365 research outputs found
Observation of an Excited Bc+ State
Using pp collision data corresponding to an integrated luminosity of 8.5 fb-1 recorded by the LHCb experiment at center-of-mass energies of s=7, 8, and 13 TeV, the observation of an excited Bc+ state in the Bc+Ï+Ï- invariant-mass spectrum is reported. The observed peak has a mass of 6841.2±0.6(stat)±0.1(syst)±0.8(Bc+) MeV/c2, where the last uncertainty is due to the limited knowledge of the Bc+ mass. It is consistent with expectations of the Bcâ(2S31)+ state reconstructed without the low-energy photon from the Bcâ(1S31)+âBc+Îł decay following Bcâ(2S31)+âBcâ(1S31)+Ï+Ï-. A second state is seen with a global (local) statistical significance of 2.2Ï (3.2Ï) and a mass of 6872.1±1.3(stat)±0.1(syst)±0.8(Bc+) MeV/c2, and is consistent with the Bc(2S10)+ state. These mass measurements are the most precise to date
Measurement of the inelastic pp cross-section at a centre-of-mass energy of 13TeV
The cross-section for inelastic proton-proton collisions at a centre-of-mass energy of 13TeV is measured with the LHCb detector. The fiducial cross-section for inelastic interactions producing at least one prompt long-lived charged particle with momentum p > 2 GeV/c in the pseudorapidity range 2 < η < 5 is determined to be Ï acc = 62:2 ± 0:2 ± 2:5mb. The first uncertainty is the intrinsic systematic uncertainty of the measurement, the second is due to the uncertainty on the integrated luminosity. The statistical uncertainty is negligible. Extrapolation to full phase space yields the total inelastic proton-proton cross-section Ï inel = 75:4 ± 3:0 ± 4:5mb, where the first uncertainty is experimental and the second due to the extrapolation. An updated value of the inelastic cross-section at a centre-of-mass energy of 7TeV is also reported
Quantum numbers of the state and orbital angular momentum in its decay
Angular correlations in decays, with , and , are used to measure
orbital angular momentum contributions and to determine the value of
the meson. The data correspond to an integrated luminosity of 3.0
fb of proton-proton collisions collected with the LHCb detector. This
determination, for the first time performed without assuming a value for the
orbital angular momentum, confirms the quantum numbers to be .
The is found to decay predominantly through S wave and an upper limit
of at C.L. is set on the fraction of D wave.Comment: 16 pages, 4 figure
Updated Determination of Dâ°âDÂŻâ°Mixing and CP Violation Parameters with Dâ°âKâșÏâ» Decays
We report measurements of charm-mixing parameters based on the decay-time-dependent ratio of Dâ°âKâșÏâ» to Dâ°âKâ»Ïâș rates. The analysis uses a data sample of proton-proton collisions corresponding to an integrated luminosity of 5.0ââfbâ»Âč recorded by the LHCb experiment from 2011 through 2016. Assuming charge-parity (CP) symmetry, the mixing parameters are determined to be xâČÂČ=(3.9±2.7)Ă10â»â”, yâČ=(5.28±0.52)Ă10â»Âł, and R[subscript D]=(3.454±0.031)Ă10â»Âł. Without this assumption, the measurement is performed separately for Dâ° and D[over ÂŻ]â° mesons, yielding a direct CP-violating asymmetry A[subscript D]=(-0.1±9.1)Ă10â»Âł, and magnitude of the ratio of mixing parameters 1.00<|q/p|<1.35 at the 68.3% confidence level. All results include statistical and systematic uncertainties and improve significantly upon previous single-measurement determinations. No evidence for CP violation in charm mixing is observed
Observation of CP Violation in Charm Decays
