arXiv subjects

M. Abdelfatah

Publications and source records attributed to M. Abdelfatah.

At least 19 recordsLinked to original sources

arXiv2026

Search for the decays $B_{(s)}^0\to J/ψγ$ at LHCb

A search for the rare decays $B_{(s)}^0\to J/ψγ$ is performed with proton-proton collision data collected by the LHCb experiment, corresponding to integrated luminosities of $3~\rm{fb}^{-1}$ at centre-of-mass energies of 7 and 8 TeV, and $6~\rm{fb}^{-1}$ at 13 TeV. Assuming no contribution from $B^0\to J/ψγ$ decay, an upper limit is set on the branching fraction $\mathcal{B}(B_{s}^0\to J/ψγ)<2.9\times10^{-6}$ at the 90% confidence level. If instead no contribution from $B_{s}^0\to J/ψγ$ decay is assumed, the limit is $\mathcal{B}(B^0\to J/ψγ)<2.5\times10^{-6}$ at the 90% confidence level. These results supersede the previous LHCb results, with the limit for $B_{s}^0\to J/ψγ$ improved by a factor of 2.5.

hep-ex↗

arXiv2026

Observation of $Ξ_{b}^{0} \to Ξ^{0} J/ψ$ and evidence for $Ξ_{b}^{0} \to Ξ^{0} ψ(2S)$ decays

The first search for the beauty baryon decays $Ξ_{b}^{0} \to Ξ^{0} J/ψ$ and $Ξ_{b}^{0} \to Ξ^{0} ψ(2S)$ is presented using the proton-proton collision dataset collected by the LHCb experiment between 2016 and 2018, corresponding to an integrated luminosity of $5.4\,\mathrm{fb}^{-1}$. The first observation of the decay $Ξ_{b}^{0} \to Ξ^{0} J/ψ$ is reported and evidence of the decay $Ξ_{b}^{0} \to Ξ^{0} ψ(2S)$ is presented. The $Ξ^{0}$ hyperon is fully reconstructed for the first time at an LHC experiment, which is achieved using the $Ξ^{0} \to Λπ^{0}$ decay. The ratio of the branching fractions is measured as $\frac{\cal{B}(Ξ_{b}^{0} \to Ξ^{0} ψ(2S))}{\cal{B}(Ξ_{b}^{0} \to Ξ^{0} J/ψ)} = 0.59 \pm 0.19 \text{(stat)} \pm 0.04 \text{(syst)}$.

hep-ex↗

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 $D_s^-π^{+}$ 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 $Δa_μ$ 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 $ψ(2S)$-to-$J/ψ$ inclusive production in $p\mathrm{Ar}$ and $pp$ collisions at $\sqrt{s_{\mathrm{NN}}} =113\,\mathrm{GeV}$ with SMOG2

A measurement of the $ψ(2S)$-to-$J/ψ$ 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 $ψ(2S)$-to-$J/ψ$ 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 $ψ(2S)$-to-$J/ψ$ 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 $Ξ_c^0 \to pK^-$ decay and measurement of its decay asymmetry

A search for the Cabibbo-suppressed decay $Ξ_c^0 \to pK^-$ 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 $Ξ_b^- \to Ξ_c^0 (\to p K^- K^- π^+) π^-$. Using the decay chain $Ξ_b^- \to Ξ_c^0(\to pK^-)π^-$, the decay asymmetry parameter of the $Ξ_c^0 \to pK^-$ decay is determined to be $α_{Ξ_c^0}=0.32\pm0.15\pm0.01$.

hep-ex↗

arXiv2026

First measurement of the decay-time-integrated $C\!P$ asymmetry in $B_s^0 \to D_s^- π^+$ decays

A measurement of the flavor-untagged decay-time-integrated ${C\!P}$ asymmetry in the flavor-specific decay ${B_s^0 \to D_s^-π^+}$, ${\langle A^s_{\rm untagged}\rangle}$, is performed using proton-proton collision data collected by the LHCb experiment between 2016 and 2018 at a center-of-mass energy of ${13\,{\rm TeV}}$, corresponding to a total integrated luminosity of ${5.4\,{\rm fb}^{-1}}$. The ${C\!P}$ asymmetry is measured in two $D_s^-$ meson decay modes, ${D_s^- \to K^-K^+π^-}$ and ${D_s^- \to π^-π^+π^-}$. The combined result, $\langle A^s_{\rm untagged}\rangle = ( -1.4 \pm 5.9\,\rm{(stat)} \pm 1.1\,\rm{(syst)}) \times 10^{-3}$, is consistent with the Standard Model expectation and provides a direct constraint on new physics in tree-level $b$-hadron decays.

