abstract

One of the key physics goals of the LHCb experiment at the LHC is the measurement of mixing induced CP violation in decays of \(B_s \rightarrow J/\psi \phi \). The interference between mixing and decay gives rise to a CP-violating phase, \(\phi ^{J/\psi \phi }_s\). Assuming a proper-time resolution and tagging performance as observed in simulated data, together with an expected luminosity of 1 fb\(^{-1}\) by the end of 2011, LHCb is expected to be able to measure \(\phi ^{J/\psi \phi }_s\) with an error of 0.07 rad.

abstract

The observation of long range near side angular correlation (the so-called ridge effect) in \(pp\) collisions at the LHC is presented. Data on such correlations in heavy ion collisions at RHIC are shown. Previous informations on angular correlations in high energy \(pp\) collisions are critically reviewed. A spectrum of many recent interpretations concerning the effect is presented.

abstract

This article discusses the recent tests of the Standard Model using \(pp\)-collision events at \(\sqrt {s}=7\) TeV collected with the ATLAS detector at the Large Hadron Collider (LHC) during 2010 data taking period. The paper focuses on measurements of hard and soft sectors of quantum chromodynamics (QCD), a theory describing interactions of quarks and gluons.

abstract

New experimental findings and theoretical trends concerning the cosmic ray exotic phenomena are reviewed. Motivation and possibilities of their searches at LHC experiments are discussed.

abstract

The heavy-ion program at the Large Hadron Collider has been commenced in November 2010 by three experiments including ATLAS, a multipurpose detector. It was originally constructed to study high-energy proton–proton collisions but now it also proves to be an excellent tool for studying nuclear interactions. In these proceedings results from the lead–lead run at \(\sqrt {s_{NN}}=2.76\) TeV based on the minimum-bias data sample are reviewed. In particular, an observation of the centrality-dependent dijet asymmetry is reported. Also a centrality-dependent suppression in the yield of \(J/\psi \) mesons decaying to \(\mu ^+\mu ^-\) pairs is discussed along with an observation of the \(Z\) boson production. These evidences may bring new insight to the dynamics of heavy-ion collisions.

abstract

The ALICE TPC provides excellent charged particle tracking to study \(pp\) and Pb–Pb collisions at LHC. The TPC allows also particle identification (PID) via the measurement of the specific ionisation \(dE/dx\). At high \(p_{\rm T}\) (\(p_{\rm T} \gt 3\) GeV/\(c\)) this is accomplished in the region of the relativistic rise of the energy loss, and provides a measurement of the yields of charged pions, kaons, and protons. Here, we present the performance of such an analysis in \(pp\) collisions at 7 TeV for charged pions up to 10 GeV/\(c\). On the relativistic rise, statistical PID can be used to evaluate the yields for pions, protons and kaons for \(p_{\rm T}\gt 3\) GeV/\(c\). Here, we show first performance results from such an analysis for charged pions up to 10 GeV/\(c\).

abstract

We present the prospects for the early Higgs boson searches at the CMS experiment. We discuss the sensitivity projections for searches for Standard Model and MSSM Higgs bosons with data expected to be collected during 2011 data taking period. We also report some of the 2010 data analyses validating the key aspects of Higgs searches.

abstract

The Higgs sector of the minimal \(R\)-symmetric supersymmetry theory is analyzed. Decay modes and production channels of the novel Higgs bosons at the LHC and \(e^+e^-\) colliders are studied.

abstract

The Compact Muon Solenoid (CMS) detector is a general purpose experiment at the Large Hadron Collider (LHC) accelerator. The CMS trigger performance with proton–proton collisions during the first year of the LHC’s operation in 2010 is presented. The CMS trigger system is also described and trigger efficiency results and selected applications for physics analyses are presented.

abstract

The year 2010 was the first full year of operation of the Large Hadron Collider (LHC). The Compact Muon Solenoid (CMS) experiment has recorded integrated luminosity of over 43 pb\(^{-1}\) of proton–proton data at center-of-mass energy \(\sqrt {s}=7\) TeV and 8 \(\mu \)b\(^{-1}\) of lead–lead data at \(\sqrt {s_{NN}}=2.76\) TeV. In this paper the CMS detector is briefly introduced. Its initial readiness for data taking and status of operation in 2010 is given. The performance of CMS subsystems is shown. Selected measurements from proton–proton and lead–lead runs are described.

