F. Juget
– D. Duchesneau Ankara, April 1rst 2009
1

• Tau decay channel study
– Summary of last Physics coordination meeting
• Charm study
– Charm analysis status for 2008 data
– Strategy for 2008 and 2009 data
2

• Work from Tiem: t
m
• Re-estimation of the efficiency for long decay DIS, using “beamfile” was done – compatible with proposal values
• Possible improvement to investigate w.r.t to proposal:
– Changing the range of kink angle (see next slide):
– Proposal: 20 mrad < q < 500 mrad
– Investigate: 10 mrad < q < 700 mrad

Understand efficiency for angles > 500 mrad
– Optimized kinematical cuts – study correlation
– Investigate decay in plastic base
• The efficiency re-estimation will be redone with OpEmurec data
• Work already started on likelihood function to separate tau to charm background
3

From Tiem 4

From Tiem 5

t
• From Frank
– From the proposal estimation of the efficiency investigate where we can improve:
– Long decay (DIS-QE) – For short decay DIS
• Electron energy cut ( e
E
~90%)
• P
T
~ 100 MeV ( e
PT
~99%) e kine
= e
B2B x e
E x e
PT x e e->e
~ 83%-84%
•Track momentum > 1 GeV ( e p
~ 66%)
•IP cut 5-20 micron
(depends on Z of vertex in lead) ( e
IP
~45%)
•Electron energy cut ( e
E
~79%)
•Min P
T
~ 50 MeV ( e
PT
~97%) e kine
= e p x e
IP x e
E x e
PT x e e->e
~ 22%
Small room for improvement Possible improvement to be investigate
6

t
– Investigate possible improvement of kinematical cuts (mainly possible in short decay)
– Re-estimate all the efficiency using MC and information from 2008 data
– Re-estimate and study all the background
• Remark: no n e
CC event found yet in 2008 data! We should expect 10-20 events

Do we need dedicated work for n e event search?
7

(from Giulia)
 Kinematical Analysis : Variables obtained (E e
, E vis
,P
T miss ) with a smearing according to OPERA resolutions:

Cut on the visible energy to reduce γ component and the prompt n e component from the background

Cut on the number of grains associated with the e-track to reduce B( n m
CC→ n m
NC)

Cut on P
T miss @ the primary vertex to reduce NC contamination and suppress B( t →e)

Efficiencies: Brick finding, Vertex finding, Trigger and Fiducial
Volume cut
Previous analysis ( see arXiv:hep-ph/0210043v1
)
Signal and BG efficiencies:
Signal t →e n m
CC→ n m
NC n m
NC

0.53
0.53
0.52
0.48
e
0.31
0.032
0.34 10 -4 7.0 10 -4

= Brick Finding*Vertex Finding*Trigger*Fiducial Volume Cut e
= Final efficiencies according to the considered smearing n e beam
0.53
0.082
8

analysis
(from Giulia)
• Cuts to be re-optimized
• Study of vertex location efficiency: full simulation needed, real data comparison
 Important for QE events
• Study of gamma conversion: full simulation needed, real data comparison
• n m
CC data needed to validate the analysis on E vis
, P
T miss
• Data needed to validate the π/e mis-ID study
• Demonstrate the knowledge of the in order to study n e n e component in the beam, wrt other beam distributions ( n m
, n m
)
9

t
10

t 
al
Propos p
= DIS 20%
QE 28%
LM : low multiplicity, HM : High Multiplicity
To reduce hadronic int BG, severe cut is applied.
Pt > 600 MeV/c (most severe cut)
Daughter momentum > 2GeV/c
Kinematical analysis at the decay vertex.
Pt mis < 1GeV/c at 1ry vertex
Large in NC int, small in CC int.
f
> p
/2 for t candidate
Kinematical analysis at the primary vertex.
Only for HM events
11 11 AATA

