The LHCb Collaboration measures production of the exotic hadron χ_{c1}(3872) in proton-nucleus collisions for the first time. Comparison with the charmonium state ψ(2S) suggests that the exotic ...χ_{c1}(3872) experiences different dynamics in the nuclear medium than conventional hadrons, and comparison with data from proton-proton collisions indicates that the presence of the nucleus may modify χ_{c1}(3872) production rates. This is the first measurement of the nuclear modification factor of an exotic hadron.The LHCb Collaboration measures production of the exotic hadron χ_{c1}(3872) in proton-nucleus collisions for the first time. Comparison with the charmonium state ψ(2S) suggests that the exotic χ_{c1}(3872) experiences different dynamics in the nuclear medium than conventional hadrons, and comparison with data from proton-proton collisions indicates that the presence of the nucleus may modify χ_{c1}(3872) production rates. This is the first measurement of the nuclear modification factor of an exotic hadron.
Direct Dark Matter searches are nowadays one of the most fervid research topics with many experimental efforts devoted to the search for nuclear recoils induced by the scattering of Weakly ...Interactive Massive Particles (WIMPs). Detectors able to reconstruct the direction of the nucleus recoiling against the scattering WIMP are opening a new frontier to possibly extend Dark Matter searches beyond the neutrino background. Exploiting directionality would also prove the galactic origin of Dark Matter with an unambiguous signal-to-background separation. Indeed, the angular distribution of recoiled nuclei is centered around the direction of the Cygnus constellation, while the background distribution is expected to be isotropic. Current directional experiments are based on gas TPC whose sensitivity is limited by the small achievable detector mass. In this paper we present the discovery potential of a directional experiment based on the use of a solid target made of newly developed nuclear emulsions and of optical read-out systems reaching unprecedented nanometric resolution.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
A
bstract
Searches for
CP
violation in the decays
D
s
+
→
η
π
+
and
D
s
+
→
η
′
π
+
are performed using
pp
collision data corresponding to 6 fb
−
1
of integrated luminosity collected by the LHCb ...experiment. The calibration channels
D
s
+
→
ϕ
π
+
are used to remove production and detection asymmetries. The resulting
CP
-violating asymmetries are
A
CP
=
D
+
→
η
π
+
=
0.34
±
0.66
±
0.16
±
0.05
%
,
A
CP
=
D
s
+
→
η
π
+
=
0.32
±
0.51
±
0.12
%
,
A
CP
=
D
+
→
η
′
π
+
=
0.49
±
0.18
±
0.06
±
0.05
%
,
A
CP
=
D
s
+
→
η
′
π
+
=
0.01
±
0.12
±
0.08
%
,
where the first uncertainty is statistical, the second is systematic and the third, relevant for the
D
+
channels, is due to the uncertainty on
A
CP
=
D
+
→
ϕ
π
+
. These measurements, currently the most precise for three of the four channels considered, are consistent with the absence of
CP
violation. A combination of these results with previous LHCb measurements is presented.
The OPERA experiment discovered muon neutrino into tau neutrino oscillations in appearance mode, detecting tau leptons by means of nuclear emulsion films. The apparatus was also endowed with ...electronic detectors with tracking capability, such as scintillator strips and resistive plate chambers. Because of its location in the underground Gran Sasso laboratory, under 3800 m.w.e., the OPERA detector has also been used as an observatory for TeV muons produced by cosmic rays in the atmosphere. In this paper the measurement of the single muon flux modulation and its correlation with the seasonal cycle of atmospheric temperature is reported.
A
bstract
The first measurement of the
Z
boson production cross-section at centre-of-mass energy
s
= 5
.
02 TeV in the forward region is reported, using
pp
collision data collected by the LHCb ...experiment in year 2017, corresponding to an integrated luminosity of 100 ± 2 pb
−
1
. The production cross-section is measured for final-state muons in the pseudorapidity range 2
.
0
< η <
4
.
5 with transverse momentum
p
T
>
20 GeV/
c
. The integrated cross-section is determined to be
σ
Z
→
μ
+
μ
−
=
39.6
±
0.7
stat
±
0.6
syst
±
0.8
lumi
pb
for the di-muon invariant mass in the range 60
< M
μμ
<
120 GeV/
c
2
. This result and the differential cross-section results are in good agreement with theoretical predictions at next-to-next-to-leading order in the strong coupling constant.
Based on a previous LHCb measurement of the
Z
boson production cross-section in
p
Pb collisions at
s
NN
= 5
.
02 TeV, the nuclear modification factor
R
p
Pb
is measured for the first time at this energy. The measured values are
1.2
−
0.3
+
0.5
(stat)
±
0
.
1(syst) in the forward region (1.53
<
y
μ
∗
<
4
.
03) and
3.6
−
0.9
+
1.6
(stat)
±
0
.
