The Quest for New Physics at CLEO

Transcription

1 The Quest for New Physics at CLEO Hanna Mahlke-Krueger

2 Narrowing the CKM constraints from V cb and V ub : A Roadmap Introduction 2 B X u l ν HQET b sγ B π,ρlν V ub Form factors CKM V cb B D * lν B X c lν moments? Hanna Mahlke-Krueger 2

3 CKM matrix V Connects mass and weak CKM = eigenstates Each V ij has real and imaginary parts, move imaginary phase into V ub and V td Elements are model parameters that have to be measured V V=1 gives six triangles for the off-diagonal elements V V ud us V ub V ud V cd V cs V cb V cd V td V us V cs V ts V cb V tb This talk is mostly about V cb and V ub obtained by studying semileptonic decays. Hanna Mahlke-Krueger 3

4 An example unitarity triangle: V ud V ub* +V cd V cb * + V td V tb* =0 o o o Vub Vcb V tb * V V V ud cd td o 1 o = 0 o α ϕ 2 V ud V ub* V td V tb* γ ϕ 3 β ϕ 1 V cd V cb* V ub measures one side, sin2β one angle Want to overconstrain to look for new physics Hanna Mahlke-Krueger 4

5 B physics at the CLEO detector σ(e + e hadrons) (nb) CESR accelerator operates ON the ϒ(4S) resonance (10.58GeV), just above B pair production threshold at rest, very clean Parts of data taken 60MeV below resonance (OFF) to aid in background subtraction Datasets: CleoII(.V): 9.1fb -1 ON ϒ(4S) (10M BB), 4.4fb -1 OFF CleoIII: 6.9fb -1 ON ϒ(4S) (7M BB), 2.3fb -1 OFF ``continuum e + e - γ * qq; 3nb e + e - γ * ϒ(4S) BB; 1nb CLEO II He µ DR ToF CsI meters Hanna Mahlke-Krueger 5

6 Two CLEO events: e + e - γ* qq e + e - γ* ϒ(4S) BB Hanna Mahlke-Krueger 6

7 A direct route to V cb and V ub : Semileptonic b u,c transitions b u exclusive inclusive V u,cb 2 V u,cb 2 W - q 2 u,c l H ν l b u W - q 2 u,c l ν l X Why use several techniques? Independent systematics, cross check, different theoretical problems! Hanna Mahlke-Krueger 7

8 exclusive b u V u,cb 2 l q 2 F H (q 2 ) 2 W - Form factor u,c A direct route to V cb and V ub : semileptonic b c,u transitions H ν l Rate for a final state with a particular hadron: dγ dq sl 2 ( B H lν) u,c kinematic factor V u,cb (q Form factor can be measured or taken from theory 2 2 F H 2 ) Hanna Mahlke-Krueger 8

9 A direct route to V cb and V ub : semileptonic b c,u transitions Theory can predict total inclusive rate On average, integrate over enough exclusive bound states and phase space inclusive hadronic result will match quark level calculations Framework: Heavy Quark Effective Theory to calculate observables, example see next slide b u W - q 2 inclusive V u,cb 2 l u,c ν l X Hanna Mahlke-Krueger 9

10 b u q 2 W - u,c l ν l X Γ sl (B X c lν) V cb using OPE/HQET Expansion in powers of α S and Λ QCD /m B : Γ sl (B X c lν) (1/M B ) 2 1/M B (1/M B ) 3 O(M -1 B ): Λ, energy of light quark and gluon dof inside B (m B -m b ) O(M -2 B ): λ 1, average kinetic energy of b, and λ 2 (hyperfine splitting, from m(b,b * ) O(M -3 B ): ρ 1,2, τ 1..4 (estimated) Hanna Mahlke-Krueger 10

11 (λ 1,Λ) plane and V cb So how do we get to λ 1, Λ? 3 approaches. Hanna Mahlke-Krueger 11

12 A helper process with its own virtue: b sγ DETOUR, inclusive b c afterwards hep-ex/ FCNC process, vanishes at tree level b s Heavy to light transition Can easily be confused e.g. with e + e - e + e - γ qqγ Photons/50MeV/pb -1 E γ [GeV] Signal: Use event shape cuts and neural net Goals: rate, E γ spectrum Hanna Mahlke-Krueger 12 γ

