708 research outputs found
Top-Quark Charge Asymmetry with a Jet Handle
Pairs of top and antitop quarks are produced at the LHC to a large extent in
association with a hard jet. We investigate the charge asymmetry in top pair +
jet production in quantum chromodynamics (QCD) and with additional massive
color-octet vector bosons. The total charge asymmetry at the LHC is suppressed
by the large charge-symmetric background from gluon-gluon fusion. We show to
what extent the asymmetry can be enhanced by suitable phase space cuts and, in
particular, elaborate on the kinematics of the hard jet in the top pair + jet
final state. We demonstrate that in QCD, the asymmetry amounts to -1.5% for
central jets without an excessive reduction of the cross section. By applying
additional kinematical cuts, the asymmetry can be enhanced to -4%, but at the
cost of a strong reduction of the cross section. Massive color-octet states can
generate sizeable effects in top pair + jet production, both on the charge
asymmetry and on the cross section. The charge asymmetry probes both vector and
axial-vector couplings to quarks. We show that massive color octets can
generate asymmetries up to +-10% for moderate and up to +-30% for strong
kinematical cuts to be used in experimental analyses at the LHC. Jet kinematics
can be used to obtain further information about the nature of the couplings and
thereby to discriminate between different models.Comment: 29 pages, 12 figure
Evidence for an excess of B -> D(*) Tau Nu decays
Based on the full BaBar data sample, we report improved measurements of the
ratios R(D(*)) = B(B -> D(*) Tau Nu)/B(B -> D(*) l Nu), where l is either e or
mu. These ratios are sensitive to new physics contributions in the form of a
charged Higgs boson. We measure R(D) = 0.440 +- 0.058 +- 0.042 and R(D*) =
0.332 +- 0.024 +- 0.018, which exceed the Standard Model expectations by 2.0
sigma and 2.7 sigma, respectively. Taken together, our results disagree with
these expectations at the 3.4 sigma level. This excess cannot be explained by a
charged Higgs boson in the type II two-Higgs-doublet model. We also report the
observation of the decay B -> D Tau Nu, with a significance of 6.8 sigma.Comment: Expanded section on systematics, text corrections, improved the
format of Figure 2 and included the effect of the change of the Tau
polarization due to the charged Higg
Top Quark Charge Asymmetry: Searching for Light Axigluons in top pair + jet Production at the LHC
We investigate the discovery potential of light color-octet bosons in the
mass range of 100 - 400 GeV in exclusive top-pair plus jet production at the
LHC. We study the impact of such bosons on the incline, the energy and the
rapidity asymmetries. We show that light axigluons with large couplings to
quarks can be discovered at the LHC with a luminosity of a few inverse fb.
Almost all of the considered axigluon parameter space can be probed using the
already available 2011/2012 LHC data. In a small-coupling scenario, axigluons
could be discovered using the charge asymmetry with 65 inverse fb at the LHC
and a center of mass energy of 14 TeV. We furthermore show that top pair+jet
production could reveal the existence of scenarios where axigluons couple with
a different strength to up- and down-type quarks.Comment: 25 pages, 11 figures, 1 tabl
Physical observables in the decay
We analyze the tauonic semileptonic baryon decays with particular emphasis on the lepton
helicity flip contributions which vanish for zero lepton masses. We calculate
the total rate, differential decay distributions, the longitudinal and
transverse polarization components of the and the , and
the lepton-side forward-backward asymmetries. We use the covariant confined
quark model to provide numerical results on these observables.Comment: 6 pages, 1 figure. Talk given by Nurgul Habyl at the 9th joint
International HADRON STRUCTURE'15 Conference, GRAND HOTEL BELLEVUE, Horny
Smokovec, Slovak Republic, 29 June - 3 July, 201
Collider constraints and new tests of color octet vectors
We analyze the collider sensitivity for new colored resonances in ,
, and final states. While searches in the single production
channel are model-dependent, the pair production rate is model independent and
the existing and searches impose strong constraints on the
relevant branching fractions, where or . We point out the missing,
complementary searches in the mixed decay modes, ,
, and . We propose analysis strategies for
the and decays and find their sensivity
surpasses that of existing searches when the decay widths to tops and light
jets are comparable. If no other decays are present, collective lower limits on
the resonance mass can be set at 1.5~TeV using 37~fb of 13~TeV data.Comment: 22 pages, 3 figures, 2 table
In Vitro Synthesis of Chlorophyll A in the Dark Triggers Accumulation of Chlorophyll A Apoproteins in Barley Etioplasts”
An in vitro translation system using lysed etioplasts was developed to test if the accumulation of plastid-encoded chlorophyll a apoproteins is dependent on the de novo synthesis of chlorophyll a. The P700 apoproteins, CP47 and CP43, were not radiolabeled in pulsechase translation assays employing lysed etioplasts in the absence of added chlorophyll precursors. When chlorophyllide a plus phytylpyrophosphate were added to lysed etioplast translation assays in the dark, chlorophyll a was synthesized and radiolabeled P700 apoproteins, CP47 and CP43, and a protein which comigrates with D1 accumulated. Chlorophyllide a or phytylpyrophosphate added separately to the translation assay in darkness did not induce chlorophyll a formation or chlorophyll a apoprotein accumulation. Chlorophyll a formation and chlorophyll a apoprotein accumulation were also induced in the lysed etioplast translation system by the photoreduction of protochlorophyllide to chlorophyllide a in the presence of exogenous phytylpyrophosphate. Accumulation of radiolabeled CP47 was detectable when very low levels of chlorophyll a were synthesized de novo (less than 0.01 nmol/10(7) plastids), and radiolabel increased linearly with increasing de novo chlorophyll a formation. Higher levels of de novo synthesized chlorophyll a were required prior to detection of radiolabel incorporation into the P700 apoproteins and CP43 (greater than 0.01 nmol/10(7) plastids). Radiolabel incorporation into the P700 apoproteins, CP47 and CP43, saturated at a chlorophyll a concentration which corresponds to 50% of the etioplast protochlorophyllide content (0.06 nmol of chlorophyll a/10(7) plastids)
Theoretical overview on top pair production and single top production
In this talk I will give an overview on theoretical aspects of top quark
physics. The focus lies on top pair production and single top production.Comment: Presented at the 2011 Hadron Collider Physics symposium (HCP-2011),
Paris, France, November 14-18 2011, 6 pages, 5 figure
Helicity Amplitudes and Angular Decay Distributions
I discuss how to obtain angular decay distributions for sequential cascade
decays using helicity methods. The angular decay distributions follow from a
reasonably simple master formula involving bilinear forms of helicity
amplitudes and Wigner's functions. I discuss in some detail the issue of
gauge invariance for off-shell gauge bosons. As a technical exercise I
calculate the linear relation between the helicity amplitudes and the invariant
amplitudes of semileptonic and rare baryon decays. I discuss two explicit
examples of angular decay distributions for (i) the decay (which leads to the notion of the helicity fractions of the
), and (ii) the sequential decay .Comment: 16 pages, 2 figures, Lecture given at the Helmholtz International
Summer School "Physics of Heavy Quarks and Hadrons", Dubna, Russia, July
15--28, 2013 (to be published in the Proceedings
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