Polarized radiative Lb decays Selections: Lb L1115 g Lb L1670 g

1
Polarized radiative Lb decaysSelections Lb ?
L(1115) g Lb ? L(1670) g
2
Outline

• Theoretical motivations (reminder)
• Angular distributions
• Observables
• Lb production
• Simulation with EvtGen
• Selection of Lb ? L(x) g events
• Status and perspectives

3
Theoretical motivations

• Lb ? (L(x) ? p k) g

• Lb ? (L(1115) ? p p) g

g
g
s
b
k
s
b
u
Lb
L
Lb
d
d
u
p
u
u
d
d
u
u

• Angular asymmetries (with respect to Lb spin)
• constrain
• Direct CP violation at NLO O(1) in SM but ?10
  if NP!

• PB Lb polarization
• ap weak decay parameter

sensitive to NP
4
Observables for Lb ? L(1115) g
Helicity formalism
HQET

• 2 independent measurements for r
• PB measurement
• a discrepancy with the value measured in
  semileptonic Lb?cl?lX decays would indicate the
  presence of non-standard right-handed b ? c
  currents.
• Lb ? L(1670) g only Ag

5
Lb production at LHC

• ?10 of produced bb hadronize in B hadrons
• Lb dominates (?90)
• Lb produced with transversal polarization
• Predictions are PB 20
• ATLAS plans to measure it with a statistical
  precision better than 0.01
• BR (Lb ? L(1115) g ) 4.15 10-5
• BR (Lb ? L(1670) g ) 0.70 10-5

Lb
n
p1
p2
Ajaltouni, Conte, Leitner, ?b into ?-vector
decays, Phys Lett B, 614 (2005)
Feasibility of Beauty Baryon Polarization
Measurement in Lb ? J/Y L decay channel by ATLAS
Atlas note
My last talk _at_RD WG
6
Generation with EvtGen

• Lb polarization
• polarized Lb from Gauss v15r17
• Polarization was hardcoded and only longitudinal
• Fully polarized Lb PB 1
• It is now possible to set the polarization via
  job options (from Gauss v15r21)
• Polarization can be longitudinal or transversal
  or anything in between
• Angular distributions
• HELAMP model for Lb ? Lg decay
• Helicity amplitudes and phases as input
• L fully polarized ag -1
• HELAMP model for L ? px decay
• agap 0.639 L? pp
• ap 0 L? pk (P cons)

7
Data sample Tools

• Lb ? L(1115) g pol long, full 300k evts
• Lb ? L(1670) g pol long, full 300k evts
• bb inclusive (DC04-v2) 40M evts

• DaVinci v12r14 private version of VertexFit
• Selection code 100 option files
• No particular method to optimize cuts values
• PT, IPS (with respect to all primaries) cuts on
  final states
• Mass window 4s for resonances with intrinsic
  width
• Lb primary vertex smallest IPS
• Cut values chosen to kill bb events while
  maintaining higher possible efficiencies

8
L(1115) ? p p

• ct 7.89 cm
• About 14 of L interact before decay or decay
  after LHCb spectrometer ? lost
• 305000 (generated) ? 262464 (DoI)

L candidates (associated to MC truth)
9
Vertexing issues

• Unconstrained vertex fit
• Lb vertex L(x) photon
• the photon does not have a definite direction,
  therefore it is simply attached to the Lb vertex,
  and its origin is transported to the L vertex,
• the L(1115) flies , transporting the photon to
  the L vertex not correct any more, especially for
  DD case (mass peak shifted above 6 GeV!)
• rapid fix if the L is formed with 2 downstream
  tracks, the photon origin is not transported to
  the L vertex

BUT ...
Still under study...
10
Lb ? (L(1670) ? p K) g
bb incl signal
bb incl signal
Charged tracks

• Protons
• Only Long tracks
• DLL p-p gt 5
• DLL p-k gt 0
• Exclusive DLL
• Kaons
• Only Long tracks
• DLL K-p gt 5
• DLL K-p gt 0
• Exclusive DLL

false p true p
false K true K
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Lb ? (L(1670) ? p K) g
bb incl signal
bb incl signal
Charged tracks

• Protons
• PT gt 1000 MeV
• sIPS gt 4
• Kaons
• PT gt 800 MeV
• sIPS gt 4

bb incl signal
bb incl signal
12
Lb ? (L(1670) ? p K) g
g selection

• PT gt 2500 MeV/c
• PT (with respect to Lb direction) ? 1600, 2800
  MeV/c

bb incl signal
13
Lb ? (L(1670) ? p K) g
bb incl signal
bb incl signal
L(1670) selection

