Hadronic Moments in Semileptonic B Decays Ramon Miquel

Hadronic Moments in Semileptonic B Decays Ramon Miquel Lawrence Berkeley National Laboratory (for the CDF II Collaboration) 7/2/04 Ramon Miquel BEACH 04

Motivation (I) Most precise determination of Vcb comes from Gsl (“inclusive” determination): U(4 S), LEP/SLD, CDF measurements. Experimental |Vcb|~1% Theory with pert. and non-pert. corrections. |Vcb|~2. 5% Ftheory evaluated using OPE in HQET: expansion in s and 1/m. B powers: O(1/m. B) 1 parameter: (Bauer et al. , PRD 67 (2003) 071301) O(1/m. B 2) 2 more parameters: 1, 2 O(1/m. B 3) 6 more parameters: 1, 2, T 1 -4 7/2/04 Ramon Miquel BEACH 04 2

Motivation (II) Many inclusive observables can be written using the same expansion (same non-perturbative parameters): the spectral moments: • Photonic moments: Photon energy in b s (CLEO) • Leptonic moments: B Xcl , lepton E in B rest frame • Hadronic moments: B Xcl , recoil mass M(Xc) (CLEO, DELPHI, BABAR, CDFII) Constrain the unknown non-pert. parameters and reduce |Vcb| uncertainty. With enough measurements: test of underlying assumptions (duality…). 7/2/04 Ramon Miquel BEACH 04 3

What is Xc? Semi-leptonic widths (PDG 03): Higher mass states: D** Br (%) B+ Xc l 10. 89 0. 26 B+ D* l 6. 00 0. 24 B+ D l 2. 23 0. 15 (b/B+/B 0 combination, b u subtracted) ~25% of semi-leptonic width is poorly known Possible D’ D(*) contributions neglected: • No experimental evidence so far • DELPHI limit: We assume no D’ contribution in our sample 7/2/04 Ramon Miquel BEACH 04 4

Analysis Strategy Typical mass spectrum M(X 0 c) (Monte Carlo): D 0 and D*0 well-known measure only f** only shape needed 1) Measure f**(s. H) 2) Correct for background, acceptances, bias moments of D** 3) Add D and D* M 1, M 2 4) Extract , 1 7/2/04 Ramon Miquel BEACH 04 5

Channels Must reconstruct all channels to get all the D** states. However CDF has limited capability for neutrals • B 0 D**- l+ always leads to neutral particles ignore it • B- D**0 l- better, use isospin for missing channels: − D**0 D+ - OK – D**0 D 0 0 Not reconstructed. Half the rate of D+ – D**0 D*+ • D*+ D 0 + OK • D*+ D+ 0 Not reconstructed. Feed-down to D+ – D**0 D*0 0 Not reconstructed. Half the rate of D*+ 7/2/04 Ramon Miquel BEACH 04 6

Event Topology Exclusive reconstruction of D**: D**0 D+ **K- + + (Br=9. 1%) “D+” 7/2/04 D**0 “D*+” Ramon Miquel BEACH 04 D*+ **D 0 *+ (Br=67. 7%) K- + (Br=3. 8%) K- + (Br=7. 5%) K- + 0 (Br=13. 1%) 7

Backgrounds Physics background: B D(*)+Ds-, D(s) Xl MC, subtracted Combinatorial background under the D(*) peaks: sideband subtraction Prompt pions faking **: • fragmentation • underlying event separate B and primary vertices (kills also prompt charm) use impact parameters to discriminate model: wrong-sign **+ - combinations 7/2/04 Ramon Miquel BEACH 04 Feed-down in signal: D**0 D*+( D+ 0) irreducible background to D**0 D+ -. subtracted using data: shape from D 0 - in D**0 D*+( D 0 +) rate: ½ (isospin) x eff. x BR 8

Lepton + D(*)+ Reconstruction Data Sample: • e/ + displaced track • ~ 180 pb-1 ( Sept 2003) Track Selection: • e/ : p. T > 4 Ge. V • other: p. T > 0. 4 Ge. V 7/2/04 Lepton + D(*)+: • D vertex: • 3 D • l+D(+ *) vertex (“B”): • 3 D • Lxy(B) > 500 m • M(B) < 5. 3 Ge. V Total: ~ 28000 events Ramon Miquel BEACH 04 9

** Selection Based on topology: • impact parameter significances w. r. t. primary, B and D vertices ** 3 D IP signif. wrt BV ** 2 D IP signif. wrt PV Cuts are optimized using MC and background data: • p. T > 0. 4 Ge. V • R < 1. 0 7/2/04 • |d 0 PV/ | > 3. 0 • |d 0 BV/ | < 2. 5 Ramon Miquel BEACH 04 Additional cuts only for D+: |d 0 DV/ | > 0. 8 Lxy B D > 500 m 10

Raw m** Distribution Measured in m**, shifted by M(D(*)+), side-band subtracted. D 1, D 1*, D 2* 7/2/04 Feed-down Ramon Miquel BEACH 04 D 2*, D 0* 11

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 Me. V/c. 7/2/04 Ramon Miquel BEACH 04 12

