Measurements of f D + and f Ds

Transcription

1 Measurements of f D + and f Ds Jim Libby (University of Oxford) With thanks to S. Stone, L. Zhang and D. Asner 1

2 Outline Introduction and motivation f D + determination at CLEO-c f Ds determinations at: CLEO-c with D s µν and D s τ(πν)ν CLEO-c with D s τ(eνν)ν Belle with D s µν BABAR with D s µν Conclusions and outlook

3 Leptonic Decays: D l + ν _ c and q can annihilate, probability is proportional to wave function overlap Standard Model decay diagram: gluons V cd or cs In general for all pseudoscalars: + 1 m ν GF fpm M + l l l P V Qq 8π MP Γ(P ) = 1 Calculate, or measure f D if V Qq is known, here take V cd =V us = 0.56, V cs =V ud = (s) (s) 3

4 Relationship to CKM Only a few measurements are independent of strong interaction calculations CP violation where we interfere one decay diagram with a mixing diagram (B o J/ψ K o ) Many important quantities measured in CKM are combinations of strong and weak parameters Interpreting B and B S mixing in terms of CKM parameters requires knowledge of f B /f s B Extracting V ub requires knowledge of absolute value of form-factors for B π(ρ)lν at least at one value of q 4

5 New Unquenched Lattice Calc Follana et al HPQCD & UKQCD collaborations (PRL 100, 0600 (008)) New predictions of f D += 07±4 MeV f Ds = 41±3 MeV Older unquenched from FNAL+MILC +HPQCD are: f D += 01±3±17 MeV f Ds = 49±3±16 MeV (Aubin et al., PRL 95, 100 (005)) 5

6 Beyond the SM sensitivity Besides the obvious interest in comparing with lattice & other calculations of f D there are NP possibilities CLEO s previous measurement of f Ds + Belle s (see Rosner & Stone arxiv: ) give f Ds =74±10 MeV as compared with 41±3 MeV +1 unquenched lattice QCD calculation of Follana et.al (PRL 100, 0600 (008)) Dobrescu & Kronfeld (arxiv: ) argue that this can well be the effect of NP, either charged Higgs (their own model) or leptoquarks CLEOs previous measurement of f D + was too inaccurate to challenge Follana et al., theory 07±4 versus 3±17 MeV (CLEO) 6

7 Situation Prior To FPCP 008 Experiment f Ds : CLEO measures both µ + ν & τ + ν, & Belle measures µ + ν. Average is 3.3 σ away, could be a fluctuation D + too inaccurate to say anything Updates to both CLEO measurements 7

8 > Favoured methods at CLEO-c Two-body production e + e DD Double tags at 3770 MeV: fully reconstruct one D 0 or D +, then one can either fully reconstruct the other D for absolute branching ratios and quantum correlations or look for events with one missing particle in leptonic decays, semileptonic decays or hadronic K L decays Similarly, double tags at 4170 MeV: here look for a D S or a D S * Some measurements also done using single tags e K > > > > + - D > D > π e 8

9 Basic Technique for D + µ + ν 1. Fully reconstruct a D ±, and count total # of tags. Seek events with only one additional oppositely charged track within cosθ <0.9 & no additional photons > 50 MeV (to veto D + π + π o ) 3. Charged track must deposit only minimum energy (from ionization) in calorimeter, E < 300 MeV True for 98.8% of muons Rejects 45% of π s 4. Compute missing-mass squared (MM ). If close to zero then almost certainly we have a µ + ν decay. MM = ( E E ) ( p p ) D We know that E D + =E beam and p D + = p D - l D l 9

10 Tags mbc = Ebeam p i i Particle ID from RICH & de/dx Total of 460,000 tags Background 89,400 10

11 The MM Distribution K o π + peak µ + ν peak τ + ν, τ + π + ν region 11

12 MM Signal Shapes MM = ( E E ) ( p p ) Beam + + l D l Events/0.01 GeV Check with shape of K o π + peak, fit with double- Gaussian MM (GeV ) Monte Carlo Signal µν Monte Carlo Signal τν, τ πν 1

13 Model of K o π + Tail Use double tag D 0 D 0 events, where both D 0 K π ± K π ± K π ± π o Make loose cuts on nd D 0 so as not to bias distribution: require only 4 charged tracks in the event Compute MM ignoring K ± Expectation from residual π + π (1.1 events) Gives an excellent description of shape of low mass tail Extra 1.3 event background in signal region 13

14 Additional floating backgrounds Background cocktail composed of three-body modes τ + decays: ρ + ν and µ + νν Semileptonic decays: π 0 µ + ν (check with e + ) Hadronic decays: ρ + π 0 We only use the shape in MM, not the absolute number 14

15 Fit MM to sum of signal & bkgrd Case(i) E< 300 MeV where τ + ν/µ + ν is fixed to SM ratio 149.7±1.0 µν 8.5 τν Case(i) E< 300 MeV where τ + ν/µ + ν is allowed to float 153.9±13.5 µν 13.5±15.3 τν π + π ο µν Background cocktail K o π τν, τ πν 15

