2,690 research outputs found
Optimisation of variables for studying dilepton transverse momentum distributions at hadron colliders
In future measurements of the dilepton () transverse momentum,
\Qt, at both the Tevatron and LHC, the achievable bin widths and the ultimate
precision of the measurements will be limited by experimental resolution rather
than by the available event statistics. In a recent paper the variable \at,
which corresponds to the component of \Qt\ that is transverse to the dilepton
thrust axis, has been studied in this regard. In the region, \Qt\ 30 GeV,
\at\ has been shown to be less susceptible to experimental resolution and
efficiency effects than the \Qt. Extending over all \Qt, we now demonstrate
that dividing \at\ (or \Qt) by the measured dilepton invariant mass further
improves the resolution. In addition, we propose a new variable, \phistarEta,
that is determined exclusively from the measured lepton directions; this is
even more precisely determined experimentally than the above variables and is
similarly sensitive to the \Qt. The greater precision achievable using such
variables will enable more stringent tests of QCD and tighter constraints on
Monte Carlo event generator tunes.Comment: 8 pages, 5 figures, 2 table
Detecting bit-flip errors in a logical qubit using stabilizer measurements
Quantum data is susceptible to decoherence induced by the environment and to
errors in the hardware processing it. A future fault-tolerant quantum computer
will use quantum error correction (QEC) to actively protect against both. In
the smallest QEC codes, the information in one logical qubit is encoded in a
two-dimensional subspace of a larger Hilbert space of multiple physical qubits.
For each code, a set of non-demolition multi-qubit measurements, termed
stabilizers, can discretize and signal physical qubit errors without collapsing
the encoded information. Experimental demonstrations of QEC to date, using
nuclear magnetic resonance, trapped ions, photons, superconducting qubits, and
NV centers in diamond, have circumvented stabilizers at the cost of decoding at
the end of a QEC cycle. This decoding leaves the quantum information vulnerable
to physical qubit errors until re-encoding, violating a basic requirement for
fault tolerance. Using a five-qubit superconducting processor, we realize the
two parity measurements comprising the stabilizers of the three-qubit
repetition code protecting one logical qubit from physical bit-flip errors. We
construct these stabilizers as parallelized indirect measurements using
ancillary qubits, and evidence their non-demolition character by generating
three-qubit entanglement from superposition states. We demonstrate
stabilizer-based quantum error detection (QED) by subjecting a logical qubit to
coherent and incoherent bit-flip errors on its constituent physical qubits.
While increased physical qubit coherence times and shorter QED blocks are
required to actively safeguard quantum information, this demonstration is a
critical step toward larger codes based on multiple parity measurements.Comment: 6 pages, 4 figures, 10 supplementary figure
Electroweak Gauge-Boson Production at Small q_T: Infrared Safety from the Collinear Anomaly
Using methods from effective field theory, we develop a novel, systematic
framework for the calculation of the cross sections for electroweak gauge-boson
production at small and very small transverse momentum q_T, in which large
logarithms of the scale ratio M_V/q_T are resummed to all orders. These cross
sections receive logarithmically enhanced corrections from two sources: the
running of the hard matching coefficient and the collinear factorization
anomaly. The anomaly leads to the dynamical generation of a non-perturbative
scale q_* ~ M_V e^{-const/\alpha_s(M_V)}, which protects the processes from
receiving large long-distance hadronic contributions. Expanding the cross
sections in either \alpha_s or q_T generates strongly divergent series, which
must be resummed. As a by-product, we obtain an explicit non-perturbative
expression for the intercept of the cross sections at q_T=0, including the
normalization and first-order \alpha_s(q_*) correction. We perform a detailed
numerical comparison of our predictions with the available data on the
transverse-momentum distribution in Z-boson production at the Tevatron and LHC.Comment: 34 pages, 9 figure
Large-scale long-term passive-acoustic monitoring reveals spatio-temporal activity patterns of boreal bats
The distribution ranges and spatio-temporal patterns in the occurrence and activity of boreal bats are yet largely unknown due to their cryptic lifestyle and lack of suitable and efficient study methods. We approached the issue by establishing a permanent passive-acoustic sampling setup spanning the area of Finland to gain an understanding on how latitude affects bat species composition and activity patterns in northern Europe. The recorded bat calls were semi-automatically identified for three target taxa; Myotis spp., Eptesicus nilssonii or Pipistrellus nathusii and the seasonal activity patterns were modeled for each taxa across the seven sampling years (2015-2021). We found an increase in activity since 2015 for E. nilssonii and Myotis spp. For E. nilssonii and Myotis spp. we found significant latitude -dependent seasonal activity patterns, where seasonal variation in patterns appeared stronger in the north. Over the years, activity of P. nathusii increased during activity peak in June and late season but decreased in mid season. We found the passive-acoustic monitoring network to be an effective and cost-efficient method for gathering bat activity data to analyze spatio-temporal patterns. Long-term data on the composition and dynamics of bat communities facilitates better estimates of abundances and population trend directions for conservation purposes and predicting the effects of climate change
Journal Staff
We present the first measurements of the differential cross section d sigma/dp(T)(gamma) for the production of an isolated photon in association with at least two b-quark jets. The measurements consider photons with rapidities vertical bar y(gamma)vertical bar < 1.0 and transverse momenta 30 < p(T)(gamma) < 200 GeV. The b-quark jets are required to have p(T)(jet) > 15 GeVand vertical bar y(jet)vertical bar < 1.5. The ratio of differential production cross sections for gamma + 2 b-jets to gamma + b-jet as a function of p(T)(gamma) is also presented. The results are based on the proton-antiproton collision data at root s = 1.96 TeV collected with the D0 detector at the Fermilab Tevatron Collider. The measured cross sections and their ratios are compared to the next- to- leading order perturbative QCD calculations as well as predictions based on the k(T)- factorization approach and those from the sherpa and pythia Monte Carlo event generators
Precise measurement of the top quark mass in the dilepton channel at D0
We measure the top quark mass (mt) in ppbar collisions at a center of mass
energy of 1.96 TeV using dilepton ttbar->W+bW-bbar->l+nubl-nubarbbar events,
where l denotes an electron, a muon, or a tau that decays leptonically. The
data correspond to an integrated luminosity of 5.4 fb-1 collected with the D0
detector at the Fermilab Tevatron Collider. We obtain mt = 174.0 +- 1.8(stat)
+- 2.4(syst) GeV, which is in agreement with the current world average mt =
173.3 +- 1.1 GeV. This is currently the most precise measurement of mt in the
dilepton channel.Comment: 7 pages, 4 figure
Direct measurement of the mass difference between top and antitop quarks
We present a direct measurement of the mass difference between top and
antitop quarks (dm) in lepton+jets top-antitop final states using the "matrix
element" method. The purity of the lepton+jets sample is enhanced for
top-antitop events by identifying at least one of the jet as originating from a
b quark. The analyzed data correspond to 3.6 fb-1 of proton-antiproton
collisions at 1.96 TeV acquired by D0 in Run II of the Fermilab Tevatron
Collider. The combination of the e+jets and mu+jets channels yields dm = 0.8
+/- 1.8 (stat) +/- 0.5 (syst) GeV, which is in agreement with the standard
model expectation of no mass difference.Comment: submitted to Phys. Rev.
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