lhcb: preparing for data (a talk on mc events and data expectations) nikhef colloquium feb 4, 2005...
TRANSCRIPT
![Page 1: LHCb: Preparing for Data (A talk on MC events and data expectations) NIKHEF Colloquium Feb 4, 2005 Marcel Merk](https://reader035.vdocuments.site/reader035/viewer/2022070414/5697c0271a28abf838cd66d5/html5/thumbnails/1.jpg)
LHCb: Preparing for Data(A talk on MC events and data expectations)
NIKHEF Colloquium
Feb 4, 2005
Marcel Merk
![Page 2: LHCb: Preparing for Data (A talk on MC events and data expectations) NIKHEF Colloquium Feb 4, 2005 Marcel Merk](https://reader035.vdocuments.site/reader035/viewer/2022070414/5697c0271a28abf838cd66d5/html5/thumbnails/2.jpg)
2
Contents
Last year: Several excellent overviews of latest B physics results An overview of the status of the LHCb detector
This talk: What does LHCb plan to do with incoming data in ~ 2008?
Illustrate with a single decay mode: Bs→Ds h
Topics: Bs→Ds & Bs→DsK
Detector Simulation
Reconstruction and Trigger Event Selection and Flavour Tagging Physics Sensitivity studies
![Page 3: LHCb: Preparing for Data (A talk on MC events and data expectations) NIKHEF Colloquium Feb 4, 2005 Marcel Merk](https://reader035.vdocuments.site/reader035/viewer/2022070414/5697c0271a28abf838cd66d5/html5/thumbnails/3.jpg)
3
The Decay Bs→Ds h
Two decays with identical topology: Bs → Ds
-
Bs -> Ds∓ K±
bt
Bs K
K
,K
Ds
Primary vertex
Experiment: Trigger on B decay of interest.
Signatures:• “high” Pt tracks• displaced vertices
p p
Select the B decay and reject the background
Tag the flavour of the B decay Plot the tagged decay rate as
function of the decay time
Physics of these two decays however is different….
![Page 4: LHCb: Preparing for Data (A talk on MC events and data expectations) NIKHEF Colloquium Feb 4, 2005 Marcel Merk](https://reader035.vdocuments.site/reader035/viewer/2022070414/5697c0271a28abf838cd66d5/html5/thumbnails/4.jpg)
4
cos( )A tm
( ) (1 cos( ))
( ) (1 cos( ))
s s
s s
B D
B D
t e t
t e t
m
m
( ) 1 cos( )
s sB Dt e mt
exp( ) 1 co( ) (1 2 s( [ ]))tag
s sD agB tA tt e mw tt
Dilutions: A(t) : Trigger acceptance Wtag : Flavour Tagging
t : Decay time Resolution
Fit them together with m
Physics with Bs-→Ds
- + : m
b
s
c
s
du
Bs Ds-
+BR~10-4
1 year data LHCbMeasure Oscillation Frequency! In the fitting
procedure we use the individual decay rates
![Page 5: LHCb: Preparing for Data (A talk on MC events and data expectations) NIKHEF Colloquium Feb 4, 2005 Marcel Merk](https://reader035.vdocuments.site/reader035/viewer/2022070414/5697c0271a28abf838cd66d5/html5/thumbnails/5.jpg)
5
Physics with Bs→Ds∓ K± :
b
s
c
s
s
u
Bs Ds-
K+
Bss
b
b
s
Ds-
b
s
u
s
s
c
Bs K++
BR~10-5
iud us ub
CKM cd cs cbi
td ts tb
V V V e
V V V V
V e V V
Vub
Introduce also:
= strong phase difference ; r = ratio between amplitudes
![Page 6: LHCb: Preparing for Data (A talk on MC events and data expectations) NIKHEF Colloquium Feb 4, 2005 Marcel Merk](https://reader035.vdocuments.site/reader035/viewer/2022070414/5697c0271a28abf838cd66d5/html5/thumbnails/6.jpg)
6
Physics with Bs→Ds∓ K± :
2 asymmetries to fit the unknown parameters: Ration between diagrams: r Strong phase: Weak phase
b
s
c
s
s
u
Bs Ds-
K+
Bss
b
b
s
Ds-
b
s
u
s
s
c
Bs K++
2
2
2sin( )cos
1
2sin( ) cos
1
s
s
D K
D K
A t
A
m
tm
r
r
r
r
2
2 2
2
2 2
(1 ) (2 )( ) 1 cos( ) sin( )sin( )
(1 ) (1 )
(1 ) (2 )( ) 1 cos( ) sin( )sin( )
(1 ) (1 )
s s
s s
t
B D K
t
B D K
t e t tm m
m mt e t t
r r
r r
r r
r r
BR~10-5
Measure Oscillation Amplitude!
