New results from the CHORUS New results from the CHORUS Neutrino Oscillation ExperimentNeutrino Oscillation Experiment

Pasquale MigliozziPasquale Migliozzi

CERNCERN

XXIX International Conference on High Energy PhysicsXXIX International Conference on High Energy PhysicsUBC, Vancouver, B. C., CanadaUBC, Vancouver, B. C., Canada

July 23-29 1998July 23-29 1998

OutlineOutline

The CHORUS experimentThe CHORUS experiment DataData Present resultsPresent results OutlookOutlook ConclusionsConclusions

Search forSearch for using the WBB at CERN using the WBB at CERN

at the Dark Matter scale (at the Dark Matter scale (mm22~1 eV~1 eV22))

Philosophy:Philosophy:

direct detection of decay (kink)

The CHORUS experiment The CHORUS experiment

XN heh

noscillatio

3,,,

EMULSION AS “ACTIVE” TARGETEMULSION AS “ACTIVE” TARGET

The neutrino beamThe neutrino beam

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The mean energy of the The mean energy of the beam beam

at the CHORUS emulsion surface isat the CHORUS emulsion surface is

GeV 07.062.26

The anti-neutrino contaminationThe anti-neutrino contaminationof the beam isof the beam is

%09.034.5

The prompt The prompt contaminationcontamination

61043

target and target trackertarget and target tracker Purpose of electronic detectorPurpose of electronic detector

predict tracks back into emulsion kinematical cuts suppress background, e.g. D decays

(particle id, kinematics)

Target:Target: ~800 kg nuclear emulsion (<1m space resolution) Observe the decay topology (kink) in emulsion

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Data Data (data taking finished in 1997)(data taking finished in 1997)

1994 1995 1996 1997 All

Pot/1019 0.81 1.20 1.38 1.67 5.06Chorus efficiency 0.77 0.88 0.94 0.94 0.90

Potato/1019 *) 0.62 1.06 1.30 1.76 4.74Deadtime 0.10 0.10 0.13 0.12

Main triggers 388 k 547 k 617 k 719 k 2271KCC per main trigger 0.30 0.37 0.38 0.40 0.37

1 events 66911 110916 129669 151105 460K

0 events 17731 27841 32548 37929 120K

1 scanned so far 63% 45% 56% 0% 36%

0 scanned so far 50% 15% 0% 0% 19%

1 located so far 18286 20642 30128 0 68156

0 located so far 3401 3805 0 0 7206*) Protons On Target And Tape On

Microscope event viewMicroscope event view

150m

120

m

Emulsion to the beam

Good tracks appear as dots (grains)

Tracking impliesconnection of dotsin different layers

Automatic scanning: Track SelectorAutomatic scanning: Track Selector(developed in Nagoya)(developed in Nagoya)

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11channelchannel

Identify the muon track Identify the muon track and require 0>Pand require 0>P>-30 >-30 GeV/cGeV/c

no other leptons at the no other leptons at the primary vertexprimary vertex

require a kink along the require a kink along the muon track with Pmuon track with PTT>250 >250 MeVMeV

Flight length cut Flight length cut (l<5plates)(l<5plates)

Antineutrino charm Antineutrino charm production (Dproduction (D--) with the ) with the primary lepton not primary lepton not identifiedidentified

1.61.6xx1010-6-6xxNNCCCC

Signal definition (BR=~18%) Background

00channelchannel

Identify a non-muon Identify a non-muon track and require -track and require -1>P1>Phh>-20 GeV/c>-20 GeV/c

no other leptons at the no other leptons at the primary vertexprimary vertex

require a kink along the require a kink along the hadron track with Phadron track with PTT>250 >250 MeVMeV

Flight length cut Flight length cut (l<3plates)(l<3plates)

Antineutrino charm Antineutrino charm production (Dproduction (D--) with the ) with the primary lepton not identifiedprimary lepton not identified

2.32.3xx1010-6-6xxNNCCCC

Neutral current events with Neutral current events with a a - kink-like interaction - kink-like interaction ((white kinkwhite kink))

22xx1010-5-5xxNNCCCC

Signal definition (BR=~68%) Background

Analysis stepsAnalysis steps

Event reconstruction by electronic detectorsEvent reconstruction by electronic detectors track predictions in emulsion

