arXiv subjects

Bin Gong

Publications and source records attributed to Bin Gong.

35 records · Page 2Linked to original sources

arXiv2020

The complete study on polarization of $Υ(nS)$ hadroproduction at QCD next-to-leading order

Applying the nonrelativistic quantum chromodynamics factorization formalism to the $Υ(1S,2S,3S)$ hadroproduction, a complete analysis on the polarization parameters $λ_θ$, $λ_{θϕ}$, $λ_ϕ$ for the production are presented at QCD next-to-leading order. With the long-distance matrix elements extracted from experimental data for the production rate and polarization parameter $λ_θ$ of $Υ$ hadroproduction, our results provide a good description for the measured parameters $λ_{θϕ}$ and $λ_ϕ$ in both the helicity and the Collins-Soper frames. In our calculations the frame invariant parameter $\tildeλ$ is consistent in the two frames. Finally, it is pointed out that there are discrepancies for $\tildeλ$ between available experimental data and corresponding theoretical predictions.

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arXiv2019

Perturbative QCD for $J/ψ$ Inclusive Production Via Initial State Radiation at $e^+e^-$ collider

Up to the next-leading order (NLO) of quantum chromodynamics (QCD), the process $e^+e^-\to J/ψ+X$ with the center-of-mass (CM) energy range from 3.7 to 10.6 GeV is calculated. At 10.6 GeV, the results is consistent with the experiment results at the Belle. However, the predictions are much smaller than the measurement at BESIII at low CM energy range from 3.7 to 4.6 GeV. This indicates that the convergence of QCD perturbative expansion becomes worse as the CM energy becomes lower and closer to the inclusive $J/ψ$ production threshold. For a further study of the QCD mechanism on $J/ψ$ production at $e^+e^-$ collider with different CM energy, the initial state radiation effect of $e^+e^-\to J/ψ+gg$ and $e^+e^-\to J/ψ+c \bar{c}$ are calculated at the QCD NLO. The results are plotted and the numbers of events for different CM energy bins are provided for the designed SuperKEKB. This provides a method to precisely test the validity of perturbative prediction on $J/ψ$ production in future measurements.

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arXiv2018

The remaining parts for the long-standing J/psi polarization puzzle

Based on the non-relativistic quantum chromodynamics factorization formalism, the polarization parameters $λ_{θϕ}$ and $λ_ϕ$ of $J/ψ$ hadroproduction are analyzed in helicity frame and calculated at QCD next-to-leading order for the first time. For prompt $J/ψ$ production, we take into account the feeddown contributions from $χ_{cJ}$ and $ψ(2S)$ decays. The theoretical predictions for the polarization parameters $λ_{θϕ}$ and $λ_ϕ$ of $J/ψ$ are presented. With the theoretical results we have done the fit to the experimental measurements on yield and polarization for $J/ψ$ hadroproduction simultaneously, and found that the results are coincide with the experimental measurements at the LHC quite well.

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arXiv2015

An Updated Study for $Υ$ Production and Polarization at the Tevatron and LHC

Following the nonrelativistic QCD factorization scheme, by taking latest available measurement on $χ_b(3P)$ into consideration, we present an updated study on the yield and polarization of $Υ(1S,2S,3S)$ hadroproduction, and the fractions of $χ_b(mP)$ feed-down in $Υ(nS)$ production at QCD next-to-leading order. In the fitting, three schemes are applied with different choice of $χ_b(mP)$ feed-down ratios and NRQCD factorization scale. The results can explain the measurements on yield very well as in our previous work. The polarization puzzle to $Υ(3S)$ is now solved by considering the $χ_b(3P)$ feed-down contributions. The ratio of $σ[χ_{b2}(1P)]/σ[χ_{b1}(1P)]$ measurements from CMS can also be reproduced in our prediction. Among the different schemes, the results show little difference, but there are sizeable difference for the fitted long-distance color-octet matrix elements. It may bring large uncertainty when the values are applied in other experiments such as in $ee,~ep$ colliders.

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arXiv2014

Complete next-to-leading-order study on the yield and polarization of Upsilon(1S,2S,3S) at the Tevatron and LHC

Based on nonrelativistic QCD factorization scheme, we present the first complete next-to-leading order study on the yield and polarization of Upsilon(1S,2S,3S) hadroproduction. By using the color-octet long-distance matrix elements obtained from fits of the experimental measurements on Upsilon yield and polarization at the Tevatron and LHC, our results can explain the measurements on the yield very well, and for the polarizations of Upsilon(1S,2S,3S), they are in (good, good, bad) agreement with recent CMS measurement, but still have some distance from the CDF measurement.

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arXiv2013

Polarization for Prompt J/psi, psi(2s) production at the Tevatron and LHC

Based on nonrelativistic QCD, we present the first complete next-to-leading order study on the polarization of prompt J/psi hadroproduction by including feeddown from chi_c(^3P_J^1,^3S_1^8) and psi(2s) which turn out to be a very important part. By using the color-octet long-distance matrix elements obtained from a combined fit of the differential cross section measurements at the Tevatron and LHC for J/psi, psi(2s) and chi_c with p_t>7GeV, the prompt J/psi polarization predictions are presented, and the results are in agree with the CDF Run-I data (except two points), but in conflict with the CDF Run-II data, while are close to the ALICE data (inclusive J/psi) at LHC. The experimental measurements at the LHC are strongly expected to clarify the situation.

