International Journal of Modern Physics A

BESIII is a high precision, general purpose detector for the high luminosity e⁺e^- collider, BEPCII, running at the tau-charm energy region. Its design and current status of construction is presented.

The role of charm in testing the Standard Model description of quark mixing and CP violation through measurements of lifetimes, decay constants and semileptonic form factors is reviewed. Together with Lattice QCD, charm has the potential this decade to maximize the sensitivity of the entire flavor physics program to new physics and pave the way for understanding physics beyond the Standard Model at the LHC in the coming decade. The status of indirect searches for physics beyond the Standard Model through charm mixing, CP-violation and rare decays is also reported.

Detailed studies of weak charm decays fill an important future role in high energy physics. Chief among them are: (i) validating the theoretical control achieved over hadronization as a worthwhile goal in its own right; (ii) calibrating our tools to saturate the discovery potential for New Physics in B decays; (iii) searching for New Physics in charm decays through hypothesis-generating research. The most promising area for the last item is a comprehensive study of CP violation. Since we need a new CP paradigm to implement baryogenesis, this is not an idle goal. Charm decays provide opportunities unique among up-type quarks. While items (i) and (ii) will be addressed in a meaningful way and hopefully completed in the next few years, item (iii) will presumably require statistics that can be accumulated only by LHCb and a Super-B factory.

From analysis of the data collected with the BES-II detector at the BEPC Collider at the energies around the peak of ψ(3770) resonance and below the threshold, BES Collaboration have measured the cross sections for e⁺e^- → hadrons, the corss section for e⁺e^- → ψ(3770), the parameters of ψ(2S) and ψ(3770) resonances, the branching fractions for , D⁺D^-, , non , the leptonic branching fractions for ψ(2S) → e⁺e^- and ψ(3770) → e⁺e^-, and the R_uds in the energy region from 3.660 to 3.872 GeV. With these data BES also searched for some non- decays of ψ(3770). In this paper we report some results on these measurements.

The CLEO-c experiment at the CESR e⁺e^- storage ring has collected data with E_cm = 3.77 GeV and E_cm ~ 4.17 GeV to study the decays of charmed mesons. This paper discusses results on the hadronic branching fractions of the D⁰, D⁺, and .

Based on the data sample of 33 pb^-1 collected at and around 3.773 GeV with the BESII detector at the BEPC collider, the absolute branching fractions for some exclusive semileptonic decays and inclusive decays of D mesons have been measured. With the measured branching fractions, the ratio of the two partial widths of the decays D⁰ → K^-μ⁺ν_μ and is determined to be 0.87 ± 0.24 ± 0.15, which supports that the isospin conversation holds in the exclusive semimuonic decays of D⁰ and D^- mesons. The ratio of the vector to pseudoscalar semileptonic decay rates is determined to be 0.57 ± 0.17 ± 0.02.

Recent results relating to charm baryon and meson decays from the Belle and BABAR experiments are presented. In addition to recent observations for charm hyperons, evidence for a new charm baryon state, the Λ_c(2940), observed in its decay to D⁰p is also reported. No evidence for doubly charmed baryons is seen in e⁺e^- interactions. A measurement of the spin of the Ω^- hyperon is made using decays of the and baryons. On the assumption that the spin of the parent baryons are J = 1/2, the assignment J = 3/2 is confirmed and both J = 1/2 and also higher spins are excluded. New results on rare, Cabibbo-suppressed decays of charm mesons are also presented.

We report measurements of the branching fractions for the leptonic decays D⁺ → μ⁺ν_μ and from the CLEO-c experiment. From these measurements we extract the decay constants and f_Ds = 280.1 ± 11.6 ± 6.0 MeV.

We present a study of D⁰ decaying to K^-ℓ⁺ν and π^-ℓ⁺ν final states using a 282 fb^-1 data sample collected by the Belle experiment at the KEKB e⁺e^- collider. The D⁰ flavor and momentum are tagged through a full reconstruction of the recoiling charm meson and additional mesons from fragmentation. The reconstruction method provides very good resolution in neutrino momentum and in q² = (p_ℓ + p_ν)². Normalizing to the total number of D⁰ tags, we measure the absolute branching fractions to be and and the semi-leptonic form factors (within the modified pole model) and .

Because of the quantum correlation between the pair-produced D⁰ and from the decay of the ψ(3770), the time-integrated single and double tag decay rates depend on charm mixing amplitudes, doubly-Cabibbo-suppressed amplitudes, and the relative strong phase δ between D⁰ and decays to identical final states. Using 281 pb^-1 collected with the CLEO-c detector on the ψ(3770) resonance, we measure the absolute branching fractions of D⁰ decays to hadronic flavored states, CP eigenstates, and semileptonic final states to determine the relative strong phase cos δ and to limit the mixing amplitude y.

We report the recent results of mixing and CP violation studies in D⁰ decays from Belle, which include the time-dependent measurements of D⁰ wrong-sign semileptonic decay, wrong-sign hadronic decay to K⁺π^-, as well as the wrong-sign ratio of hadronic decays to K⁺π^-n(π).

