Vertex location reconstruction and analysis in opera
This presentation is the property of its rightful owner.
Sponsored Links
1 / 24

Vertex Location, Reconstruction and Analysis in OPERA PowerPoint PPT Presentation


  • 56 Views
  • Uploaded on
  • Presentation posted in: General

Vertex Location, Reconstruction and Analysis in OPERA. Regina Rescigno Salerno Emulsion Group - IPNL Lyon Erice, 48th Course of the International School of Subnuclear Physics 29 Aug 2010 – 07 Sept 010. The OPERA experiment.

Download Presentation

Vertex Location, Reconstruction and Analysis in OPERA

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript


Vertex location reconstruction and analysis in opera

Vertex Location, Reconstruction and Analysis in OPERA

Regina Rescigno Salerno Emulsion Group - IPNL Lyon Erice, 48th Course of the International

School of Subnuclear Physics

29 Aug 2010 – 07 Sept 010


The opera experiment

The OPERA experiment

  • The OPERA (Oscillation Project with Emulsion-tRacking Apparatus )experimentis designed to study the nm→nt oscillation observing the nt appearance in a pure nm beam.

  • The OPERA detector is installed underground in the Gran Sasso Laboratory, 730 km away from CERN, where the CNGS (CERN neutrino beam to Gran Sasso) nm beam is produced.


The signal

m

NO OSCILLATION

nm

nm

t

m

(BR. 17.8 %)

t

e

(BR. 17.3 %)

h

t

(BR. 50.1 %)

h

(BR. 65.3 %)

t

Decay “kink”

t

3h

(BR. 15.2 %)

OSCILLATION

t

m-, e-, h-

nt

nm

 1 mm

(...plus 3-prong decay modes)

The Signal

  • The signal of the occurrence of nm→ntoscillation is the CC interaction nN→X. The tau lepton in the final state is detected through the decay topology (electron, muon and hadron channels available):


Vertex location reconstruction and analysis in opera

1 mm

t

n

Pb

300mm

Emulsion Film

Hybrid target structure

The heart of the experiment:

THE ECC TARGET BRICKS

The acquisition of emulsion images is performed by computer-controlled microscopes able to reconstruct particle tracks with sub-micron precision at high speed

Stack of

57 OPERA films,

56 lead plates (10 X0 )


Vertex location and confirmation

Scan-Back Track

Stop

Vertex location and confirmation

  • Procedure steps:

  • CS scanning to confirm the brick suggested by electronic detectors

  • CS-Brick connection to locate CS tracks in ECC

  • Scan-back in the ECC until track disappearance (hint for primary vertex point)

CS

PB

Beam

4) Volume scan in 1 cm × 1 cm (16 plates) around the track disappearance point

5) Reconstruction of scanning data and topological analysis

6) Visual inspection by operator to confirm/refine the output of the automatic reconstruction


An interesting event

An interesting event

Muonless event 9234119599, taken on 22 August 2009, 19:27

(as seen by the electronic detectors)


Topological features of the event

Topological features of the event

Large area scanning – full reconstruction of vertices and gammas

g2

g1


Analysis

Analysis


Decay kinematics

Decay Kinematics

Kink angle

OPERA nominal analysis flow applied to the hadronic kink candidates

Used exp. Proposal selection criteria

Pt at decay vertex

cut

9

rad

GeV/c

9


Global kinematics

Global Kinematics


Background sources

Background Sources

  • Prompt nt ~ 10-7/CC

  • Decay of charmed particles produced in ne interactions ~ 10-6/CC

  • Double charm production ~ 10-6/CC

  • Decay of charmed particles produced in nm interactions ~ 10-5/CC

  • Hadronic reinteractions (UPDATE wrt OPERA Proposal) ~ 10-5/CC


Vertex location reconstruction and analysis in opera

m

m



h

 -

h

Signal and background

Signal

 CC interaction

Backgrund from hadron interaction in

mNC interaction

To discriminate signal from background → variables in OPERA Proposal:

  • Missing Transverse Momentum (Missing Pt)

  • F Angle

  • Daughter Transverse Momentum

  • Daughter Momentum,

  • Kink angle

Primary Vertex

Decay Vertex


Missing pt

Missing Pt

  • WHAT is Missing Pt ?

