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Trigger and Tagging Systematics . Introduction What is the problem?? Affect of trigger on tagging Tagging performance w/o trigger Compare full simulation with PYTHIA Two other systematic effects: K+/K- asymmetry B production asymmetry. Introduction. - PowerPoint PPT Presentation
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2 April 2004 Bfys Meeting, N.Tuning 1
Trigger and Tagging Systematics
• Introduction What is the problem??
• Affect of trigger on tagging Tagging performance w/o trigger Compare full simulation with PYTHIA
• Two other systematic effects: K+/K- asymmetry B production asymmetry
2 April 2004 Bfys Meeting, N.Tuning 2
Introduction• Flavour tagging is necessary for
asymmetry measurement: Was it a B, or was it aB ?? Tag with muons, electrons or kaons:
Not 100% efficient…• ε= N tag found /N all
Not 100% correct:• ω= N wrong tag found /N tag found
W+
b
B
b c
e+,μ+
ν
s K+
2 April 2004 Bfys Meeting, N.Tuning 3
Introduction
• Use control channels: B0
dJ/(+-) K*(K+-) B+
uJ/(+-) K+
B0sDs
-+
• But… is the tagging the same for B0dJ/(+-) K* and B0
d+_ ?• Example (TDR):
)()(
)()()(
BtagBtag
BtagBtagmeasCP nn
nnA
theoryCP
measCP AA )21()(
• Need to know tagging performance in asymmetry measurement:
(%) (%)B0
sJ/(+-) 50.40.3 33.40.4B0
sDs-+ 54.61.2 30.01.6
(3.4) (2.1)
(NB1: =(), = ())(NB2: ()())
=0.35=0.25
Rutger Hierck
2 April 2004 Bfys Meeting, N.Tuning 4
Effect of trigger on tagging
• Study at generator level: Sel: all decay part. in acc. L0: PT,e,h >threshold L1:
• 2d-cut on IP vs PT of 2 charged particles in acc.
• Overrule if 2 in acc. Tag:
,e,K not from signal B, and in acc.
• PT ,e,K >threshold• P ,e,K >threshold• IP/IPSK > threshold
Dependenceon triggerSmall dependence
on b-b correlation
No dependenceon b-b correlation
PYTHIA
=AccL1 is more efficient for B0 -+ events withtagging part. than without
2 April 2004 Bfys Meeting, N.Tuning 5
Effect of trigger on tagging
• Tagging in full simulation suffers from signal decay. “clones” see Massi
• PYTHIA and full simulation: same trends after trigger.
DaVinciPYTHIA
Clones from J/
Coincidence
2 April 2004 Bfys Meeting, N.Tuning 6
Effect of trigger on tagging
• Full simulation (DaVinci)
• Muons and kaon from B0
d J/(+-) K*(K+_) affect tagging +-: add random tags K+: add “correct” tag
• Differences B0dJ/ K*
andB0dJ/K* not
understood.
DaVinci
2 April 2004 Bfys Meeting, N.Tuning 7
What triggers L1?
• The track from other B is used at L1
Increase in tagging performance after L1
Origin of tracks, used in L1:
2 April 2004 Bfys Meeting, N.Tuning 8
The problem…The trigger changes the tagging performance
differently for different channels!
Therefore it will be difficult to determine ε and ω experimentally…
Solution: following slides (maybe…)
In addition (independent of the trigger), the tagging is different per channel Change (i.e. correct) the tagging algorithm
2 April 2004 Bfys Meeting, N.Tuning 9
Compare tagging efficiency• Muon channels:
Enhanced muon tagging
• KS channels: Enhanced kaon tagging?
Solution: masking signal: 1) Reconstruct decay2) Mask all hits and
clusters from decay3) Perform tagging
See also Hans’ talk 12 November:http://agenda.cern.ch/fullAgenda.php?ida=a021827
2 April 2004 Bfys Meeting, N.Tuning 10
MaskingWhy masking?
1) Get unbiased tagging before trigger, unbiased by signal decay: Mask signal decay, and redo tagging.
2) Get unbiased sample after trigger, unbiased by trigger: Mask signal decay, and redo trigger.
Split triggered data in separate samples:
I. After masking signal: triggered YESII. Else: triggered purely on signalIII. Else: triggered on signal+other B
Unbiased sample!But small…
2 April 2004 Bfys Meeting, N.Tuning 11
Tagging for different trigger samples
Compare tagging performance for different samples:
TOT: could have triggered without signal tracks
• Unbiased but small… TOS: triggered without
tagging B• 2 signal tracks• 1 signal, 1 other track
TOB: triggered on both B’s
DaVinci
2 April 2004 Bfys Meeting, N.Tuning 12
Masking • Consider the unbiased sample:
Mask signal decay Redo trigger Take events that pass
• This is only unbiased if the events pass the trigger in the first place L1: the event passes with track 2+3, but not with 1+2 …
• Need to be repaired, eg:– Cut only on PT, not the 2d-cut on IP vs PT – Take OR of tracks (1,2), (2,3), (3,4), …
L0: event might pass after masking, but is vetoed in the first place…
Keep this in mind for future trigger algorithms…
2 April 2004 Bfys Meeting, N.Tuning 13
Two other effects…
• Difference in K+ and K- reconstruction efficiencies
• Difference in B and B production rates
2 April 2004 Bfys Meeting, N.Tuning 14
K+/K- asymmetry?
• Different cross section with matter:
• Different probability of reaching TT2: 2-3% difference in
reconstruction efficiency directly affects kaon tag
PDG:
DaVinci:
Tagging kaons
2 April 2004 Bfys Meeting, N.Tuning 15
B production asymmetry• Two effects:
leading parton: • enhance B0
d at high pT • Valence quark forms b-hadron• Not present for B0
s! “drag effect”:
• enhance B0d (or B0
s) at high • Remnant pulls b-hadron
Small Bd0 asymmetry:
Amax = 8 3‰ @ high pT, high
PYTHIA
2 April 2004 Bfys Meeting, N.Tuning 16
Conclusions
• Tagging is biased by signal decay products: Solution: Mask the signal decay products before doing tagging. (But it remains difficult…)
• Tagging is biased by trigger: Solution:
Split the data in separate samples.
• See: H.Dijkstra, N.T., N.Brook: LHCb note 2003-157