308,641 research outputs found
Branching fraction and CP asymmetry of the decays B+→K0Sπ+ and B+→K0SK+
No full textAn analysis of B+ → K0
Sπ+ and B+ → K0
S K+ decays is performed with the LHCb experiment. The pp
collision data used correspond to integrated luminosities of 1 fb−1 and 2 fb−1 collected at centre-ofmass
energies of
√
s = 7 TeV and
√
s = 8 TeV, respectively. The ratio of branching fractions and the
direct CP asymmetries are measured to be B(B+ → K0
S K+
)/B(B+ → K0
Sπ+
) = 0.064 ± 0.009 (stat.) ±
0.004 (syst.), ACP(B+ → K0
Sπ+
) = −0.022 ± 0.025 (stat.) ± 0.010 (syst.) and ACP(B+ → K0
S K+
) =
−0.21 ± 0.14 (stat.) ± 0.01 (syst.). The data sample taken at
√
s = 7 TeV is used to search for
B+
c
→ K0
S K+ decays and results in the upper limit ( fc · B(B+
c
→ K0
S K+
))/( fu · B(B+ → K0
Sπ+
)) <
5.8 × 10−2 at 90% confidence level, where fc and fu denote the hadronisation fractions of a ¯b
quark
into a B+
c or a B+ meson, respectively
An Upper Limit on the Branching Ratio for
No full textWe have searched for decays of the ø lepton into seven or more charged particles, using data collected with the OPAL detector from 1990 to 1995 in e + e \Gamma collisions at p s ß M Z . No candidate event was found and an upper limit on the branching ratio for ø decays into seven charged particles of 1:7 \Theta 10 \Gamma5 at the 95% confidence level was determined. This note describes preliminary OPAL results, and is intended primarily for the members of the collaboration 1 Introduction In the years 1990 to 1995 of LEP operation, an integrated luminosity of 163 pb \Gamma1 has been recorded with the OPAL detector at p s ß 91 GeV, corresponding to approximately 5 million observed Z 0 decays. This large data sample which contains more than 210000 ø pair events allows searches for rare decays of the ø lepton, with branching ratios down to about 10 \Gamma5 . The high-multiplicity decays of the ø are particularly interesting for a measurement of the ø neutrino mass. Recen..
Non-leptonic B-decays in and beyond QCD factorisation
No full textThis thesis examines the non-leptonic B-decays within QCD factorization and beyond, to challenge the assumptions and limitations of the method. We analyse the treatment of the distribution amplitudes of light mesons and present a new model described by simple physical parameters. The leading twist distribution amplitudes of light mesons describe the leading non-perturbative hadronic contributions to exclusive QCD reactions at large energy transfer, for instance electromagnetic form factors. Importantly, they also enter into the two-body B decay amplitudes described by QCD factorisation. They cannot be calculated from first principles and are described by models based on a fixed-order conformal expansion, which is not always sufficient in phenomenological applications. We derive new models that are valid to all orders in the conformal expansion and characterised by a small number of parameters related to experimental observables. Motivated by the marginal agreement between the QCD factorisation results with the experimental data, in particular for B → ππ, we scrutinise the incalculable non-factorisable corrections to charmless non-leptonic decays. We use the available results on B → ππ, to extract information about the size and nature of the required non-factorisable corrections that are needed to reconcile the predictions and data. We find that the best-fit scenarios do not give reasonable agreement to 2a until at least a 40% non-factorisable contribution is added. Finally we consider the exclusive B → V γ decays, where we analyse the recently updated experimental data within QCD factorization and present constraints on generic super symmetric models using the mass insertion approximation
Search for top quark decays t → qH with H → γγ using the ATLAS detector
No full textA search is performed for flavour-changing neutral currents in the decay of a top quark to an up-type (c, u) quark and a Higgs boson, where the Higgs boson decays to two photons. The proton-proton collision data set used corresponds to 4.7 fb-1 at √ = 7TeV and 20.3fb-1 at √ = 8TeV collected by the ATLAS experiment at the LHC. Top quark pair events are searched for in which one top quark decays to qH and the other decays to bW. Both the hadronic and the leptonic decay modes of the W boson are used. No significant signal is observed and an upper limit is set on the t → qH branching ratio of 0.79 at the 95% confidence level. The corresponding limit on the tqH coupling combination λtcH 2 + λtuH 2 is 0.17
Observations of Bºs→ψ(2S)η and Bº(s)→ψ(2S)π+π- decays
No full textFirst observations of the B0s
→ψ(2S)η, B0 →ψ(2S)π
+
π
− and B0s
→ψ(2S)π
+
π
− decays are made
using a dataset corresponding to an integrated luminosity of 1.0 fb−1 collected by the LHCb experiment in
proton–proton collisions at a centre-of-mass energy of
√
s = 7 TeV. The ratios of the branching fractions
of each of the ψ(2S) modes with respect to the corresponding J/ψ decays are
B(B0s
→ψ(2S)η)
÷
B(B0s
→J/ψη)
= 0.83± 0.14 (stat)±0.12 (syst) ±0.02 (B),
;
B(B0→ψ(2S)π
+
π
−
)
÷
B(B0→J/ψπ
+
π
−
)
= 0.56± 0.07 (stat)±0.05 (syst)± 0.01 (B),
;
B(B0s
→ψ(2S)π
+
π
−
)
÷
B(B0s
→J/ψπ
+
π
−
)
= 0.34± 0.04 (stat)±0.03 (syst)± 0.01 (B),
where the third uncertainty corresponds to the uncertainties of the dilepton branching fractions of the J/ψ
and ψ(2S) meson decays
Effective lifetime measurements in the B-s(0) -> K+K-, B-0 -> K+pi(-) and B-s(0) -> pi K-+(-) decays
No full textMeasurements of the effective lifetimes in the View the MathML source, B0→K+π− and View the MathML source decays are presented using 1.0 fb−1 of pp collision data collected at a centre-of-mass energy of 7 TeV by the LHCb experiment. The analysis uses a data-driven approach to correct for the decay time acceptance.
