Measurements of the cross section for producing b quarks in the reaction pp→bbover ¯X are reported in 7 and 13 TeV collisions at the LHC as a function of the pseudorapidity η in the range 2<η<5 ...covered by the acceptance of the LHCb experiment. The measurements are done using semileptonic decays of b-flavored hadrons decaying into a ground-state charmed hadron in association with a muon. The cross sections in the covered η range are 72.0±0.3±6.8 and 154.3±1.5±14.3 μb for 7 and 13 TeV. The ratio is 2.14±0.02±0.13, where the quoted uncertainties are statistical and systematic, respectively. The agreement with theoretical expectation is good at 7 TeV, but differs somewhat at 13 TeV. The measured ratio of cross sections is larger at lower η than the model prediction.
A
bstract
The production cross-section of
J/ψ
pairs is measured using a data sample of
pp
collisions collected by the LHCb experiment at a centre-of-mass energy of
s
=
13
TeV, corresponding to an ...integrated luminosity of 279 ±11 pb
−1
. The measurement is performed for
J/ψ
mesons with a transverse momentum of less than 10 GeV/
c
in the rapidity range 2
.
0
< y <
4
.
5. The production cross-section is measured to be 15
.
2 ± 1
.
0 ± 0
.
9 nb. The first uncertainty is statistical, and the second is systematic. The differential cross-sections as functions of several kinematic variables of the
J/ψ
pair are measured and compared to theoretical predictions.
From samples of pp collision data collected by the LHCb experiment at sqrts=7, 8 and 13 TeV, corresponding to integrated luminosities of 1.0, 2.0 and 1.5 fb^{-1}, respectively, a peak in both the ...Λ_{b}^{0}K^{-} and Ξ_{b}^{0}π^{-} invariant mass spectra is observed. In the quark model, radially and orbitally excited Ξ_{b}^{-} resonances with quark content bds are expected. Referring to this peak as Ξ_{b}(6227)^{-}, the mass and natural width are measured to be m_{Ξ_{b}(6227)^{-}}=6226.9±2.0±0.3±0.2 MeV/c^{2} and Γ_{Ξ_{b}(6227)^{-}}=18.1±5.4±1.8 MeV/c^{2}, where the first uncertainty is statistical, the second is systematic, and the third, on m_{Ξ_{b}(6227)^{-}}, is due to the knowledge of the Λ_{b}^{0} baryon mass. Relative production rates of the Ξ_{b}(6227)^{-}→Λ_{b}^{0}K^{-} and Ξ_{b}(6227)^{-}→Ξ_{b}^{0}π^{-} decays are also reported.
The associated production of a W boson with a jet originating from either a light parton or heavy-flavor quark is studied in the forward region using proton-proton collisions. The analysis uses data ...corresponding to integrated luminosities of 1.0 and 2.0fb−1 collected with the LHCb detector at center-of-mass energies of 7 and 8 TeV, respectively. The W bosons are reconstructed using the W→μν decay and muons with a transverse momentum, pT, larger than 20 GeV in the pseudorapidity range 2.0<η<4.5. The partons are reconstructed as jets with pT>20 GeV and 2.2<η<4.2. The sum of the muon and jet momenta must satisfy pT>20 GeV. The fraction of W+jet events that originate from beauty and charm quarks is measured, along with the charge asymmetries of the W+b and W+c production cross-sections. The ratio of the W+jet to Z+jet production cross-sections is also measured using the Z→μμ decay. All results are in agreement with Standard Model predictions.
A
bstract
The first observation of
Z
boson production in proton-lead collisions at a centre-of-mass energy per proton-nucleon pair of
s
N
N
= 5 TeV is presented. The data sample corresponds to an ...integrated luminosity of 1
.
6 nb
−1
collected with the LHCb detector. The
Z
candidates are reconstructed from pairs of oppositely charged muons with pseudorapidities between 2.0 and 4.5 and transverse momenta above 20 GeV
/
c. The invariant dimuon mass is restricted to the range 60 − 120 GeV
/
c. The
Z
production cross-section is measured to be
σ
Z
→
μ
+
μ
−
fwd
=
13.5
−
4.0
+
5.4
stat
.
