arXiv subjects

S. Benson

Publications and source records attributed to S. Benson.

At least 19 recordsLinked to original sources

arXiv2025

Search for resonances decaying to photon pairs with masses between 4.9 and 19.4 GeV

A search is presented for axion-like particles (ALPs) with masses between 4.9 and 19.4 GeV decaying to a pair of photons, using proton-proton collisions collected with the LHCb detector during 2018 at a centre-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 2.1 fb$^{-1}$. The same strategy and sample is used to search for the decays of the $B^0_s$, $B^0$ and $\eta_b$ mesons into photon pairs. No significant excess is found. Upper limits on the photon-pair branching fraction times the cross-section of ALP production are determined as a function of the ALP mass. Limits on the branching fractions of the beauty states are determined to be $\mathcal{B}(B^0_s\to\gamma\gamma)<2.7\times10^{-5}$, $\mathcal{B}(B^0\to\gamma\gamma)<0.83\times10^{-5}$, and $ \sigma(pp\to\eta_b X)\times\mathcal{B}(\eta_b\to\gamma\gamma)<765\,\text{pb}$ at 95 % confidence level.

hep-ex↗

arXiv2022

Searching for New Physics with DarkLight at the ARIEL Electron-Linac

The search for a dark photon holds considerable interest in the physics community. Such a force carrier would begin to illuminate the dark sector. Many experiments have searched for such a particle, but so far it has proven elusive. In recent years the concept of a low mass dark photon has gained popularity in the physics community. Of particular recent interest is the $^8$Be and $^4$He anomaly, which could be explained by a new fifth force carrier with a mass of 17 MeV/$c^2$. The proposed DarkLight experiment would search for this potential low mass force carrier at ARIEL in the 10-20 MeV e$^+$e$^-$ invariant mass range. This proceeding will focus on the experimental design and physics case of the DarkLight experiment.

nucl-ex↗

arXiv2022

Performance of the LHCb RICH detectors during LHC Run 2

The performance of the ring-imaging Cherenkov detectors at the LHCb experiment is determined during the LHC Run 2 period between 2015 and 2018. The stability of the Cherenkov angle resolution and number of detected photons with time and running conditions is measured. The particle identification performance is evaluated with data and found to satisfy the requirements of the physics programme.

physics.ins-det↗

arXiv2021

Photoinjector Generation of High-Charge Magnetized Beams for Electron-Cooling Applications

Electron-cooling offers a relatively simple scheme to enable high-luminosity collisions in future electron-ion and hadron colliders. Contemplated TeV-energy hadron colliders require relativistic (sub 100 MeV) high-charge [${\cal O}(\mbox{nC})$] electron beams with a specific transverse eigenemittance partition. This paper discusses the generation of high-charge ($Q\le 3.2$~nC) 40 MeV electron bunches with eigenemittance partition consistent with requirements associated with electron-cooling option for future electron-ion colliders. The supporting experiment was performed at the FAST facility at FermiLab. The data are compared with numerical simulations and the results discussed in the context of beam requirement for future electron-ion colliders.

physics.acc-ph↗

arXiv2021

Search for the doubly heavy baryons $\it{\Omega}_{bc}^{\rm0}$ and $\it{\Xi}_{bc}^{\rm0}$ decaying to $\it{\Lambda_{c}^{+}\pi^{-}}$ and $\it{\Xi_{c}^{+}\pi^{-}}$

