A broad peaking structure is observed in the dimuon spectrum of B+ → K+ μ+ μ- decays in the kinematic region where the kaon has a low recoil against the dimuon system. The structure is consistent ...with interference between the B+ → K+ μ+ μ- decay and a resonance and has a statistical significance exceeding six standard deviations. The mean and width of the resonance are measured to be 4191(-8)(+9) MeV/c2 and 65(-16)(+22) MeV/c2, respectively, where the uncertainties include statistical and systematic contributions. These measurements are compatible with the properties of the ψ(4160) meson. First observations of both the decay B+ → ψ(4160)K+ and the subsequent decay ψ(4160) → μ+ μ- are reported. The resonant decay and the interference contribution make up 20% of the yield for dimuon masses above 3770 MeV/c2. This contribution is larger than theoretical estimates.
Measurements of charm mixing and CP violation parameters from the decay-time-dependent ratio of D0→K+π− to D0→K−π+ decay rates and the charge-conjugate ratio are reported. The analysis uses ...B¯→D*+μ−X, and charge-conjugate decays, where D*+→D0π+, and D0→K∓π±. The pp collision data are recorded by the LHCb experiment at center-of-mass energies s=7 and 8 TeV, corresponding to an integrated luminosity of 3 fb−1. The data are analyzed under three hypotheses: (i) mixing assuming CP symmetry, (ii) mixing assuming no direct CP violation in the Cabibbo-favored or doubly Cabibbo-suppressed decay amplitudes, and (iii) mixing allowing either direct CP violation and/or CP violation in the superpositions of flavor eigenstates defining the mass eigenstates. The data are also combined with those from a previous LHCb study of D0→Kπ decays from a disjoint set of D*+ candidates produced directly in pp collisions. In all cases, the data are consistent with the hypothesis of CP symmetry.
(ProQuest: ... denotes formulae and/or non-USASCII text omitted; see image) Abstract A measurement of the Z(arrow right mu ^sup +^ mu ^sup -^) + jet production cross-section in pp collisions at a ...centre-of-mass energy ... = 7 TeV is presented. The analysis is based on an integrated luminosity of 1.0 fb^sup -1^ recorded by the LHCb experiment. Results are shown with two jet transverse momentum thresholds, 10 and 20 GeV, for both the overall cross-section within the fiducial volume, and for six differential cross-section measurements. The fiducial volume requires that both the jet and the muons from the Z boson decay are produced in the forward direction (2.0 < eta < 4.5). The results show good agreement with theoretical predictions at the second-order expansion in the coupling of the strong interaction. Figure not available: see fulltext.
(ProQuest: ... denotes formulae and/or non-USASCII text omitted; see image).Measurements are presented of electroweak boson production using data from pp collisions at a centre-of-mass energy of ... ...TeV. The analysis is based on an integrated luminosity of 2.0 fb super(-1) recorded with the LHCb detector. The bosons are identified in the W arrow right mu nu and Z arrow right mu super(+) mu super(-) decay channels. The cross-sections are measured for muons in the pseudorapidity range 2.0 < eta < 4.5, with transverse momenta p sub(T) > 20 GeV/c and, in the case of the Z boson, a dimuon mass within ... GeV/c super(2). The results are ... ... ... ... ... ... ... ... where the first uncertainties are statistical, the second are systematic, the third are due to the knowledge of the LHC beam energy and the fourth are due to the luminosity determination. The evolution of the W and Z boson cross-sections with centre-of-mass energy is studied using previously reported measurements with 1.0 fb super(-1) of data at 7 TeV. Differential distributions are also presented. Results are in good agreement with theoretical predictions at next-to-next-to-leading order in perturbative quantum chromodynamics. Figure not available: see fulltext.
Using a pp collision data sample corresponding to an integrated luminosity of 3.0 fb–1, collected by the LHCb detector, we present the first search for the strangeness-changing weak decay Ξb– → ...Λ0bπ–. No b hadron decay of this type has been seen before. A signal for this decay, corresponding to a significance of 3.2 standard deviations, is reported.
A
bstract
The first observation of
Z
boson production in proton-lead collisions at a centre-of-mass energy per proton-nucleon pair of
s
N
N
= 5 TeV is presented. The data sample corresponds to an ...integrated luminosity of 1
.
6 nb
−1
collected with the LHCb detector. The
Z
candidates are reconstructed from pairs of oppositely charged muons with pseudorapidities between 2.0 and 4.5 and transverse momenta above 20 GeV
/
c. The invariant dimuon mass is restricted to the range 60 − 120 GeV
/
c. The
Z
production cross-section is measured to be
σ
Z
→
μ
+
μ
−
fwd
=
13.5
−
4.0
+
5.4
stat
.
±
1.2
syst
.
nb
in the direction of the proton beam and
σ
Z
→
μ
+
μ
−
bwd
=
10.7
−
5.1
+
8.4
stat
.
±
1.0
syst
.
nb
in the direction of the lead beam, where the first uncertainty is statistical and the second systematic.
A search is presented for long-lived particles with a mass between 25 and 50
GeV
/
c
2
and a lifetime between 1 and 200
ps
in a sample of proton–proton collisions at a centre-of-mass energy of
s
=
7
... TeV, corresponding to an integrated luminosity of 0.62
fb
-
1
, collected by the LHCb detector. The particles are assumed to be pair-produced by the decay of a standard model-like Higgs boson. The experimental signature of the long-lived particle is a displaced vertex with two associated jets. No excess above the background is observed and limits are set on the production cross-section as a function of the long-lived particle mass and lifetime.
Study of the D^sup 0^p amplitude decays Adeva, B; Ajaltouni, Z; Amhis, Y ...
The journal of high energy physics,
05/2017, Letnik:
2017, Številka:
5
Journal Article
Recenzirano
Odprti dostop
An amplitude analysis of the decay Lambda ^sub b ^ ^sup 0^ right arrowD ^sup 0^ ppi ^sup -^ is performed in the part of the phase space containing resonances in the D ^sup 0^ p channel. The study is ...based on a data sample corresponding to an integrated luminosity of 3.0 fb^sup -1^ of pp collisions recorded by the LHCb experiment. The spectrum of excited Lambda ^sub c ^ ^sup +^ states that decay into D ^sup 0^ p is studied. The masses, widths and quantum numbers of the Lambda^sub c^(2880)^sup +^ and Lambda^sub c^(2940)^sup +^ resonances are measured. The constraints on the spin and parity for the Lambda^sub c^(2940)^sup +^ state are obtained for the first time. A near-threshold enhancement in the D ^sup 0^ p amplitude is investigated and found to be consistent with a new resonance, denoted the Lambda^sub c^(2860)^sup +^, of spin 3/2 and positive parity. Figure not available: see fulltext.
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