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1. chinaXiv:201609.01035 [pdf]

Next-to-next-to-leading-order QCD corrections to $\chi_c0,2\rightarrow \gamma\gamma$

Wen-Long Sang; Feng Feng; Yu Jia; Shuang-Ran Liang
Subjects: Physics >> Nuclear Physics

We calculate the next-to-next-to-leading-order (NNLO) perturbative corrections to?P-wave quarkonia annihilation decay to two photons, in the framework of nonrelativistic QCD (NRQCD) factorization. The order-α2s?short-distance coefficients associated with each helicity amplitude are presented in a semi-analytic form, including the "light-by-light" contributions. With substantial NNLO corrections, we find disquieting discrepancy when confronting our state-of-the-art predictions with the latest \textsf{BESIII} measurements, especially fail to account for the measured?χc2→γγwidth. Incorporating the effects of spin-dependent forces would even exacerbate the situation, since it lifts the degeneracy between the nonperturbative NRQCD matrix elements of?χc0?and?χc2?toward the wrong direction. We also present the order-α2s?predictions to?χb0,2→γγ, which await the future experimental test.

submitted time 2016-09-14 Hits1560Downloads841 Comment 0

2. chinaXiv:201609.00930 [pdf]

Can NRQCD Explain the $\gamma\gamma^* \to \eta_c$ Transition Form Factor Data?

Feng Feng; Yu Jia; Wen-Long Sang
Subjects: Physics >> Nuclear Physics

Unlike the bewildering situation in the?γγ?→π?form factor, a widespread view is that perturbative QCD can decently account for the recent \textsc{BaBar} measurement of?γγ?→ηc?transition form factor. The next-to-next-to-leading order (NNLO) perturbative correction to the?γγ?→ηc,b?form factor, is investigated in the NRQCD factorization framework for the first time. As a byproduct, we obtain by far the most precise order-α2s?NRQCD matching coefficient for the?ηc,b→γγ?process. After including the substantial negative order-α2s?correction, the good agreement between NRQCD prediction and the measured?γγ?→ηc?form factor is completely ruined over a wide range of momentum transfer squared. This eminent discrepancy casts some doubts on the applicability of NRQCD approach to hard exclusive reactions involving charmonium.

submitted time 2016-09-13 Hits1481Downloads864 Comment 0

3. chinaXiv:201605.01180 [pdf]

Structural and Functional Characterization of Acinetobacter baumannii Nucleoside Diphosphate Kinase

Hu Ying-Song; Feng Feng; Liu Ying-Fang; Hu Ying-Song
Subjects: Biology >> Biophysics >> Biochemistry & Molecular Biology

A cinetobacter baumannii is a new threat in intensive care units (ICUs) for its multiresistance to antibiotics, but little is known about this bacterium. Nucleoside diphosphate kinase (NDK) is an evolutionarily conserved enzyme that catalyzes phosphoryl transformation between nucleosides. In our study, the crystal structure of wild type A cinetobacter baumannii NDK along with its mutant generated through truncation of the C-terminal arginine-threonine-arginine (RTR) residues, were solved. In comparison with Myxococcus xanthus NDK structure, we speculated that A cinetobacter baumannii NDK shared a similar catalytic mechanism with Myxococcus xanthus. Activity assay and CD spectra analysis revealed that E28A mutant might interrupt the secondary structure of the protein leading to declined enzymatic activity. Truncation of the C-terminal RTR residues would lead to the instability of the tertiary structure resulting in reduced kinase activity. Lys33 was a key residue for maintaining dimer interaction when RTR residues were truncated but was not sufficient to keep efficient enzymatic reaction. The structural data can provide a potential target to develop novel therapeutic approaches to overcome multiresistance of the bacterium against antibiotics.

submitted time 2016-05-11 Hits972Downloads476 Comment 0

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