A
bstract
The forward-backward charge asymmetry for the process
q
q
¯
→
Z
/
γ
∗
→
μ
+
μ
−
is measured as a function of the invariant mass of the dimuon system. Measurements are performed using proton ...proton collision data collected with the LHCb detector at
s
=
7
and 8 TeV, corresponding to integrated luminosities of 1 fb
−1
and 2 fb
−1
respectively. Within the Standard Model the results constrain the effective electroweak mixing angle to be
sin
2
θ
W
eff
=
0.23142
±
0.00073
±
0.00052
±
0.00056
,
where the first uncertainty is statistical, the second systematic and the third theoretical. This result is in agreement with the current world average, and is one of the most precise determinations at hadron colliders to date.
The production of Upsilon(1S), Upsilon(2S) and Upsilon(3S) mesons in proton-proton collisions at the centre-of-mass energy of sqrt(s)=7 TeV is studied with the LHCb detector. The analysis is based on ...a data sample of 25 pb-1 collected at the Large Hadron Collider. The Upsilon mesons are reconstructed in the decay mode Upsilon -> mu+ mu- and the signal yields are extracted from a fit to the mu+ mu- invariant mass distributions. The differential production cross-sections times dimuon branching fractions are measured as a function of the Upsilon transverse momentum pT and rapidity y, over the range pT < 15 GeV/c and 2.0 < y < 4.5. The cross-sections times branching fractions, integrated over these kinematic ranges, are measured to be sigma(pp -> Upsilon(1S) X) x B(Upsilon(1S)->mu+ mu-) = 2.29 {\pm} 0.01 {\pm} 0.10 -0.37 +0.19 nb, sigma(pp -> Upsilon(2S) X) x B(Upsilon(2S)->mu+ mu-) = 0.562 {\pm} 0.007 {\pm} 0.023 -0.092 +0.048 nb, sigma(pp -> Upsilon(3S) X) x B(Upsilon(3S)->mu+ mu-) = 0.283 {\pm} 0.005 {\pm} 0.012 -0.048 +0.025 nb, where the first uncertainty is statistical, the second systematic and the third is due to the unknown polarisation of the three Upsilon states.
The time-integrated untagged Dalitz plot of the three-body hadronic charmless decay ¯ B 0 → K 0 S π + π − is studied using a p p collision data sample recorded with the LHCb detector, corresponding ...to an integrated luminosity of 3.0 fb − 1 . The decay amplitude is described with an isobar model. Relative contributions of the isobar amplitudes to the ¯ B 0 → K 0 S π + π − decay branching fraction and C P asymmetries of the flavor-specific amplitudes are measured. The C P asymmetry between the conjugate ¯ B 0 → K ∗ ( 892 ) − π + and B 0 → K ∗ ( 892 ) + π − decay rates is determined to be − 0.308 ± 0.062.
The decays χc 1→J /ψ μ+μ- and χc 2→J /ψ μ+μ- are observed and used to study the resonance parameters of the χc 1 and χc 2 mesons. The masses of these states are measured to be m (χc 1)=3510.71 ±0.04 ...(stat ) ±0.09 (syst ) MeV and m (χc 2)=3556.10 ±0.06 (stat ) ±0.11 (syst ) MeV , where the knowledge of the momentum scale for charged particles dominates the systematic uncertainty. The momentum-scale uncertainties largely cancel in the mass difference m (χc 2)-m (χc 1)=45.39 ±0.07 (stat ) ±0.03 (syst ) MeV . The natural width of the χc 2 meson is measured to be Γ (χc 2)=2.10 ±0.20 (stat ) ±0.02 (syst ) MeV . These results are in good agreement with and have comparable precision to the current world averages.
A search for
C
P
violation in charmless four-body decays of
Λ
b
0
and
Ξ
b
0
baryons with a proton and three charged mesons in the final state is performed. To cancel out production and detection ...charge-asymmetry effects, the search is carried out by measuring the difference between the
C
P
asymmetries in a charmless decay and in a decay with an intermediate charmed baryon with the same particles in the final state. The data sample used was recorded in 2011 and 2012 with the LHCb detector and corresponds to an integrated luminosity of
3
fb
-
1
. A total of 18
C
P
asymmetries are considered, either accounting for the full phase space of the decays or exploring specific regions of the decay kinematics. No significant
C
P
-violation effect is observed in any of the measurements.
