JHEP 05 (2024) 259 The cross-section of associated $J/\psi$-$\psi(2S)$ production in
proton-proton collisions at a centre-of-mass energy of $\sqrt{s}=13$ TeV is
measured using a data sample ...corresponding to an integrated luminosity of 4.2
fb$^{-1}$, collected by the LHCb experiment. The measurement is performed for
both $J/\psi$ and $\psi(2S)$ mesons having transverse momentum
$p_{\text{T}}<14$ GeV/$c$ and rapidity $2.0<y<4.5$, assuming negligible
polarisation of the $J/\psi$ and $\psi(2S)$ mesons. The production
cross-section is measured to be $4.5\pm0.7\pm0.3$ nb, where the first
uncertainty is statistical and the second systematic. The differential
cross-sections are measured as functions of several kinematic variables of the
$J/\psi$-$\psi(2S)$ candidates. The results are combined with a measurement of
$J/\psi$-$J/\psi$ production, giving a cross-section ratio between
$J/\psi$-$\psi(2S)$ and $J/\psi$-$J/\psi$ production of
$0.274\pm0.044\pm0.008$, where the first uncertainty is statistical and the
second systematic.
(ProQuest: ... denotes formulae and/or non-USASCII text omitted; see image) Abstract The production of J/psi mesons with rapidity 1.5 < y < 4.0 or -5.0 < y < -2.5 and transverse momentum p ^sub T^ < ...14 GeV/c is studied with the LHCb detector in proton-lead collisions at a nucleon-nucleon centre-of-mass energy ... = 5TeV. The J/psi mesons are reconstructed using the dimuon decay mode. The analysis is based on a data sample corresponding to an integrated luminosity of about 1.6 nb^sup -1^. For the first time the nuclear modification factor and forward-backward production ratio are determined separately for prompt J/psi mesons and J/psi from b-hadron decays. Clear suppression of prompt J/psi production with respect to proton-proton collisions at large rapidity is observed, while the production of J/psi from b-hadron decays is less suppressed. These results show good agreement with available theoretical predictions. The measurement shows that cold nuclear matter effects are important for interpretations of the related quark-gluon plasma signatures in heavy-ion collisions. Figure not available: see fulltext.
JHEP 03 (2024) 088 The production cross-section of $J/\psi$ pairs in proton-proton collisions at
a centre-of-mass energy of $\sqrt{s}=13$ TeV is measured using a data sample
corresponding to an ...integrated luminosity of 4.2 fb$^{-1}$ collected by the
LHCb experiment. The measurement is performed with both $J/\psi$ mesons in the
transverse momentum range $0<p_{\text{T}}<14$ GeV/$c$ and rapidity range
$2.0<y<4.5$. The cross-section of this process is measured to be
16.36$\pm$0.28(stat)$\pm$0.88(syst) nb. The contributions from single-parton
scattering and double-parton scattering are separated based on the dependence
of the cross-section on the absolute rapidity difference $\Delta y$ between the
two $J/\psi$ mesons. The effective cross-section of double-parton scattering is
measured to be $\sigma_{\text{eff}}=$13.1$\pm$1.8(stat)$\pm$2.3(syst) mb. The
distribution of the azimuthal angle $\phi_{\text{CS}}$ of one of the $J/\psi$
mesons in the Collins-Soper frame and the $p_{\text{T}}$-spectrum of the
$J/\psi$ pairs are also measured for the study of the gluon transverse-momentum
dependent distributions inside protons. The extracted values of
$\langle\cos2\phi_{\text{CS}}\rangle$ and $\langle\cos4\phi_{\text{CS}}\rangle$
are consistent with zero, but the presence of azimuthal asymmetry at a few
percent level is allowed.
The production of prompt $D^+_{s}$ and $D^+$ mesons is measured by the LHCb
experiment in proton-lead ($p\mathrm{Pb}$) collisions in both the forward
($1.5<y^*<4.0$) and backward ($-5.0<y^*<-2.5$) ...rapidity regions at a
nucleon-nucleon center-of-mass energy of $\sqrt {s_{\mathrm{NN}}}=8.16\,$TeV.
The nuclear modification factors of both $D^+_{s}$ and $D^+$ mesons are
determined as a function of transverse momentum, $p_{\mathrm{T}}$, and
rapidity. In addition, the $D^+_{s}$ to $D^+$ cross-section ratio is measured
as a function of the charged particle multiplicity in the event. An enhanced
$D^+_{s}$ to $D^+$ production in high-multiplicity events is observed for the
whole measured $p_{\mathrm{T}}$ range, in particular at low $p_{\mathrm{T}}$
and backward rapidity, where the significance exceeds six standard deviations.
