What we learned from DC1 B-physics validations

M.Smizanska, Lancaster Universityfor B-physics validation team.

pp B(J/() K0) X

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DC1 B-physics validation teams:

University of Lancaster, Lancaster, UK E.Bouhova-Thacker, R.Jones, V.Kartvelishvili, M.Smizanska

Institute for Experimental Physics,

University of Innsbruck, Austria

B.Epp, V.M.Ghete

Moscow State University, Russia N.Nikitine, S.Sivoklokov, K.Toms

Physics Department, Thessaloniki T.Lagouri

Charles University, Prague P.Reznicek

CEA, Saclay J.F.Laporte

CERN N. Benekos, A.Nairz

INFN, Frascati, Italy H.Bilokon

INFN, Roma-1, Italy M.Testa

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List of Physics processes

Process Detector layouts

pp Bs X

Bs Ds D s K+K-

TDR,

Complete layout, 400m

Initial layout, 400m

Complete layout, 300m (DC1)pp Bs X

Bs

pp Bs X

Bs J/K+K- )

pp Bd X

Bd J/K(+-)

pp b X

b J/0 (p)

pp bb X, b6X’

Bs Ds D s K+K-

b J/0 (p)

+ min bias for L =2 x 1033 cm-2 s-1

Initial layout, 400m

Complete layout, 400m

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Software tools, status at the start of DC0:

1. Detector simulation

a) ‘TDR’ detector layout was obsolent for several years, but the changes were not implemented in ATLAS software. atlsim 98_2 was identical to 97_6 for the ID description, which corresponded to a description in ID TDR.

b) … so an impact of important changes in the ID: increasing the radius of b-layer, eliminating second pixel layer and some other parts in the endcap - had to be estimated by ATLFAST – using simple approximations of the resolutions derived from TDR ones.

c) Physics performance for conferences was for a long time presented for TDR layout.

d) DC1 validation was important step forward: first publicly presentable B-physics results with new ID layout.

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Software tools, status at the start of DC0, cont

2. ATHENA, Generators

a) TDR B-physics generator Atgenb – a branch of Atgen an ATLAS interface package that stop to be supported in 97.

b) In DC0 – Atgenb – rewritten to PythiaB – ATHENA algorithm, was in use for DC1 production.

3. Reconstruction:

a) atsim, atrecon – longest survivors over TDR-DC0-DC1 … finally were useful for ATHENA validations – most of our DC1 done in parallel using atrecon (or atlsim!) and ATHENA

b) ATHENA-reconstruction much progress during DC1 …

c) … but we did not reach the same performance for the 3 packages in DC1. The sources of differences are more-less understood, but all these packages stop at DC1. All manpower - to DC2.

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Detector Layouts in DC1 validations

Detector layouts Complete Initial Complete-300 m

TDR

Radius of b-layer 5 cm 5 cm 5 cm 4.3 cm

Longitudinal pixel size of b-layer

400 400 300 300

Middle pixel layer yes missing yes yes

Pixel disk #2 and forward TRT wheels

yes missing yes yes

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Software in DC1 validations

Layout

Software

Complete Initial Complete-300 m

TDR

Event Generation PythiaB(Athena)

and old data from TDR – for consistency checks

atgenb

Detector simulation atsim 6.0.2 atlsim 6.0.2 atsim 3.2.1 atlsim98_3 TDR

Reconstruction mostly xKalman in Inner Detector

*)

atrecon6.5.0 (6.0.3, 4.5.0)

atlsim4.5.0 (only 1chan)

Athena 6.5.0, 7.0.0

atrecon6.5.0 (6.0.3, 4.5.0)

Athena 6.5.0, 7.0.0

atrecon4.5.0 atreconTDR

1. optimal strategy for Initial layout (4)

2. default strategy(7)

Physics Analyses

Vertexing

CBNT analyses (from atrecon or from athena)

CTVMFT vertexing from TDR

*) part of Complete and Initial also with iPatrec, 6.0.3

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Performance results

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Mass reconstruction

Mass resolution

single Gauss fit

[MeV/c2]

Complete Initial Complete-300 m (dc1)

TDR

Bs Ds( 46 46 45 42

B 79 80 80 69

Bs J/ 17 17 16 15

Bd J/K 21 21 - 19

b J/p 25 26 - 22

J/ 42 43 43 39

Core of mass distributions similar with Complete and Initial layouts and Complete-300m.

Degradation vrt TDR: 10-15%

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Complete vs Initial layout: reconstruction of B-signal mass xKalman6.5.0 optimized track finding strategy

Complete Layout Initial Layout

Initial Layout:

1. Efficiency to reconstruct B only 4.5% smaller then in Complete.

2. Only 0.3 % fails the vertex fit in both Complete and Initial layouts.

Example for channel Bs J/()

… and B-vertex reconstructed= 82.3% (5% B in tails)= 77.7% (6% B in tails)

All four tracks of B reconstructed= 82.5% (5% B in tails)=77.9% (6% B in tails)

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…the same events with default xKalman track search strategy – failed for Initial layout, ok for Complete layout.

