893 research outputs found

### The Nobel Prize in Physics 1999

The last Nobel Prize of the Millenium in Physics has been awarded jointly to
Professor Gerardus 't Hooft of the University of Utrecht in Holland and his
thesis advisor Professor Emeritus Martinus J.G. Veltman of Holland. According
to the Academy's citation, the Nobel Prize has been awarded for 'elucidating
the quantum structure of electroweak interaction in Physics'. It further goes
on to say that they have placed particle physics theory on a firmer
mathematical foundation. In this short note, we will try to understand both
these aspects of the award. The work for which they have been awarded the Nobel
Prize was done in 1971. However, the precise predictions of properties of
particles that were made possible as a result of their work, were tested to a
very high degree of accuracy only in this last decade. This was done in a
series of measurements in the experiments in the accelerator laboratories at
CERN (Geneva) and Fermilab. To understand the full significance of this Nobel
Prize, we will have to summarise briefly the developement of our current
theoretical framework about the basic constituents of matter and the forces
which hold them together. In fact the path can be partially traced in a chain
of Nobel prizes starting from one in 1965 to S. Tomonaga, J. Schwinger and R.
Feynman, to the one to S.L. Glashow, A. Salam and S. Weinberg in 1979, and then
to C. Rubia and Simon van der Meer in 1984 ending with the current one.Comment: 5 pages, LateX, no inline figures. Six 'boxes' included separately as
six jpg files. These jpg files as well as 10 separate pdf files (one for each
printed page) can be accessed from
http://144.16.74.196/~www/resonance/npp99res.htm. added journal re

### Predictions for Higgs and SUSY Higgs properties and their signatures at the Hadron Colliders

In this talk I present a discussion of the theoretical bounds on the mass of
the Higgs in the Standard Model (SM) as well as in the Minimal Supersymmetric
Standard Model (MSSM). Then I will point out a few facts about the couplings of
scalars that are relevant for its search at hadronic colliders. After that I
discuss the search possibilities at the Tevatron and the LHC, paying special
attention to the issue of how well one can establish the quantum numbers and
the couplings of the Higgs, when (if) it is discovered.Comment: 12 pages, 7 figures, Latex, requires mprocl.sty included, Invited
talk at the 'Hadron Collider Physics XIII', Jan.14-20, 1999, Bombay, India.
(To appear in the proceedings

### Beamstrahlung induced Minijet Backgrounds at future colliders and a model for sigma^{inel}_{\gamma \gamma}

The phenomenon of beamstrahlung can give rise to potentially dangerous
hadronic backgrounds due to minjet production at the future linear colliders as
well as at the \gamma \gamma colliders that are under consideration. In this
talk I will review briefly the current estimates of these backgrounds and
predictions of the eikonalised minijet model for \siginel. I end by pointing
out issues that need to be studied in more detail to firm up our estimates of
these backgrounds.Comment: 13 pages, LaTeX, 3 figures, requires epsfig.sty, sprocl.sty,
axocolor.sty, invited talk presented at the International Conf. on Quantum
aspects of beam physics, to appear in the proceeding

### Eikonalized mini-jet cross-sections in $\gamma \gamma$ collisions

In this note we assess the validity and uncertainties in the predictions of
the eikonalised mini-jet model for $\sigma^{inel}_{\gamma \gamma}$. We are able
to find a choice of parameters where the predictions are compatible with the
current data. Even for this restricted range of parameters the predictions at
the high c.m. energies, which can be reached at the TeV energy $e^+e^-$
colliders, differ by about $\pm 25\%$. LEP 2 data can help pinpoint these
parameters and hence reduce the uncertainties in the predictions.Comment: 5 pages, latex, requires epsfig.sty, a4wide.sty, full ps file
available at http://hpteor.lnf.infn.it/pancheri/lc2000.p

### Strange freezeout

We argue that known systematics of hadron cross sections may cause different
particles to freeze out of the fireball produced in heavy-ion collisions at
different times. We find that a simple model with two freezeout points is a
better description of data than that with a single freezeout, while still
remaining predictive. The resulting fits seem to present constraints on the
late stage evolution of the fireball, including the tantalizing possibility
that the QCD chiral transition influences the yields at sqrt(S)=2700 GeV and
the QCD critical point those at sqrt(S)=17.3 GeV

### Total Cross-sections

We examine the energy dependence of total cross-sections for photon processes
and discuss the QCD contribution to the rising behaviourComment: 5 pages, LaTeX, 2 figures, talk presented by G. Pancheri at Photon -
2001, The International Conference on Structure and Interactions of Photons,
Ascona, Sept. 2-7,2001. To appear in the proceeding

### Invisible Decays of the Supersymmetric Higgs and Dark Matter

We discuss effects of the light sparticles on decays of the lightest Higgs in
a supersymmetric model with nonuniversal gaugino masses at the high scale,
focusing on the `invisible' decays into neutralinos. These can impact
significanlty the discovery possibilities of the lightest Higgs at the LHC. We
show that due to these decays, there exist regions of the $M_2-\mu$ space where
the B.R. $(h \to \gamma \gamma)$ becomes dangerously low even after imposing
the LEP constraints on the sparticle masses, implying a possible preclusion of
its discovery in the $\gamma \gamma$ channel. We find that there exist regions
in the parameter space with acceptable relic density and where the ratio ${B.R.
(h \to \gamma \gamma)_{SUSY} \over B.R. (h \to \gamma \gamma)_{SM}}$ falls
below 0.6, implying loss of signal in the $\gamma \gamma$ channel. These
regions correspond to $\tilde \chi_1^+, \tilde \chi_2^0$ masses which should be
accessible already at the Tevatron. Further we find that considerations of
relic density put lower limit on the U(1) gaugino mass parameter $M_1$
independently of $\mu, \tan \beta$ and $m_0$.Comment: 17 pages, 11 figures, Talk presented at Appi2002, Accelerator and
Particle Physics Institute, Appi, Iwate, Japan, February 13--16 200

### QCD and Total Cross-sections

We discuss models for total cross-sections, show their predictions for
photon-photon collisions and compare them with the recent LEP measurements. We
show that the extrapolations to high center of mass energies within various
models differ by large factors at high energies and discuss the precision
required from future measurements at the proposed Linear Collider which would
allow to distinguish between them.Comment: 7 pages, 4 figures, laTeX, requires sprocl.sty, added at the end. To
appear in the Proceedings of XXIX International Symposium on Mutliparticle
Dynamics, Brwon University, U.S.A., June 9

### Photon-Photon total inelastic cross-section

We discuss predictions for the total inelastic gamma-gamma cross-section and
their model dependence on the input parameters. We compare results from a
simple extension of the Regge Pomeron exchange model as well as predictions
from the eikonalized mini-jet model with recent LEP data.Comment: 7 pages, LateX, 2 eps figures. Talk presented at Photon'97, Egmond
aan Zee, May 199

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