The $pp \to W^{\pm} (\to μ^{\pm} ν_μ) X$ cross-sections are measured at a proton-proton centre-of-mass energy $\sqrt{s} = 5.02$ TeV using a dataset corresponding to an integrated luminosity of 100 pb$^{-1}$ recorded by the LHCb experiment. Considering muons in the pseudorapidity range $2.2 < η< 4.4$, the cross-sections are measured differentially in twelve intervals of muon transverse momentum between $28 < p_\mathrm{T} < 52$ GeV. Integrated over $p_\mathrm{T}$, the measured cross-sections are \begin{align*} σ_{W^+ \to μ^+ ν_μ} &= 300.9 \pm 2.4 \pm 3.8 \pm 6.0~\text{pb}, \\ σ_{W^- \to μ^- \barν_μ} &= 236.9 \pm 2.1 \pm 2.7 \pm 4.7~\text{pb}, \end{align*} where the first uncertainties are statistical, the second are systematic, and the third are associated with the luminosity calibration. These integrated results are consistent with theoretical predictions. This analysis introduces a new method to determine the $W$-boson mass using the measured differential cross-sections corrected for detector effects. The measurement is performed on this statistically limited dataset as a proof of principle and yields \begin{align*} m_W = 80369 \pm 130 \pm 33~\text{MeV}, \end{align*} where the first uncertainty is experimental and the second is theoretical.
The measured differential cross sections ($d\sigma/dp_T$) for $W^+$. The first systematic uncertainty is statistical and the second is systematic.
The measured differential cross sections ($d\sigma/dp_T$) for $W^-$. The first systematic uncertainty is statistical and the second is systematic.
The correlation matrix corresponding to the statistical uncertainties on the differential cross-section ($d\sigma/dp_T$) fit results for $W^+$. To combine with $W^-$, use the rows and columns ordered as $W^+$ and then $W^-$. Assume no correlation in the statistical uncertainties between $W^+$ and $W^-$ (zero entries in the off-diagonal blocks).
A study on the Bose-Einstein correlations for triplets of same-sign pions is presented. The analysis is performed using proton-proton collisions at a centre-of-mass energy of $\sqrt{s}$ = 7 TeV, recorded by the LHCb experiment, corresponding to an integrated luminosity of 1.0 fb$^{-1}$. For the first time, the results are interpreted in the core-halo model. The parameters of the model are determined in regions of charged-particle multiplicity. This measurement provides insight into the nature of hadronisation in terms of coherence, showing a coherent emission of pions.
Results of the fit to the three-particle double ratio ($r_{d_{3}}$) for same-sign pion triplets, VELO track multiplicity for pp collision: 5-10.
Results of the fit to the three-particle double ratio ($r_{d_{3}}$) for same-sign pion triplets, VELO track multiplicity for pp collision: 11-20.
Results of the fit to the three-particle double ratio ($r_{d_{3}}$) for same-sign pion triplets, VELO track multiplicity for pp collision: 21-60.
The LHCb collaboration presents a novel suite of heavy-flavour jet substructure measurements at forward rapidity in proton-proton collisions at a centre-of-mass energy of $\sqrt{s} = 13$ TeV. The jet mass is a perturbatively calculable probe of the virtuality of hard-scattered quarks and gluons, connecting small-distance quantum chromodynamics (QCD) with long-distance experimental measurement. It becomes dominated by nonperturbative corrections at small values, presenting an excellent test of QCD across a broad range of energies. Measuring heavy-flavour jet mass with a theoretically unambiguous flavour definition for the first time probes the gluon splitting mechanism for heavy-flavour production and pushes tests of perturbative QCD to unprecedented theoretical precision. Utilising the soft drop jet-grooming technique to access the perturbative jet core further enhances constraints on first-principles theory. Measurements of the jet mass for jets containing fully reconstructed $B^\pm$ hadrons are reported with and without grooming. These results offer unparalleled tests of quark flavour and mass dependence in QCD and provide a baseline for future studies of heavy-flavour jet quenching in heavy-ion collisions.
Groomed $B^\pm$-tagged jet invariant mass $m_{\textrm{jet,gr}}/p_{\textrm{T,jet}}$ for $R=0.5$ jets reconstructed in pp data, without any WTA flavour requirement. Normalization is set to unity. $10 < p_{\textrm{T,jet}} < 12$ GeV, soft drop $z_{\textrm{cut}}=0.1, \beta=0$.
Groomed $B^\pm$-tagged jet invariant mass $m_{\textrm{jet,gr}}/p_{\textrm{T,jet}}$ for $R=0.5$ jets reconstructed in pp data, without any WTA flavour requirement. Normalization is set to unity. $12 < p_{\textrm{T,jet}} < 15$ GeV, soft drop $z_{\textrm{cut}}=0.1, \beta=0$.