We present a preliminary search for mixing using the decays D⁰ → K⁺π^-π⁰, additionally presenting Dalitz-plot distributions and a measurement of the branching ratio for this mode. A new tagging technique is used to produce the doubly Cabibbo-suppressed Dalitz plot, which in turn is used to motivate the method used for the D-mixing search. We analyze 230.4 fb^-1 of data collected from the BABAR detector at the PEP-II collider. Assuming CP conservation, we find R_M < 0.054% with 95% confidence, and we estimate that the data are consistent with no mixing at a 4.5% confidence level. We present D-mixing results both with and without the assumption of CP conservation.

Recent results from leptonic and semi-leptonic charm decays at the BABARB–factory are presented. The measurement of f_Ds from the channel is presented. Form-factor studies from the channel are described along with a search for flavor-changing neutral-current decays.

Heavy flavor baryons are attractive systems for testing effective theories for weak lifetime and decay systematics. Recently, new experimental results have mitigated one historic problem in the weak lifetime systematics and continued another. The charm baryon system continues to show new high mass, narrow states well isolated from one another. The spectroscopy of these states will challenge new advances in lattice gauge theoretic calculations of baryon structure. Double charm baryons still are seen only by SELEX, which showed a new candidate. High-sensitivity searches by BELLE and BaBar show only featureless background.

The fragmentation functions of D⁰, D^±, , D*^o, D*^± and at are measured with a data set of 102.7 fb^-1. Fragmentation model parametrizations (Peterson, Kartvelishvili, Collins-Spiller, Lund, and Bowler models) are compared to the data. The data at high x≃1 indicate a contribution of non-perturbative QCD processes.

Identifying a zero-range exchange of vector mesons as the driving force for the s-wave scattering of pseudo-scalar mesons off the baryon ground states, a rich spectrum of hadronic nuclei is formed. We argue that chiral symmetry and large-N_c considerations determine that part of the interaction which generates the spectrum. We suggest the existence of strongly bound crypto-exotic baryons, which contain a charm-anti-charm pair. Such states are narrow since they can decay only via OZI-violating processes.

Dalitz analyses are introduced as the method for studying hadronic decays. An accurate description of hadron final states is critical not only to an understanding of the strong coupling regime of QCD, but also to the precision extraction of CKM matrix elements. The relation of such final state interactions to scattering processes is discussed.

Dalitz plot analyses of D⁰ events reconstructed for the hadronic decay and are presented here. The analyses are based on a data sample of 91.5 fb^-1. All data have been collected with the BABAR detector at the PEP-II asymmetric-energy e⁺e^- storage rings at SLAC running at center-of-mass energies on and 40 MeV below the ϒ(4S) resonance.

In this conference presentation I discuss CLEO-c opportunities in Dalitz plot analyzes with the data samples available now and projected by the end of CESR-c run. Using 281 pb^-1 of e⁺e^- collisions at mass of ψ(3770) we present results of the Dalitz plot analysis of D⁺ → π^-π⁺π⁺. Using the CLEO-c and CLEO III samples of 5 pb^-1, accrued at mass of ψ(2S), we study three body decays of χ_cJ produced in the radiative decay ψ(2S) → γχ_cJ, where J=0,1,2. A clear signal from at least one of χ_cJ is found in eight final states: π⁺π^-η, π⁺π^-η′, K⁺K^-π⁰, , ηK⁺K^-, , , and . For these modes we measured or set an upper limit on the branching fraction. A Dalitz plot analysis is performed on three modes χ_c1 → π⁺π^-η, K⁺K^-π⁰, and .

We discuss the scalar meson mixing scenario and present an OZI rule violation mechanism for understanding the scalar productions in charmoium hadronic decays. We stress that the OZI violation could play a key role in disentangling the structure of the scalars: f₀(1370), f₀(1500) and f₀(1710).

The search for the ground state scalar glueball G₀ is reviewed. Spin zero glueballs will have unique dynamical properties if the amplitude is suppressed by chiral symmetry, as it is to all orders in perturbation theory: for instance, mixing of G₀ with mesons would be suppressed, radiative Ψ decay would be a filter for new physics in the spin zero channel, and the decay could be enhanced relative to G₀ → ππ. These properties are consistent with the identification of f₀(1710) as the largely unmixed ground state scalar glueball, while recent BES data implies that f₀(1500) does not contain the dominant glueball admixture. Three hypotheses are discussed: that G₀ is 1) predominantly f₀(1500) or 2) predominantly f₀(1710) or 3) is strongly mixed between f₀(1500) and f₀(1710).

Results of high statistic two-photon collisions at Belle are presented. Only process is included in this report, here could be π⁺π^-, K⁺K^-, , , , or . Measurements of for charmonia resonance states are listed. A new χ′_c2 candidate in has been identified as a spin-2 (helicity-2) object. Cross section and production angle distributions are measured and compared with various QCD calculations.

