Feed-down Contributions Research Articles

An updated study of ϒ production and polarization at the Tevatron and LHC**Supported by National Nature Science Foundation of China (11475183) and Youth Innovation Promotion Association of CAS (2014010)

Following the nonrelativistic QCD factorization scheme, by taking the latest available measurements of χbJ(3P) into consideration, we present an updated study on the yield and polarization of ϒ(1S, 2S, 3S) hadroproduction, and the fractions of χbJ(mP) feed-down in ϒ(nS) production at QCD next-to-leading order. In the fitting, three schemes are applied with different choices of χbJ(mP) feed-down ratios and NRQCD factorization scale. The results can explain the measurements of yield very well. The polarization puzzle to ϒ(3S) is now solved by considering the χbJ(3P) feed-down contributions. The ratio of σ[χb2(1P)]/σ[χb1(1P)] measured by the CMS experiment can also be reproduced in our prediction. Among the different schemes, the results show little difference, but there are sizeable differences for the fitted long-distance color-octet matrix elements. This may bring large uncertainties when the values are applied in theoretical predictions for other experiments such as those at ee, ep colliders.

PromptJ/ψproduction in association with acc¯pair within the framework of nonrelativistic QCD via photon-photon collisions at the International Linear Collider

We present a systematical study on the prompt $J/\psi$ production in association with a $c\bar{c}$ pair via the process, $\gamma\gamma \to H(c\bar{c}) +c+\bar{c}$, within the framework of non-relativistic QCD at the future high-energy $e^{+}e^{-}$ collider - International Linear Collider (ILC), including both direct and feed-down contributions. For direct $J/\psi$ production, the states with color-octet channels, especially the $^3P_J^{[8]}$ and $^1S_0^{[8]}$ ones, provide dominant contribution to the production cross-section, which are about fifty-two times over that of the color-singlet one. This is clearly shown by the transverse momentum ($p_t$) and rapidity distributions. The feed-down contribution from $\psi'$ and $\chi_{cJ}$ ($J=0,1,2$) is sizable, which is about $20\%$ to the total prompt cross-section. Besides the yields, we also calculate the $J/\psi$ polarization parameter $\lambda$. In small $p_t$ region, the polarization of the prompt $J/\psi$ is longitudinal due to large contributions through the $^3P_J^{[8]}$ channel, and becomes transverse in high $p_t$ region due to $^3S_1^{[8]}$ channel. Thus the $J/\psi$ production via photon-photon collisions at the ILC shall provide a useful platform for testing the color-octet mechanism.

Yields and polarizations of prompt J/ψ and ψ(2S) production in hadronic collisions

We give predictions of J/ψ and ψ(2S) yields and polarizations in prompt production at hadron colliders based on non-relativistic QCD factorization formula. We calculate short-distance coefficients of all important color-octet intermediate channels as well as color-singlet channels up to $$ \mathcal{O}\left({\alpha}_S^4\right) $$ , i.e. next-to-leading order in α S . For prompt J/ψ production, we also take into account feeddown contributions from χ cJ (J=0,1,2) and ψ(2S) decays. Color-singlet long-distance matrix elements (LDMEs) are estimated by using potential model, and color-octet LDMEs are extracted by fitting the Tevatron yield data only. The predictions are satisfactory for both yields and polarizations of prompt J/ψ and prompt ψ(2S) production at the Tevatron and the LHC. In particular, we find our predictions for polarizations of prompt J/ψ production have only a little difference from our previous predictions for polarizations of direct J/ψ production.

