Advances in High Energy Physics
[SJR: 1.334] [H-I: 12] [12 followers] Follow
Open Access journal
ISSN (Print) 1687-7357 - ISSN (Online) 1687-7365
Published by Hindawi Publishing Corporation [404 journals]
- Physics at a Fixed-Target Experiment Using the LHC Beams
PubDate: Wed, 07 Oct 2015 08:11:31 +000
- Next-to-Leading Order Differential Cross Sections for , , and Production
in Proton-Proton Collisions at a Fixed-Target Experiment Using the LHC
Abstract: Using nonrelativistic QCD (NRQCD) factorization, we calculate the yields for , , and hadroproduction at GeV and 115 GeV including the next-to-leading order QCD corrections. Both these center-of-mass energies correspond to those obtained with 7 TeV and 2.76 TeV nucleon beam impinging a fixed target. We study the cross section integrated in as a function of the (center-of-mass) rapidity as well as the differential cross section in the central rapidity region. Using different NLO fit results of the NRQCD long-distance matrix elements, we evaluate a theoretical uncertainty which is certainly much larger than the projected experimental uncertainties with the expected 20 fb−1 to be collected per year with AFTER@LHC for collision at the center of mass energy GeV.
PubDate: Mon, 05 Oct 2015 08:17:47 +000
- Supersymmetry beyond the NMSSM
PubDate: Mon, 05 Oct 2015 07:55:03 +000
- Vacuum Condensates as a Mechanism of Spontaneous Supersymmetry Breaking
Abstract: A possible mechanism for the spontaneous breaking of SUSY, based on the presence of vacuum condensates, is reviewed. Such a mechanism could occur in many physical examples, at both the fundamental and emergent levels, and would be formally analogous to spontaneous SUSY breaking at finite temperature in the TFD formalism, in which case it can be applied as well. A possible experimental setup for detecting such a breaking through measurement of the Anandan-Aharonov invariants associated with vacuum condensates in an optical lattice model is proposed.
PubDate: Sun, 04 Oct 2015 14:05:30 +000
- The Gluon Sivers Distribution: Status and Future Prospects
Abstract: We review what is currently known about the gluon Sivers distribution and what are the opportunities to learn more about it. Because single transverse spin asymmetries in provide only indirect information about the gluon Sivers function through the relation with the quark-gluon and tri-gluon Qiu-Sterman functions, current data from hadronic collisions at RHIC have not yet been translated into a solid constraint on the gluon Sivers function. SIDIS data, including the COMPASS deuteron data, allow for a gluon Sivers contribution of natural size expected from large arguments, which is times the nonsinglet quark Sivers contribution. Several very promising processes to measure the gluon Sivers effect directly have been suggested, which besides RHIC investigations, would strongly favor experiments at AFTER@LHC and a possible future Electron-Ion Collider. Due to the inherent process dependence of TMDs, the gluon Sivers TMD probed in the various processes are different linear combinations of two universal gluon Sivers functions that have different behavior under charge conjugation and that therefore satisfy different theoretical constraints. For this reason both hadronic and DIS type of collisions are essential in the study of the role of gluons in transversely polarized protons.
PubDate: Sun, 04 Oct 2015 12:58:11 +000
- Studies of Backward Particle Production with a Fixed-Target Experiment
Using the LHC Beams
Abstract: The foreseen capability to cover the far backward region at a Fixed-Target Experiment using the LHC beams allows one to explore the dynamics of the target fragmentation in hadronic collisions. In this report we briefly outline the required theoretical framework and discuss a number of studies of forward and backward particle production. By comparing this knowledge with the one accumulated in Deep Inelastic Scattering on target fragmentation, the basic concept of QCD factorisation could be investigated in detail.
PubDate: Sun, 04 Oct 2015 12:56:02 +000
- Antishadowing Effect on Charmonium Production at a Fixed-Target Experiment
Using LHC Beams
Abstract: We investigate charmonium production in Pb + Pb collisions at LHC beam energy TeV at fixed-target experiment ( = 72 GeV). In the frame of a transport approach including cold and hot nuclear matter effects on charmonium evolution, we focus on the antishadowing effect on the nuclear modification factors and for the yield and transverse momentum. The yield is more suppressed at less forward rapidity () than that at very forward rapidity () due to the shadowing and antishadowing in different rapidity bins.