4 decay rates to fit the unknown parameters: Ration between diagrams: r Strong phase: Weak phase
Same experimental dilutions as in Ds should be added:
Use the value of A, wtag and t as obtained with Ds fit…
Bs→ Ds- K+
Bs→ Ds-K+
Bs→ Ds+
K-
Bs→ Ds+K-
![Page 7: LHCb: Preparing for Data (A talk on MC events and data expectations) NIKHEF Colloquium Feb 4, 2005 Marcel Merk](https://reader035.vdocuments.site/reader035/viewer/2022070414/5697c0271a28abf838cd66d5/html5/thumbnails/7.jpg)
7
B Production @ LHC
Forward (and backward) productionBuild a forward spectrometer
b b
O(50%)
O(10%)
O(40%)
Pyt
hia
& h
ep
-ph/
000
511
0 (
Sjö
stra
nd
et a
l)
![Page 8: LHCb: Preparing for Data (A talk on MC events and data expectations) NIKHEF Colloquium Feb 4, 2005 Marcel Merk](https://reader035.vdocuments.site/reader035/viewer/2022070414/5697c0271a28abf838cd66d5/html5/thumbnails/8.jpg)
8
LHCb detector: a quick reminder
p p
~ 200 mrad~ 300 mrad (horizontal)
10 mrad
Inner acceptance ~ 15 mrad (10 mrad conical beryllium beampipe)
![Page 9: LHCb: Preparing for Data (A talk on MC events and data expectations) NIKHEF Colloquium Feb 4, 2005 Marcel Merk](https://reader035.vdocuments.site/reader035/viewer/2022070414/5697c0271a28abf838cd66d5/html5/thumbnails/9.jpg)
9
LHCb tracking: vertex region
VELO: resolve ms oscillations in e.g. Ds events
![Page 10: LHCb: Preparing for Data (A talk on MC events and data expectations) NIKHEF Colloquium Feb 4, 2005 Marcel Merk](https://reader035.vdocuments.site/reader035/viewer/2022070414/5697c0271a28abf838cd66d5/html5/thumbnails/10.jpg)
10
Pile-Up Stations
Interaction Region=5.3 cm
LHCb tracking: vertex region
y
x
y
x
![Page 11: LHCb: Preparing for Data (A talk on MC events and data expectations) NIKHEF Colloquium Feb 4, 2005 Marcel Merk](https://reader035.vdocuments.site/reader035/viewer/2022070414/5697c0271a28abf838cd66d5/html5/thumbnails/11.jpg)
11
LHCb tracking: momentum measurement
0.15 Tm
By[T]
Total Bdl = 4 TmBdl Velo-TT=0.15 Tm
Tracking: Mass resolution for background suppression in eg. DsK
![Page 12: LHCb: Preparing for Data (A talk on MC events and data expectations) NIKHEF Colloquium Feb 4, 2005 Marcel Merk](https://reader035.vdocuments.site/reader035/viewer/2022070414/5697c0271a28abf838cd66d5/html5/thumbnails/12.jpg)
12
LHCb tracking: momentum measurement
All tracking stations have four layers:0,-5,+5,0 degree stereo angles.
~65 m2
~1.41.2 m2
![Page 13: LHCb: Preparing for Data (A talk on MC events and data expectations) NIKHEF Colloquium Feb 4, 2005 Marcel Merk](https://reader035.vdocuments.site/reader035/viewer/2022070414/5697c0271a28abf838cd66d5/html5/thumbnails/13.jpg)
13
LHCb Hadron Identification: RICH
3 radiators to coverfull momentum range: Aerogel C4F10
CF4
RICH2 100 m3 CF4 n=1.0005
RICH: K/ separation e.g. to distinguish Ds and DsK events.
RICH1 5 cm aerogel n=1.03 4 m3 C4F10 n=1.0014
![Page 14: LHCb: Preparing for Data (A talk on MC events and data expectations) NIKHEF Colloquium Feb 4, 2005 Marcel Merk](https://reader035.vdocuments.site/reader035/viewer/2022070414/5697c0271a28abf838cd66d5/html5/thumbnails/14.jpg)
14
LHCb calorimeters
e
h
Calorimeter system to identify electrons, hadrons and neutrals and used in the L0 trigger: hadron Pt trigger for Dsh events
![Page 15: LHCb: Preparing for Data (A talk on MC events and data expectations) NIKHEF Colloquium Feb 4, 2005 Marcel Merk](https://reader035.vdocuments.site/reader035/viewer/2022070414/5697c0271a28abf838cd66d5/html5/thumbnails/15.jpg)
15
LHCb muon detection
Muon system to identify muons and used in L0 trigger e.g. unbiased trigger on “other B” for Ds events
![Page 16: LHCb: Preparing for Data (A talk on MC events and data expectations) NIKHEF Colloquium Feb 4, 2005 Marcel Merk](https://reader035.vdocuments.site/reader035/viewer/2022070414/5697c0271a28abf838cd66d5/html5/thumbnails/16.jpg)
16
Simulation Software: “Gaudi” Applications
Event Generator: Pythia: Final state generation Evtgen: B decays
Detector Simulation: Gauss: GEANT4 tracking MC particles through the detector and storing MC Hits
Detector Response (“digitization”): Boole: Converting the MC Hits into a raw buffer emulating the real data format
Reconstruction: Brunel: Reconstructing the tracks from the raw buffer.
