The process pp -> W (+/-) J/psi provides a powerful probe of the production mechanism of charmonium in hadronic collisions, and is also sensitive to multiple parton interactions in the colliding ...protons. Using the 2011 ATLAS dataset of 4.5 fb(-1) of root s= 7 TeV pp collisions at the LHC, the first observation is made of the production of W (+/-) + prompt J/psi events in hadronic collisions, using W (+/-) -> mu nu(mu) and J/psi -> mu(+)mu(-) center dot A yield of W (+/-) + prompt J/psi events is observed, with a statistical significance of 5.1 sigma. The production rate as a ratio to the inclusive W (+/-) boson production rate is measured, and the double parton scattering contribution to the cross section is estimated.
A search is presented for the direct pair production of a chargino and a neutralino
p
p
→
χ
~
1
±
χ
~
2
0
, where the chargino decays to the lightest neutralino and the
W
boson,
χ
~
1
±
→
χ
~
1
0
(
W
...±
→
ℓ
±
ν
)
, while the neutralino decays to the lightest neutralino and the 125 GeV Higgs boson,
χ
~
2
0
→
χ
~
1
0
(
h
→
b
b
/
γ
γ
/
ℓ
±
ν
q
q
)
. The final states considered for the search have large missing transverse momentum, an isolated electron or muon, and one of the following: either two jets identified as originating from bottom quarks, or two photons, or a second electron or muon with the same electric charge. The analysis is based on 20.3
fb
-
1
of
s
=
8
TeV
proton–proton collision data delivered by the Large Hadron Collider and recorded with the ATLAS detector. Observations are consistent with the Standard Model expectations, and limits are set in the context of a simplified supersymmetric model.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
A
bstract
The results of a search for charged Higgs bosons decaying to a
τ
lepton and a neutrino,
H
±
→
τ
±
ν
, are presented. The analysis is based on 19.5 fb
−1
of proton-proton collision data at
s
...= 8 TeV collected by the ATLAS experiment at the Large Hadron Collider. Charged Higgs bosons are searched for in events consistent with top-quark pair production or in associated production with a top quark, depending on the considered
H
±
mass. The final state is characterised by the presence of a hadronic
τ
decay, missing transverse momentum,
b
-tagged jets, a hadronically decaying
W
boson, and the absence of any isolated electrons or muons with high transverse momenta. The data are consistent with the expected background from Standard Model processes. A statistical analysis leads to 95% confidence-level upper limits on the product of branching ratios ℬ(
t
→
bH
±
) × ℬ(
H
±
→
τ
±
ν
), between 0.23% and 1.3% for charged Higgs boson masses in the range 80-160GeV. It also leads to 95% confidence-level upper limits on the production cross section times branching ratio,
σ
(
pp
→
tH
±
+
X
) × ℬ(
H
±
→
τ
±
ν
), between 0.76 pb and 4.5 fb, for charged Higgs boson masses ranging from 180 GeV to 1000 GeV. In the context of different scenarios of the Minimal Supersymmetric Standard Model, these results exclude nearly all values of tan
β
above one for charged Higgs boson masses between 80 GeV and 160 GeV, and exclude a region of parameter space with high tan
β
for
H
±
masses between 200 GeV and 250 GeV.