PubDate: Sun, 04 Oct 2015 12:16:15 +000
- Bremsstrahlung from Relativistic Heavy Ions in a Fixed Target Experiment
at the LHC
Abstract: We calculate the emission of bremsstrahlung from lead and argon ions in ultraperipheral collisions in a fixed target experiment (AFTER) that uses the LHC beams. With nuclear charges of Ze equal to 82e and 18e, respectively, these ions are accelerated to energies of 7 Tev × Z. The bremsstrahlung peaks around ≈100 GeV and the spectrum exposes the nuclear structure of the incoming ion. The peak structure is significantly different from the flat power spectrum pertaining to a point charge. Photons are predominantly emitted within an angle of 1/γ to the direction of ion propagation. Our calculations are based on the Weizsäcker-Williams method of virtual quanta with application of existing experimental data on photonuclear interactions.
PubDate: Sun, 04 Oct 2015 11:35:27 +000
- Quarkonium Production and Proposal of the New Experiments on Fixed Target
at the LHC
Abstract: The brief review of the experimental data on quarkonium productions measured at the CERN SPS, at the Brookhaven Collider RHIC, and at the LHC is presented. The dissociation of quarkonium resonances produced in heavy ion collisions was suggested as a possible signal of the Quark-Gluon Plasma formation. At the CERN SPS, the anomalous suppression of the production was observed in central Pb-Pb collisions by the NA50 collaboration. However, the effects of suppression on cold nuclear matter, feed-down production from higher charmonium states, and regeneration processes should be taken into account. If proton and ion beams at the LHC will be used with fixed targets, the energy interval between the SPS energy and the nominal RHIC energy (200 GeV) could be investigated. The high statistics data on quarkonium productions at these energies will give the possibility of clarifying the mechanism of charmonium productions to investigate the importance of the recombination process, since the probability of recombination decreases with decreasing the energy of collisions.
PubDate: Sun, 04 Oct 2015 11:09:14 +000
- Quarkonium Suppression from Coherent Energy Loss in Fixed-Target
Experiments Using LHC Beams
Abstract: Quarkonium production in proton-nucleus collisions is a powerful tool to disentangle cold nuclear matter effects. A model based on coherent energy loss is able to explain the available quarkonium suppression data in a broad range of rapidities, from fixed-target to collider energies, suggesting coherent energy loss in cold nuclear matter to be the dominant effect in quarkonium suppression in p-A collisions. This could be further tested in a high-energy fixed-target experiment using a proton or nucleus beam. The nuclear modification factors of and as a function of rapidity are computed in p-A collisions at GeV, and in p-Pb and Pb-Pb collisions at GeV. These center-of-mass energies correspond to the collision on fixed-target nuclei of 7 TeV protons and 2.76 TeV (per nucleon) lead nuclei available at the LHC.
PubDate: Sun, 04 Oct 2015 09:42:48 +000
- Transverse Single-Spin Asymmetries in Proton-Proton Collisions at the
AFTER@LHC Experiment in a TMD Factorisation Scheme
Abstract: The inclusive large- production of a single pion, jet or direct photon, and Drell-Yan processes, are considered for proton-proton collisions in the kinematical range expected for the fixed-target experiment AFTER, proposed at LHC. For all these processes, predictions are given for the transverse single-spin asymmetry, , computed according to a Generalised Parton Model previously discussed in the literature and based on TMD factorisation. Comparisons with the results of a collinear twist-3 approach, recently presented, are made and discussed.
PubDate: Sun, 04 Oct 2015 09:41:32 +000
- Transverse Single-Spin Asymmetries in Proton-Proton Collisions at the
Abstract: We present results for transverse single-spin asymmetries in proton-proton collisions at kinematics relevant for AFTER, a proposed fixed-target experiment at the Large Hadron Collider. These include predictions for pion, jet, and direct photon production from analytical formulas already available in the literature. We also discuss specific measurements that will benefit from the higher luminosity of AFTER, which could help resolve an almost 40-year puzzle of what causes transverse single-spin asymmetries in proton-proton collisions.