Physics: DaVinci: Reconstruction of B decays and flavour tags. LoKi : “Loops and Kinematics” toolkit.
Visualization: Panoramix: Visualization of detector geometry and data objects
![Page 17: LHCb: Preparing for Data (A talk on MC events and data expectations) NIKHEF Colloquium Feb 4, 2005 Marcel Merk](https://reader035.vdocuments.site/reader035/viewer/2022070414/5697c0271a28abf838cd66d5/html5/thumbnails/17.jpg)
17
Event Generation: Pythia
Pythia 6.2: proton-proton interactions at √s = 14 TeV . Minimum bias includes hard QCD processes, single and
double diffractive events inel = 79.2 mb
bb events obtained from minimum bias events with b or b-hadron bb = 633 b
Use parton-parton interaction “Model 3”, with continuous turn-off of the cross section at PT
min.
The value of PTmin depends on the choice of Parton
Density Function. Energy dependence, with “CTEQ4L” at 14 TeV:
• PTmin=3.47 ± 0.17 GeV/c. Gives:
Describes well direct fit of multiplicity data:
Robustness tests…
direct fit
0
6.11 0.29chdN
d
TP fit
0
6.30 0.42chdN
d
![Page 18: LHCb: Preparing for Data (A talk on MC events and data expectations) NIKHEF Colloquium Feb 4, 2005 Marcel Merk](https://reader035.vdocuments.site/reader035/viewer/2022070414/5697c0271a28abf838cd66d5/html5/thumbnails/18.jpg)
18
Charged multiplicity distributions at generator level
In LHCb acceptance ( 1.8 < < 4.9 )
Average charged multiplicity Minimum bias bb
CDF tuning at 14 TeV 16.53 ± 0.02 27.12 ± 0.03
LHCb tuning, default pTmin 21.33 ± 0.02 33.91 ± 0.03
LHCb tuning, 3 low pTmin 25.46 ± 0.03 42.86 ± 0.03
![Page 19: LHCb: Preparing for Data (A talk on MC events and data expectations) NIKHEF Colloquium Feb 4, 2005 Marcel Merk](https://reader035.vdocuments.site/reader035/viewer/2022070414/5697c0271a28abf838cd66d5/html5/thumbnails/19.jpg)
19
The LHC environment
pp collisions @ s=14 TeV
Bunch crossing @ 40MHz 25 ns separation
inelastic = 80mb At high L >>1 collision/crossing
Prefer single interaction events Easier to analyze!
• Trigger• Flavor tagging
Prefer L ~ 2 x 1032 cm-2s-1
Simulate 10 hour lifetime,7 hour fill
Beams are defocused locally Maintain optimal luminosity even
when Atlas & CMS run at 1034
![Page 20: LHCb: Preparing for Data (A talk on MC events and data expectations) NIKHEF Colloquium Feb 4, 2005 Marcel Merk](https://reader035.vdocuments.site/reader035/viewer/2022070414/5697c0271a28abf838cd66d5/html5/thumbnails/20.jpg)
20
Simulation: Switched from GEANT3…
VELORICH1
TT
T1T2
T3
![Page 21: LHCb: Preparing for Data (A talk on MC events and data expectations) NIKHEF Colloquium Feb 4, 2005 Marcel Merk](https://reader035.vdocuments.site/reader035/viewer/2022070414/5697c0271a28abf838cd66d5/html5/thumbnails/21.jpg)
21
…to GEANT4 (“Gauss”)
Note: simulation and reconstruction use identical geometry description.
