arXiv subjects

Yu Jia

Publications and source records attributed to Yu Jia.

139 records · Page 8Linked to original sources

arXiv2007

Hunting eta_b through radiative decay into J/psi

We propose that the radiative decay process, η_b\to J/ψγ, may serve as a clean searching mode for η_b in hadron collision facilities. By a perturbative QCD calculation, we estimate the corresponding branching ratio to be of order 10^{-7}. Though very suppressed, this radiative decay channel in fact has larger branching ratio than the hadronic decay process η_b\to J/ψJ/ψ, which was previously hoped to be a viable mode for ferreting out η_b in Tevatron Run 2. The discovery potential of η_b through this channel seems promising in the forthcoming LHC experiments and maybe even in Tevatron Run 2, thanks to the huge statistics of η_b to be accumulated in these experiments. The same calculational scheme is also used to estimate the branching ratios for the processes η_b (η_c) \to ϕγ.

hep-ph↗

arXiv2006

Variational Study of Weakly Coupled Triply Heavy Baryons

Baryons made of three heavy quarks become weakly coupled, when all the quarks are sufficiently heavy such that the typical momentum transfer is much larger than Lambda_QCD. We use variational method to estimate masses of the lowest-lying bcc, ccc, bbb and bbc states by assuming they are Coulomb bound states. Our predictions for these states are systematically lower than those made long ago by Bjorken.

hep-ph↗

arXiv2006

Model-independent Study of Magnetic Dipole Transitions in Quarkonium

We study magnetic dipole (M1) transitions between two quarkonia in the framework of non-relativistic effective field theories of QCD. Relativistic corrections of relative order v^2 are investigated in a systematic fashion. Non-perturbative corrections due to color-octet effects are considered for the first time and shown to vanish at leading order. Exact, all order expressions for the relevant 1/m and 1/m^2 operators are derived. The results allow us to scrutinize several potential model claims. In particular, we show that QCD excludes both contributions to the anomalous magnetic moment of the quarkonium induced by low-energy fluctuations and contributions to the magnetic dipole operators of the type induced by a scalar potential. Finally, we apply our results to the transitions J/psi -> eta_c gamma, Upsilon(1S) -> eta_b gamma, Upsilon(2S) -> eta_b(2S) gamma, Upsilon(2S) -> eta_b gamma, eta_b(2S) -> Upsilon(1S) gamma, h_b(1P) -> chi_{b0,1}(1P) gamma and chi_{b2}(1P) -> h_b(1P) gamma by assuming these quarkonium states in the weak-coupling regime. Our analysis shows that the J/psi -> eta_c gamma width is consistent with a weak-coupling treatment of the charmonium ground state, while such a treatment for the hindered transition Upsilon(2S) -> eta_b gamma appears difficult to accommodate within the CLEO III upper limit.

hep-ph↗

arXiv2006

Model-independent Study on Magnetic Dipole Transition in Heavy Quarkonium

Some new results on magnetic dipole (M1) transitions in heavy quarkonium from nonrelativistic effective field theories of QCD are briefly reported. This model-independent approach not only facilitates a systematic and lucid way to investigate the relativistic corrections, it also clarifies some inconsistent treatment in previous potential model approach. The impact of our formalism on J/Psi -> eta_c gamma, Upsilon(Upsilon') -> eta_b gamma and h_c -> chi_{c0} gamma are discussed.

hep-ph↗

arXiv2004

Short-range Interaction and Nonrelativistic Phi**4 Theory in Various Dimensions

We employ the effective field theory method to systematically study the short-range interaction in two-body sector in 2, 3 and 4 spacetime dimensions, respectively. The phi**4 theory is taken as a specific example and matched onto the nonrelativistic effective theory to one loop level. An exact, Lorentz-invariant expression for the S-wave amplitude is presented, from which the nonperturbative information can be easily extracted. We pay particular attention to the renormalization group analysis in the 3 dimensions, and show that relativistic effects qualitatively change the renormalization group flow of higher-dimensional operators. There is one ancient claim that triviality of the 4-dimensional phi**4 theory can be substantiated in the nonrelativistic limit. We illustrate that this assertion arises from treating the interaction between two nonrelativistic particles as literally zero-range, which is incompatible with the Uncertainty Principle. The S-wave effective range in this theory is identified to be approximately 16/3pi times the Compton wavelength.

hep-th↗

arXiv2003

Heavy-quark recombination in Z^0 decay

We briefly review the recent advances of heavy-quark recombination mechanism. This mechanism predicts a class of power-suppressed 3-jet events in $Z^0$ decay, such as $b\bar{b}q$ and $b\bar{b}\bar{q}$. Furthermore, heavy quark fragmentation function also receives a contribution from this mechanism. Some light can be shed on the scaling of the maximum of the fragmentation function for S-wave heavy hadrons. We finally comment on a new variant of this mechanism which has important impact on the precision electroweak physics.