The first search for the doubly heavy $\it{\Omega}_{bc}^{\rm0}$ baryon and a search for $\it{\Xi}_{bc}^{\rm0}$ baryon are performed using $pp$ collision data collected via the LHCb experiment from 2016 to 2018 at a centre-of-mass energy of $13TeV$, corresponding to an integrated luminosity of 5.2$fb^{-1}$. The baryons are reconstructed via their decays to $\it{\Lambda_{c}^{+}\pi^{-}}$ and $\it{\Xi_{c}^{+}\pi^{-}}$. No significant excess is found for invariant masses between 6700 and 7300$MeV/c^2$, in a rapidity range from 2.0 to 4.5 and a transverse momentum range from 2 to 20$GeV/c$. Upper limits are set on the ratio of the $\it{\Omega}_{bc}^{\rm0}$ and $\it{\Xi}_{bc}^{\rm0}$ production cross-section times the branching fraction to $\it{\Lambda_{c}^{+}\pi^{-}}$ ($\it{\Xi_{c}^{+}\pi^{-}}$) relative to that of the $\it{\Lambda_b^{\rm0}}$ ($\it{\Xi_b^{\rm0}}$) baryon, for different lifetime hypotheses, at $95\%$ confidence level. The upper limits range from $0.5\times10^{-4}$ to $2.5\times10^{-4}$ for the $\it{\Omega}_{bc}^{\rm0}\rightarrow\it{\Lambda_{c}^{+}\pi^{-}}$ ($\it{\Xi}_{bc}^{\rm0}\rightarrow\it{\Lambda_{c}^{+}\pi^{-}}$) decay, and from $1.4\times10^{-3}$ to $6.9\times10^{-3}$ for the $\it{\Omega}_{bc}^{\rm0}\rightarrow\it{\Xi_{c}^{+}\pi^{-}}$ ($\it{\Xi}_{bc}^{\rm0}\rightarrow\it{\Xi_{c}^{+}\pi^{-}}$) decay, depending on the considered mass and lifetime of the $\it{\Omega}_{bc}^{\rm0}$ ($\it{\Xi}_{bc}^{\rm0}$) baryon.

hep-ex↗

arXiv2020

Searches for 25 rare and forbidden decays of $D^+$ and $D_s^+$ mesons

A search is performed for rare and forbidden charm decays of the form $D_{(s)}^+ \to h^\pm \ell^+ \ell^{(\prime)\mp}$, where $h^\pm$ is a pion or kaon and $\ell^{(')\pm}$ is an electron or muon. The measurements are performed using proton-proton collision data, corresponding to an integrated luminosity of $1.6\text{fb}^{-1}$, collected by the LHCb experiment in 2016. No evidence is observed for the 25 decay modes that are investigated and $90\%$ confidence level limits on the branching fractions are set between $1.4\times10^{-8}$ and $6.4\times10^{-6}$. In most cases, these results represent an improvement on existing limits by one to two orders of magnitude.

hep-ex↗

arXiv2020

Demonstration of electron cooling using a pulsed beam from an electrostatic electron cooler

Cooling of hadron beams is critically important in the next generation of hadron storage rings for delivery of unprecedented performance. One such application is the electron-ion collider presently under development in the US. The desire to develop electron coolers for operation at much higher energies than previously achieved necessitates the use of radio-frequency (RF) fields for acceleration as opposed to the conventional, electrostatic approach. While electron cooling is a mature technology at low energy utilizing a DC beam, RF acceleration requires the cooling beam to be bunched, thus extending the parameter space to an unexplored territory. It is important to experimentally demonstrate the feasibility of cooling with electron bunches and further investigate how the relative time structure of the two beams affects the cooling properties; thus, a set of four pulsed-beam cooling experiments was carried out by a collaboration of Jefferson Lab and Institute of Modern Physics (IMP). The experiments have successfully demonstrated cooling with a beam of electron bunches in both the longitudinal and transverse directions for the first time. We have measured the effect of the electron bunch length and longitudinal ion focusing strength on the temporal evolution of the longitudinal and transverse ion beam profile and demonstrate that if the synchronization can be accurately maintained, the dynamics are not adversely affected by the change in time structure.

physics.acc-ph↗

arXiv2020

Search for $CP$ violation in $\Xi_c^+\rightarrow pK^-\pi^+$ decays using model-independent techniques

A first search for $CP$ violation in the Cabibbo-suppressed $\Xi_c^+\rightarrow pK^-\pi^+$ decay is performed using both a binned and an unbinned model-independent technique in the Dalitz plot. The studies are based on a sample of proton-proton collision data, corresponding to an integrated luminosity of $3.0~{\rm fb^{-1}}$, and collected by the LHCb experiment at centre-of-mass energies of $7$ and $8~\rm TeV$. The data are consistent with the hypothesis of no $CP$ violation.

