hadronic moments in semileptonic b decays ramon miquel lawrence berkeley national laboratory (for...

Hadronic Moments in Semileptonic B Decays

Ramon Miquel

Lawrence Berkeley National Laboratory

(for the CDF II Collaboration)

7/2/04 Ramon Miquel BEACH 04 2

Ftheory evaluated using OPE in HQET: expansion in s and 1/mB powers:

O(1/mB) 1 parameter: (Bauer et al., PRD 67 (2003) 071301)

O(1/mB2) 2 more parameters: 1, 2

O(1/mB3) 6 more parameters: 1, 2, T1-4

Motivation (I)

(4S), LEP/SLD, CDF measurements. Experimental |Vcb|~1%

Theory with pert. and non-pert. corrections. |Vcb|~2.5%

Most precise determination of Vcb comes from sl (“inclusive” determination):

}{ )π

α()

m

1()λcλc(Λ

m

c)

π

αc(1Λ

m

c

π

αc1cm

192π

GΓ

2s

3B

27162

2B

54

B

321

5B

2

3

2F

sl OOV

sscb

theorycbb

sl FVcbBR

cb

2)()(


Motivation (II)

• Hadronic moments: BXcl, recoil mass M(Xc)

• Leptonic moments: BXcl, lepton E in B rest frame

• Photonic moments: Photon energy in b s

(CLEO, DELPHI, BABAR)

(CLEO)

(CLEO, DELPHI, BABAR, CDFII)

Many inclusive observables can be written using the same expansion (same

non-perturbative parameters): the spectral moments:

Constrain the unknown non-pert. parameters and reduce |Vcb| uncertainty.

With enough measurements: test of underlying assumptions (duality…).


What is Xc?

~25% of semi-leptonic width is poorly known

Higher mass states: D**Semi-leptonic widths (PDG 03):

Br (%)

B+ Xc l 10.89 0.26

B+ D* l 6.00 0.24

B+ D l 2.23 0.15

(b/B+/B0 combination, bu subtracted)

Possible D’D(*) contributions neglected:

• No experimental evidence so far

• DELPHI limit:

We assume no D’ contribution in our sample

CLDbBR

CLDbBR

%90@%17.0

%90@%18.0*


Analysis Strategy

Typical mass spectrum M(X0c) (Monte Carlo):

D0 and D*0 well-known measure only f** only shape needed

1) Measure f**(sH)2) Correct for background,acceptances, bias moments of D**3) Add D and D* M1,M2

4) Extract , 1


Channels

− D**0 D+ OK– D**0 D0 0 Not reconstructed. Half the rate of D+

– D**0 D*+

• D*+ D0 + OK• D*+ D+ 0 Not reconstructed. Feed-down to D+

– D**0 D*0 0 Not reconstructed. Half the rate of D*+

Must reconstruct all channels to get all the D** states. However CDF has limited capability for neutrals

• B0D** l+ always leads to neutral particles ignore it

• B- D**0 l better, use isospin for missing channels:


D**0 D*+ **- D0 *+ (Br=67.7%)

K- + (Br=3.8%) K- + - + (Br=7.5%) K- + 0 (Br=13.1%)

Event Topology

Exclusive reconstruction of D**:

D**0 D+ **- K- + + (Br=9.1%)

“D+” “D*+”


Backgrounds

Combinatorial backgroundunder the D(*) peaks: sideband subtraction

Physics background:BD(*)+Ds

, D(s)Xl MC, subtracted

Prompt pions faking **:• fragmentation• underlying eventseparate B and primary vertices (kills also prompt charm) use impact parameters to discriminate model: wrong-sign **+ combinations

Feed-down in signal:D**0 D*+( D+0) irreducible background toD**0 D+.subtracted using data:

shape from D0 in D**0 D*+( D0+)rate: ½ (isospin) x eff. x BR


Lepton + D(*)+ ReconstructionLepton + D(*)+:• D vertex:

• 3D• l+D(+*) vertex (“B”):

• 3D• Lxy(B) > 500 m

• M(B) < 5.3 GeV

Data Sample:• e/ + displaced track• ~ 180 pb-1

( Sept 2003)

Track Selection:• e/: pT > 4 GeV• other: pT > 0.4 GeV Total: ~ 28000 events


** SelectionBased on topology:

• impact parameter significances w.r.t. primary, B and D vertices

** 3D IP signif. wrt BV** 2D IP signif. wrt PV

•pT > 0.4 GeV

R < 1.0

•|d0PV/| > 3.0

•|d0BV/| < 2.5

|d0DV/| > 0.8

Lxy BD > 500m

Cuts are optimized using MC and background data: Additional cuts only for D+:


Raw m** DistributionMeasured in m**, shifted by M(D(*)+), side-band subtracted.

D1,D1*,D2

* D2*,D0

*Feed-down


Efficiency Corrections

1) Correct the raw mass for any dependence of reco on M(D**):

• Possible dependence on the D** species (spin).• Monte-Carlo for all D** (Goity-Roberts for non-resonant), cross-checked with pure phase space decays.

2) Cut on lepton energy in B rest frame:• Theoretical predictions need well-defined pl* cut.

• We can’t measure pl*, but we can correct our measurement to a given cut: pl* > 700 MeV/c.


Corrected Mass and D** Moments

Procedure:

• Unbinned procedure using weighted events.

• Assign negative weights to background samples.

• Propagate efficiency corrections to weights.

• Take care of the D+ / D*+ relative normalization.

• Compute mean and sigma of distribution.

42

12

**2

22**1

69.030.1

16.083.5

GeVmmm

GeVmm

statD

statD

Results:

No Fit !


