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Trigger and Tagging Systematics

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.

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Trigger and Tagging Systematics

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  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 Bfys Meeting, N.Tuning

  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… • ε= N tag found /N all • Not 100% correct: • ω= N wrong tag found /N tag found B b c s b K+ W+ ν e+,μ+ Bfys Meeting, N.Tuning

  3. Introduction • Need to know tagging performance in asymmetry measurement: • Use control channels: • B0dJ/(+-) K*(K+-) • B+uJ/(+-) K+ • B0sDs-+ • But… is the tagging the same for B0dJ/(+-) K* and B0d+_ ? • Example (TDR): (NB1: =(), = ()) (NB2: ()()) =0.25 =0.35 Rutger Hierck (3.4) (2.1) Bfys Meeting, N.Tuning

  4. PYTHIA Dependence on trigger Small dependence on b-b correlation No dependence on b-b correlation =Acc 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 L1 is more efficient for B0 -+ events with tagging part. than without 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. PYTHIA DaVinci Coincidence Clones from J/ Bfys Meeting, N.Tuning

  6. DaVinci   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. Bfys Meeting, N.Tuning

  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 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… In addition (independent of the trigger), the tagging is different per channel  Change (i.e. correct) the tagging algorithm Solution: following slides (maybe…) Bfys Meeting, N.Tuning

  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?ida=a021827 Bfys Meeting, N.Tuning

  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 signal+other B Unbiased sample! But small… Bfys Meeting, N.Tuning

  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 B’s 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… Bfys Meeting, N.Tuning

  13. Two other effects… • Difference in K+ and K- reconstruction efficiencies • Difference in B and Bproduction rates Bfys Meeting, N.Tuning

  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 Bfys Meeting, N.Tuning

  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‰ @ high pT, high  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 Bfys Meeting, N.Tuning

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