![Page 22: LHCb: Preparing for Data (A talk on MC events and data expectations) NIKHEF Colloquium Feb 4, 2005 Marcel Merk](https://reader035.vdocuments.site/reader035/viewer/2022070414/5697c0271a28abf838cd66d5/html5/thumbnails/22.jpg)
22
Event example: detector hits
![Page 23: LHCb: Preparing for Data (A talk on MC events and data expectations) NIKHEF Colloquium Feb 4, 2005 Marcel Merk](https://reader035.vdocuments.site/reader035/viewer/2022070414/5697c0271a28abf838cd66d5/html5/thumbnails/23.jpg)
23
Event example (Vertex region zoom)
![Page 24: LHCb: Preparing for Data (A talk on MC events and data expectations) NIKHEF Colloquium Feb 4, 2005 Marcel Merk](https://reader035.vdocuments.site/reader035/viewer/2022070414/5697c0271a28abf838cd66d5/html5/thumbnails/24.jpg)
24
Detector Response Simulation: e.g.: the Outer Tracker
Geant event displayOT double layer cross section
5mm straws
pitch 5.25 mm
Tracke- e
-e-
e-e
-
1 bunch+ Spill-over+ Electronics+ T0 calibration
TDC spec.:
![Page 25: LHCb: Preparing for Data (A talk on MC events and data expectations) NIKHEF Colloquium Feb 4, 2005 Marcel Merk](https://reader035.vdocuments.site/reader035/viewer/2022070414/5697c0271a28abf838cd66d5/html5/thumbnails/25.jpg)
25
Track finding strategy
VELO seeds
Long track (forward)
Long track (matched)
T seeds
Upstream track
Downstream track
T track
VELO track
T tracks useful for RICH2 pattern recognition
Long tracks highest quality for physics (good IP & p resolution)Downstream tracks needed for efficient KS finding (good p resolution)Upstream tracks lower p, worse p resolution, but useful for RICH1 pattern recognition
VELO tracks useful for primary vertex reconstruction (good IP resolution)
![Page 26: LHCb: Preparing for Data (A talk on MC events and data expectations) NIKHEF Colloquium Feb 4, 2005 Marcel Merk](https://reader035.vdocuments.site/reader035/viewer/2022070414/5697c0271a28abf838cd66d5/html5/thumbnails/26.jpg)
26
Result of track finding
Typical event display:Red = measurements (hits)
Blue = all reconstructed tracks
Efficiency vs p : Ghost rate vs pT :
Eff = 94% (p > 10 GeV)
Ghost rate = 3%(for pT > 0.5 GeV)
VELO
TT
T1 T2T3On average:
26 long tracks11 upstream tracks4 downstream tracks5 T tracks26 VELO tracks
2050 hits assigned to a long track: 98.7% correctly assigned
Ghosts:Ghosts:Negligible effect onNegligible effect onb decay reconstructionb decay reconstruction
![Page 27: LHCb: Preparing for Data (A talk on MC events and data expectations) NIKHEF Colloquium Feb 4, 2005 Marcel Merk](https://reader035.vdocuments.site/reader035/viewer/2022070414/5697c0271a28abf838cd66d5/html5/thumbnails/27.jpg)
27
Robustness Test: Quiet and Busy Events
Monitor efficiency and ghost rate as function of nrel: “relative number of detector hits”
<nrel> = 1
![Page 28: LHCb: Preparing for Data (A talk on MC events and data expectations) NIKHEF Colloquium Feb 4, 2005 Marcel Merk](https://reader035.vdocuments.site/reader035/viewer/2022070414/5697c0271a28abf838cd66d5/html5/thumbnails/28.jpg)
28
Kalman Track Fit
Reconstruct tracks including multiple scattering.
Main advantage: correct covariance matrix for track parameters!!