• Cut with 600 MeV/c in the proposal.  too high?
MC
MC
Daughter particle of τ
Pt(GeV/c)
AATA
Daughter particle of hadronic interactions
Pt(GeV/c)
12

– Pt distribution of the daughter particles from had-int.
– Fraction of white kink.
– Big uncertainty in MC.
– Hopefully to set lower threshold for Pt cut.
– Most of t decay include p
0 in decay daughter.
– By detecting g from 2ry vertex, reduce background  set lower threshold for Pt cut.
13

t  h
t Long decay
Kink detection
 h MC
Gamma detection
Hadronic interaction study
Scan
Forth Momentum measurement
Detection efficiency g
Energy reconstruction
Pointing resolution
MC
MC
Short decay
IP accuracy improvement
MC
A lot of work to do…
14

t
15

t analysis and charm separation in the 3-prong channel :
(D. Duchesneau); report based on Magali’s thesis work
•Charm background discrimination in the t 
3h channel has been studied for the first time at detector level, after vertex reconstruction.
•The
D 0 events have been taken into account with reconstruction inefficiency for each decay channel .
•
Vertex reconstruction is a key issue for this particular topology
Prospects:
Clear possibility of improvements to be investigated; this analysis should be redone using similar approach but:
• adapt the official charm rate and branching fractions
• using new more discriminating variables (like phi angle etc…) in the likelihood
• using more refined muon misidentification estimates for charm rejection
• study a different vertex algorithm as suggested in OPERA Internal note #97
• re-evaluate background (ex Fluka)
16

• The work of efficiency estimation has started for each channel
• Some work are common for each channel
– m ID, vertex reconstruction, kink angle, gamma detection, IP ….
• 2008 data has to be used to validate the simulation results (vertex reconstruction, MCS, kink, gamma, Ptmiss, kinematical analysis….)
• Simulation and 2008 data will be used to study background

• Number of events in bricks 1690, i.e. 1190 CC
– Based on Talks of Dario (Japan) and Francesco (Sorrento)
 (D 0 )/  (CC)=(1.91±0.13)%
 (C + )/  (CC)=(2.47±0.22)% neutral charm charged charm
Inclusive charm production at OPERA energy
 (Charm)/  (CC)=(4.38±0.26)% ~ 52.1±3.6 Events
N
D
0 =22.7±1.5
N fully neutrals
N
2p
3±1
16±0.2
N
4p
3.3±0.3
N
C
+ =29.4±2.0
N
N
1p
3p
=19±2
=10±1 by Francecso

• Trigger 99.9%
• Brick Finding 70-80%
• Geometry 96.5%
• Vertex localisation 85-90%
• Muon requested 80-90%
• Decay category
– Long ~50%, short ~50%
• Charm candidate selection
– Muon energy > 1 Gev, primary vertex in plate 56 or lower
– 88% of all charm events (from MC)
– Reconstruction efficency Not included yet, O(75%)
• Overall ~44%  22.9
± 1.6 Charm Events
N
D
0 =10.0±0.6
N fully neutrals
N
2p
N
4p
1.3±0.4
7±0.1
1.5±0.1
N
C
+
N
=12.9±0.9
1p
=8.4±0.9
N
3p
=4.4±0.4
by Thomas

• Up to know ~400 events found (in Europe)

~320 CC events (~25% of the total)
• Expected charm: 22.9x0.25 = 5.7 ± 0.4
N
D
0 =2.5±0.1
N fully neutrals
N
2p
N
4p
0.3±0.1
1.7±0.2
0.4±0.03
N
C
+ =3.2±0.3
N
1p
=2.1±0.3
N
3p
=1.1±0.1
• Charm events found:
 Long charged 3 prong Charm decay in Padova
 Very short 2 prong in Bern
 3 new candidates: (to be confirmed)
- 2 short (1 or 2 prong) and 1 short ( 3 prong)
(- 1 in Japan + 1 new)
N
1p
= 0 (1) N
2p
= 1 (2) N
3p
= 1(2) N
4p
= 0