Corrected Mass and D** Moments Procedure: Results: • 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. No Fit ! 7/2/04 Ramon Miquel BEACH 04 13

Final Results 0. 61 0. 69 Pole mass scheme 1 S mass scheme 7/2/04 Ramon Miquel BEACH 04 14

Systematic Errors m 1 (Ge. V 2) m 2 (Ge. V 4) M 1 (Ge. V 2) M 2 (Ge. V 4) (Ge. V) 1 (Ge. V 2) 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. 01 0. 004 0. 002 D+ / D*+ BR 0. 01 0. 02 0. 01 0. 004 0. 002 D+ / D*+ Eff. 0. 02 0. 03 0. 004 0. 01 0. 005 0. 002 0. 062 0. 10 0. 064 0. 022 1 0. 041 0. 069 Ti 0. 032 0. 031 s 0. 018 0. 007 mb , m c 0. 001 0. 008 Choice of pl* cut 0. 019 0. 009 Semileptonic BRs 7/2/04 Ramon Miquel BEACH 04 15

Comparison with Previous Measurements Pole mass scheme 7/2/04 Ramon Miquel BEACH 04 16

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. 7/2/04 Ramon Miquel BEACH 04 17

BACK-UP SLIDES 7/2/04 Ramon Miquel BEACH 04

CKM and Vcb | = A 2 (defines the scale of UT) 7/2/04 Ramon Miquel BEACH 04 19

Vcb measurements |Vcb| from exclusive B decays • Large statistics on Bd 0 D(*) - 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. 1 exp 1. 9 theo) 10 -3 (PDG 2002, Vcb review) |Vcb| from inclusive B decays • Experiment: large statistics on BR(B Xc - ) and t. B and small systematics |Vcb|incl= (40. 4 ± 0. 5 exp ± 0. 5 , ± 0. 8 theo) 10 -3 (PDG 2002, Vcb review) 7/2/04 Ramon Miquel BEACH 04 20

Lepton + D Reconstruction Data Sample: • e/ + displaced track • ~ 180 pb-1 ( Sept 2003) Track Selection: • e/ : p. T > 4 Ge. V • other: p. T > 0. 4 Ge. V 7/2/04 Lepton + D(*)+: • D vertex: • 3 D • l+D(+ *) vertex (“B”): • 3 D • Lxy(B) > 500 m • Lxy(D/B) > -200 m • m(B) < 5. 3 Ge. V Ramon Miquel BEACH 04 21

D*+ Reconstruction and Yields D*+ channels: m* M(D 0 *) – M(D 0) D(*)+ l- (+cc) yields: ~ 28000 events 7/2/04 Ramon Miquel BEACH 04 22

Monte-Carlo Validation (I) MC vs. semileptonic sample: K , e K 0, e K , Matching 2 probability for those plots: 7/2/04 K , K , e Ramon Miquel K , e 67% 74% 23% 43% 69% 87% BEACH 04 23

Monte-Carlo Validation (II) Relative yield prediction K 3 /K : (cross-check) efficiency for adding tracks understood Relative yield prediction K 2 /K : Rdata = 0. 77± 0. 02 Rpred = 0. 80± 0. 04 Rpred/Rdata = 1. 04± 0. 06 (needed for D+/D* normalization) Two methods (a, b) to derive this BR + PDG BR + MC efficiency ratios Rdata Rpred/Rdata a) Based on inclusive b D(*)+l 3. 71± 0. 08 3. 31± 0. 58 0. 89± 0. 16 b) Based on exclusive B D(*)+l , D**l 3. 71± 0. 08 3. 23± 0. 29 0. 87± 0. 08 uncertainties in Br (incl. ) and D** spectroscopy (excl. ) compromise prediction 1. – 0. 87 = 13% used as systematics 7/2/04 Ramon Miquel BEACH 04 24

Impact Parameters in MC Comparison data/MC for IP: (worst case) K K ** 2 D IP signif. wrt PV ** 3 D IP signif. wrt BV Residual corrections: • derived from data: • * • non-SVT D daughters (p. T > 1. 5 Ge. V) • corrections from double ratios • in p. T • in m** 7/2/04 Ramon Miquel BEACH 04 25

Background Subtraction • Use mass side-bands to subtract combinatorial background. • Use D*+[® D 0 +] - 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 7/2/04 Ramon Miquel BEACH 04 26

Combination with D 0, D*0 Take M(D 0), M(D*0), Gsl, G 0, G* from PDG 2003 : − Gsl, G 0, G* are obtained combining BR’s for B-, B 0 and admixture, assuming the widths are identical (not the BR’s themselves), and using f- / f 0 = 1. 04 ± 0. 08 t(B-) / t(B 0) = 1. 085 ± 0. 017 – Results: BR(B+ ® X 0 c l+ l) = 0. 1089 ± 0. 0026 BR(B+ ® D 0 l+ l) = 0. 0223 ± 0. 0015 BR(B+ ® D*0 l+ l) = 0. 0600 ± 0. 0024 7/2/04 Ramon Miquel BEACH 04 27

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 Me. V • Prompt background scale − Charge correlations WS / RS: ± 4% • Other: D+/D* normalization, physics, pl* cut, theory… 7/2/04 Ramon Miquel BEACH 04 28