z
Impact parameter pull distribution:
= 1.0
rec truer r
r
Momentum pull distribution:
= 1.2
rec truep p
p
![Page 29: LHCb: Preparing for Data (A talk on MC events and data expectations) NIKHEF Colloquium Feb 4, 2005 Marcel Merk](https://reader035.vdocuments.site/reader035/viewer/2022070414/5697c0271a28abf838cd66d5/html5/thumbnails/29.jpg)
29
Experimental Resolution
p/p = 0.35% – 0.55%
p spectrum B tracks
IP= 14 + 35 /pT
1/pT spectrum B tracks
Momentum resolution Impact parameter resolution parameter resolution
![Page 30: LHCb: Preparing for Data (A talk on MC events and data expectations) NIKHEF Colloquium Feb 4, 2005 Marcel Merk](https://reader035.vdocuments.site/reader035/viewer/2022070414/5697c0271a28abf838cd66d5/html5/thumbnails/30.jpg)
30
Particle IDRICH 1 RICH 2
(K->K) = 88%
(p->K) = 3%
Example:Bs->Dsh
K
Bs
K
,K
DsPrim vtx
![Page 31: LHCb: Preparing for Data (A talk on MC events and data expectations) NIKHEF Colloquium Feb 4, 2005 Marcel Merk](https://reader035.vdocuments.site/reader035/viewer/2022070414/5697c0271a28abf838cd66d5/html5/thumbnails/31.jpg)
31
Trigger40 MHz
pil
e-u
p
1 MHz
40 kHz
2 kHz output
Level-1:Impact parameterRough pT ~ 20%
HLT:Final state
reconstruction
CalorimeterMuon system
Pile-up system
Vertex LocatorTrigger TrackerLevel 0 objects
Full detectorinformation
L0L0
Level-0:Level-0:ppTT of of
, e, h, , e, h,
ln pT ln pT
ln
IP/
IP
ln
IP/
IP
L1L1
Signal
Min.Bias
B-> Bs->DsK
![Page 32: LHCb: Preparing for Data (A talk on MC events and data expectations) NIKHEF Colloquium Feb 4, 2005 Marcel Merk](https://reader035.vdocuments.site/reader035/viewer/2022070414/5697c0271a28abf838cd66d5/html5/thumbnails/32.jpg)
32
Trigger Acceptance function
Impact parameter cuts lead to a decay time dependent efficiency function: “Acceptance”
Bs→DsKAcc
![Page 33: LHCb: Preparing for Data (A talk on MC events and data expectations) NIKHEF Colloquium Feb 4, 2005 Marcel Merk](https://reader035.vdocuments.site/reader035/viewer/2022070414/5697c0271a28abf838cd66d5/html5/thumbnails/33.jpg)
33
Bs→Dsh Reconstruction
Final state reconstruction Combine K+K-- into a Ds
-
• Good vertex + mass
Combine Ds- and “bachelor”
into Bs
• Good vertex + mass
Pointing Bss to primary vtx
K/ separation
Mass distribution:
Ds
BsK
K
,K
d
p47 m 144 m
440 m
![Page 34: LHCb: Preparing for Data (A talk on MC events and data expectations) NIKHEF Colloquium Feb 4, 2005 Marcel Merk](https://reader035.vdocuments.site/reader035/viewer/2022070414/5697c0271a28abf838cd66d5/html5/thumbnails/34.jpg)
34
Annual Yields and B/S
Efficiency Estimation:
det (%) rec/det (%) sel/rec (%) trg/sel (%) tot (%)
Bs→Ds 5.4 80.6 25.0 31.1 0.337
Bs→Ds 5.4 82.0 20.6 29.5 0.269
Background Estimation: Currently assume that the only background is due to bb events Background estimates limited by available statistics
Decay Annual yield B/S
Bs→Ds 82k 0.32 ± 0.10
Bs→Ds 5.4k <1.0 (90%) C.L.
Estimation of Bs→Dsbackground in the Bs→Ds sample: B/S = 0.111 ± 0.056
![Page 35: LHCb: Preparing for Data (A talk on MC events and data expectations) NIKHEF Colloquium Feb 4, 2005 Marcel Merk](https://reader035.vdocuments.site/reader035/viewer/2022070414/5697c0271a28abf838cd66d5/html5/thumbnails/35.jpg)
35
Decay time reconstruction: t = m d / p
B decay time resolution:
Pull distribution:
Error distribution
Measurement errors understood!
As an illustration, 1 year Bs→Ds-
![Page 36: LHCb: Preparing for Data (A talk on MC events and data expectations) NIKHEF Colloquium Feb 4, 2005 Marcel Merk](https://reader035.vdocuments.site/reader035/viewer/2022070414/5697c0271a28abf838cd66d5/html5/thumbnails/36.jpg)
36
Flavour tag
l
B0
B0D
Ds-
K-
bb
s
u
s
u
Bs0
K+
tagging strategy: opposite side lepton tag ( b → l ) opposite side kaon tag ( b → c → s ) (RICH, hadron trigger) same side kaon tag (for Bs) opposite B vertex charge tagging
43542
eff [%]Wtag [%] tag [%]
63354
Bd
Bs Ds h
Combining tags
effective efficiency:
eff = tag (1-2wtag )2
sources for wrong tags:
Bd-Bd mixing (opposite side)b → c → l (lepton tag) conversions…
Knowledge of the B flavour at production is needed for the asymmetries
![Page 37: LHCb: Preparing for Data (A talk on MC events and data expectations) NIKHEF Colloquium Feb 4, 2005 Marcel Merk](https://reader035.vdocuments.site/reader035/viewer/2022070414/5697c0271a28abf838cd66d5/html5/thumbnails/37.jpg)
37
Sensitivity Studies
Many GEANT events generated, but: How well can we measure ms with Bs→Dsevents? How well can we measure angle with Bs→DsK events?
as function of ms, s, r,,, and dilutions wtag, t, …?