Missing Pt is the unbalance in the total momentum in the neutrino transverse plane

  • WHICH are missing Pt sources?

  • Neutrinos

Even for events without neutrinos in the final state there are other possible sources:

  • Nuclear re-interaction and Fermi motion

  • Measurement Errors

  • Undetected particles:

  • Neutral particles

  • Particles with large angles (stopping in lead, or appearing very far from vertex point) or protons with low energies


Vertex location reconstruction and analysis in opera

Daughter momentum used

Missing Pt due to undetected neutrino of decay vertex

Tau

Tau daughter

Neutrino

Visible particle

Not visible particle

Missing Pt – nmNC and ntCC events

For nmNC and ntCC events: the initial Missing Pt is determined by the presence of neutrinos in the direction opposite the hadronic system

Tau momentum not measurable

X

Neutrino not detected

nmNC

X

ntCC


Missing pt1

Missing Pt

Missing Pt at primary vertex

Blue: MC NC

Black: MC - t

Missing Pt at primary vertex

cut

cut

GeV/c


Vertex location reconstruction and analysis in opera

nmNC

F

F

ntCC

j Angle

j angle: the angle in neutrino transverse plane between parent track and total momentum of hadron

t

h

Hadron Momentum in transverse plane


Vertex location reconstruction and analysis in opera

j Angle

j Angle

Blue: MC - NC

Black: MC - t

cut

17

rad


Reinteraction background

Reinteraction background

Search for “kinks” and interactions along a total of 9 m of hadron track measured for scanned events. About 100 m are needed to fully validate the MC information

Signal region

  • no events in the signal region

  • 90% CL upper limit of 1.54 x 10-3 kinks/NC event

  • the number of events outside the signal region is confirmed by MC (within the ~30% statistical accuracy of the measurement)


Conclusion and outlook

Conclusion and outlook

  • The OPERA experiment at LNGS is aimed at the first detection of neutrino oscillations in appearance mode through the study of the nm- nt channel

  • The technique of vertex location, reconstruction and analysis in OPERA has been shown to work

  • The Collaboration has conducted the analysis of a sub-sample of the neutrino data taken in the CERN CNGS beam in the 2008-2009 runs.

  • One muonless event showing a t →1-prong hadron decay topology has been detected and studied in detail. It passes all kinematical cuts required to reduce the physics background. It is the first nt candidate event in OPERA.


Vertex location reconstruction and analysis in opera

Thank you for your attention


Backup slides

Backup Slides


Statistical considerations

Statistical considerations

We observe 1 event in the 1-prong hadron t decay channel,

with a background expectation (estimating a 50% error for each component) of:

0.011 events (reinteraction)

0.007 events (charm)

0.018 ± 0.007 (syst) events 1-prong hadron

all decay modes: 1-prong hadron, 3-prongs + 1-prong μ + 1-prong e

0.045 ± 0.020 (syst) events total BG

(here we add up the errors linearly)

By considering the 1-prong hadron channel only, the probability to observe 1 event

due to a background fluctuation is 1.8%, for a statistical significance of 2.36 s on the

measurement of a first nt candidate event in OPERA.

If one considers all t decay modes that were included in the search, the probability

to observe 1 event for a background fluctuation is 4.5%.

This corresponds to a significance of 2.01 s.


Event statistics

Event statistics

Event statistics

  • Events collected by 2008-2009 run 5391

  • Brick tagging efficiency times vertex location efficiency:~ 60%

  • Total neutrino vertices found: 1921

    (This is ~60% of the total 2008-2009 run statistics )

  • Events for which “decay search” was completed: 1088 (187 NC)

    (This is ~35% of the total 2008-2009 run statistics,

    corresponding to 1.85 x 1019 pot)

  • With the above statistics, and for Dm223 = 2.5 x10-3 eV2 and full mixing, OPERA expects:

    ~ 0.5 ntevents

23


  • Login