Leptonic and Semileptonic Charm Decays

Transcription

1 Leptonic and Semileptonic Charm Decays Hanna Mahlke Cornell University Heavy Quarks and Leptons Munich, Germany October 006

2 The Big Picture Theory s difficulties in calculating strong phenomena seriously hamper some measurements in the B sector that need such input, eg. V ub from semileptonic or leptonic B decays, extraction of V td from B 0 -B 0bar mixing measurement. In addition to being of interest in and of itself, experimental charm results thus have an impact on bottom results. B experiment D experiment B theory D theory Both b and c are heavy quarks, similar methods apply, b c transfer is easy. The charm system provides stringent experimental tests of theoretical heavy quark tools at the percent level. This talk: semileptonic and leptonic D decays Charm (semi-)leptonic decays

3 Overview: (Semi-)Leptonic Decays Leptonic: Examples: Similar for D s, B, B s, Semileptonic: V cd c μ W + W + e + D + c d V ν D + cd π Decay Challenge: d understand QCD constant Form factor f + (q ) portion in a simple f D weak process ν q : momentum transfer or m(w * ) D + μν D + τν D s+ μν D s+ τν FCNC, LFV D + K/π/ρ/η/η /ω/kππ + lν D s+ φ + eν * BR measurements and/or * Form factors (K/π/ρ/φ) Charm (semi-)leptonic decays 3

4 Experimental Issues for precision studies of D[ s ] lν, hlν decays B Factories: Use charm from e + e - cc bar (separate from bb bar through topological requirements) D from D *+ π S D 0, D s+ from D s *+ γd s+, check D (s)* -D (s) mass difference Can tag, or not tag, the other D Normalization: mostly reference mode Belle D s μν using tagged D s events hep-ex/ MeV ΔM=M(D s* )-M(D s ) Tag signal Tag sideband Running at charm threshold (CLEO-c, BES): Very clean event environment, well-defined kinematics D from ψ(3770) D + D -, D 0 D 0bar ; D s from e + e - D s* D s γd s D s DD bar analyses mostly identify one D through a well-known decay mode ( tagged ), but untagged turned out to work very well, too Normalization: number of decays Cross-section in e + e - collisions CLEO Charm (semi-)leptonic decays 4

5 Reconstruction of (semi)leptonic decays at ψ(3770) 81pb -1 : ~310k D +, ~160k D 0 tags D 0 K + e ν CLEO D 0 π e + ν K - ν ~7000 events + π e ν 117 events K - e + ν π - e + K + Signal events: U = E miss P miss = 0 D 0 Compare cleanliness at ϒ(4S): K + e ν D 0 π + e ν CLEO PRL94, (005) ψ (3770) D 0 K π D Tagging creates a single D beam of known 4-momentum. 0, D D K e ν Signal Peaking background Other background Charm (semi-)leptonic decays 5 ΔM=M(D *+/- )-M(D 0 ) (GeV)

6 Leptonic Decays D μν D τν D s τν D s μν

7 Leptonic Decays: D (s)+ l + ν _ c and q can annihilate, probability is to wave function overlap Hadronic interaction described by decay constant f D challenge for theory Goals: 1) put calculations to the test, ) check lepton universality (s) (s) V cd or or csv cs General case for pseudoscalars: Γ ( P + l ν) 1 m + = GF fp m MP 1 8 l l π MP V Qq Other mesons: f π =131.73±0.15MeV (0.1%), f K =160.6±1.3MeV (0.8%) Calculate, or measure if V Qq is known τ: μ : e is 9.7:1: for P=D + s V cq is O(1) P=D s.65:1: for P= D + O(0.1) for P= D + τ most copiously produced, but is not stable D s+ leptonic BR s larger than D + μpreferable experimentally, esp. for D + (lifetimes only a factor of two apart) Charm (semi-)leptonic decays 7 +

8 Number of Events/0.01 GeV D + l + ν from experiment signal candidates,.8 bgd MM (GeV ) ( BR f D ) D + μ + ν 81pb -1, tagged D K π Missing mass = (E beam -E mu ) -(p D -p m ) (GeV) Tag D μ + ν Signal D Variations: * Similar technique applied to measure D τν with τ πν; 0 candidates on 11 background * Require e instead of μ no candidates, upper limit set BR(D μν)=(4.4±0.7±0.1) 10-4 BR(D eν) < BR(D τν) < Times SM ratio: Background: BES, 33pb -1, tagged (3 signal, 0.3 bgd): D + π + π 0, τ + ( π ν)ν, K BR(D μν)=( π +, -5 ±1) 10-4 estimated from data or MC With D + lifetime of ps, V cd = f D =.6 ± MeV (11%) Charm (semi-)leptonic decays CLEO: PRL96, (005) 8 BES: PLB610, 183 (005)

