Highlights from the LHCb experiment

We report recent results by the LHCb collaboration in heavy-ion collisions in collider and fixed-target mode at the LHC. A large variety of measurements show the potential of LHCb in nuclear collisions

Measurement of D s ^± production asymmetry in pp collisions at √s=7 and 8 TeV

The inclusive $D_s^{\pm}$ production asymmetry is measured in $pp$ collisions collected by the LHCb experiment at centre-of-mass energies of $\sqrt{s} =7$ and 8 TeV. Promptly produced $D_s^{\pm}$ mesons are used, which decay as $D_s^{\pm}\to\phi\pi^{\pm}$, with $\phi\to K^+K^-$. The measurement is performed in bins of transverse momentum, $p_{\rm T}$, and rapidity, $y$, covering the range $2.5<p_{\rm T}<25.0$ GeV$/c$ and $2.0<y<4.5$. No kinematic dependence is observed. Evidence of nonzero $D_s^{\pm}$ production asymmetry is found with a significance of 3.3 standard deviations.Comment: All figures and tables, along with any supplementary material and additional information, are available at https://cern.ch/lhcbproject/Publications/p/LHCb-PAPER-2018-010.htm

Direct photon production at LHCb

At small Bjorken-x, the large gluon number density in the nucleon leads to gluon recombination competing with gluon splitting, which could result in saturation of the gluon PDF. This gluon saturation has yet to be conclusively observed. Direct photon production provides sensitivity to gluon densities in protons and nuclei, and the forward acceptance of LHCb detector allows for measurements of this process at low Bjorken-x, providing an ideal probe of saturation effects. Progress towards the measurement of forward direct photon production using the LHCb detector is presented

Measurement of Z -&gt; tau(+)tau(-) production in proton-proton collisions at root s=8 TeV

A measurement of Z → τ$^{+}$τ$^{−}$ production cross-section is presented using data, corresponding to an integrated luminosity of 2 fb$^{−1}$, from pp collisions at $\sqrt{s}=8$ TeV collected by the LHCb experiment. The τ$^{+}$τ$^{−}$ candidates are reconstructed in final states with the first tau lepton decaying leptonically, and the second decaying either leptonically or to one or three charged hadrons. The production cross-section is measured for Z bosons with invariant mass between 60 and 120 GeV/c$^{2}$, which decay to tau leptons with transverse momenta greater than 20 GeV/c and pseudorapidities between 2.0 and 4.5. The cross-section is determined to be ${\sigma}_{pp}{{}_{\to Z\to {\tau}^{+}}}_{\tau^{-}}=95.8 \pm 2.1 \pm 4.6 \pm 0.2 \pm 1.1$ pb, where the first uncertainty is statistical, the second is systematic, the third is due to the LHC beam energy uncertainty, and the fourth to the integrated luminosity uncertainty. This result is compatible with NNLO Standard model predictions. The ratio of the cross-sections for Z → τ$^{+}$τ$^{−}$ to Z → μ$^{+}$μ$^{−}$ (Z → e$^{+}$e$^{−}$), determined to be 1.01 ± 0.05 (1.02 ± 0.06), is consistent with the lepton-universality hypothesis in Z decays.A measurement of $Z\rightarrow\tau^+\tau^-$ production cross-section is presented using data, corresponding to an integrated luminosity of 2 fb$^{-1}$, from $pp$ collisions at $\sqrt{s}=8$ TeV collected by the LHCb experiment. The $\tau^+\tau^-$ candidates are reconstructed in final states with the first tau lepton decaying leptonically, and the second decaying either leptonically or to one or three charged hadrons. The production cross-section is measured for $Z$ bosons with invariant mass between 60 and 120 GeV/$c^2$, which decay to tau leptons with transverse momenta greater than 20 GeV/$c$ and pseudorapidities between 2.0 and 4.5. The cross-section is determined to be $\sigma_{pp\rightarrow{}Z\rightarrow{}\tau^+\tau^-} = 95.8 \pm 2.1 \pm 4.6 \pm 0.2 \pm 1.1 \mathrm{pb}$, where the first uncertainty is statistical, the second is systematic, the third is due to the LHC beam energy uncertainty, and the fourth to the integrated luminosity uncertainty. This result is compatible with NNLO Standard model predictions. The ratio of the cross-sections for $Z\rightarrow\tau^+\tau^-$ to $Z\rightarrow\mu^+\mu^-$ ($Z\rightarrow{}e^+e^-$), determined to be $1.01 \pm 0.05$ ($1.02 \pm 0.06$), is consistent with the lepton-universality hypothesis in $Z$ decays

