538 research outputs found
Fairness Versus Reason in the Ultimatum Game
In the Ultimatum Game, two players are offered a chance to win a certain sum of money. All they must do is divide it. The proposer suggests how to split the sum. The responder can accept or reject the deal. If the deal is rejected, neither player gets anything. The rational solution, suggested by game theory, is for the proposer to offer the smallest possible share and for the responder to accept it. If humans play the game, however, the most frequent outcome is a fair share. In this paper, we develop an evolutionary approach to the Ultimatum Game. We show that fairness will evolve if the proposer can obtain some information on what deals the responder has accepted in the past. Hence, the evolution of fairness, similar to the evolution of cooperation, is linked to reputation
Suppression of matching field effects by splay and pinning energy dispersion in YBa_2Cu_3O_7 with columnar defects
We report measurements of the irreversible magnetization M_i of a large
number of YBa_2Cu_3O_7 single crystals with columnar defects (CD). Some of them
exhibit a maximum in M_i when the density of vortices equals the density of
tracks, at temperatures above 40K. We show that the observation of these
matching field effects is constrained to those crystals where the orientational
and pinning energy dispersion of the CD system lies below a certain threshold.
The amount of such dispersion is determined by the mass and energy of the
irradiation ions, and by the crystal thickness. Time relaxation measurements
show that the matching effects are associated with a reduction of the creep
rate, and occur deep into the collective pinning regime.Comment: 7 pages, 5 figures, submitted to Phys. Rev.
Initial State Interactions for -Proton Radiative Capture
The effects of the initial state interactions on the radiative
capture branching ratios are examined and found to be quite sizable. A general
coupled-channel formalism for both strong and electromagnetic channels using a
particle basis is presented, and applied to all the low energy data
with the exception of the {\it 1s} atomic level shift. Satisfactory fits are
obtained using vertex coupling constants for the electromagnetic channels that
are close to their expected SU(3) values.Comment: 16 pages, uses revte
Properties of the Bose glass phase in irradiated superconductors near the matching field
Structural and transport properties of interacting localized flux lines in
the Bose glass phase of irradiated superconductors are studied by means of
Monte Carlo simulations near the matching field B_Phi, where the densities of
vortices and columnar defects are equal. For a completely random columnar pin
distribution in the xy-plane transverse to the magnetic field, our results show
that the repulsive vortex interactions destroy the Mott insulator phase which
was predicted to occur at B = B_Phi. On the other hand, for ratios of the
penetration depth to average defect distance lambda/d <= 1, characteristic
remnants of the Mott insulator singularities remain visible in experimentally
accessible quantities as the magnetization, the bulk modulus, and the
magnetization relaxation, when B is varied near B_Phi. For spatially more
regular disorder, e.g., a nearly triangular defect distribution, we find that
the Mott insulator phase can survive up to considerably large interaction range
\lambda/d, and may thus be observable in experiments.Comment: RevTex, 17 pages, eps files for 12 figures include
Search for the Flavor-Changing Neutral Current Decay with the HERA-B Detector
We report on a search for the flavor-changing neutral current decay using events recorded with a dimuon trigger in
interactions of 920 GeV protons with nuclei by the HERA-B experiment. We find
no evidence for such decays and set a 90% confidence level upper limit on the
branching fraction .Comment: 17 pages, 4 figures (of which 1 double), paper to be submitted to
Physics Letters
Measurement of the J/Psi Production Cross Section in 920 GeV/c Fixed-Target Proton-Nucleus Interactions
The mid-rapidity (dsigma_(pN)/dy at y=0) and total sigma_(pN) production
cross sections of J/Psi mesons are measured in proton-nucleus interactions.
Data collected by the HERA-B experiment in interactions of 920 GeV/c protons
with carbon, titanium and tungsten targets are used for this analysis. The
J/Psi mesons are reconstructed by their decay into lepton pairs. The total
production cross section obtained is sigma_(pN)(J/Psi) = 663 +- 74 +- 46
nb/nucleon. In addition, our result is compared with previous measurements
Observation of hard scattering in photoproduction events with a large rapidity gap at HERA
Events with a large rapidity gap and total transverse energy greater than 5
GeV have been observed in quasi-real photoproduction at HERA with the ZEUS
detector. The distribution of these events as a function of the
centre of mass energy is consistent with diffractive scattering. For total
transverse energies above 12 GeV, the hadronic final states show predominantly
a two-jet structure with each jet having a transverse energy greater than 4
GeV. For the two-jet events, little energy flow is found outside the jets. This
observation is consistent with the hard scattering of a quasi-real photon with
a colourless object in the proton.Comment: 19 pages, latex, 4 figures appended as uuencoded fil
Search for a W' boson decaying to a bottom quark and a top quark in pp collisions at sqrt(s) = 7 TeV
Results are presented from a search for a W' boson using a dataset
corresponding to 5.0 inverse femtobarns of integrated luminosity collected
during 2011 by the CMS experiment at the LHC in pp collisions at sqrt(s)=7 TeV.
The W' boson is modeled as a heavy W boson, but different scenarios for the
couplings to fermions are considered, involving both left-handed and
right-handed chiral projections of the fermions, as well as an arbitrary
mixture of the two. The search is performed in the decay channel W' to t b,
leading to a final state signature with a single lepton (e, mu), missing
transverse energy, and jets, at least one of which is tagged as a b-jet. A W'
boson that couples to fermions with the same coupling constant as the W, but to
the right-handed rather than left-handed chiral projections, is excluded for
masses below 1.85 TeV at the 95% confidence level. For the first time using LHC
data, constraints on the W' gauge coupling for a set of left- and right-handed
coupling combinations have been placed. These results represent a significant
improvement over previously published limits.Comment: Submitted to Physics Letters B. Replaced with version publishe
Search for the standard model Higgs boson decaying into two photons in pp collisions at sqrt(s)=7 TeV
A search for a Higgs boson decaying into two photons is described. The
analysis is performed using a dataset recorded by the CMS experiment at the LHC
from pp collisions at a centre-of-mass energy of 7 TeV, which corresponds to an
integrated luminosity of 4.8 inverse femtobarns. Limits are set on the cross
section of the standard model Higgs boson decaying to two photons. The expected
exclusion limit at 95% confidence level is between 1.4 and 2.4 times the
standard model cross section in the mass range between 110 and 150 GeV. The
analysis of the data excludes, at 95% confidence level, the standard model
Higgs boson decaying into two photons in the mass range 128 to 132 GeV. The
largest excess of events above the expected standard model background is
observed for a Higgs boson mass hypothesis of 124 GeV with a local significance
of 3.1 sigma. The global significance of observing an excess with a local
significance greater than 3.1 sigma anywhere in the search range 110-150 GeV is
estimated to be 1.8 sigma. More data are required to ascertain the origin of
this excess.Comment: Submitted to Physics Letters
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