Trigger and Tagging Systematics

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
Introduction

• Flavour tagging is necessary for asymmetry
  measurement
• Was it a B, or was it a?B ??
• Tag with muons, electrons or kaons
• Not 100 efficient
• e N tag found /N all
• Not 100 correct
• ? N wrong tag found /N tag found

?B
b
?c
?s
?b
K
W
?
e,µ
3
Introduction

• Need to know tagging performance in asymmetry
  measurement

(NB1 ??(?), ? ?(?)) (NB2 ?(?)???(?))

• Use control channels
• B0d?J/?(??-) K(K?-)
• Bu?J/?(??-) K
• B0s?Ds-?
• But is the tagging the same for B0d?J/?(??-) K
  and B0d???_ ?
• Example (TDR)

?0.35
?0.25
Rutger Hierck
(3.4?)
(2.1?)
4
Effect of trigger on tagging

• Study at generator level
• Sel all decay part. in acc.
• L0 PT?,e,h gtthreshold
• 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 gtthreshold
• P ?,e,K gtthreshold
• IP/IPSK gt threshold

L1 is more efficient for B0? ? -? events
with tagging part. than without
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.

DaVinci
PYTHIA
Coincidence
Clones from J/?
6
Effect of trigger on tagging

• Full simulation (DaVinci)
• Muons and kaon from B0d? J/?(??-) K(K?_)
  affect tagging
• ??- add random tags
• K add correct tag
• Differences B0d?J/? K and?B0d?J/??K not
  understood.

7
What triggers L1?
Origin of tracks, used in L1

• The track from other B is used at L1
• ? Increase in tagging performance after L1

8
The problem

• The trigger changes the tagging performance
  differently for different channels!
• ? Therefore it will be difficult to determine e
  and ? experimentally

In addition (independent of the trigger), the
tagging is different per channel ? Change (i.e.
correct) the tagging algorithm
Solution following slides (maybe)
9
Compare tagging efficiency

• Muon channels
• Enhanced muon tagging
• KS channels
• Enhanced kaon tagging?

• Solution masking signal
• Reconstruct decay
• Mask all hits and clusters from decay
• Perform tagging
• See also Hans talk 12 November
• http//agenda.cern.ch/fullAgenda.php?idaa021827

10
Masking

• Why masking?
• Get unbiased tagging before trigger, unbiased by
  signal decay
• Mask signal decay, and redo tagging.
• Get unbiased sample after trigger, unbiased by
  trigger
• Mask signal decay, and redo trigger.

• Split triggered data in separate samples
• After masking signal triggered YES
• Else triggered purely on signal
• Else triggered on signalother B

Unbiased sample! But small
11
Tagging for different trigger samples
DaVinci

• 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 Bs

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 23, but not with
  12
• 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

13
Two other effects

• Difference in K and K- reconstruction
  efficiencies
• Difference in B and ?B production rates

14
K/K- asymmetry?
PDG

• Different cross section with matter

DaVinci

• Different probability of reaching TT2
• 2-3 difference in reconstruction efficiency
• ? directly affects kaon tag

Tagging kaons
15
B production asymmetry

• Two effects
• leading parton
• enhance B0d at high pT
• Valence quark forms ?b-hadron
• Not present for B0s!
• drag effect
• enhance ?B0d (or ?B0s) at high ?
• Remnant pulls b-hadron

PYTHIA

• Small Bd0 asymmetry
• Amax 8 ? 3
• _at_ high pT, high ?

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