Automatic scanning in interface emulsion sheetsAutomatic scanning in interface emulsion sheets Automatic scanning in bulk emulsion: vertex location and Automatic scanning in bulk emulsion: vertex location and

rejection of not-rejection of not- candidates by candidates by search for short decays (decay inside the vertex plate) search for long decays (decay outside the vertex plate)

Semi-automatic eye scan and remeasuring of retained eventsSemi-automatic eye scan and remeasuring of retained events Event topology and kinematics Event topology and kinematics (emulsion+electronic detector)(emulsion+electronic detector)

candidate or identified background

Vertex locationVertex location

Vertex location procedure

Location efficiency

scan-back track

Vertex validationVertex validation

Impact parameter measurement

Small IP = normal event

Big IP = interesting event (?)

Semi-automatic eye checkSemi-automatic eye check

scan-back track

Offline selectionOffline selection small impact parameter between parent and daughter kink point is in the vertex plate

Semi-automatic eye checkSemi-automatic eye check the events selected automatically are checked by eye for the final judgement

- kink detection (- kink detection (parent searchparent search))

or h

PrinciplePrinciple:Parent track () can be detected bywider view and general angle scanningat the vertex plate

general scanning area

Impact parameter

scan-back track

Experimental check of theExperimental check of the detection detection efficiencyefficiency

Computed using Montecarlo simulationComputed using Montecarlo simulation Checked using events with 2 muons in the final Checked using events with 2 muons in the final

state (~2% of the total)state (~2% of the total) locate the muon tracks in the emulsion scan the emulsion searching for a kink

charm dimuon candidates (muonic D+ decays) Yield in agreement with Montecarlo assuming Yield in agreement with Montecarlo assuming

charmcharm//CCCC = 5% = 5% (measured)(measured)

Run (Year) 1995 1996Expected events

Events found 8 177.04.7 2.24.15

A special eventA special event

sD

s NDN *

CERN-EP/98-87CERN-EP/98-87

Parallel session 5 July 25thParallel session 5 July 25thtalk given by O. Melzertalk given by O. Melzer

ResultsResults

73)-EP/98-(CERN B Lett. Phys. on npublicatio for Accepted 01 684436182 NN

New data: 31974New data: 31974NN++362362NNevents have been analysedevents have been analysed

No candidate has been found!

4100.6][

38.2

eqA

NNBR

rr

P

BR

BR

A

ANN ii

i

ieq

4

20where

if i=4 the is not identified

@ 90% C.L.

CHORUS efficienciesCHORUS efficiencies

1994 1995 1996N 18286 20642 30128

r 1.89 1.89 1.89

rA 0.93 0.93 0.93

<A> 0.39 0.39 0.39

<Ah> 0.17 0.17 -

<Ae> 0.093 0.093 -

<A> 0.026 0.026 -

<> 0.53 0.35 0.37

<h> 0.24 0.25 -

<e> 0.12 0.13 -

<> 0.22 0.23 -

Neq 11987 12743 -

The exclusion plot The exclusion plot (@ 90% C.L.)(@ 90% C.L.)Title:vancouver98.epsCreator:HIGZ Version 1.23/09Preview:This EPS picture was not savedwith a preview included in it.Comment:This EPS picture will print to aPostScript printer, but not toother types of printers.

OutlookOutlook Phase I Phase I (the present till the end of the year)(the present till the end of the year)

we will just complete the scanning of the whole statistics we gain a factor 3 in the 1 sample we gain a factor 6.7 in the 0 sample

PP~2~2xx1010-4-4

Phase II Phase II (towards the final result)(towards the final result)

improvements on the reconstruction algorithms are going

on

because of the increasing scanning power the kink finding

efficiency will improve by about a factor 2

if no if no candidate will be found, the proposal candidate will be found, the proposal

sensitivity will be reachedsensitivity will be reachedPP~1~1xx1010-4-4

ConclusionsConclusions

Neutrino data taking finished in 1997Neutrino data taking finished in 1997 Emulsion data taking in progressEmulsion data taking in progress CHORUS has shown that automatic scanning CHORUS has shown that automatic scanning

procedures are reliable and fastprocedures are reliable and fast No No candidate has been found so far candidate has been found so far

The proposal sensitivity can be reachedThe proposal sensitivity can be reached

LCP .%90100.6 4 @