Charm Physics Potential at BESIII Kanglin He Jan. 2004, Beijing

Outline  Charm physics at threshold  Absolute Branching Ratio  Leptonic Decay and Decay Constant  Semileptonic Decay and CKM Matrix  Physics Beyond Standard Model  D 0 D 0 Mixing  CP violation  Rare Charm Decay  Summary

Charm Physics at Threshold  Charm threshold  D  Ds  Why charm threshold  Pair production of charmed D and Ds mesons  With less or without background  Take the advantage of BEPCII and BESIII  Large data sample  Better mass resolution and particle identification

Charm Cross Section and Event Number for 1 yr running PhysicsC.M.S (GeV) Peak Lum cm -2 s -1 cross section (nb) Event Number D ~5~25M Ds ~0.32~1M Ds ~0.67~2M

Absolute Branching Ratio  Precision of Br(D 0 →Kπ), Br(D + →Kππ), Br(Ds→φπ) are normalization constants for  Precision D, Ds physics  Precision B physics  Precision of Br(D 0 →Kπ), Br(D + →Kππ), Br(Ds→φπ) are needed for  Decay constants  Precision of CKM elements  Model independent measurements at BESIII

Tagging Technology(1)  Pair Production of D and Ds mesons  Large Brs (1~10%) of hadronic decay modes  High tagged efficiency  ~5M D tags, >0.2M Ds tags

Tagging Technology(2) Beam Constrain Mass D + →Kππ Mode GeV/c 2

Tagging Technology(3) Kinematic constrain for Double tags D + Double Tags D 0 Double Tags 80 pb -1 Monte Carlo

Number of observed double tags in 5fp -1 Ds Data at 4.03GeV ~7000 double tags

Tagging Technology(4) Number of expected double tags Number of expected single tags Combining the single tags and double tags

Precision of Absolute Branching Ratio NowBESIII D 0 →Kπ~2.4%<1% D + →Kππ~6.6%<1% Ds→φπ~25%<2% Improvement after BESIII

Leptonic Decay and Decay Constant

Measurement of Decay constants at BESIII  Take the advantage of running at charm threshold  Pair production →Double tag method, model independent  Take the advantage of BESIII detector  High muon identification efficiency →suppress background  Take the advantage of BEPCII  Large data sample →reduce statistic error  Information on the meson wave function  Test lattice QCD  Extract CKM elements  |V cd |, |V cs |  Theory→ extract |V td |, |V ts |

Analysis Technique  Double tag measurements  Tagged D(s) with hadronic decay modes  muon identification  Absent of isolated photons  Reconstruction of missing mass square →0

Measurement of f Ds

Precision of f D(s) (1) Major Uncertainty

Precision of f D(s) (2) Great improvement after BESIII

Semileptonic decay and CKM Matrix p D(s) Form Factor

Measurement of CKM at BESIII  Good performance of BESIII detector  e/π/μ identification  mass resolution  Extract |V cd |, |V cs |  Form factor shape and normalization  Γ(q 2 ) describe the contribution of form factor, it was calculated from lattice QCD.  The shape of form factor are helpful to theory.  Extract the ratio of |V cd /V cs |  Extract |V ub | from B physics →Theory

Analysis Technique  Hadronic tag  PID  U miss Signal Background (GeV/c)

Precision of Branching Ratio of D 0, D + Semileptonic Decay PrecisionNowBESIII D 0 →K lν ~4.4%<1% D0→πlνD0→πlν ~17%<2% D + →K lν ~12%<2%

Precision of CKM Form factor term ΔΓ/Γ ， come from theory (Lattice QCD). Supposing ΔΓ/Γ ~3%, BESIII will get

Form Factors From semileptonic decay of charm meson, dN/dq 2 will provide information on form factors (under studying)

Physics Beyond Standard Model  D 0 D 0 Mixing at ψ(3770)  In SM, mixing is very small(10 -6 ).  BESIII is sensitive to  Possible to measure the phase shift  CP violation in charm decays  SM predicts the A CP may be as big as  BESIII is sensitive to A CP >10 -2  Rare Charm Decay

D 0 D 0 Mixing D 0 decays as D 0 Separate Mixing from DCS

Mixing Phenomenology(1) Like the K 0 K 0 mixing, constructing D S and D L

Experimental Situation x y x and y are in the orders of ─10 -1

Mixing Phenomenology(2) DCS Mixing CF Measuring the Asymmetry of CP eigenstate (K + K - (+), K s ρ 0 (-) …) Supposing CP violation is small Possible to measure the phase shift

Mixing at ψ(3770)  The D 0 and D 0 are produced coherently in J PC =1 -- state  DCSD (Double Cabbibo Suppressed Decay) contribution is 0 at ψ(3770)  D 0 produced ~at rest, cannot measure ΔΓ (y) directly by using lifetime difference Useful for measuring r D

Experimental Searching for D 0 D 0 Mixing  Big challenge to PID (Kπchannel)  Main backgrounds come from the double miss-PID  Searching in semi-leptonic decay modes are experimental difficulty with 2 missing neutrino (hard to reduce background contribution to )  Monte Carlo study with different PID (TOF resolution)

Detection efficiency vs TOF resolution

Background rates vs TOF resolution

Probing New Physics to r D ~10 -4  The detection efficiency is ~40%, ~20K events with D 0 →K + π - are expected to be found in 5fb -1 ψ(3770) data  The background contamination rate is 0.1─0.5x10 -4 while the TOF resolution varies from 65ps to 100ps  BESIII is sensitive to for the mixing rate if the TOF resolution is designed to be around 100ps.

CP Violation at ψ(3770) Suppose Both D 0 decay to CP eigenstate f 1 and f 2. Any oberservations of CP( f 1 )=CP( f 2 ) at ψ(3770) are the direct evidence of CP Violation Several hundreds events with 100% CP eigenstate will be found in 5fb -1 ψ(3770) data. The sensitivity of direct CP violation is A CP ~10 -2 ─10 -1

Rare Charm Decay The Up limit for most modes listed above are estimated in the range of ─10 -5, will update PDG data.

Summary BESIII contributes to charm physics on  Precision absolute branching ratio of charm mesons (<1% for D, <2% for Ds)  Precision decay constants (2~3%)  Precision CKM Matrix (<2%)  Sensitive to r D ~10 -4 for mixing  Sensitive to A CP ~10 -2 ─10 -1 for CP violation  Set the up limit of branching ratio for most rare charm decays to ─10 -5 range  And more, more,……

Comparison of BES3, CLEO-c and B-factories On Charm physics topics Measurement B-factoriesCLEO-cBES3 —20041yr (2~3)%~0.6%<1% (3~5)%~0.7%<1% (5~10)%~1.9%<2% >10%~2.3%~3% (6~9)%~1.7%~2.5% Major ErrorSys.Stat. * D/Ds cross section over estimated by a factor of 2 this number need confirming

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