13 Rate: γ New physics in b sγ? b sensitive to non-sm contributions (considerable interest from theorists ) Br(b γ)/10-4 stat sys th CLEO fb -1 ON, 4.4fb -1 OFF BaBar ICHEP 02 (B X S γ) 54.6 fb -1 ON, 6.4 OFF Belle 2001 (B X S γ) 5.8fb -1 ON, 0.6fb -1 OFF SM (Chetyrkin et al. 1997) SM (Gambino et al., 2001) Consistency with SM (also for A CP ) Hanna Mahlke-Krueger 13 s

14 E γ spectrum in b sγ: From partons to hadrons Doppler broadening due to Fermi motion of the b within the B Leaves total rate unaffected Options include the Spectator Model (need m b and p F ) and Shape Functions (convolute with parton level calculation, eg. b sgγ ANY heavy to light transition!!) Cannot be calculated from first principles, need experimental input s b u B meson Parton level + shape function (B rest frame) Parton level Hanna Mahlke-Krueger 14 γ m b /2

15 Using the b sγ photon energy spectrum monoenergetic photon mean controlled by m b, smeared by gluon bremsstrahlung pqcd Doppler broadening due to Fermi motion (p F ) Boost and detector resolution experimental problem Moments of E γ related to HQET parameters: Mean Λ (m b or energy of light q s and g s), RMS λ 1 (Λ) (kinetic energy of b) p F m b E γ Hanna Mahlke-Krueger 15

16 b sγ: Photon Energy Spectrum Results Data Determine shape function parameters! Data/MC <E γ >=2.346±0.032±0.011GeV <E γ2 >-<E γ > 2 = ± ± GeV 2 HQET: <E γ >, <E γ2 >-<E γ > 2 Λ, λ 1 Hanna Mahlke-Krueger 16

17 hep-ex/ Hadronic Mass Moments in B X c lν Decays A second way of getting Λ, λ 1 Select b clν events, p l >1.5GeV, subtract continuum & ulν backgrounds ~ Fit M X = MB + Mlν 2EBElν distribution with B Dlν,D * lν Higher resonances Non-resonant production Input (ISGW2): D D * Fit result: X H 2 ( ) 2 M ~ X GeV 2 ( ) 2 M ~ X GeV Hanna Mahlke-Krueger 17 D. Cronin-Hennessy

18 B X C lν: Hadronic mass moments Theory provides M 2 X M 2 2 ( M M ) X M 2 B M 4 B 2 D ( λ, Λ;ρ, τ ) ( λ, Λ;ρ, τ ) Convergence concerns for second moment for both b sγ (E γ ) and B X C lν (hadronic mass moments) X = f 2 Spin-averaged D meson mass 1 = g 1 1, , O (M λ 1 3 B Combining b sγ and B X C lν gives:,β 0 α 2 S ),MS: Λ = 0.35 ± 0.07 ± 0.10GeV = ± 0.071± 0.078GeV 2 Hanna Mahlke-Krueger 18

19 B X c lν lepton moments hep-ex/ A third way of getting Λ, λ 1 Measure lepton spectrum, p>1.5gev, l=e,µ Subtract background (cont, fake leptons, real background leptons), correct E l spectrum Moments: R 0 [ R ] 1 = 1.7 = (theory :) f [ 1.5] 1.5 [ El ]( dγ sl / del ) ( dγ / de ) de ( Λ, λ ) 1 sl l l de l Corrected p l spectrum: e µ λ 1 = -0.25±0.02±0.05±0.14 Λ = 0.39±0.03±0.06±0.12 stat syst theo Hanna Mahlke-Krueger 19

20 From the HQET parameters to V cb 3 results on HQE parameters (Λ,λ 1 ): (Λ -- (m B -m b ), λ 1 -- average kinetic energy of b in B) b sγ: <E γ >+theory Λ B X c lν: <M X2 -M D2 >+theory λ 1 (Λ) B X c lν: lepton moments R 0 and R 1 + theory 2xλ 1 (Λ) At O(M B -3 ): Λ, λ 1, λ 2, ρ 1,2, T 1..4 (only estimates, must rely on rapid convergence) Could, in principle, determine all parameters conducting multiple experiments Consistent results? Is parton hadron duality a good assumption, and how to quantify resulting uncertainties? Hanna Mahlke-Krueger 20

