A personal perspective is given on physics of charmless rare B decays: 1997
-- 2003.Comment: 6 pages, 2 eps figures included. Invited talk presented at joint
  session of the 8th Asia Pacific Physics Conference (APPC 2000) and 3rd ACFA
  Workshop on Physics/Detector at the Linear Collider (ACFA-LC3), Taipei,
  Taiwan, August 200

Hou, George W. S.

English

arXiv

A personal perspective is given on physics of charmless rare B decays: 1997 -- 2003

Hou, G W S

CERN Document Server

WHAT CAN WE LEARN FROM CHARMLESSRARE B DECAYS — THE PAST/NEXT 3 YEARSGEORGE W.S. HOUDepartment of Physics, National Taiwan University, Taipei, Taiwan, R.O.C.A personal perspective is given on physics of charmless rare B decays: 1997 { 2003.1 Prelude: Berkeley to OsakaMy rst ICHEP was Berkeley 1986, where I heard about CLEO limits on rareB decays. A host of strong (P, e.g. B ! K+), radiative or electromagnetic(EMP, e.g. B ! Kγ) and electroweak (EWP, e.g. B ! K‘+‘−) modes weregiven, with limits typically a few 10−4, but EMP limits were only  10−3,reflecting the time before the advent of CsI-based EM calorimetry. aThough still contending with limits, I embarked on a study of these modes,encountering (and missing) a few surprises. I found that the Z penguin dom-inated the EWP’s.1 While obvious for b ! s, for b ! s‘+‘− the EMP hadnaively been assumed to be dominant. Although I missed the \large QCDcorrections" to EMP that enhanced b ! sγ to a few 10−4, I did uncover thesensitivity2 to H+ eect, which later lead to the stringent bound on mH+ inSUSY type of two Higgs models. I encountered the surprise of \higher orderdominance" that3 b ! sg ! sqq > b ! sg. Much of the above has to dowith GIM cancellation subtleties or the non-decoupling of mt in SM.Why did I bother only with inclusive processes at that time? Well,these can be, by argument of duality, viewed as quark level processes hencedominated by S.D. physics ( virtual collider). But for exclusive processes,hadronization brings in L.D. physics that is likely to blur S.D. information.Unless, . . . ugh, . . . one has factorization!? Factorization means separating theproduct of quark currents and forming hadronic matrix elements of bilinears.Naively, for b ! duu to mediate B ! −, the du current created by virtualW projects directly into a pion (decay constant), while the b ! u currentmediates B !  transition (form factor). That is, one assumes (wishes)hj( du)(ub)jBi fac: hj duj0ihjubjBi:But this was too big an \if" for me. Despite the ease for detection, I could notbring myself to believe in factorization, and hence never worked on exclusiveaThe rst penguin, B → Kγ, emerged ∼ 5× 10−5 soon after CLEO-II (w/ CsI) started.0009220: submitted to World Scientific on September 21, 2000 1modes . . . until I had a data–driven conversion experience at end of 1998!Strong penguins have emerged en masse since 1997 at CLEO, where 107B B’s have been collected, and at Osaka 2000, Belle and BaBar both reportedrst results with comparable amounts of data, collected in first year of run-ning! The four K modes and relatively small +− mode observed by CLEOare conrmed by Belle, but BaBar reports a higher (lower) +− (K+−).More data is needed, and certainly expected, but Golutvin4 already states:\Present data favour large arg Vub and FSI." We shall address why this is so,but let me step a few years back to the time of the emerging strong penguins.2 Experimental Surprise of 0Xs and 0KWith a few 106 B B’s, CLEO announced in 1997 that B ! 0Xs  6 10−4for 2 < p0 < 2:7 GeV, and 0K a tenth less. This was not predicted by anytheorist. Many models and speculations ensued. It is puzzling that, with 0the heaviest and stickiest (gluey) member of the 0− nonet, how can it come so\fast"? One interesting idea,5;6 the only one so far that can explain the mXsspectrum, links 0 production to the gluon anomaly: The derivative couplingnature of the g-g-0 anomaly vertex spits out 0 with high momentum inb ! sg ! sg0. A criticism is that such coupling must be cut o by someform factor. However, the gg channel has 0−+ quantum numbers, and thehigh glueball mass scale ( 2:5 GeV from lattice) may well delay the formfactor suppression. One way6 to check this is to study Z ! qqg + 0.The 0K analysis of CLEO is now very robust, and is starting to bechecked by Belle/BaBar, but inclusive study has not yet been updated by anygroup (even CLEO). This is certainly a volatile area where more insight, ifnot surprises, can be attained. We still lack a clear theory.3 The