±
1.2
syst
.
nb
in the direction of the proton beam and
σ
Z
→
μ
+
μ
−
bwd
=
10.7
−
5.1
+
8.4
stat
.
±
1.0
syst
.
nb
in the direction of the lead beam, where the first uncertainty is statistical and the second systematic.
A search is presented for a Higgs-like boson with mass in the range 45 to 195
GeV
/
c
2
decaying into a muon and a tau lepton. The dataset consists of proton-proton interactions at a centre-of-mass ...energy of 8
TeV
, collected by the LHCb experiment, corresponding to an integrated luminosity of 2
fb
-
1
. The tau leptons are reconstructed in both leptonic and hadronic decay channels. An upper limit on the production cross-section multiplied by the branching fraction at 95% confidence level is set and ranges from 22
pb
for a boson mass of 45
GeV
/
c
2
to 4
pb
for a mass of 195
GeV
/
c
2
.
Amplitude models are constructed to describe the resonance structure of
and
decays using
collision data collected at centre-of-mass energies of 7 and 8 TeV with the LHCb experiment, corresponding to ...an integrated luminosity of 3.0
. The largest contributions to both decay amplitudes are found to come from axial resonances, with decay modes
and
being prominent in
and
, respectively. Precise measurements of the lineshape parameters and couplings of the
,
and
resonances are made, and a quasi model-independent study of the
resonance is performed. The coherence factor of the decays is calculated from the amplitude models to be
, which is consistent with direct measurements. These models will be useful in future measurements of the unitary-triangle angle
and studies of charm mixing and
violation.
A
bstract
A search for the rare two-body charmless baryonic decay
B
+
→
p
Λ
¯
is performed with
pp
collision data, corresponding to an integrated luminosity of 3 fb
−1
, collected by the LHCb ...experiment at centre-of-mass energies of 7 and 8 TeV. An excess of
B
+
→
p
Λ
¯
candidates with respect to background expectations is seen with a statistical significance of 4.1 standard deviations, and constitutes the first evidence for this decay. The branching fraction, measured using the
B
+
→
K
S
0
π
+
decay for normalisation, is
ℬ
B
+
→
p
Λ
¯
=
2
.
4
−
0.8
+
1.0
±
0.3
×
1
0
−
7
,
where the first uncertainty is statistical and the second systematic.
Search for excited B c + states Akar, S.; Alves, A. A.; Amerio, S. ...
The journal of high energy physics,
01/2018, Volume:
2018, Issue:
1
Journal Article
Peer reviewed
Open access
A search is performed in the invariant mass spectrum of the Bc+π+π− system for the excited Bc+ states Bc(21S0)+ and Bc(23S1)+ using a data sample of pp collisions collected by the LHCb experiment at ...the centre-of-mass energy of s=8 TeV, corresponding to an integrated luminosity of 2 fb−1. No evidence is seen for either state. Upper limits on the ratios of the production cross-sections of the Bc(21S0)+ and Bc(23S1)+ states times the branching fractions of Bc(21S0)+ → Bc+π+π− and Bc(23S1)+ → Bc*+π+π− over the production cross-section of the Bc+ state are given as a function of their masses. They are found to be between 0.02 and 0.14 at 95% confidence level for Bc(21S0)+ and Bc(23S1)+ in the mass ranges 6830, 6890 MeV/c2 and 6795, 6890 MeV/c2, respectively.
A
bstract
A search for the doubly charmed baryon
$ \Xi_{cc}^{+} $
in the decay mode
$ \Xi_{cc}^{+}\to \Lambda_c^{+}{K^{-}}{\pi^{+}} $
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
$ \Xi_{cc}^{+} $
production cross-section times branching fraction to that of the
$ \Lambda_c^{+} $
,
R
, are given as a function of the
$ \Xi_{cc}^{+} $
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.
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