625 research outputs found
Search for Anomalous Couplings in Top Decay at Hadron Colliders
We present a quantitative study on sensitivities to the top-decay anomalous
couplings, taking into account realistic experimental conditions expected at
Tevatron and LHC. A double angular distribution of W and charged lepton in the
top decay is analyzed, using ttbar events in the lepton+jets channel. In order
to improve sensitivities to the anomalous couplings, we apply two techniques:
(1) We use a likelihood fitting method for full kinematical reconstruction of
each top event. (2) We develop a new effective spin reconstruction method for
leptonically-decayed top quarks; this method does not require spin information
of the antitop side. For simplicity, we neglect couplings of right-handed
bottom quark as well as CP violating couplings. The 95% C.L. estimated bound on
a ratio of anomalous couplings reads -0.81 < f_2/f_1 < -0.70,
-0.12<f_2/f_1<0.14 using 1000 reconstructed top events at Tevatron, while
-0.74<f_2/f_1<-0.72, -0.01<f_2/f_1<0.01 is expected with 100k reconstructed top
events at LHC, where only statistical errors are taken into account. A two-fold
ambiguity in the allowed range remains when the number of events exceeds a few
hundred.Comment: 21 pages, 15 figure
A Start-Timing Detector for the Collider Experiment PHENIX at RHIC-BNL
We describe a start-timing detector for the PHENIX experiment at the
relativistic heavy-ion collider RHIC. The role of the detector is to detect a
nuclear collision, provide precise time information with an accuracy of 50ps,
and determine the collision point along the beam direction with a resolution of
a few cm. Technical challenges are that the detector must be operational in a
wide particle-multiplicity range in a high radiation environment and a strong
magnetic field. We present the performance of the prototype and discuss the
final design of the detector.Comment: 12 pages, LaTeX, 9 gif and 4 ps figures. Submitted to NIM
New Method for Reconstructing Effective Top Quark Spin
We propose a new method for reconstructing an effective spin direction of a
semi-leptonically decayed top quark. The method is simple: for instance, it
does not require the spin information of the antitop quark in a ttbar event.
The reconstructed effective spin is expected to be useful in hadron collider
experiments. We demonstrate its usefulness in an analysis of the top decay
vertex.Comment: 10 pages, 6 figures; one reference added; version to appear in
Phys.Lett.
Measurement of the electron transmission rate of the gating foil for the TPC of the ILC experiment
We have developed a gating foil for the time projection chamber envisaged as
a central tracker for the international linear collider experiment. It has a
structure similar to the Gas Electron Multiplier (GEM) with a higher optical
aperture ratio and functions as an ion gate without gas amplification. The
transmission rate for electrons was measured in a counting mode for a wide
range of the voltages applied across the foil using an Fe source and a
laser in the absence of a magnetic field. The blocking power of the foil
against positive ions was estimated from the electron transmissions.Comment: 25 pages containing 14 figures and 1 tabl
Cosmic ray tests of a GEM-based TPC prototype operated in Ar-CF4-isobutane gas mixtures
Argon with an admixture of CF4 is expected to be a good candidate for the gas
mixture to be used for a time projection chamber (TPC) in the future linear
collider experiment because of its small transverse diffusion of drift
electrons especially under a strong magnetic field. In order to confirm the
superiority of this gas mixture over conventional TPC gases we carried out
cosmic ray tests using a GEM-based TPC operated mostly in Ar-CF4-isobutane
mixtures under 0 - 1 T axial magnetic fields. The measured gas properties such
as gas gain and transverse diffusion constant as well as the observed spatial
resolution are presented.Comment: 22 pages, 18 figures. Published in Nuclear Instruments and Methods in
Physics Research A. Fig. 3 in the introduction was corrected since it had not
been properly normalized. Minor corrections and no changes in the conclusio
Efficacy of capillary pattern type IIIA/IIIB by magnifying narrow band imaging for estimating depth of invasion of early colorectal neoplasms
<p>Abstract</p> <p>Background</p> <p>Capillary patterns (CP) observed by magnifying Narrow Band Imaging (NBI) are useful for differentiating non-adenomatous from adenomatous colorectal polyps. However, there are few studies concerning the effectiveness of magnifying NBI for determining the depth of invasion in early colorectal neoplasms. We aimed to determine whether CP type IIIA/IIIB identified by magnifying NBI is effective for estimating the depth of invasion in early colorectal neoplasms.</p> <p>Methods</p> <p>A series of 127 consecutive patients with 130 colorectal lesions were evaluated from October 2005 to October 2007 at the National Cancer Center Hospital East, Chiba, Japan. Lesions were classified as CP type IIIA or type IIIB according to the NBI CP classification. Lesions were histopathologically evaluated. Inter and intraobserver variabilities were assessed by three colonoscopists experienced in NBI.</p> <p>Results</p> <p>There were 15 adenomas, 66 intramucosal cancers (pM) and 49 submucosal cancers (pSM): 16 pSM superficial (pSM1) and 33 pSM deep cancers (pSM2-3). Among lesions diagnosed as CP IIIA 86 out of 91 (94.5%) were adenomas, pM-ca, or pSM1; among lesions diagnosed as CP IIIB 28 out of 39 (72%) were pSM2-3. Sensitivity, specificity and diagnostic accuracy of the CP type III for differentiating pM-ca or pSM1 (<1000 μm) from pSM2-3 (≥1000 μm) were 84.8%, 88.7 % and 87.7%, respectively. Interobserver variability: κ = 0.68, 0.67, 0.72. Intraobserver agreement: κ = 0.79, 0.76, 0.75</p> <p>Conclusion</p> <p>Identification of CP type IIIA/IIIB by magnifying NBI is useful for estimating the depth of invasion of early colorectal neoplasms.</p
Clinical significance of midkine expression in pancreatic head carcinoma
Midkine (MK) is a heparin-binding growth factor and a product of a retinoic acid-responsive gene. Midkine is overexpressed in many carcinomas and thought to play an important role in carcinogenesis. However, no studies have been focussed on the role of MK in pancreatic carcinoma. This study sought to evaluate the clinical significance of MK expression in pancreatic head carcinoma, including the relationship between immunohistochemical expression and clinicopathologic factors such as prognosis. Immunohistochemical expression of MK and CD34 was evaluated in pancreatic head carcinoma specimens from 75 patients who underwent surgical resection. Midkine was expressed in 53.3% of patients. Midkine expression was significantly correlated with venous invasion, microvessel density, and liver metastasis (P=0.0063, 0.0025, and 0.0153, respectively). The 5-year survival rate was significantly lower for patients positive for MK vs patients negative for MK (P=0.0073). Multivariate analysis revealed that MK expression was an independent prognostic factor (P=0.0033). This is the first report of an association between MK expression and pancreatic head carcinoma. Midkine may play an important role in the progression of pancreatic head carcinoma, and evaluation of MK expression is useful for predicting malignant properties of pancreatic head carcinoma
- …