Double parton distributions in the nucleon from lattice QCD

We evaluate nucleon four-point functions in the framework of lattice QCD in order to extract the first Mellin moment of double parton distributions (DPDs) in the unpolarized proton. In this first study, we employ an nf = 2+1 ensemble with pseudoscalar masses of mπ = 355 MeV and mK = 441 MeV. The results are converted to the scale μ = 2 GeV. Our calculation includes all Wick contractions, and for almost all of them a good statistical signal is obtained. We analyze the dependence of the DPD Mellin moments on the quark flavor and the quark polarization. Furthermore, the validity of frequently used factorization assumptions is investigated.

Quark flavor physics and lattice QCD

For a long time, investigation into the weak interactions of quarks has guided us toward understanding the Standard Model we know today. Now in the era of high precision, these studies are still one of the most promising avenues for peering beyond the Standard Model. This is a large-scale endeavour with many tales and many protagonists. In these pages I follow a few threads of a complex story, those passing through the realm of lattice gauge theory.

Flavorful leptoquarks at the LHC and beyond: spin 1

Evidence for electron-muon universality violation that has been revealed in b → sℓℓ transitions in the observables $$ {R}_{KK^{\ast }} $$ R KK ∗ by the LHCb Collaboration can be explained with spin-1 leptoquarks in SU(2)L singlet V1 or triplet V3 representations in the $$ \mathcal{O} $$ O (1 − 10) TeV range. We explore the sensitivity of the high luminosity LHC (HL-LHC) and future proton-proton colliders to V1 and V3 in the parameter space connected to $$ {R}_{KK^{\ast }} $$ R KK ∗ -data. We consider pair production and single production in association with muons in different flavor benchmarks. Reinterpreting a recent ATLAS search for scalar leptoquarks decaying to bμ and jμ, we extract improved limits for the leptoquark masses: for gauge boson-type leptoquarks (κ = 1) we obtain $$ {M}_{V_1} $$ M V 1 > 1.9 TeV, $$ {M}_{V_1} $$ M V 1 > 1.9 TeV, and $$ {M}_{V_1} $$ M V 1 > 1.7 TeV for leptoquarks decaying predominantly according to hierarchical, flipped and democratic quark flavor structure, respectively. Future sensitivity projections based on extrapolations of existing ATLAS and CMS searches are worked out. We find that for κ = 1 the mass reach for pair (single) production of V1 can be up to 3 TeV (2.1 TeV) at the HL-LHC and up to 15 TeV (19.9 TeV) at the FCC-hh with $$ \sqrt{s} $$ s = 100 TeV and 20 ab−1. The mass limits and reach for the triplet V3 are similar or higher, depending on flavor. While there is the exciting possibility that leptoquarks addressing the $$ {R}_{KK^{\ast }} $$ R KK ∗ -anomalies are observed at the LHC, to fully cover the parameter space pp-collisions beyond the LHC-energies are needed.

Photoproduction of strange hidden-charm and hidden-bottom states

Recently BESIII collaboration discovered a charged strange hidden-charm state $$Z_{cs}$$ Z cs (3985) in the $$D_s^-D^{*0} + D_s^{*-}D^{0}$$ D s - D ∗ 0 + D s ∗ - D 0 spectrum. A higher $$Z'_{cs}$$ Z cs ′ state coupling to $${\bar{D}}_s^{*-}D^{*0}$$ D ¯ s ∗ - D ∗ 0 is expected by SU(3)-flavor symmetry, and their bottom partners are anticipated by heavy quark flavor symmetry. Here we study the photoproduction of these exotic states and investigate carefully the background from Pomeron exchange. Our results indicate that the maximal photoproduction cross section of strange partner is around 1–2 orders of magnitude smaller than that of the corresponding non-strange states. The possibility of searching for them in future electron-ion colliders (EIC) is briefly discussed.

Branching fractions of $$B^-\rightarrow D^-X_{0,1}(2900)$$ and their implications

The exotic states $$X_{0,1}(2900)$$ X 0 , 1 ( 2900 ) with the quark flavor of $$cs\bar{u}\bar{d}$$ c s u ¯ d ¯ are recently observed in the mass spectrum of $$D^+K^-$$ D + K - in $$B^-\rightarrow D^-D^+K^-$$ B - → D - D + K - by the LHCb collaboration. To explore the nature of $$X_{0,1}(2900)$$ X 0 , 1 ( 2900 ) , except for analyzing their masses and decay widths as usually did in literatures, the study of their production mechanism in B-meson weak decays would provide another important information. The amplitude of $$B^-\rightarrow D^- X_{0,1}$$ B - → D - X 0 , 1 is non-factorizable. We consider the final-state-interaction effects and calculate them via the rescattering mechanism. The measured branching fractions of $$B^-\rightarrow D^- X_{0,1}$$ B - → D - X 0 , 1 are revealed. It is manifested by $${B}^-\rightarrow \Lambda _c^-\Xi _c^{(\prime )0}$$ B - → Λ c - Ξ c ( ′ ) 0 and $$\Lambda _b^0\rightarrow P_c^+K^-$$ Λ b 0 → P c + K - that the rescattering mechanism can result in the relatively large branching fractions. The similar processes of $$B^-\rightarrow \pi ^-X_{0,1}$$ B - → π - X 0 , 1 are also analyzed. The isospins of $$X_{0,1}$$ X 0 , 1 can be investigated by $$B\rightarrow DX_{0,1}^{\pm ,0}$$ B → D X 0 , 1 ± , 0 decays.