Report on the CHORUS analyses

For the For the CollaborationCollaborationBelgium (Brussels, Louvain-la-Neuve), CERN, Germany (Berlin, Münster), Israel (Haifa), Italy (Bari, Cagliari, Ferrara, Naples, Rome, Salerno),Japan (Toho, Kinki, Aichi, Kobe, Nagoya,Osaka, Utsunomiya) ,Korea (Gyeongsang),The Netherlands (Amsterdam), Russia (Moscow), Turkey (Adana, Ankara,Istanbul)

Alessia SattaAlessia Satta Università degli studi di Roma La Sapienza and INFNUniversità degli studi di Roma La Sapienza and INFN

APS meeting

Contents

• Chorus design• Experimental layout• Results from first phase of the analysis• Status of the second phase of the analysis

• designed to search for oscillation

• proposal exclusion plot

• aim: explore with high sensitivity the m2 region -

suggested by the hypothesis of a large contribution of neutrinos to dark matter-

The experiment proposal

ELm

μ

2sin22sinP

Conceptual design of the experiment

• Search for the “appearance” of in an “pure” beam

• the is detected through CC interactions oscillation signature = identify as one of the products

of a interaction

• the identification is possible exploiting its short decay path (~ 1.5 mm at CHORUS energy)

• use of emulsion (-1 m spatial resolution)as neutrino target and detector + electronic detector to help distinguishing from background

CHORUS apparatuscGeV

p

p/5@%25~

)/100(

%2010~

cGeVp

p

p

%)(

33)(

GevEE

E

spectrometercalorimeter

Hadron spectrometer

Emulsion target + scintillating tracker

Analysis chain

Preselection

Scanning

Post-scanning

• Use electronic detector information.• Select events compatible with the decay modes -BR h-nBR

• Select the events with a daughter candidate reduce the scanning load daughter 1) with P< 30 GeV/ccandidates 2) h with 1<Ph<20 GeV/c

• Starting from the reconstructed events in the electronic detector the daughter candidate tracks are followed back through emulsion to the neutrino vertex searching for a kink topology along their path

•Validation of the hypothesis for the events with a kink topology, i.e. background reduction

Automatic Emulsion Scanning(developed in Nagoya)

The major part of the scanning is fully automated: anhardware video processor (Track Selector) digitizes images (focused at 16 different depths). A track is found searching for grains coincidence in adjacent layers

year views/s

1994 0.008

1996 0.25

1999 3

2001 ~10

Background sources

SOURCE COMMON TO ALL APPEARANCE EXPERIMENT• The prompt component of the beam gives negligible

background, less than 0.1 events is expected at the end of the analysis

SOURCE TYPICAL OF CHORUS EXPERIMENT• The kink signature may originate from:

– Short-lifetime particles decay – mainly charmed hadrons produced in neutrino or antineutrino interactions where the primary lepton is not identified

– Hadrons-emulsion interactions if no nuclear recoil or break-up signs are detected (known as White Star Kink)

Status of the scanning1994 1995 1996 1997 Total

Protons on target/1019 0.81 1.20 1.38 1.67 5.06

Emulsion trigger/103 422 547 617 719 2305

0 sample

Events reconstructed and vertex predicted in emulsion

56111

77443 95751 106093 335398

Events with at least 1 selected negative track

19846

29350 37143 36073 122412

Events scanned so far 13047

17859 29773 24532 85211

Vertex located 3024 4424 8704 7054 23206

1 sample

Events reconstructed and vertex predicted in emulsion

96995

168668 209136 238552 713351

Events with at least 1 negative muon

66309

112943 139077 159296 477625

Events scanned so far 50025

62568 114923 127879 355395

Vertex located 20400

21610 44867 56865 143742

Results of phase I analysis

Let’s look at the data !