Some recent progresses in our understanding of penta-quark components in baryons is briefly reviewed. The diquark cluster picture for the penta-quark components in baryons gives a natural explanation not only to the empirical indications for a positive strangeness magnetic moment μ_s and positive strangeness radius of the proton but also the longstanding mass-reverse problem of N*(1535), N*(1440) and Λ*(1405) resonances as well as the unusual decay pattern of the N*(1535) resonance. Evidence supporting this picture from available BES data on J/ψ decays is pointed out.

The results of pentaquark searches at the B-factories are reviewed. No pentaquark signal has been seen; the resulting bounds (on pentaquark production rates, branching fractions, and widths) vary in strength, and in their relationship to positive results from other experiments.

BaBar has measured with unprecedented accuracy from the threshold up to , finding out an unexpected cross section, with plateaux and drops. In particular it is well established a sharp drop near threshold, where evidence for structures in multihadronic channels has also been found. Other unexpected and spectacular features of the Nucleon form factors are reminded, the behaviour of space-like and the neutron time-like form factors.

The subject of determining the significance of observations in particle physics is discussed. Several dangers are identified, all related to the problem of knowing the sampling probability distribution. Techniques for mitigating these pitfalls are presented.

In this contribution I review some recent developments in charmonium spectroscopy, and discuss related theoretical predictions. The spectrum of states, strong decays of states above open charm threshold, electromagnetic transitions, and issues related to the recent discoveries of the "XYZ" states are discussed. Contributions that BES can make to our understanding of charmonium and related states are stressed in particular.

Belle and BaBar have recently reported observations of meson states that decay to final states containing a c and -quark but with properties that do not match well to those expected for any of the as-yet unassigned charmonium meson states. Among the suggested interpretations for these states are meson-antimeson molecular states, diquark-antidiquark tetraquarks and/or -gluon hybrid mesona. I briefly review what is experimentally known about these states and comment on the status of recent attempts to classify them.

New and recent results are presented on charm and charmonium spectroscopy from BABAR experiment at SLAC. In particular, measurements on D_sJ states branching fractions have been performed both in B-decays and inclusive interactions. Here a search for D_sj(2632) has been performed and a new D_sJ state at a mass of 2.856 GeV/c² has been observed. A search for Y(4260) has been performed in exclusive production from initial-state radiation.

Recent lattice QCD results on charmonium properties are reviewed. I comment on molecules and hybrid states as well as on future studies of states near strong decay thresholds.

In the 90s of the last century high statistics experiments with fully equipped 4π detectors have lead to a better insight in the spectrum of hadrons. In particular the finding of crypto-exotic and J^PC exotic states tremendously improved the experimental situation in meson spectroscopy. All this was possible only with sophisticated analysis methods like the decomposition of measured phase-space distribution into partial waves and to express the partial waves in terms of complicated dynamical functions. This paper acts as an appetizer and gives an introduction about the concepts and formalisms involved.

We review the theoretical and experimental evidence for the candidacy of the , and the for charmed tetraquarks. We briefly review the 't Hooft interaction's influence on the single-charm (C=1) tetraquark mass spectrum: its consequences for other observed mesons such as the , as well as its predictions of the (thus far) unobserved exotic tetraquark states. In particular we show that the near mass degeneracy of and was naturally predicted by the tetraquark model with 't Hooft interaction, and thus may constitute the first "smoking gun" evidence for tetraquark existence. A short outlook of possible future research directions is given.

Based on 14 M ψ′ events, systematic studies have been make for hadronic decays, which are conerned with 12% rule test, phase analysis and form factor measurement. All these studies are helpful for understanding the decay dynamics in charmonium region.

Based on 14M ψ′ events collected by BESII detector, the decays of χ_cJ into the final states π⁺π^-K⁺K^-, , 2(K⁺K^-), , ηπ⁺π^- and are studied. The branching fractions of these decays or intermediate states involved are reported. These results shed light on the understanding of scalar meson properties and the χ_cJ decay mechanisms.

Latest experimental results, obtained from the ψ(2S) data, collected with the CLEO detector are reviewed.

Precise measurements of the τ lepton properties provide stringent tests of the Standard Model structure and accurate determinations of its parameters. We overview the present status of a few selected topics: lepton universality, QCD tests and the determination of α_s, m_s and |V_us| from hadronic τ decays, and lepton flavor violation phenomena.

Some recent τ-physics results are presented from the BaBar and Belle experiments at the SLAC and KEK B factories, which produce copious numbers of τ-lepton pairs. Measurements of the tau mass and lifetime allow to test lepton universality and CPT invariance, while searches for lepton-flavour violation in tau decays are powerful ways to look for physics beyond the Standard Model. In semihadronic, non-strange tau decays, the vector hadronic final state is particularly important in helping determine the hadronic corrections to the anomalous magnetic moment of the muon, while studies of strange final states are the best available ways to measure the CKM matrix element V_us and the mass of the strange quark.

The presentation summarizes the excellent experimental conditions for tau physics at a tau-charm factory. A rough overview of the physics potential is given.

The motivation most often cited in searches for mixing and CP-violation in charm system lies with the possibility of observing a signal from New Physics which dominates that from the Standard Model. We review recent theoretical predictions and experimental constraints on mixing parameters, concentrating on possible effects of New Physics.