A
bstract
The production of
ϒ
(
nS
) mesons (
n
= 1, 2, 3) in
p
Pb and Pb
p
collisions at a centre-of-mass energy per nucleon pair
s
N
N
=
8.16
TeV is measured by the LHCb experiment, using a data ...sample corresponding to an integrated luminosity of 31.8 nb
−1
. The
ϒ
(
nS
) mesons are reconstructed through their decays into two opposite-sign muons. The measurements comprise the differential production cross-sections of the
ϒ
(1
S
) and
ϒ
(2
S
) states, their forward-to-backward ratios and nuclear modification factors. The measurements are performed as a function of the transverse momentum
p
T
and rapidity in the nucleon-nucleon centre-of-mass frame
y
*
of the
ϒ
(
nS
) states, in the kinematic range
p
T
< 25 GeV/
c
and 1.5 <
y
*
< 4.0 (−5.0 <
y
*
< −2.5) for
p
Pb (Pb
p
) collisions. In addition, production cross-sections for
ϒ
(3
S
) are measured integrated over phase space and the production ratios between all three
ϒ
(
nS
) states are determined. Suppression for bottomonium in proton-lead collisions is observed, which is particularly visible in the ratios. The results are compared to theoretical models.
A
bstract
A measurement of the production cross-section of Z bosons in pp collisions at
s
=
13
TeV is presented using dimuon and dielectron final states in LHCb data. The cross-section is measured ...for leptons with pseudorapidities in the range 2
.
0
< η <
4
.
5, transverse momenta
p
T
>
20 GeV and dilepton invariant mass in the range 60
< m
(
ℓℓ
)
<
120 GeV. The integrated cross-section from averaging the two final states is
σ
Z
ℓℓ
= 194.3 ± 0.9 ± 3.3 ± 7.6 pb
,
where the first uncertainty is statistical, the second is due to systematic effects, and the third is due to the luminosity determination. In addition, differential cross-sections are measured as functions of the Z boson rapidity, transverse momentum and the angular variable
ϕ
η
*
.
The first observation of the decays Λ$^0_b$ → $χ$c1$pK$- and Λ$^0_b$ → $χ$c2$pK$- is reported using a data sample corresponding to an integrated luminosity of 3.0 fb-1, collected by the LHCb ...experiment in $pp$ collisions at center-of-mass energies of 7 and 8 TeV. The following ratios of branching fractions are measured: $$\frac{\mathscr{B}(Λ^0_b→Χ_{c1}pK^-)}{\mathscr{B}(Λ^0_b→J/ψpK^-)}=0.242 ± 0.014 ± 0.013 ± 0.009$$ $$\frac{\mathscr{B}(Λ^0_b→Χ_{c2}pK^-)}{\mathscr{B}(Λ^0_b→J/ψpK^-)}= 0.248 ± 0.020 ± 0.014 ± 0.009$$ $$\frac{\mathscr{B}(Λ^0_b→Χ_{c2}pK^-)}{\mathscr{B}(Λ^0_b→Χ_{c1}pK^-)}= 1.02 ± 0.10 ± 0.02 ± 0.05$$ where the first uncertainty is statistical, the second systematic, and the third due to the uncertainty on the branching fractions of the $Χ_{c1}$ → $Jψγ$ and $Χ_{c2}$ → $Jψγ$ decays. Using both decay modes, the mass of the Λ$^0_b$ baryon is also measured to be $m$Λ$^0_b$ = 5619.44 ± 0.28 ± 0.26 MeV/$c$2, where the first and second uncertainties are statistical and systematic, respectively.
A search for time-dependent violation of the charge-parity symmetry in D0→K+K− and D0→π+π− decays is performed at the LHCb experiment using proton-proton collision data recorded from 2015 to 2018 at ...a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 6 fb−1. The D0 meson is required to originate from a D*(2010)+→D0π+ decay, such that its flavor at production is identified by the charge of the accompanying pion. The slope of the time-dependent asymmetry of the decay rates of D0 and D0 mesons into the final states under consideration is measured to be ΔYK+K−=(−2.3±1.5±0.3)×10−4, ΔYπ+π−=(−4.0±2.8±0.4)×10−4, where the first uncertainties are statistical and the second are systematic. These results are compatible with the conservation of the charge-parity symmetry at the level of 2 standard deviations and improve the precision by nearly a factor of 2.