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arXiv2012

Next-to-leading-order QCD corrections to the yields and polarisations of J/Psi and Upsilon directly produced in association with a Z boson at the LHC

We update the study of the production of direct J/Psi in association with a Z boson at the Next-to-Leading Order (NLO) in alpha_s by evaluating both the yield differential in P_T and the J/Psi polarisation in the QCD-based Colour-Singlet Model (CSM). Contrary to an earlier claim, QCD corrections at small and mid P_T are small if one assumes that the factorisation and the renormalisation scales are commensurate with the Z boson mass. As it can be anticipated, the t-channel gluon-exchange (t-CGE) topologies start to be dominant only for P_T > mZ/2. The polarisation pattern is not altered by the QCD corrections. This is thus far the first quarkonium-production process where this is observed in the CSM. Along the same lines, our predictions for direct Upsilon+Z are also given.

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arXiv2011

Testing the QCD fragmentation mechanism on heavy quarkonium production at LHC

We calculate the fragmentation function for charm quark into J/psi at the QCD next-to-leading-order (NLO) and find that the produced J/psi is of larger momentum fraction than it is at the leading-order. Based on the fragmentation function and partonic processes calculated at the NLO, the transverse momentum distribution on J/psi hadroproduction associated with a charm c (or \bar{c}) jet are predicted. We find that the distribution is enhanced by a factor of 2.0--3.3 at the NLO as p_t increased from 10 GeV to 100 GeV and it is measurable at the LHC with charm tagger. The measurement at the LHC will supply a first chance to directly test the QCD fragmentation mechanism on heavy quarkonium production where the fragmentation function is calculable in perturbative QCD. It is also applied to J/psi (Upsilon) production in the decay of Z^0 (top quark).

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arXiv2010

QCD corrections to J/psi production via color octet states at Tevatron and LHC

The remarkable discrepancy between theory and data on the p_t distribution of J/psi polarization in the process pp -> J/psi+X has been standing as a puzzle for a long time. Our early work indicates that if only considering the color-singlet state, NLO corrections may drastically change the distribution, but are not sufficient to accommodate the data. The color-octet intermediate state was suggested to make up the gap. Therefore a direct motivation is to evaluate if the NLO corrections to the J/psi production via a color-octet can indeed remedy the problem. Unfortunately, our results show that even the NLO corrections to both color-singlet and octet states are accounted, the data cannot be understood yet in the framework of the present theory, but there, as observed, still a small window remains, namely a P-wave octet might substantially contribute.

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arXiv2010

QCD corrections to Upsilon production via color-octet states at the Tevatron and LHC

The NLO QCD corrections to Upsilon production via S-wave color-octet states Upsilon(^1S_0^8,^3S_1^8) at the Tevatron and LHC is calculated. The K factors of total cross section (ratio of NLO to LO) are 1.313 and 1.379 for Upsilon(^1S_0^8) and Upsilon(^3S_1^8) at the Tevatron, while at the LHC they are 1.044 and 1.182, respectively. By fitting the experimental data from the D0, the matrix elements for S-wave color-octet states are obtained. And new predictions for Upsilon production are presented. The prediction for the polarization of inclusive Upsilon contains large uncertainty rising from the polarization of Upsilon from feed-down of chi_b. To further clarify the situation, new measurements on the production and polarization for direct Upsilon are expected.

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arXiv2009

Next-to-Leading-Order QCD Corrections to e+ e- --> J/psi c c_bar at the B Factories

We calculate the next-to-leading-order (NLO) QCD correction to $e^+e^-\to J/ψc \bar{c}$ at the B factories, and present theoretical predictions on the momentum and production angular distribution for $J/ψ$ production, and momentum distribution for $J/ψ$ polarization at NLO for the first time. By applying Brodsky, Lepage and Mackenzie scale setting for the renormalization scale, it is found that the QCD perturbative expansion is significantly improved with the unique scale choice $μ^*=1.65$GeV. Together with the $ψ^\prime$ feed-down contribution, the total cross section and momentum distribution can account for the recent experimental measurement by the Belle collaboration. The total cross section and momentum distribution are also found to be consistent with the experimental measurement in the previous study on $e^+e^-\to J/ψgg$. However, the production angular distribution of $J/ψ$ production for either the $J/ψc\bar{c}$ or the $J/ψgg$ channel has a quite different shape in contrast with the new experimental data, although it fits with the experimental data when the two channels are added together. This situation is difficult to explain. To clarify the puzzle of $J/ψ$ polarization, further experimental measurements are strongly expected to testify our predictions on the momentum distribution for $J/ψ$ polarization. Our total cross section agrees with that given in the previous study of Zhang and Chao by using their renormalization scheme and input parameters.