Toy MC and Fitting program: Generator: Generate Events according to theory B decay formula
• An event is simply a generated B decay time + a true tag.
Simulator: Assign an observed time and an error• Use the full MC studies to do the smearing
Fitter: Create a pdf for the experimentally observed time distribution and fit the relevant parameters
![Page 38: LHCb: Preparing for Data (A talk on MC events and data expectations) NIKHEF Colloquium Feb 4, 2005 Marcel Merk](https://reader035.vdocuments.site/reader035/viewer/2022070414/5697c0271a28abf838cd66d5/html5/thumbnails/38.jpg)
38
Toy Generator
Generate events according to the “master” formula for B decay
2
2
2
( )
)
2
(2
s
s
f t
D
f t
D K
K
A
A pR t
R t e I t
e I t I t
I t
q
2
2
1 cosh 2 cos sinh2 2
1 cos 2 sin( )sin
t tr r
r m rI tm
I
t
t
t
, , , , ,m r Relevant physics parameters:
For Ds+K-:
replace by-
For Ds: Simplify: r=0
Bs→Ds-K+
Bs→Ds-K+
Bs→Ds+K
Bs→Ds+K-
With:
![Page 39: LHCb: Preparing for Data (A talk on MC events and data expectations) NIKHEF Colloquium Feb 4, 2005 Marcel Merk](https://reader035.vdocuments.site/reader035/viewer/2022070414/5697c0271a28abf838cd66d5/html5/thumbnails/39.jpg)
39
Toy Simulation
Smear theoretical events (t=ttrue) into experimental events (trec) and
assign an experimental error (trec). Method:
From the full simulation make a lookup table with selected events:
ttruei, trec
i, treci
Generate ttrue in toy and assign trec and trec from look-up table, such that
non-Gausian effects of the full simulation are included
For tag fraction of the events assign an event tag:
Statistically assign 1-wtag correct tags, and wtag wrong tags.
Current studies tag = 54% wtag = 33% .
Apply an acceptance function A(trec) by statistically accepting events according to the acceptance value for a given event time.
![Page 40: LHCb: Preparing for Data (A talk on MC events and data expectations) NIKHEF Colloquium Feb 4, 2005 Marcel Merk](https://reader035.vdocuments.site/reader035/viewer/2022070414/5697c0271a28abf838cd66d5/html5/thumbnails/40.jpg)
40
Dilutions in Bs→Ds
Plot the MC toy decay rate with the following situation:
1 year data Bs→Ds-+
Experimental Situation:
• Ideal resolution and tag
![Page 41: LHCb: Preparing for Data (A talk on MC events and data expectations) NIKHEF Colloquium Feb 4, 2005 Marcel Merk](https://reader035.vdocuments.site/reader035/viewer/2022070414/5697c0271a28abf838cd66d5/html5/thumbnails/41.jpg)
41
Dilutions in Bs→Ds
Plot the MC toy decay rate with the following situation:
1 year data Bs→Ds-+
Experimental Situation:
• Ideal resolution and tag• Realistic tag
![Page 42: LHCb: Preparing for Data (A talk on MC events and data expectations) NIKHEF Colloquium Feb 4, 2005 Marcel Merk](https://reader035.vdocuments.site/reader035/viewer/2022070414/5697c0271a28abf838cd66d5/html5/thumbnails/42.jpg)
42
Dilutions in Bs→Ds
Plot the MC toy decay rate with the following situation:
1 year data Bs→Ds-+
Experimental Situation:
• Ideal resolution and tag• Realistic tag• Realistig tag and resolution
![Page 43: LHCb: Preparing for Data (A talk on MC events and data expectations) NIKHEF Colloquium Feb 4, 2005 Marcel Merk](https://reader035.vdocuments.site/reader035/viewer/2022070414/5697c0271a28abf838cd66d5/html5/thumbnails/43.jpg)
43
Dilutions in Bs→Ds
Plot the MC toy decay rate with the following situation:
1 year data Bs→Ds-+
Experimental Situation:
• Ideal resolution and tag• Realistic tag• Realistig tag and resolution• Realistic tag + reso + background
![Page 44: LHCb: Preparing for Data (A talk on MC events and data expectations) NIKHEF Colloquium Feb 4, 2005 Marcel Merk](https://reader035.vdocuments.site/reader035/viewer/2022070414/5697c0271a28abf838cd66d5/html5/thumbnails/44.jpg)
44
Dilutions in Bs→Ds
Plot the MC toy decay rate with the following situation:
Experimental Situation:
• Ideal resolution and tag• Realistic tag• Realistig tag and resolution• Realistic tag + reso + background• Realistic tag+reso+bg+acceptance