PubDate: Sun, 04 Oct 2015 09:39:11 +000
- A Chargeless Complex Vector Matter Field in Supersymmetric Scenario
Abstract: We construct and study a formulation of a chargeless complex vector matter field in a supersymmetric framework. To this aim we combine two nochiral scalar superfields in order to take the vector component field to build the chargeless complex vector superpartner where the respective field strength transforms into matter fields by a global gauge symmetry. For the aim of dealing with consistent terms without breaking the global symmetry we imposes a choice to the complex combination revealing a kind of symmetry between the choices and eliminates the extra degrees of freedom which is consistent with the supersymmetry. As the usual case the mass supersymmetric sector contributes as a complement to dynamics of the model. We obtain the equations of motion of the Proca’s type field for the chiral spinor fields and for the scalar field on the mass-shell which show the same mass as expected. This work establishes the first steps to extend the analysis of charged massive vector field in a supersymmetric scenario.
PubDate: Sun, 04 Oct 2015 09:39:11 +000
- Feasibility Studies for Quarkonium Production at a Fixed-Target Experiment
Using the LHC Proton and Lead Beams (AFTER@LHC)
Abstract: Being used in the fixed-target mode, the multi-TeV LHC proton and lead beams allow for studies of heavy-flavour hadroproduction with unprecedented precision at backward rapidities, far negative Feynman-, using conventional detection techniques. At the nominal LHC energies, quarkonia can be studied in detail in , , and collisions at GeV and in Pb + and Pb + collisions at GeV with luminosities roughly equivalent to that of the collider mode that is up to 20 fb−1 yr−1 in and collisions, up to 0.6 fb−1 yr−1 in collisions, and up to 10 nb−1 yr−1 in Pb + collisions. In this paper, we assess the feasibility of such studies by performing fast simulations using the performance of a LHCb-like detector.
PubDate: Sun, 04 Oct 2015 07:59:56 +000
- Gluon Shadowing Effects on and Production in Collisions at GeV and
Collisions at GeV at AFTER@LHC
Abstract: We explore the effects of shadowing on inclusive and production at AFTER@LHC. We also present the rates as a function of and rapidity for and collisions in the proposed AFTER@LHC rapidity acceptance.
PubDate: Sun, 04 Oct 2015 07:54:51 +000
- Prospects for Open Heavy Flavor Measurements in Heavy Ion and Collisions
in a Fixed-Target Experiment at the LHC
Abstract: High luminosity data in a fixed-target experiment allow studying interactions of heavy quarks with nuclear matter in the intermediate energy range with extremely high precision. We present a feasibility study for open charm and bottom production measurements in the energy range of a fixed-target experiment at the LHC (AFTER@LHC). We demonstrate, that high-precision data from AFTER will allow answering two open questions: if there is a collective behavior of charm quarks in collisions at RHIC energy and if charm production is suppressed in the energy range of = 60–80 GeV. We argue that simultaneous measurement of suppression as a function of traverse momentum at midrapidity and forward rapidity can help to pin down the mechanism of charm energy loss in the hot and dense nuclear medium.
PubDate: Sun, 04 Oct 2015 07:15:04 +000
- A Gas Target Internal to the LHC for the Study of pp Single-Spin
Asymmetries and Heavy Ion Collisions
Abstract: We discuss the application of an open storage cell as gas target for a proposed LHC fixed-target experiment AFTER@LHC. The target provides a high areal density at minimum gas input, which may be polarized 1H, 2H, or 3He gas or heavy inert gases in a wide mass range. For the study of single-spin asymmetries in pp interaction, luminosities of nearly 1033/cm2 s can be produced with existing techniques.
PubDate: Sun, 04 Oct 2015 07:14:27 +000
- The Quark-Gluon Plasma Equation of State and the Generalized Uncertainty
Abstract: The quark-gluon plasma (QGP) equation of state within a minimal length scenario or Generalized Uncertainty Principle (GUP) is studied. The Generalized Uncertainty Principle is implemented on deriving the thermodynamics of ideal QGP at a vanishing chemical potential. We find a significant effect for the GUP term. The main features of QCD lattice results were quantitatively achieved in case of , , and flavors for the energy density, the pressure, and the interaction measure. The exciting point is the large value of bag pressure especially in case of flavor which reflects the strong correlation between quarks in this bag which is already expected. One can notice that the asymptotic behavior which is characterized by Stephan-Boltzmann limit would be satisfied.
