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.
Observation of a New Ξ_{b}^{-} Resonance Ajaltouni, Z; Ali, S; Arnau Romeu, J ...
Physical review letters,
2018-Aug-17, Letnik:
121, Številka:
7
Journal Article
Recenzirano
Odprti dostop
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.
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
.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
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.
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.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
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.
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.
A search for the CP-violating strong decays η→π+π− and η′(958)→π+π− has been performed using approximately 2.5×107 events of each of the decays D+→π+π+π− and Ds+→π+π+π−, recorded by the LHCb ...experiment. The data set corresponds to an integrated luminosity of 3.0 fb−1 of pp collision data recorded during LHC Run 1 and 0.3 fb−1 recorded in Run 2. No evidence is seen for D(s)+→π+η(′) with η(′)→π+π−, and upper limits at 90% confidence level are set on the branching fractions, B(η→π+π−)<1.6×10−5 and B(η′→π+π−)<1.8×10−5. The limit for the η decay is comparable with the existing one, while that for the η′ is a factor of three smaller than the previous limit.