b Production Cross Sections and Fragmentation Fractions at LHCb Laurence Carson (University of Santiago de Compostela) on behalf of the LHCb collaboration Phenomenology 2011 Symposium University of Wisconsin-Madison May 9 th – 11 th 2011

Overview Beauty production cross section in √s = 7 TeV pp collisions can be compared to QCD predictions – also needed to estimate sensitivity to New Physics in B decays Will present two measurements of σ(pp  bbX) – using b  D 0 Xμν and using b  J/ψX 2 Ratio of fragmentation fractions f s /f d needed for precise measurement of B s branching fractions, e.g. B s  μμ Long-standing disagreement in fragmentation fractions f Λ b /(f u +f d ) measured at LEP and at TeVatron Will present measurements of f s /f d and f Λ b /(f u +f d ) using semileptonic modes, and of f s /f d using hadronic modes

The LHCb Experiment 3 Single forward arm spectrometer covering 2.0 < η < 5.5 (η= -ln[tan(θ/2)])

b Cross Section using b  D 0 Xμν Vertex D 0 (  K  ) with right-sign μ, cut on Impact Parameter (IP) of μ then distinguish prompt D 0 and D 0 from B using IP of D 0 ~3 nb -1 Prompt D D from b IP D 0 (NO  requirement)IP of D 0 (  required) Prompt D D from b Fake D Two independent samples used: 3nb -1 taken with unbiased trigger, and 12nb -1 requiring single muon trigger Fake D subtracted B ~12 nb -1 4

b Cross Section using b  D 0 Xμν 5 15nb -1 used theory error Source Size Tracking efficiency10% Luminosity10% Branching/frag. fractions8% Published in Phys. Lett. B 694, 209 (2010) Use: Dominant systematics (MCFM) (FONLL) σ(pp  bbX) = (284 ± 20 ± 49) μb (stat) (syst) η σ(pp  bbX) = (75.3 ± 5.4 ± 13.0) μb Using TeVatron (instead of LEP) fragmentation fractions gives: For 2 < η < 6 (measured): Extrapolate to 4π (using Pythia): σ(pp  bbX) = (338 ± 24 ± 58) μb (increase of 19%)

b Cross Section using b  J/ψX Fit to pseudo-proper time, 6 Prompt J/ψ J/ψ from b Submitted to Eur. Phys. J C Preprint: hep-ex/ in bins of p T and y (with LEP fragmentation fractions, 2% change when using TeVatron fractions is included in syst. error) Source Size Tracking efficiency8% Luminosity10% B.R.(b  J/ψX) 9% 5.2pb -1 used Dominant systematics: σ(pp  bbX) = (288 ± 4 ± 48) μb (also prompt J/ψ cross section) Reconstruct J/ψ  μμ, using both single muon and dimuon triggers

Fragmentation Fractions using Semileptonic Decays 7 Can measure f s /(f u +f d ) and f Λ b /(f u +f d ) using D 0 Xμν, D + Xμν, D s Xμν, Λ c Xμν Similar strategy to x-sec measurement, but must correct for cross-feeds from such decays as B s  D s1,2 (  D 0 K)Xμν, B 0/+  D s KXμν, and Λ b  D 0 pXμν Use Γ SL (B + ) = Γ SL (B 0 ) = Γ SL (B s ) (known to hold within 1% from e.g. HQET) and Γ SL (Λ b ) /Γ SL (B 0 ) = 1.04 ± 0.02 b  D s Xμνb  Λ c Xμν 3pb -1 used

3pb -1 20pb -1 D s1 (2536) +  D *0 K + missing  /  0 D s2 * (2573) +  D 0 K +  RS D 0 K +  WS Kaon: D 0 K  First observation of 8 Evidence for resonance seen whilst checking b  D 0 KXμν mass spectrum Published in Phys. Lett. B 698, 14 (2011) Confirmed in larger data sample, with significance of ≈8σ Also: measured mass and width of confirmed DØ observation of D s1 mode

Semileptonic f s /(f u + f d ) Result 9 No evidence for dependence of f s /(f u + f d ) on either η or p T f s /(f u + f d ) = ± (stat) – pb -1 used Source Size Branching fractions of charm hadrons±5.5% Subtraction of B s  D 0 KXμν bkg +4.1% -1.1% cf. LEP: ± (HFAG), and TeVatron: ± (CDF semilep.) Dominant systematics (syst) Good agreement with LEP and TeVatron values