abstract

We investigate phenomenology of color octet scalars that appear in e.g. the supersymmetric \(N = 1/N = 2\) hybrid model. Prospects for their discovery at the 7 TeV LHC in the \(t\bar {t}\) decay channel are discussed.

abstract

Some results on the \(pp\) collisions at \(\sqrt {s}=900\) GeV, 2.36 and 7 TeV are presented. This includes multiplicity distributions, pseudorapidity and transverse momentum spectra and the antibaryon-to-baryon ration. Preliminary results from Pb + Pb collisions are shown as well.

abstract

We investigate the differences between the NLO evolution kernels in the Curci–Furmanski–Petronzio (CFP) and Monte Carlo (MC) factorization schemes for the non-singlet case. We show the origin of these differences and present them explicitly. We examine the influence of the choice of the factorization scale in the MC scheme (given by the upper phase space limit) on the evolution kernels in this scheme.

abstract

We overview some of theory and phenomenology aspects of high energy factorization. In the theory part we focus on basic equations of high energy factorization i.e. BFKL, CCFM, BK. In the phenomenology part we focus on forward-central jets correlations at Large Hadron Collider and on production of charged particles in HERA.

abstract

The analysis of the Drell–Yan lepton pair production at forward rapidities at the Large Hadron Collider is presented, using the dipole approach with saturation effects.

abstract

First results for the \(W\) and \(Z\) boson production cross-sections at \(\sqrt {s}=7\) TeV obtained with the ATLAS detector are presented. The measurements are performed in electron and muon channels, with a data sample of around \(320\) nb\(^{-1}\) collected between March and July 2010. Methods of signal extraction and background estimation are briefly presented. The measured values of \(W\) production cross-sections in electron and muon channels are \(\sigma _{W}\times {\rm BR}(W\to e\nu )=10.51\pm 1.45\) nb and \(\sigma _{W}\times {\rm BR}(W\to \mu \nu )=9.58\pm 1.20\) nb. The \(Z\) cross-section measurements yield \(\sigma _Z\times {\rm BR}(Z\to ~ee)=0.75\pm 0.14\) nb and \(\sigma _Z\times {\rm BR}(Z\to \mu \mu )=0.87\pm 0.14\) nb. The obtained results are in good agreement with theoretical predictions. A preliminary measurement of the \(W\) boson charge asymmetry is also presented.

abstract

Both \(\pi ^0\) and \(\eta \) neutral mesons have been measured by the ALICE experiment at LHC. These results have been obtained via two photon decay measurement, using the two electro-magnetic calorimeters (PHOS and EMCal), as well as via photon conversion in the central tracking system, CTS. We present preliminary \(\pi ^0\) transverse momentum spectra obtained with PHOS and CTS, measured in proton–proton collisions at \(\sqrt {s}=900\) GeV and \(\sqrt {s}=7\) TeV. Results obtained in PHOS and in the CTS are consistent. We also report on the \(\eta / \pi ^0\) ratio at \(\sqrt {s}=7\) TeV. Also we compare our experimental \(\pi ^0\) \(p_{\rm T}\) spectra with NLO pQCD theoretical predictions.

abstract

Results are presented on the production of \(Z\rightarrow \mu \mu \) and \(W\rightarrow \mu \nu \) in the forward region at LHCb. The analysis is based on an integrated luminosity of \(16.5 \pm 1.7 \) pb\(^{-1}\). The production cross-section for \(Z\) with muons in the pseudorapidity range \(2\lt \eta _\mu \lt 4.5\) and \(81\lt m_Z \lt 101\) GeV is \(74\pm 2\pm 3\pm 7\) pb and is also measured differentially in rapidity of the \(Z\). The total cross-section for \(W\) production is \(\sigma _{W^+}(2\lt \eta \lt 4.5)= 1007\pm 48\pm 101\) pb and \(\sigma _{W^-}(2\lt \eta \lt 4.5)= 680\pm 40\pm 68\) pb in the lepton pseudorapidity range \(2 \lt \eta \lt 4.5\). The charge asymmetry is measured as a function of the lepton pseudorapidity. All results are in agreement with next to leading order perturbative QCD predictions.

