D0 --> l+l-

Bill Ashmanskas and Robert Harr

Physics Motivation

The FCNC decay of the D0 to two muons is highly suppressed in the Standard Model. The suppression results from the combination of nearly perfect GIM cancellation for charm, and helicity suppression of the muon pair. The Standard Model expectation for the branching ratio ranges from 10-19 up to 10-13 with the addition of long range effects. Such vanishingly small branching ratios are essentially unobservable.

Aside from the fact that this is a flavor changing neutral current decay, no conservation laws are violated in this decay. Therefore, New Physics which circumvents the GIM cancellation can potentially enhance the branching ratio to a measurable level, and an observation of this mode is a signal of Physics beyond the Standard Model.

Summary of Previous Analyses

D0 --> μ+μ-


Total triggers

3.0×106 (dimuon)2×1010 (ET)

Total unlike sign dimuon events in data

muon impact parameter>50mm(!) for 1 track
muon pair DCA<500mm<500mm
C2 of the vertex fit<50
Total dimuon vertices16338514
Dimuon mass window (GeV)1.80 - 1.921.56 - 2.171.83 - 1.90
DMD± 2sD± 1.96sD
sD17.2MeV30.5 MeV8MeV12MeV
Mother point backDCA<40mmDq<0.9°
SDL3mm<Dz<3cm; Dr<3mm

D+(s) --> X+/- μ+μ-/+

Bibliography, with links

Previous measurements

D0 --> μ+μ-

BABAR, B. Aubert et al., Phys. Rev. Lett. 93, 191801 (2004).

HERA-B, I. Abt et al., Phys. Lett. B 596, 173 (2004).

CDF, D. Acosta et al., Phys. Rev. D 68, 091101R (2003).

BEATRICE, M. Adamovich et al., Phys. Lett. B 408, 469 (1997).

E771, T. Alexopoulos et al., Phys. Rev. Lett. 77, 2380 (1996).

E789, D. Pripstein et al., Phys. Rev. D 61, 032005 (2000)

E791, E.M. Aitala et al., FERMILAB-Pub-00/280-E (2000).

Search for Rare and Forbidden Dilepton Decays of the D+, Ds+, and D0 Charmed Mesons, E791, E.M. Aitala et al., Phys. Lett. B 462, 401 (1999).

D0 --> X l+l-

Search for Rare and Forbidden Charm Meson Decays D0--> V l+l- and h h l l, E791, E.M. Aitala et al., Phys. Rev. Lett. 86, 3969 (2001).

D+(s) --> X μμ

Rare Decays Recent Results from FOCUS (+Theory), Will E. Johns (for the FOCUS collaboration), arXiv:hep-ex/0207015 (2002).


D0 --> l+l-

Flavor changing neutral currents in charm sector, S. Pakvasa, hep-ph/9705397 .

Indirect probes of new physics, J.L. Hewett, T. Takeuchi, S. Thomas, hep-ph/9603391, 44-53.

Probing new physics in the charm sector, J. Hewett, SLAC-PUB 95-6821 (1995).

Radiative Weak Decays of Charm Mesons, G. Burdman, E. Golowich, J.L. Hewett, S. Pakvasa, Phys. Rev. D 52, 6383 (1995) or SLAC-PUB-6692 (1995).

D+ --> X+ l+l-

Rare Charm Decays in the Standard Model and Beyond, G. Burdman, E. Golowich, J.L. Hewett, S. Pakvasa, Phys. Rev. D 66, 014009 (2002) or hep-ph/0112235

Rare charm meson decays D->Pl+l- and c->ul+l- in SM and MSSM, S. Fajfer, S. Prelovsek, P. Singer, Phys. Rev. D 64, 114009 (2001) or hep-ph/0106333

Computing confidence level limits

Setting confidence belts, Byron P. Roe and Michael B. Woodroofe, Phys. Rev. D 63, 013009 (2000).

Unified approach to the classical statistical analysis of small signals, G.J. Feldman and R.D. Cousins, Phys. Rev. D 57, 3873 (1998).

Incorporating systematic uncertainties into an upper limit, R.D. Cousins and V.L. Highland, Nucl. Instrum. Meth. A320, 331 (1992).

© Robert Harr 2003