9 D S+ μ + ν and τ + ν(1) ~00pb -1 at 4170MeV, D s tags, CLEO preliminary e + e - D s *D s γd s D s, find D s tag, γ, D s μνor τ( πν)ν or eν; distinguish by energy deposition in calorimeter 64ev 4ev <0.3GeV in CC Track is μ or π Sum of case (i) & case (ii) μν +τν signal line shape 100 events K 0 π + CLEO preliminary results using SM μν/τν ratio of 1:9.7: MM * Data ~1k tags = M(D s ) ( E E E ) ( p p ) CM Ds γ Ds γ >0.3GeV in CC π 1ev B(D S+ e + ν) < e Combined fit for μ+τ B(D S+ μ + ν) = (0.657±0.090±0.08)% B(D S+ τ + ν) = (7.1±1.4±0.3)% Combining μ and τ: B eff (D S+ μ + ν) = (0.664±0.076±0.08)% f Ds =8 ± 16 ± 7 MeV (6%) hep-ex/ (ICHEP paper) Charm (semi-)leptonic decays 9

10 B(D S+ τ + ν) B(τ + e + νν) ~1.3%; large compared with expected B(D S+ Xe + ν) 8% Signal candidates: (1) e + opposite D S- tag, () no other tracks, (3) Σ calorimeter energy < 400 MeV (don t care about the 140MeV photon) 00pb -1, DTagged at 4170MeV, e + e - D s *D s γd s D s Xe + ν D S+ τ + ν() using D S+ τ + ν, τ + e + νν This analysis: B(D S+ τ + ν) = (6.3±0.8±0.5)% f Ds = (78±17±1) MeV (7%) Recall from previous slide: B(D S+ τ + ν) = (7.1±1.4±0.3)% f Ds =(8 ± 16 ± 7) MeV (6%) Combined: f Ds = (80±1±6) MeV (5%) CLEO preliminary f D =.6 ± MeV (11%): f Ds /f D = 1.6 ± 0.11 ± 0.03 CLEO (9%) f Ds /f D = 1.4 ± 0.07 FNAL/MILC/HPQCD (6%) Charm (semi-)leptonic decays 10

11 hep-ex/ , subm to PRL BaBar D s μν 30fb -1 of data in the ϒ(4S) region from e + e - cc bar Use kinematic constraints: invariant masses, angle(muon,d s ) Peak in m(d S* )-m(d S ) ~ 143 MeV signifies decay chain ~50k charm tags, ~500 signal events Normalization: D s* production rate in cc bar fragmentation unknown; measure partial width ratio to φπ Γ(D s+ μ + ν) Γ(D s+ φπ + ) Tag: D,D s,d * (13 modes) D * S ( ) + γd γ μν at ϒ(4S) s D s μ ± 55 signal ( γμν ) ( μν ) Δ m = m m BR(D 13% s+ φπ + )=(4.71±0.46)% ( BaBar ave ): 4% =0.143±0.018±0.006 BR(D s+ μ + ν)=(6.74±0.83±0.6±0.66) 10-3 Largest sys: bgd shape parametrization Charm (semi-)leptonic decays 11 * γ D s f Ds =(83±17±7±14)MeV (8%) BR(D s + φπ + )=(3.6±0.9)% (PDG04): BR(D s + μ + ν)=(5.15±0.63±0.0±1.9) 10-3 f Ds =(48±15±6±31)MeV (14%) ν

12 Decay Constants, Summary choices of D s φπ Leptonic charm decays: D μν: fairly precise measurement of f D (8%) D e,τν: upper limits on BF D s μν,τν: two nice new measurements of f Ds (5% CLEO, 8% BaBar) Dominant errors are statistical (BaBar also normalization) error reduction easy Most precise calculations are matching the experimental precision, but systematics limited Charm (semi-)leptonic decays 1

13 D φlν Semileptonic Decays D η( )lν D ρlν D πlν Topics: rare decays precision BR form factors incl vs excl D ωlν D K * lν D Klν D Xlν D Kππlν D s φlν

14 D π/keν Branching Fractions & Form Factors e - Dtagged e + hlν Specific D decay modes, "D tags Unspecified other-side D decay, collect all other showers and tracks e - Neutrino reconstruction like B π/ρlν in Y(4S) data e + hlν 699±8 6796±84 81pb -1, plots, caution: samples overlap! 1347± ±13 95±0 910±55 450±9 5846±88 U = E miss P miss (GeV) Reconstructed D candidate mass (substituting E beam for E D ) Charm (semi-)leptonic decays 14