hep-ex↗

arXiv2020

Study of the lineshape of the $\chi_{c1}(3872)$ state

A study of the lineshape of the $\chi_{c1}(3872)$ state is made using a data sample corresponding to an integrated luminosity of $3\,$fb$^{-1}$ collected in $pp$ collisions at centre-of-mass energies of 7 and 8\,TeV with the LHCb detector. Candidate $\chi_{c1}(3872)$ and $\psi(2S)$ mesons from b-hadron decays are selected in the $ J/\psi \pi^+ \pi^-$ decay mode. Describing the {\mbox{lineshape}} with a Breit--Wigner function, the mass splitting between the $\chi_{c1}(3872)$ and $\psi(2S)$ states, $\Delta m$, and the width of the $\chi_{c1}(3872)$ state, $\Gamma_{\mathrm{BW}}$, are determined to be \begin{eqnarray*} \Delta m & = & 185.598 \pm 0.067 \pm 0.068\, \mathrm{MeV} \,, \\ \Gamma_{\mathrm{BW}} & = & \phantom{00}1.39\phantom{0} \pm 0.24\phantom{0} \pm 0.10\phantom{0} \mathrm{MeV} \,, \end{eqnarray*} where the first uncertainty is statistical and the second systematic. Using a Flatt\'e-inspired model, the mode and full width at half maximum of the lineshape are determined to be \begin{eqnarray*} \mathrm{mode} & = 3871.69^{\,+\,0.00\,+\,0.05}_{\,-\,0.04\,-\,0.13} &\mathrm{MeV} \\ \mathrm{FWHM} & = 0.22^{\,+\,0.07\,+\,0.11}_{\,-\,0.06\,-\,0.13}& \mathrm{MeV} . \end{eqnarray*} An investigation of the analytic structure of the Flatt\'e amplitude reveals a pole structure, which is compatible with a quasi-bound $D^0\bar{D}^{*0}$ state but a quasi-virtual state is still allowed at the level of $2$ standard deviations.

hep-ex↗

arXiv2020

Measurement of branching fraction ratios for $B^+\to D^{+}D^-K^+$, $B^+\to D^{-}D^+K^+$, and $B^0\to D^{*-}D^0K^+$ decays

A measurement of four branching-fraction ratios for three-body decays of $B$ mesons involving two open-charm hadrons in the final state is presented. Run 1 and Run 2 $pp$ collision data are used, recorded by the LHCb experiment at centre-of-mass energies $7$, $8$, and $13$ TeV and corresponding to an integrated luminosity of $9$ fb$^{-1}$. The measured branching-fraction ratios are \[ \begin{eqnarray} \frac{\mathcal{B} (B^+\to D^{*+}D^-K^+)}{\mathcal{B} (B^+\to \kern 0.2em\overline{\kern -0.2em D}{}^0 D^0 K^+)} &=& 0.517 \pm 0.015 \pm 0.013 \pm 0.011 , \\ \frac{\mathcal{B} (B^+\to D^{*-}D^+K^+)}{\mathcal{B} (B^+\to \kern 0.2em\overline{\kern -0.2em D}{}^0 D^0 K^+)} &=& 0.577 \pm 0.016 \pm 0.013 \pm 0.013 , \\ \frac{\mathcal{B} (B^0\to D^{*-}D^0K^+)}{\mathcal{B} (B^0\to D^- D^0 K^+)} &=& 1.754 \pm 0.028 \pm 0.016 \pm 0.035 , \\ \frac{\mathcal{B} (B^+\to D^{*+}D^-K^+)}{\mathcal{B} (B^+\to D^{*-}D^+K^+)} &=& 0.907 \pm 0.033 \pm 0.014 ,\end{eqnarray} \] where the first of the uncertainties is statistical, the second systematic, and the third is due to the uncertainties on the $D$-meson branching fractions. These are the most accurate measurements of these ratios to date.

hep-ex↗

arXiv2020

Measurement of the $\Lambda^0_b\rightarrow J/\psi\Lambda$ angular distribution and the $\Lambda^0_b$ polarisation in $pp$ collisions

This paper presents an analysis of the $\Lambda^0_b\rightarrow J/\psi\Lambda$ angular distribution and the transverse production polarisation of $\Lambda^0_b$ baryons in proton-proton collisions at centre-of-mass energies of 7, 8 and 13 TeV. The measurements are performed using data corresponding to an integrated luminosity of 4.9 fb$^{-1}$, collected with the LHCb experiment. The polarisation is determined in a fiducial region of $\Lambda^0_b$ transverse momentum and pseudorapidity of $1 < p_{T} < 20$ GeV$/c$ and $2 < \eta < 5$, respectively. The data are consistent with $\Lambda^0_b$ baryons being produced unpolarised in this region. The parity-violating asymmetry parameter of the $\Lambda\rightarrow p\pi^-$ decay is also determined from the data and its value is found to be consistent with a recent measurement by the BES\,III collaboration.

