Search

Abstract: The Silicon Transition Radiation Detector (SiTRD) combines the excellent space resolution of a silicon tracker with the particle identification capability of a conventional TRD. The detector consists of multiple modules, each composed by a radiator and a tracker plane, separated by a gap and immersed in a magnetic field. This layout allows the separation of the TR photons possibly produced by radiating particles from their trajectories. Provided that the separation in the tracker plane is larger than the granularity of the tracker, the SiTRD can identify radiating particles from non-radiating ones. Moreover, the small amount of material encountered by the particles along their path does not significantly affect the momentum reconstruction performance of the tracker. These features make the SiTRD an attractive option when designing the inner tracker of a collider experiment. We have studied a possible SiTRD layout for the inner tracker of a collider experiment at LHC. The detector parameters have been optimized taking into account the geometry constraints derived from an upgrade proposal of the ATLAS inner tracker. A Monte Carlo simulation has been also developed in which the detector performance has been investigated. [Copyright &y& Elsevier]

The new particle around 125 GeV observed at the Large Hadron Collider (LHC) is almost consistent with the standard model (SM) Higgs boson, except that the diphoton decay mode may be excessive. We summarize a number of possibilities. While at the LHC the dominant production mechanism for the Higgs boson of SM and some other extensions is via the gluon fusion process, the alternative vector-boson fusion (VBF) is more sensitive to electroweak symmetry breaking. Using the well-known dijet-tagging technique to single out the VBF mechanism, we investigate potential of VBF to discriminate a number of models suggested to give an enhanced inclusive diphoton production rate. [ABSTRACT FROM AUTHOR]

The transition radiation tracker of the ATLAS setup, which is one of the two multipurpose detectors at the Large Hadron Collider (LHC), its design, and the tasks it performs are described. The tracker is fully assembled and commissioned. The first physical results obtained by the tracker in the ATLAS cosmic muon runs are presented. [ABSTRACT FROM AUTHOR]

The potential of pp → pggp → pGp process in scenarios of the Arkani-Hamed, Dimopoulos, Dvali (ADD) and Randall-Sundrum (RS) model at the LHC is examined, and 95% C.L. bounds on the model parameters are obtained. It is found that the sensitivity of the model parameters can be improved in the present colliders by using this reaction. [ABSTRACT FROM AUTHOR]

The ALICE Collaboration has studied J/&psgr; production in pp collisions at √s = 7 TeV at the LHC through its muon pair decay. The polar and azimuthal angle distributions of the decay muons were measured, and results on the J/&psgr; polarization parameters &lgr;&thgr; and &lgr;&phgr; were obtained. The study was performed in the kinematic region 2.5 < y < 4, 2 < pt < 8 GeV/c, in the helicity and Collins-Soper reference frames. In both frames, the polarization parameters are compatible with zero, within uncertainties. [ABSTRACT FROM AUTHOR]

Abstract: We study the phenomenology of same sign top pair production at the LHC in a model-independent way. The complete set of dimension six operators involving two top (or anti-top) quarks is introduced and the connection with all possible t- or s-channel heavy particle exchanges is established. Only in the former case, same and opposite sign top pair production can be related. We find that while current Tevatron data disfavor t-channel models, other production mechanisms are viable and can be tested at the LHC. [Copyright &y& Elsevier]

We perform a joint jet tomographic analysis of the data on the nuclear modification factor R from PHENIX at RHIC and ALICE at LHC. The computations are performed accounting for radiative and collisional parton energy loss with running coupling constant. Our results show that the observed slow variation of R from RHIC to LHC indicates that the QCD coupling constant is suppressed in the quark-gluon plasma produced at LHC. [ABSTRACT FROM AUTHOR]

Abstract: We provide a status report on the calculation of the Equation of State (EoS) of QCD at finite temperature using lattice QCD. Most of the discussion will focus on comparison of recent results obtained by the HotQCD and Wuppertal-Budapest (W-B) collaborations. We will show that very significant progress has been made towards obtaining high precision results over the temperature range of . The various sources of systematic uncertainties will be discussed and the differences between the two calculations highlighted. Our final conclusion is that the lattice results of EoS are getting precise enough to justify being used in the phenomenological analysis of heavy ion experiments at RHIC and LHC. [Copyright &y& Elsevier]

Abstract: We predict the exact gaugino mass relation near the electroweak scale at one loop for gravity mediated supersymmetry breaking in F-theory and models with and fluxes, respectively. The gaugino mass relation introduced here differs from the typical gaugino mass relations studied thus far, and in general, should be preserved quite well at low energy. Therefore, these F-theory models can be tested at the Large Hadron Collider and future International Linear Collider. We present two typical scenarios that satisfy all the latest experimental constraints and are consistent with the CDMS II experiment. In particular, the gaugino mass relation is indeed satisfied at two-loop level with only a very small deviation around the electroweak scale. [Copyright &y& Elsevier]

