97 research outputs found
Observation of the decay Î <sub>b</sub> <sup>0</sup> âââÏ(2S)pÏ<sup>â</sup>
International audienceThe Cabibbo-suppressed decay Î âââÏ(2S)pÏ is observed for the first time using a data sample collected by the LHCb experiment in proton-proton collisions corresponding to 1.0, 2.0 and 1.9 fb of integrated luminosity at centre-of-mass energies of 7, 8 and 13 TeV, respectively. The Ï(2S) mesons are reconstructed in the ΌΌ final state. The branching fraction with respect to that of the Î âââÏ(2S)pK decay mode is measured to b
Evidence for an nc(1S)ff- resonance in B0 yc(1S)K+ decays
A Dalitz plot analysis of B0âηc(1S)K+Ï- decays is performed using data samples of pp collisions collected with the LHCb detector at centre-of-mass energies of s=7,8 and 13TeV , corresponding to a total integrated luminosity of 4.7fb-1 . A satisfactory description of the data is obtained when including a contribution representing an exotic ηc(1S)Ï- resonant state. The significance of this exotic resonance is more than three standard deviations, while its mass and width are 4096±20-22+18MeV and 152±58-35+60MeV , respectively. The spin-parity assignments JP=0+ and JP=1- are both consistent with the data. In addition, the first measurement of the B0âηc(1S)K+Ï- branching fraction is performed and gives B(B0âηc(1S)K+Ï-)=(5.73±0.24±0.13±0.66)Ă10-4, where the first uncertainty is statistical, the second systematic, and the third is due to limited knowledge of external branching fractions
Search for CP violation in Îb0âpKâ and Îb0âpÏâ decays
A search for CP violation in Îb0âpKâ and Îb0âpÏâ decays is presented using a sample of pp collisions collected with the LHCb detector and corresponding to an integrated luminosity of 3.0fbâ1. The CP -violating asymmetries are measured to be ACPpKâ=â0.020±0.013±0.019 and ACPpÏâ=â0.035±0.017±0.020, and their difference ACPpKââACPpÏâ=0.014±0.022±0.010, where the first uncertainties are statistical and the second systematic. These are the most precise measurements of such asymmetries to date
Observation of B(s)0âJ/ÏppÂŻ decays and precision measurements of the B(s)0 masses
The first observation of the decays
B
0
(
s
)
â
J
/
Ï
p
ÂŻ
p
is reported, using proton-proton collision data corresponding to an integrated luminosity of
5.2
â
â
fb
â
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
â
J
/
Ï
p
ÂŻ
p
)
=
[
4.51
±
0.40
(
stat
)
±
0.44
(
syst
)
]
Ă
10
â
7
,
B
(
B
0
s
â
J
/
Ï
p
ÂŻ
p
)
=
[
3.58
±
0.19
(
stat
)
±
0.39
(
syst
)
]
Ă
10
â
6
. For the
B
0
s
meson, the result is much higher than the expected value of
O
(
10
â
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
)
â
â
MeV
and the
B
0
s
mass as
5366.85
±
0.19
(
stat
)
±
0.13
(
syst
)
â
â
MeV
Flow Dominance and Factorization of Transverse Momentum Correlations in Pb-Pb Collisions at the LHC
We present the first measurement of the two-particle transverse momentum differential correlation function, P2⥠ÎpTÎpT/ pT2, in Pb-Pb collisions at sNN=2.76 TeV. Results for P2 are reported as a function of the relative pseudorapidity (Îη) and azimuthal angle (ÎÏ) between two particles for different collision centralities. The ÎÏ dependence is found to be largely independent of Îη for |Îη|â„0.9. In the 5% most central Pb-Pb collisions, the two-particle transverse momentum correlation function exhibits a clear double-hump structure around ÎÏ=Ï (i.e., on the away side), which is not observed in number correlations in the same centrality range, and thus provides an indication of the dominance of triangular flow in this collision centrality. Fourier decompositions of P2, studied as a function of the collision centrality, show that correlations at |Îη|â„0.9 can be well reproduced by a flow ansatz based on the notion that measured transverse momentum correlations are strictly determined by the collective motion of the system
K*(892)(0) and phi(1020)meson production at high transverse momentum in pp and Pb-Pb collisions at root sNN=2.76 TeV
The production of Kâ(892)0 and Ï(1020) mesons in proton-proton (pp) and lead-lead (Pb-Pb) collisions
at âsNN = 2.76 TeV has been analyzed using a high luminosity data sample accumulated in 2011 with the
ALICE detector at the Large Hadron Collider (LHC). Transverse momentum (pT) spectra have been measured
for Kâ(892)0 and Ï(1020) mesons via their hadronic decay channels for pT up to 20 GeV/c. The measurements
in pp collisions have been compared to model calculations and used to determine the nuclear modification factor
and particle ratios. The Kâ(892)0/K ratio exhibits significant reduction from pp to central Pb-Pb collisions,
consistent with the suppression of the Kâ(892)0 yield at low pT due to rescattering of its decay products in
the hadronic phase. In central Pb-Pb collisions the pT dependent Ï(1020)/Ï and Kâ(892)0/Ï ratios show an
enhancement over pp collisions for pT â 3 GeV/c, consistent with previous observations of strong radial flow.
