Recent results on D meson decays from BES 陈江川 (for BES Collaboration) Institute of High Energy Physics, Beijing China 高能物理学会第七届全国会员代表大会暨学术年会 广西 桂林 2006 年 10 月 27 日 -11 月 1 日

Outline  Introduction  Semileptonic decays of D mesons  Summary  Inclusive decays of D mesons

The Beijing Electron Positron Collider (BEPC) L ~ 1  /cm 2  s at  (3770) peak E cm ~2-5 GeV

BESII Detector VC:  xy = 100  m TOF:  T = 180 ps  counter:  r  = 3 cm MDC:  xy = 220  m BSC:  E/  E= 22 %  z = 5.5 cm  dE/dx = 8.5 %   = 7.9 mr B field: 0.4 T  p/p=1.7%  (1+p 2 )  z = 3.1 cm

Muon identification can be done by the Muon Counter for the charged track with momentum of great than 0.55 GeV/c dE/dx TOF

  (3770) data sample ~18 pb -1 data taken at GeV ~7 pb -1 data taken at the region from GeV to GeV ~8 pb -1 data taken in the energy region from to GeV The total Luminosity is about 33 pb -1.

Near DD-bar production threshold region π–π– With the singly tagged D sample, we can do some absolute measurements e+e+ e-e- D D K+K+ π–π– tag D+D+ D-D- π–π– e-e- e+e+ D D K+K+ Singly tagged D sample  Absolute Measurements

Semileptonic D Decays (1) e+e+ e-e- D tag D+D+ D-D- π-π- K+K+ π-π- e+e+ e-e- D D0D0 π-π- K+K+ D D

Motivation Isospin conservation requires From PDG Br It is called “Longstanding puzzle” in Charm decay ! Is isospin conservation held in the D semileptonic decays? Recently: BES-II published on Phys. Let. B608(2005)24-30 CLEO-c contributed paper at LP05 reports: Solved the puzzle in Charm decays !

CKM matrix elements & Form factors & Branching fractions * * * Motivation From PDG04 Br

Charged track photon <0.08 m & |z| < 0.2 m > 0.1 GeV Good track selection Charged track with good helix fit To be consistent with originating from the primary events vertex Vxy <0.02 m & |z| < 0.2 m

Singly tagged modes,,,,,,,, PID made by combining TOF, dE/dx & BSC information CL > 0.1% ; : > CL K : CL prob (, n )> 0.1%, n = 1, 2, 3 Singly tagged D sample 1C kinematic fit (mKnπ),,, (Throughout the talk, charge conjugation is implied.)

Invariant mass distribution for tags 9 modes

Candidate modes, π: K : ; μ :μ : selection  Double-tagged D decays (1) e+e+ e-e- D D tag D+D+ D-D- π-π- K+K+ π-π- Missing energy and momentum Should be around zero N γ =0 (on recoil side of the D tag) (or Nhit > 2 on μ counter) Combined TOF, dE/dx & BSC information

data Bckgrd DD-bar MC Data (subtracted bck)

Distribution of the Inv. masses of combinations for the events for which the and are observed in the recoil side Preliminary

Branching fraction Experiment BES MARKIII E687(93) E687(95) PDG 04 Results An up limit at 90% C.L is set to be <0.89% Preliminary hep-ex/ &

BES MARK IIIPDG04  Ratio of partial width Obtained based on the branching fractions quoted from PDG04 Preliminary The ratio of Br. for D 0 decays to K(π)μν is:

Semileptonic D Decays (2) e+e+ e-e- D tag D+D+ D-D- π-π- K+K+ π-π- e+e+ e-e- D D0D0 π-π- K+K+ D D

Motivation There are some controversies on the relative rates of charm vector (K * ) semileptonic decay to charm pseudoscalar (K) semileptonic decay.  Some theorist expected and MARKIII measured the rate to be.  But other theoretical predictions and experimental measurements tend to support a smaller rate.

Candidate modes π: K : e :e : selection  Combined TOF and dE/dx information e+e+ e-e- D D tag D+D+ D-D- π-π- K+K+ π-π- Missing energy and momentum Should be around zero Double-tagged D decays (2) Combined TOF, dE/dx & BSC information KS0:KS0: νeνe

MC DATA U miss.vs.D - tags Signal region Umiss (GeV) 3σ3σ MC data

Events found in REC. of Dtag

Results: Published in Eur. Phys. J. C47 (2006) 31

Results: With the measured branching fractions in this work and quoted from BES-II earlier work, we obtain: Published in Eur. Phys. J. C47 (2006) 31

Comparison uncertainty of theoretical prediction

Inclusive Decay Branching Fractions for e+e+ e-e- D tag D+D+ D-D- π-π- K+K+ π-π- e+e+ e-e- D D0D0 π-π- K+K+ D D X X=any particles K–K– π+π+ π –

Motivation  Serving as a check on the sum of the branching fractions for the exclusive D decay.  Providing information about the relative strength of Cabibbo-favored and Cabibbo suppressed D decays.

Candidate modes π: K :  Combined TOF and dE/dx information Double-tagged D decays KS0:KS0: e+e+ e-e- D tag D+D+ D-D- π-π- K+K+ π-π- D X=any particles K–K– π+π+ e+e+ D0D0 D X π – e-e- The Kπ with maximum CL(K)CL(π) retained in an event

Neutral K * Decay of D: (mKnπ) Mass GeV/c 2 3σ3σ 3σ3σ 3σ3σ signal region (M D ±3σ) sideband region outside M D ±4σ K–π+K–π+

D 0 signal region D 0 sideband K + π – K –π+K –π+ Cabibbo favored decay Cabibbo suppressed decay K –π+K –π+ K + π – D – signal region D – sideband

Results Cabibbo favored decay: Cabibbo suppressed decay: Published in PLB625 (2005) 196

Neutral K decay of D: Charged K * Decay of D: e+e+ e-e- D tag D0D0 K+K+ D X π – π + π – KS0KS0 Removing double counting with sideband background. 3σ3σ

D 0 signal region D 0 sideband D + signal region D + sideband π + π – Preliminary

D 0 signal region D 0 sideband K S 0 π – K S 0 π + Preliminary Mass(GeV/c 2 ) D – signal region D – sideband

Results Cabibbo favored decay: Cabibbo suppressed decay (at 90% C.L.): The results submitted to PLB

Comparison

BES measured semileptonic D decay branching fractions . The ratio of branching fractions is Summary Ratio of partial width BES MARK IIIPDG04 . Preliminary hep-ex/ &

Summary . Measured semileptonic D decay branching fractions With the measured branching fractions in this work and quoted from BES-II earlier work, we obtain: . Published in Eur. Phys. J. C47 (2006) 31

Summary . Measured branching fractions for inclusive Cabibbo favored and suppressed decays of D mesons: Cabibbo favored decay: Cabibbo suppressed decay: Published in PLB 625(2005)196

Summary Cabibbo favored decay: Cabibbo suppressed decay (at 90% C.L.): Branching fractions of inclusive neutral K decay of D . The results submitted to PLB

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