hep-ex↗

arXiv2026

Measurement of the average transverse momentum of forward prompt charged particles in $pp$ and $p\mathrm{Pb}$ collisions at $\sqrt{s_{NN}} = 5.02\; \mathrm{TeV}$

This letter presents the first measurements of the average transverse momentum of prompt charged particles in $pp$ and $p\mathrm{Pb}$ collisions as a function of collision multiplicity and pseudorapidity. The data were recorded at nucleon-nucleon centre-of-mass energy $\sqrt{s_{NN}} = 5.02\; \mathrm{TeV}$ with the LHCb experiment. The pseudorapidity dependence of the multiplicity distribution is also measured. The average transverse momentum results show a decreasing trend with pseudorapidity, more pronounced in high-multiplicity events, consistent with the collective behaviour of the produced matter. The measurements are reproduced by state-of-the-art (3+1D) hydrodynamic calculations, while saturation models are not compatible with the data.

nucl-ex↗

arXiv2026

Search for $B$ meson decays to multimuon final states

A search for decays of $B$ mesons to final states with four or six muons using $pp$ collision data recorded by the LHCb experiment corresponding to an integrated luminosity of $5.4~\text{fb}^{-1}$ is presented. The decay modes of interest are $B_{(s)}^0 \rightarrow μ^+μ^-μ^+μ^-$, $B^+ \rightarrow K^+μ^+μ^-μ^+μ^-$, $B_{(s)}^0 \rightarrow μ^+μ^-μ^+μ^-μ^+μ^-$ and $B^+ \rightarrow K^+μ^+μ^-μ^+μ^-μ^+μ^-$, proceeding via both prompt and long-lived intermediate particles. No evidence for any of the signal modes is found, and upper limits spanning the range of $0.6\times10^{-9}$ to $5.4\times10^{-7}$ at the $95\%$ confidence level are set on their branching fractions, depending on the intermediate-particle masses and lifetimes. In addition, mass-integrated limits across the intermediate-particle lifetime ranges considered in this analysis are determined.

hep-ex↗

arXiv2026

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

The first angular analysis of ${\it Λ}_{\it b}^{0} \to {\it Λ}(1520){\it μ^{+}μ^{-}}$ 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

Study of muon-tagged $D_{s1}(2460)^+$ and $D_{s1}(2536)^+$ decays to the $D_s^{+}π^+π^-$ final state

Decays of the pseudovector $D_{s1}(2460)^+$ and $D_{s1}(2536)^+$ mesons to the three-body $D_{s}^+π^+π^-$ final state are studied. The data sample is based on decays of beauty hadrons into $D_{s1}^+$ states accompanied by a muon from the $b$-hadron decay chain collected by the LHCb detector during 2016--2018, corresponding to an integrated luminosity of 5.4 fb${}^{-1}$. The \mbox{$D_{s1}(2536)^+\to D_s^+π^+π^-$} branching fraction is measured for the first time, with the $D_{s1}(2536)^+\to D^+K^+π^-$ decay used as a reference. A simultaneous amplitude analysis of the $D_{s1}(2460)^+$ and $D_{s1}(2536)^+\to D_s^+π^+π^-$ decays is performed. The Dalitz-plot distributions of the two decays are found to be significantly different, suggesting differences in the internal structure of the two states, with evidence of exotic contributions to the $D_{s}^+π^{\pm}$ channel with the pole below the $DK$ threshold. Measurements of the masses of the $D_{s1}(2460)^+$ and $D_{s1}(2536)^+$ states are performed, and an upper limit on the $D_{s1}(2460)^+$ width is set.