This constitutes the first observation of strangeness enhancement in charm
quark hadronization in high-multiplicity $p\mathrm{Pb}$ collisions. The results
are also qualitatively consistent with the presence of quark coalescence as an
additional charm quark hadronization mechanism in high-multiplicity proton-lead
collisions.
The longitudinal polarization fraction of the $D^{*}$ meson is measured in
$B^0\to D^{*-}\tau^{+}\nu_{\tau}$ decays, where the $\tau$ lepton decays to
three charged pions and a neutrino, using ...proton-proton collision data
collected by the LHCb experiment at center-of-mass energies of 7, 8 and 13 TeV
and corresponding to an integrated luminosity of 5 fb$^{-1}$. The $D^{*}$
polarization fraction $F_{L}^{D^{*}}$ is measured in two $q^{2}$ regions, below
and above 7 GeV$^{2}/c^{4}$, where $q^{2}$ is defined as the squared invariant
mass of the $\tau\nu_{\tau}$ system. The $F_{L}^{D^{*}}$ values are measured to
be $0.51 \pm 0.07 \pm 0.03$ and $0.35 \pm 0.08 \pm 0.02$ for the lower and
higher $q^{2}$ regions, respectively. The first uncertainties are statistical
and the second systematic. The average value over the whole $q^{2}$ range is:
$$F_{L}^{D^{*}} = 0.43 \pm 0.06 \pm 0.03.$$ These results are compatible with
the Standard Model predictions.
Search for the doubly charmed baryon Adinolfi, M.; Albrecht, J.; Anderlini, L. ...
The journal of high energy physics,
12/2013, Letnik:
2013, Številka:
12
Journal Article
Recenzirano
Odprti dostop
A
bstract
A search for the doubly charmed baryon
in the decay mode
is performed with a data sample, corresponding to an integrated luminosity of 0.65 fb
−1
, of
pp
collisions recorded at a ...centre-of-mass energy of 7 TeV. No significant signal is found in the mass range 3300-3800 MeV
/c
2
. Upper limits at the 95% confidence level on the ratio of the
production cross-section times branching fraction to that of the
,
R
, are given as a function of the
mass and lifetime. The largest upper limits range from
R
< 1.5 × 10
−
2 for a lifetime of 100 fs to
R <
3
.
9 × 10
−4
for a lifetime of 400 fs.
The study of quark jets in e+e− reactions at LEP has demonstrated that the hadronisation process is reproduced well by the Lund string model. However, our understanding of gluon fragmentation is less ...complete. In this study enriched quark and gluon jet samples of different purities are selected in three-jet events from hadronic decays of the Z collected by the DELPHI experiment in the LEP runs during 1994 and 1995. The leading systems of the two kinds of jets are defined by requiring a rapidity gap and their sum of charges is studied. An excess of leading systems with total charge zero is found for gluon jets in all cases, when compared to Monte Carlo simulations with JETSET (with and without Bose–Einstein correlations included) and ARIADNE. The corresponding leading systems of quark jets do not exhibit such an excess. The influence of the gap size and of the gluon purity on the effect is studied and a concentration of the excess of neutral leading systems at low invariant masses (≲2 GeV/c2) is observed, indicating that gluon jets might have an additional hitherto undetected fragmentation mode via a two-gluon system. This could be an indication of a possible production of gluonic states as predicted by QCD.
JHEP 03 (2024) 107 A search for $\textit{CP}$ violation in $D^{0} \rightarrow K_{S}^{0} K^{+}
\pi^{-} $ and $D^{0} \rightarrow K_{S}^{0} K^{-} \pi^{+} $ decays is reported.
The search is performed ...using an unbinned model-independent method known as the
energy test that probes local $\textit{CP}$ violation in the phase space of the
decays. The data analysed correspond to an integrated luminosity of
$5.4~$fb$^{-1}$ collected in proton-proton collisions by the LHCb experiment at
a centre-of-mass energy of $\sqrt{s}=13$~TeV, amounting to approximately 950
thousand and 620 thousand signal candidates for the $D^{0} \rightarrow
K_{S}^{0} K^{-} \pi^{+} $ and $D^{0} \rightarrow K_{S}^{0} K^{+} \pi^{-} $
modes, respectively. The method is validated using $D^{0} \rightarrow K^{-}
\pi^{+} \pi^{-} \pi^{+} $ and $D^{0} \rightarrow K_{S}^{0} \pi^{+} \pi^{-} $
decays, where $\textit{CP}$-violating effects are expected to be negligible,
and using background-enhanced regions of the signal decays. The results are
consistent with $\textit{CP}$ symmetry in both the $D^{0} \rightarrow K_{S}^{0}
K^{-} \pi^{+} $ and the $D^{0} \rightarrow K_{S}^{0} K^{+} \pi^{-} $ decays,
with $p$-values for the hypothesis of no $\textit{CP}$ violation of 70% and
66%, respectively.
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