PubDate: Sun, 04 Oct 2015 05:58:38 +000
- The Higgs Sector of the Minimal SUSY Model
Abstract: I review the Higgs sector of the extension of the minimal supersymmetric standard model (MSSM). I will show that the gauge kinetic mixing plays a crucial role in the Higgs phenomenology. Two light bosons are present, a MSSM-like one and a -like one, which mix at one loop solely due to the gauge mixing. After briefly looking at constraints from flavour observables, new decay channels involving right-handed (s)neutrinos are presented. Finally, how model features pertaining to the gauge extension affect the model phenomenology, concerning the existence of R-Parity-conserving minima at loop level and the Higgs-to-diphoton coupling, will be reviewed.
PubDate: Thu, 01 Oct 2015 14:10:26 +000
- A Review of the Intrinsic Heavy Quark Content of the Nucleon
Abstract: We present a review of the state of the art of our understanding of the intrinsic charm and bottom content of the nucleon. We discuss theoretical calculations, constraints from global analyses, and collider observables sensitive to the intrinsic heavy quark distributions. A particular emphasis is put on the potential of a high energy and high luminosity fixed target experiment using the LHC beams (AFTER@LHC) to search for intrinsic charm.
PubDate: Thu, 01 Oct 2015 14:08:41 +000
- Supersymmetry: Early Roots That Did Not Grow
Abstract: This paper is about early roots of supersymmetry, as found in the literature from 1940s and early 1950s. There were models where the power of “partners” in alleviating divergences in quantum field theory was recognized. However, other currently known remarkable features of supersymmetry, such as its role in the extension of the Poincaré group, were not known. There were, of course, no supersymmetric nonabelian quantum field theories in those days.
PubDate: Thu, 01 Oct 2015 14:07:32 +000
- Two-Loop Correction to the Higgs Boson Mass in the MRSSM
Abstract: We present the impact of two-loop corrections on the mass of the lightest Higgs boson in the minimal R-symmetric supersymmetric standard model (MRSSM). These shift the Higgs boson mass up by typically 5 GeV or more. The dominant corrections arise from strong interactions, and from the gluon and its superpartners, the sgluon and Dirac gluino, and these corrections further increase with large Dirac gluino mass. The two-loop contributions governed purely by Yukawa couplings and the MRSSM , parameters are smaller. We also update our earlier analysis which showed that the MRSSM can accommodate the measured Higgs and W boson masses. Including the two-loop corrections increases the parameter space where the theory prediction agrees with the measurement.
PubDate: Thu, 01 Oct 2015 12:44:22 +000
- Searches for Prompt -Parity-Violating Supersymmetry at the LHC
Abstract: Searches for supersymmetry (SUSY) at the LHC frequently assume the conservation of -parity in their design, optimization, and interpretation. In the case that -parity is not conserved, constraints on SUSY particle masses tend to be weakened with respect to -parity-conserving models. We review the current status of searches for -parity-violating (RPV) supersymmetry models at the ATLAS and CMS experiments, limited to 8 TeV search results published or submitted for publication as of the end of March 2015. All forms of renormalisable RPV terms leading to prompt signatures have been considered in the set of analyses under review. Discussing results for searches for prompt -parity-violating SUSY signatures summarizes the main constraints for various RPV models from LHC Run I and also defines the basis for promising signal regions to be optimized for Run II. In addition to identifying highly constrained regions from existing searches, also gaps in the coverage of the parameter space of RPV SUSY are outlined.
PubDate: Thu, 01 Oct 2015 12:03:59 +000
- Two Higgs Bosons near 125 GeV in the Complex NMSSM and the LHC Run
Abstract: We analyse the impact of explicit CP-violation in the Higgs sector of the Next-to-Minimal Supersymmetric Standard Model (NMSSM) on its consistency with the Higgs boson data from the Large Hadron Collider (LHC). Through detailed scans of the parameter space of the complex NMSSM for certain fixed values of one of its CP-violating (CPV) phases, we obtain a large number of points corresponding to five phenomenologically relevant scenarios containing ∼125 GeV Higgs boson(s). We focus, in particular, on the scenarios where the visible peaks in the experimental samples can actually be explained by two nearly mass-degenerate neutral Higgs boson states. We find that some points corresponding to these scenarios give an overall slightly improved fit to the data, more so for nonzero values of the CPV phase, compared to the scenarios containing a single Higgs boson near 125 GeV.
PubDate: Thu, 01 Oct 2015 11:56:39 +000
- Partial Quark-Lepton Universality and Neutrino CP Violation
Abstract: We study a model with partial quark-lepton universality that can naturally arise in grand unified theories. We find that constraints on the model can be reduced to a single condition on the Dirac CP phase in the neutrino sector. Using our current knowledge of the CKM and PMNS mixing matrices, we predict at .