Differential branching fraction and angular moments analysis of the decay B0→K+π−μ+μ− in the K∗0,2(1430)0 region

See paper for full list of authors - All figures and tables, along with any supplementary material and additional information, are available at this https URL - Submitted to JHEPInternational audienceMeasurements of the differential branching fraction and angular moments of the decay B0→K+π−μ+μ− in the K∗0,2(1430)0 in the K+π− invariant mass range 1330<m(K+π−)<1530 MeV/c2 are presented. Proton-proton collision data are used, corresponding to an integrated luminosity of 3 fb−1 collected by the LHCb experiment. Differential branching fraction measurements are reported in five bins of the invariant mass squared of the dimuon system, q2, between 0.1 and 8.0 GeV2/c4. For the first time, an angular analysis sensitive to the S-, P- and D-wave contributions of this rare decay is performed. The set of 40 normalised angular moments describing the decay is presented for the q2 range 1.1--6.0 GeV2/c4

Search for the rare decay Λ[subscript c][superscript +] → pμ[superscript +]μ[superscript −]

A search for the flavor-changing neutral-current decay Λ[subscript c][superscript +]→pμ[superscript +]μ[superscript -] is reported using a data set corresponding to an integrated luminosity of 3.0  fb[superscript -1] collected by the LHCb Collaboration. No significant signal is observed outside of the dimuon mass regions around the ϕ and ω resonances, and an upper limit is placed on the branching fraction of B(Λ[subscript c][superscript +]→pμ[superscript +]μ[superscript -])<7.7(9.6)×10[superscript -8] at  90%(95%) confidence level. A significant signal is observed in the ω dimuon mass region for the first time.National Science Foundation (U.S.

Search for the rare decay Λc+→pμ+μ−

A search for the flavor-changing neutral-current decay Λ + c → p μ + μ − is reported using a data set corresponding to an integrated luminosity of 3.0     fb − 1 collected by the LHCb Collaboration. No significant signal is observed outside of the dimuon mass regions around the ϕ and ω resonances, and an upper limit is placed on the branching fraction of B ( Λ + c → p μ + μ − ) < 7.7 ( 9.6 ) × 10 − 8 at  90%(95%) confidence level. A significant signal is observed in the ω dimuon mass region for the first time

Search for the rare decay Λc+→pμ+μ−

A search for the flavor-changing neutral-current decay Lambda(+)(c) -> p mu(+)mu(-) is reported using a data set corresponding to an integrated luminosity of 3.0 fb(-1) collected by the LHCb Collaboration. No significant signal is observed outside of the dimuon mass regions around the phi and omega resonances, and an upper limit is placed on the branching fraction of B(Lambda(+ )(c)-> p mu(+)mu(-)) < 7.7(9.6) x 10(-8) at 90%(95%) confidence level. A significant signal is observed in the omega dimuon mass region for the first time

Study of coherent J/psi production in lead-lead collisions at root s(NN)=5 TeV with the LHCb experiment

Coherent production of J/psi mesons is studied in lead-lead collision data at a nucleon-nucleon centre-of-mass energy of 5 TeV collected by the LHCb experiment. The data set corresponds to an integrated luminosity of about 10 mu b(-1). The J/psi, mesons are reconstructed in the dimuon final state, where the muons are detected within the pseudorapidity region 2.0 &lt; eta &lt; 4.5. The J/psi mesons are required to have transverse momentum P-T &lt; 1 GeV and rapidity 2.0 &lt; y &lt; 4.5. The cross-section within this fiducial region is measured to be sigma = 5.3 +/- 0.2 (stat) +/- 0.5 (syst) +/- 0.7 (lumi) mb. The differential cross-section is also measured in five bins of J/psi rapidity. The results are compared to predictions from phenomenological models