arXiv subjects

L. Bertsch

Publications and source records attributed to L. Bertsch.

6 recordsLinked to original sources

arXiv2026

Stringent limits on $C\!PT$- and Lorentz-invariance violation from $B_s^0$ meson decays

Tests of fundamental symmetries, such as $C\!PT$ and Lorentz invariance, provide sensitive probes of physics beyond the standard quantum-field-theory framework. Possible violations of these symmetries are investigated through interference effects in decays of $B_s^0$ mesons to $D_s^-\pi^{+}$ states. The analysis uses proton-proton collision data collected with the LHCb detector in 2015-2018 at a centre-of-mass energy of $13~\mathrm{TeV}$, corresponding to an integrated luminosity of $6~\mathrm{fb}^{-1}$. The results are interpreted within the Standard Model Extension framework, yielding sensitivities to the Lorentz-violating parameter $\Delta a_{\mu}$ at the ${\cal O}(10^{-14})\,\mathrm{GeV}$ level. Without assuming Lorentz-invariance violation, the $C\!PT$-violating parameter $z$ in the $B_s^0$ system is measured to be $\mathcal{R}e(z) = 0.018 \pm 0.016 \pm 0.003$ and $\mathcal{I}m(z) = 0.003 \pm 0.004 \pm 0.002$, where the first uncertainties are statistical and the second systematic. These results represent the most precise constraints on $C\!PT$ violation in the $B_s^0$ system.

hep-ex↗

arXiv2026

First measurement of the ratio of $\psi(2S)$-to-$J/\psi$ inclusive production in $p\mathrm{Ar}$ and $pp$ collisions at $\sqrt{s_{\mathrm{NN}}} =113\,\mathrm{GeV}$ with SMOG2

A measurement of the $\psi(2S)$-to-$J/\psi$ production cross-section ratio is performed in proton-argon ($p\mathrm{Ar}$) and proton-proton ($pp$) collisions in fixed-target mode at $\sqrt{s_{\mathrm{NN}}}=113\,\mathrm{GeV}$. Data samples were collected by the LHCb experiment during argon and hydrogen gas injections in the SMOG2 storage cell, resulting in $p\mathrm{Ar}$ and $pp$ collisions, respectively. The $\psi(2S)$-to-$J/\psi$ production cross-section ratio is measured as a function of the charmonium transverse momentum, $p_{\mathrm{T}}$, and rapidity in the centre-of-mass system, $y^{*}$. The $\psi(2S)$-to-$J/\psi$ ratio in $p\mathrm{Ar}$ collisions over that in $pp$ collisions is measured to be $0.90 \pm 0.04 \pm 0.02$ for $-2.3<y^{*}<0.0$ and $0<p_{\mathrm{T}}<8\mathrm{GeV}/c$, indicating the emergence of nuclear effects in the $p\mathrm{Ar}$ system. This study acts as a baseline for the interpretation of future measurements with larger systems accessible by the LHCb experiment.

hep-ex↗

arXiv2026

Observation of the $\Xi_c^0 \to pK^-$ decay and measurement of its decay asymmetry

A search for the Cabibbo-suppressed decay $\Xi_c^0 \to pK^-$ is performed using $pp$ collision data corresponding to an integrated luminosity of $5.4\,\mathrm{fb}^{-1}$, collected by the LHCb experiment at a centre-of-mass energy of $13\,\mathrm{TeV}$. The decay is observed for the first time and its branching fraction measured to be $(4.5\pm0.5\pm0.2\pm0.9)\times10^{-5}$, where the uncertainties are statistical, systematic and from the branching fraction of the normalisation channel $\Xi_b^- \to \Xi_c^0 (\to p K^- K^- \pi^+) \pi^-$. Using the decay chain $\Xi_b^- \to \Xi_c^0(\to pK^-)\pi^-$, the decay asymmetry parameter of the $\Xi_c^0 \to pK^-$ decay is determined to be $\alpha_{\Xi_c^0}=0.32\pm0.15\pm0.01$.

hep-ex↗

arXiv2026

Angular analysis of the decay ${\it \Lambda}_{\it b}^{0} \to {\it \Lambda}(1520){\it \mu^{+}\mu^{-}}$

The first angular analysis of ${\it \Lambda}_{\it b}^{0} \to {\it \Lambda}(1520){\it \mu^{+}\mu^{-}}$ decays is presented, using proton-proton collision data collected with the LHCb detector between 2011 and 2018, corresponding to an integrated luminosity of 9 fb$^{-1}$. The leptonic forward-backward asymmetry, $A_\text{FB, 3/2}^\ell$, and the $CP$-averaged angular observable, $S_{1cc}$, are determined by fitting projections of the angular distributions in four intervals of the square of the dimuon invariant mass between 0.1 and 12.5 GeV$^2/c^4$. The results are in good agreement with predictions based on the Standard Model of particle physics.

hep-ex↗

arXiv2026

Model-independent measurement of the transversity amplitudes of the $B^0\to K^{*0}\mu^+\mu^-$ decay

An analysis of the decay amplitudes of $B^0 \to K^{*0}(\to K^+\pi^-)\mu^+\mu^-$ is presented, using proton-proton collision data recorded by the LHCb experiment at centre-of-mass energies of 7, 8, and 13 TeV, corresponding to an integrated luminosity of 8.4 fb$^{-1}$. The amplitudes are constructed from Legendre polynomials in the $\mu^+\mu^-$ invariant mass squared region $1.1<q^2<8.0$ GeV$^2/c^4$. $C\!P$-averaged observables are obtained from the amplitudes. Some of these observables present deviations with respect to the Standard Model, which can be interpreted as shifts in the effective Wilson coefficients. This model-independent approach enables tests of theoretical predictions that can help disentangle hadronic effects from potential contributions from physics beyond the Standard Model. This allows flexibility in the choice of $q^2$ binning for global analyses. Depending on the binning scheme, the deviation of the Wilson coefficient $C_9$ from its Standard Model expectation varies from $4.3\sigma$ to $4.8\sigma$.

hep-ex↗

arXiv2026

Modification of $\Upsilon$ production in $p$O and OO collisions at LHCb

The production rates of $\mathit{\Upsilon}(2S)$ and $\mathit{\Upsilon}(3S)$ mesons relative to that of the $\mathit{\Upsilon}(1S)$ state are measured in $pp$, $p$O, and OO collisions by the LHCb collaboration. The ratios measured in $pp$ data are consistent with previous LHCb measurements at different center-of-mass energies. Only slight relative suppression of the $\mathit{\Upsilon}(2S)$ and $\mathit{\Upsilon}(3S)$ states is found in $p$O collisions, while in OO collisions the $\mathit{\Upsilon}(2S)$ is suppressed by a factor of $\sim2$, with evidence for suppression of the $\mathit{\Upsilon}(3S)$. The significant suppression in OO data, compared to the small effect in $p$O data, shows the emergence of additional suppression mechanisms in the relatively small OO collision system. Models incorporating quark-gluon plasma formation in OO collisions successfully describe the data. Implications for the interplay between cold nuclear matter effects and color screening in a deconfined quark-gluon plasma are discussed.

nucl-ex↗