Path to γ > 90 and Factorization (and FSI?)Factorization and γ ∼> 90◦CLEO data has driven phenomenology in a ne way in the last 3 years.71997 : K0− > K−+ |{ This lead to the Fleischer{Mannel bound (thoughK0− was just above 3), and a boom in theory work, eventually leadingto model-independent methods for extracting γ.1998 : K−0 > K0− ’ K−+ ’ 1:4 10−5 |{ K0 ’ K prompted therst suggestion8 for large γ; surprising strength of K0 indicated EWP.0009220: submitted to World Scientific on September 21, 2000 21999 : 0−, , ! (!K disappear) |{ Evidence for b ! u tree (T).K0 ’ 23 ( K0 ’ K) |{ Fine, EWP at work.8  14 K |{ Further indication for large γ.9K00  K; K0 =) Problem.10The host of emerging modes lead to the observation9 that, bFactorization works in two body charmless rare B decays, if cos γ < 0It even lead to11 a \global (rare B) t" of more than 10 modes that gaveγ ’ 105, seemingly in some conflict with the well-known \CKM Fit" value ofγ ’ 60. Sucie it to say that, by end of 1999, all B practioners had switchedto γ > 80-90, as reflected in the 5 rare B theory talks at Osaka. This couldhave harbingered the lower central value of sin 2 seen by BaBar/Belle thissummer, although dust is far from settled.ubqqu ;K VujVubjubqqu ;K jVtjVtbWhat is the physics eect? Let us illustrate with K vs. . Withonly T contributions, jVusj2  jVudj2 implies K  . Thus, the observedK >  implies P dominance in K, and substantial \penguin pollution"to . As data rened, it was realized9 that T-P interference contains moreinformation. As V usVub = jVubje−iγ = V udVub has the same phase, whilethe real part of V tsVtb = −jVcbj and V tdVtb = jVcbj[1 −√2 + 2e−iγ ] haveopposite sign since√2 + 2  jVubj=jVcbj ’ 0:4, hence T-P interference isanticorrelated in K vs. . Thus, K * implies  +, and vice versa.9FSI?A problem was already apparent by summer 1999: K00 seems too large10(Again a chorus line of theorists at Osaka)! As mentioned, K0=K ’ 0:65conrms constructive EWP-P interference for K0 in SM. From the operatorsand the 0 w.f. (change from uu to d d) one expects destructive EWP-Pinterference in K00, hence K00 > K0 is very hard to reconcile.We proposed a half-way solution, resorting to large nal state interaction(FSI) phases.10 If we start with e.g. γ = 110, then K : K0 : K0 :bOnly the sign change in cos γ was conservatively advocated in original paper.0009220: submitted to World Scientific on September 21, 2000 3K00 = 1 : 0:94 : 0:65 : 0:35, as compared to the experimental (CLEO only)1 : 1:06 : 0:67 : 0:85. Allowing K (strong phase dierence between I = 32and 12 amplitudes) to be  90, we nd the ratio becomes 1 : 1:12 : 0:61 : 0:47.This is far from resolving the problem, but it is in the right direction. What’smore, we nd that  < 0 can be achieved (taking   K) and centralvalues for aCP in K, K0, K0 modes become \just right", and there arefurther dramatic consequences: 00    3{5 10−6 < 0 (still satisfy CLEO bound). aK¯00CP  −aK−0CP large; aCP; a00CP as large as  −60%, −30% possible.These would be measurable in a couple of years.So now we have an oxymoron: Factorization works, but FSI is large. Ourview is, however, phenomenological: Data indicates that factorization worksfor the rst 10-20 or so two body rare B modes. The K and  phases arethe minimal extension of parameters allowed in the factorization framework.We do not pretend to know their origin. They could be eective parametersarising from e.g. annihilation diagrams. But if they genuinely arise from L.D.physics, they would then pose a real problem for PQCD.4 New Physics: Probing Flavor and/or CP ViolationAs a \virtual collider", B decays and mixings provide a natural hunting groundfor New Physics, esp. flavor and CP violation. Let us illustrate with SUSY.It is known that ~g-~q loops could easily generate FNP2 s imbR b G typecouplings, and also bL ! sR chirality flips that are absent in SM. For example,aCP in inclusive B ! 0 + Xs at 10% level.6 A late 1997 rumor that CLEOhad aCP(K)  100% led us to put in a sizable FNP2 and managed12 to yankaCP’s up to 50%. Unfortunately, the rumor ended with CLEO 1999 directaCP results in 5 modes, all consistent with zero with errors  20%.Along a dierent line, we compiled13 measurables which could test bLsRγcouplings that would denitely indicate New Physics: mixing dependent anddirect CP violation in B ! Kγ, and  polarization in b ! γ decay.It turns out that b ! d penguins may be more promising and accessiblein a couple of years. Let us illustrate the interplay of flavor symmetries andSUSY in a relatively extreme case.14 For an underlying Abelian horizontalsymmetry for observed quark mass and mixing hierarchy pattern, 1-3 and2-3 mixings in dR sector are naturally the largest, and likewise for ~dR withSUSY. Cabibbo (1-2) mixing must come from up sector because of " and "0constraints. One would have to accept TeV scale squarks and gluinos, but? Bd- Bd, Bs- Bs and D0- D0 mixing all have common source=) strength and CP patterns dierent from SM!0009220: submitted to World Scientific on September 21, 2000 4? B ! γ, !