16 Residual Backgrounds for µυ Monte Carlo of continuum, D o, radiative return and other D + modes, in µν signal region This we subtract off the fitted yields 16

17 Background Check Use case (ii) E>300 MeV Fix τν & µν from case (i) µν. Consider signal region MM <0.05 GeV. Expect 1.7 µν π + π ο τν = 11.1 Find 11 events Additional background 0.1±3.3 events π + π ο Background cocktail K o π τν, τ πν µν 17

18 Systematic Errors Source of Error % Finding the µ + track 0.7 Minimum ionization of µ + in EM cal 1.0 Particle identification of µ MM width 0. Extra showers in event > 50 MeV 0.4 Background 0.7 Number of single tag D Total. 18

19 Branching Fractions & f D + Fix τν/µν at SM ratio of.65 PRD 78, (008) BF(D + µ + ν)= (3.8±0.3±0.09)x10-4 f D +=(05.8±8.5±.5) MeV This is best number in context of SM Float τν/µυ BF(D + µ + ν)= (3.93±0.35±0.10)x10-4 f D +=(07.6±9.3±.5) MeV This is best number for use with BSM models These numbers have been radiatively corrected by 1% in the branching ratio for D + γd* + γµ + ν Also, limits on BF(D + e + ν), BF(D + τ + ν) and A CP (D + µ + ν) All agree with SM expectation 19

20 CLEO-c s improved measurement of f Ds CLEO has two methods of measuring f Ds Measure µ + ν & τ + ν, τ + π + ν using similar MM technique used for D +. Update result using new analysis & 30% more data (~400 pb 1 ) Updated 008 Measure τ + e + νν by using missing energy. This result has not been updated (~300 pb 1 ) PRL 100, (008) 0

21 Use e + e - D S D S * at 4170 MeV Presence of D S * causes analysis changes: Reconstruct D S Find the γ from the D S * & compute MM* from D S & γ MM * = ( E E E ) ( p p ) CM - - D γ D γ Select combinations consistent with a missing D S + & count the number Find MM from candidate muon for (i) E< 300 MeV in Ecal, (ii) E>300 MeV or (iii) e - cand. MM = ( E E E E ) ( p p p ) CM - - D γ µ D γ µ 1

22 D S - Tags: Invariant Mass K + K - π K S K ηπ Events / ( 0.00 GeV ) η'π η' π π + η K + K - π π ο 4000 π π π K* o K* η ρ η'π η' ργ LHCb Presentation July, M(D s) (GeV)

23 ) ) ) ) ) ) ) ) ) MM* Distributions From D S + γ Events / ( 0.01 GeV Events / ( 0.01 GeV K + K - π 500 K 300 S K - ηπ MM* (GeV ) η'π η' π π + η Multi γ bkgrnd Sideband bkgrnd MM* (GeV ) Events / ( 0.01 GeV Events / ( 0.01 GeV MM* (GeV ) MM* (GeV ) Events / ( 0.01 GeV Events / ( 0.01 GeV K + K - π π ο π π π MM* (GeV ) MM* (GeV ) Events / ( 0.01 GeV K* o K* - η ρ Events / ( 0.01 GeV Events / ( 0.01 GeV η'π η' ργ MM* (GeV ) MM* (GeV ) MM* (GeV ) 3

24 MM data for D S Total of 30848±695 tags 98.% of µ + ν in E < 300 MeV 55%/45% split of τ + ν, τ + π + ν in two cases Events/ 0.01 GeV case (i) case (ii) E < 300 MeV E > 300 MeV K o π, ηπ region Track consistent with electron Small e - background MM (GeV ) 4

25 Fit to signal & background 60 Case (i) + Case(ii) Events / ( 0.0 GeV ) µ + ν τ + ν MM (GeV ) Background D S sidebands Extra background from real D S+, mainly 3-body LHCb Presentation July, 008 5

26 Systematic Errors Source of Error % Finding the µ + track 0.7 Particle identification of µ MM width 0. Extra showers in event > 300 MeV 0.4 Background 0.5 Number of single tag D - S 3.0 Total 3.3 6

27 Branching Ratio & f Ds (preliminary) Mode BF (%) f D (MeV) (1) µν+τν (fix SM ratio) BF eff (D s µν) = (0.613±0.044±0.00) () µν only BF(D s µν) = (0.600±0.054±0.00) (3) τν, τ πν BF(D s τν) = (6.1±0.9±0.) s 68.±9.6± ±11.9±4.4 71±0±4 7

28 CLEO: D S+ τ + ν, τ + e + νν BF(D S+ τ + ν) BF(τ + e + νν) 1.3% is significant compared with expected BF(D S+ Xe + ν) 8% Search for events opposite a tag with one electron and very little additional energy Opt to use only a subset of the cleanest tags 8

29 Measuring D S+ τ + ν, τ + e + νν Technique is to find events with an e + opposite D S- tags & no other tracks, with Σ calorimeter energy < 400 MeV No need to find γ from D S * BF(D S+ τ + ν) =(6.17±0.71±0.36)% f Ds =73±16±8 MeV 400 MeV PRL 100, (008) 9

