arXiv subjects

Yan-Qing Ma

Publications and source records attributed to Yan-Qing Ma.

100 records · Page 6Linked to original sources

arXiv2011

QCD corrections to e^+ e^- to J/ψ(ψ(2S))+χ_{cJ} (J=0,1,2) at B Factories

We analytically calculate the cross sections of double charmonium production in $e^+ e^- \to J/ψ(ψ(2S))χ_{cJ}$ (J=0,1,2) at next-to-leading order (NLO) in $α_s$ in nonrelativistic QCD, and confirm factorization of these processes. In contrast to $χ_{c0}$ production, for which the NLO correction is large and positive, the NLO corrections for $χ_{c1,2}$ production can be negative, resulting in decreased $K$ factors of 0.91 and 0.78 for J=1 and 2 respectively when $μ= 2 m_{c}$. Consequently, the NLO QCD corrections markedly enlarge the difference between cross sections of $χ_{c0}$ and $χ_{c1,2}$. This may explain why $e^+ e^- \to J/ψ(ψ(2S))χ_{c0}$ but not $e^+ e^- \to J/ψ(ψ(2S))χ_{c1,2}$ is observed experimentally. Moreover, for $J/ψ(ψ(2S))χ_{c1,2}$, the NLO QCD corrections substantially reduce the $μ$ dependence and lead to predictions with small theoretical uncertainties.

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arXiv2011

$χ_{cJ}$ production associated with a $c\bar c$ pair at hadron colliders

$χ_{cJ}$ (J=0,1,2) production associated with a charm quark pair in hadron collisions is calculated in the framework of nonrelativistic QCD at the Tevatron and LHC. It is found that the color-singlet contribution is small and the color-octet contribution may be dominant in the large $p_T$ region. The differential cross section of $p\bar p\toχ_c+c\bar{c}$ is at least one order of magnitude smaller than the next-to-leading order result of $χ_{cJ}$ inclusive production $p\bar p\toχ_c+X$, therefore $χ_{cJ}$ production in $p\bar p\toχ_c+c\bar{c}$ may have negligible influence on the ratio $R_{χ_c}=\frac{σ_{χ_{c2}}}{σ_{χ_{c1}}}$ measured by CDF at the Tevatron. The feeddown contribution from $χ_{cJ}+c+\bar{c}$ to $J/ψ+c+\bar{c}$ is found to be large compared with $J/ψ$ direct production and may have important influence on the measurement of $J/ψ+c+\bar{c}$. The validity of fragmentation approximation for the process is also discussed.

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arXiv2011

$O(α_s v^2)$ Corrections to Hadronic and Electromagnetic Decays of $^1S_0$ Heavy Quarkonium

We study $O(α_sv^2)$ corrections to decays of $^1S_0$ heavy quarkonium into light hadrons and two photons within the framework of nonrelativistic QCD, and find these $O(α_sv^2)$ corrections to have significant contributions especially for the decay into light hadrons. With these new results, experimental measurements of the hadronic width and the $γγ$ width of $η_c$ can be described more consistently. By fitting experimental data, we find the long-distance matrix elements of $η_c$ to be $|\mathcal{R}_{η_c}(0)|^2=0.834^{+0.281}_{-0.197}\ \textrm{GeV}^3$ and $< \bm{v}^2 >_{η_c}=0.232^{+0.121}_{-0.098}$. Moreover, $η_c(2S)$ is also discussed and the $γγ$ decay width is predicted to be $3.34^{+2.06}_{-2.10}\ \textrm{KeV}$.