hep-ex↗

arXiv2026

Amplitude analysis of $B^+ \!\to K^+ π^+ π^-$ decays

The branching fractions and quasi-two-body $C\!P$-violating asymmetries of intermediate states obtained through an amplitude analysis of the charmless three-body decay $B^+ \!\to K^+ π^+ π^-$ are reported. The analysis is based on $pp$ collision data at centre-of-mass energies $\sqrt{s}=7$ and $8\,\text{TeV}$ recorded with the LHCb detector, corresponding to an integrated luminosity of $3\,\text{fb}^{-1}$. The most challenging aspect of the amplitude modelling lies in the description of the dominant $K^+ π^-$ and $π^+ π^-$ S-wave contributions. This is achieved by three complementary approaches based on a physically motivated analytic model built on the isobar approximation, the K-matrix formalism, and a quasi-model-independent procedure in which overlapping crossing partial waves are simultaneously studied. In addition, alternative sets of results are presented, considering the $π^+ π^-$ final state to manifest either through direct $ω(782)$ decays or $ρ(770)^0\textrm{-}ω(782)$ mixing. The most precise measurements of branching fractions and $C\!P$ asymmetries are obtained for the vast majority of intermediate states, establishing firmer reference points against which to cleanly probe model-independent physics beyond the Standard Model. The results from all three approaches agree and provide new insight into strong dynamics and the origin of $C\!P$-violation effects in $B^+ \!\to K^+ π^+ π^-$ decays.

hep-ex↗

arXiv2026

Resolution of outstanding puzzles in $B^+ \!\to K^+ π^+ π^-$ decays

An amplitude analysis of $B^+ \!\to K^+ π^+ π^-$ decays is presented, based on $pp$ collision data recorded with the LHCb detector in 2011--2012, corresponding to an integrated luminosity of $3\,\text{fb}^{-1}$. Previous studies of the $B \!\to K ππ$ sector have left key unresolved questions concerning the model of the S-wave contributions. A pivotal finding is that relaxing unitarity-based assumptions about the relation between the $K^*_0(1430)^0$ resonance and the slowly varying scalar part in $K^+π^-$ leads to considerably better agreement between the model and data. The $B^+ \!\to K^*_0(1430)^0 π^+$ branching fraction now challenges the experimental consensus that $B \!\to K^*_0(1430) π$ decays dominate the $B \!\to K ππ$ phase space, aligning with the predictions of QCD factorisation rather than perturbative QCD, thus reversing the agreement found in previous measurements. With this increased flexibility, it also becomes possible to model the scalar $π^+ π^-$ amplitude using established states, eliminating the need for the ad-hoc ``$f_X(1300)$'' component included in previous analyses of the $B \!\to Kππ$ sector. These advances facilitate the discovery of ten intermediate decays.

hep-ex↗

arXiv2026

Observation of several sources of $C\!P$ violation in $B^+ \!\to K^+ π^+ π^-$ decays

An amplitude analysis of $B^+ \!\to K^+ π^+ π^-$ decays is presented in which six $C\!P$-violating phenomena are judged to be of significance for the first time. This analysis is based on $pp$ collision data recorded with the LHCb detector in 2011-2012, corresponding to an integrated luminosity of $3\,\text{fb}^{-1}$. Quasi-two-body $C\!P$ violation in $B^+ \!\to ρ(770)^0 K^+$ decays is discovered, while $C\!P$ violation at amplitude level is established in $B^+ \!\to f_2(1270) K^+$ decays. First evidence for $C\!P$ violation is reported in both the fully elastic S-wave $ππ$-$ππ$ rescattering region and also for any decay involving a spin-3 resonance. Additionally, significant $C\!P$-violation effects are identified in the interference between different $ππ$ partial waves, with observation in S-P wave interference and evidence in S-D wave interference, both of which must be driven by long-distance interactions.

hep-ex↗

arXiv2026

Improved measurement of $C\!P$ violation in $B^{0}_{s} \!\to J/ψπ^{+}π^{-}$ decays

The time-dependent $C\!P$ asymmetry in $B^{0}_{s} \!\to J/ψπ^{+}π^{-}$ decays is measured using proton-proton collision data, corresponding to an integrated luminosity of $6\,\text{fb}^{-1}$, collected with the LHCb detector at a centre-of-mass energy of $13\,\text{TeV}$ during $\mbox{2015--2018}$. The $C\!P$-violating phase, $ϕ_{s}$, the direct $C\!P$-violation parameter, $\left|λ\right|$, and the decay width of the heavy mass eigenstate in the $B^{0}_{s}$ system, $Γ_{\mathrm{ H}}$, are measured respectively to be $ϕ_{s} = -0.077 \pm 0.034 \pm 0.007\,\text{rad}$, $\left|λ\right| = 0.993 \pm 0.026 \pm 0.007$ and $Γ_{\mathrm{ H}} = 0.610 \pm 0.002 \pm 0.004\,\text{ps}^{-1}$, where the first uncertainties are statistical and the second systematic. These results are consistent with previous measurements and the expectation based on the Standard Model. The combination with previous measurements in $B^{0}_{s} \!\to J/ψπ^{+}π^{-}$ decays using $7\,\text{TeV}$ and $8\,\text{TeV}$ proton-proton collision data yields $ϕ_{s} = -0.046 \pm 0.031\,\text{rad}$, $\left|λ\right| = 0.975 \pm 0.024$ and $Γ_{\mathrm{ H}} = 0.610 \pm 0.004\,\text{ps}^{-1}$, while the combination including all other LHCb measurements gives $ϕ_{s} = -0.041 \pm 0.017\,\text{rad}$.

