A
bstract
The polarization of the Y(1S), Y(2S) and Y(3S) mesons, produced in pp collisions at centre-of-mass energies
s
=
7
and 8 TeV, is measured using data samples collected by the LHCb experiment, ...corresponding to integrated luminosities of 1 and 2 fb
−1
, respectively. The measurements are performed in three polarization frames, using Y →
μμ
decays in the kinematic region of the transverse momentum
p
T
Υ
< 30 GeV/
c
and rapidity 2.2 <
y
Y
< 4.5. No large polarization is observed.
A
bstract
A measurement of
Z
→
τ
+
τ
−
production cross-section is presented using data, corresponding to an integrated luminosity of 2 fb
−1
, from
pp
collisions at
s
=
8
TeV collected by the LHCb ...experiment. The
τ
+
τ
−
candidates are reconstructed in final states with the first tau lepton decaying leptonically, and the second decaying either leptonically or to one or three charged hadrons. The production cross-section is measured for
Z
bosons with invariant mass between 60 and 120 GeV
/c
2
, which decay to tau leptons with transverse momenta greater than 20 GeV
/c
and pseudorapidities between 2.0 and 4.5. The cross-section is determined to be
σ
pp
→
Z
→
τ
+
τ
−
=
95.8
±
2.1
±
4.6
±
0.2
±
1.1
pb, where the first uncertainty is statistical, the second is systematic, the third is due to the LHC beam energy uncertainty, and the fourth to the integrated luminosity uncertainty. This result is compatible with NNLO Standard model predictions. The ratio of the cross-sections for
Z
→
τ
+
τ
−
to
Z
→
μ
+
μ
−
(
Z
→
e
+
e
−
), determined to be 1
.
01 ± 0
.
05 (1
.
02 ± 0
.
06), is consistent with the lepton-universality hypothesis in
Z
decays.
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
bstract
Bose-Einstein correlations of same-sign charged pions, produced in proton-proton collisions at a 7 TeV centre-of-mass energy, are studied using a data sample collected by the LHCb ...experiment. The signature for Bose-Einstein correlations is observed in the form of an enhancement of pairs of like-sign charged pions with small four-momentum difference squared. The charged-particle multiplicity dependence of the Bose-Einstein correlation parameters describing the correlation strength and the size of the emitting source is investigated, determining both the correlation radius and the chaoticity parameter. The measured correlation radius is found to increase as a function of increasing charged-particle multiplicity, while the chaoticity parameter is seen to decrease.
Kinematic correlations for pairs of beauty hadrons, produced in high energy proton-proton collisions, are studied. The data sample used was collected with the LHCb experiment at centre-of-mass ...energies of 7 and 8 TeV and corresponds to an integrated luminosity of 3 fb−1. The measurement is performed using inclusive b → J/ψX decays in the rapidity range 2 < yJ/ψ < 4.5. The observed correlations are in good agreement with theoretical predictions.
Amplitude models are constructed to describe the resonance structure of
and
decays using
collision data collected at centre-of-mass energies of 7 and 8 TeV with the LHCb experiment, corresponding to ...an integrated luminosity of 3.0
. The largest contributions to both decay amplitudes are found to come from axial resonances, with decay modes
and
being prominent in
and
, respectively. Precise measurements of the lineshape parameters and couplings of the
,
and
resonances are made, and a quasi model-independent study of the
resonance is performed. The coherence factor of the decays is calculated from the amplitude models to be
, which is consistent with direct measurements. These models will be useful in future measurements of the unitary-triangle angle
and studies of charm mixing and
violation.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The production of charged hadrons within jets recoiling against a Z boson is measured in proton-proton collision data at sqrts=8 TeV recorded by the LHCb experiment. The charged-hadron structure of ...the jet is studied longitudinally and transverse to the jet axis for jets with transverse momentum p_{T}>20 GeV and in the pseudorapidity range 2.5<η<4. These are the first measurements of jet hadronization at these forward rapidities and also the first where the jet is produced in association with a Z boson. In contrast to previous hadronization measurements at the Large Hadron Collider, which are dominated by gluon jets, these measurements probe predominantly light-quark jets which are found to be more longitudinally and transversely collimated with respect to the jet axis when compared to the previous gluon dominated measurements. Therefore, these results provide valuable information on differences between quarks and gluons regarding nonperturbative hadronization dynamics.
A
bstract
A search for the rare two-body charmless baryonic decay
B
+
→
p
Λ
¯
is performed with
pp
collision data, corresponding to an integrated luminosity of 3 fb
−1
, collected by the LHCb ...experiment at centre-of-mass energies of 7 and 8 TeV. An excess of
B
+
→
p
Λ
¯
candidates with respect to background expectations is seen with a statistical significance of 4.1 standard deviations, and constitutes the first evidence for this decay. The branching fraction, measured using the
B
+
→
K
S
0
π
+
decay for normalisation, is
ℬ
B
+
→
p
Λ
¯
=
2
.
4
−
0.8
+
1.0
±
0.3
×
1
0
−
7
,
where the first uncertainty is statistical and the second systematic.
A
bstract
A search for the doubly charmed baryon
$ \Xi_{cc}^{+} $
in the decay mode
$ \Xi_{cc}^{+}\to \Lambda_c^{+}{K^{-}}{\pi^{+}} $
is performed with a data sample, corresponding to an integrated ...luminosity of 0.65 fb
−1
, of
pp
collisions recorded at a centre-of-mass energy of 7 TeV. No significant signal is found in the mass range 3300-3800 MeV
/c
2
. Upper limits at the 95% confidence level on the ratio of the
$ \Xi_{cc}^{+} $
production cross-section times branching fraction to that of the
$ \Lambda_c^{+} $
,
R
, are given as a function of the
$ \Xi_{cc}^{+} $
mass and lifetime. The largest upper limits range from
R
< 1.5 × 10
−
2 for a lifetime of 100 fs to
R <
3
.
9 × 10
−4
for a lifetime of 400 fs.
A search for Formula omitted violation in charmless four-body decays of Formula omitted and Formula omitted 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 Formula omitted 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 Formula omitted. A total of 18 Formula omitted asymmetries are considered, either accounting for the full phase space of the decays or exploring specific regions of the decay kinematics. No significant Formula omitted-violation effect is observed in any of the measurements.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
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