γ: More detectable (vs. K0γ) mixing-dep. CP asymmetries.Thus, the B system probes New Physics even when elusive at colliders.5 The Next 3 Years: A SamplerB Factories will reach 1034, and Tevatron Run-II will have 20 Run-I dataduring 2001-2003. Clearly the next 3 years would be even more exciting thanthe last 3: > 108 B B by 2003 , and comparable jump at Tevatron!What could be revealed?γ (or 3) Program : Model-indep. methods (e.g. R) vs. \Global Fit".Question of model indep. vs. stat. power; both can be PQCD-improved. (or 2) Program :    − ( + γ)Since B0 ! +− (direct: γ in V ub) and B0 ! B0 ! +− (mixing: )interfere, mixing-dep. CP probes . However, \P-pollution" severe.=) Two Paths: +− and 00 plus isospin analysis+−0 (, 00) Dalitz plot analysisThis is an area where a lot of new development is expected.′ Program : Conrm CLEO, esp. inclusive! (Maybe B ! Glueball+K?).Direct CP Asymmetries : aCP sensitivity down to few %.=) New impact and info on/for theory. (Perhaps just testing FSI...?)–crosscheck/NP probe : Mixing-dep. CP study in? B ! KS : c Pure P (sss) w/o SM phase ) KS 6=  KS means NP.? B ! 0KS : Not pure-P (has T) but possibility of NP source.EWP & b → dγ :? B ! K()‘+‘− will appear: AFB via γ-Z interference at mb scale!? B ! γ, !γ (+−(0): vertex) vs. K0γ (K0 ! KS0 no vertex)=) Good mixing-dep. CP probe: Nonzero amixCP  New Physics.D mixing : Conrm CLEO/FOCUS? mD 6= 0 implies New Physics.Charmless Rare Baryons :15 B ! 0 p; γ p?CLEO just reported16 B ! D−pn, D−pp  10−3 < D; D!=) 0 p; γ p  10−5  p plausible, could be first charmless baryon! ! p self-analyze spin: probe B ! 0; γ dynamics (and CP/T).cBelle reported at Osaka a large K+ signal > 10−5, in some conflict with a smaller numberreported by CLEO. Note that the new CLEO number is above their previous upper limit.0009220: submitted to World Scientific on September 21, 2000 56 ConclusionWe have witnessed the riches of rare B decays from the past on weak dynamics,weak phases, new physics, and strong interaction. The highlights have been:B ! Kγ, K + n + γ; 0K, 0 + K + n; K=.The timeline is illustrated as follows:Time # B B Discovery Signicance1986 105 B- B Mixing !!1993 few 106 B ! Kγ, Xsγ EMP1997{2000 107 B ! 0K, 0Xs, K, K. . . Strong b ! s PB ! , !,  b ! u T & P2000{2003 108 1=, 3=γ, 2= (?) Unitarity 4Direct aCP FSI, or . . . ?B ! K()‘+‘− EWPB ! γ; !γ b ! d EMP. . . . . . New Physics!?With advent of B Factories, we expect an order or more jump in numberof B B’s, boosted. Detectors now have good PID plus vertexing. Boom timelies ahead | Era of BaBar/Belle/CLEO competition, and with Tevatron.References1. W.S. Hou, R.S. Willey and A. Soni, Phys. Rev. Lett. 58, 1608 (1987).2. W.S. Hou and R.S. Willey, Phys. Lett. B 202, 591 (1988).3. W.S. Hou, A. Soni and H. Steger, Phys. Rev. Lett. 59, 1521 (1987).4. A. Golutvin, plenary talk at ICHEP2000, Osaka, Japan.5. D. Atwood and A. Soni, Phys. Lett. B 405, 150 (1997).6. W.S. Hou and B. Tseng, Phys. Rev. Lett. 80, 434 (1998).7. For a little more, see my Osaka 2000 talk: G.W.S. Hou, hep-ph/0009197.8. N.G. Deshpande et al., Phys. Rev. Lett. 82, 2240 (1999).9. X.G. He, W.S. Hou and K.C. Yang, Phys. Rev. Lett. 83, 1100 (1999);W.S. Hou and K.C. Yang, Phys. Rev. D 61, 073014 (2000).10. W.S. Hou and K.C. Yang, Phys. Rev. Lett. 84, 4806 (2000).11. W.S. Hou, J.G. Smith and F. Wu¨rthwein, e-print hep-ex/9910014.12. X.G. He, W.S. Hou and K.C. Yang, Phys. Rev. Lett. 81, 5738 (1998).13. C.K. Chua, X.G. He and W.S. Hou, Phys. Rev. D 60, 014003 (1999).14. C.K. Chua and W.S. Hou, e-print hep-ph/0005015.15. W.S. Hou and A. Soni, e-print hep-ph/0008079.16. S. Anderson et al. (CLEO Collaboration), e-print hep-ex/0009011.0009220: submitted to World Scientific on September 21, 2000 6

What Can We Learn from Charmless Rare B Decays: the Past/Next 3 Years

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What Can We Learn from Charmless Rare B Decays - the Past/Next 3 Years

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