Search for new physics in rare D meson decays

Transcription

1 Search for new physics in rare D meson decays Svjetlana Fajfer and Sasa Prelovsek Department of Physics, University of Ljubljana and J. Stefan Institute, Ljubljana, Slovenia XXXIII INTERNATIONAL CONFERENCE ON HIGH ENERGY PHYSICS ICHEP'06 Moscow, ,

2 Outline Motivation FCNC from models with an extra singlet up-like quark transition and new physics NP in exclusive decay modes most promising candidates for experimental searches: and Conclusions 2

3 Motivation In low energy physics new physics is usually expected in transitions with down-like quarks: Is there any possibility to search for new physics in the up-like quark sector? for example: c u γ transition 3

4 c u γ transition dominated by SM (long distance contributions) BGHP PRD 52 (1996) 6383 FPS EPJ C6 (1999) 471 Belle collaboration New physics might appear by gluino exchange in MSSM (PW PLB 500 (2001) 304) 4

5 Another possibility to search for new physics in charm sector is offered in the studies of is significantly suppressed by QCD (FSZ EPJ C27 (2003) 201) SM: QCD effects -RGE 5

6 the branching ratio distribution R- parity MSSM invariant dilepton mass square SM FSZ EPJ C27 (2003) 201, BGHP, PRD66 (2002) , FPS PRD 64 (2001) Intensive searches of exclusive rare D decays at CLEO and FERMILAB; 6

7 FCNC and new physics coming from an extra up-like quark singlet In many extension of SM appears an extra quark singlet. The implications of an extra down like quark singlet were extensively studied. The up-like quark singlet s might appear too within some of models of new physics: as GUT, models with an extra dimension, intersecting branes. Important: there are two effects caused by an extra up-like quark : induces tree level FCNC for the up-like sector contributes in the box diagram for 7

8 References for extra up-like quark - for a general framework: V. Barger, M.S. Berger and R. J. N. Phillips, PRD 52 (1995); P. Langacker and D. London, PRD 38 (1988) 886; J. A. Aguilar-Saavedra, PLB 625 (2005) 234; K. Higuchi and K. Yamamoto, PRD 62 (2000) ; J. Alwal et al, hep-ph/ GUT approaches: R. Barbieri and L. Hall, NPB 319 (1989) 1; E. Ma PLB 322 (1994) 363 -up-like quark from extra dimension: F.del Aguila and J. Santiago, JHEP 03 (2002) 010 -intersecting brane models S.A. Abel et al., JHEP 04 (2003) 057 -Little Higgs Model -Jae Yong Lee, JHEP 04 (2004) 065 8

9 FCNC Z With an additional up-like quark there is a tree level FCNC for the up-like sector For example there is a cuz tree level vertex - (unitarity of extended CKM) 9

10 Using unitarity limit one gets (we use the lowest value of CKM as given in PDG to get maximal effects ) The stringent limit comes from Exp. Result (PDG): Maximal value is This corresponds to the maximal effect that any new physics possibly have on rare D decays given by model independent constraints on Z mediated flavor changing currents. 10

11 New Physics model modifies Wilson coefficients: for inclusive decays 11

12 CLEO s and FOCUS upper upper bounds This is consistent with It already indicates that resonant decay channels with intermediate resonances constitute an important longdistance contribution to the charmed meson decay, which may shadow interesting long distance contribution induced by 12

13 The SM short distance contribution is dominated by the We use experimental information on and D* pole dominance of the form factor (this holds strictly in the heavy quark limit!) 13

14 Instead of using theoretical model we take full advantage of the experimental input that is available to determine long distance contribution. The dominant contribution is: The success of narrow width approximation allows to write That indicates that the amplitude for a cascade via resonances can be written as overall phase is unknown comes from the experimental data 14

15 We argue that the relative sign of amplitudes can be determined by considering the cascade decays (using vector meson dominance of the electromagnetic current). The remaining part of the difference I s due to the weak transition which is induced by the operators and can proceed via three ways (detail in appendix) 15

16 Due to the lack of experimental data we are forced to use a model: we use factorization of the amplitude: it reduces calculation on the products of the matrix elements of the two currents; we use Lorentz decomposition of the matrix elements: form factors, decay constants; we use heavy quark symmetries for D and D* and chiral symmetry for light pseudoscalar and vector mesons References + new experimental input parameters 16

17 The long distance contributions in D P (V) γ * 17

18 The dilepton mass distribution and the forward-backward asymmetry n SM it is 0! New physics produces nonzero forward-backward asymmetry! 18

19 Table 1: Branching ratios for the hadronic decays, which are most suitable to probe transition experimentally. The total rates in Standard and New Physics models are completely dominated by the resonant long-distance contribution of D decays. We also provide the short-distance contribution in SM together with its maximal modification in NP model. The SM short distance contribution is not shown since it is completely negligible in comparison to the long distance contribution. 19

20 FCNC in Littlest Higgs model (S.Fajfer and S. Prelovsek, PRD 73 (2006) ) rather simple solution to the gauge hierarchy problem; new massive gauge bosons and new heavy quark states; the quadratic divergences the spin ½ contribution of the top quark is cancelled by the new fermion; the spin 1 contributions are cancelled by new gauge bosons; the spin 0 quadratically divergent contributions are vanishing due to the fact that all scalars in the model are Goldstone bosons at tree level. model Lae Yong Lee, JHEP 0412 (2004) 065, hep-ph/ ; (there is an extra vector like heavy quark, which is a single of SU(2) group and which mixes with the third generation) ; this mixing induces new tree level flavor changing charged and neutral currents in which parameters are: 20

21 21

22 Conclusions search for new physics in charm decays very difficult due to dominance of long distance contributions; an extra up-like singlet quark induces FCNC at tree level; in the excusive decay NP can moderately modify dilepton mass distributions; the forward backward asymmetry in vanishes in SM while it can be ~ 0.05 in NP model with an extra up-like quark; the effects of LH model in FCNC charm quark inclusive decay into u quark and the lepton pair are insignificant. 22

23 Additional slides c u γ transition in SM QCD enhancement GIM cancellation at one loop level and QCD enhancement C.Greub, T.Hurth, M.Misiak, D. Wyler, Phys. Lett. B 382 (1996)

24 MSSM in c u γ The gluino exchange diagrams give largest enhancement SM S.Prelovsek, D. Wyler Phys.Lett.B 500 (2001)

25 Appendix Theoretical framework 25

26 Dominated by the 1-loop insertion of the Inami Lim result recovered 26

27 Explaining the signs in: 27

28 The branching ratios in SM 28

29 The Littlest Higgs model begins with SU(5) global symmetry, with two locally gauged subgroups SU(2) x U(1). The global SU(5) is spontaneously broken to its subgropup SO(5) at scale f close to 1 TeV. The global symmetry breaking results in fourteen massless Goldstone bosons. Among them four massless Goldstone bosons are eaten by the gauge bosons, so that the two SU(2)xU(1) are broken down to its diagonal subgroup SU(2)xU(1). The remaining 10 Goldstone bosons give complex doublet (SM Higgs) and complex triplet. Higgs doublet is a Goldstone boson at the scale f so there is no mass term for the Higgs doublet at the tree level. The Higgs potential arises from the Coleman Weinberg potential. Additional heavy gauge bosons and the Higgs triplet give the Higgs doublet a logarithmically enhanced possitive mass squared. In order to cancel out these positive contributions and get a negative Higgs mass quared an additional quark is introduced in vector - like representation of the SM 29