We report on the first observation of time-reversal symmetry violation through a comparison of the probabilities of
K
0
transforming into K
0 and K
0 into
K
0
as a function of the neutral-kaon ...eigentime
t. The comparison is based on the analysis of the neutral-kaon semileptonic decays recorded in the CPLEAR experiment. There, the strangeness of the neutral kaon at time
t=0 was tagged by the kaon charge in the reaction
p
p
→
K
±π
∓
K
0
(
K
0
)
at rest, whereas the strangeness of the kaon at the decay time
t=
τ was tagged by the lepton charge in the final state. An average decay-rate asymmetry
〈
R(
K
0
t=0→
e
+
π
−
ν
t=τ)−R(
K
0
t=0→
e
−
π
+
ν
t=τ)
R(
K
0
t=0→
e
+
π
−
ν
t=τ)+R(
K
0
t=0→
e
−
π
+
ν
t=τ)
〉=(6.6±1.3
stat
±1.0
syst
)×10
−3
was measured over the interval
1
τ
S
<τ<20
τ
S
, thus leading to evidence for time-reversal non-invariance.
The search for supersymmetric particles is one of the major goals in the next high luminosity phase of the Large Hadron Collider. Supersymmmetric top (stop) searches play a very important role in ...this respect, but the unprecedented collision rate that will be attained at this phase poses new challenges for the separation between any new signal and the Standard Model background. While classical multivariate techniques might be insufficient in this new environment, the massive parallelism provided by quantum computing techniques may yield an efficient solution for the problem. In this paper we make a novel application of the QAML-Z approach to classify the stop signal versus the background, and implement it in a quantum annealer machine. We show that this approach together with the pre-processing of the data with Principal Component Analysis may yield better results than conventional multivariate approaches.
We present the first measurements at a hadron collider of differential cross sections for Z+jet+X production in delta phi(Z, jet), |delta y(Z, jet)| and |y_boost(Z, jet)|. Vector boson production in ...association with jets is an excellent probe of QCD and constitutes the main background to many small cross section processes, such as associated Higgs production. These measurements are crucial tests of the predictions of perturbative QCD and current event generators, which have varied success in describing the data. Using these measurements as inputs in tuning event generators will increase the experimental sensitivity to rare signals.
In a data sample of approximately 1.3 fb-1 collected with the D0 detector between 2002 and 2006, the orbitally excited charm state D_s1(2536) has been observed with a measured mass of 2535.7 +/- 0.6 ...(stat) +/- 0.5 (syst) MeV via the decay mode B0_s -> D_s1(2536) mu nu X. A first measurement is made of the branching ratio product Br(b(bar) -> D_s1(2536) mu nu X).Br(D_s1(2536)->D* K0_S). Assuming that D_s1(2536) production in semileptonic decay is entirely from B0_s, an extraction of the semileptonic branching ratio Br(B0_s -> D_s1(2536) mu nu X) is made.
First measurements of the differential cross sections for the inclusive production of a photon in association with a heavy quark (c, b) jet are presented, covering photon transverse momenta 30-150 ...GeV, photon rapidities | y_gamma| < 1.0, jet rapidities |y_jet| < 0.8, and jet transverse momenta pT_jet > 15 GeV. The results are based on an integrated luminosity of 1 fb^-1 in ppbar collisions at sqrt(s)=1.96 TeV recorded with the D0 detector at the Fermilab Tevatron Collider. The results are compared with next-to-leading order perturbative QCD predictions.
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