This work shows how it is possible to reconstruct SuperKEKB’s beam parameters using a Neural Network with beamstrahlung signal from the Large Angle Beamstrahlung Monitor (LABM) as input. We describe ...the device, the model, and discuss the results.
Gaseous time projection chambers (TPCs) with high readout segmentation are capable of reconstructing detailed 3D ionization distributions of nuclear recoils resulting from elastic neutron scattering. ...Using a system of six compact TPCs with pixel ASIC readout, filled with a 70:30 mixture of He:CO2 gas, we analyze the first directional measurements of beam-induced neutron backgrounds in the tunnel regions surrounding the Belle II detector at the SuperKEKB e+e− collider. With the use of 3D recoil tracking, we show that these TPCs are capable of maintaining nearly 100% nuclear recoil purity to reconstructed ionization energies (Ereco) as low as 5keV˙ee. Using a large sample of Monte-Carlo (MC)-simulated 4He, 12C, and 16O recoil tracks, we find consistency between predicted and measured recoil energy spectra in five of the six TPCs, providing useful validation of the neutron production mechanisms modeled in simulation. Restricting this sample to 4He recoil tracks with Ereco>40keV˙ee, we further demonstrate axial angular resolutions within 8° and we introduce a procedure that under suitable conditions, correctly assigns the vector direction to 91% of these simulated 4He recoils. Applying this procedure to assign vector directions to measured 4He recoil tracks, we observe consistency between the angular distributions of observed and simulated recoils, providing first experimental evidence of localized neutron “hotspots” in the accelerator tunnel. Observed rates of nuclear recoils in these TPCs suggest that simulation overestimates the neutron flux from these hotspots. Despite this, we estimate these hotspots to produce the majority of neutron backgrounds in the accelerator tunnel at SuperKEKB’s target luminosity of 6.3×1035cm−2s−1, making them important regions to continue to monitor.
The Belle II experiment at the SuperKEKB electron–positron collider aims to collect an unprecedented data set of 50ab−1 to study CP-violation in the B-meson system and to search for Physics beyond ...the Standard Model. SuperKEKB is already the world’s highest-luminosity collider. In order to collect the planned data set within approximately one decade, the target is to reach a peak luminosity of 6 × 1035cm−2s−1 by further increasing the beam currents and reducing the beam size at the interaction point by squeezing the betatron function down to βy∗=0.3mm. To ensure detector longevity and maintain good reconstruction performance, beam backgrounds must remain well controlled. We report on current background rates in Belle II and compare these against simulation. We find that a number of recent refinements have significantly improved the background simulation accuracy. Finally, we estimate the safety margins going forward. We predict that backgrounds should remain high but acceptable until a luminosity of at least 2.8 × 1035cm−2s−1 is reached for βy∗=0.6mm. At this point, the most vulnerable Belle II detectors, the Time-of-Propagation (TOP) particle identification system and the Central Drift Chamber (CDC), have predicted background hit rates from single-beam and luminosity backgrounds that add up to approximately half of the maximum acceptable rates.
First measurement of the Λc+→ pη′ decay Li, S. X.; Shen, C. P.; Adachi, I. ...
The journal of high energy physics,
03/2022, Letnik:
2022, Številka:
3
Journal Article
Recenzirano
Odprti dostop
A
bstract
We present the first measurement of the branching fraction of the singly Cabibbo-suppressed (SCS) decay
Λ
c
+
→ pη
′ with
η
′
→ ηπ
+
π
−
, using a data sample corresponding to an integrated ...luminosity of 981 fb
−
1
, collected by the Belle detector at the KEKB
e
+
e
−
asymmetric-energy collider. A significant
Λ
c
+
→ pη
′ signal is observed for the first time with a signal significance of 5.4
σ
. The relative branching fraction with respect to the normalization mode
Λ
c
+
→ pK
−
π
+
is measured to be
B
Λ
c
+
→
pη
′
B
Λ
c
+
→
pK
−
π
+
=
7.54
±
1.32
±
0.73
×
10
−
3
,
where the uncertainties are statistical and systematic, respectively. Using the world-average value of
B
Λ
c
+
→
pK
−
π
+
= (6
.
28
±
0
.
32)
×
10
−
2
, we obtain
B
Λ
c
+
→
pη
′
=
4.73
±
0.82
±
0.46
±
0.24
×
10
−
4
,
where the uncertainties are statistical, systematic, and from
B
Λ
c
+
→
pK
−
π
+
, respectively.
A
bstract
We measure the cross section of
e
+
e
−
→
η
c
J/ψ
at the Υ(
nS
)(
n
= 1–5) on-resonance and 10.52 GeV off-resonance energy points using the full data sample collected by the Belle detector ...with an integrated luminosity of 955 fb
−
1
. We also search for double charmonium production in
e
+
e
−
→
η
c
J/ψ
via initial state radiation near the
η
c
J/ψ
threshold. No evident signal of the double charmonium state is found, but evidence for the
e
+
e
−
→ η
c
J/ψ
process is found with a statistical significance greater than 3
.
3
σ
near the
η
c
J/ψ
threshold. The average cross section near the threshold is measured and upper limits of cross sections are set for other regions.
A
bstract
We present a search for the lepton-flavor-violating decays
B
s
0
→
ℓ
∓
τ
±
, where
ℓ
=
e, μ
, using the full data sample of 121 fb
−
1
collected at the Υ(5
S
) resonance with the Belle ...detector at the KEKB asymmetric-energy
e
+
e
−
collider. We use
B
s
0
B
¯
s
0
events in which one
B
s
0
meson is reconstructed in a semileptonic decay mode and the other in the signal mode. We find no evidence for
B
s
0
→ ℓ
∓
τ
±
decays and set upper limits on their branching fractions at 90% confidence level as
B
(
B
s
0
→ e
∓
τ
±
)
<
14
×
10
−
4
and
B
(
B
s
0
→ μ
∓
τ
±
)
<
7
.
3
×
10
−
4
. Our result represents the first upper limit on the
B
s
0
→ e
∓
τ
±
decay rate.
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