Abstract: We study the collider phenomenology of sbottom–bino co-annihilation scenario at both the 7 TeV and 14 TeV LHC. This co-annihilation scenario requires that the NLSP sbottom and LSP bino masses are apart by no more than about 20% or so, and for , the sbottom decays exclusively into . We propose a search for sbottom pairs through plus missing energy. By scanning the mass parameters and , we investigate the discovery limits of sbottom and bino in the plane with at least 5σ significance at the LHC, for varying integrated luminosities. It is shown that with at least 5 fb−1 luminosity, the 7 TeV LHC can explore a narrow region satisfying the 20% co-annihilation condition. For the 14 TeV LHC with 10 (100) fb−1 luminosity, the discovery limit of is 360 (570) GeV. [Copyright &y& Elsevier]

Abstract: Spin correlations of top quarks produced in hadron collisions have not been observed experimentally with large significance. In this Letter, we propose a new variable that may enable demonstration of the existence of spin correlations with significance using just a few hundred dilepton events both at the Tevatron and the LHC. Such number of dilepton events has been observed at the Tevatron. At the LHC, it will become available once integrated luminosity of a few hundred inverse picobarns is collected. [Copyright &y& Elsevier]

I discuss LHC physics in the historical perspective of the progress in particle physics. After a recap of the Standard Model (SM) of particle physics, I discuss the high energy colliders leading up to LHC and their role in the discovery of these SM particles. Then I discuss the two main physics issues of LHC, i.e. Higgs mechanism and supersymmetry. I briefly touch upon Higgs and SUSY searches at LHC along with their cosmological implications. [ABSTRACT FROM AUTHOR]

This is a summary of the activities of the Physics at the LHC working group in the XIth Workshop on High Energy Physics Phenomenology (WHEPP-XI) held at the Physical Research Laboratory, Ahmedabad, India in January 2010. We discuss the activities of each sub-working group on physics issues at colliders such as Tevatron and Large Hadron Collider (LHC). The main issues discussed involve (1) results on W mass measurement and associated QCD uncertainties, (2) an attempt to understand the asymmetry measured at Tevatron in the top quark production, and (3) phenomenology of warped space dimension model. [ABSTRACT FROM AUTHOR]

Abstract: We examine the possibility that one could measure partonic charge symmetry violation (CSV) by comparing neutrino or antineutrino production through charged-current reactions induced by electrons or positrons at a possible electron collider at the LHC. We calculate the magnitude of CSV that might be expected at such a facility. We show that this is likely to be a several percent effect, substantially larger than the typical CSV effects expected for partonic reactions. [Copyright &y& Elsevier]

As the LHC prepares to start taking data, this review is intended to provide a QCD theorist’s understanding and views on jet finding at hadron colliders, including recent developments. My hope is that it will serve both as a primer for the newcomer to jets and as a quick reference for those with some experience of the subject. It is devoted to the questions of how one defines jets, how jets relate to partons, and to the emerging subject of how best to use jets at the LHC. [ABSTRACT FROM AUTHOR]

Abstract: We propose to construct and install a limited acceptance detector to identify hadrons (pions, K, p) up to 30GeV/c on a track-by-track basis in space available in ALICE. Details and PID performance simulation results will be presented for two possible options, including a high transverse momentum () trigger for this detector. The first option is a RICH design with a gas UV-photon radiator, UV-mirror, quartz window and pad-readout. This design requires additional tracking detectors to enable high triggering. A second option is a combination of three detectors: a RICH with gas both as a UV-photon radiator and as a gas amplification medium (a windowless approach); and a threshold Cherenkov detector () with a quartz window and pad readout. The response for minimum ionizing particles (MIP) and UV-photons in these detectors can be well separated. With an additional tracking detector this design will also provide high triggering. The simulation includes UV-photon production due to scintillation. [Copyright &y& Elsevier]

