1,203 research outputs found
Limits on extra dimensions in orbifold compactifications of superstrings
Perturbative breaking of supersymmetry in four-dimensional string theories
predict in general the existence of new large dimensions at the TeV scale. Such
dimensions can be consistent with perturbative unification up to the Planck
scale in a class of string models and open the exciting possibility of lowering
a part of the massive string spectrum at energies accessible to future
accelerators. The main signature is the production of Kaluza-Klein excitations
which have a very particular structure, strongly correlated with the
supersymmetry breaking mechanism. We present a model independent analysis of
the physics of these states in the context of orbifold compactifications of the
heterotic superstring. In particular, we compute the limits on the size of
large dimensions used to break supersymmetry.Comment: 16 pages, CPTH-A257.079
Serenissimi Verordnung, die gegen die abermals eindringende Viehseuche vorzukehrenden Anstalten betreffend : de dato, Braunschweig, den 28. Nov. 1754
Large-Area Scintillator Hodoscope with 50 ps Timing Resolution Onboard BESS
We describe the design and performance of a large-area scintillator hodoscope
onboard the BESS rigidity spectrometer; an instrument with an acceptance of 0.3
m^{2}sr.
The hodoscope is configured such that 10 and 12 counters are respectively
situated in upper and lower layers.
Each counter is viewed from its ends by 2.5 inch fine-mesh photomultiplier
tubes placed in a stray magnetic field of 0.2 Tesla.
Various beam-test data are presented.
Use of cosmic-ray muons at ground-level confirmed 50 ps timing resolution for
each layer, giving an overall time-of-flight resolution of 70 ps rms using a
pure Gaussian resolution function.
Comparison with previous measurements on a similar scintillator hodoscope
indicates good agreement with the scaling law that timing resolution is
proportional to 1/, where is the effective
number of photoelectrons.Comment: 16 pages, 14 figure
Transverse momentum spectra of identified particles in high energy collisions with statistical hadronisation model
A detailed analysis is performed of transverse momentum spectra of several
identified hadrons in high energy collisions within the framework of the
statistical model of hadronisation. The effect of the decay chain following
hadron generation is accurately taken into account. The considered
centre-of-mass energies range from ~ 10 to 30 GeV in hadronic collisions (pi+
p, pp and Kp) and from ~ 15 to 45 GeV in e+e- collisions. A clear consistency
is found between the temperature parameter extracted from the present analysis
and that obtained from fits to average hadron multiplicities in the same
collision systems. This finding indicates that in the hadronisation, the
production of different particle species and their momentum spectra are two
closely related phenomenons governed by one parameter.Comment: Talk given by F. Becattini in "Correlations and Fluctuations 2000",
12 pp., 11 figure
MTSS1 is a critical epigenetically regulated tumor suppressor in CML
Chronic myeloid leukemia (CML) is driven by malignant stem cells that can persist despite therapy. We have identified Metastasis suppressor 1 (Mtss1/MIM) to be downregulated in hematopoietic stem and progenitor cells from leukemic transgenic SCLtTA/Bcr-Abl mice and in patients with CML at diagnosis, and Mtss1 was restored when patients achieved complete remission. Forced expression of Mtss1 decreased clonogenic capacity and motility of murine myeloid progenitor cells and reduced tumor growth. Viral transduction of Mtss1 into lineage depleted SCLtTA/Bcr-Abl bone marrow cells decreased leukemic cell burden in recipients, and leukemogenesis was reduced upon injection of Mtss1 overexpressing murine myeloid 32D cells. Tyrosine kinase inhibitor (TKI) therapy and reversion of Bcr-Abl expression increased Mtss1 expression but failed to restore it to control levels. CML patient samples revealed higher DNA methylation of specific Mtss1 promoter CpG sites that contain binding sites for Kaiso and Rest transcription factors. In summary, we identified a novel tumor suppressor in CML stem cells that is downregulated by both Bcr-Abl kinase-dependent and -independent mechanisms. Restored Mtss1 expression markedly inhibits primitive leukemic cell biology in vivo, providing a therapeutic rationale for the Bcr-Abl-Mtss1 axis to target TKI resistant CML stem cells in patients
Off-diagonal parton distributions and their evolution
We construct off-diagonal parton distributions defined on the interval 0 < X
< 1 starting from the off-forward distributions defined by Ji. We emphasize the
particular role played by the symmetry relations in the "ERBL-like" region. We
find the evolution equations for the off-diagonal distributions which conserve
these symmetries. We present numerical results of the evolution, and verify
that the analytic asymptotic forms of the parton distributions are reproduced.
