260 research outputs found
Search for CP violation in D+→ϕπ+ and D+s→K0Sπ+ decays
A search for CP violation in D + → ϕπ + decays is performed using data collected in 2011 by the LHCb experiment corresponding to an integrated luminosity of 1.0 fb−1 at a centre of mass energy of 7 TeV. The CP -violating asymmetry is measured to be (−0.04 ± 0.14 ± 0.14)% for candidates with K − K + mass within 20 MeV/c 2 of the ϕ meson mass. A search for a CP -violating asymmetry that varies across the ϕ mass region of the D + → K − K + π + Dalitz plot is also performed, and no evidence for CP violation is found. In addition, the CP asymmetry in the D+s→K0Sπ+ decay is measured to be (0.61 ± 0.83 ± 0.14)%
Updated measurements of exclusive J/ψ and ψ(2S) production cross-sections in pp collisions at √s = 7 TeV
The differential cross-section as a function of rapidity has been measured for the exclusive production of J/ψ and ψ(2S) mesons in proton–proton collisions at √s = 7 TeV, using data collected by the LHCb experiment, corresponding to an integrated luminosity of 930 pb−1. The cross-sections times branching fractions to two muons having pseudorapidities between 2.0 and 4.5 are measured to be where the first uncertainty is statistical and the second is systematic. The measurements agree with next-to-leading order QCD predictions as well as with models that include saturation effects
Measurement of the Λb0, Ξb-, and Ωb- Baryon Masses
Bottom baryons decaying to a J/ψ meson and a hyperon are reconstructed using 1.0 fb-1 of data collected in 2011 with the LHCb detector. Significant Λb0→J/ψΛ, Ξb-→J/ψΞ- and Ωb-→J/ψΩ- signals are observed and the corresponding masses are measured to be M(Λb0)=5619.53±0.13(stat.)±0.45(syst.) MeV/c2, M(Ξb-)=5795.8±0.9(stat.)±0.4(syst.) MeV/c2, M(Ωb-)=6046.0±2.2(stat.)±0.5(syst.) MeV/c2, while the differences with respect to the Λb0 mass are M(Ξb-)-M(Λb0)=176.2±0.9(stat.)±0.1(syst.) MeV/c2, M(Ωb-)-M(Λb0)=426.4±2.2(stat.)±0.4(syst.) MeV/c2. These are the most precise mass measurements of the Λb0, Ξb- and Ωb- baryons to date. Averaging the above Λb0 mass measurement with that published by LHCb using 35 pb-1 of data collected in 2010 yields M(Λb0)=5619.44±0.13(stat.)±0.38(syst.) MeV/c2
First Measurement of the Charge Asymmetry in Beauty-Quark Pair Production
The difference in the angular distributions between beauty quarks and antiquarks, referred to as the charge asymmetry, is measured for the first time in b (b) over bar pair production at a hadron collider. The data used correspond to an integrated luminosity of 1.0 fb(-1) collected at 7 TeV center-of-mass energy in proton-proton collisions with the LHCb detector. The measurement is performed in three regions of the invariant mass of the b (b) over bar system. The results obtained are A(C)(b (b) over bar) (40 10(5) GeV/c(2)) = 1.6 +/- 1.7 +/- 0.6%,where A(C)(b (b) over bar) is defined as the asymmetry in the difference in rapidity between jets formed from the beauty quark and antiquark, where in each case the first uncertainty is statistical and the second systematic. The beauty jets are required to satisfy 2 20 GeV, and have an opening angle in the transverse plane Delta phi > 2.6 rad. These measurements are consistent with the predictions of the standard model
Observation of B(s)0→J/ψpp¯ decays and precision measurements of the B(s)0 masses
The first observation of the decays
B
0
(
s
)
→
J
/
ψ
p
¯
p
is reported, using proton-proton collision data corresponding to an integrated luminosity of
5.2
fb
−
1
, collected with the LHCb detector. These decays are suppressed due to limited available phase space, as well as due to Okubo-Zweig-Iizuka or Cabibbo suppression. The measured branching fractions are
B
(
B
0
→
J
/
ψ
p
¯
p
)
=
[
4.51
±
0.40
(
stat
)
±
0.44
(
syst
)
]
×
10
−
7
,
B
(
B
0
s
→
J
/
ψ
p
¯
p
)
=
[
3.58
±
0.19
(
stat
)
±
0.39
(
syst
)
]
×
10
−
6
. For the
B
0
s
meson, the result is much higher than the expected value of
O
(
10
−
9
)
. The small available phase space in these decays also allows for the most precise single measurement of both the
B
0
mass as
5279.74
±
0.30
(
stat
)
±
0.10
(
syst
)
MeV
and the
B
0
s
mass as
5366.85
±
0.19
(
stat
)
±
0.13
(
syst
)
MeV
Measurement of D s <sup>±</sup> production asymmetry in pp collisions at √s=7 and 8 TeV
The inclusive production asymmetry is measured in collisions
collected by the LHCb experiment at centre-of-mass energies of
and 8 TeV. Promptly produced mesons are used, which decay as
, with . The measurement is
performed in bins of transverse momentum, , and rapidity, ,
covering the range GeV and . No kinematic
dependence is observed. Evidence of nonzero production asymmetry is
found with a significance of 3.3 standard deviations.Comment: All figures and tables, along with any supplementary material and
additional information, are available at
https://cern.ch/lhcbproject/Publications/p/LHCb-PAPER-2018-010.htm
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