Abstract: The CDF detector at Tevatron collider is at present the most long-lasting high energy physics experiment. Since its first data taking in 1992 it has produced many results of primary importance, such as the discovery of top quark and, more recently, the observations of Bs oscillations and single-top production. None of them would have been possible without a fast and efficient trigger system. Based on a three level architecture, the CDF trigger takes decisions on simple calorimetric and tracking objects and assures both high efficiency on signal events and low dead time. It reduces the data flow rate from 2.53MHz, the collision rate, to 150Hz, the current limit on tape writing and is flexible enough to be easily adapted to the continuously growing instantaneous luminosity. In the last years the Tevatron instantaneous luminosity has rapidly increased and is now reaching . The CDF trigger system has been widely upgraded to cope with increasing trigger rates. The upgrade result is online reconstruction of missing transverse energy, jets and tracks with a quality comparable to the offline one. Jet energy and direction can be precisely determined and tracks can be subjected to 3-D reconstruction with good resolution. These upgrades reduce high trigger rates to acceptable levels and have provided invaluable tools to increase the purity of the collected samples. They also represent a helpful experience for LHC experiments where background rates will be much more demanding. [Copyright &y& Elsevier]

Abstract: Recent fits of electroweak precision data to the Standard Model (SM) with a 4th sequential family (SM4) point to a possible “three-prong composite solution”: (1) the Higgs mass is at the TeV-scale, (2) the masses of the 4th family quarks are of and (3) the mixing angle between the 4th and 3rd generation quarks is of the order of the Cabibbo angle, . Such a manifestation of the SM4 is of particular interest as it may suggest that the Higgs is a composite state, predominantly of the 4th generation heavy quarks. Motivated by the above, we show that the three-prong composite solution to the SM4 can have interesting new implications for Higgs phenomenology. For example, the Higgs can decay to a single heavy 4th generation quark via the 3-body decays (through an off-shell or ) and . These flavor diagonal decays can be dramatically enhanced at the LHC (by several orders of magnitudes) due to the large width effects of the resonating heavy Higgs in the processes and , thus yielding a viable signal above the corresponding continuum QCD production rates. In addition, the Higgs can decay to a single and in the loop-generated flavor changing (FC) channels . These FC decays are essentially “GIM-free” and can, therefore, have branching ratios as large as . [Copyright &y& Elsevier]

Abstract: Avalanche PhotoDiodes (APD) have been chosen as photonsensors for the new Electromagnetic Calorimeter (EMCal) of the ALICE experiment at the LHC. The size of the calorimeter requires the overall use of more than 12000 APDs, all of which have to be tested and characterized individually. A procedure for the test of a large amount of APDs has been developed and is here described in detail, together with results from a first sample of devices. [Copyright &y& Elsevier]

Abstract: The Standard Model (SM) of Particle Physics was tested to great precision by experiments at the highest energy colliders (LEP, Hera, Tevatron, Slac). The only missing particle is the Higgs boson, which will be the first particle to be searched for at the new Large Hadron Collider (LHC) at CERN. The SM anticipated that there are 3 types of left handed neutrinos. Experiments on atmospheric and solar neutrinos (made in Japan, Italy, Canada, Russia and the US) have shown the existence of neutrino oscillations, which imply that neutrinos have very small mass differences and violate the conservation of individual leptonic numbers. Neutrino oscillations were verified in long baseline neutrino experiments (in Japan and in the USA); and cosmology has given reasonably precise indications on the sum of the neutrino masses. In this paper will be summarized some of the main properties of the SM and some of the main results obtained in the field and the experiments in preparation. Some of the main open questions will be briefly discussed. [Copyright &y& Elsevier]

Abstract: The use of nuclear track detectors at accelerators to directly search for the magnetic monopole and other highly ionizing objects is discussed. Recent searches at LEP are used as examples. Finally, the MoEDAL experiment, which is designed to continue the search at the LHC, is described. [Copyright &y& Elsevier]

Abstract: Pixel detectors, as the current technology of choice for the innermost vertex detection, have reached a stage at which large detectors have been built for the LHC experiments and a new era of developments, both for hybrid and for monolithic or semi-monolithic pixel detectors is in full swing. This is largely driven by the requirements of the upgrade programme for the superLHC and by other collider experiments which plan to use monolithic pixel detectors for the first time. A review on current pixel detector developments for particle tracking and vertexing is given, comprising hybrid pixel detectors for superLHC with its own challenges in radiation and rate, as well as on monolithic, so-called active pixel detectors, including monolithic active pixels (MAPS) and DEPFET pixels for RHIC and superBelle. [Copyright &y& Elsevier]

Abstract: In models with extended Higgs sectors, Higgs-boson-mediated Lepton Flavour Violation (LFV) can naturally appear. We study the physics potential of an electron–photon collider on searching LFV processes (; ) where H and A are extra CP even and odd Higgs bosons, respectively, in the minimal supersymmetric standard model and the effective two Higgs doublet model. The production cross section can be significantly large for the maximal allowed values of the LFV coupling constants under the current experimental data. Present experimental upper bounds on the effective LFV coupling constants would be considerably improved by searching these processes, which would be better than MEG and COMET experiments and also those at LHCb and SuperKEKB. Moreover, one can separately measure chirality of effective LFV coupling constants via these processes by selecting electron polarizations. [Copyright &y& Elsevier]

