Precision measurement of the Bc+ meson mass Alexander, M.; Alkhazov, G.; Aslanides, E. ...
The journal of high energy physics,
07/2020, Letnik:
2020, Številka:
7
Journal Article
Recenzirano
Odprti dostop
A
bstract
A precision measurement of the
B
c
+
meson mass is performed using proton- proton collision data collected with the LHCb experiment at centre-of-mass energies of 7
,
8 and 13 TeV, ...corresponding to a total integrated luminosity of 9
.
0 fb
−
1
. The
B
c
+
mesons are reconstructed via the decays
B
c
+
→ J/ψπ
+
,
B
c
+
→ J/ψπ
+
π
−
π
+
,
B
c
+
→
J
/
ψp
p
¯
π
+
,
B
c
+
→
J
/
ψ
D
s
+
,
B
c
+
→ J/ψ D
0
K
+
and
B
c
+
→
B
s
0
π
+
. Combining the results of the individual decay channels, the
B
c
+
mass is measured to be 6274
.
47
±
0
.
27 (stat)
±
0
.
17 (syst) MeV
/c
2
. This is the most precise measurement of the
B
c
+
mass to date. The difference between the
B
c
+
and
B
s
0
meson masses is measured to be 907
.
75
±
0
.
37 (stat)
±
0
.
27 (syst) MeV
/c
.
Using a data sample of 980 fb−1 of e+e− annihilation data taken with the Belle detector operating at the KEKB asymmetric-energy e+e− collider, we report the results of a study of excited Ξc states ...that decay, via the emission of photons and/or charged pions, into Ξc0 or Ξc+ ground state charmed-strange baryons. We present new measurements of the masses of all members of the Ξc′, Ξc(2645), Ξc(2790), Ξc(2815), and Ξc(2980) isodoublets, measurements of the intrinsic widths of those that decay strongly, and evidence of previously unknown transitions.
A
bstract
A search is presented for the lepton flavour violating decay
B
+
→
K
+
μ
−
τ
+
using a sample of proton-proton collisions at centre-of-mass energies of 7, 8, and 13 TeV, collected with the ...LHCb detector and corresponding to a total integrated luminosity of 9 fb
−
1
. The
τ
leptons are selected inclusively, primarily via decays with a single charged particle. The four-momentum of the
τ
lepton is determined by using
B
+
mesons from
B
s
2
∗
0
→
B
+
K
−
decays. No significant excess is observed, and an upper limit is set on the branching fraction
ℬ(
B
+
→
K
+
μ
−
τ
+
) < 3.9 × 10
−5
at 90 % confidence level.
The obtained limit is comparable to the world-best limit.
We report a measurement of the differential cross section of π^0 pair production in single-tag two-photon collisions, y*y->π^0π^0, in e+e- scattering. The cross section is measured for Q^2up to 30 ...GeV^2 is the negative of the invariant mass squared of the tagged photon
A
bstract
The differential cross-section of prompt inclusive production of long-lived charged particles in proton-proton collisions is measured using a data sample recorded by the LHCb experiment at ...a centre-of-mass energy of
s
= 13 TeV. The data sample, collected with an unbiased trigger, corresponds to an integrated luminosity of 5
.
4 nb
−
1
. The differential cross-section is measured as a function of transverse momentum and pseudorapidity in the ranges
p
T
∈ 80
,
10 000) MeV
/c
and
η
∈ 2
.
0
,
4
.
8) and is determined separately for positively and negatively charged particles. The results are compared with predictions from various hadronic-interaction models.
A
bstract
The production cross-section of the
χ
c
1
(3872) state relative to the
ψ
(2
S
) meson is measured using proton-proton collision data collected with the LHCb experiment at centre-of-mass ...energies of
s
= 8 and 13 TeV, corresponding to integrated luminosities of 2.0 and 5.4 fb
−
1
, respectively. The two mesons are reconstructed in the
J/ψπ
+
π
−
final state. The ratios of the prompt and nonprompt
χ
c
1
(3872) to
ψ
(2
S
) production cross-sections are measured as a function of transverse momentum,
p
T
, and rapidity,
y
, of the
χ
c
1
(3872) and
ψ
(2
S
) states, in the kinematic range 4
< p
T
<
20 GeV/
c
and 2
.
0
< y <
4
.
5. The prompt ratio is found to increase with
p
T
, independently of
y
. For the prompt component, the double ratio of the
χ
c
1
(3872) and
ψ
(2
S
) production cross-sections between 13 and 8 TeV is observed to be consistent with unity, independent of
p
T
and centre-of-mass energy.
A
bstract
The production cross-sections of
J/ψ
mesons in proton-proton collisions at a centre-of-mass energy of
s
= 5 TeV are measured using a data sample corresponding to an integrated luminosity of ...9
.
13 ± 0
.
18 pb
−
1
, collected by the LHCb experiment. The cross-sections are measured differentially as a function of transverse momentum,
p
T
, and rapidity,
y
, and separately for
J/ψ
mesons produced promptly and from beauty hadron decays (nonprompt). With the assumption of unpolarised
J/ψ
mesons, the production cross-sections integrated over the kinematic range 0
< p
T
<
20 GeV/
c
and 2
.
0
< y <
4
.
5 are
σ
prompt
J
/
ψ
=
8.154
±
0.010
±
0.283
μb
,
σ
nonprompt
J
/
ψ
=
0.820
±
0.003
±
0.034
μb
,
where the first uncertainties are statistical and the second systematic. These cross-sections are compared with those at
s
= 8 TeV and 13 TeV, and are used to update the measurement of the nuclear modification factor in proton-lead collisions for
J/ψ
mesons at a centre-of-mass energy per nucleon pair of
s
NN
= 5 TeV. The results are compared with theoretical predictions.
A
bstract
This paper presents an analysis of the
Λ
b
0
→ J/ψ
Λ angular distribution and the transverse production polarisation of
Λ
b
0
baryons in proton-proton collisions at centre-of-mass energies ...of 7, 8 and 13 TeV. The measurements are performed using data corresponding to an integrated luminosity of 4.9 fb
−
1
, collected with the LHCb experiment. The polarisation is determined in a fiducial region of
Λ
b
0
transverse momentum and pseudorapidity of 1
< p
T
<
20 GeV/
c
and 2
< η <
5, respectively. The data are consistent with
Λ
b
0
baryons being produced unpolarised in this region. The parity-violating asymmetry parameter of the Λ →
pπ
−
decay is also determined from the data and its value is found to be consistent with a recent measurement by the BES III collaboration.
A
bstract
A search is performed for rare and forbidden charm decays of the form
D
s
+
→
h
±
ℓ
+
ℓ
′
∓
, where
h
±
is a pion or kaon and
ℓ
(′)±
is an electron or muon. The measurements are performed ...using proton-proton collision data, corresponding to an integrated luminosity of 1
.
6 fb
−
1
, collected by the LHCb experiment in 2016. No evidence is observed for the 25 decay modes that are investigated and 90 % confidence level limits on the branching fractions are set between 1
.
4
×
10
−
8
and 6
.
4
×
10
−
6
. In most cases, these results represent an improvement on existing limits by one to two orders of magnitude.
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