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arXiv2011

QCD radiative corrections to $χ_{cJ}$ production at hadron colliders

To clarify the outstanding problem in charmonium production that existing theories cannot explain the observed cross sections of $χ_{cJ}$ (J=0,1,2) and ratio $R_{χ_c}=σ_{χ_{c2}}/σ_{χ_{c1}}\approx 0.75$ (in contrast to the spin counting value 5/3) at the Tevatron, we study the complete next-to-leading order radiative corrections in nonrelativistic QCD, and find next-to-leading order contributions of $^3P_J^{[1]}$ are more important than leading order at high $p_T$, and $^3P_1^{[1]}$ decreases slower than $^3P_2^{[1]}$, implying a natural explanation for the $R_{χ_c}$ puzzle. By fitting $R_{χ_c}$, the predicted cross sections of $χ_{cJ}$ are found to agree with data. The result indicates color-octet contribution is crucially needed, thus providing a unique test for heavy quarkonium production mechanisms. Feed-down contributions of $χ_{cJ}$ to prompt $J/ψ$ production are estimated to be substantial, about $30-40%$ at $p_T=20$ GeV. Production of $χ_{cJ}$ (J=0,1,2) at the LHC is also predicted.

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arXiv2011

J/psi (psi') production at the Tevatron and LHC at O(α_s^4v^4) in nonrelativistic QCD

We present a complete evaluation for $\jpsi(\psip)$ prompt production at the Tevatron and LHC at next-to-leading order in nonrelativistic QCD, including color-singlet, color-octet, and higher charmonia feeddown contributions. The short-distance coefficients of $\pj$ at next-to-leading order are found to be larger than leading order by more than an order of magnitude but with a minus sign at high transverse momentum $p_T$. Two new linear combinations of color-octet matrix elements are obtained from the CDF data, and used to predict $\jpsi$ production at the LHC, which agrees with the CMS data. The possibility of $\sa$ dominance and the $\jpsi$ polarization puzzle are also discussed.

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arXiv2009

QCD radiative correction to color-octet $J/ψ$ inclusive production at B Factories

In nonrelativistic Quantum Chromodynamics (NRQCD), we study the next-to-leading order (NLO) QCD radiative correction to the color-octet $J/ψ$ inclusive production at B Factories. Compared with the leading-order (LO) result, the NLO QCD corrections are found to enhance the short-distance coefficients in the color-octet $J/ψ$ production $ e^+ e^-\to c \bar c (^3P_0^{(8)} {\rm or} ^3P_0^{(8)})g$ by a factor of about 1.9. Moreover, the peak at the endpoint in the $J/ψ$ energy distribution predicted at LO can be smeared by the NLO corrections, but the major color-octet contribution still comes from the large energy region of $J/ψ$. By fitting the latest data of $σ(e^{+}e^{-}\to J/ψ+X_{\mathrm{non-c\bar{c}}})$ observed by Belle, we find that the values of color-octet matrix elements are much smaller than expected earlier by using the naive velocity scaling rules or extracted from fitting experimental data with LO calculations. As the most stringent constraint by setting the color-singlet contribution to be zero in $e^{+}e^{-}\to J/ψ+X_{\mathrm{non-c\bar{c}}}$, we get an upper limit of the color-octet matrix element, $<0| {\cal O}^{J/ψ}[{}^1S_0^{(8)}]|0> + 4.0 <0| {\cal O}^{J/ψ} [{}^3P_0^{(8)}]|0>/m_c^2 <(2.0 \pm 0.6)\times 10^{-2} {\rm GeV}^3$ at NLO in $α_s$.

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arXiv2009

Relativistic Correction to J/ψProduction at Hadron Colliders

Relativistic corrections to the color-singlet J/ψhadroproduction at the Tevatron and LHC are calculated up to O(v^2) in nonrelativistic QCD (NRQCD). The short distance coefficients are obtained by matching full QCD with NRQCD results for the subprocess g+g\to J/ψ+g. The long distance matrix elements are extracted from observed J/ψhadronic and leptonic decay widths up to O}(v^2). Using the CTEQ6 parton distribution functions, we calculate the LO production cross sections and relativistic corrections for the process p+\bar{p}(p)\to J/ψ+X at the Tevatron and LHC. We find that the enhancement of O(v^2) relativistic corrections to the cross sections over a wide range of large transverse momentum p_t is negligible, only at a level of about 1 %. This tiny effect is due to the smallness of the correction to short distance coefficients and the suppression from long distance matrix elements. These results indicate that relativistic corrections can not help to resolve the large discrepancy between leading order prediction and experimental data for J/ψproduction at the Tevatron.