15 D π,keν Branching Fractions Comparison D K e + ν D π e + ν preliminary preliminary preliminary preliminary Good consistency between measurements. LQCD precision lags experiment. Charm (semi-)leptonic decays 15

16 Rare semileptonic CLEO preliminary 3.7 ± 6.7 D decays Dtagged, 81pb -1 D 0 K - π + π e + ν ε Mode BR (10-4 ) ηe + ν 1.9±1.9±0.7 η e + ν φe + ν <3 (90%CL) < (90%CL) 13.3 ± 4.0 K - π + π e + ν K 1 (170)e + ν ± ±0. ωe + ν 14.9±.7±0.5 D + ωe + ν 37.3 ± 6.7 * First observation ** Improved UL (factor 100) *** Error improved by factor of two E miss -P miss (GeV ) Two predictions: B(D + η [η ] e + ν)= 10 [1.6] 10-4 Fajfer & Kamenik, PRD71, [5] 10-4 Charm (semi-)leptonic decays 16 Scora & Isgur, RD5, 783

17 D + Example: c d V cs ν e + W + s d K- f + (q ) dγ dq ( D πlν ) 3 ( q ) p π V cd Cannot calculate from first principles Many different parametrizations on the market Quantities of interest: shape and normalization Experiment can only determine V cq f(0) Unitarity constrains V cq, hence stringent tests possible HQET links D and B decay q resolutions down to O(0.01GeV ) have been achieved f π + q = m W* : momentum transfer to the W* f + (q ): form factor function Form factors Events Rate p P 3 f + W c d ( q ) s Form factor ~1/(1-q / M pole ) M pole = GeV special cases: W D 0 Kμν, E687 (1995) s d q E687, PLB 364, 17 (1995) Charm (semi-)leptonic decays 17

18 Form factor fit plots D 0 D 0 K CLEO preliminary + e ν π e + ν + 0 D K e + ν D + 0 π e + ν 3 FF parameterizations: Simple Pole Model f + (q ) = f + (0) 1 q ( m pole ) + Hill series expansion (Phys. Lett. B 633, 61 (006))) Modified Pole Model f + (q ) = f + (0) ( 1 q m pole )1 α q m pole ( ) Tagged Modified Pole (BK) Model shown: Charm (semi-)leptonic decays 18

19 D π/keν: Which Form Factor Parameterization? CLEO preliminary All these models describe the data pretty well (except when forcing pole mass to nominal value in pole model). Charm (semi-)leptonic decays 19

20 Belle,BaBar,FOCUS D K,πlν form factors + FOCUS published BELLE: PRL 97, (006) [hep-ex/ ] BaBar: hep-ex/ FOCUS: PLB607, 33 (005) [hep-ex/ ] Belle, 8fb -1, fully reconstructed events, excellent q resolution Unquenched LQCD Quenched LQCD Simple pole model Belle Aubin et al., PRL94, (005) Abada et al., NuclPhys B619, 565 (001) Klν ~.5k signal events Klν Belle LQCD: Aubin et al., PRL94, (005) FOCUS: ~13k events 75fb -1 3 signal events πlν q (GeV ) Charm (semi-)leptonic decays 0

21 Form Factors as a Stringent Test of LQCD Normalization f + (0) D 0 Shape; α + π e ν LQCD: PRL94,011601(005) Belle: PRL 97, (006) CLEO: preliminary LQCD Belle DATA FIT D 0 K e + ν LQCD Belle DATA FIT Charm (semi-)leptonic decays 1

22 CLEO preliminary V cs and V cd Precision Experimental V cx f + (0) from fits f + (0) from unquenched LQCD V cs and V cd : PRL 94, (005) Decay Mode V cx ±(stat) ± (syst) ± (theory) PDG/HF Value D πeν (tagged) 0.34 ± ± ± 0.04 D πeν (untagged) 0.9 ± ± ± ± 0.01 D Keν (tagged) ± ± ± D Keν (untagged) ± ± ± ± Tagged and untagged consistent. 40% of events are common to both analyses: DO NOT AVERAGE! Uncertainties: experiment: V cs <%, V cd ~4% / LQCD f + (0) prediction: 10% V cs (W cs LEP) and V cd (vn) well measured good agreement between PDG(HF) and CLEO-c results primarily a check of the LQCD value for f + (0). Nevertheless, the most precise & robust V cs & V cd determinations using semileptonic decays to date. Charm (semi-)leptonic decays