Υ(1S)prompt production at the Tevatron and LHC in nonrelativistic QCD

With nonrelativistic QCD factorization, we calculate the $\Upsilon(1S)$ prompt production at hadron colliders at next-to-leading order in $\alpha_s$. In addition to the color-singlet contribution, color-octet channels (especially the P-wave channel) up to $O(v^4)$ are all considered. Aside from direct production, the feed-down contributions from higher excited S-wave and P-wave $b\bar b$ states to $\Upsilon(1S)$ production are also included. We use the potential model estimates as input for color-singlet long-distance matrix elements (LDMEs). While for color-octet contributions, we find they can be approximately described by three LDMEs: $\mo{}{3}{S}{1}{8}$, $\mo{}{1}{S}{0}{8}$ and $\mo{}{3}{P}{0}{8}$. By fitting the Tevatron data we can determine some linear combinations of these LDMEs, and then use them to predict $\Upsilon(1S)$ production at the LHC. Our predictions are consistent with the new experimental data of CMS and LHCb.

PromptJ/ψproduction at the LHC: New evidence for thekTfactorization

In the framework of the kt-factorization approach, the production and polarization of prompt J/Psi mesons in pp collisions at the LHC energy 7 TeV is studied. Both the direct production mechanism as well as feed-down contributions from chic1, chic2 and psi' decays are taken into account. Our consideration is based on the color singlet model supplemented with the off-shell matrix elements for the corresponding partonic subprocesses. The unintegrated gluon densities in a proton are determined using the CCFM evolution equation as well the Kimber-Martin-Ryskin prescription. We compare our numerical predictions with the first experimental data taken by the CMS, ATLAS and LHCb collaborations. The estimation of all polarization parameters which determine J/Psi spin density matrix is performed.

QCD radiative corrections toχcJproduction at hadron colliders

To clarify the outstanding problem in charmonium production that existing theories cannot explain the observed cross sections of $\chi_{cJ}$ (J=0,1,2) and ratio $R_{\chi_c}=\sigma_{\chi_{c2}}/\sigma_{\chi_{c1}}\approx 0.75$ (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 $R_{\chi_c}$ puzzle. By fitting $R_{\chi_c}$, the predicted cross sections of $\chi_{cJ}$ 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 $\chi_{cJ}$ to prompt $J/\psi$ production are estimated to be substantial, about $30-40%$ at $p_T=20$ GeV. Production of $\chi_{cJ}$ (J=0,1,2) at the LHC is also predicted.

J/ψ(ψ′)Production at the Tevatron and LHC atO(αs4v4)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.

Study of ψ′ and χcdecays as feed-down sources ofJ/ψ hadro-production

The interpretation of the J/psi suppression patterns observed in nuclear collisions, at CERN and RHIC, as a signature of the formation of a deconfined phase of QCD matter, requires knowing which fractions of the measured J/psi yields, in pp collisions, are due to decays of heavier charmonium states. From a detailed analysis of the available mid-rapidity charmonium hadro-production cross sections, or their ratios, we determine that the J/psi feed-down contributions from psi' and chi_c decays are, respectively, (8.1 +/- 0.3) % and (25 +/- 5) %. These proton-proton values are derived from global averages of the proton-nucleus measurements, assuming that the charmonium states are exponentially absorbed with the length of matter they traverse in the nuclear targets.

Double-Charm Productione+e−→J/ψ+cc¯atBFactories with Next-to-Leading-Order QCD Corrections

The inclusive J/psi production in e;{+}e;{-}-->J/psicc at B factories is one of the most challenging open problems in heavy quarkonium physics. The observed cross section of this double-charm production process is larger than existing leading order (LO) QCD predictions by a factor of 5. In the nonrelativistic QCD (NRQCD) factorization formalism, we calculate the next-to-leading order (NLO) QCD virtual and real corrections to this process, and find that these corrections can substantially enhance the cross section with a K factor of about 1.8. We further take into account the feeddown contributions from higher charmonium states [mainly the psi(2S) as well as chi_{cJ}] and the two-photon contributions, and find that the discrepancy between theory and experiment can be largely removed.

Statistical model predictions for Pb–Pb collisions at LHC

The systematics of statistical model parameters extracted from heavy-ion collisions at lower energies are exploited to extrapolate in the LHC regime. Predictions of various particle ratios are presented and particle production in central Pb–Pb collisions at LHC is discussed in the context of the statistical model. The sensitivity of several ratios on the temperature and the baryon chemical potential is studied in detail, and some of them, which are particularly appropriate to determine the chemical freeze-out point experimentally, are indicated. The impact of feed-down contributions from resonances, especially to light hadrons, is illustrated.

