The first measurement of transverse-spin-dependent azimuthal asymmetries in the pion-induced Drell-Yan (DY) process is reported. We use the CERN SPS 190 GeV/c π^{-} beam and a transversely polarized ...ammonia target. Three azimuthal asymmetries giving access to different transverse-momentum-dependent (TMD) parton distribution functions (PDFs) are extracted using dimuon events with invariant mass between 4.3 GeV/c^{2} and 8.5 GeV/c^{2}. Within the experimental uncertainties, the observed sign of the Sivers asymmetry is found to be consistent with the fundamental prediction of quantum chromodynamics (QCD) that the Sivers TMD PDFs extracted from DY have a sign opposite to the one extracted from semi-inclusive deep-inelastic scattering (SIDIS) data. We present two other asymmetries originating from the pion Boer-Mulders TMD PDFs convoluted with either the nucleon transversity or pretzelosity TMD PDFs. A recent COMPASS SIDIS measurement was obtained at a hard scale comparable to that of these DY results. This opens the way for possible tests of fundamental QCD universality predictions.
A
bstract
Using proton-proton collision data, corresponding to an integrated luminosity of 9 fb
−1
, collected with the LHCb detector between 2011 and 2018, a new narrow charmonium state, the X(3842) ...resonance, is observed in the decay modes
$$ \mathrm{X}(3842)\to {D}^0{\overline{D}}^0 $$
X
3842
→
D
0
D
¯
0
and X(3842) →
D
+
D
−
. The mass and the natural width of this state are measured to be
$$ \begin{array}{l}{m}_{X(3842)}=3842.71\pm 0.16\pm 0.12\ MeV/{c}^2,\hfill \\ {}{\varGamma}_{X(3842)}=2.79\pm 0.51\pm 0.35\ MeV,\hfill \end{array} $$
m
X
3842
=
3842.71
±
0.16
±
0.12
M
e
V
/
c
2
,
Γ
X
3842
=
2.79
±
0.51
±
0.35
M
e
V
,
where the first uncertainty is statistical and the second is systematic. The observed mass and narrow natural width suggest the interpretation of the new state as the unobserved (spin-3
ψ
3
1
3
D
3
) charmonium state.
In addition, prompt hadroproduction of the
ψ
(3770) and
χ
2
(3930) states is observed for the first time, and the parameters of these states are measured to be
$$ \begin{array}{l}{m}_{\psi (3770)}=3778.1\pm 0.7\pm 0.6\ MeV/{c}^2,\hfill \\ {}{m}_{\chi_2(3930)}=3921.9\pm 0.6\pm 0.2\ MeV/{c}^2,\hfill \\ {}{\varGamma}_{\chi_2(3930)}=36.6 \pm 1.9 \pm 0.9\ MeV,\hfill \end{array} $$
m
ψ
3770
=
3778.1
±
0.7
±
0.6
M
e
V
/
c
2
,
m
χ
2
3930
=
3921.9
±
0.6
±
0.2
M
e
V
/
c
2
,
Γ
χ
2
3930
=
36.6
±
1.9
±
0.9
M
e
V
,
where the first uncertainty is statistical and the second is systematic.
We report on the first measurement of exclusive single-photon muoproduction on the proton by COMPASS using 160GeV/c polarised μ+ and μ− beams of the CERN SPS impinging on a liquid hydrogen target. We ...determine the dependence of the average of the measured μ+ and μ− cross sections for deeply virtual Compton scattering on the squared four-momentum transfer t from the initial to the final proton. The slope B of the t-dependence is fitted with a single exponential function, which yields B=(4.3±0.6stat|sys−0.3+0.1)(GeV/c)−2. This result can be converted into a transverse extension of partons in the proton, 〈r⊥2〉=(0.58±0.04stat|sys−0.02+0.01±0.04model)fm. For this measurement, the average virtuality of the photon mediating the interaction is 〈Q2〉=1.8(GeV/c)2 and the average value of the Bjorken variable is 〈xBj〉=0.056.