At high pT, particle ratios in Pb-Pb collisions are similar to those measured in pp collisions. In central Pb-Pb
collisions, the production of Kâ(892)0 and Ï(1020) mesons is suppressed for pT > 8 GeV/c. This suppression is
similar to that of charged pions, kaons, and protons, indicating that the suppression does not depend on particle
mass or flavor in the light quark sector
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Evidence for an η c ( 1 S ) Ï - resonance in B 0 â η c ( 1 S ) K + Ï - decays.
A Dalitz plot analysis of B 0 â η c ( 1 S ) K + Ï - decays is performed using data samples of pp collisions collected with the LHCb detector at centre-of-mass energies of s = 7 , 8 and 13 Te V , corresponding to a total integrated luminosity of 4.7 fb - 1 . A satisfactory description of the data is obtained when including a contribution representing an exotic η c ( 1 S ) Ï - resonant state. The significance of this exotic resonance is more than three standard deviations, while its mass and width are 4096 ± 20 - 22 + 18 Me V and 152 ± 58 - 35 + 60 Me V , respectively. The spin-parity assignments J P = 0 + and J P = 1 - are both consistent with the data. In addition, the first measurement of the B 0 â η c ( 1 S ) K + Ï - branching fraction is performed and gives B ( B 0 â η c ( 1 S ) K + Ï - ) = ( 5.73 ± 0.24 ± 0.13 ± 0.66 ) Ă 10 - 4 , where the first uncertainty is statistical, the second systematic, and the third is due to limited knowledge of external branching fractions
Physics case for an LHCb Upgrade II - Opportunities in flavour physics, and beyond, in the HL-LHC era
The LHCb Upgrade II will fully exploit the flavour-physics opportunities of the HL-LHC, and study additional physics topics that take advantage of the forward acceptance of the LHCb spectrometer. The LHCb Upgrade I will begin operation in 2020. Consolidation will occur, and modest enhancements of the Upgrade I detector will be installed, in Long Shutdown 3 of the LHC (2025) and these are discussed here. The main Upgrade II detector will be installed in long shutdown 4 of the LHC (2030) and will build on the strengths of the current LHCb experiment and the Upgrade I. It will operate at a luminosity up to , ten times that of the Upgrade I detector. New detector components will improve the intrinsic performance of the experiment in certain key areas. An Expression Of Interest proposing Upgrade II was submitted in February 2017. The physics case for the Upgrade II is presented here in more depth. -violating phases will be measured with precisions unattainable at any other envisaged facility. The experiment will probe and transitions in both muon and electron decays in modes not accessible at Upgrade I. Minimal flavour violation will be tested with a precision measurement of the ratio of . Probing charm violation at the level may result in its long sought discovery. Major advances in hadron spectroscopy will be possible, which will be powerful probes of low energy QCD. Upgrade II potentially will have the highest sensitivity of all the LHC experiments on the Higgs to charm-quark couplings. Generically, the new physics mass scale probed, for fixed couplings, will almost double compared with the pre-HL-LHC era; this extended reach for flavour physics is similar to that which would be achieved by the HE-LHC proposal for the energy frontier
Measurement of asymmetry in decays
We report the measurements of the -violating parameters in decays observed in collisions, using a data set corresponding to an integrated luminosity of recorded with the LHCb detector. We measure , , , , , where the uncertainties are statistical and systematic, respectively. These parameters are used together with the world-average value of the mixing phase, , to obtain a measurement of the CKM angle from decays, yielding \gamma = (128\,_{-22}^{+17})^\circ modulo , where the uncertainty contains both statistical and systematic contributions. This corresponds to evidence for violation in the interference between decay and decay after mixing.We report the measurements of the CP -violating parameters in B âââD K decays observed in pp collisions, using a data set corresponding to an integrated luminosity of 3.0 fb recorded with the LHCb detector. We measure C = 0.73 ± 0.14 ± 0.05, A â=â0.39â±â0.28â±â0.15, , S = â0.52 ± 0.20 ± 0.07, , where the uncertainties are statistical and systematic, respectively. These parameters are used together with the world-average value of the B mixing phase, â2ÎČ , to obtain a measurement of the CKM angle Îł from B âââD K decays, yielding Îłâ=â(128 )° modulo 180°, where the uncertainty contains both statistical and systematic contributions. This corresponds to 3.8 Ï evidence for CP violation in the interference between decay and decay after mixing
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