Measurements of multistrange baryon resonances in STAR at RHIC

A large fraction of particles emanating from high-energy particle collisions are often decay products of primary higher-mass resonances. A clear understanding of the feed-down contributions to the ground state spectra and yields is crucial to the understanding of primary particle dynamics. Also, comparison of ratios from p+p to central Au+Au may provide information on the evolution of the collision system between chemical and thermal freeze-out. We present the first measurement of the Ξ0(1530) baryon resonance at RHIC in both p+p and d+Au collisions at by the STAR experiment. Invariant mass distributions are shown to demonstrate signal quality and the analysis technique is described. Raw ratios are presented and compared to the ratios from both systems as a function of transverse momentum.

Polarizations ofJ/ψandψ′in Hadroproduction at the Tevatron in thektFactorization Approach

We present a calculation for the polarizations of $J/\psi$ and $\psi'$ produced in the hadron collisions at the Fermilab Tevatron. Various color octet channels including ${}^1S_0^{(8)}$, ${}^3P_J^{(8)}$, and ${}^3S_1^{(8)}$ as well as contributions from $\chi_{cJ}$ decays are considered in the $k_t$ factorization approach. We find that in a rather wide range of the transverse momenta of $J/\psi$ and $\psi'$, the production rates could be dominated by the ${}^1S_0^{(8)}$ channel, and the predicted polarizations from the ${}^1S_0^{(8)}$ channel and $\chi_{cJ}$ feeddown contributions are roughly compatible with the preliminary CDF data. This might provide a possible release from the conflict between the NRQCD collinear parton model calculations and the CDF data.

Heavy quarkonium production in double pomeron exchange processes in perturbative QCD

We calculate the heavy quarkonium production in double pomeron exchange processes in perturbative QCD by using two-gluon exchange model. For the $P$-wave $\chi_J$ productions, we find $\chi_1$ and $\chi_2$ production amplitudes which vanish in the forward scattering limit. We also calculate direct $J/\psi(\Upsilon)+\gamma$ production in the same approach, and these direct contributions are much smaller than the feeddown contributions from the $P$-wave states.

Antideuteron yield and coalescence implications at the AGS

We present the preliminary results of Experiment 864's search for antideuterons in 11.5 GeV/c per nucleon Au + Pt collisions at the AGS. The data represents 14 billion 10% central interactions selectively triggered for events with high mass candidates. Antideuteron invariant yields are found to be 3.5 ± 1.5( stat.) +0.9 −0.5( sys.) × 10 −8 GeV −2 c 2 in the rapidity range between y = 1.8 and 2.2 ( y cm = 1.6) for 〈 p t 〉= 0.35 GeV/c and 3.7±2.7( stat.) +1.4 −1.5( sys.) × 10 −8 GeV −2 c 2 between rapidities y = 1.4 and 1.8 at 〈 p t 〉= 0.26 GeV/c. These yields, along with E864 antiproton measurements, lead to a most probable value for the coalescence factor B 2 of 4.1 ± 2.9( stat.) +2.3 −2.4( sys.) × 10 −3 GeV −2 c 3 after correcting antiproton yields for antihyperon feeddown contributions. Implications for the coalescence model and antimatter annihilation from an antideuteron measurement are also discussed.

Quarkonium polarization in nonrelativistic QCD and the quark-gluon plasma

We examine angular distributions of leptons arising from the decay of J/psi in inclusive hadroproduction. Taking into account feed-down contributions from chi_{1,2}, a flat distribution emerges without fine tuning parameters. Changes in the ratio of direct to total J/psi cross sections would change this distribution significantly. Such angular distributions are, therefore, confirmatory tests of the J/psi suppression signal for the production of a quark-gluon plasma. Related effects are predicted for the Upsilon.