1 year data Bs→Ds-+
![Page 45: LHCb: Preparing for Data (A talk on MC events and data expectations) NIKHEF Colloquium Feb 4, 2005 Marcel Merk](https://reader035.vdocuments.site/reader035/viewer/2022070414/5697c0271a28abf838cd66d5/html5/thumbnails/45.jpg)
45
The signal for Ds and DsK
5 years data:Bs→ Ds
-
Bs→ Ds-K+
ms = 20)
The CP signal is not self-evidentUse full statistical power in the data
![Page 46: LHCb: Preparing for Data (A talk on MC events and data expectations) NIKHEF Colloquium Feb 4, 2005 Marcel Merk](https://reader035.vdocuments.site/reader035/viewer/2022070414/5697c0271a28abf838cd66d5/html5/thumbnails/46.jpg)
46
Fitting time dependent decay rates
Why use complicated Likelihood fit method? Weigh precisely measured events
differently from badly measured events Rely on the reconstructed event error
• Allow for a scale factor in the analysis
Error distr Pull distr
![Page 47: LHCb: Preparing for Data (A talk on MC events and data expectations) NIKHEF Colloquium Feb 4, 2005 Marcel Merk](https://reader035.vdocuments.site/reader035/viewer/2022070414/5697c0271a28abf838cd66d5/html5/thumbnails/47.jpg)
47
Likelihood Fitter (general idea)
The likelihood that nature produces an event at a given time t =
The probability that this event is reconstructed (i.e. observed) at a
reconstructed time trec with measurement error trec=
Thus the likelihood of observing an event (trec, trec) =
Fit the physics parameters (m, ,…) in R such that the likelihood is maximal:.i.e. maximize:
, ; ),..( .sD h mR t L
( ; ), ,...s
recD h
rec
t tR t G
tm
L
, ,.. ).( ;s
recD h
rec
t tR t G
tm dt
L
1
logeventsN
i L
![Page 48: LHCb: Preparing for Data (A talk on MC events and data expectations) NIKHEF Colloquium Feb 4, 2005 Marcel Merk](https://reader035.vdocuments.site/reader035/viewer/2022070414/5697c0271a28abf838cd66d5/html5/thumbnails/48.jpg)
48
, 1 , ,
, ,
[
]rec rec recsig
B
sig
BG G
rec
r
BG
BG ec rec
P t t dt t t t tf
t t t t
G
GRf
R
Likelihood Fitter (for the die-hard)
Maximize an unbinned likelihood describing the best theory curves simultaneously matching simultaneously the 4 decay rates for Bs->Ds and 4 decay rates for Bs-> Ds K
Normalization of the Likelihood is interesting!See also LHCb note…LHCb 2003-124(Include information of the relative overall rates)
i
,Prob
,rec rec
rec rec rec rec
P t t
P t t dt d t
(Slow computation!)
Event probab:
Normalization of the probability:
Create the Likelihood: ( ) (Prob )ii
Log L LogFit parameters:-Physics:
-Experimental:
2
2
3 1
2
3
11 ; ; = /( )
2
1( ) = ;
21
rec
rec
t
t t
trec recrec
r
BGsig B
ec re
G
cr c
S
e
w w f
ab
R R R Rt t t t e B B S
t t tt e
ttG
aA
t
, , , , ,sm r
, , , ,BGw f S a b
1 year data: Bs -> Ds
- +
Bs -> Ds-
K+
![Page 49: LHCb: Preparing for Data (A talk on MC events and data expectations) NIKHEF Colloquium Feb 4, 2005 Marcel Merk](https://reader035.vdocuments.site/reader035/viewer/2022070414/5697c0271a28abf838cd66d5/html5/thumbnails/49.jpg)
49
Strategy for Ds/ DsK fits
It turns out to be difficult to fit simultaneously the wrong tag fraction, resolution and acceptance function. A small bias in the acceptance function biases the resolution fit
A possible solution could be a 4 step procedure:1. Calibrate the experimental time resolution
2. Fit the acceptance function on the untagged sample of Bs->Ds events
3. Fit simultaneously the values of ms, wtag with Ds events.
4. Fit the values of the r, , with the DsK sample
![Page 50: LHCb: Preparing for Data (A talk on MC events and data expectations) NIKHEF Colloquium Feb 4, 2005 Marcel Merk](https://reader035.vdocuments.site/reader035/viewer/2022070414/5697c0271a28abf838cd66d5/html5/thumbnails/50.jpg)
50
1.Fitting the measurement errors
Resolution can be determined from the negative tail of the lifetime distribution. Fit with 10% of 1 year data: S· trec . => S = 0.99 ± 0.04
Can L1 trigger be tuned to provide unbiased Bs-> Ds events? What would be the required bandwidth for this?