23 D Vector l ν Decay A i Traditional Method : Rewrite H ± (q ), H 0 (q ) as functions of A 1 (q ), A (q ), V(q ), spectroscopic pole dominance: Ai ( ) ( 0) V ( ) ( 0) q = V q = 1 q /M Ai 1 q /M V ((1+ cos θl)sin θv ) H+ ( q ) BW + ((1 cos θl)sin θv ) H ( q ) BW 1 A dχ = q + ( sinθl cos θv ) H0( q ) BW 8 + 8sin cos ( ) ( ) e + O( A ) iδ ( θl θv ) H0 q ho q R { Ae BW} Present in K*lν; what about ρlν? φlν? M v =.1GeV M A1 =M A =.5GeV R V =V(0)/A 1 (0) R =A (0)/A 1 (0) Assume shape, end up with only two shape parameters. H 0 (q ), H + (q ), H - (q ) are helicity-basis form factors computable by LQCD A new factor h 0 (q ) is needed to describe s-wave interference piece. Charm (semi-)leptonic decays 3

24 An earlier controversy Expect form factor similarity: D + D s + c d c s V cs V cs ν W + e + K * W + ν e + φ D s φlν world ave D K * lν world ave Discrepancy for R : FOCUS φlν agrees with K * lν world ave Resolved? Confirm? PLB586, 183 (004) hep-ex/ Charm (semi-)leptonic decays 4

25 D + K π + e + ν Form Factors H 0 (q ), H + (q ), H - (q ) are helicity-basis form factors computable by LQCD A new factor h 0 (q ) is needed to describe s-wave interference piece. data (81 pb -1 ) overlay (not fit) M V =.1 M A =.5 qh + ( q) qh ( q) qh ( q ) 0 CLEO PRD 74, (006) Data fits spectroscopic poles and constant form factors equally well. No evidence for d- or f-wave contributions. Charm (semi-)leptonic decays 5

26 hep-ex/ , ICHEP prelim BaBar D s φeν form factors e + e - cc bar from 78.5fb -1, about 13k signal events D s φ e ν cos θ e Data signal BB cc peaking cc non-peaking uds q cos θ v χ Fit in the simple pole model, using m V =.1GeV Charm (semi-)leptonic decays 6

27 D ρeν (BR+FF) Interest: 1 st measurement of FF in Cabibbo-suppressed charm PS V decay ( ρe ν) /dq Vub * ( K ll) /dq dγ B + Need D K * eν dγ B and D ρeν FF V ts Grinstein & Pirjol [hep-ph/040450] q Dtagged, 81/pb cos θ π No-interference MC describes data D + D 0 56pb -1 56pb -1 81pb -1 81pb -1 Fixed background shape and signal tails from MC cos θ e Line is projection for fitted R V, R B(D 0 ρ - e + ν)= (1.56±0.16±0.09) 10-3 B(D + ρ 0 e + ν)= (.3±0.0±0.1) 10-3 Isospin average: Γ(D 0 ρ - e + ν) = (0.41±0.03±0.0) 10 - ps -1 this analysis Γ(D 0 ρ - e + ν) = (0.44±0.06±0.0) 10 - ps -1 χ FOCUS PLB 637,3 (006) CLEO preliminary Charm (semi-)leptonic Simultaneous decays fit to D + ρ 0 eν, D 0 ρ7 - eν R v = 1.40 ± 0.5 ± 0.03, R = 0.57 ± 0.18 ± 0.06

28 Inclusive Semileptonic Results mode Branching Fraction D 0 Xe + ν (6.46 ± 0.17 ± 0.13)% Σ i Β i (D 0 Xe + ν) (6.1 ± 0. ± 0.)% D + Xe + ν (16.13 ± 0.0 ± 0.33)% Σ i Β i (D + Xe + ν) (15.1 ± 0.5 ± 0.5)% Consistent with the known exclusive modes saturating the inclusive branching fractions. Extrapolated below 0. Γ Γ B SL SL D D D SL SL 0 B 0 τ D D D = = ± ± Consistent with isospin symmetry τ CLEO-c 81pb -1, DTagged hep-ex/ , subm to PRL Charm (semi-)leptonic decays 8

29 Summary Leptonic and semileptonic charm decays are a very active area of research: Insight into QCD phenomena that occur in charm as well as in bottom Experimental accuracy provides stringent tests for theoretical tools, to be applied in bottom physics A variety of experimental techniques explored, with great success Conclusions: 1) The race between theory and experiment is still on. ) It s all connected! Leptonic decays: theory and experiment are at the same level of precision for f D and f Ds ; most significant improvements: experiment statistics, theory systematics Semileptonic decays: Critical measurements of branching fractions and form factors for pseudoscalar and vector final state hadrons Consistency checks Much improved precision in normalization and shape Charm (semi-)leptonic decays 9