hep-ex↗

arXiv2020

Precision measurement of the $B_{c}^{+}$ meson mass

A precision measurement of the $B_{c}^{+}$ meson mass is performed using proton-proton collision data collected with the LHCb experiment at centre-of-mass energies of $7, 8$ and $13$ TeV, corresponding to a total integrated luminosity of $9.0 \,{\rm fb}^{-1}$. The $B_{c}^{+}$ mesons are reconstructed via the decays $B_{c}^{+} \rightarrow J\mskip -3mu/\mskip -2mu\psi\mskip 2mu \pi^+$, $B_{c}^{+} \rightarrow J\mskip -3mu/\mskip -2mu\psi\mskip 2mu \pi^+ \pi^- \pi^+$, $B_{c}^{+} \rightarrow J\mskip -3mu/\mskip -2mu\psi\mskip 2mu p \bar{p} \pi^+$, $B_{c}^{+} \rightarrow J\mskip -3mu/\mskip -2mu\psi\mskip 2mu D_{s}^{+}$, $B_{c}^{+} \rightarrow J\mskip -3mu/\mskip -2mu\psi\mskip 2mu D^{0} K^{+}$ and $B_{c}^{+} \rightarrow B_{s}^{0} \pi^{+}$. Combining the results of the individual decay channels, the $B_{c}^{+}$ mass is measured to be $6274.47 \pm 0.27 \,({\rm stat}) \pm 0.17 \,({\rm syst}) \mathrm{\,Me\kern -0.1em V}/c^{2}$. This is the most precise measurement of the $B_{c}^{+}$ mass to date. The difference between the $B_{c}^{+}$ and $B_{s}^{0}$ meson masses is measured to be $907.75 \pm 0.37 \,({\rm stat}) \pm 0.27 \,({\rm syst}) \mathrm{\,Me\kern -0.1em V}/c^{2}$.

hep-ex↗

arXiv2020

Observation of new $\Xi_c^0$ baryons decaying to $\Lambda_c^+ K^-$

The $\Lambda_c^+K^-$ mass spectrum is studied with a data sample of $pp$ collisions at a centre-of-mass energy of 13 TeV corresponding to an integrated luminosity of 5.6 fb$^{-1}$ collected by the LHCb experiment. Three $\Xi_c^0$ states are observed with a large significance and their masses and natural widths are measured to be \begin{eqnarray*} m(\Xi_c(2923)^0)&=& 2923.04 \pm 0.25 \pm 0.20 \pm 0.14 ~\mathrm{MeV}, \Gamma(\Xi_c(2923)^0) &=& 7.1 \pm 0.8 \pm 1.8 ~\mathrm{MeV}, \end{eqnarray*} \begin{eqnarray*} m(\Xi_c(2939)^0) &=& 2938.55 \pm 0.21 \pm 0.17 \pm 0.14 ~\mathrm{ MeV}, \Gamma(\Xi_c(2939)^0) &=& 10.2 \pm 0.8 \pm 1.1 ~\mathrm{ MeV}, \end{eqnarray*} \begin{eqnarray*} m(\Xi_c(2965)^0) &=& 2964.88 \pm 0.26 \pm 0.14 \pm 0.14~\mathrm{ MeV}, \Gamma(\Xi_c(2965)^0) &=& 14.1 \pm 0.9 \pm 1.3~\mathrm{ MeV}, \end{eqnarray*} where the uncertainties are statistical, systematic, and due to the limited knowledge of the $\Lambda_c^+$ mass. The $\Xi_c(2923)^0$ and $\Xi_c(2939)^0$ baryons are new states. The $\Xi_c(2965)^0$ state is in the vicinity of the known $\Xi_c(2970)^0$ baryon; however, their masses and natural widths differ significantly.

hep-ex↗

arXiv2020

Measurement of the shape of the $B_s^0\rightarrow D_s^{*-}\mu^{+}\nu_{\mu}$ differential decay rate