A search for a new resonance decaying to a W or Z boson and a Higgs boson in the ll/lv/vv + b (b) over bar final states is performed using 20.3 fb(-1) of pp collision data recorded at root s = 8 TeV ...with the ATLAS detector at the Large Hadron Collider. The search is conducted by examining the WH/ZH invariant mass distribution for a localized excess. No significant deviation from the Standard Model background prediction is observed. The results are interpreted in terms of constraints on the Minimal Walking Technicolor model and on a simplified approach based on a phenomenological Lagrangian of Heavy Vector Triplets.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The large difference between the Planck scale and the electroweak scale, known as the hierarchy problem, is addressed in certain models through the postulate of extra spatial dimensions. A search for ...evidence of extra spatial dimensions in the diphoton channel has been performed using the full set of proton-proton collisions at radicals = 7 TeV recorded in 2011 with the ATLAS detector at the CERN Large Hadron Collider. This dataset corresponds to an integrated luminosity of 4.9 fb super(-1). The diphoton invariant mass spectrum is observed to be in good agreement with the Standard Model expectation. In the context of the model proposed by Arkani-Hamed, Dimopoulos and Dvali, 95% confidence level lower limits of between 2.52 and 3.92 TeV are set on the ultraviolet cutoff scale M sub(S) depending on the number of extra dimensions and the theoretical formalism used. In the context of the Randall-Sundrum model, a lower limit of 2.06 (1.00) TeV at 95% confidence level is set on the mass of the lightest graviton for couplings of k/Mlogical and, bar above sub(Pl) = 0.1(0.01). Combining with the ATLAS dilepton searches based on the 2011 data, the 95% confidence level lower limit on the Randall-Sundrum graviton mass is further tightened to 2.23 (1.03) TeV for k/Mlogical and, bar above sub(Pl) = 0.1(0.01).
A new pixel module concept is presented utilizing thin sensors and a novel vertical integration technique for the ATLAS pixel detector in view of the foreseen LHC luminosity upgrades. A first set of ...pixel sensors with active thicknesses of 75 and
150
μ
m
has been produced from wafers of standard thickness using a thinning process developed at the Max-Planck-Institut Halbleiterlabor (HLL) and the Max-Planck-Institut für Physik (MPP). Pre-irradiation characterizations of these sensors show a very good device yield and high break down voltage. First proton irradiations up to a fluence of 10
15
n
eq
cm
−2 have been carried out and their impact on the electrical properties of thin sensors has been studied.
The novel ICV-SLID vertical integration technology will allow for routing signals vertically to the back side of the readout chips. With this, four-side buttable detector devices with an increased active area fraction are made possible. A first production of SLID test structures was performed and showed a high connection efficiency for different pad sizes and a mild sensitivity to disturbances of the surface planarity.
We present a search for the direct production of a light pseudoscalar a decaying into two photons with the Belle II detector at the SuperKEKB collider. We search for the process e+e−→γa, a→γγ in the ...mass range 0.2<ma<9.7 GeV/c2 using data corresponding to an integrated luminosity of (445±3) pb−1. Light pseudoscalars interacting predominantly with standard model gauge bosons (so-called axionlike particles or ALPs) are frequently postulated in extensions of the standard model. We find no evidence for ALPs and set 95% confidence level upper limits on the coupling strength gaγγ of ALPs to photons at the level of 10−3 GeV−1. The limits are the most restrictive to date for 0.2<ma<1 GeV/c2.
Since modern synchrotrons with highly intense X-ray beams are in use to investigate organic materials, the stability of soft matter materials during beam exposure is a crucial issue. Grazing ...incidence X-ray diffraction and specular X-ray reflectivity measurements were performed on thin films of organic semiconducting materials, like poly(3-hexylthiophene) (P3HT), sexithiophene and pentacene. These films were irradiated with an average flux density between 1015 and 1016photons/(smm2) and evidenced a different stability in synchrotron X-ray radiation. The semi-crystalline P3HT showed a clear intensity decrease of the 100 Bragg peak and 020 Bragg peak compared to the rather stable diffraction features of the molecular crystals sexithiophene and pentacene. The difference in synchrotron X-ray radiation stability is explained by the interaction of the X-ray beam with the individual chemical components in the molecules as well as by the different crystallinities of the materials. Furthermore, the semi-crystalline P3HT film exhibited an increase of film thickness after irradiation and the surface roughness slightly decreased. To summarize, this study shows a strong influence of synchrotron X-ray radiation to specific organic thin films like e.g. P3HT, while others like pentacene and sexithiophene are observed as quite stable.
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