We also compare the constructed off-diagonal distributions with the non-forward
distributions defined by Radyushkin and comment on the singularity structure of
the basic amplitude written in terms of the off-diagonal distributions.Comment: 22 pages, Latex, 6 ps figures. Improved presentation after
discussions with X.Ji and A.Radyushki
Pion and Kaon Production in and Collisions at Next-to-Leading Order
We present new sets of fragmentation functions for charged pions and kaons,
both at leading and next-to-leading order. They are fitted to data on inclusive
charged-hadron production in annihilation taken by TPC at PEP (~GeV) and to similar data by ALEPH at LEP, who discriminated between
events with charm, bottom, and light- flavour fragmentation in their
charged-hadron sample. We treat all partons independently and to properly
incorporate the charm and bottom thresholds. Due to the sizeable energy gap
between PEP and LEP, we are sensitive to the scaling violation in the
fragmentation process, which allows us to extract a value for the asymptotic
scale parameter of QCD, . Recent data on inclusive charged-hadron
production in tagged three-jet events by OPAL and similar data for longitudinal
electron polarization by ALEPH allow us to pin down the gluon fragmentation
functions. Our new fragmentation functions lead to an excellent description of
a multitude of other data on inclusive charged-hadron production,
ranging from ~GeV to LEP energy. In addition, they agree nicely
with the transverse-momentum spectra of single charged hadrons measured by H1
and ZEUS in photoproduction at the collider HERA, which represents a
nontrivial check of the factorization theorem of the QCD-improved parton model.Comment: 22 pages, latex, 13 compressed ps figures in separate fil
The human telomerase RNA gene (hTERC) is regulated during carcinogenesis but is not dependent on DNA methylation
Telomerase, the ribonucleoprotein complex involved in telomere maintenance, is composed of two main components: hTERT and hTERC. hTERT seems to be the rate-limiting factor for telomerase activity, although hTERC expression was also shown to correlate to a certain extent with telomerase reactivation. To determine whether the absence of hTERC expression could be the consequence of DNA methylation, we quantified hTERC RNA in 60 human samples (19 telomerase-negative normal tissues, nine telomerase-positive and 22 telomerase-negative tumor tissues, eight telomerase-positive and two telomerase-negative cell lines) using a quantitative dot blot on RT-PCR products. Most of the normal tissues did not express hTERC whereas, in telomerase-positive cell lines and in telomerase-positive tumor tissues, a strong up-regulation was observed, suggesting that hTERC transcription is up-regulated during tumorigenesis. The two telomerase-negative cell lines did not express hTERC. In a series of 22 telomerase-negative soft tissue sarcomas (STS), half did not express hTERC at all, or only weakly, whereas a wide range of expression was observed in the other half. As methylation might be involved in hTERC silencing, we examined the methylation pattern in all samples by direct sequencing and methylation-specific single stand conformation analysis after bisulfite modification. hTERC methylation was never observed, neither in normal nor in tumor tissues. Furthermore, there was no correlation between hTERC expression and proliferation, telomere length or hTERT expression in telomerase-negative STS. In contrast, three of eight telomerase-positive cell lines and the two telomerase negative cell lines were found to be hypermethylated, suggesting that the methylation observed may occur during cell line establishment. In conclusion, this study shows that hTERC expression is indeed regulated during carcinogenesis, but this regulation is unlikely to depend on hTERC methylation, cell proliferation rate, telomere length or hTERT expressio
Primakoff effect in eta-photoproduction off protons
We analyse data on forward eta-meson photoproduction off a proton target and
extract the eta to gamma gamma decay width utilizing the Primakoff effect. The
hadronic amplitude that enters into our analysis is strongly constrained
because it is fixed from a global fit to available gamma p to p eta data for
differential cross sections and polarizations. We compare our results with
present information on the two-photon eta-decay from the literature. We provide
predictions for future PrimEx experiments at Jefferson Laboratory in order to
motivate further studies.Comment: 5 pages, 6 figures, gamma-gamma*-eta form factor included, version to
appear in Eur. Phys. J. A
Proof of Factorization for Deeply Virtual Compton Scattering in QCD
We show that factorization holds for the deeply virtual Compton scattering
amplitude in QCD, up to power suppressed terms, to all orders in perturbation
theory. Furthermore, we show that the virtuality of the produced photon does
not influence the general theorem.Comment: 14 pages, Revtex, postscript figures. Improved treatement of
"endpoint/breakpoint" regions. Corrected references to earlier wor
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