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 $J/\psi\phi$ 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 $J/\psi\phi$ production but are consistent with a resonant model including several resonant states observed previously only in $B^+ \to J/\psi\phi K^+$ decays. The $\chi_{c0}(4500)$ state is observed with a significance over $5\sigma$ and the $\chi_{c1}(4274)$ is confirmed with a significance of more than $4\sigma$.
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.
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.
Using a sample of $(10087\pm44)\times 10^6$$J/\psi$ events, which is about 45 times larger than that was previously analyzed, a further investigation on the $J/\psi\rightarrow \gamma 3(\pi^+\pi^-)$ decay is performed. A significant distortion at 1.84 GeV/$c^2$ in the line-shape of the $3(\pi^+\pi^-)$ invariant mass spectrum is observed for the first time, which could be resolved by two overlapping resonant structures, $X(1840)$ and $X(1880)$. The new state $X(1880)$ is observed with a statistical significance larger than $10\sigma$. The mass and width of $X(1880)$ are determined to be $1882.1\pm1.7\pm0.7$ MeV/$c^2$ and $30.7\pm5.5 \pm2.4$ MeV, respectively, which indicates the existence of a $p\bar{p}$ bound state.
The binned invariant mass spectrum of 6pi. The data correspond to Figure 3 of the event sample collected by BESIII. The mass range 1.55 < M(6pi) < 2.07 GeV is subdivided into 130 equidistant M(6pi) bins with a width of 4 MeV. The binned mass spectrum has been corrected by efficiency and the background Jpsi -> pi0 3(pi+ pi-) has been removed.
The first measurement of the $Z$ boson production cross-section at centre-of-mass energy $\sqrt{s} = 5.02\,$TeV in the forward region is reported, using $pp$ collision data collected by the LHCb experiment in year 2017, corresponding to an integrated luminosity of $100 \pm 2\,\rm{pb^{-1}}$. The production cross-section is measured for final-state muons in the pseudorapidity range $2.0<\eta<4.5$ with transverse momentum $p_{\rm{T}}> 20\,\rm{GeV/}\it{c}$. The integrated cross-section is determined to be \[ \sigma_{Z \rightarrow \mu^{+}\mu^{-}} = 39.6 \pm 0.7\,(\rm{stat}) \pm 0.6\,(\rm{syst}) \pm 0.8\,(\rm{lumi}) \ \rm{pb} \] for the di-muon invariant mass in the range $60<M_{\mu\mu}<120\,\rm{GeV/}\it{c^{2}}$. This result and the differential cross-section results are in good agreement with theoretical predictions at next-to-next-to-leading order in the strong coupling. Based on a previous LHCb measurement of the $Z$ boson production cross-section in $p$Pb collisions at $\sqrt{s_{NN}}=5.02$ TeV, the nuclear modification factor $R_{p\rm{Pb}}$ is measured for the first time at this energy. The measured values are $1.2^{+0.5}_{-0.3}\,(\rm{stat}) \pm 0.1\,(\rm{syst})$ in the forward region ($1.53<y^*_{\mu}<4.03$) and $3.6^{+1.6}_{-0.9}\,(\rm{stat}) \pm 0.2\,(\rm{syst})$ in the backward region ($-4.97<y^*_{\mu}<-2.47$), where $y^*_{\mu}$ represents the muon rapidity in the centre-of-mass frame.
Systematic uncertainties on the single differential cross-sections in bins of $y^{Z}$, presented in percentage.
Systematic uncertainties on the single differential cross-sections in bins of $p_{T}^{Z}$, presented in percentage.
Systematic uncertainties on the single differential cross-sections in bins of $\phi_{\eta}^{*}$, presented in percentage.