PubDate: Thu, 01 Oct 2015 11:55:49 +000
- Lepton Flavor Violation beyond the MSSM
Abstract: Most extensions of the Standard Model lepton sector predict large lepton flavor violating rates. Given the promising experimental perspectives for lepton flavor violation in the next few years, this generic expectation might offer a powerful indirect probe to look for new physics. In this review we will cover several aspects of lepton flavor violation in supersymmetric models beyond the Minimal Supersymmetric Standard Model. In particular, we will concentrate on three different scenarios: high-scale and low-scale seesaw models as well as models with R-parity violation. We will see that in some cases the LFV phenomenology can have characteristic features for specific scenarios, implying that dedicated studies must be performed in order to correctly understand the phenomenology in nonminimal supersymmetric models.
PubDate: Thu, 01 Oct 2015 11:41:39 +000
- Singlet Extensions of the MSSM with Symmetry
Abstract: We discuss singlet extensions of the MSSM with symmetry. We show that holomorphic zeros can avoid a potentially large coefficient of the term linear in the singlet. The emerging model has both an effective term and a supersymmetric mass term for the singlet which are controlled by the gravitino mass. The term turns out to be suppressed against by about one or two orders of magnitude. We argue that this class of models might provide us with a solution to the little hierarchy problem of the MSSM.
PubDate: Thu, 01 Oct 2015 11:37:55 +000
- Status of LHC Searches for SUSY without R-Parity
Abstract: In this contribution we briefly review the status of current searches for supersymmetry at the Large Hadron Collider, focusing especially on viable sub-TeV colored superpartners which can appear in nonstandard scenarios. The presented material covers mostly signals that do not crucially rely on the presence of large missing transverse momentum, with special emphasis on R-parity violating supersymmetry. For some scenarios the prospects for the next run of the Large Hadron Collider and future machines are also presented.
PubDate: Thu, 01 Oct 2015 11:12:51 +000
- Quasi-Classical Gravity Effect on Neutrino Oscillations in a Gravitational
Field of a Heavy Astrophysical Object
Abstract: In the framework of quantum field theory, a graviton interacts locally with a quantum state having definite mass, that is, the gravitational mass eigenstate, while a weak boson interacts with a state having definite flavor, that is, the flavor eigenstate. An interaction of a neutrino with an energetic graviton may trigger the collapse of the neutrino to a definite mass eigenstate with probability expressed in terms of PMNS mixing matrix elements. Thus, gravitons would induce quantum decoherence of a coherent neutrino flavor state similarly to how weak bosons induce quantum decoherence of a neutrino in a definite mass state. We demonstrate that such an essentially quantum gravity effect may have strong consequences for neutrino oscillation phenomena in astrophysics due to relatively large scattering cross sections of relativistic neutrinos undergoing large angle radiation of energetic gravitons in gravitational field of a classical massive source (i.e., the quasi-classical case of gravitational Bethe-Heitler scattering). This graviton-induced decoherence is compared to decoherence due to propagation in the presence of the Earth matter effect. Based on this study, we propose a new technique for the indirect detection of energetic gravitons by measuring the flavor composition of astrophysical neutrinos.
PubDate: Thu, 01 Oct 2015 11:10:58 +000
- Near-Threshold Production of , , and at a Fixed-Target Experiment at the
Future Ultrahigh-Energy Proton Colliders
Abstract: We outline the opportunities to study the production of the Standard Model bosons, , , and , at “low” energies at fixed-target experiments based on possible future ultrahigh-energy proton colliders, that is, the High-Energy LHC, the Super proton-proton Collider, and the Future Circular Collider hadron-hadron. These can be indeed made in conjunction with the proposed future colliders designed to reach up to TeV by using bent crystals to extract part of the halo of the beam which would then impinge on a fixed target. Without disturbing the collider operation, this technique allows for the extraction of a substantial amount of particles in addition to serving for a beam-cleaning purpose. With this method, high-luminosity fixed-target studies at centre-of-mass energies above the , , and masses, –300 GeV, are possible. We also discuss the possibility offered by an internal gas target, which can also be used as luminosity monitor by studying the beam transverse shape.
PubDate: Thu, 01 Oct 2015 11:04:10 +000