Studies of open heavy flavour production at LHCb Artur Ukleja

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


Motivation

16/06/2011 3

• 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)>


b or anti-b hadrons cross-section: using b→D0Xm- n

16/06/2011 4

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



16/06/2011 5

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


Tracking efficiency 10 %Luminosity 10 %

5 %


16/06/2011 6

-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%


b or anti-b hadrons cross-section: using b→J/yX

16/06/2011 7

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:


b or anti-b hadrons cross-section: using b→J/yX

16/06/2011 8

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


Fragmentation fractions

16/06/2011 9

• 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)


Ratio of fragmentation fractions fs / (fu+fd)

16/06/2011 10

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)


Semileptonic modes

16/06/2011 11


Ratio of fragmentation fractions fs / (fu+fd)

16/06/2011 12

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:


Ratio of fragmentation fractions fLb / (fu+fd)

16/06/2011 13

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


Ratio of fragmentation fractions fs / fd

16/06/2011 14

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)



16/06/2011 15

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



16/06/2011 16

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)


Summary

16/06/2011 17

• 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

A.Ukleja Studies of open heavy flavour production at LHCb 16/06/2011 18

Backup


D0 cross section – example

16/06/2011 19

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)





Documents

Studies of open heavy flavour production at LHCb Artur Ukleja