21 V cb inclusive comparison Important test of HQE 3% precision on V cb, good agreement Theoretical error needs to improve Note the impact of Γ sl Hadronic mass in B X c lν + b sγ: V cb =( 40.4 ± 0.9(Γ sl CLEO ) ±0.5(λ 1,Λ) ± 0.8(th) ) 10-3 E l : V cb =( 40.8 ± 0.5(Γ sl WW ) ±0.4(λ 1,Λ) ± 0.9(th) ) 10-3 Hanna Mahlke-Krueger 21

22 You are here Introduction 2 B X u l ν HQET b sγ B π,ρlν V ub Form factors CKM V cb B D * lν B X c lν moments? Hanna Mahlke-Krueger 22

23 V cb exclusive: B D ( * ) lν From semileptonic decay rate to V cb : dγ B D(*)lν /dw=g F2 /48π 3 K(w) V cb 2 F D(*)2 (w) w=v B v D, Lorentz boost of D* in B rest frame; also w=(m B2 +m D*2 - q 2 )/(2m B m D* ) K(w): known kinematical factor Theory constrains shape of F and normalization F(1) ( 1 in HQET) w=1 D is at rest w.r.t. B. fct of various form factors, F(w)= =ƒ(f(1),ρ 2 ;w) related, parametrized (slope ρ) Can measure shape and F(1) 2 V cb 2. Hanna Mahlke-Krueger 23

24 V cb exclusive: B 0 D* + l ν, B D* 0 l ν signal yield hep-ex/ D* + lν D* 0 lν cos θ B,D*l (1.10<w<1.15) Reconstruct D * π s D 0 π s (K - π + ), add e or µ Use cosθ B,D*l, assume there is exactly one ν, to compute w and to suppress background: 1..1 for signal events combinatorically rec d D * s constitute largest background Fit for composition and obtain true D*lν yield for each w bin Hanna Mahlke-Krueger 24

25 V cb fit Yield: (dγ B D*lν /dw= V cb 2 F(1) 2 f(ρ;w) 2 ) F (1)= (lattice) ρ 2 =1.61 ± 0.09 ± 0.21 Extrapolation to w=0 1.0 w 1.5 Br(B 0 D *+ l ν)=(6.09±0.19±0.40)% Br(B D *0 l ν)=(6.50±0.20±0.43)% V cb =(46.9±1.4±2.0±1.8) 10-3 stat syst theo Hanna Mahlke-Krueger 25

26 B D (*) lν (hep-ph/ ) F(1) V cb /10-3 ρ 2 V cb worldwide Inclusive determination and inclusive/exclusive averages: V cb / CLEO Hadr mass CLEO l energy Belle Γ sl LEP + ϒ(4S) incl B D (*) lν world average δv cb / V cb =3...5% Hanna Mahlke-Krueger 26

27 You are here Introduction 2 B X u l ν HQET b sγ B π,ρlν V ub Form factors CKM V cb B D * lν B X c lν moments? Hanna Mahlke-Krueger 27

28 A direct route to V cb and V ub : Semileptonic b u,c transitions YOU HAVE SEEN THIS SLIDE BEFORE!!! exclusive inclusive V V ub 2 ub 2 b u q 2 W - u l ν l H Why use several techniques? Independent systematics, cross check, different theoretical problems! b u q 2 W - u l ν l X Hanna Mahlke-Krueger 28

29 From V cb to V ub b u l W V - ub 2 ν l q 2 (V ub /V cb ) 2 =0.01 Exclusive Formation of hadrons is similar; form factor is one of the big uncertainties u X Inclusive Differs theoretically as u is not heavy (heavy quark symmetries not valid) Regions in phase space where ulν is enhanced w.r.t. clν usually are regions with either theoretical challenges (lepton endpoint) or experimentally not clean (high q 2, low M X ) Hanna Mahlke-Krueger 29

30 1 st ulν preferred region V ub : the endpoint lepton spectrum 3 Br( B X ) 1.6ps ( 3.07 ± 0.12) 10 u lν Vub = Measure lepton energy spectrum for E l =p min l 2.6GeV/c Trade experimental against theoretical uncertainties by varying the lower limit (extrap n clν bkgd) hep-ex/ Hanna Mahlke-Krueger 30 τ B 1/ 2 p l min (vary)

31 V ub inclusive measurement I: the lepton endpoint spectrum ( V ub = (B(b ulν)/ τ B ) 1/2 ) Measure lepton spectrum for E l =2.x 2.6GeV/c, extrapolate to full range Previously had to resort to models for extrapolation Remember b sγ, another heavy to light transition: shape function! calculate parton level, use b sγ shape function (check with models) Hanna Mahlke-Krueger 31

