Physical Program of Tau-charm Factory V.P.Druzhinin, Budker INP, Novosibirsk

Processes at tau-charm factory  D DsDs 

Main topics  Physics of charmonia  Light hadron spectroscopy  Open charm hadrons  Physics of  -lepton

Current and future experiments CLEO-CBES-III/ year  -charm/year J/  10  10 9  100  (2S) 54 pb   10 9  (3770) 818 pb -1 5  10 6 D-pair3  GeV586 pb -1 7  10 5 D s -pair2  10 6 ++ 4   10 7 B-Factories produced about charmed hadrons and 10 9  -pairs

Charmonium Vector states: J/    (2S)   (3770)  2  10 9 Higher  ’s  10 8 In decays:  c (1S),  cJ  h c  10 8 (  (2S)  h c  0 ) Comprehensive study of charmonium decays

Charmonium states above open charm threshold Recently observed new charmonium states:  C + : X(3872), X(3940), Y(3940), Z(3930)  cJ (2P),  c (3S) ? Study of radiative decays of  (4040),  (4160),  (4415). Search for hadronic transition  X,Y,Z  1 -- : X(4260),Y(4361),Y(4664)  (e + e -  X)  50 pb. Scan of energy region GeV with integrated luminosity 100 fb -1

Rare J/  decay Number of J/  ’s   Weak decays: J/  D s (*) l, D s *+  -, D s +   B  (3-4)   SM for  S=0 weak decays: J/  D 0  0, D 0  0 B  Probe for New Physics, FCNC c  u transition.  cc  ss transition with W exchange: C-parity violation decay J/ , B   Search for NP in Lepton Flavor Violation decays J/  l + l  B(  -  - e + e - ) < 2.7  (5  10 8  pairs)  B(J/  +  - )< (2-6)  o CP-violation in J/  decays: 3 and more body decays to construct CP-odd observables or 2 body decays with polarization measurement, J/ .

Light meson spectroscopy Low-lying charmonium states decay into light hadrons with relatively small multiplicity Choosing specific cc-meson decay mode one can study states with practically any quantum numbers Example: B(J/    )=0.5%  5  10 9 tagged   mesons. Recently CLEO performed precise measurement of   mass and observed decay    3 . Search for glueballs (gg) and hybrids (qqg)

Search for glueballs and hybrids o Lattice QCD predicts glueball spectrum o Glueball states mix with ordinary mesons o Detailed study of the meson properties in different reactions and decay modes Scalar glueball  (f 0,a 0,K 0 * ) family J/  f 0,  f 0,  f 0,  a 0, K * K 0 *  f 0,a 0 For decays into PP,VP,VV,V   Lowest mass hybrid meson has exotic quantum numbers 1 -+  Its mass is expected in the range GeV  Two possible candidates  1 (1400),  1 (1600) in   N  1  N reaction  S-wave decay  c1  1, P-wave decay J/  1

D-mesons Three types of D-mesons: D  (cd), D 0 (du), D s  (ds) Maximum cross section for D-pair production D J states can be produced in reactions e + e   D (*) D J with  1 nb (4.3-5 GeV) Tau-charm factory can produce 6  10 9 D-pairs and 10 9 D s pairs per year. B-factories  charmed hadrons

Advantages of near threshold production Particle multiplicity at 3.77 GeV is about two times lower than at 10.6 GeV Two body production e + e -  DD. This allows to use double tag method: fully reconstruct one D then either fully reconstruct the other D (absolute branching ratios) or look for events with one missing particle (leptonic, semileptonic decays) Coherent production of D pairs allows to use quantum correlations for D-meson mixing and CP violation studies

Leptonic and semileptonic decays Measurement decay constants and form factors. Improve understanding of hadronization mechanisms. Validation of lattice QCD. With improved theoretical input  determination Vcs and Vcd. Important for B-physics  extracting Vub from semileptonic B decay. Current lattice values: f D =207  4 MeV f Ds =241  3 MeV Experiment (CLEO): f D =206  9 MeV f Ds =270  8 MeV Tau-charm factory can provide measurement of the decay constants with accuracy better than 0.5%.