The differential cross-section for the inclusive production of ψ(2S) mesons in pp collisions at s√=7 TeVs=7 TeV has been measured with the LHCb detector. The data sample corresponds to an integrated ...luminosity of 36 pb−1. The ψ(2S) mesons are reconstructed in the decay channels ψ(2S)→μ + μ − and ψ(2S)→J/ψπ + π −, with the J/ψ meson decaying into two muons. Results are presented both for promptly produced ψ(2S) mesons and for those originating from b-hadron decays. In the kinematic range p T(ψ(2S))≤16 GeV/c and 2<y(ψ(2S))≤4.5 we measure
https://static-content.springer.com/image/art%3A10.1140%2Fepjc%2Fs10052-012-2100-4/MediaObjects/10052_2012_2100_Equa_HTML.gif
where the last uncertainty on the prompt cross-section is due to the unknown ψ(2S) polarization. Recent QCD calculations are found to be in good agreement with our measurements. Combining the present result with the LHCb J/ψ measurements we determine the inclusive branching fraction
https://static-content.springer.com/image/art%3A10.1140%2Fepjc%2Fs10052-012-2100-4/MediaObjects/10052_2012_2100_Equb_HTML.gif
where the last uncertainty is due to the (b→J/ψX)B(b→J/ψX) , (J/ψ→μ+μ−)B(J/ψ→μ+μ−) and (ψ(2S)→e+e−)B(ψ(2S)→e+e−) branching fraction uncertainties.
The CP violation observables S and C in the decay channel B0→D+D− are determined from a sample of proton-proton collisions at centre-of-mass energies of 7 and 8 TeV, collected by the LHCb experiment ...and corresponding to an integrated luminosity of 3 fb−1. The observable S describes CP violation in the interference between mixing and the decay amplitude, and C parametrizes direct CP violation in the decay. The following values are obtained from a flavour-tagged, decay-time-dependent analysis:SC=−0.54+0.17−0.16(stat)±0.05(syst),=0.26+0.18−0.17(stat)±0.02(syst).These values constrain higher-order Standard Model corrections to be small.
We report on a measurement of the flavor-specific Bs0 lifetime and of the Ds- lifetime using proton-proton collisions at center-of-mass energies of 7 and 8 TeV, collected by the LHCb experiment and ...corresponding to 3.0 fb-1 of integrated luminosity. Approximately 407 000 Bs0→Ds(*)-μ+νμ decays are partially reconstructed in the K+K-π-μ+ final state. The Bs0 and Ds- natural widths are determined using, as a reference, kinematically similar B0→D(*)-μ+νμ decays reconstructed in the same final state. The resulting differences between widths of Bs0 and B0 mesons and of Ds- and D- mesons are ΔΓ(B )=-0.0115 ±0.0053 (stat ) ±0.0041 (syst ) ps-1 and ΔΓ(D )=1.0131 ±0.0117 (stat ) ±0.0065 (syst ) ps-1, respectively. Combined with the known B0 and D- lifetimes, these yield the flavor-specific Bs0 lifetime, τBs 0 fs =1.547 ±0.013 (stat ) ±0.010 (syst ) ±0.004 (τB) ps and the Ds- lifetime, τDs-=0.5064 ±0.0030 (stat ) ±0.0017 (syst ) ±0.0017 (τD) ps . The last uncertainties originate from the limited knowledge of the B0 and D- lifetimes. The results improve upon current determinations.
Search for excited Bc+ states Alfonso Albero, A.; Alkhazov, G.; Alves, A. A. ...
The journal of high energy physics,
29/1, Letnik:
2018, Številka:
1
Journal Article
Recenzirano
Odprti dostop
A
bstract
A search is performed in the invariant mass spectrum of the
B
c
+
π
+
π
−
system for the excited
B
c
+
states
B
c
(2
1
S
0
)
+
and
B
c
(2
3
S
1
)
+
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
B
c
(2
1
S
0
)
+
and
B
c
(2
3
S
1
)
+
states times the branching fractions of
B
c
(2
1
S
0
)
+
→
B
c
+
π
+
π
−
and
B
c
(2
3
S
1
)
+
→
B
c
*
+
π
+
π
−
over the production cross-section of the
B
c
+
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
B
c
(2
1
S
0
)
+
and
B
c
(2
3
S
1
)
+
in the mass ranges 6830
,
6890 MeV
/c
2
and 6795
,
6890 MeV
/c
2
, respectively.
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