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

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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

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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

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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

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What triggers L1?

• The track from other B is used at L1

Increase in tagging performance after L1

Origin of tracks, used in L1:

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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

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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…

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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

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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…

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Two other effects…

• Difference in K+ and K- reconstruction efficiencies

• Difference in B and B production rates

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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

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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

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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