• ?2 lt 6
• Dm lt 100 MeV
• PT gt 1500 MeV
• sIPS gt 4

Lb selection

• Dm lt 200 MeV
• PT gt 2000 MeV
• ?(Lb) lt 0.0165

bb incl signal
bb incl signal
?
p
PV
Lb
14
Lb ? (L(1670) ? p K) g
Mass resolutions
Det only
Det width Tight mass window 4 s
Bs,d ? f/K g, s 64 MeV (TDR)
15
Efficiencies for Lb ? L(1670) g

• etot edet x erec/det x esel/rec x etrg/sel
  0.233
• edet 0.1
• erec/det 0.87
• esel/rec 0.07
• etrg/sel eL0/sel x eL1/L0 x eHLTgen/L1 0.37
• Purity 88.6

After HLT generic!!!
Bs ? f g, etot 0.220 (TDR, after L0 x
L1) Bd ? K g, etot 0.156 (TDR, after L0
x L1)
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Lb ? (L(1115) ? p p) g

• UP
• DLL p-p gt 7
• DLL p-k gt 0
• PT gt 600 MeV
• sIP gt .2 mm
• sIPS gt 7

• DOWN
• DLL p-p gt 10
• DLL p-k gt 8
• PT gt 2000 MeV
• sIP gt .6 mm
• sIPS gt 3

• LONG
• DLL p-p gt 6
• DLL p-k gt 0
• PT gt 1900 MeV
• sIP gt .2 mm
• sIPS gt 5

p

• UP
• PT gt 200 MeV
• sIP gt .5 mm
• sIPS gt 7

• DOWN
• PT gt 300 MeV
• sIP gt 6 mm
• sIPS gt 7

• LONG
• PT gt 250 MeV
• sIP gt .5 mm
• sIPS gt 6

p

• Hard DLL and PT cuts on protons to suppress
  background
• Slow momentum pions

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Lb ? (L(1115) ? p p) g

• DD
• ?2 lt 20
• Dm lt 15 MeV
• PT gt 2500 MeV
• sIP gt .5 mm
• sIPS gt 2
• FD gt 300 mm
• FS gt 0

• LL
• ?2 lt 10
• Dm lt 6 MeV
• PT gt 2000 MeV
• sIP gt .2 mm
• sIPS gt 4
• FD gt 30 mm
• FS gt 10

L selection

• UL
• ?2 lt 20
• Dm lt 25 MeV
• PT gt 2500 MeV
• sIP gt .2 mm
• sIPS gt 2
• FD gt 20 mm
• FS gt 4

• LD
• ?2 lt 20
• Dm lt 16 MeV
• PT gt 2500 MeV
• sIP gt .2 mm
• sIPS gt 1
• FD gt 100 mm
• FS gt 3

• Hardest PT cuts on DD combinations
• UL worse mass resolution

18
L(1115) mass resolution
Mean 1116.2 MeV/c2
Mean 1116.2.5 MeV/c2
Mean 1114.5 MeV/c2
Mean 1117.5 MeV/c2
Low stat
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Lb ? (L(1115) ? p p) g

• g selection
• PT gt 3500 MeV/c
• PT gt 4000 MeV/c for DD combinations
• PT (in Lb direction) ? 2200, 3000 MeV/c

• UL
• PT gt 2500 MeV
• sIP gt .7 mm

Lb selection

• LL
• PT gt 2000 MeV
• sIP gt .6 mm

• DD
• PT gt 3000 MeV

• LD
• PT gt 2500 MeV

• No IP/IPS cut on DD/ LD combinations
• butbad Lb vertexing ? still under study

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Lb ? L(1115) g mass plots
Mean 5616 MeV/c2
Mean 5699 MeV/c2
Low stat
21
Efficiencies for Lb ? L(1115) g

• etot edet x erec/det x esel/rec x etrg/sel
  0.009
• edet 0.009
• erec/det 0.78
• esel/rec 0.10
• etrg/sel eL0/sel x eL1/L0 x eHLTgen/L1 0.12
• Purity 92.9
• L(1115) after selection

After HLT generic!!!
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Event yield for Lb ? L(X) g