32 Scaled OFF ON Data B bkd MC + scaled OFF data Data, bkg subtracted, ε corrected, and prediction using b sγ shape fct V ub incl from lepton endpoint analysis Background suppression: Cont: neural net for event shape information B clν: account for in fit using MC Check analysis with different p l min cuts V ub =4.08±0.63 ( GeV/c) (dominant error from extrapolating to the full p l range) Hanna Mahlke-Krueger 32

33 2 nd ulν preferred region: high q 2 & low M X 2 B X u lν (MC) B X c lν (MC) background ISGW2. non-res B D,D ** lν,b D * lν, B X c non-resonant qq, fake and sec leptons Keep all semileptonic B events, again determine BR(b ulν) M X 2 (GeV 2 ) b u V ub 2 q 2 W - u l ν l X M X Q 2 hep-ex/ (ICHEP 02 prelim) Use clν to determine moments V cb (in progress) Hanna Mahlke-Krueger 33

34 2 nd ulν preferred region: high q 2 & low M X 2 B X u lν (MC) B X c lν (MC) background ISGW2. non-res B D,D ** lν,b D * lν, B X c non-resonant cont, fake and sec leptons Keep all semileptonic B events, again determine BR(b u,clν) V ub : ulν in R=(high q 2, low M X2 )! R theoretically preferred scale down by fraction of events in R, do this with several models to evaluate systematic error, use HQET in R hep-ex/ (ICHEP 02 prelim) M X 2 M X 2 (GeV 2 ) V ub =(4.05± 0.18± 0.58±0.25±0.21±0.56) 10-3 R stat syst X c lν X u lν theo 22% Hanna Mahlke-Krueger 34 q 2

35 You are here Introduction 2 B X u l ν HQET b sγ B π,ρlν V ub Form factors CKM V cb B D * lν B X c lν moments? Hanna Mahlke-Krueger 35

36 V ub exclusive: B mlν b u V ub 2 q 2 W - u F m (q 2 ) 2 l ν l Form factor m=π/ρ/ ω/η dγ(b mlν)/dq 2 V ub 2 K(p m )F m (q 2 ) 2 K(p m ) kinematic factor F m (q 2 ) form factor function, depends on m Reconstruct q 2 =(p l +p ν ) 2 Hanna Mahlke-Krueger 36

37 (paper in preparation) B mlν yields ν: p ν = Pmiss;E ν = Pmiss p l >1.0[1.5]GeV for πlν [ρlν] B πlν Fit M B and E to get yield, all modes together, apply isospin constraints πlν sees much feeddown from ρlν, ρlν does not have much from πlν Binning in q 2 reduces systematic uncertainty greatly (variation of ε(q 2 ), cross feed(q 2 ) over bin reduced) GeV M(mlν) E = M B =(E ν +E l +E m )-E beam Hanna Mahlke-Krueger 37

38 dγ/dq 2 (q 2 ), q 2 =0..30GeV 2 : Form factors B πlν One method: Fit with different form factor models Fit quality discrimination among form factors! Normalization V ub spread between models in B πlν less than uncertainties of each model Or, use LCSR or LQCD calculations for form factors where applicable B ρlν and V ub Branching fractions per q 2 interval: ISGWII LCSR B πlν SPD Same for ρlν, but form factors differ more there Hanna Mahlke-Krueger 38

39 Extracting V ub from B π,ρlν three different Form factors from: 1. Models 2. Lattice QCD (high q 2 only) 3. Light cone sum rules (low q 2 only) CLEO result: Averaged values extracted using LQCD and LCSR ways Hanna Mahlke-Krueger 39

40 V ub comparison inclusive exclusive CLEO πlν 2003 CLEO ρlν 2003 BaBar ρlν 2002 CLEO ρlν 1999 CLEO endpoint 2001 CLEO Xlν prelim 2002 LEP V ub /10-3 Values are in good agreement. Status: δv ub / V ub = % Hanna Mahlke-Krueger 40