Semileptonic decays o.5% accuracy of BF10 6 events

D-mixing at tau-charm factory Only time integrated measurements Study of quantum correlations in e + e -  D 0 D 0 (  0 ) (C-odd) and e + e -  D 0 D* 0  D 0 D 0  (C-even) At  (3770) R M =(x 2 +y 2 )/2 can be measured using the ratios For 10 9 D-pairs about 150 events will be detected. Sensitivity to R M is about 5  10 -6

D-mixing at C-tau factory Probabilities of inclusive decays are proportional to (1  y). S + or S - are CP-even or CP-odd final states. For 10 9 D-pairs sensitivity for y is about 8  Fit of the inclusive and exclusive rates for decays of DDbar system into different final states allows to determine x, y, r f and  f. Expected sensitivity to mixing parameters: 1 ab -1 at tau-charm factory = 10 ab -1 at Super B-factory

Search for CP-violation Direct CP violation in D decays is expected to be small in SM. For CF and DCS decays direct CP violation requires New Physics. Exception: D   K S,L   with A CP =3.3  For Singly Cabibbo Suppressed (SCS) decays SM CPV could reach Best limits: Belle: D 0  K + K -,  +  - A CP (K + K - )=(0.43  0.30  0.11)% A CP (  +  - )=(0.43  0.52  0.12)% CLEO: D +  K S  +, K S  +  0 A CP (K S  + )=(-0.6  1.0  0.3)% A CP (K S  +  0 )=(0.3  0.9  0.3)% At Tau-charm factory CP asymmetry can be tested with sensitivity for many final states.

Search for CP-violation CV violation in mixing: With 10 9 D-pairs about 30 (K + e - )(K + e - ) events will be detected. |q/p| can be measured with 6% accuracy. Current value is 0.86  0.16 Use of quantum correlations: At  (3770) : f1 and f 2 are CP eigenstates of the same CP-parity. The decay D 0 D 0  f 1 f 2 is forbidden by CP-invariance. The rate is proportional to difference CP-breaking parameters for f 1 and f D pairs  difference between  +  - and K + K - final states. Similar approach can be used for final states with different CP-parities in e + e -  D 0 D o  reaction.

Search for CP-violation For C-odd D 0 D 0 state CPV in mixing does not contribute to asymmetry, for C-even state it contributes with twice intensity. For multibody final states the analysis of Dalitz plots and T-odd moments distribution can increase sensitivity to CPV effects. Tau-charm factory can provide sensitivity for CPV in D-decays Using quantum correlations allows to separate contributions from direct CPV and CPV in mixing

Rare D decay Flavor Changing Neutral Current (c  u l + l - ) D 0  +  - SM ~ NP CDF B< 4.3  D  X u l + l - SM ~10 -6 NP D0 B(D +  +  +  - )< 3.9  CLEO B(D +  + e + e - )< 7.4  Lepton Flavor Violation NP BABAR B(D 0  + e - ) <0.81  BABAR B(D +  + e +  - ) <1.1  C-tau factory can provide sensitivity

Rare D decay SM: short distance B(c  ull)~10 -8 long distance B(D  ll )  New physics can introduce new particles into loop B  10 -6

 -physics  -pairs ▫B-factories  10 9 ▫Super-B ~ 5   Special run near threshold ▫2E=3.55 GeV,  =0.1 nb, N  =10 8 ▫  ’s are produced at rest  kinematic constraint for hadronic decay  very clean data sample ▫Non-  background measured below threshold

Physical goals High precision measurement BF and structure function for hadronic decays ▫e /  /  /K  lepton universality ▫  s ▫m s,V us Study of Lorentz structure of leptonic decay ▫Lepton energy spectrum  4 Michel parameters, two depend on  polarization  Polarized initial beam  Measured via decay of second  : 

LFV decays Super-B, 75 ab -1 7   -pairs  decay Current best limit: 4.5  by Belle with 5  10 8  At Y(4S): ISR background from e+e-  +  -  Upper Limit  1/  L tau-charm factory with  has similar or better sensitivity

Search of CP-violation in  decays CP-violation  new physics, charged Higgs Two amplitudes with different weak and strong phases  -  K S  -, A CP =3   -  K -  0 Observables ▫Rate asymmetry:  (  +  f + )-  (  -  f  )~sin  sin  ▫Modified rate asymmetry ~sin  sin  ▫Triple product asymmetry  (p 1  p 2 )~cos  sin  For complete description of matrix element, polarization and direction of  should be known ▫Threshold production – low statistics ▫Polarization may increase sensitivity by several times

Polarization Michel parameters CP-violation in  -decays ▫Increase sensitivity by several times ? ▫Decrease luminosity ?

Tau-charm physics Charmonia  Spectroscopy, BFs  Light hadron spectroscopy  J/  rare decays  … Charm  Spectroscopy  (Semi)leptonic decays  Rare decays  Mixing  CP violaton  … Tau  Spectral functions, BFs  Lorentz structure  CP violation  LFV decays  … Charm baryons  BFs  Semileptonic decays  …