hep-ex↗

arXiv2026

Observation of the charmless purely baryonic decay $\mathinner{\mathitΛ^0_b\!\to \mathitΛ p \overline{p}}$

A search for the charmless purely baryonic decay $\mathinner{\mathitΛ^0_b\!\to \mathitΛ p \overline{p}}$ is performed using proton-proton collision data recorded by the LHCb experiment at a centre-of-mass energy of $\sqrt{s}=13\,\text{TeV}$ and corresponding to an integrated luminosity of $6.0\,\text{fb}^{-1}$. The signal decay is observed with a significance of 5.1 standard deviations. Its branching fraction is measured for the first time, relative to that of the topologically similar decay $\mathinner{\mathitΛ^0_b\!\to \mathitΛ K^+ K^-}$. Contributions from intermediate charmonium resonances decaying to the $p \overline{p}$ and $K^+ K^-$ final states are explicitly excluded with a requirement on the invariant mass of the companion hadron system, $m(h\bar{h}) < 2.85\,\text{GeV}$, where $h$ stands for a proton or a charged kaon. The relative branching fraction is found to be $$ \frac{B(\mathinner{\mathitΛ^0_b\!\to \mathitΛ p \overline{p}})}{B(\mathinner{\mathitΛ^0_b\!\to \mathitΛ K^+ K^-})} = (5.1 \pm 1.3_{\text{(stat)}} \pm 0.3_{\text{(syst)}}) \times 10^{-2} \,. $$

hep-ex↗

arXiv2026

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

An analysis of the decay amplitudes of $B^0 \to K^{*0}(\to K^+π^-)μ^+μ^-$ 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 $μ^+μ^-$ 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 $4.3σ$ to $4.8σ$.

hep-ex↗

arXiv2026

Measurement of $γ$ using $B^{\pm}\rightarrow DK^{\pm}$ and $B^{\pm}\rightarrow Dπ^{\pm}$ decays with $D\rightarrow K_{\rm S}^{0}π^{+}π^{-}$ and $D\rightarrow K_{\rm S}^{0}K^{+}K^{-}$

A measurement of the CKM angle $γ$ using the decay channels $B^{\pm}\rightarrow DK^{\pm}$ and $B^{\pm}\rightarrow Dπ^{\pm}$, where the $D$ meson decays to $D\rightarrow K_{\rm S}^{0}π^{+}π^{-}$ or $D\rightarrow K_{\rm S}^{0}K^{+}K^{-}$, is performed with a data sample corresponding to an integrated luminosity of 5.8 fb$^{-1}$, collected during 2024 by the upgraded LHCb experiment. $C\!P$ violation is observed through a difference in the distributions of the Dalitz plot of the $D$ decay between the $B^{+}$ and $B^{-}$ mesons. The CKM angle $γ$ is determined to be $γ=(68.1\pm 6.7)^{\circ}$. Other parameters related to the examined $B$ meson decay modes are also measured. This is the first measurement of the CKM angle $γ$ using the upgraded LHCb detector.

hep-ex↗

arXiv2026

$C\!P$ violation analysis of local and nonlocal amplitudes in the $\overline{B}^0 \to \overline{K}^{*0}μ^+μ^-$ decay

A search for $C\!P$ violation in the $\overline{B}^0 \to \overline{K}^{*0}μ^+μ^-$ decay is performed using proton-proton collision data collected by the LHCb experiment during Run 1 and Run 2, corresponding to an integrated luminosity of 8.4 fb$^{-1}$. The analysis exploits the full angular distribution of the decay, providing sensitivity to $C\!P$-violating effects in both vector and axial-vector contributions to this flavour-changing neutral-current process. The complex Wilson coefficients are determined within the Weak Effective Theory through an unbinned maximum-likelihood fit to the angular observables, incorporating nonlocal hadronic amplitudes across the full dimuon mass spectrum. The precision of the $C\!P$-violation observables is improved by an order of magnitude relative to previous measurements, with the imaginary parts of the Wilson coefficients now determined more precisely than the real parts. No significant $C\!P$ violation is observed, and the results are consistent with Standard Model.

hep-ex↗