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arXiv2009

QCD corrections to $\bm{e^+ e^- \to J/ψg g}$ at B Factories

In heavy quarkonium production, the measured ratio $R_{c \bar c}=σ[J/ψ+ c\bar c + X]/σ[J/ψ+X]$ at B factories is much larger than existing theoretical predictions. To clarify this discrepancy, in nonrelativistic QCD (NRQCD) we find the next-to-leading-order (NLO) QCD correction to $e^+ e^- \to J/ψ+gg$ can enhance the cross section by about 20%. Together with the calculated NLO result for $e^+ e^- \to J/ψ+c\bar c$, we show that the NLO corrections can significantly improve the fit to the ratio $R_{c \bar c}$. The effects of leading logarithm resummation near the end point on the $J/ψ$ momentum distribution and total cross section are also considered. Comparison of the calculated cross section for $e^+ e^- \to J/ψ+gg$ with observed cross section for $e^+ e^- \to J/ψ+non(c\bar c)$ is expected to provide unique information on the issue of color-octet contributions.

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arXiv2009

Predictions of Light Hadronic Decays of Heavy Quarkonium 1D_2 States in NRQCD

The inclusive light hadronic decays of 1D_2 heavy quarkonia are studied within the framework of NRQCD at the leading order in $v$ and up to the order of $α_s^3$. With one-loop QCD corrections, the infrared divergences and Coulomb singularities in the decay amplitudes are proved to be absorbed by the renormalization of the matrix elements of corresponding NRQCD operators, and the infrared finite short-distance coefficients are obtained through the matching calculations. By taking the factorization scale to be 2m_Q, the light hadronic decay widths are estimated to be about 274, 4.7, and 8.8 KeV for the $η_{c2}, η_{b2}$, and $η_{b2}'$ respectively. Based on the above estimates, and using the E1 transition width and dipion transition width for the $η_{c2}$ estimated elsewhere, we get the total width of $η_{c2}$ to be about 660-810 KeV, and the branching ratio of the E1 transition $η_{c2}\toγh_c$ to be about (44-54)%, which will be useful in searching for this missing charmonium state through, e.g., the process $η_{c2}\toγh_c$ followed by $h_c\toγη_c$.

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arXiv2008

Factorization and NLO QCD correction in e^+ e^- \to J/ψ(ψ(2S))+ χ_{c0} at B Factories}

In nonrelativistic QCD (NRQCD), we study $e^+ e^- \to J/ψ(ψ(2S)) +χ_{c0}$ at $B$ factories, where the P-wave state $χ_{c0}$ is associated with an S-wave state $J/ψ$ or $ψ(2S)$. In contrast to the failure of factorization in most cases involving P-wave states, e.g. in B decays, we find that factorization holds in this process at next to leading order (NLO) in $α_s$ and leading order (LO) in $v$, where the associated S-wave state plays a crucial rule in canceling the infrared (IR) divergences. We also give some general analyses for factorization in various double charmonium production. The NLO corrections in $e^+ e^- \to J/ψ(ψ(2S)) +χ_{c0}$ at $\sqrt{s}=10.6$ GeV are found to substantially enhance the cross sections by a factor of about 2.8; hence crucially reduce the large discrepancy between theory and experiment. With $m_c=1.5{\rm GeV}$ and $μ=2m_c$, the NLO cross sections are estimated to be $17.9(11.3)$ fb for $e^+ e^- \to J/ψ(ψ(2S))+ χ_{c0}$, which reach the lower bounds of experiment.

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