3,883 research outputs found
Multiloop Superstring Amplitudes from Non-Minimal Pure Spinor Formalism
Using the non-minimal version of the pure spinor formalism, manifestly
super-Poincare covariant superstring scattering amplitudes can be computed as
in topological string theory without the need of picture-changing operators.
The only subtlety comes from regularizing the functional integral over the pure
spinor ghosts. In this paper, it is shown how to regularize this functional
integral in a BRST-invariant manner, allowing the computation of arbitrary
multiloop amplitudes. The regularization method simplifies for scattering
amplitudes which contribute to ten-dimensional F-terms, i.e. terms in the
ten-dimensional superspace action which do not involve integration over the
maximum number of 's.Comment: 23 pages harvmac, added acknowledgemen
A heterotic sigma model with novel target geometry
We construct a (1,2) heterotic sigma model whose target space geometry
consists of a transitive Lie algebroid with complex structure on a Kaehler
manifold. We show that, under certain geometrical and topological conditions,
there are two distinguished topological half--twists of the heterotic sigma
model leading to A and B type half--topological models. Each of these models is
characterized by the usual topological BRST operator, stemming from the
heterotic (0,2) supersymmetry, and a second BRST operator anticommuting with
the former, originating from the (1,0) supersymmetry. These BRST operators
combined in a certain way provide each half--topological model with two
inequivalent BRST structures and, correspondingly, two distinct perturbative
chiral algebras and chiral rings. The latter are studied in detail and
characterized geometrically in terms of Lie algebroid cohomology in the
quasiclassical limit.Comment: 83 pages, no figures, 2 references adde
Forward pi^0 Production and Associated Transverse Energy Flow in Deep-Inelastic Scattering at HERA
Deep-inelastic positron-proton interactions at low values of Bjorken-x down
to x \approx 4.10^-5 which give rise to high transverse momentum pi^0 mesons
are studied with the H1 experiment at HERA. The inclusive cross section for
pi^0 mesons produced at small angles with respect to the proton remnant (the
forward region) is presented as a function of the transverse momentum and
energy of the pi^0 and of the four-momentum transfer Q^2 and Bjorken-x.
Measurements are also presented of the transverse energy flow in events
containing a forward pi^0 meson. Hadronic final state calculations based on QCD
models implementing different parton evolution schemes are confronted with the
data.Comment: 27 pages, 8 figures and 3 table
Study of B0(s)âK0Sh+hâ˛â decays with first observation of B0sâK0SKÂąĎâ and B0sâK0SĎ+Ďâ
A search for charmless three-body decays of B 0 and B0s mesons with a K0S meson in the final state is performed using the pp collision data, corresponding to an integrated luminosity of 1.0 fbâ1, collected at a centre-of-mass energy of 7 TeV recorded by the LHCb experiment. Branching fractions of the B0(s)âK0Sh+hâ˛â decay modes (h (â˛) = Ď, K), relative to the well measured B0âK0SĎ+Ďâ decay, are obtained. First observation of the decay modes B0sâK0SKÂąĎâ and B0sâK0SĎ+Ďâ and confirmation of the decay B0âK0SKÂąĎâ are reported. The following relative branching fraction measurements or limits are obtained B(B0âK0SKÂąĎâ)B(B0âK0SĎ+Ďâ)=0.128Âą0.017(stat.)Âą0.009(syst.), B(B0âK0SK+Kâ)B(B0âK0SĎ+Ďâ)=0.385Âą0.031(stat.)Âą0.023(syst.), B(B0sâK0SĎ+Ďâ)B(B0âK0SĎ+Ďâ)=0.29Âą0.06(stat.)Âą0.03(syst.)Âą0.02(fs/fd), B(B0sâK0SKÂąĎâ)B(B0âK0SĎ+Ďâ)=1.48Âą0.12(stat.)Âą0.08(syst.)Âą0.12(fs/fd)B(B0sâK0SK+Kâ)B(B0âK0SĎ+Ďâ)â[0.004;0.068]at90%CL
Observation of the decay
The decay is observed for the first
time, using proton-proton collisions collected with the LHCb detector
corresponding to an integrated luminosity of 3fb. A signal yield of
decays is reported with a significance of 6.2 standard deviations.