hep-ph↗

arXiv2003

A New QCD Correction to Gauge Boson Decay into Heavy Flavor

We find that, at order alpha_s, the partial width of Z^0 to heavy flavors receives a power correction from a novel QCD mechanism, which is not suppressed by inverse powers of M_Z, but only by two unknown O(\lambdaqcd/m) constants. The hadronic W width also receives a similar correction. These parameters may be fitted from the global electroweak analysis, and consequently the Standard Model predictions of various electroweak observables will be updated. This new mechanism is of no help to reconcile the discrepancy in b forward-backward asymmetry. We also point out the implication of this mechanism to heavy flavor production in other collider experiments.

hep-ph↗

arXiv2003

Anomalous 3-jet and Heavy Quark Fragmentation

Heavy hadron production in $e^+e^-$ annihilation is studied in the framework of heavy-quark recombination mechanism. This mechanism predicts a new type of 3-jet event such as $b\bar{b}q$ or $b\bar{b}\bar{q}$, which is power-suppressed relative to the standard $b\bar{b}g$ event. Furthermore, heavy quark fragmentation function also receives a contribution from this mechanism, which is {\it calculable} in perturbative QCD as long as the momentum fraction $z$ is not too close to unity. We conjecture that the height of the peak of fragmentation function for S-wave heavy hadron scales as $α_s^2(m) m/\lambdaqcd$.

hep-ph↗

arXiv2003

Lambda_c^+/Lambda_c^- Asymmetry in Hadroproduction from Heavy-Quark Recombination

Asymmetries in the hadroproduction of charm particles directly probe power corrections to the QCD factorization theorems. In this paper, the heavy-quark recombination mechanism, a power correction that explains charm meson asymmetries, is extended to charm baryons. In this mechanism, a light quark participates in the hard scattering that creates a charm quark and they hadronize together into a charm baryon. This provides a natural and economical explanation for the Λ_c^+/Λ_c^- asymmetries measured in πN and p N collisions.

hep-ph↗

arXiv2002

Charm-Anticharm Asymmetries in Photoproduction from Heavy-Quark Recombination

The asymmetries between charm and anticharm mesons observed in fixed-target photoproduction experiments are an order of magnitude larger than the asymmetries predicted by conventional perturbative QCD. We show that these charm meson asymmetries can be explained by a heavy-quark recombination mechanism for heavy meson production. In this process, a charm quark combines with a light antiquark from the hard-scattering process and they subsequently hadronize into a state including the charm meson. This recombination mechanism can be calculated within perturbative QCD up to some nonperturbative constants. After using symmetries of QCD to reduce the number of free parameters to two, we obtain a good fit to all the data on the asymmetries for charmed mesons from the E687 and E691 experiments.

hep-ph↗

arXiv2002

B Production Asymmetries in Perturbative QCD

This paper explores a new mechanism for B production in which a b quark combines with a light parton from the hard-scattering process before hadronizing into the B hadron. This recombination mechanism can be calculated within perturbative QCD up to a few nonperturbative constants. Though suppressed at large transverse momentum by a factor Lambda_QCD m_b/p_t^2 relative to b quark fragmentation production, it can be important at large rapidities. A signature for this heavy-quark recombination mechanism in proton-antiproton colliders is the presence of rapidity asymmetries in B cross sections. Given reasonable assumptions about the size of nonperturbative parameters entering the calculation, we find that the asymmetries are only significant for rapidities larger than those currently probed by collider experiments.

hep-ph↗

arXiv2002

The Leading Particle Effect from Heavy-Quark Recombination

The leading particle effect in charm hadroproduction is an enhancement of the cross section for a charmed hadron D in the forward direction of the beam when the beam hadron has a valence parton in common with the D. The large D+/D- asymmetry observed by the E791 experiment is an example of this phenomenon. We show that the heavy-quark recombination mechanism provides an economical explanation for this effect. In particular, the D+/D- asymmetry can be fit reasonably well using a single parameter whose value is consistent with a recent determination from charm photoproduction.

hep-ph↗

arXiv2000

Power-suppressed Thermal Effects from Heavy Particles

In quantum field theory, heavy particles with mass $M$ much greater than the temperature $T$ give not only effects suppressed by the Boltzmann factor $e^{-M/T}$, but also effects suppressed by powers of $T/M$. We show that power-suppressed terms in equilibrium observables arise from effective interactions among light particles due to virtual heavy particles. We study a model introduced by Matsumoto and Yoshimura in which study a model introduced by Matsumoto and Yoshimura in which heavy bosons interact only through a term that allows pair annihilation into light particles. We construct an effective Lagrangian for the light field by integrating out the heavy field, and use it to calculate the leading power-suppressed terms in the energy density. The thermal average of the Hamiltonian density for the heavy field includes a term proportional to $T^6/M^2$, but we show that this term can be eliminated by a field redefinition and therefore cannot have any physical significance.

hep-ph↗