic charm, cc,{ i
University of Hawaii Physics Seminar14 July 2004
Individual Event Probability 1-D example: vs hadron interaction
1. Assume the only possibilities are
or hadron interaction.
2. Use only one parameter to evaluate event.
3333_17665 has = 2.8 rad
| |
| |
int
PDFAPDFA
PDFAP
Expect 0.22 interaction evts. Aint = 0.22
Expect 6.4 events A = 6.4
PDF(int. | = 2.8) = 0.23
PDF( | = 2.8) = 0.81
0
intPDF
measured
99.0
23.22.81.4.6
81.4.68.2|
P
V
University of Hawaii Physics Seminar14 July 2004
Single Prong Event Parameters Track production angle Event angular symmetry Track decay length Daughter decay angle Daughter momentum
Tau Candidate Individual Event Probabilities
Probability all events are background = 7.6 x 10^-8
+
3333
_176
65
3039
_019
10
3263
_251
02
.70 .98 .16 .99
charm .30 .02 .14 .01
hadron scatter 0 0 .70 0
+
cc
3024
_301
75
Single Prong
3334
_199
20
3296
_188
16
.99 .85
.01 .15
0 0
Tridents
Trident Event Parameters Track production angle Event angular symmetry Track decay length Sum of daughter IP’s
University of Hawaii Physics Seminar14 July 2004
Single Prong Event Parameters Track production angle Event angular symmetry Track decay length Daughter decay angle Daughter momentum
Charm Candidate Individual Event Prob.
Trident Event Parameters Track production angle Event angular symmetry Track decay length Sum of daughter IP’s
3065
_032
38
3193
_013
61
0 0 0
charm .99 .94 .98
hadron scatter .01 .06 .02
+
cc
+
Single Prong
3245
_227
86
0
1.0
0
Trident
2986
_003
55
7 Charm Candidates:3 Single Prong1 Trident3 Neutral Vees
University of Hawaii Physics Seminar14 July 2004
Cross Section Measurement
Check to see if the number of tau neutrino charged current interactions DONUT observed agrees with theory – check lepton universality
Cross section can be calculated in different wayso Absolute cross section - first principleso Relative cross section – normalize against number of
muon neutrino and electron neutrinos For second approach, the following quantities are
necessary:o Must define specific cuts to create data set (neutrino
and tau neutrino data sets)o Must know efficiencies (trigger, selection, location,
identification)o Must know the number of electron and muon neutrino
charged current interactions • Electrons – emulsion data, electron ID in
spectrometer• Muons – muon ID in spectrometer
University of Hawaii Physics Seminar14 July 2004
Conclusion Sampling emulsion + spectrometer works even better
than expected Still learning to use all of its power
Near 100% reconstruction efficiency possible (66% now) (<50% was previously “excellent” ie CHORUS)
Particle id, Momentum measurement, Single event probabilities
Increasing event sample continues From 203 to 417
Better understanding of efficiencies and more tau and charm events Improved understanding of backgrounds and systematics Cross section measurements
Technology for future detectors to study short lived particles. OPERA
University of Hawaii Physics Seminar14 July 2004
Single Prong Event Parameters Track production angle Event angular symmetry Track decay length Daughter decay angle Daughter momentum
Comparison of Individual Event and Neural Net Analysis
3333
_176
65
3039
_019
10
3263
_251
02
.70 .98 .16 .99 cc
3024
_301
75Individual Event
3333
_176
65
3039
_019
10
3263
_251
02
.97 1.0 .14 1.0
3024
_301
75
Neural Net Analysis
University of Hawaii Physics Seminar14 July 2004
Individual Event Probabilities
How Many Events Do We Expect?For the 433 neutrino interactions we calculate how many tau neutrino
charged current events we expect to observe using:
where Rate is the calculated rate of a type i event, and is the total efficiency of a type i event, where
.Rate (per kg proton) Expected Number
0.59 92
0.57 104
0.34 108
0.51 96
0.57 14.6
total
ccprompt
ccprompt non
cc e
cc nc
18105.03.2 18106.07.2 18107.04.4
18108.00.3 181013.037.0
iii
NNtotal
total
dataRate
Rate
icc} nc, cc,nonprompt cc, cc,prompt { ei
i
University of Hawaii Physics Seminar14 July 2004
Individual Event ProbabilitiesPrior Probability Calculation
To calculate the prior probability, must know
1. Expected number of neutrino interactions in detector
2. Probability of the process resulting in a kinked track (trident)
3. Trigger, selection, and location efficiencies
4. Probability that the event passes the tau selection criteria
Example: Calculating the prior probability of event 3333_17665
(single prong decay to electron)
Num.exp. interactions:
BR to single prong:
Selection probability: Prior Probability:
Tau D Ds Charm
14.6 5.2 1.9 2.16
0.85 0.46 0.37 0.65
0.52 0.13 0.14 0.09
6.4 0.3 0.1 0.1 0.54
c
University of Hawaii Physics Seminar14 July 2004
Individual Event ProbabilitiesProbability Density Function CalculationCalculating multi-dimensional probability density for a candidate event
1. Each event has measured values of parameters (,p,L) or (,p,L,k,P)
2. Define a (small) interval in parameter space around measured values: v
3. Simulate hypothesis event type:
count number of events which pass all tau selection cuts (Ntotal)
count number of events which are within the interval v (Nv)
Tridents Single Prong
p p p p
L L L L probability density for event
k k
v P P
v
vN
N
total
v