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


Outline

Goals/Motivation/Status Experimental Setup Data Analysis Results (Nu Tau Events & Charm Events) Individual Event Probabilities Cross Section Measurement Conclusion


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


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


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


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


Emulsion Target Stand

500 Scintillating Fibers

Image Intensifier - CCD Readout.

Lead Shield

260 kg total mass


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


• 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


Locating Vertices in Emulsion Data

Segment detection efficiency >98%


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


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


WXN

Spectrometer

Fiber tracker Emulsion

Results Charged Current Interaction


From spectrometer

From emulsion

Emulsion tracks to spectrometer

Results Charged Current Interactione


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


Typical Event – No Emulsion DataU View

V View


Atypical Event – Emulsion Data, Not Located


Phase 1 Candidates


Phase 2 Candidates


Results Charm Candidates


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


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


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


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


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

PDF

intPDF

measured

99.0

23.22.81.4.6

81.4.68.2|

P

V


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


3263_25102 (Scatter) & 3333_17665 (Tau)



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


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


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


More Charm Candidates



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


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


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


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

14 july 2004university of hawaii physics seminar new nu’s from the donut experiment emily maher...

Documents

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