Groomed $B^\pm$-tagged jet invariant mass $m_{\textrm{jet,gr}}/p_{\textrm{T,jet}}$ for $R=0.5$ jets reconstructed in pp data, without any WTA flavour requirement. Normalization is set to unity. $15 < p_{\textrm{T,jet}} < 20$ GeV, soft drop $z_{\textrm{cut}}=0.1, \beta=0$.
Using $e^+e^-$ collision data collected with the BESIII detector operating at the Beijing Electron Positron Collider, the cross section of $e^+e^-\to \pi^+\pi^- h_c$ is measured at 59 points with center-of-mass energy $\sqrt{s}$ ranging from $4.009$ to $4.950~\mathrm{GeV}$ with a total integrated luminosity of $22.2~\mathrm{fb}^{-1}$. The cross section between $4.3$ and $4.45~\mathrm{GeV}$ exhibits a plateau-like shape and drops sharply around $4.5~\mathrm{GeV}$, which cannot be described by two resonances only. Three coherent Breit-Wigner functions are used to parameterize the $\sqrt{s}$-dependent cross section line shape. The masses and widths are determined to be $M_1=(4223.6_{-3.7-2.9}^{+3.6+2.6})~\mathrm{MeV}/c^2$, $\Gamma_1=(58.5_{-11.4-6.5}^{+10.8+6.7})~\mathrm{MeV}$, $M_2=(4327.4_{-18.8-9.3}^{+20.1+10.7})~\mathrm{MeV}/c^2$, $\Gamma_2=(244.1_{-27.1-18.0}^{+34.0+23.9})~\mathrm{MeV}$, and $M_3=(4467.4_{-5.4-2.7}^{+7.2+3.2})~\mathrm{MeV}/c^2$, $\Gamma_3=(62.8_{-14.4-6.6}^{+19.2+9.8})~\mathrm{MeV}$. The first uncertainties are statistical and the other two are systematic. The statistical significance of the three Breit-Wigner assumption over the two Breit-Wigner assumption is greater than $5\sigma$.
Dressed cross section at the 19 XYZ-I energy points with large statistics. The table also lists the integral luminosity, the number of signal events, the weighted efficiency, the radiative correction factor, and the dressed cross section. For the dressed cross section, the first error is statistical, the second error is the systematic, and the third error comes from the input branching ratios which is the dominant one in the multiplicative systematic uncertainties.
Dressed cross section at the 25 XYZ-II energy points with lower statistics. The table also lists the integral luminosity, the number of signal events, the weighted efficiency, the radiative correction factor, and the dressed cross section. For the dressed cross section, the first error is statistical, the second error is the systematic, and the third error comes from the input branching ratios which is the dominant one in the multiplicative systematic uncertainties.
Dressed cross section and its upper limit at the 15 R-scan energy points with small statistics. The table also lists the integral luminosity, the number of signal events, the weighted efficiency, the radiative correction factor, and the dressed cross section. For the dressed cross section, the first error is statistical, the second error is the systematic, and the third error comes from the input branching ratios which is the dominant one in the multiplicative systematic uncertainties.
The first study of $J/ψϕ$ production in diffractive processes in proton-proton collisions is presented. The study is based on an LHCb dataset recorded at centre-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 5 fb$^{-1}$. The data disfavour a nonresonant $J/ψϕ$ production but are consistent with a resonant model including several resonant states observed previously only in $B^+ \to J/ψϕK^+$ decays. The $χ_{c0}(4500)$ state is observed with a significance over $6σ$ and the $χ_{c1}(4274)$ is confirmed with a significance of more than $4σ$.
Total $J/\psi(\to \mu^+ \mu^-)\phi(\to K^+ K^-)$ diffractive production cross-section, multiplied by $\mathcal{B}(J/\psi \to \mu^+ \mu^-)$ and $\mathcal{B}(\phi \to K^+ K^-)$ branching ratios.
$\chi_{c1}(4140) \to J/\psi(\to \mu^+ \mu^-)\phi(\to K^+ K^-)$ diffractive production cross-section, multiplied by $\mathcal{B}(J/\psi \to \mu^+ \mu^-)$ and $\mathcal{B}(\phi \to K^+ K^-)$ branching ratios.
$\chi_{c1}(4274) \to J/\psi(\to \mu^+ \mu^-)\phi(\to K^+ K^-)$ diffractive production cross-section, multiplied by $\mathcal{B}(J/\psi \to \mu^+ \mu^-)$ and $\mathcal{B}(\phi \to K^+ K^-)$ branching ratios.