Final Results

Pole mass scheme

1S mass scheme

0.61

0.69


Systematic Errorsm1

(GeV2)m2

(GeV4)

M1

(GeV2)

M2

(GeV4)

(GeV)

1

(GeV2)

Stat. 0.16 0.69 0.037 0.25 0.075 0.055

Syst. 0.08 0.20 0.065 0.12 0.090 0.082

Mass resolution 0.02 0.13 0.005 0.04 0.012 0.009

Eff. Corr. (data) 0.03 0.13 0.006 0.05 0.014 0.011

Eff. Corr. (MC) 0.06 0.05 0.016 0.03 0.017 0.006

Bkgd. (scale) 0.01 0.03 0.002 0.01 0.003 0.002

Physics bkgd. 0.01 0.02 0.002 0.01 0.004 0.002

D+ / D*+ BR 0.01 0.02 0.002 0.01 0.004 0.002

D+ / D*+ Eff. 0.02 0.03 0.004 0.01 0.005 0.002

Semileptonic BRs 0.062 0.10 0.064 0.022

1 0.041 0.069

Ti 0.032 0.031

s 0.018 0.007

mb, mc 0.001 0.008

Choice of pl* cut 0.019 0.009


Comparison with Previous Measurements

Pole mass scheme


Summary

• First measurement of hadronic moments in semileptonic B decays performed at a hadron collider.

• Good agreement with HQET and previous determinations.

• Competitive with other experiments. Little model dependency. No assumptions on shape or rate of D** components.

• Increased statistics and improved tracking will lead to substantially more precise results in the near future.

BACK-UP SLIDES


CKM and Vcb

| Vcb | = A2

(defines the scale of UT)


|Vcb| from inclusive B decays

• Experiment: large statistics on BR(BXc-) and B and small systematics

Vcb measurements

|Vcb| from exclusive B decays

• Large statistics on Bd0D(*)- available and new measurements are coming

• Present precision (5%) is systematics limited:

Experiments: D** states, D’s BR

Theory: form factor extrapolation, corrections to F(1)=1 can be reduced in the future

|Vcb|excl=(42.1 1.1exp 1.9theo) 10-3

(PDG 2002, Vcb review)

|Vcb|incl= (40.4 ± 0.5exp ± 0.5, ± 0.8theo) 10-3

(PDG 2002, Vcb review)


Lepton + D ReconstructionLepton + D(*)+:• D vertex:

• 3D• l+D(+*) vertex (“B”):

• 3D• Lxy(B) > 500 m• Lxy(D/B) > -200 m • m(B) < 5.3 GeV

Data Sample:• e/ + displaced track• ~ 180 pb-1

( Sept 2003)

Track Selection:• e/: pT > 4 GeV• other: pT > 0.4 GeV


D*+ Reconstruction and YieldsD*+ channels: m* M(D0*) – M(D0)

D(*)+ l(+cc)yields:

~ 28000 events


Monte-Carlo Validation (I)

K, e K, e K,

K0, e K, K, e

MC vs. semileptonic sample:

Matching 2 probability for those plots: 67% 74% 23%

43% 69% 87%


Monte-Carlo Validation (II)

Relative yield prediction K3/K: (cross-check)

Rdata = 0.77±0.02Rpred = 0.80±0.04Rpred/Rdata = 1.04±0.06 efficiency for adding tracks understood

Relative yield prediction K2/K: (needed for D+/D* normalization)

Two methods (a,b) to derive this BR

a) Based on inclusive bD(*)+l

b) Based on exclusive BD(*)+l, D**l

+ PDG BR + MC efficiency ratios

uncertainties in Br (incl.) and D** spectroscopy (excl.) compromise prediction 1. – 0.87 = 13% used as systematics

RdataRpred Rpred/Rdata

3.71±0.08 3.31±0.58 0.89±0.16

3.71±0.08 3.23±0.29 0.87±0.08


Impact Parameters in MC

Comparison data/MC for IP: (worst case)

K

** 2D IP signif. wrt PV

K

** 3D IP signif. wrt BV

Residual corrections:• derived from data:

• * • non-SVT D daughters (pT > 1.5 GeV)

• corrections from double ratios• in pT

• in m**


Background Subtraction

• Use mass side-bands to subtract combinatorial background.

• Use D*+[ D0+] to subtract feed-down from D*+[ D+0] to D+.

• Use wrong-sign **+ l combinations to subtract prompt background to **.– Possible charge asymmetry of prompt background studied with fully

reconstructed B’s: 4% contribution at most.

• Possible D’ D(*)contributions neglected:– No experimental evidence so far.

– DELPHI limit:

We assume no D’ contribution in our sample

CLDbBR

CLDbBR

%90@%17.0

%90@%18.0*


Combination with D0, D*0

Take M(D0), M(D*0), sl, 0, * from PDG 2003 :

− sl0, * are obtained combining BR’s for B, B0 and admixture, assuming the widths are identical (not the BR’s themselves), and using

f / f0 = 1.04 ± 0.08

(B) / (B0) = 1.085 ± 0.017

– Results:

BR(B+ X0c l+ l) = 0.1089 ± 0.0026

BR(B+ D0 l+ l) = 0.0223 ± 0.0015

BR(B+ D*0 l+ l) = 0.0600 ± 0.0024


Main Systematics

• Semileptonic branching ratios when combining D** with D and D*

• Efficiency corrections from data− Use data-corrected efficiency. vs. pure MC efficiency

• Efficiency corrections from D** Monte-Carlo− D** states + NR Goity-Roberts vs. pure phase-space

• Mass resolution:− Dominated by satellite: ± 60 MeV

• Prompt background scale − Charge correlations WS / RS: ± 4%

• Other: D+/D* normalization, physics, pl* cut, theory…

hadronic moments in semileptonic b decays ramon miquel lawrence berkeley national laboratory (for...

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