The shape of the $B_s^0\rightarrow D_s^{*-}\mu^+\nu_{\mu}$ differential decay rate is obtained as a function of the hadron recoil using proton-proton collision data at a centre-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 1.7 fb$^{-1}$ collected by the LHCb detector. The $B_s^0\rightarrow D_s^{*-}\mu^+\nu_{\mu}$ decay is reconstructed through the decays $D_s^{*-}\rightarrow D_s^{-}\gamma$ and $D_s^{-}\rightarrow K^-K^+\pi^-$. The differential decay rate is fitted with the Caprini-Lellouch-Neubert (CLN) and Boyd-Grinstein-Lebed (BGL) parametrisations of the form factors, and the relevant quantities for both are extracted.

hep-ex↗

arXiv2020

Measurement of $C\!P$-averaged observables in the $B^{0}\rightarrow K^{*0}\mu^{+}\mu^{-}$ decay

An angular analysis of the $B^{0}\rightarrow K^{*0}(\to K^{+}\pi^{-})\mu^{+}\mu^{-}$ decay is presented using a data set corresponding to an integrated luminosity of 4.7 fb$^{-1}$ of $pp$ collision data collected with the LHCb experiment. The full set of $C\!P$-averaged observables are determined in bins of the invariant mass squared of the dimuon system. Contamination from decays with the $K^{+}\pi^{-}$ system in an S-wave configuration is taken into account. The tension seen between the previous LHCb results and the Standard Model predictions persists with the new data. The precise value of the significance of this tension depends on the choice of theory nuisance parameters.

hep-ex↗

arXiv2020

Search for the lepton flavour violating decay $B^+ \rightarrow K^+ \mu^- \tau^+$ using $B_{s2}^{*0}$ decays

A search is presented for the lepton flavour violating decay $B^+ \rightarrow K^+ \mu^- \tau^+$ using a sample of proton--proton collisions at centre-of-mass energies of 7, 8, and 13 TeV, collected with the LHCb detector and corresponding to a total integrated luminosity of 9 fb${}^{-1}$. The $\tau$ leptons are selected inclusively, primarily via decays with a single charged particle. The four-momentum of the $\tau$ lepton is determined by using $B^+$ mesons from $B_{s2}^{*0} \rightarrow B^+ K^-$ decays. No significant excess is observed, and an upper limit is set on the branching fraction $B(B^+ \rightarrow K^+ \mu^- \tau^+) < 3.9 \times 10^{-5}$ at 90% confidence level. The obtained limit is comparable to the world-best limit.

hep-ex↗

arXiv2020

Search for the rare decays $B^0_s\to e^+e^-$ and $B^0\to e^+e^-$

A search for the decays $B^0_s\to e^+e^-$ and $B^0\to e^+e^-$ is performed using data collected with the LHCb experiment in proton-proton collisions at center-of-mass energies of $7$, $8$ and $13\,\text{TeV}$, corresponding to integrated luminosities of $1$, $2$ and $2\,\text{fb}^{-1}$, respectively. No signal is observed. Assuming no contribution from $B^0\to e^+e^-$ decays, an upper limit of $\mathcal{B}(B^0_s\to e^+e^-)<9.4\,(11.2)\times10^{-9}$ is obtained at $90\,(95)\,\%$ confidence level. If no $B^0_s\to e^+e^-$ contribution is assumed, a limit of $\mathcal{B}(B^0\to e^+e^-)<2.5\,(3.0)\times10^{-9}$ is determined at $90\,(95)\,\%$ confidence level. These upper limits are more than one order of magnitude lower than the previous values.

hep-ex↗

arXiv2020

Measurement of $CP$ observables in $B^{\pm} \to D K^{\pm}$ and $B^{\pm} \to D \pi^{\pm}$ with $D \to K_{\rm{S}}^0 K^\pm \pi^\mp$ decays

Measurements of $CP$ observables in $B^\pm \to D K^\pm$ and $B^\pm \to D \pi^\pm$ decays are presented, where $D$ represents a superposition of $D^0$ and $\bar{D}^0$ states. The $D$ meson is reconstructed in the three-body final state $K_{\rm{S}}^0K^\pm \pi^\mp$. The analysis uses samples of $B$ mesons produced in proton-proton collisions, corresponding to an integrated luminosity of 1.0, 2.0, and 6.0 fb$^{-1}$ collected with the LHCb detector at centre-of-mass energies of $\sqrt{s} = $ 7, 8, and 13 TeV, respectively. These measurements are the most precise to date, and provide important input for the determination of the CKM angle $\gamma$.

hep-ex↗