$eta_c$ production at LHC and indications on the understanding of $J/psi$ production

We present a complete evaluation for the prompt $eta_c$ production at the LHC at next-to-leading order in $alpha_s$ in nonrelativistic QCD. By assuming heavy quark spin symmetry, the recently observed $eta_c$ production data by LHCb results in a very strong constraint on the upper bound of the color-octet long distance matrix element $1S0$ of $J/psi$. We find this upper bound is consistent with our previous study of the $J/psi$ yield and polarization and can give good descriptions for the measurements, but inconsistent with some other theoretical estimates. This may provide important information for understanding the nonrelativistic QCD factorization formulism.

Impact of $J/psi$ pair production at the LHC and predictions in nonrelativistic QCD

For $J/psi$ pair production at hadron colliders, we present the full next-to-leading order (NLO) calculations with the color-singlet channel in nonrelativistic QCD. We find that the NLO result can reasonably well describe the LHCb measured cross section, but exhibits very different behaviors from the CMS data in the transverse momentum distribution and mass distribution of $J/psi$ pair. Moreover, by adding contributions of gluon fragmentation and quark fragmentation, which occur at even higher order in $alpha_s$, it is still unable to reduce the big differences. In particular, the observed flat distribution in the large invariant mass region is hard to explain. New processes or mechanisms are needed to understand the CMS data for $J/psi$ pair production.

X(3872) and its production at hadron colliders

We evaluate the production cross sections of $X(3872)$ at the LHC and Tevatron at NLO in $alpha_s$ in NRQCD by assuming that the short-distance production proceeds dominantly through its $chi_{c1}$ component in our $chi_{c1}mbox{-}D^0bar{D}^{*0}$ mixing model for $X(3872)$. The outcomes of the fits to the CMS $p_T$ distribution can well account for the recent ATLAS data in a much larger range of transverse momenta ($10~mbox{GeV}<p_T<70~mbox{GeV}$), and the CDF total cross section data, and are also consistent with the value of $k=Z_{cbar c}cdot Br(Xto J/psipi^+pi^-)$ constrained by the $B$-meson decay data. %It can also well describe the behavior of the CDF $psi(2S)$ data, which show a strong %resemblance to that of the X(3872). For LHCb the predicted X(3872) total cross section is larger than the data by a factor of 2, which is due to the problem of the fixed-order NRQCD calculation that may not be applicable for the region with small $p_T$ ($p_Tsim 5 ~mbox{GeV}$) and large forward rapidity $(2.5<y<4.5)$. In comparison, the prediction of molecule production mechanism for $X(3872)$ is inconsistent with both $p_T$ distributions and total cross sections of CMS and ATLAS, and the total cross section of CDF.