Complete Layout Initial Layout

All four tracks of B reconstructed= 83% (4% B in tails)=77% (11% B in tails)

… and B-vertex reconstructed= 82% (4% B in tails)= 67% (8% B in tails)

Initial Layout: 1. More B’s in tails.

2. Efficiency to reconstruct B tracks only 6% smaller,

3. however next 10% fails the vertex fit

Example for channel Bs J/()

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B-hadrons - proper time resolution

Single-Gauss fit Complete Initial Complete-300 m (dc1)

TDR

Bs Ds 100 fs 98 fs 86 fs 67 fs

B 99 fs 98 fs 92 fs 69 fs

Bs J/ 85 fs 82 fs 85 fs 63 fs

Bd J/K 89 fs 86 fs - 69 fs

b J/p 101 fs 95 fs - 73 fs

Core of proper-time distribution similar in Complete and Initial layouts.Degradation vrt TDR: 20-35%.Degradation Complete 400m vrt 300m : 14%

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B-hadrons proper-time resolution, optimized xKalman

Both Complete and Initial layout similar: Bs proper-time reconstruction:

8% in tailsonly 0.3% fails vertex fit in both layouts

Example for channel Bs J/()

Complete Layout Initial Layout

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B-hadrons proper-time resolution, default xKalman

Bs proper-time resolution:

1. Complete layout 7% in tails2. Initial layout 16% in tails

… and lower efficiency of track reconstruction and less sucessful vertex fits

-> all these factors lead to decrease of efficiency. After final selection cuts in this channelInitial : Complete 3:5

Complete Layout Initial Layout

Example for channel Bs J/()

All four tracks of B reconstructed and B-vertex reconstructed= 82% (7% B in tails)

= 67% (16% B in tails)

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Efficiency of reconstruction of B-signal including vertex fit Initial vs Complete, optimal xKalman

Initial/Complete

Bs Ds D s K+0.5K- 0.5) 0.94

Bs J/(K+0.5K-0.5) 0.93

Bd J/K0.5 0.5 0.937

b J/p0.5 0.5 0.94

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Complete layout vrt Initial layout similar performance.

… so are we going to miss second pixel layer?

1. The simulation was optimistic 2. inefficiencies underestimated3. no misalignement

4. degradation appears at higher multiplicities - already at L =2 x 1033 cm-2 s-1

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Single-track performance:

Detector layout Complete layout

400m

Initial layout

400m

Process pp Bs X

Bs J/pp BsX

BsJ/pp bb X, b6X’

+ min bias for

L =2 x 1033 cm-2 s-1

pT ( 0.5-1.0 ) GeV 0.021 0.029 0.075

pT ( 1. - 3. ) GeV 0.020 0.022 0.039

pT ( 3. - 6. ) GeV 0.016 0.024 0.038

pT > 6. GeV 0.013 0.018 0.039

Complete layout vrt Initial similar - if only a signal event simulated.

Degradation at higher multiplicities (already at L =2 x 1033 cm-2 s-1 ).

wrong hit on track in b-layer; dependence on: layout, multiplicity and pT.

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Athena7.0.0 versus atrecon… different performance

Can ATHENA7.0.x be corrected ?? 

 B-proper-time resolution[fs] Bs->Ds Bs->J/ b->J/

atrecon6.5.0 89.6 82.2 92.9

ATHENA7.0.0 97.3 92.1 107.7

atrecon6.5.0 'private' with pixel cluster errors as

95.3 87.3 103.9

   ATHENA worse by 

~10% than atrecon6.5.0

atrecon 'private'  ~8% worse than atrecon6.5.0.

Degradation due to pixel clusters errors.

Other -smaller factor:  ATHENA

more inefficiencies  

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Athena7.0.0 versus atrecon… different performance

1. We finish DC1 with ATHENA reconstruction in which we are aware of errors

2. Degraded performance in proper-time vrt atrecon.3. Can ATHENA 7.0.x be improved?? NO

a) cannot invest time for old code – need people for 7.3.0…b) DC1 Simulation not realistic anyway, for instance

misalignment…

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Conclusions

1. Initial vrt Complete layout - similar performance – if no pileup, with optimized track search strategy in atrecon6.5.0.

a) Track-finding efficiency -7% for pt (0.5-1.0) GeV, only -2%. for pT>1GeV

b) Tracks with wrong hit in B-layer: Initial 3%, in Complete 2% for pT<1GeV

c) Efficiency of B-signal reconstruction Initial vrt Complete: lower by ~6% - due to track search inefficiency. Only 0.3% fails vertex fit in both Initial and Complete layouts.

2. Comparisons with other layouts

a) Mass resolution: degraded 10-15% vrt TDR,

b) Time resolution: degraded 20-30% vrt TDR, and 14% 400m vrt 300m.

3. Still to be done in DC1: Signal events with minimum bias.

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Conclusions,cont

4. We are aware of insufficiencies of DC1 and we understand their impact on performance.

5. This will alllow us to use reasonably the DC1 software validation results as a starting point to validate DC2 software.