Object partitioning considered harmful : space subdivision for BVHs

A major factor for the efficiency of ray tracing is the use of good acceleration structures. Recently, bounding volume hierarchies (BVHs) have become the preferred acceleration structures, due to their competitive performance and greater flexibility compared to KD trees. In this paper, we present a study on algorithms for the construction of optimal BVHs. Due to the exponential nature of the problem, constructing optimal BVHs for ray tracing remains an open topic. By exploiting the linearity of the surface area heuristic (SAH), we develop an algorithm that can find optimal partitions in polynomial time. We further generalize this algorithm and show that every SAH-based KD tree or BVH construction algorithm is a special case of the generic algorithm. Based on a number of experiments with the generic algorithm, we conclude that the assumption of non-terminating rays in the surface area cost model becomes a major obstacle for using the full potential of BVHs. We also observe that enforcing space subdivision helps to improve BVH performance. Finally, we develop a simple space partitioning algorithm for building efficient BVHs

Odderon Exchange from Elastic Scattering Differences between pp and pp−^{-} Data at 1.96 TeV and from pp Forward Scattering Measurements

We describe an analysis comparing the p¯p elastic cross section as measured by the D0 Collaboration at a center-of-mass energy of 1.96 TeV to that in pp collisions as measured by the TOTEM Collaboration at 2.76, 7, 8, and 13 TeV using a model-independent approach. The TOTEM crosssections, extrapolated to a center-of-mass energy of √s=1.96  TeV, are compared with the D0 measurement in the region of the diffractive minimum and the second maximum of the pp cross section. The two data sets disagree at the 3.4σ level and thus provide evidence for the t-channel exchange of a colorless, C-odd gluonic compound, also known as the odderon. We combine these results with a TOTEM analysis of the same C-odd exchange based on the total cross section and the ratio of the real to imaginary parts of the forward elastic strong interaction scatteringamplitude in pp scattering for which the significance is between 3.4σ and 4.6σ. The combined significance is larger than 5σ and is interpreted as the first observation of the exchange of a colorless, C-odd gluonic compound

Hard color-singlet exchange in dijet events in proton-proton collisions at root s=13 TeV

Events where the two leading jets are separated by a pseudorapidity interval devoid of particle activity, known as jet-gap-jet events, are studied in proton-proton collisions at root s = 13 TeV. The signature is expected from hard color-singlet exchange. Each of the highest transverse momentum (p(T)) jets must have p(T)(jet) > 40 GeV and pseudorapidity 1.4 0.2 GeV in the interval vertical bar eta vertical bar < 1 between the jets are observed in excess of calculations that assume only color-exchange. The fraction of events produced via color-singlet exchange, f(CSE), is measured as a function of p(T)(jet2), the pseudorapidity difference between the two leading jets, and the azimuthal angular separation between the two leading jets. The fraction f(CSE) has values of 0.4-1.0%. The results are compared with previous measurements and with predictions from perturbative quantum chromodynamics. In addition, the first study of jet-gap-jet events detected in association with an intact proton using a subsample of events with an integrated luminosity of 0.40 pb(-1) is presented. The intact protons are detected with the Roman pot detectors of the TOTEM experiment. The f(CSE) in this sample is 2.91 +/- 0.70(stat)(-1.01)(+1.08)(syst) times larger than that for inclusive dijet production in dijets with similar kinematics.Peer reviewe

Map view restoration of Aegean–West Anatolian accretion and extension since the Eocene

The Aegean region (Greece, western Turkey) is one of the best studied continental extensional provinces. Here, we provide the first detailed kinematic restoration of the Aegean region since 35 Ma. The region consists of stacked upper crustal slices (nappes) that reflect a complex paleogeography. These were decoupled from the subducting African-Adriatic lithospheric slab. Especially since !25 Ma, extensional detachments cut the nappe stack and exhumed its metamorphosed portions in metamorphic core complexes. We reconstruct up to 400 km of trench-perpendicular (NE-SW) extension in two stages. From 25 to 15 Ma, the Aegean forearc rotated clockwise relative to the Moesian platform around Euler poles in northern Greece, accommodated by extensional detachments in the north and an inferred transfer fault SE of the Menderes massif. The majority of extension occurred after 15 Ma (up to 290 km) by opposite rotations of the western and eastern parts of the region. Simultaneously, the Aegean region underwent up to 650 km of post-25 Ma trench-parallel extension leading to dramatic crustal thinning on Crete. We restore a detachment configuration with the Mid-Cycladic Lineament representing a detachment that accommodated trench-parallel extension in the central Aegean region. Finally, we demonstrate that the Sakarya zone and Cretaceous ophiolites of Turkey cannot be traced far into the Aegean region and are likely bounded by a pre-35 Ma N-S fault zone. This fault became reactivated since 25 Ma as an extensional detachment located west of Lesbos Island. The paleogeographic units south of the Izmir-Ankara-Sava suture, however, can be correlated from Greece to Turkey

Odderon Exchange from Elastic Scattering Differences between pp and p(p)over-bar Data at 1.96 TeV and from pp Forward Scattering Measurements

We describe an analysis comparing the $p\bar{p}$ elastic cross section as measured by the D0 Collaboration at a center-of-mass energy of 1.96 TeV to that in $pp$ collisions as measured by the TOTEM Collaboration at 2.76, 7, 8, and 13 TeV using a model-independent approach. The TOTEM cross sections extrapolated to a center-of-mass energy of $\sqrt{s} =$ 1.96 TeV are compared with the D0 measurement in the region of the diffractive minimum and the second maximum of the $pp$ cross section. The two data sets disagree at the 3.4$\sigma$ level and thus provide evidence for the $t$-channel exchange of a colorless, $C$-odd gluonic compound, also known as the odderon. We combine these results with a TOTEM analysis of the same $C$-odd exchange based on the total cross section and the ratio of the real to imaginary parts of the forward elastic scattering amplitude in $pp$ scattering. The combined significance of these results is larger than 5$\sigma$ and is interpreted as the first observation of the exchange of a colorless, $C$-odd gluonic compound

Measurement of pseudorapidity distributions of charged particles in proton-proton collisions at sqrt(s) = 8 TeV by the CMS and TOTEM experiments

Pseudorapidity ( $\eta$ ) distributions of charged particles produced in proton–proton collisions at a centre-of-mass energy of 8 $~\text {TeV}$ are measured in the ranges $|\eta | < 2.2$ and $5.3 < |\eta | < 6.4$ covered by the CMS and TOTEM detectors, respectively. The data correspond to an integrated luminosity of $\mathcal {L} = 45 \mu {\mathrm {b}}^{-1}$ . Measurements are presented for three event categories. The most inclusive category is sensitive to 91–96 % of the total inelastic proton–proton cross section. The other two categories are disjoint subsets of the inclusive sample that are either enhanced or depleted in single diffractive dissociation events. The data are compared to models used to describe high-energy hadronic interactions. None of the models considered provide a consistent description of the measured distributions