The ratio of the branching fraction of \B_c \rightarrow J/\psi K^+ K^- \pi^+
decays to that of decays is measured to be
, where the first uncertainty is statistical and the
second is systematic.Comment: 18 pages, 2 figure
Observation of the decay B+câBÂşsĎ+
The result of a search for the decay B+câBÂşsĎ+ is presented, using the BÂşsâDs-Ď+ and BÂşsâJ/ĎĎ channels. The analysis is based on a data sample of pp collisions collected with the LHCb detector, corresponding to an integrated luminosity of 1ââfb-1 taken at a center-of-mass energy of 7 TeV, and 2ââfb-1 taken at 8 TeV. The decay B+câBÂşsĎ+ is observed with significance in excess of 5 standard deviations independently in both decay channels. The measured product of the ratio of cross sections and branching fraction is [Ď(Bc+)/Ď(BÂşs)]ĂB(Bc+âBÂşsĎ+)=[2.37Âą0.31â(stat)Âą0.11â(syst)-0.13+0.17(ĎBc+)]Ă10-3, in the pseudorapidity range 2<Ρ(B)<5, where the first uncertainty is statistical, the second is systematic, and the third is due to the uncertainty on the Bc+ lifetime. This is the first observation of a B meson decaying to another B meson via the weak interaction
Observations of BÂşsâĎ(2S)Ρ and BÂş(s)âĎ(2S)Ď+Ď- decays
First observations of the B0s
âĎ(2S)Ρ, B0 âĎ(2S)Ď
+
Ď
â and B0s
âĎ(2S)Ď
+
Ď
â decays are made
using a dataset corresponding to an integrated luminosity of 1.0 fbâ1 collected by the LHCb experiment in
protonâproton collisions at a centre-of-mass energy of
â
s = 7 TeV. The ratios of the branching fractions
of each of the Ď(2S) modes with respect to the corresponding J/Ď decays are
B(B0s
âĎ(2S)Ρ)
á
B(B0s
âJ/ĎΡ)
= 0.83Âą 0.14 (stat)Âą0.12 (syst) Âą0.02 (B),
;
B(B0âĎ(2S)Ď
+
Ď
â
)
á
B(B0âJ/ĎĎ
+
Ď
â
)
= 0.56Âą 0.07 (stat)Âą0.05 (syst)Âą 0.01 (B),
;
B(B0s
âĎ(2S)Ď
+
Ď
â
)
á
B(B0s
âJ/ĎĎ
+
Ď
â
)
= 0.34Âą 0.04 (stat)Âą0.03 (syst)Âą 0.01 (B),
where the third uncertainty corresponds to the uncertainties of the dilepton branching fractions of the J/Ď
and Ď(2S) meson decays
Open and Hidden Charm Production in 920 GeV Proton-Nucleus Collisions
The HERA-B collaboration has studied the production of charmonium and open
charm states in collisions of 920 GeV protons with wire targets of different
materials. The acceptance of the HERA-B spectrometer covers negative values of
xF up to xF=-0.3 and a broad range in transverse momentum from 0.0 to 4.8
GeV/c. The studies presented in this paper include J/psi differential
distributions and the suppression of J/psi production in nuclear media.
Furthermore, production cross sections and cross section ratios for open charm
mesons are discussed.Comment: 5 pages, 9 figures, to be published in the proceedings of the 6th
International Conference on Hyperons, Charm & Beauty Hadrons (BEACH04),
Chicago, IL, June 27 - July 3, 200
Model-independent search for CP violation in D0âKâK+ĎâĎ+ and D0âĎâĎ+Ď+Ďâ decays
A search for CP violation in the phase-space structures of D0 and View the MathML source decays to the final states KâK+ĎâĎ+ and ĎâĎ+Ď+Ďâ is presented. The search is carried out with a data set corresponding to an integrated luminosity of 1.0 fbâ1 collected in 2011 by the LHCb experiment in pp collisions at a centre-of-mass energy of 7 TeV. For the KâK+ĎâĎ+ final state, the four-body phase space is divided into 32 bins, each bin with approximately 1800 decays. The p-value under the hypothesis of no CP violation is 9.1%, and in no bin is a CP asymmetry greater than 6.5% observed. The phase space of the ĎâĎ+Ď+Ďâ final state is partitioned into 128 bins, each bin with approximately 2500 decays. The p-value under the hypothesis of no CP violation is 41%, and in no bin is a CP asymmetry greater than 5.5% observed. All results are consistent with the hypothesis of no CP violation at the current sensitivity
Performance of CMS muon reconstruction in pp collision events at sqrt(s) = 7 TeV
The performance of muon reconstruction, identification, and triggering in CMS
has been studied using 40 inverse picobarns of data collected in pp collisions
at sqrt(s) = 7 TeV at the LHC in 2010. A few benchmark sets of selection
criteria covering a wide range of physics analysis needs have been examined.
For all considered selections, the efficiency to reconstruct and identify a
muon with a transverse momentum pT larger than a few GeV is above 95% over the
whole region of pseudorapidity covered by the CMS muon system, abs(eta) < 2.4,
while the probability to misidentify a hadron as a muon is well below 1%. The
efficiency to trigger on single muons with pT above a few GeV is higher than
90% over the full eta range, and typically substantially better. The overall
momentum scale is measured to a precision of 0.2% with muons from Z decays. The
transverse momentum resolution varies from 1% to 6% depending on pseudorapidity
for muons with pT below 100 GeV and, using cosmic rays, it is shown to be
better than 10% in the central region up to pT = 1 TeV. Observed distributions
of all quantities are well reproduced by the Monte Carlo simulation.Comment: Replaced with published version. Added journal reference and DO
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