41 Another heavy-to-light transition: From D πlν to B πlν c V cd 2 d l ν l D 0 u B 0 π V ub 2 b d u π l ν l Γ sl =ƒ( V Hl 2, form factor f + D,B π, kinematics): f + D π f + B π from HQET V cd known to 7%, extract f + D π in D decays Principal background comes from D Klν. CleoIII RICH particle ID should reduce this background substantially. Analysis underway Hanna Mahlke-Krueger 41

42 So far so good... 15% B X u lν E l endpoint 22% B X u lν HQET b sγ hi q 2 lo M X 3% Form factors 15-20% V ub B π, ρlν? V cb B D * lν 5% B X c lν moments Hanna Mahlke-Krueger 42

43 Where do we go from here? B factories will provide vast data samples More information at new level of precision on CKM matrix elements, CP violation etc to be expected soon Precision of CKM ME s limited by theoretical understanding of strong interaction Theoretical tools are being developed, but they need to be calibrated Hanna Mahlke-Krueger 43

44 Strong interaction and non-perturbative QCD QED QCD: strong coupling and nonlinearity due to gluon self-coupling a new feature: confinement Perturbative QCD saved the day for high energies and has been extremely successful Confinement is a low energy phenomenon but an essential component of our physics picture need to master this area too!! Theoretical tools available but must be verified, e.g. lattice QCD Hanna Mahlke-Krueger 44

45 Lattice version of QCD The only complete definition of QCD: comprises pert. and non-perturbative aspects Also B factories welcome LQCD input, e.g. f B Recent advances to allow unquenched calculations improved the precision of predictions from 15% down to the percent level, but Need data to calibrate! yrecent results (fall 02) ytune m u =m d,m s,m c,m b and α S using m π,m K, m ϒ,m ψ, E ϒ (1P-1S), n f =3, a=1/8fm ymuch more precise results (errors reduced 3-4x) yremarkable agreement with experimental data G.P. Lepage for HPQCD+MILC Collaborations (Preliminary Results) Hanna Mahlke-Krueger 45

46 Recent LQCD results Hanna Mahlke-Krueger 46

47 GeV 10.5 Recent LQCD results: ϒ spectrum --- Experiment S 1 1 P 3 1 D 2 HPQCD: Davies, Gray et al. (2002) : Quenched MILC : 2+1 flavors MILC with m u,d =m s /5 (Recent CLEO result: ϒ 2 (1D), ICHEP02) Hanna Mahlke-Krueger 47

48 CLEO-c / CESR-c Ref: CLEO-c and CESR-c: A New Frontier of Weak and Strong Interactions (CLNS 01/1742) 3 years of charm and QCD physics ( ) 1 CESR: add wigglers to enhance transverse cooling 1 CLEO: silicon vertex detector inner drift chamber 1 Solenoid: Tesla (compensation, reconstruction) ϒ(1,2,3S), 1-2fb -1 each, finished in June 2002 precision spectroscopy CLEO, ICHEP02: ϒ 2 (1D) ψ(3700), 3fb -1 ; ψ(4100), 3fb -1 ; ψ(3100), 1fb -1 orders of magnitude more than was available before (MarkIII, BESII) Large samples of extremely clean events in an interesting energy region Hanna Mahlke-Krueger 48

49 A Cleo-c (MC) event Clean events, low multiplicity Spherical event topology Good signal/bkd ratio... Hanna Mahlke-Krueger 49

50 Cleo-c - a unique opportunity Calibration of LQCD tools such that they can be trusted when applied to b physics ~1% measurements of V cs and V cd Direct Beyond the Standard Model searches unique to Cleo-c Sensitive searches of glueballs and exotic states Vastly more low energy data A modern detector New theory tools Unprecedented precision Hanna Mahlke-Krueger 50

51 Friday 2/7/ h: --> Dear CLEO Colleagues, We just received the following short announcement from Maury Tigner: To CLEO, CESR and CHESS Colleagues We learned this morning that the National Science Board, the governing board of the NSF, has approved the 5 year proposals of both LEPP and CHESS. There will be a celebration in the Wilson Commons on Feb. 28 Needless to say, we are delighted that we can now move forward confidently with CLEO-c knowing that the project is approved! David and Ian Hanna Mahlke-Krueger 51

52 Summary CLEO continues to contribute to a precise understanding of the SM: V cb V ub Confinement remains one of the challenges New tools are becoming available, but we need testing grounds: Recent advances in Lattice QCD Cleo-c is on its way More than ever, it is essential to combine knowledge from all areas to obtain the best possible results. Hanna Mahlke-Krueger 52