• Yield (Lb ? L(1115) g ) 787 / year
• Yield (Lb ? L(1670) g ) 3267 / year
• Yield Linty x sbb x 2 x fLb x BR x etot
• Linty 2 fb-1
• sbb 500 mb
• fLb 10.1
• BR (Lb ? L(1115) g ) 4.15 10-5
• BR (Lb ? L(1670) g ) 0.70 10-5

Expected Lb/yrs 2 x 1011
Check the numbers
23
bb background Lb ? L(X) g

• Lb ? L(1115) g
• 30 M analyzed (of 40M bb inclusive)
• 9 events selected
• Only 2 after HLT Gen
• 0 left after HLT
• Lb ? L(1670) g
• 18 M analyzed (of 40M bb inclusive)
• 0 events selected
• B/S (Lb ? L(1115) g ) lt 0.04 _at_ 90 CL
• B/S (Lb ? L(1670) g ) lt 0.06 _at_ 90 CL

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Conclusions

• Lb ? L(1115) g
• First selection code (800 evts/year)
• drop asymmetries study, finalize BR
• Lb vertex fit still under study
• Write HLT exclusive selection.
• Lb ? L(1670) g
• Selection ready (3200 evts/year)
• Generation of unpolarized/transversally polarized
  Lb to check if we can measure asymmetries
• Write HLT exclusive selection.

25
Backup slides
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Lb ? L(1115) g

• PB 1
• ag -1
• ap 0.642

27
Lb ? L(1670) g

• PB 1
• ag -1
• ap 0

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Trigger for Lb ? L(1115) g
L1

• Trigger breakdown
• eL0/sel 0.75
• eL1/L0 0.30
• eHLTgen/L1 0.54
• eHLTgen/HLT 0.09

HLT
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Trigger for Lb ? L(1670) g
L1

• Trigger breakdown
• eL0/sel 0.71
• eL1/L0 0.63
• eHLTgen/L1 0.80
• eHLTgen/HLT 0.04

HLT
30
Lb ? L(1115) g DLL cuts
bb incl signal
bb incl signal
bb incl signal
false p true p
false p true p
false p true p
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Lb ? L(1115) g PT cuts (p and p)
bb incl signal
bb incl signal
bb incl signal
bb incl signal
bb incl signal
bb incl signal
32
Lb ? L(1115) g IP cuts (p and p)
bb incl signal
bb incl signal
bb incl signal
bb incl signal
bb incl signal
bb incl signal
33
Lb ? L(1115) g IPS cuts (p and p)
bb incl signal
bb incl signal
bb incl signal
bb incl signal
bb incl signal
bb incl signal
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Lb ? L(1115) g PT and ?2 cuts (L)
bb incl signal
bb incl signal
bb incl signal
bb incl signal
bb incl signal
bb incl signal
bb incl signal
bb incl signal
35
Lb ? L(1115) g IP and IPS cuts (L)
bb incl signal
bb incl signal
bb incl signal
bb incl signal
bb incl signal
bb incl signal
bb incl signal
bb incl signal
36
Lb ? L(1115) g FD cuts (L)
bb incl signal
bb incl signal
bb incl signal
bb incl signal
bb incl signal
bb incl signal
bb incl signal
bb incl signal
37
Lb ? L(1115) g PT cuts (Lb, g)
bb incl signal
bb incl signal
bb incl signal
bb incl signal
bb incl signal
bb incl signal
bb incl signal
bb incl signal
38
Lb ? L(1115) g IP and IPS cuts (Lb)
bb incl signal
bb incl signal
bb incl signal
bb incl signal
bb incl signal
bb incl signal
bb incl signal
bb incl signal
39
Lb ? L(1115) g mass plots
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Lb ? L(1670) g selection

• g
• PT gt 2500 MeV
• 1600 MeV lt PT (in Lb direction) lt 2800 MeV
• L(1670)
• ?2 lt 6, Dm lt 100 MeV
• PT gt 1500 MeV
• sIPS gt 4
• Lb
• Dm lt 200 MeV
• PT gt 2000 MeV
• ?(Lb) lt 0.0165

• Protons
• Only Long tracks
• DLL p-p gt 5
• DLL p-K gt 0
• Exclusive DLL selection
• PT gt 1000 MeV
• sIPS gt 4
• Kaons
• Only Long tracks
• DLL K-p gt 5
• DLL K-p gt 0
• Exclusive DLL selection
• PT gt 800 MeV
• sIPS gt 4

etot 0.233 , purity 88 , B/S 0.05 _at_
90 CL