The standard model of particle physics is our best description yet of fundamental particles and their interactions, but it is known to be incomplete. As yet undiscovered particles and interactions ...might exist. One of the most powerful ways to search for new particles is by studying processes known as flavour-changing neutral current decays, whereby a quark changes its flavour without altering its electric charge. One example of such a transition is the decay of a beauty quark into a strange quark. Here we review some intriguing anomalies in these decays, which have revealed potential cracks in the standard model-hinting at the existence of new phenomena.
(ProQuest: ... denotes formulae and/or non-USASCII text omitted) Measurements of b hadron production ratios in proton-proton collisions at a center-of-mass energy of 7 TeV with an integrated ...luminosity of 3 pb super(-1) are presented. We study the ratios of strange B meson to light B meson production functionof sub(s)/(functionof sub(u) + functionof sub(d)) and ... baryon to light B meson production functionof sub(Lambda)b/(functionof sub(u) + functionof sub(d)) as a function of the charmed hadron-muon pair transverse momentum p sub(T) and the b hadron pseudorapidity eta, for p sub(T) between 0 and 14 GeV and eta between 2 and 5. We find that functionof sub(s)/(functionof sub(u) + functionof sub(d)) is consistent with being independent of p sub(T) and eta, and we determine ..., where the first error is statistical and the second systematic. The corresponding ratio functionof sub(Lambda)b/(functionof sub(u) + functionof sub(d)) is found to be dependent upon the transverse momentum of the charmed hadron-muon pair, functionof sub(Lambda)b/(functionof sub(u) + functionof sub(d)) = (0.404 + or - 0.017(stat) + or - 0.027(syst) + or - 0.105(Br)), where Br reflects an absolute scale uncertainty due to the poorly x 1 - (0.031 + or - 0.004(stat) + or - 0.003(syst)) x p sub(T)(GeV) known branching fraction ... We extract the ratio of strange B meson to light neutral B meson production functionof sub(s)/functionof sub(d) by averaging the result eported here with two previous measurements derived from the relative abundances of ... to B super(0 arrow right )D super(+)K super(-) and B super(0) arrow right a D super(+)pi super(-). We obtain ...
A search for a long-lived scalar particle χ is performed, looking for the decay B+→K+χ with χ→μ+μ− in pp collision data corresponding to an integrated luminosity of 3 fb−1, collected by the LHCb ...experiment at center-of-mass energies of s=7 and 8 TeV. This new scalar particle, predicted by hidden sector models, is assumed to have a narrow width. The signal would manifest itself as an excess in the dimuon invariant mass distribution over the Standard Model background. No significant excess is observed in the accessible ranges of mass 250<m(χ)<4700 MeV/c2 and lifetime 0.1<τ(χ)<1000 ps. Upper limits on the branching fraction B(B+→K+χ(μ+μ−)) at 95% confidence level are set as a function of m(χ) and τ(χ), varying between 2×10−10 and 10−7. These are the most stringent limits to date. The limits are interpreted in the context of a model with a light inflaton particle.
Two-particle angular correlations are studied in proton-lead collisions at a nucleon–nucleon centre-of-mass energy of sNN=5 TeV, collected with the LHCb detector at the LHC. The analysis is based on ...data recorded in two beam configurations, in which either the direction of the proton or that of the lead ion is analysed. The correlations are measured in the laboratory system as a function of relative pseudorapidity, Δη, and relative azimuthal angle, Δϕ, for events in different classes of event activity and for different bins of particle transverse momentum. In high-activity events a long-range correlation on the near side, Δϕ≈0, is observed in the pseudorapidity range 2.0<η<4.9. This measurement of long-range correlations on the near side in proton-lead collisions extends previous observations into the forward region up to η=4.9. The correlation increases with growing event activity and is found to be more pronounced in the direction of the lead beam. However, the correlation in the direction of the lead and proton beams are found to be compatible when comparing events with similar absolute activity in the direction analysed.
