Studies of open heavy flavour production at LHCb Artur Ukleja (The Andrzej Sołtan Institute for Nuclear Studies, Warsaw) on behalf of the LHCb Collaboration XIV International Conference on Hadron Spectroscopy München, 13-17 June 2011
Feb 23, 2016
Studies of open heavy flavour production at LHCb
Artur Ukleja(The Andrzej Sołtan Institute for Nuclear Studies, Warsaw)
on behalf of the LHCb Collaboration
XIV International Conference on Hadron SpectroscopyMünchen, 13-17 June 2011
A.Ukleja Studies of open heavy flavour production at LHCb
Outlook
16/06/2011 2
• Motivation
• Inclusive cross-section to produce b-flavoured hadrons (two measurements):
semileptonic: inclusive J/y (mm):
also measured open charm cross-section≈ 20 times higher than b cross-section
• Fragmentation fractions: fs / (fu+fd)
using semileptonic modes:
fLb / (fu+fd) using semileptonic modes:
fs / fd using hadronic modes:
• Summary
A.Ukleja Studies of open heavy flavour production at LHCb
Motivation
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• Knowledge of b-yield is critical in ascertaining sensitivity of experiments in B flavour sector (searching of new sources of CPV)• b-flavour hadrons cross-section can be compared to QCD predictions
also needed to estimate sensitivity to NP in B decays
Fragmentation fractions fs / fd• input to inclusive b cross-section measurement• fs needed for all B0
s branching ratios measurement
In particular for precise measurements
Fragmentation fraction fLb:• CDF’s value is substantially larger then LEP’s explained by CDF: it’s because of difference of <pT(B)>
A.Ukleja Studies of open heavy flavour production at LHCb
b or anti-b hadrons cross-section: using b→D0Xm- n
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D0→K- p+
D from b(Signal)
Prompt D (Back-ground)
Background >> Signal
D from b: large IP (the smallest distance between D reconstr. trajectory and PV)
Prompt D and Dfb components can be separated using IP with respect to the closest PV
-
Prompt D3 nb-1
3 nb-1
IP of D0 NO m requirement
PV
PV
Prompt D: IP ≈ 0
D from b: IP > 0
A.Ukleja Studies of open heavy flavour production at LHCb
b or anti-b hadrons cross-section: using b→D0Xm- n
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Now: Background (solid) << Signal (dashed)
-D0→K- p+
RS WS
To select decay chain we match D0 candidates with tracks identified as muons: • RS combinations: m sign of charge the same as K in D decay• WS combinations: opposite signs of charges of K and m
IP of D0 ; Now m required
12 nb-1 12 nb-1
Prompt D (Background)
Prompt D (Background)
D from b(Signal)
sidebands
As expected: prompt yields are consistent between RS and WS
A.Ukleja Studies of open heavy flavour production at LHCb
Tracking efficiency 10 %Luminosity 10 %
5 %
b or anti-b hadrons cross-section: using b→D0Xm- n
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-D0→K- p+
(MCFM)
Dominant systematics:[Phys.Lett.B694,209 (2010)]
Summing over h (2<h<6)[using LEP frag. fractions]: s(pp→HbX) = (75.3 ± 5.4 ± 13.0) mb (stat) (syst) consistent with predictions
The measured value changes if the b-hadron fractions differIf Tevatron frag. fractions are used: s(pp→HbX) = (89.6 ± 6.4 ± 15.5) mbTotal b anti-b cross-sections (extrapolate using Pythia):
s(pp→HbX) = (284 ± 20 ± 49) mbUsing Tevatron frag. fractions result increases by 19%
A.Ukleja Studies of open heavy flavour production at LHCb
b or anti-b hadrons cross-section: using b→J/yX
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Pseudo lifetime used to separate prompt and J/y from b:
J/y→m- m+
PVPV b
Prompt J/y: tz ≈ 0
J/y from b: tz > 0
J/y from b:
A.Ukleja Studies of open heavy flavour production at LHCb
b or anti-b hadrons cross-section: using b→J/yX
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J/y→m- m+
Tracking efficiency 8 %Luminosity 10 %BR(b→J/yX) 9 %
Dominant systematics:
[Submitted to Eur.Phys.J C: hep-ex/1103.0423]
• Measured cross-sections depend on y and pT
• Total – extrapolate using Pythia (using LEP frag. frac.): s(pp→HbX) = (288 ± 4stat ± 48syst) mb (2% change when using Tevatron fractions is included in systematic error)• Good agreement among both measurements from : s(pp→HbX) = (284 ± 20 ± 49) mb• Good agreement with QCD predictions
A.Ukleja Studies of open heavy flavour production at LHCb
Fragmentation fractions
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• Input to inclusive b cross-section measurement• fs needed for all B0
s branching ratios measurement in particular for precise measurements
Two methods:1) semileptonic modes:
2) hadronic modes:
Probability of b quark hadronizing with an antiquark (anti-d,u,s) or a di-quark pair (ud)
A.Ukleja Studies of open heavy flavour production at LHCb
Ratio of fragmentation fractions fs / (fu+fd)
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semileptonic modes
ncorr – efficiency, branching fractions and cross-feed corrected yields
Cross-feed between channels is taken into account
(C.Weiser, DELPHI 99-162 TALK 6, 1999)
A.Ukleja Studies of open heavy flavour production at LHCb
Semileptonic modes
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A.Ukleja Studies of open heavy flavour production at LHCb
Ratio of fragmentation fractions fs / (fu+fd)
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semileptonic modes
LEP: 0.128 ± 0.012CDF: 0.135 ± 0.016
• No evidence for dependence on h or pT(charm+m)
• Good agreement with LEP and Tevatron values
pT(charm+m) [GeV]
LHCb: 3 pb-1
f s / (
f u+f d)
h [2,3]
h [3,5]
Branching fractions of charm hadrons ±5.5 %
Subtraction of Bs→D0KXmn background
+4.1 %-1.1 %
Dominant systematics:
A.Ukleja Studies of open heavy flavour production at LHCb
Ratio of fragmentation fractions fLb / (fu+fd)
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pT(charm+m) [GeV]
LHCb: 3 pb-1
f Lb / (
f u+f d)
h [2,3]
h [3,5]
Systematic error dominates 26% uncertainty on BR(Lc→pKp)
• Slope with pT not consistent with zero• Parameterising with straight line gives
(for pT < 14 GeV):
semileptonic modes
A.Ukleja Studies of open heavy flavour production at LHCb
Ratio of fragmentation fractions fs / fd
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hadronic modes
The ratio: B0s→D-
sp+ / B0d→D-K+
only tree diagrams are involved theoretically well understood, branching
ratios calculable suffers from reconstructed yield of B0
d→D-K+
εX – total detector efficiencyNX – observed number of decaysNa=1.00±0.02 – non factorizable U-spin breaking effectsNF=1.24±0.08 – ratio of form factors
K+
D-
B0dB0
s
D-s
p+
World average for B0s-to-B0
d lifetime ratio:
(R.Fleisher, N.Serra, N.Tuning, Phys.Rev.D83:014017,2011)
A.Ukleja Studies of open heavy flavour production at LHCb
Ratio of fragmentation fractions fs / fd
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hadronic modes
The ratio: B0s→D-
sp+ / B0d→D-p+
suffers from theoretical uncertainties due to contribution from W exchange diagram
p+
D-
B0dB0
s
D-s
p+
εX – total detector efficiencyNX – observed number of decaysNa=1.00±0.02 – non factorizable U-spin breaking effectsNF=1.24±0.08 – ratio of form factorsNE=0.966±0.075 – additional correction term for the W exchange in B0
d→D-p+ decay
W
A.Ukleja Studies of open heavy flavour production at LHCb
Ratio of fragmentation fractions fs / fd
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hadronic modesModes topologically identical and using identical selection criteria to minimizing efficiency differences between modes
From B0s→D-
sp+ and B0d→D-K+: fs / fd = 0.242 ± 0.024stat ± 0.018syst ± 0.016theor
From B0s→D-
sp+ and B0d→D-p+ : fs / fd = 0.249 ± 0.013stat ± 0.020syst ± 0.025theor
Combined: fs / fd = 0.245 ± 0.017stat ± 0.018syst ± 0.018theor
• Theoretical uncertainty dominated by uncertainty on form factor ratio• Agrees well with semileptonic result and LEP and Tevatron
• Extra result: extract world best BR(B0d→D-K+)=(2.02 ± 0.17 ± 0.12) × 10-4
LHCb35 pb-1
(LHCb-CONF-2011-013)
A.Ukleja Studies of open heavy flavour production at LHCb
Summary
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• LHCb has measured the b or anti-b hadrons cross-section in √s=7 TeV pp collisions (total):
in agreement with (and more precise than) QCD predictions measured open charm cross-section (≈20 times higher)
• LHCb has measured the ratios of fragmentation fractions
fs / fd in good agreement with LEP and Tevatron
fLb / (fu+fd) partially for different pT (pT<14GeV) than Tevatron (〈 pT〉≈ 14GeV), in common region of pT good agreement
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Backup
A.Ukleja Studies of open heavy flavour production at LHCb
D0 cross section – example
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Also measured for: D+ , D*+ , D+
s
The shape and absolute normalization are in good agreement with theoretical predictions
20 times higher than s(b anti-b)
Combining all (pT<8 GeV , 2<y<4.5):
Full pT and y using Pythia extrapolation:
LHCb: 2 nb-1
(LHCb-CONF-2010-013)
A.Ukleja Studies of open heavy flavour production at LHCb 16/06/2011 20 (C.Weiser, DELPHI 99-162 TALK 6, 1999)
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