3,387 research outputs found
Weak Decays of Doubly Heavy Baryons: the case
Very recently, the LHCb collaboration has observed in the final state
a resonant structure that is identified as the
doubly-charmed baryon . Inspired by this observation, we
investigate the weak decays of doubly heavy baryons ,
, , ,
, , ,
and and focus on the decays into spin
baryons in this paper. At the quark level these decay processes are induced by
the or transitions, and the two spectator quarks can be
viewed as a scalar or axial vector diquark. We first derive the hadronic form
factors for these transitions in the light-front approach and then apply them
to predict the partial widths for the semi-leptonic and non-leptonic decays of
doubly heavy baryons. We find that a number of decay channels are sizable and
can be examined in future measurements at experimental facilities like LHC,
Belle II and CEPC.Comment: 40 pages, 4 figures, to appear in EPJ
Resummation prediction on top quark transverse momentum distribution at large pT
We study the factorization and resummation of t-channel top quark transverse
momentum distribution at large pT in the SM at both the Tevatron and the LHC
with soft-collinear effective theory. The cross section in the threshold region
can be factorized into a convolution of hard, jet and soft functions. In
particular, we first calculate the NLO soft functions for this process, and
give a RG improved cross section by evolving the different functions to a
common scale. Our results show that the resummation effects increase the NLO
results by about 9%-13% and 4%-9% when the top quark pT is larger than 50 and
70 GeV at the Tevatron and the 8 TeV LHC, respectively. Also, we discuss the
scale independence of the cross section analytically, and show how to choose
the proper scales at which the perturbative expansion can converge fast.Comment: 32 pages, 10 figures, version published in Phys.Rev.
The Importance of Proper Renormalization Scale-Setting for Testing QCD at Colliders
A primary problem for perturbative QCD analyses is how to set the
renormalization scale of the QCD running coupling in order to achieve maximally
precise fixed-order predictions for physical observables. The Principle of
Maximum Conformality (PMC) eliminates the ambiguities associated with the
conventional renormalization scale-setting procedure, giving predictions which
are independent of the choice of renormalization scheme. The scales of the QCD
couplings and the effective number of quark flavors are set order by order in
the pQCD series. The PMC has a solid theoretical foundation, satisfying the
standard renormalization group invariance and all of the the self-consistency
conditions derived from the renormalization group......In this brief report, we
summarize the results of our recent PMC applications for a number of collider
processes, emphasizing their generality and applicability....... These results
demonstrate that the application of the PMC systematically eliminates a major
theoretical uncertainty for pQCD predictions, thus increasing the sensitivity
of the colliders to possible new physics beyond the Standard Model.Comment: 10 pages, 4 figures. The title has been changed. This review,
submitted to Frontiers of Physics, is based on a contribution by S.J.B. at
the Conference {\it Workshop on Physics at a Future High Intensity Collider @
2-7 GeV in China} Hefei, China January 14-16, 201
Time-reversal-symmetry-broken quantum spin Hall effect
Quantum spin Hall (QSH) state of matter is usually considered to be protected
by time-reversal (TR) symmetry. We investigate the fate of the QSH effect in
the presence of the Rashba spin-orbit coupling and an exchange field, which
break both inversion and TR symmetries. It is found that the QSH state
characterized by nonzero spin Chern numbers persists when the
TR symmetry is broken. A topological phase transition from the TR
symmetry-broken QSH phase to a quantum anomalous Hall phase occurs at a
critical exchange field, where the bulk band gap just closes. It is also shown
that the transition from the TR symmetry-broken QSH phase to an ordinary
insulator state can not happen without closing the band gap.Comment: 5 pages, 5 figure
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