A
bstract
This report details the capabilities of LHCb and its upgrades towards the study of kaons and hyperons. The analyses performed so far are reviewed, elaborating on the prospects for some key ...decay channels, while proposing some new measurements in LHCb to expand its strangeness research program.
A
bstract
Production cross-sections of prompt charm mesons are measured using data from
pp
collisions at the LHC at a centre-of-mass energy of 5 TeV. The data sample corresponds to an integrated ...luminosity of 8
.
60 ± 0
.
33 pb
−1
collected by the LHCb experiment. The production cross-sections of
D
0
,
D
+
,
D
s
+
, and
D
∗+
mesons are measured in bins of charm meson transverse momentum,
p
T
, and rapidity,
y
. They cover the rapidity range 2
.
0
< y <
4
.
5 and transverse momentum ranges 0
< p
T
<
10 GeV
/c
for
D
0
and
D
+
and 1
< p
T
<
10 GeV
/c
for
D
s
+
and
D
∗+
mesons. The inclusive cross-sections for the four mesons, including charge-conjugate states, within the range of 1
< p
T
<
8 GeV
/c
are determined to be
σ
pp
→
D
0
X
=
1004
±
3
±
54
μ
b
,
σ
pp
→
D
+
X
=
402
±
2
±
30
μ
b
,
σ
pp
→
D
s
+
X
=
170
±
4
±
16
μ
b
,
σ
pp
→
D
∗
+
X
=
421
±
5
±
36
μ
b
,
where the uncertainties are statistical and systematic, respectively.
(ProQuest: ... denotes formulae and/or non-USASCII text omitted; see image) Abstract The production cross-sections of B mesons are measured in pp collisions at a centre-of-mass energy of 7 TeV, using ...data collected with the LHCb detector corresponding to a integrated luminosity of 0.36 fb^sup -1^. The B ^sup +^, B ^sup 0^ and ... mesons are reconstructed in the exclusive decays B ^sup +^ arrow right J/psiK ^sup +^, B ^sup 0^ arrow right J/psiK ^sup *0^ and ..., with J/psi arrow right mu ^sup +^ mu ^sup -^, K ^sup *0^ arrow right K ^sup +^pi^sup -^ and arrow right K ^sup +^ K ^sup -^. The differential cross-sections are measured as functions of B meson transverse momentum p ^sub T^ and rapidity y, in the range 0 < p ^sub T^ < 40 GeV/c and 2.0 < y < 4.5. The integrated cross-sections in the same p ^sub T^ and y ranges, including charge-conjugate states, are measured to be ...where the third uncertainty arises from the pre-existing branching fraction measurements. Figure not available: see fulltext.
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.
LHCb Silicon Tracker DAQ and ECS Online Systems Esperante, Daniel; Rodriguez, P; Buchler, A ...
IEEE transactions on nuclear science,
2010-April, 2010-04-00, 20100401, Letnik:
57, Številka:
2
Journal Article
Recenzirano
The LHCb experiment at CERN is designed to perform precision measurements of b quark decays. The Silicon Tracker plays a crucial role in reconstructing particle trajectories and consists of two ...silicon micro-strip detectors, the Tracker Turicensis and the Inner Tracker. The radiation environment and the magnetic field represent new challenges for the implementation of the Experiment Control System (ECS) and the data acquisition (DAQ). The DAQ has to deal with ~272 000 analog read-out channels and real-time DAQ at a rate of ~ 1.1 MHz with data processing at the Trigger Electronics and L1 (TELL1) board level. The TELL1 real-time algorithms for clustering thresholds and other computations run on dedicated FPGAs. After data processing the total throughput amounts to about 6.4 GB from an input data rate of ~ 337 GB per second. The ECS is based on the hierarchical finite state machine paradigm and allows distributed control access and multi-platform use. The ECS is able to control and monitor the detector hardware infrastructure (power supplies, DAQ electronics ...) as well as monitor the environmental parameters. It can also take automated actions on warnings or alarms. Finally a completely independent, hardware based safety system ensures the detector safe operation.