A precision measurement of the matrix elements for $\eta\to\pi^+\pi^-\pi^0$ and $\eta\to\pi^0\pi^0\pi^0$ decays is performed using a sample of $(10087\pm44)\times10^6$$J/\psi$ decays collected with the BESIII detector. The decay $J/\psi \to \gamma \eta$ is used to select clean samples of 631,686 $\eta\to\pi^+\pi^-\pi^0$ decays and 272,322 $\eta\to\pi^0\pi^0\pi^0$ decays. The matrix elements for both channels are in reasonable agreement with previous measurements. The non-zero $gX^2Y$ term for the decay mode $\eta\to\pi^+\pi^-\pi^0$ is confirmed, as reported by the KLOE Collaboration, while the other higher-order terms are found to be insignificant. Dalitz plot asymmetries in the $\eta\to\pi^+\pi^-\pi^0$ decay are also explored and are found to be consistent with charge conjugation invariance. In addition, a cusp effect is investigated in the $\eta\to\pi^0\pi^0\pi^0$ decay, and no obvious structure around the $\pi^+\pi^-$ mass threshold is observed.
The acceptance corrected $\eta\to\pi^+\pi^-\pi^0$ data from 10 billion $J/\psi$ events collected at BESIII and the corresponding statistical uncertainties in the Dalitz plot variables $X$ and $Y$. The data are divided into $20\times20$ bins in $X$ and $Y$, and only the bins with non-zero event are listed in the table. The first two columns in the table are the center values of $X$ and $Y$, respectively. The last column is the acceptance corrected data and the corresponding statistical uncertainties.
The acceptance corrected $\eta\to\pi^0\pi^0\pi^0$ data from 10 billion $J/\psi$ events collected at BESIII and the corresponding statistical uncertainties in the Dalitz plot variables $X$ and $Y$. The data are divided into $20\times20$ bins in $X$ and $Y$, and only the bins with non-zero event are listed in the table. The first two columns in the table are the center values of $X$ and $Y$, respectively. The last column is the acceptance corrected data and the corresponding statistical uncertainties.
The helicity-dependent single $\pi^{0}$ photoproduction cross section on the deuteron and the angular dependence of the double polarisation observable $E$ for the quasi-free single $\pi^0$ production off the proton and the neutron have been measured for the first time from the threshold region up to the photon energy 1.4 GeV. The experiment was performed at the tagged photon facility of the MAMI accelerator and used a circularly polarised photon beam and longitudinally polarised deuteron target. The reaction products were detected using the large acceptance Crystal Ball/TAPS calorimeter, which covered 97% of the full solid angle. Comparing the cross section from the deuteron with the sum of free nucleon cross sections provides a quantitative estimate of the effects of the nuclear medium on pion production. In contrast, comparison of $E$ helicity asymmetry data from quasi-free protons off deuterium with data from a free proton target indicates that nuclear effects do not significantly affect this observable. As a consequence, it is deduced that the helicity asymmetry $E$ on a free neutron can be reliably extracted from measurements on a deuteron in quasi-free kinematics.
Inclusive polarized total cross section as a function of photon beam energy.
Helicity-dependent differential cross section on deuteron at Egamma= 161. MeV
Helicity-dependent differential cross section on deuteron at Egamma= 178. MeV
The reactions $\gamma p\to \eta p$ and $\gamma p\to \eta' p$ have been measured from their thresholds up to the center-of-mass energy $W=1.96$GeV with the tagged-photon facilities at the Mainz Microtron, MAMI. Differential cross sections were obtained with unprecedented accuracy, providing fine energy binning and full production-angle coverage. A strong cusp is observed in the total cross section and excitation functions for $\eta$ photoproduction at the energies in vicinity of the $\eta'$ threshold, $W=1896$MeV ($E_\gamma=1447$MeV). This behavior is explained in a revised $\eta$MAID isobar model by a significant branching of the $N(1895)1/2^-$ nucleon resonance to both, $\eta p$ and $\eta' p$, confirming the existence and constraining the properties of this poorly known state.
Run 1. Total cross section as a function of c.m. energy W.
Run 2. Total cross section as a function of c.m. energy W.
Run 3. Total cross section as a function of c.m. energy W.
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