An angular analysis of B0 → J / ψ K+ π− decays is performed, using proton-proton collision data corresponding to an integrated luminosity of 3 fb−1 collected with the LHCb detector. The m (K+ π−) ...spectrum is divided into fine bins. In each m(K+ π−) bin, the hypothesis that the three-dimensional angular distribution can be described by structures induced only by K* resonances is examined, making minimal assumptions about the K+ π− system. The data reject the K*-only hypothesis with a large significance, implying the observation of exotic contributions in a model-independent fashion. Inspection of the m(J / ψπ−) vs m(K+ π−) plane suggests structures near m(J / ψπ−) = 4200 and 4600 MeV.
A search for the flavor-changing neutral-current decay Λc+→pμ+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(Λc+→pμ+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.
A time-dependent analysis of the Bs0→ϕγ decay rate is performed to determine the CP -violating observables Sϕγ and Cϕγ and the mixing-induced observable AϕγΔ. The measurement is based on a sample of ...pp collision data recorded with the LHCb detector, corresponding to an integrated luminosity of 3 fb−1 at center-of-mass energies of 7 and 8 TeV. The measured values are Sϕγ=0.43±0.30±0.11, Cϕγ=0.11±0.29±0.11, and AϕγΔ=−0.67−0.41+0.37±0.17, where the first uncertainty is statistical and the second systematic. This is the first measurement of the observables S and C in radiative Bs0 decays. The results are consistent with the standard model predictions.
The production of charged hadrons within jets recoiling against a Z boson is measured in proton-proton collision data at √s = 8 TeV recorded by the LHCb experiment. The charged-hadron structure of ...the jet is studied longitudinally and transverse to the jet axis for jets with transverse momentum pT > 20 GeV and in the pseudorapidity range 2.5 < η < 4. These are the first measurements of jet hadronization at these forward rapidities and also the first where the jet is produced in association with a Z boson. In contrast to previous hadronization measurements at the Large Hadron Collider, which are dominated by gluon jets, these measurements probe predominantly light-quark jets which are found to be more longitudinally and transversely collimated with respect to the jet axis when compared to the previous gluon dominated measurements. Therefore, these results provide valuable information on differences between quarks and gluons regarding nonperturbative hadronization dynamics.
The CP asymmetry in the mixing of B0s and B¯0s mesons is measured in proton-proton collision data corresponding to an integrated luminosity of 3.0 fb-1, recorded by the LHCb experiment at ...center-of-mass energies of 7 and 8 TeV. Semileptonic B0s and B¯0s decays are studied in the inclusive mode D∓sμ±ν(–)μX with the D∓s mesons reconstructed in the K+K–π∓ final state. Correcting the observed charge asymmetry for detection and background effects, the CP asymmetry is found to be assl = (0.39 ± 0.26 ± 0.20)%, where the first uncertainty is statistical and the second systematic. This is the most precise measurement of assl to date. It is consistent with the prediction from the standard model and will constrain new models of particle physics.
Violations of $ CPT$ symmetry and Lorentz invariance are searched for by studying interference effects in $ B^0$ mixing and in $ B^0_s$ mixing. Samples of $ B^0\to J/\psi K^0_{\mathrm{S}}$ and $ ...B^0_s\to J/\psi K^+ K^-$ decays are recorded by the LHCb detector in proton--proton collisions at centre-of-mass energies of 7 and 8 TeV, corresponding to an integrated luminosity of 3 fb$^{-1}$. No periodic variations of the particle-antiparticle mass differences are found, consistent with Lorentz invariance and $ CPT$ symmetry. Results are expressed in terms of the Standard Model Extension parameter $\Delta a_{\mu}$ with precisions of $ \mathcal{O}(10^{-15})$ and $ \mathcal{O}(10^{-14})$ GeV for the $ B^0$ and $ B^0_s$ systems, respectively. With no assumption on Lorentz (non-)invariance, the $ CPT$-violating parameter $z$ in the $ B^0_s$ system is measured for the first time and found to be $ \mathcal{R}e(z) = -0.022 \pm 0.033 \pm 0.005$ and $ \mathcal{I}m(z) = 0.004 \pm 0.011\pm 0.002$, where the first uncertainties are statistical and the second systematic.
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