Using a novel analysis technique, the gluon polarisation in the nucleon is re-evaluated using the longitudinal double-spin asymmetry measured in the cross section of semi-inclusive single-hadron ...muoproduction with photon virtuality
Q
2
>
1
(
GeV
/
c
)
2
. The data were obtained by the COMPASS experiment at CERN using a 160 GeV/
c
polarised muon beam impinging on a polarised
6
LiD target. By analysing the full range in hadron transverse momentum
p
T
, the different
p
T
-dependences of the underlying processes are separated using a neural-network approach. In the absence of pQCD calculations at next-to-leading order in the selected kinematic domain, the gluon polarisation
Δ
g
/
g
is evaluated at leading order in pQCD at a hard scale of
μ
2
=
⟨
Q
2
⟩
=
3
(
GeV
/
c
)
2
. It is determined in three intervals of the nucleon momentum fraction carried by gluons,
x
g
, covering the range
0.04
<
x
g
<
0.28
and does not exhibit a significant dependence on
x
g
. The average over the three intervals,
⟨
Δ
g
/
g
⟩
=
0.113
±
0
.
038
(
stat
.
)
±
0
.
036
(
syst
.
)
at
⟨
x
g
⟩
≈
0.10
, suggests that the gluon polarisation is positive in the measured
x
g
range.
In Fig. 5 on p. 311 of our Phys. Lett. B 740 (2015) 303 an adjustment by 180∘ is required for the phases with respect to the L=2,M=1 wave, of the following waves: L=1,3,5 with M=1, and L=2 with M=2. ...After this correction (Fig. 5 (corrected) below), the extracted partial waves describe the angular distribution of the η(′) in the Gottfried-Jackson (GJ) frame, using Eq. (4) with implicit Condon-Shortley phase convention. The other results of our paper are not affected. The right-handed GJ coordinate system was defined by the z-axis pointing in the direction of the beam in the η(′)π− center-of-mass system and the y-axis pointing in the direction of precoilGJ×pbeamGJ.
We report on a measurement of hard exclusive π0 muoproduction on the proton by COMPASS using 160GeV/c polarised μ+ and μ− beams of the CERN SPS impinging on a liquid hydrogen target. From the average ...of the measured μ+ and μ− cross sections, the virtual-photon proton cross section is determined as a function of the squared four-momentum transfer between initial and final proton in the range 0.08(GeV/c)2<|t|<0.64(GeV/c)2. The average kinematics of the measurement are 〈Q2〉=2.0(GeV/c)2, 〈ν〉=12.8GeV, 〈xBj〉=0.093 and 〈−t〉=0.256(GeV/c)2. Fitting the azimuthal dependence reveals a combined contribution by transversely and longitudinally polarised photons of (8.2±0.9stat−1.2+1.2|sys)nb/(GeV/c)2, as well as transverse-transverse and longitudinal-transverse interference contributions of (−6.1±1.3stat−0.7+0.7|sys)nb/(GeV/c)2 and (1.5±0.5stat−0.2+0.3|sys)nb/(GeV/c)2, respectively. Our results provide important input for modelling Generalised Parton Distributions. In the context of the phenomenological Goloskokov-Kroll model, the statistically significant transverse-transverse interference contribution constitutes clear experimental evidence for the chiral-odd GPD E‾T.
Decays of Bs0 and B‾0s mesons into J/ψπ+π− final states are studied in a data sample corresponding to 1.9 fb−1 of integrated luminosity collected with the LHCb detector in 13 TeV pp collisions. A ...time-dependent amplitude analysis is used to determine the final-state resonance contributions, the CP-violating phase ϕs=−0.057±0.060±0.011 rad, the decay-width difference between the heavier mass Bs0 eigenstate and the B0 meson of −0.050±0.004±0.004 ps−1, and the CP-violating parameter |λ|=1.01−0.06+0.08±0.03, where the first uncertainty is statistical and the second systematic. These results are combined with previous LHCb measurements in the same decay channel using 7 TeV and 8 TeV pp collisions obtaining ϕs=0.002±0.044±0.012 rad, and |λ|=0.949±0.036±0.019.