A comprehensive study of the local and nonlocal amplitudes contributing to the decay $B^0\rightarrow K^{*0}(\to K^+\pi^-) \mu^+\mu^-$ is performed by analysing the phase-space distribution of the decay products. The analysis is based on $pp$ collision data corresponding to an integrated luminosity of 8.4fb$^{-1}$ collected by the LHCb experiment. This measurement employs for the first time a model of both one-particle and two-particle nonlocal amplitudes, and utilises the complete dimuon mass spectrum without any veto regions around the narrow charmonium resonances. In this way it is possible to explicitly isolate the local and nonlocal contributions and capture the interference between them. The results show that interference with nonlocal contributions, although larger than predicted, only has a minor impact on the Wilson Coefficients determined from the fit to the data. For the local contributions, the Wilson Coefficient $C_9$, responsible for vector dimuon currents, exhibits a $2.1\sigma$ deviation from the Standard Model expectation. The Wilson Coefficients $C_{10}$, $C_{9}'$ and $C_{10}'$ are all in better agreement than $C_{9}$ with the Standard Model and the global significance is at the level of $1.5\sigma$. The model used also accounts for nonlocal contributions from $B^{0}\to K^{*0}\left[\tau^+\tau^-\to \mu^+\mu^-\right]$ rescattering, resulting in the first direct measurement of the $b s\tau\tau$ vector effective-coupling $C_{9\tau}$.
Signal parameter results. See Table 1 in README.pdf in the attached resources for an explicit mapping between text-based parameter names and their symbolic representations in the main paper.
Total covariance matrix including both statistical and systematic effects. See Sec. 5 in the main paper for a description of the dominant systematic uncertainties. See Table 1 in README.pdf in the attached resources for an explicit mapping between text-based parameter names and their symbolic representations in the main paper.
Statistical covariance matrix. See Table 1 in README.pdf in the attached resources for an explicit mapping between text-based parameter names and their symbolic representations in the main paper.
With the STAR experiment at the BNL Relativisic Heavy Ion Collider, we characterize $\sqrt{s_\mathrm{NN}}$ = 200 GeV p+Au collisions by event activity (EA) measured within the pseudorapidity range $eta$$in$ [-5, -3.4] in the Au-going direction and report correlations between this EA and hard- and soft- scale particle production at midrapidity ($\eta$$\in$ [-1, 1]). At the soft scale, charged particle production in low-EA p+Au collisions is comparable to that in p+p collisions and increases monotonically with increasing EA. At the hard scale, we report measurements of high transverse momentum (pT) jets in events of different EAs. In contrast with the soft particle production, high-pT particle production and EA are found to be inversely related. To investigate whether this is a signal of jet quenching in high-EA events, we also report ratios of pT imbalance and azimuthal separation of dijets in high- and low-EA events. Within our measurement precision, no significant differences are observed, disfavoring the presence of jet quenching in the highest 30% EA p+Au collisions at $\sqrt{s_\mathrm{NN}}$ = 200 GeV.
Distributions of Event Activity (as measured by the BBC) from MB and HT events with the latter satisfying an offline trigger of $E_\mathrm{T}^\mathrm{trig}>4 \mathrm{GeV}$.
Density of charged particles with $p_\mathrm{T}>0.2$ GeV/$c$ and $|\eta|\le0.9$ in ten ranges of EA for MB events and HT events selected with several offline trigger values.
Charged particle density as a function of EA, UE $\eta$, and $p_\mathrm{T,jet}^\mathrm{lead}$ for HT ($E_\mathrm{T}^\mathrm{trig}>4$ GeV) events with $p_\mathrm{T,jet}^\mathrm{raw,lead}>4~\mathrm{GeV}/c$.
Based on a data sample of 10 billion $J/\psi$ events collected with the BESIII detector, improved measurements of the Dalitz decays $\eta/\eta'\rightarrow\gamma e^+e^-$ are performed, where the $\eta$ and $\eta'$ are produced through the radiative decays $J/\psi\rightarrow\gamma \eta/\eta'$. The branching fractions of $\eta\rightarrow\gamma e^+e^-$ and $\eta'\rightarrow\gamma e^+e^-$ are measured to be $(7.07 \pm 0.05 \pm 0.23)\times10^{-3}$ and $(4.83\pm0.07\pm0.14)\times10^{-4}$, respectively. Within the single pole model, the parameter of electromagnetic transition form factor for $\eta\rightarrow\gamma e^+e^-$ is determined to be $\Lambda_{\eta}=(0.749 \pm 0.027 \pm 0.007)~ {\rm GeV}/c^{2}$. Within the multi-pole model, we extract the electromagnetic transition form factors for $\eta'\rightarrow\gamma e^+e^-$ to be $\Lambda_{\eta'} = (0.802 \pm 0.007\pm 0.008)~ {\rm GeV}/c^{2}$ and $\gamma_{\eta'} = (0.113\pm0.010\pm0.002)~ {\rm GeV}/c^{2}$. The results are consistent with both theoretical predictions and previous measurements. The characteristic sizes of the interaction regions for the $\eta$ and $\eta'$ are calculated to be $(0.645 \pm 0.023 \pm 0.007 )~ {\rm fm}$ and $(0.596 \pm 0.005 \pm 0.006)~ {\rm fm}$, respectively. In addition, we search for the dark photon in $\eta/\eta^\prime\rightarrow\gamma e^{+}e^{-}$, and the upper limits of the branching fractions as a function of the dark photon are given at 90% confidence level.
