Constraints on the decay rates of quarkonium

We derive inequalities between the leptonic decay rates of 1S and 2S states of quarkonium, when the binding potential is an increasing concave (convex) function of the inter-quark distance in a framework where some relativistic corrections have been made to the Van Royen-Weisskopf formula for these rates. Experimental decay rates of the γ and γ′ rule out the convex increasing potential.     

Radiative corrections to the light muonic atoms decay rate

Radiative corrections to the decay rate in low-Z hydrogen-like muonic atoms are considered. The correction is due to the Uehling potential and it has the relative order of α. The numerical results are reported for the 2p → 1s transition for atoms with nuclear charge up to Z = 10.     

The 3 gluon decay of quarkonium

We discuss the process $$e^ + e^ - \to Q\bar Q \to 3gluons \to 3jets$$ with attention to the kinematics and observability of the jets. We also show how to check the gluon spin through jet or hadron angular distributions. Gluon flavor can be checked by looking for quantum number correlations between opposite jets. We predict that correlations exist off resonance for \(e^ + e^ - \to q\bar q\) , but not on resonance for \(Q\bar Q \to 3g\) .     

Lepton decay channels of egret gluinos at the LHC

Prospects for observing a SUSY-like signal from two gluinos are investigated within a certain region of the mSUGRA parameter space, where the cross section of the two gluino production in pp collisions at the LHC ( = 14 TeV) via gluon-gluon fusion (gg → ) is estimated at a rather high level of 17.3 pb. In this so-called EGRET region, the lightest stable neutralinos can serve as cold dark matter particles and are natural explanations of the excess of diffuse galactic gamma rays observed by the EGRET space apparatus. The -event selection relies on a very clear signature when decay products of each gluino contain one b-anti-b pair, one or two lepton-antilepton pair(s) and a neutralino. Rather high transverse-missing energy, carried away by the two neutralinos, is an essential signature of the events and also allows the relevant Standard Model background to be reduced significantly. In particular, it was found that the clear signatures of the selected processes demonstrate good prospects discovering the EGRET gluinos at the LHC. Furthermore, these signatures allow one to distinguish different mSUGRA parameters m _1/2 inside the EGRET region. The text was submitted by the authors in English.     

Heavy quarkonium in vector and scalar channels

We study quarkonium in hot QCD, emphasizing its nature as a short-lived transient with an exponentially decaying wave function. The heavy quark mass allows for a nonrelativistic expansion around the two-quark threshold, and the static potential is then seen to contain a temperature-dependent imaginary part, which leads to an unstable quark-antiquark state. We solve the corresponding Schrödinger equation and estimate the spectral functions in different channels. In particular, through careful evaluation we find a peak also in the scalar channel, although it is strongly suppressed with respect to the vector channel peak. We also plot the dilepton production rate, which shows a peak-like structure even at temperatures so high that the peak in the spectral function has disappeared.     

Hadron multiplicities in the presence of light gluinos

We consider the effect of a massless gluino on the evolution of a parton shower. The hadron multiplicity distribution is predicted to evolve as a function of the collider energy in the same way as in the absence of gluinos, except for a slower running of _s. A comparison of the predicted average hadron multiplicity with experimental data is presented as a fit constraining the values of the strong coupling constant at the Z⁰ peak _s(m_Z) and the scale of the onset of hadronizationm ₀. It appears that light gluinos are unlikely to be detected this way with less than 500 GeV of centre of mass energy.     

Radiative decay of neutrino and primordial nucleosynthesis

Radiative decay of massive unstable neutrinos is examined in detail. Constraints on their mass and lifetime are established by solving the networks of nucleosynthesis and calculating the spectra of high-energy photons produced by massive neutrino decay. It is found that primordial nucleosynthesis sets stringent constraints on the mass and the lifetime of massive unstable neutrinos. According to these constraints together with constraints derived from other cosmological consideration and laboratory experiments, radiative decay of massive τ neutrinos is not allowed except for the case that the mass and the lifetime of the τ neutrino satisfy rather strict constraints; 30 MeV ≲ m_ντ ≲ 70 MeV, 10² s ≲ τ_ντ ≲ 10⁴ s. Constraints on neutrinos in the 4th generation are also derived.     

Exclusive decay of 1 heavy quarkonium into photon and two pions

We study the exclusive decay of 1⁻⁻ heavy quarkonium into one photon and two pions in the kinematic region, where the two-pion system has a invariant mass which is much smaller than the mass of heavy quarkonium. Neglecting effects suppressed by the inverse of the heavy quark mass, the decay amplitude can be factorized, in which the nonperturbative effect related to heavy quarkonium is represented by a non-relativistic QCD matrix element, and that related to the two pions is represented by a distribution amplitude of two gluons in the isoscalar pion pair. By taking the asymptotic form for the distribution amplitude and by using chiral perturbative theory we are able to obtain numerical predictions for the decay. Numerical results show that the decay of J/ψ can be observed at BEPC and at CESR. Experiment observation of this process in this kinematic region at BEPC and CESR can provide information about how gluons are converted into the two pions and may supply a unique approach to study I=0 s-wave ππ scattering.     

Soft photon spectrum in orthopositronium and vector quarkonium decays

QED gauge invariance, when combined with analyticity, leads to constraints on the low energy end of the emitted photon spectra. This is known as Low's theorem. It is shown that the Ore–Powell result, as well as further developments for the orthopositronium differential decay rate, are in contradiction with Low's theorem, i.e., that their predicted soft photon spectra are incorrect.A solution to this problem is presented. The implications for the orthopositronium lifetime puzzle, the charmonium ρ–π puzzle, the prompt photon spectrum in inclusive quarkonium decays and the extraction of α_S from quarkonium annihilation rates are briefly commented.