Abstract The cross-sections of $$\psi {(2S)}$$ ψ(2S) meson production in proton-proton collisions at $$\sqrt{s} =13\text { TeV} $$ s=13TeV are measured with a data sample collected by the LHCb ...detector corresponding to an integrated luminosity of $$275\text { pb} ^{-1} $$ 275pb-1 . The production cross-sections for prompt $$\psi {(2S)}$$ ψ(2S) mesons and those for $$\psi {(2S)}$$ ψ(2S) mesons from b-hadron decays ($${\psi {(2S)}} \text{-from- }{b} $$ ψ(2S)-from-b ) are determined as functions of the transverse momentum, $$p_{\mathrm {T}}$$ pT , and the rapidity, y, of the $$\psi {(2S)}$$ ψ(2S) meson in the kinematic range $$2<p_{\mathrm {T}} <20\text { GeV/}c $$ 2<pT<20GeV/c and $$2.0<y<4.5$$ 2.0<y<4.5 . The production cross-sections integrated over this kinematic region are $$\begin{aligned} \begin{aligned}&\sigma (\text{ prompt } {\psi {(2S)}},13\text { TeV})\\&\quad =1.430\pm 0.005\text { (stat)} \pm 0.099\text { (syst)} \,\upmu \text {b} ,\\&\sigma ({\psi {(2S)}} \text{-from- }{b},13\text { TeV})\\&\quad =0.426\pm 0.002\text { (stat)} \pm 0.030\text { (syst)} \,\upmu \text {b} . \end{aligned} \end{aligned}$$ σ(promptψ(2S),13TeV)=1.430±0.005(stat)±0.099(syst)μb,σ(ψ(2S)-from-b,13TeV)=0.426±0.002(stat)±0.030(syst)μb. A new measurement of $$\psi {(2S)}$$ ψ(2S) production cross-sections in pp collisions at $$\sqrt{s}=7\text { TeV} $$ s=7TeV is also performed using data collected in 2011, corresponding to an integrated luminosity of $$614\text { pb} ^{-1} $$ 614pb-1 . The integrated production cross-sections in the kinematic range $$3.5<p_{\mathrm {T}} <14\text { GeV/}c $$ 3.5<pT<14GeV/c and $$2.0<y<4.5$$ 2.0<y<4.5 are $$\begin{aligned} \begin{aligned}&\sigma (\text{ prompt } {\psi {(2S)}},7\text { TeV})\\&\quad =0.471\pm 0.001\text { (stat)} \pm 0.025\text { (syst)} \,\upmu \text {b} ,\\&\sigma ({\psi {(2S)}} \text{-from- }{b},7\text { TeV})\\&\quad =0.126\pm 0.001\text { (stat)} \pm 0.008\text { (syst)} \,\upmu \text {b} . \end{aligned} \end{aligned}$$ σ(promptψ(2S),7TeV)=0.471±0.001(stat)±0.025(syst)μb,σ(ψ(2S)-from-b,7TeV)=0.126±0.001(stat)±0.008(syst)μb. All results show reasonable agreement with theoretical calculations.
Abstract A search for the rare leptonic decay $${{{B} ^+}} \!\rightarrow {\mu ^+} {\mu ^-} {\mu ^+} {{\upnu } _\mu } $$ B+→μ+μ-μ+νμ is performed using proton-proton collision data corresponding to an ...integrated luminosity of $$4.7 \, {\hbox {fb}}^{-1}$$ 4.7fb-1 collected by the LHCb experiment. The search is carried out in the region where the lowest of the two $${\mu ^+\mu ^-} $$ μ+μ- mass combinations is below $$980 {\mathrm {\,MeV\!/}c^2} $$ 980MeV/c2 . The data are consistent with the background-only hypothesis and an upper limit of $$1.6 \times 10^{-8}$$ 1.6×10-8 at 95% confidence level is set on the branching fraction in the stated kinematic region.
The Large Hadron Collider beauty (LHCb) experiment at CERN is undergoing an upgrade in preparation for the Run 3 data collection period at the Large Hadron Collider (LHC). As part of this upgrade, ...the trigger is moving to a full software implementation operating at the LHC bunch crossing rate. We present an evaluation of a CPU-based and a GPU-based implementation of the first stage of the high-level trigger. After a detailed comparison, both options are found to be viable. This document summarizes the performance and implementation details of these options, the outcome of which has led to the choice of the GPU-based implementation as the baseline.
PDF
