A' Starodumov INFNPisa Vertex 2001 Workshop 27 September 2001

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A. StarodumovINFN-PisaVertex 2001 Workshop27
September 2001
HLT for B-Physics in CMS

• DAQ/HLT Architecture
• First Level Trigger
• B channels topology and kinematics
• HLT algorithm
• Kinematics and selection
• Results
• Conclusion

A. Starodumov/INFN-Pisa HLT for B-Physics in CMS
Vertex 2001, Brunnen, Switzerland 23-28 September
2001
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Trigger DAQ in CMS

• Level 1 detectors, front-end pipelines and
  readout buffers
• Level 2 processor farm
• Task reduce 40MHz input rate to 100Hz on tape
• HLT 100KHz?10KHz? 100Hz

• 2LT part of event data
• - calorimeter, muon, pixel
• - fine granularity precise reconstruction
• 3LT full event data
• - tracker information
• - full event reconstruction

Pass 10
100 KHz
10 KHz
of event
2LT 25 data
3LT 75 data
A. Starodumov/INFN-Pisa HLT for B-Physics in CMS
Vertex 2001, Brunnen, Switzerland 23-28 September
2001
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First Level Trigger

• 1LT output rate - 30 KHz
• Single muon rate - 10 KHz
• Composition at PT 10 GeV
• - b ? ? 60
• - c ? ? 20
• - K/? ? ? 20
• After 1LT about 50 of muons have PT lt 10 GeV
  due to efficiency curve of at 1LT
• Generally no trigger from calorimeters in B
  events

• One needs to use Tracker at 2LT
• (small part of it) to reduce rate
• and keep B events

A. Starodumov/INFN-Pisa HLT for B-Physics in CMS
Vertex 2001, Brunnen, Switzerland 23-28 September
2001
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B channels

• Bs ? Ds?
• Bs ? Dsa1
• Bs ? DsK
• Bs ? DsDs
• Bs ? Ds?X etc.

• Very rich Physics mixing parameter xs, angle
  ? of Unitarity triangle, semileptonic decays of
  Bs etc.
• Use a Ds trigger

Ds ? ? ? ? K K ?

• All this channels will be triggered with single
  muon at 1LT
• Basic task at 2LT - to find three tracks to
  compose Ds meson
• High efficiency for signal Bs events and
  significant suppression factor (gt20) for the rest
  of events in single muon trigger sample are
  required

A. Starodumov/INFN-Pisa HLT for B-Physics in CMS
Vertex 2001, Brunnen, Switzerland 23-28 September
2001
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B channel topology and kinematics
?
?

• B events are soft low multiplicity of hard
  tracks and low PT 1?10 GeV
• Bs ? Ds? ? ??? ? KK??
• ltNgt 14, ltPTgt 3 GeV

K
K
?
B
Bs
ltNtrgt20
ltPTgt2.4GeV
A. Starodumov/INFN-Pisa HLT for B-Physics in CMS
Vertex 2001, Brunnen, Switzerland 23-28 September
2001
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HLT algorithm introduction
Momentum resolution in

• At 2LT use part of Tracker information (5?10)
• 2 pixel layers and 1 strip layer (3D hits)
• Fast track candidates reconstruction based on 3
  stereo hits 3 parameters to calculate (no track
  fitting!)
• Select track candidates with PT gt 1GeV
• Cleaning track candidates (remove clone tracks,
  see next slide)
• Based on topology of event, reconstruct invariant
  masses of ? and Ds

Nhits
A. Starodumov/INFN-Pisa HLT for B-Physics in CMS
Vertex 2001, Brunnen, Switzerland 23-28 September
2001
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HLT algorithm reconstruction

• Linear Impact Parameter in XY based on 2 pixel
  hits
• IP lt 2 mm
• 70 combinations per event

7 cm
4 cm
0 cm
XY
21 cm

• Propagate track candidate to a third layer in RZ
  and find Zexp
• ?Z3Zexp-Zreclt1.5 mm
• 26 combinations per event

7 cm
4 cm
RZ

• Reconstruct PT based on 3 stereo hits and
  select PT gt 0.9GeV
• 14 combinations per event

A. Starodumov/INFN-Pisa HLT for B-Physics in CMS
Vertex 2001, Brunnen, Switzerland 23-28 September
2001
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HLT algorithm cleaning
Zexp

• Leave only one of track candidates with 2 common
  hits Z1-Zexp lt Z2-Zexp

Z2
Z1
21 cm
7 cm
4 cm
RZ

• Remove one of track candidates with 1 common hit
  if PT(1)-PT(2) / PT(max) lt 2 and
  Pz(1)-Pz(2) / Pz(max) lt 2

21 cm
7 cm
4 cm
RZ
A. Starodumov/INFN-Pisa HLT for B-Physics in CMS
Vertex 2001, Brunnen, Switzerland 23-28 September
2001
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Kinematical selections
-

• ? reconstruction
• - 2 opposite charge hadrons (tracks)
• - ?Rhh ? 0.3 (?R sqrt(?? ?? ) )
• - Mhh-M? ? 14MeV (Mh ? MK)

K

K
2
2
?
?
?R

• Ds reconstruction
• - third thadron near reconstructed ?
• - ?Rh? ? 1.2
• - M?h -MDs ? 70MeV (Mh ? M?)

?R
A. Starodumov/INFN-Pisa HLT for B-Physics in CMS
Vertex 2001, Brunnen, Switzerland 23-28 September
2001
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Results I

• Signal Bs ? Ds?, ?rec75, ghost tracks 10

A. Starodumov/INFN-Pisa HLT for B-Physics in CMS
Vertex 2001, Brunnen, Switzerland 23-28 September
2001
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Results II
Signal Bs ? Ds?? ??? ? KK??
Reconstructed ? ?4.3MeV
Reconstructed Ds ?24MeV
A. Starodumov/INFN-Pisa HLT for B-Physics in CMS
Vertex 2001, Brunnen, Switzerland 23-28 September
2001
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Results III

• MB events b/c/K/? ? ?, ?rec3.5, ghost tracks
  8

Rate 10KHz ?350Hz
A. Starodumov/INFN-Pisa HLT for B-Physics in CMS
Vertex 2001, Brunnen, Switzerland 23-28 September
2001
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Summary

• High Level Trigger algorithm for B Physics is
  proposed based on fraction (5-10) of Tracker
  information
• Pixel detector and 1-2 strip layers play a
  crucial role for fast triggering of B events
• As an example of Ds trigger a decay channel
  Bs?Ds? (following by Ds??? and ????) is
  considered
• Efficiency for signal events is about 75 with
  ghost tracks of about 10
• Efficiency for background b?? and QCD (?/K??)
  is about 3.5 (suppression factor of 30) with 8
  of ghost tracks
• The algorithm allows us to reduce single muon
  rate from 10KHz to 350Hz what fits with a goal of
  2 LT in CMS

A. Starodumov/INFN-Pisa HLT for B-Physics in CMS
Vertex 2001, Brunnen, Switzerland 23-28 September
2001
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