5,415 research outputs found
Another look at anomalous J/Psi suppression in Pb+Pb collisions at P/A = 158 GeV/c
A new data presentation is proposed to consider anomalous
suppression in Pb + Pb collisions at GeV/c. If the inclusive
differential cross section with respect to a centrality variable is available,
one can plot the yield of J/Psi events per Pb-Pb collision as a function of an
estimated squared impact parameter. Both quantities are raw experimental data
and have a clear physical meaning. As compared to the usual J/Psi over
Drell-Yan ratio, there is a huge gain in statistical accuracy. This
presentation could be applied advantageously to many processes in the field of
nucleus-nucleus collisions at various energies.Comment: 6 pages, 5 figures, submitted to The European Physical Journal C;
minor revisions for final versio
Arithmeticity vs. non-linearity for irreducible lattices
We establish an arithmeticity vs. non-linearity alternative for irreducible
lattices in suitable product groups, such as for instance products of
topologically simple groups. This applies notably to a (large class of)
Kac-Moody groups. The alternative relies on a CAT(0) superrigidity theorem, as
we follow Margulis' reduction of arithmeticity to superrigidity.Comment: 11 page
A lattice in more than two Kac--Moody groups is arithmetic
Let be an irreducible lattice in a product of n infinite irreducible
complete Kac-Moody groups of simply laced type over finite fields. We show that
if n is at least 3, then each Kac-Moody groups is in fact a simple algebraic
group over a local field and is an arithmetic lattice. This relies on
the following alternative which is satisfied by any irreducible lattice
provided n is at least 2: either is an S-arithmetic (hence linear)
group, or it is not residually finite. In that case, it is even virtually
simple when the ground field is large enough.
More general CAT(0) groups are also considered throughout.Comment: Subsection 2.B was modified and an example was added ther
The Bs -> Ds pi and Bs -> Ds K selections
The decay channels Bs->Dspi and Bs->DsK will be used to extract the physics parameters , and . Simulation studies based on Monte Carlo samples produced in 2004 and 2005 show that a total of 140k Bs->Dspi and 6.2k Bs->DsK events are expected to be triggered, reconstructed and selected in of data ( of data taking at a luminosity of 2\times 10^{32}\unit{cm^{-2}s^{-1}}). The combinatorial background-over-signal ratio originating from inclusive bb events is expected to be B/S < 0.18~\at~90\%$~CL
Addendum to `Fake Projective Planes'
The addendum updates the results presented in the paper `Fake Projective
Plane, Invent Math 168, 321-370 (2007)' and makes some additions and
corrections. The fake projective planes are classified into twenty six classes.
Together with a recent work of Donald Cartwright and Tim Steger, there is now a
complete list of fake projective planes. There are precisely one hundred fake
projective planes as complex surfaces classified up to biholomorphism.Comment: A more refined classification is given in the new versio
Ideals of Quasi-Symmetric Functions and Super-Covariant Polynomials for S_n
The aim of this work is to study the quotient ring R_n of the ring
Q[x_1,...,x_n] over the ideal J_n generated by non-constant homogeneous
quasi-symmetric functions. We prove here that the dimension of R_n is given by
C_n, the n-th Catalan number. This is also the dimension of the space SH_n of
super-covariant polynomials, that is defined as the orthogonal complement of
J_n with respect to a given scalar product. We construct a basis for R_n whose
elements are naturally indexed by Dyck paths. This allows us to understand the
Hilbert series of SH_n in terms of number of Dyck paths with a given number of
factors.Comment: LaTeX, 3 figures, 12 page
The algorithm for FIR corrections of the VELO analogue links and its performance
The data from the VELO front-end is sent to the ADCs on the read-out board over a serial analogue link. Due imperfections in the link, inter-symbol cross talk occurs between adjacent time-bins in the transfer. This is corrected by an FIR filter implemented in the pre-processing FPGA locacted on the read-out board. This note reports on a method to determine the coefficients for the filter using date taken in-situ. Simulations are presented that show the performance of the methods as it is implemented in the LHCb read-out board. The effectiveness of the algorithm is demonstrated by the improvements in tracking performance on beam test data it brings
Reduction and approximation in gyrokinetics
The gyrokinetics formulation of plasmas in strong magnetic fields aims at the
elimination of the angle associated with the Larmor rotation of charged
particles around the magnetic field lines. In a perturbative treatment or as a
time-averaging procedure, gyrokinetics is in general an approximation to the
true dynamics. Here we discuss the conditions under which gyrokinetics is
either an approximation or an exact operation in the framework of reduction of
dynamical systems with symmetryComment: 15 pages late
Modular Lie algebras and the Gelfand-Kirillov conjecture
Let g be a finite dimensional simple Lie algebra over an algebraically closed
field of characteristic zero. We show that if the Gelfand-Kirillov conjecture
holds for g, then g has type A_n, C_n or G_2.Comment: 20 page
Berry phase in homogeneous K\"ahler manifolds with linear Hamiltonians
We study the total (dynamical plus geometrical (Berry)) phase of cyclic
quantum motion for coherent states over homogeneous K\"ahler manifolds X=G/H,
which can be considered as the phase spaces of classical systems and which are,
in particular cases, coadjoint orbits of some Lie groups G. When the
Hamiltonian is linear in the generators of a Lie group, both phases can be
calculated exactly in terms of {\em classical} objects. In particular, the
geometric phase is given by the symplectic area enclosed by the (purely
classical) motion in the space of coherent states.Comment: LaTeX fil
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