Abstract: The creation of lepton pairs ( and ) via multiphoton absorption in collisions of ultrarelativistic ion beams with ultrashort high-frequency laser pulses is considered. Both the free and the bound-free production channels are addressed, where in the latter case the negatively charged lepton is created in a bound atomic state. It is shown that these nonlinear QED processes are observable when a table-top source of intense xuv or X-ray laser radiation is operated in conjunction with the LHC. We discuss the relative effectiveness of protons versus Pb ions and specify for each pair production channel the most suitable collision system. [Copyright &y& Elsevier]

Abstract: The Tevatron experiments CDF and DØ are close to making definitive statements about the technicolor discovery mode for and . We propose new incisive tests for this mode and searches for others that may be feasible at the Tevatron and certainly are at the LHC. The other searches include two long discussed, namely, and , and a new one—for the partner, , of the . Adopting the argument that the technicolor contribution to S is reduced if , we enumerate important decays and estimate production rates at the colliders. [Copyright &y& Elsevier]

The relativistic hydrodynamics together with the single-freeze-out statistical hadronization model is used to describe the mid-rapidity hadron production in ultra-relativistic heavy-ion collisions at RHIC and LHC. At the highest RHIC energy our approach gives a quite satisfactory global description of soft hadronic observables including the HBT radii. With the increased initial energy, from RHIC to LHC, we expect the saturation of the pion elliptic flow and the moderate increase of the correlation radii. [ABSTRACT FROM AUTHOR]

We consider the longitudinal hydrodynamic evolution of the fireball created in a relativistic heavy-ion collision. Nonzero shear viscosity reduces the cooling rate of the system and hinders the acceleration of the longitudinal flow. As a consequence, the initial energy density needed to reproduce the experimental data at RHIC energies is significantly reduced. At LHC energies, we expect that shear viscosity helps to conserve a Bjorken plateau in the rapidity distributions during the expansion. [ABSTRACT FROM AUTHOR]

I discuss the motivations for, and the status of, precision calculations for the Large Hadron Collider (LHC) and the planned International Linear Collider (ILC). [ABSTRACT FROM AUTHOR]

This paper discusses the techniques used to select online promising events at high energy and high luminosity colliders. After a brief introduction, explaining some general aspects of triggering, the more specific implementation options for well established machines like the Tevatron and Large Hadron Collider (LHC) are presented. An outlook on what difficulties need to be met is given when designing trigger systems at the Super Large Hadron Collider, or at the International Linear Collider. [ABSTRACT FROM AUTHOR]

The Large Hadron Collider (LHC), now close to completion at CERN will provide proton-proton collisions with unprecedented luminosity and energy. It will allow the Standard Model of physics to be explored in an energy range where new phenomena can be studied. This includes the validity of the Higgs mechanism, supersymmetry and CP violation. The machine presents a number of novel features discussed in detail below. [ABSTRACT FROM AUTHOR]

Black hole production at the Large Hadron Collider (LHC) was first discussed in 1999. Since then, much work has been performed in predicting the black hole cross-section. In light of the start up of the LHC, it is now timely to review the state of these calculations. We review the uncertainties in estimating the black hole cross-section in higher dimensions. One would like to make this estimate as precise as possible since the predicted values, or lower limits, obtain for the fundamental Planck scale and number of extra dimensions from experiments will depend directly on the accuracy of the cross-section. Based on the current knowledge of the cross-section, we give a range of lower limits on the fundamental Planck scale that could be obtained at LHC energies. [ABSTRACT FROM AUTHOR]

Abstract: The accelerator upgrade of the large hadron collider (LHC) to super-LHC is foreseen around the year 2015. The upgrade is to increase the luminosity to 1035 cm−2 s−1 and to accumulate 3000fb−1. To cope with the increased occupancy and fluence, the transition radiation tracker (TRT) will be replaced with silicon microstrip sensors, and the semiconductor tracker (SCT) with short-strip silicon microstrip sensors. Both the ATLAS Pixel and SCT communities need to develop new sensors to work to fluences of 1×1016 1-MeV-neq/cm2 and to 8×1014, respectively. Technologies being investigated include a “3D sensor” for the Pixel layers, and an “n-in-p sensor” with high-voltage operation capability for the SCT. The “n-in-p sensor” requires n-strip isolation with high onset voltage of microdischarge. We report here on new sensors with various n-strip isolation structures that have been designed and are being fabricated in the search for the best approach. [Copyright &y& Elsevier]