Outline

Charm Physics Potentialat BESIIICharm Physics Potentialat BESIII

Kanglin HeKanglin He

Jan. 2004, BeijingJan. 2004, Beijing

hekl@ihep.ac.cnhekl@ihep.ac.cn

OutlineOutline

Charm physics at threshold

Absolute Branching Ratio

Leptonic Decay and Decay Constant

Semileptonic Decay and CKM Matrix

Physics Beyond Standard Model

D0D0 Mixing

CP violation

Rare Charm Decay

Summary

Charm Physics at ThresholdCharm Physics at Threshold

Charm threshold

D physics @3.77GeV

Ds physics @4.03GeV and @4.14GeV

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 andEvent Number for 1 yr runningCharm Cross Section andEvent Number for 1 yr running

Physics

C.M.S (GeV)

Peak Lum.

1033cm-2s-1

cross section

(nb)

EventNumber

3.77

1.0

~25M

4.03

0.6

~0.32

~1M

4.14

0.6

~0.67

~2M

Absolute Branching RatioAbsolute Branching Ratio

Precision of Br(D0→Kπ), Br(D+ →Kππ),Br(Ds→φπ) are normalization constants for

Precision D, Ds physics

Precision B physics

Precision of Br(D0→Kπ), Br(D+ →Kππ) ,Br(Ds→φπ) are needed for

Decay constants

Precision of CKM elements

Model independent measurements at BESIII

Tagging Technology(1)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 MassTagging Technology(2) Beam Constrain Mass

D+→Kππ ModeD+→Kππ Mode

GeV/c2

Tagging Technology(3)Kinematic constrain for Double tagsTagging Technology(3)Kinematic constrain for Double tags

D+ Double Tags

D0 Double Tags

80 pb-1 Monte Carlo DATA @3.77GeV

Number of observed double tagsin 5fp-1 Ds Data at 4.03GeVNumber of observed double tagsin 5fp-1 Ds Data at 4.03GeV

~7000 double tags

Tagging Technology(4)Tagging Technology(4)

Number of expected double tags

Number of expected single tags

Combining the single tags and double tags

Precision ofAbsolute Branching RatioPrecision ofAbsolute Branching Ratio

Now

BESIII

D0→Kπ

~2.4%

<1%

D+→Kππ

~6.6%

<1%

Ds→φπ

~25%

<2%

Improvement after BESIII

Leptonic Decay andDecay ConstantLeptonic Decay andDecay Constant

Measurement of Decay constantsat BESIIIMeasurement of Decay constantsat 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

 |Vcd|, |Vcs|

Theory→ extract |Vtd|, |Vts|

Analysis TechniqueAnalysis 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 fDsMeasurement of fDs

Precision of fD(s) (1)Precision of fD(s) (1)

Major

Uncertainty

Precision of fD(s) (2)Precision of fD(s) (2)

Great improvement after BESIII

Semileptonic decay andCKM MatrixSemileptonic decay andCKM Matrix

D(s)

Form

Factor

Measurement of CKMat BESIIIMeasurement of CKMat BESIII

Good performance of BESIII detector

e/π/μ identification

mass resolution

Extract |Vcd|, |Vcs|

Form factor shape and normalization

Γ(q2) describe the contribution of form factor, itwas calculated from lattice QCD.

 The shape of form factor are helpful to theory.

Extract the ratio of |Vcd/Vcs|

Extract |Vub| from B physics →Theory

Analysis TechniqueAnalysis Technique

Hadronic tag

PID

Umiss

Signal

Background

(GeV/c)

Precision of Branching Ratioof D0, D+ Semileptonic DecayPrecision of Branching Ratioof D0, D+ Semileptonic Decay

Precision

Now

BESIII

D0→Klν

~4.4%

<1%

D0→πlν

~17%

<2%

D+→Klν

~12%

<2%

Precision of CKMPrecision of CKM

Form factor term ΔΓ/Γ，come from theory (LatticeQCD). Supposing ΔΓ/Γ ~3% , BESIII will get

Form FactorsForm Factors

From semileptonic decay of charm meson,dN/dq2 will provide information on form factors

(under studying)

Physics Beyond Standard ModelPhysics Beyond Standard Model

D0D0 Mixing at ψ(3770)

In SM, mixing is very small(10-6).

BESIII is sensitive to 10-4

Possible to measure the phase shift

CP violation in charm decays

SM predicts the ACP may be as big as 10-3.

BESIII is sensitive to ACP >10-2

Rare Charm Decay

D0D0 MixingD0D0 Mixing

D0 decays as D0

Separate Mixing from DCS

Mixing Phenomenology(1)Mixing Phenomenology(1)

Like the K0K0 mixing, constructing DS and DL

Experimental SituationExperimental Situation

0.1

0.2

-0.1

0.1

x and y are in the orders of 10-2─10-1

Mixing Phenomenology(2)Mixing Phenomenology(2)

DCS

Mixing

Measuring the Asymmetry ofCP eigenstate

(K+K-(+), Ksρ0(-) …)

Supposing CP violation is small

Possible to measure the phase shift

Mixing at ψ(3770)Mixing at ψ(3770)

The D0 and D0 are produced coherently inJPC=1-- state

DCSD (Double Cabbibo Suppressed Decay)contribution is 0 at ψ(3770)

D0 produced ~at rest, cannot measure ΔΓ (y)directly by using lifetime difference

Useful for measuring rD

Experimental Searching forD0D0 MixingExperimental Searching forD0D0 Mixing

Big challenge to PID (Kπchannel)

Main backgrounds come from the doublemiss-PID

Searching in semi-leptonic decay modesare experimental difficulty with 2 missingneutrino (hard to reduce backgroundcontribution to 10-4)

Monte Carlo study with different PID(TOF resolution)

Detection efficiency vsTOF resolutionDetection efficiency vsTOF resolution

Background rates vsTOF resolutionBackground rates vsTOF resolution

Probing New Physics to rD~10-4

The detection efficiency is ~40%, ~20K eventswith D0→K+π- are expected to be found in 5fb-1ψ(3770) data

The background contamination rate is0.1─0.5x10-4 while the TOF resolution variesfrom 65ps to 100ps

BESIII is sensitive to 10-4 for the mixing rate ifthe TOF resolution is designed to be around100ps.

CP Violation at ψ(3770)CP Violation at ψ(3770)

Suppose Both D0 decay to CPeigenstate f1 and f2 .

Any oberservations of

CP(f1)=CP(f2) at ψ(3770) are thedirect evidence of CP Violation

Several hundreds events with 100% CP eigenstatewill be found in 5fb-1 ψ(3770) data. The sensitivity ofdirect CP violation is ACP~10-2─10-1

Rare Charm DecayRare Charm Decay

The Up limit for most modes listed above

are estimated in the range of 10-6─10-5,will update PDG data.

Summary BESIII contributes to charm physics onSummary BESIII contributes to charm physics on

Precision absolute branching ratio of charmmesons (<1% for D, <2% for Ds)

Precision decay constants (2~3%)

Precision CKM Matrix (<2%)

Sensitive to rD~10-4 for mixing

Sensitive to ACP~10-2─10-1 for CP violation

Set the up limit of branching ratio for most rarecharm decays to 10-6─10-5 range

And more, more,……

Comparison of BES3, CLEO-c and B-factoriesOn Charm physics topicsComparison of BES3, CLEO-c and B-factoriesOn Charm physics topics

Measurement

B-factories

CLEO-c

BES3

—2004

1yr

(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 Error

Sys.

Stat.

* D/Ds cross section over estimated by a factor of 2this number need confirming

Thank you !Thank you !

谢谢谢谢