Semileptonic f Λ b /(f u + f d ) Result 10 3pb -1 used Slope with p T not consistent with zero. Parameterising with straight line gives: f Λ b /(f u +f d ) = (0.401 ± ± 0.106) – ( ± ± )*p T /GeV, for p T < 14 GeV 26% uncertainty on BR(Λ c  pK  ) completely dominates the systematics cf. LEP: ± ( ≈40 GeV), CDF: ± ( ≈14 GeV)

f s /f d using Hadronic Decays 11 Decays B d  D  K  and B s  D s    involve only tree level diagrams, hence ratio of branching fractions is theoretically calculable Phys. Rev. D 82, (2010) Similar situation for B d  D    and B s  D s   , but with exchange diagram Phys. Rev. D 83, (2011) form factordeviation from factorisation

f s /f d using Hadronic Decays 12 Multivariate selection designed to minimise efficiency differences between modes. Effect of PID cuts evaluated using D* control samples. N Dπ = 4103 ± 75 N DK = 252 ± 21 N D s π = 670 ± 34 From B s  D s    and B d  D  K  : f s /f d = ± ± ± From B s  D s    and B d  D    : f s /f d = ± ± ± (stat) (syst) (theory) Combine, accounting for correlated uncertainties: f s /f d = ± ± ± LHCb-CONF Also: extract World’s best BR(B d  D  K  ) (see talk of M. Whitehead) Agrees well with semileptonic result 35pb -1 used

Also: first observation of, and World’s best BR(B d  D  K + ) Conclusions 13 LHCb has measured the b cross section in √s = 7 TeV pp collisions: σ(pp  bbX) = (288 ± 4 ± 48) μb (b  J/ψX, 5.2pb -1 ) σ(pp  bbX) = (284 ± 20 ± 49) μb (LEP fractions) LHCb has measured the ratios of fragmentation fractions: f s /f d = ± ± ± (hadronic, 35pb -1 ) f s /f d = ± ± (semileptonic, 3pb -1 ) f Λ b /(f u +f d ) = (0.401 ± ± 0.106) – ( ± ± )*p T /GeV, for p T < 14 GeV (semileptonic, 3pb -1 ) In agreement with (and more precise than) QCD predictions f s /f d in good agreement with LEP and TeVatron; p T dependence of f Λ b /(f u +f d ) may reconcile different measurements σ(pp  bbX) = (338 ± 24 ± 58) μb (TeVatron fractions) (b  D 0 Xμν, 15nb -1 )

Backup 14

LHCb Acceptance  b 230  b Pythia production cross section (14TeV)  pTpT b’s are produced at low angles, and in the same hemisphere Nice overlap of acceptance with GPDs

Systematics for b  D 0 Xμν 16

Combination for b  D 0 Xμν 17 Unbiased trigger, 3nb -1 Single muon trigger, 12nb -1 Combination

Muon Identification 18 Eff. = (97.1±1.3)% from J/ψ tag & probe π misID = (0.71±0.05)% from K S (also Λ) Most misID is due to π →μ decays in flight

Systematics for b  J/ψX 19

b  J/ψX dependence on y 20

b  J/ψX efficiencies from MC 21 Efficiencies for prompt J/ψ and for J/ψ from b assumed equal (no cuts on impact parameter or decay length)

f s /f d for B s  μμ 22 Reach with σ(f s /f d ) = 13% (current PDG) Reach with σ(f s /f d ) = 7% (our ambition!) Phys. Rev. D 82, (2010)

Semileptonics: b  D 0 Xμν 23

Semileptonics: b  D + Xμν 24

Semileptonics: b  D s Xμν 25

Semileptonics: b  Λ c Xμν 26

Semileptonics: b  D 0 pXμν 27  RS D 0 p WS D 0 p 3pb -1 Possible contributions from Λ c (2880) + and Λ c (2940) +, both of which can decay into D 0 p

Semileptonics: Efficiencies 28 Efficiency breakdown for D 0 μ K and π p T cuts PID cuts Muon selection & trigger Track acceptance and reconstruction

Semileptonics: Cross-check 29

Systematics for Semileptonic f s /(f u + f d ) 30

Deviations from Factorisation 31 X P ≈ 1 within <1% (X V is exactly 1) Can use B Factory results to obtain: No evidence for deviation of ratio of any |a 1 |’s from 1. Use of LHCb measurements can improve value for B d  D  K  Phys. Rev. D 83, (2011)

Exchange diagram in B d  D    32 Can be constrained using Babar, PRL (2006) Ratio of tree amplitudes is Hence extract Use this to estimate Phys. Rev. D 83, (2011) To allow for differences between D and D* cases

Systematics for Hadronic f d /f s 33 Efficiency and misID of tight Kaon ID cut used to select B d  D  K 