The binned invariant mass spectrum of $e^+e^-$ pairs produced from the $\eta\to \gamma e^+e^-$ transition. The efficiency-corrected and background-subtracted data are binned in M($e^+e^-$) and the number of events in each bin is shown.
The binned invariant mass spectrum of $e^+e^-$ pairs produced from the $\eta^\prime\to \gamma e^+e^-$ transition. The efficiency-corrected and background-subtracted data are binned in M($e^+e^-$) and the number of events in each bin is shown.
We report the systematic measurement of protons and light nuclei production in Au+Au collisions at $\sqrt{s_{\mathrm{NN}}}$ = 3 GeV by the STAR experiment at the Relativistic Heavy Ion Collider (RHIC). The transverse momentum ($p_{T}$) spectra of protons ($p$), deuterons ($d$), tritons ($t$), $^{3}\mathrm{He}$, and $^{4}\mathrm{He}$ are measured from mid-rapidity to target rapidity for different collision centralities. We present the rapidity and centrality dependence of particle yields ($dN/dy$), average transverse momentum ($\langle p_{T}\rangle$), yield ratios ($d/p$, $t/p$,$^{3}\mathrm{He}/p$, $^{4}\mathrm{He}/p$), as well as the coalescence parameters ($B_2$, $B_3$). The 4$\pi$ yields for various particles are determined by utilizing the measured rapidity distributions, $dN/dy$. Furthermore, we present the energy, centrality, and rapidity dependence of the compound yield ratios ($N_{p} \times N_{t} / N_{d}^{2}$) and compare them with various model calculations. The physics implications of those results on the production mechanism of light nuclei and on QCD phase structure are discussed.
Weak decay feed-down fraction of protons (%) at different centralities in Au+Au collisions at $\sqrt{s_{NN}}$ = 3 GeV. The statistical and systematic uncertainties are shown respectively.
Transverse momentum spectra of inclusive protons in 0-10% Au+Au collisions at $\sqrt{s_{NN}}$ = 3 GeV. The statistical and systematic uncertainties are shown respectively.
Transverse momentum spectra of inclusive protons in 10-20% Au+Au collisions at $\sqrt{s_{NN}}$ = 3 GeV. The statistical and systematic uncertainties are shown respectively.
We report on the charged-particle multiplicity dependence of net-proton cumulant ratios up to sixth order from $\sqrt{s}=200$ GeV $p$+$p$ collisions at the Relativistic Heavy Ion Collider (RHIC). The measured ratios $C_{4}/C_{2}$, $C_{5}/C_{1}$, and $C_{6}/C_{2}$ decrease with increased charged-particle multiplicity and rapidity acceptance. Neither the Skellam baselines nor PYTHIA8 calculations account for the observed multiplicity dependence. In addition, the ratios $C_{5}/C_{1}$ and $C_{6}/C_{2}$ approach negative values in the highest-multiplicity events, which implies that thermalized QCD matter may be formed in $p$+$p$ collisions.
(c) Charged-particle multiplicity distribution.
(d) Event-by-event net-proton multiplicity distributions for $|y|<0.5$ and $0.4<p_{\rm{T}}<2.0$ GeV/$c$ at two ranges of charged particle multiplicity as indicated in the legend.
Net-proton cumulant ratios, (a) $C_{2}/C_{1}$, (b) $C_{3}/C_{2}$, (c) $C_{4}/C_{2}$, (d) $C_{5}/C_{1}$, and (e) $C_{6}/C_{2}$ as a function of charged-particle multiplicity from $\sqrt{s}=200$ GeV $p$+$p$ collisions. Black solid lines and red bands represent the statistical and systematic uncertainties, respectively. Cyan points represent event averages for $3 < m_{\rm ch}^{\rm TPC} < 30$, and they are plotted at the corresponding value of $m_{\rm ch}^{\rm TPC}$. The uncertainties on the cyan points are smaller than the marker size. The Skellam baselines are shown as dotted lines. The results of the PYTHIA8 calculations are shown by hatched-golden bands. The golden bands at $m_{\rm ch}^{\rm TPC}\approx 6$ are the results from the PYTHIA8 calculations averaged over multiplicities.
Forum