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
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• 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)
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