2(syst) in the backward region (
−
4
.
97
<
y
μ
∗
< −
2
.
47), where
y
μ
∗
represents the muon rapidity in the centre-of-mass frame.
The Search for Hidden Particles (SHiP) Collaboration has shown that the CERN SPS accelerator with its 400 GeV/c proton beam offers a unique opportunity to explore the Hidden Sector 1–3. The proposed ...experiment is an intensity frontier experiment which is capable of searching for hidden particles through both visible decays and through scattering signatures from recoil of electrons or nuclei. The high-intensity experimental facility developed by the SHiP Collaboration is based on a number of key features and developments which provide the possibility of probing a large part of the parameter space for a wide range of models with light long-lived super-weakly interacting particles with masses up to (10) GeV/c2 in an environment of extremely clean background conditions. This paper describes the proposal for the experimental facility together with the most important feasibility studies. The paper focuses on the challenging new ideas behind the beam extraction and beam delivery, the proton beam dump, and the suppression of beam-induced background.
A
bstract
The OPERA neutrino experiment at the underground Gran Sasso Laboratory has measured the velocity of neutrinos from the CERN CNGS beam over a baseline of about 730 km. The measurement is ...based on data taken by OPERA in the years 2009, 2010 and 2011. Dedicated upgrades of the CNGS timing system and of the OPERA detector, as well as a high precision geodesy campaign for the measurement of the neutrino baseline, allowed reaching comparable systematic and statistical accuracies.
An arrival time of CNGS muon neutrinos with respect to the one computed assuming the speed of light in vacuum of
was measured corresponding to a relative difference of the muon neutrino velocity with respect to the speed of light
. The above result, obtained by comparing the time distributions of neutrino interactions and of protons hitting the CNGS target in 10.5
μ
s long extractions, was confirmed by a test performed at the end of 2011 using a short bunch beam allowing to measure the neutrino time of flight at the single interaction level.
This paper presents a fast approach to simulating muons produced in interactions of the SPS proton beams with the target of the SHiP experiment. The SHiP experiment will be able to search for new ...long-lived particles produced in a 400 GeV/c SPS proton beam dump and which travel distances between fifty metres and tens of kilometers. The SHiP detector needs to operate under ultra-low background conditions and requires large simulated samples of muon induced background processes. Through the use of Generative Adversarial Networks it is possible to emulate the simulation of the interaction of 400 GeV/c proton beams with the SHiP target, an otherwise computationally intensive process. For the simulation requirements of the SHiP experiment, generative networks are capable of approximating the full simulation of the dense fixed target, offering a speed increase by a factor of (106). To evaluate the performance of such an approach, comparisons of the distributions of reconstructed muon momenta in SHiP's spectrometer between samples using the full simulation and samples produced through generative models are presented. The methods discussed in this paper can be generalised and applied to modelling any non-discrete multi-dimensional distribution.
A
bstract
The production cross-section of
J/ψ
pairs in proton-proton collisions at a centre-of-mass energy of
s
= 13 TeV is measured using a data sample corresponding to an integrated luminosity of 4
....
2 fb
−
1
collected by the LHCb experiment. The measurement is performed with both
J/ψ
mesons in the transverse momentum range 0
< p
T
<
14 GeV/
c
and rapidity range 2
.
0
< y <
4
.
5. The cross-section of this process is measured to be 16
.
36 ± 0
.
28 (stat) ± 0
.
88 (syst) nb. The contributions from single-parton scattering and double-parton scattering are separated based on the dependence of the cross-section on the absolute rapidity difference ∆
y
between the two
J/ψ
mesons. The effective cross-section of double-parton scattering is measured to be
σ
eff
= 13
.
1
±
1
.
8 (stat)
±
2
.
3 (syst) mb. The distribution of the azimuthal angle
ϕ
CS
of one of the
J/ψ
mesons in the Collins-Soper frame and the
p
T
-spectrum of the
J/ψ
pairs are also measured for the study of the gluon transverse-momentum dependent distributions inside protons. The extracted values of ⟨cos 2
ϕ
CS
⟩ and ⟨cos 4
ϕ
CS
⟩ are consistent with zero, but the presence of azimuthal asymmetry at a few percent level is allowed.
K
S
0,
Λ,
Ξ,
Ω and negative particle yields and transverse mass spectra have been measured at central rapidity in Pb–Pb and p–Pb collisions at 158
A GeV/
c. Yields are studied as a function of the ...number of nucleons participating in the collision
N
part, which is estimated with the Glauber model. From p–Pb to Pb–Pb collisions the particle yields per participant increase substantially. The enhancement is more pronounced for multistrange particles, and exceeds an order of magnitude for the
Ω. For a number of participants,
N
part, greater than 100, however, all yields per participant appear to be constant.
PDF