NO CANDIDATE HAS BEEN FOUND

0 1

expected 1.1 0.3 0.65 0.11

found 0 0

..%90@

4104.3max34.2)(

LC

NP

Where 2.34 takes into account the systematic uncertainty (15%)

Chorus phase II

• One year ago a second phase of the analysis has begun– New algorithms for reconstruction in electronic

detector– New scanning method for secondary vertices

detection (Net scan)

• This second phase is focused both on oscillation and charm physics

All track segments (All track segments ( < 0.4 rad) in < 0.4 rad) in

Fiducial volume: 1.5 x 1.5 mmFiducial volume: 1.5 x 1.5 mm22 x 8 plates x 8 plates

Offline analysis of emulsion dataOffline analysis of emulsion data

Increase in efficiency ~ 2 , higher purityIncrease in efficiency ~ 2 , higher purity

Track segments from 8 plates overlapped

At least 2-segment connected tracks

Eliminate passing-through tracks

Reconstruct full vertex topology

CHORUS Phase II : net scan

Charm physics Charm hadrons similar lifetime to so possible exploring also charm

physics: direct detection of decay point and topology

(unique feature in neutrino experiment)

The purity of the automatic scanning analysis is so high that almost no manual scan is needed !

• D0 production rateAlready published on a subsample (D(D00) / σ (CC) = 1.99 ) / σ (CC) = 1.99 0.13 0.13 0.17 % 0.17 %

• Inclusive charm studiesExpected 4,000 neutrino-induced charm events Fragmentation fractions D0 : D+ : Ds

+ : c+

B(c), Vcd, s(x), ...

• Associated charm production

• Exclusive channels c absolute BR - QE c production CHORUS

E531

Outlook

• First phase analysis is finished• A new MORE efficient phase is started using

– the power automatic scanning technique Net scan

– new off-line analysis algorithms

• Goals of this Phase II :– reach the proposal sensitivity in oscillation search– Charm physics exploiting the chorus unique feature to be

able to detect the decay topology event by event

WSK background evaluation

• Few measurements available• Difficult to use because the whiteness depends from the

emulsion composition and from the manual scanning rules

Internal normalization– Definition of a signal free reference region (Ldecay >3plate ~ 2800 m )– Measurement of the WSK effective cross-section using CHORUS

data in the reference region – Extrapolation in the signal region with the help of full

MonteCarlo simulation

• Automatic inclusion of the CHORUS efficiency

White Star Kink simulation• The hadron-emulsion interaction is

simulated by FLUKA (A. Ferrari).• The simulation of the emulsion “response”

to the hadron interactions is a critical point– It uses empirical criteria ( and range) to decide

if a particle, a nucleus or a nuclear fragment outgoing from the interaction can be detected during the scanning

Check with KeK data:good agreement

Comparison of WSK simulation and CHORUS data

Using data in the reference region (26 events) check Pt distributionWSK simulation + DATA h-n

Comparison of WSK simulation and CHORUS data (2)

Using data in the reference region (26 events) check kink distributionWSK simulation + DATA h-n

Automatic scanning :phase I

Vertex plate localization Kink finding

One emulsion stack = 36 plates piled-up along the beam direction

Vertex plate= where the track deseappeares

It contains the neutrino interaction or the decay point

Explore part of the vertex plate searching for a small I.P. track with the scan back one ( I.P.< 9 m)

The kink signature by I.P. is checkedmanually

Background at the 0 sample

• Charm production and missed muon– from antineutrino

bg =3.6 x 10 –6 / N located

– from neutrino if the hadron produced in charm decay is wrongly reconstructed as negative

bg =3.4 x 10 –5 / N located

• Hadronic interaction in NC

neutrals -h

XDN

neutrals h

XDN

missed

Background at the 1 sample• Charm production and missed muon

– from antineutrino

– from neutrino if the muon produced in charm decay is wrongly reconstructed as negative

• CC interactions when the primary muon is wrongly associated to an hadron that undergoes WSK interaction or to an hadron from charm decay

neutrals -

XDN

missed

neutrals

XDN