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arXiv2009

Next-to-Leading-Order QCD Corrections to e^ + e^- -> J/ψ+gg at the B Factories

We calculate the next-to-leading-order (NLO) QCD corrections to $e^+e^-\to J/ψg g$ via color singlet $J/ψ(^3{-0.8mm}S_1)$ at the B factories. The result shows that the cross section is enhanced to $0.373\pb$ by a K factor (NLO/LO) of about 1.21. By considering its dependence on the charm quark mass and renormalization scale, the NLO cross section can range from 0.294 to $0.409\pb$. Further including the $ψ^\prime$ feed-down, $σ(e^+e^-\to \jpsi X(\mathrm{non} c\bar{c}))$ is enhanced by another factor of about 1.29 and reaches $0.482\pb$. In addition, the momentum distributions of $J/ψ$ production and polarization are presented. Recent measurements from Belle agree well with our prediction for the cross section and momentum distribution. It is expected that this process can serve as a very good channel to clarify the $J/ψ$ polarization puzzle by performing further experimental measurements.

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arXiv2008

Exclusive $eta_b$ decay to double $J/ψ$ at next-to-leading order in $alpha_s$

Within the nonrelativistic QCD (NRQCD) factorization framework, we calculate the exclusive decay process η_b \to J/ψJ/ψto next-to-leading order in the strong coupling constant, while at leading order in charm quark relative velocity. It is found that this new contribution to the amplitude is comparable in magnitude with the previously calculated relativistic correction piece, but differs by a phase about 90^\circ. Including this new contribution will increase the previous prediction to B(η_b \to J/ψJ/ψ) substantially, thus brightening the discovery potential of this clean hadronic decay channel of η_b in the forthcoming LHC experiment.

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arXiv2008

QCD corrections to polarization of J/ψand Υat Fermilab Tevatron and CERN LHC

In this work, we present more detail of the calculation on the NLO QCD corrections to polarization of direct J/psi production via color singlet at Tevatron and LHC, as well as the results for Upsilon for the first time. Our results show that the J/psi polarization status drastically changes from transverse polarization dominant at LO into longitudinal polarization dominant in the whole range of the transverse momentum $p_t$ of J/psi when the NLO corrections are counted. For Upsilon production, the p_t distribution of the polarization status behaves almost the same as that for J/psi except that the NLO result is transverse polarization at small p_t range. Although the theoretical evaluation predicts a larger longitudinal polarization than the measured value at Tevatron, it may provide a solution towards the previous large discrepancy for J/psi and Upsilon polarization between theoretical predication and experimental measurement, and suggests that the next important step is to calculate the NLO corrections to hadronproduction of color octet state J/psi^(8) and Upsilon^(8). Our calculations are performed in two ways, namely we do and do not analytically sum over the polarizations, and then check them with each other.

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arXiv2008

QCD corrections to double J/ψproduction in e+e- annihilation at \sqrt{s}=10.6 GeV

Next-to-Leading-Order(NLO) QCD corrections to double J/psi production in e^+e^- annihilation at sqrt{s}=10.6 GeV are calculated. We find that they greatly decrease the cross section, with a K factor (NLO/LO) ranging from -0.31 to 0.25 depending on the renormalization scale. Although the renormalization scale dependence indicates a large uncertainty, when combined with the NLO QCD corrections to J/psi + eta_c production, it can explain why the double J/psi$ production could not be found at B factories while the J/psi + eta_c production could, despite the fact that cross section of the former is larger than that of the latter at LO by a factor of 1.8.

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arXiv2008

QCD corrections to J/psi plus eta_c production in e+e- annihilation at sqrt{s}=10.6 GeV

Next-to-Leading-Order(NLO) QCD corrections to J/jpsi plus eta_c production in e+e- annihilation at sqrt{s}=10.6 GeV is calculated in this paper, and an analytic result is obtained. By choosing proper physical parameters, a K factor (ratio of NLO to LO) of about 2, which is in agreement with the result in Ref.\cite{Zhang:2005ch}, is obtained. Our results show that the Next-Next-to-Leading-Order(NNLO) corrections might be quite large. The plot of the K-factor vs the center-of-mass energy sqrt{s} shows that it is more difficult to obtain a convergent result from the perturbative QCD without resummation of ln(s/m_c) terms as the sqrt{s} becomes larger.

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arXiv2008

QCD corrections to J/psi polarization of hadronproduction at Tevatron and LHC

The next to leading order (NLO) QCD corrections to J/psi polarization of hadronproduction at Tevatron and LHC are calculated. The results show that the J/psi polarization is extremely changed from more transversal polarization at leading order (LO) into more longitudinal polarization at NLO. Although it gives more longitudinal polarization than the recent experimental result on the J/psi polarization at Tevatron. It sheds light on the solution to the large discrepancy of J/psi polarization between theoretical predication and experimental measurement, and suggests that the next important step is to calculate the NLO correction for color octet state J/psi^{(8)} hadronproduction. Our calculations are performed in two ways where the polarizations are summed analytically or not, and they are checked with each other. It also gives a K factor for total cross section (ratio of NLO to LO) of about 2 and shows that the NLO corrections boost the J/psi production for about 2 order of magnitude in high transverse momentum p_t region of J/psi, which confirms the calculation by Campbell, Maltoni and Tramontano.

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