A search for charge-parity (CP) violation in D-0 -> K-K+ and D-0 -> pi(-)pi(+) decays is reported, using pp collision data corresponding to an integrated luminosity of 5.9 fb(-1) collected at a center-of-mass energy of 13 TeV with the LHCb detector. The flavor of the charm meson is inferred from the charge of the pion in D* (2010)(+) -> D-0 pi(+) decays or from the charge of the muon in (B) over bar -> D-0 mu(-)(nu) over bar X-mu decays. The difference between the CP asymmetries in D-0 -> K-K+ and D-0 -> pi(-)pi(+) decays is measured to be Delta A(CP) = [-18.2 +/- 3.2(stat) +/- 0.9(syst)] x 10(-4) for pi-tagged and Delta A(CP) = [-9 +/- 8(stat) +/- 5(syst)] x 10(-4) for mu-tagged D-0 mesons. Combining these with previous LHCb results leads to Delta A(CP) = (-15.4 +/- 2.9) x 10(-4), where the uncertainty includes both statistical and systematic contributions. The measured value differs from zero by more than 5 standard deviations. This is the first observation of CP violation in the decay of charm hadrons
Measurement of CP -violating and mixing-induced observables in Bs0âÏÎł decays
A time-dependent analysis of the
B
0
s
â
Ï
Îł
decay rate is performed to determine the
C
P
-violating observables
S
Ï
Îł
and
C
Ï
Îł
and the mixing-induced observable
A
Î
Ï
Îł
. The measurement is based on a sample of
p
p
collision data recorded with the LHCb detector, corresponding to an integrated luminosity of
3
â
â
fb
â
1
at center-of-mass energies of 7 and 8 TeV. The measured values are
S
Ï
Îł
=
0.43
±
0.30
±
0.11
,
C
Ï
Îł
=
0.11
±
0.29
±
0.11
, and
A
Î
Ï
Îł
=
â
0.67
+
0.37
â
0.41
±
0.17
, where the first uncertainty is statistical and the second systematic. This is the first measurement of the observables
S
and
C
in radiative
B
0
s
decays. The results are consistent with the standard model predictions
Observation of an Excited Bcâș state
Using
p
p
collision data corresponding to an integrated luminosity of
8.5
â
â
fb
â
1
recorded by the LHCb experiment at center-of-mass energies of
â
s
=
7
, 8, and 13 TeV, the observation of an excited
B
+
c
state in the
B
+
c
Ï
+
Ï
â
invariant-mass spectrum is reported. The observed peak has a mass of
6841.2
±
0.6
(
stat
)
±
0.1
(
syst
)
±
0.8
(
B
+
c
)
â
â
MeV
/
c
2
, where the last uncertainty is due to the limited knowledge of the
B
+
c
mass. It is consistent with expectations of the
B
â
c
(
2
3
S
1
)
+
state reconstructed without the low-energy photon from the
B
â
c
(
1
3
S
1
)
+
â
B
+
c
Îł
decay following
B
â
c
(
2
3
S
1
)
+
â
B
â
c
(
1
3
S
1
)
+
Ï
+
Ï
â
. A second state is seen with a global (local) statistical significance of
2.2
Ï
(
3.2
Ï
) and a mass of
6872.1
±
1.3
(
stat
)
±
0.1
(
syst
)
±
0.8
(
B
+
c
)
â
â
MeV
/
c
2
, and is consistent with the
B
c
(
2
1
S
0
)
+
state. These mass measurements are the most precise to date
Measurement of the branching fraction and CP asymmetry in B plus . J/.. plus decays
The branching fraction and direct asymmetry of the decay
are measured using proton-proton collision
data collected with the LHCb detector at centre-of-mass energies of 7 and 8
TeV, corresponding to a total integrated luminosity of 3\mbox{fb}^{-1}. The
following results are obtained: \begin{align} \mathcal{B}(B^{+}\rightarrow
J/\psi \rho^{+}) &= (3.81 ^{+0.25}_{-0.24} \pm 0.35) \times 10^{-5}, \nonumber
\\ \mathcal{A}^{C\!P} (B^{+}\rightarrow J/\psi \rho^{+}) &=
-0.045^{+0.056}_{-0.057} \pm 0.008, \nonumber \end{align} where the first
uncertainties are statistical and the second systematic. Both measurements are
the most precise to date.Comment: All figures and tables, along with any supplementary material and
additional information, are available at
https://cern.ch/lhcbproject/Publications/p/LHCb-PAPER-2018-036.htm
Evidence for the decay
International audienceA search for the decay is presented using data sets corresponding to 1.0, 2.0 and 1.6 fb of integrated luminosity collected during pp collisions with the LHCb experiment at centre-of-mass energies of 7, 8 and 13 TeV, respectively. An excess is found over the background-only hypothesis with a significance of 3.4 standard deviations. The branching fraction of the decay is determined to be , where the first and second uncertainties are statistical and systematic, respectively. The third uncertainty is due to limited knowledge of external parameters used to normalise the branching fraction measurement
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