This is the most precise determination to date of the effective lifetime in the View the MathML source decay and provides constraints on contributions from physics beyond the Standard Model to the View the MathML source mixing phase and the width difference ΔΓs
An Upper Limit on the Branching Ratio for
No full textWe have searched for decays of the ø lepton into seven or more charged particles, using data collected with the OPAL detector from 1990 to 1995 in e + e \Gamma collisions at p s ß MZ . No candidate events were found and an upper limit on the branching ratio for ø decays into seven charged particles of 1:8 \Theta 10 \Gamma5 at the 95% confidence level was determined. (Accepted by Physics Letters B) The OPAL Collaboration K. Ackerstaff 8 , G. Alexander 23 , J. Allison 16 , N. Altekamp 5 , K.J. Anderson 9 , S. Anderson 12 , S. Arcelli 2 , S. Asai 24 , D. Axen 29 , G. Azuelos 18;a , A.H. Ball 17 , E. Barberio 8 , R.J. Barlow 16 , R. Bartoldus 3 , J.R. Batley 5 , S. Baumann 3 , J. Bechtluft 14 , C. Beeston 16 , T. Behnke 8 , A.N. Bell 1 , K.W. Bell 20 , G. Bella 23 , S. Bentvelsen 8 , P. Berlich 10 , S. Bethke 14 , O. Biebel 14 , A. Biguzzi 5 , S.D. Bird 16 , V. Blobel 27 , I.J. Bloodworth 1 , J.E. Bloomer 1 , M. Bobins..
CP-violation in cascade decays at the LHC
No full textWe study the potential to observe CP-violating effects in various supersymmetric cascade
decay chains at the LHC. Asymmetries composed by triple products of
momenta of the final state particles are sensitive to CP-violating
effects. We analytically calculate the cascade decays including the relevant spin correlations to compute the parton level asymmetry. In addition, we use Monte Carlo simulations to estimate the sensitivity of the LHC to the CP-violating observables.
Due to large boosts that dilute the asymmetries, these can be
difficult to observe at the LHC. However, if all particle masses in a cascade decay are
known, it may be possible to reconstruct all momenta in the decay chains. We can then recover the full asymmetry on an
event-by-event basis even when we have missing momentum due to a stable
lightest supersymmetric particle. After the reconstruction, the non-diluted CP-violating signal gets
significantly enhanced so that an observation may become feasible.
A fully hadronic study has also been completed to produce the best estimate of the viability of these obseravbles at the LHC. We include both standard model and SUSY backgrounds in the study. Our conclusions state that given a favourable scenario, CP-violation may be observed in SUSY at the 3-sigma level over a wide range of CP-phases with 500 1/fb of data
Measurement of the CKM angle gamma from a combination of B->Dh analyses
No full textA combination of three LHCb measurements of the CKM angle gamma is presented. The decays B->DK and B->Dpi are used, where D denotes an admixture of D0 and D0-bar mesons, decaying into K+K-, pi+pi-, K+-pi-+, K+-pi-+pi+-pi-+, KSpi+pi-, or KSK+K- final states. All measurements use a dataset corresponding to 1.0 fb-1 of integrated luminosity. Combining results from B->DK decays alone a best-fit value of gamma = 72.0 deg is found, and confidence intervals are set gamma in [56.4,86.7] deg at 68% CL, gamma in [42.6,99.6] deg at 95% CL. The best-fit value of gamma found from a combination of results from B->Dpi decays alone, is gamma = 18.9 deg, and the confidence intervals gamma in [7.4,99.2] deg or [167.9,176.4] deg at 68% CL, are set, without constraint at 95% CL. The combination of results from B->DK and B->Dpi decays gives a best-fit value of gamma = 72.6 deg and the confidence intervals gamma in [55.4,82.3] deg at 68% CL, gamma in [40.2,92.7] deg at 95% CL are set. All values are expressed modulo 180 deg, and are obtained taking into account the effect of D0-D0bar mixing
Model-independent search for CP violation in D0→K−K+π−π+ and D0→π−π+π+π− decays
No full textA search for CP violation in the phase-space structures of D0 and View the MathML source decays to the final states K−K+π−π+ and π−π+π+π− is presented. The search is carried out with a data set corresponding to an integrated luminosity of 1.0 fb−1 collected in 2011 by the LHCb experiment in pp collisions at a centre-of-mass energy of 7 TeV. For the K−K+π−π+ 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 π−π+π+π− 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
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