• Charm events number found in 2008 data is lower than the expectation ( 2 (or 5) found – 5.7 expected)
• But:
– statistic is very low (~25% of the total data analyzed yet)
– The expected number is based on efficiency of 44% which should be re-estimated correctly
– The statistic will increase (wait the final 2008 analysis)
• Comment:
– All the charm events were found close to the 1ry vertex with small IP of charm daughter tracks
• No long charm decay (more than 2 plates). The actual method for vertex is not dedicated for charm. Large IP tracks are not taken into account.
This affect mainly long decay but also short with large IP.

We need a dedicated strategy for charm search for all the 2008 data and for 2009 run

• Scanning area 10 plates downstream the primary vertex
– Vertex is within 5 plates then 5 plates more are needed to reconstruct the charm vertex (~1 cm 2 )
– more plates required to reconstruct kinematics of charm decay
• Improve the detailed analysis of primary vertex by scanning lab
– Not only scanning, but also small analysis at that time
• Need dedicated tools for kink search and 2ry vertex search
- See next slide for procedure proposal (by Tomoko)
- Look for tracks with 10-15 m m< IP< 500 m m w.r.t. 1ry vertex
- Possible with 3D viewer eda.C developped by Ariga
• The previous analysis can be (has to be) performed offline with already scanned data
• Kinematical analysis (offline)

Procedure after primary vertex location
Using the interactive 3D viewer eda.C (latest version)
Proposal by
Tomoko and Ariga
• Select all the tracks and decay daughters (both for short and long decay) with:
- IP w.r.t. 1ry < 500 micron and start within 5 plates from 1ry
- Rejecting Penetrated tracks.
• Check 1 st segment of the track by scan or eyes

Reject e-pairs (when 2 BT found close).
• For the selected tracks:
– Make sure the tracks are measured at the vertex plate (in the closest emulsion w.r.t the 1 ry vertex )
• If not, Measure all the tracks by Prediction scan or Manual Check, in order to minimize measurement error for IP calculation for short decay search.
– follow down all 1ry tracks (in Scan Forth), for small kink search and for very long decay

Procedure after primary vertex location Proposal by
Tomoko and Ariga
1 . SHORT DECAY SEARCH: IP check and 2ry vertex search
- if all IP < 10 micron  all tracks attached to 1ry vertex - NO SECONDARY
(more analysis using momentum is needed to reduce the IP value)
- if one track or more have IP > 10 micron  possible decay
 Check minimum distance track by track (all pairs) - (study momentum dependence)
 to confirm 2ry track
 Re-calculate vertex position considering momentum (reject low momentum)
 Calculate IP error at primary, for 2ry tracks. if IP > 3

, preliminary decay candidate
2. LONG DECAY:
- if there are long decay daughter candidates, search for parent with eda:
- single base-track search (for the future, micro-track search)
- follow down all 1ry tracks (in Scan Forth), for small kink search and for very long decay

• Charm expected for 2008 assuming 44% efficiency and using 25% of the data:
5.7 ± 0.4
(only in Europe)
• Found events: 2 (5) confirmed
• This number is a rough estimation, we need:
– Correctly estimate the efficiency
– Use more statistics
– Japanese data not yet taken into account
– Perform a systematic search for charm
• Strategy to have a dedicated search was proposed
– Should be applied for already scanned 2008 data and 2009
• Next to be done (soon):
– Re-estimate the charm expectation using all scanned data (Europe+
Japan)
– Re-estimate the efficiency

IP of charm daughter track w.r.t. to the 1ry vertex
D + 1 prong
D + 3 prong

D +
D0
D
S
+
 c
+
Decay will be within 5 plates of primary vertex, so we have to scan at least 10 plates to see it 30

top view
side view
145 mu
541 mu beam view
2.3 GeV/c
1.3 GeV/c mu
5.5 GeV/c