In any case unbiased samples of J/events are foreseen.
S=0.99+- 0.04
L1 trigger
trec
10% of 1 year untagged Bs→Ds
![Page 51: LHCb: Preparing for Data (A talk on MC events and data expectations) NIKHEF Colloquium Feb 4, 2005 Marcel Merk](https://reader035.vdocuments.site/reader035/viewer/2022070414/5697c0271a28abf838cd66d5/html5/thumbnails/51.jpg)
51
2. Fitting the acceptance function
The acceptance function is modelled as:
The function can easily be determined using the unbiased sample
3
3( ) = 1
recrec
rec
tt
t
a
aA b
( ) ( ) biased rec unbiased recR t R tA
1 year untagged Bs→Ds
trec trec
Acc
![Page 52: LHCb: Preparing for Data (A talk on MC events and data expectations) NIKHEF Colloquium Feb 4, 2005 Marcel Merk](https://reader035.vdocuments.site/reader035/viewer/2022070414/5697c0271a28abf838cd66d5/html5/thumbnails/52.jpg)
52
3. + 4. Fit the Physics parameters
Use the 4 tagged (B) and (B) Ds decay rates to fit ms and Wtag fraction
Use the 4 tagged DsK events to fit r, ,
5 years data:Bs→ Ds
-
Bs→ Ds-K+
ms = 20)
Actually perform the Dsand DsK fits simultaneous
For each setting of the parameters repeat ~100 toy experiments A task for the GRID
![Page 53: LHCb: Preparing for Data (A talk on MC events and data expectations) NIKHEF Colloquium Feb 4, 2005 Marcel Merk](https://reader035.vdocuments.site/reader035/viewer/2022070414/5697c0271a28abf838cd66d5/html5/thumbnails/53.jpg)
53
The sensitivity of ms after 1 year
The sensitivity for ms
Amplitude fit method analogous to LEP
Curves contain 5 different assumptions for the decay time resol.
5Sensitivity:
ms = 68 ps-1
ms 15 20 25 30
(ms) 0.009 0.011 0.013 0.016
Precision on ms in ps-1
~1000 jobs
![Page 54: LHCb: Preparing for Data (A talk on MC events and data expectations) NIKHEF Colloquium Feb 4, 2005 Marcel Merk](https://reader035.vdocuments.site/reader035/viewer/2022070414/5697c0271a28abf838cd66d5/html5/thumbnails/54.jpg)
54
CP Sensitivity for many parameter settings
+ 55 65 75 85 95 105
(+)
14.5 14.2 15.0 15.0 15.0 15.1
-20 -10 0 +10 +20
(+) 13.9 14.1 14.2 14.5 14.6
ms 15 20 25 30
(+) 12.1 14.2 16.2 18.3
ss/s0 0.1 0.2
(+) 12.1 14.2 16.2
Precision on angle after one year with 1 year data:
10o
Dependence on background Dependence on resolution
(Ab-)using the GRID
![Page 55: LHCb: Preparing for Data (A talk on MC events and data expectations) NIKHEF Colloquium Feb 4, 2005 Marcel Merk](https://reader035.vdocuments.site/reader035/viewer/2022070414/5697c0271a28abf838cd66d5/html5/thumbnails/55.jpg)
55
(My) Conclusions
The decay Bs→Dscan provide an observation of ms oscillations in the first year of data taking. Important are: A working hadronic trigger A good tagging procedure Fairly good resolution
The decay Bs→DsK can provide an observation of angle
in subsequent years. Important are: Very good mass resolution for background suppression Full understanding of time resolution and tagging for systematics An efficient K/ separation
![Page 56: LHCb: Preparing for Data (A talk on MC events and data expectations) NIKHEF Colloquium Feb 4, 2005 Marcel Merk](https://reader035.vdocuments.site/reader035/viewer/2022070414/5697c0271a28abf838cd66d5/html5/thumbnails/56.jpg)
56
Outlook
A possible scenario before the LHCb measurement of
![Page 57: LHCb: Preparing for Data (A talk on MC events and data expectations) NIKHEF Colloquium Feb 4, 2005 Marcel Merk](https://reader035.vdocuments.site/reader035/viewer/2022070414/5697c0271a28abf838cd66d5/html5/thumbnails/57.jpg)
57
Outlook
A possible scenario after the LHCb measurement of
![Page 58: LHCb: Preparing for Data (A talk on MC events and data expectations) NIKHEF Colloquium Feb 4, 2005 Marcel Merk](https://reader035.vdocuments.site/reader035/viewer/2022070414/5697c0271a28abf838cd66d5/html5/thumbnails/58.jpg)
58
The End