Title: A' Starodumov INFNPisa Vertex 2001 Workshop 27 September 2001
1A. 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
1
2Trigger 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
2
3First 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
3
4B 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
4
5B 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
5
6HLT 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
6
7HLT 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
7
8HLT 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
8
9Kinematical 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
9
10Results 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
10
11Results 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
11
12Results 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
12
13Summary
- 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
13