30 Branching Ratio & f Ds (preliminary) Mode BF (%) f D (MeV) (1) µν+τν (fix SM ratio) BF eff (D s µν) = (0.613±0.044±0.00) () µν only BF(D s µν) = (0.600±0.054±0.00) (3) τν, τ πν BF(D s τν) = (6.1±0.9±0.) (4) τν, τ eνν BF(D s τν) = (6.17±0.71±0.36) CLEO Average of (1) & (4) Rad. corr. s 68.±9.6± ±11.9±4.4 71±0±4 73±16±8 69.4±8.± ±8.±3.9 30

31 Belle: D S+ µ + ν Look for e + e - DKXγ(D S ), where X=nπ & the D S is not observed but inferred from calculating the MM Then add a candidate µ + and compute MM BF(D S+ µ + ν) = (0.644±0.076±0.057)% f Ds =75±16±1 MeV Results stable as a function of final state multiplicity 548 fb 1 PRL 100, (008) 31

32 BABAR: D S+ µ + ν PRL 98, (007) Look for events with a tag D 0, D ±, D * or D s with both a µ and aγ consitant to be from D s * decay in the rest of the event Approximate neutrino 4-mom to (E miss, p miss ) Compute M = M ( µνγ ) M ( µν ) Subtract background using sidebands and electron sample Remaining background from mis- IDed muons in ccbar and misreconstructed signal Fit M distribution to extract signal f Ds =(83±17(stat)±7(syst)±14(D s φπ)) MeV 30 fb 1 3

33 f D & f / f + s Ds D Weighted Average of absolute measurements from CLEO + Belle: f Ds =70.4±7.3±3.7 MeV, the systematic uncertainty is uncorrelated between the measurements Using f D + = (05.8±8.5±.5) MeV f Ds /f D + = 1.31±0.06±0.0 larger than LQCD predictions Γ(D S+ τ + ν)/γ (D S+ µ + ν)=10.3±1.1 SM=9.7 Consistent with lepton universality 33

34 Conclusions More data required to see if experiment and theory are significantly inconsistent 06(9) 68(9) 34

35 Future datasets CLEO will further update f Ds using at total of ~600 pb -1 50% increase in data for µν 100% increase in data for τν, τ eνν Improved D s tag systematic to 3% % f D + will not see any major improvements until BES Also for f Ds can run at 4030 MeV for D s D s production only Reduce tag yield systematic < 1% B-factories plans: BABAR: absolute measurement with full set Belle: update with final ab 1 data set 35

36 Backup 36

37 Case(i) With τ + ν/µ + ν Floating Fixed 149.7±1.0 µυ 8.5 τν Floating 153.9±13.5 µυ 13.5±15.3 τν LHCb Presentation July,

38 Upper limits on τ + ν & e + ν Fit both case(i) & case(ii) constraining the relative τν yield to the pion acceptance ratio 55:45. case (i) E<300 MeV case (ii) E> 300 MeV Find BF(D + τ + ν) < 90% c.l. BF(D + τ + ν)/.65bf(d + µ + ν) < 90% c. l. Also BF(D + e + ν)< 90% c.l. 38

39 CP Violation D + tags 8,945±551 D - tags 31,107±55 µ ν events 64.8±8.1 µ + ν events 76.0±8.6 A CP + + Γ( D µ ν ) Γ( D µ ν ) = 0.08 ± Γ( D µ ν ) + Γ( D µ ν ) -0.05<A CP 90% c. l. Consistent with SM expectation of no direct CP violation 39

40 µν Signal Shape Checked K o π + data K o π + MC Data σ=0.047±0.001 GeV MC σ=0.035± GeV Both average of double Gaussians 40

41 Other Non-absolute Measurements Exp. mode BF BF(D S φπ) f Ds (MeV) (%) See arxiv: for references 41

42 Possibilities Pick your favorite of the three: Experiment will eventually converge on SM predicted value If LQCD predictions of f Ds /f D + do not agree with the data, why should we believe f Bs /f B from theory? What does this do to the CKM fits? If there is New Physics affecting leptonic D S decays, how does it affect B S mixing and other B S decays? (See A. Kundu & S. Nandi, R-parity violating supersymmetry, B S mixing, & D S+ l + ν [arxiv: ]) 4

43 If there is a Shift.. If increases the radius of the m d / m s constraint increases Red arrow indicates a shift of ~10% in f Bs /f B 43

44 New Physics Possibilities Ratio of leptonic decays could be modified e.g. in Standard Model + + τ ν m / m τ µ m 1 m τ µ µ ν MP MP Γ(P ) = Γ(P ) If H ± couple proportional to M no effect See Hewett [hepph/950546] & Hou, PRD 48, 34 (1993). 44

45 New Physics Possibilities III Leptonic decay rate is modified by H ± Can calculate in SUSY as function of m q /m c, In HDM predicted decay width is x by tan β m q rq = 1 M D M ± H m c + m q Corrected M D 1 rq = 1 + mc mq tan mc + m q M ± H See Akeryod [hep-ph/030860] Since m d is ~0, effect can be seen only in D S ( β ) = meas rate/sm rate From Akeroyd tan β/m H 45