report on the chorus analyses
DESCRIPTION
Report on the CHORUS analyses. Alessia Satta Università degli studi di Roma La Sapienza and INFN. For the. Collaboration. Belgium (Brussels, Louvain-la-Neuve), CERN, Germany (Berlin, Münster), Israel (Haifa), Italy (Bari, Cagliari, - PowerPoint PPT PresentationTRANSCRIPT
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