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CLEO's Physics

A D-Dbar event in the CLEO-c detector.

CLEO-c is a dedicated program of charm physics at the Cornell Electron Storage Ring (CESR). We are elucidating the weak physics behind both charm and bottom quark decays by helping to disentangle it from the confounding strong-interaction dynamics. In particular, our measurements of D and Ds meson decays to leptonic and semileptonic final states are crucial tests of the Lattice QCD techniques used to compute important heavy quark processes. We are also determining the hadronic branching fractions of D and Ds mesons, which normalize many measurements of both bottom and charm decays.

This physics is made possible in part by the very clean events at these energies. At the ψ(3770), each event produces only a pair of D mesons. Typically, we reconstruct one D (the tag) and then study the decay of the other D. Likewise, at the center-of-mass energy of 4170 MeV, many events contains a pair of Ds and/or Ds* mesons. The reconstruction strategy is pretty much the same as in the D anti-D case, though there is the extra complication of dealing with the presence of both Ds and Ds*.

CLEO-c also explores spectroscopy of heavy quarkonia and related states. In early 2006 our efforts uncovered new charmonium decay modes of the puzzling Y(4260) state, in addition to making the first confirmation of the BaBar discovery. In 2005 CLEO discovered the expected, but long-sought hc meson, the 1P1 state of charmonium. We cleanly observed very rare non-DDbar decays of the ψ(3770) and dispelled any notion that they could be large. Efforts in the precision realm have yielded the world's best measurements of the dileptonic widths of J/ψ, ψ(2S), ψ(3770), and the Υ(1S,2S,3S) quarkonia as well as the dominant branching fractions of ψ(2S) decays.

See more details on the CLEO-c program in the original project description and two CERN Courier articles featuring CLEO-c: Lattice QCD and CLEO-c tackle the CP challenge, CLEO cleans up below the charm threshold.


CLEO-c Data Summary

CLEO-c has collected the following data:

  • 572 pb-1 on the ψ(3770)
  • about 27 million ψ(2S) decays
  • 21 pb-1 of continuum below the ψ(2S)
  • 47 pb-1 of scan data near E_cm = 4170 MeV
  • 13 pb-1 of data at E_cm = 4260 MeV
  • 314 pb-1 of data at E_cm = 4170 MeV for D_s physics
  • December 2007: resume data taking at E_cm = 4170 MeV


Recent Highlights


The squared missing mass distribution in events with one fully reconstructed D plus a lone muon. D+ → μ+ν decays peak at zero.

  • Leptonic decays: D+ → μ+ν and fD, Ds → μ+ν and fDs: Our latest result on D+ → μ+ν uses 280 pb-1 of data collected at the ψ(3770) and achieves 8% precision on the decay constant fD. If lattice can reproduce this accurately, it will add confidence to lattice calculations of the strong interactions at work in BBbar mixing. The D+ → μ + ν decays can be seen in the peak at zero in the figure. hep-ex/0508057, Phys. Rev. Lett. 95, 251801 (2005). With a similar goal in mind as for D+ → μ + ν, we determine the decay constant fDs. In 314 pb-1 of data taken at a center-of-mass energy of 4170 MeV, we analyze decays Ds decays to μ + ν and τ+ν → (π+ anti-ν) ν. With both studies combined, we determine fDs at a relative precision of 5%. Phys. Rev. Lett. 99, 071802 (2007), arXiv:0704.0629 (hep-ex).
  • Exclusive Semileptonic Decays: For semileptonic modes as well, 56 pb-1 coupled with the cleanliness of tagged analyses has led to results more precise than previous world averages, including first observations of new modes. Both charged and neutral D decays are studied. Higher-statistics updates will concentrate on precision form-factor measurements. hep-ex/0506053, Phys. Rev. Lett. 95, 181801 (2005) (charged D decays); hep-ex/05060532, Phys. Rev. Lett. 95, 181802 (2005) (neutral D decays).
  • Hadronic Branching Ratios: Precision absolute branching ratios, using fully reconstructed D pairs from 281 pb-1, are available, world-wide leading in precision. Included are the key "golden modes" D0 → K-pi+ and D+ → K-pi+pi+. arXiv:0709.3783 (hep-ex) (submitted to Phys. Rev. D). A survey of Ds decays to a pair of pseudoscalar particles has been performed as well, with four new observations, resulting in relative branching fraction measurements: arXiv:0708.0139 (hep-ex) (to appear in Phys. Rev. Lett.).
  • Discovery of the h_c: CLEO-c has clearly observed the long-sought hc singlet P1 state of charmonium. Both exclusive and inclusive reconstructions are utilized; more details are given in the longer PRD paper. hep-ex/0505073, Phys. Rev. Lett. 95, 102003 (2005).
  • Study of the Y(4260) Resonance We confirm, at 11 sigma significance, the BaBar Y(4260) → π+ π- J/ψ discovery, make the first observation of Y(4260) → π0 π0 J/ψ (5.1 σ), and find the first evidence for Y(4260) → K+ K- J/ψ (3.7 σ). hep-ex/0602034, Phys. Rev. Lett. 96, 162003 (2006). We also confirm, at 5.4 sigma significance, the observation of Y(4260) produced in events with initial state radiation, e+e- --> gamma Y(4260), and determine its mass and width. hep-ex/0611021, Phys. Rev. D 74, 091104(R) (2006).
  • Dilepton Pair Production in J/ψ Decay We have made the world's most precise measurements of the branching fractions for J/ψ → e+e- and +- using 3M ψ(2S) decays. hep-ex/0503027, Phys. Rev. D 71, 111103 (2005).
  • The Dilepton Widths of Υ(1S, 2S, 3S): By scanning the CESR center of mass energy over the Upsilon resonances, we have measured the di-electron widths of the Υ(1S), Υ(2S) and Υ(3S) with better than 2% precision in each. Successful calculation of these results will be a critical test for Lattice QCD. hep-ex/0512056, Phys. Rev. Lett. 96, 092003 (2006).
  • Eta meson properties An interesting journey to spectroscopy of low-mass states: Analyzing η mesons produced in the decay ψ(2S)→ η J/ψ in the 27M psi(2S) sample allowed us to determine all five major η branching fractions (constituting over 99 percent of all η decays), the first time this has been done in a single experiment. arXiv:0707.1601 (hep-ex), Phys. Rev. Lett. 99, 122001 (2007). We also measure the η mass at a precision that is competitive with dedicated facilities, made possible through the exploitation of the event kinematics and superb CLEO detector resolution. arXiv:0707.1810 (hep-ex), Phys. Rev. Lett. 99, 122002 (2007).


The CLEO-c Detector

The CLEO-c Detector contains many subdetectors including:



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