Nonlocal form factor of chromomagnetic penguin in $B\to K\ell^+\ell^-$ from QCD light-cone sum rules
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| Format: | Preprint |
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2025
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| _version_ | 1866914195609485312 |
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| author | Hurth, T. Khodjamirian, A. Mahmoudi, F. Mishra, D. Monceaux, Y. Neshatpour, S. |
| author_facet | Hurth, T. Khodjamirian, A. Mahmoudi, F. Mishra, D. Monceaux, Y. Neshatpour, S. |
| contents | The branching fraction of the $B \to K\ell^+\ell^-$ decay has been measured recently by the LHC experiments, showing a deviation from theory predictions based on the Standard Model (SM). A major challenge in achieving a complete SM prediction and interpreting this discrepancy lies in the treatment of nonlocal hadronic effects. In $B \to K\ell^+\ell^-$, these effects are cast in a single nonlocal form factor, a function of squared momentum transfer $q^2$ to the lepton pair. One of the previously used methods provides this form factor in the region of spacelike momentum transfer, $q^2<0$, matching the result to the hadronic dispersion relation, which is then continued to the physical region. The calculation done so far was a combination of QCD factorisation for hard-gluon contributions with light-cone sum rules (LCSRs) for soft-gluon ones. In this work, we calculate for the first time the complete nonlocal form factor at $q^2<0$ for one of the effective operators, the chromomagnetic operator $O_{8g}$, applying the method of LCSRs with $ B$-meson distribution amplitudes. We compute, both analytically and numerically, the operator-product expansion (OPE) diagrams with hard-gluon exchanges, analyse their structure and hierarchy, and obtain their spectral density entering the LCSR together with soft-gluon contributions. This study paves the way for our next task, a complete calculation of nonlocal $B \to K\ell^+\ell^-$ form factor at spacelike $q^2$, including the dominant contributions of current-current operators, known as charm-loops. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2512_10868 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Nonlocal form factor of chromomagnetic penguin in $B\to K\ell^+\ell^-$ from QCD light-cone sum rules Hurth, T. Khodjamirian, A. Mahmoudi, F. Mishra, D. Monceaux, Y. Neshatpour, S. High Energy Physics - Phenomenology The branching fraction of the $B \to K\ell^+\ell^-$ decay has been measured recently by the LHC experiments, showing a deviation from theory predictions based on the Standard Model (SM). A major challenge in achieving a complete SM prediction and interpreting this discrepancy lies in the treatment of nonlocal hadronic effects. In $B \to K\ell^+\ell^-$, these effects are cast in a single nonlocal form factor, a function of squared momentum transfer $q^2$ to the lepton pair. One of the previously used methods provides this form factor in the region of spacelike momentum transfer, $q^2<0$, matching the result to the hadronic dispersion relation, which is then continued to the physical region. The calculation done so far was a combination of QCD factorisation for hard-gluon contributions with light-cone sum rules (LCSRs) for soft-gluon ones. In this work, we calculate for the first time the complete nonlocal form factor at $q^2<0$ for one of the effective operators, the chromomagnetic operator $O_{8g}$, applying the method of LCSRs with $ B$-meson distribution amplitudes. We compute, both analytically and numerically, the operator-product expansion (OPE) diagrams with hard-gluon exchanges, analyse their structure and hierarchy, and obtain their spectral density entering the LCSR together with soft-gluon contributions. This study paves the way for our next task, a complete calculation of nonlocal $B \to K\ell^+\ell^-$ form factor at spacelike $q^2$, including the dominant contributions of current-current operators, known as charm-loops. |
| title | Nonlocal form factor of chromomagnetic penguin in $B\to K\ell^+\ell^-$ from QCD light-cone sum rules |
| topic | High Energy Physics - Phenomenology |
| url | https://arxiv.org/abs/2512.10868 |