abstract

The 2010 LHC proton run has provided LHCb with a rich dataset. Several exclusive hadronic \(B\) decays are reconstructed with high signal to background ratios. We outline here our strategy for measurements of the angle \(\gamma \) of the Unitarity Triangle of the CKM matrix.

abstract

Although optimized for \(b\)-physics, LHCb with its unique angular coverage \(2\lt \eta \lt 5\) is also able to contribute significantly to the understanding of the hadron production mechanism in high energy collisions. Here, the first data particle production studies at LHCb are reviewed including \(K_{\rm S}^0\) and \(\phi \) production cross-section, and measurements of production ratios of \(\bar {{\mit \Lambda }}/{\mit \Lambda }\), \(\bar {{\mit \Lambda }}/K^0_{\rm S}\), \(\bar {p}/p\).

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We show that the \(p_{\rm T}\) spectra measured in \(pp\) collisions at the LHC exhibit geometrical scaling introduced earlier in the context of deep inelastic scattering. We also argue that the onset of geometrical scaling can be seen in nucleus–nucleus collisions at lower RHIC energies.

abstract

The LHCb measurement of the \(J\)/\({\mit \Psi }\) production cross-section is presented. The double differential cross-section is measured as a function of the \(J\)/\({\mit \Psi }\) transverse momentum \(p_{\rm T}\) and of the \(J\)/\({\mit \Psi }\) rapidity \(y\) in the fiducial region \(p_{\rm T} \in [0;14]\) GeV/\(c\) and \(y \in [2 ; 4.5]\). The analysis is based on a sample of 5.2 pb\(^{-1}\) collected in September 2010 at the \(p\)–\(p\) Large Hadron Collider at CERN, at a centre of mass energy of 7 TeV. The contributions from prompt \(J\)/\({\mit \Psi }\) and \(J\)/\({\mit \Psi }\) from \(B\)-meson are separated using the \(J\)/\({\mit \Psi }\) pseudo-proper time.

abstract

CP symmetry violation in \({B_s^0}\)–\({\overline {B^0_s}}\) mixing can be measured in \({B_s^0}\) decays to vector–(pseudo)scalar final state. Example of such decay is the \({B_s^0 \rightarrow \chi _{c0} \phi }\) which has never been observed so far. The CP symmetry breaking phase of \({B_s^0}\)–\({\overline {B^0_s}}\) mixing, \({\beta _s}\), can be directly extracted from the CP asymmetry observable since the final state is the CP eigenstate. This measurement can complement the one coming from the analysis of the \({B_s^0 \rightarrow J/\psi \phi }\) decay. \({B_s^0 \rightarrow J/\psi \phi }\) decay is expected to provide the best sensitivity for the \({\beta _s}\) but the angular distribution analysis is needed to disentangle the admixture of different CP eigenstates of the vector–vector final state. In this paper the CP violation in \({B_s^0}\) mesons decays is briefly introduced, the status of current state of \({\beta _s}\) measurement is presented and finally the analysis of the \({B_s^0 \rightarrow \chi _{c0} \phi }\), as a case study of \({B_s^0}\) decay to vector–(pseudo)scalar decay in LHCb experiment, is described.

abstract

The status of the LHCb experiment is presented with emphasis on the detector performance validated with the collected data. Also a particular emphasis is given to the description of the extreme running conditions that the collaboration had to handle during the first year of data taking.

abstract

Feynman diagrams with two real partons contributing to the next-to-leading-order singlet gluon–quark DGLAP kernel are analysed. The infra-red singularities of unintegrated distributions are examined numerically. The analytical formulae are also given in some cases. The role of the colour coherence effects is found to be crucial for cancellations of the double- and single-logarithmic infra-red singularities.

abstract

This paper is devoted to the implementation of the generator WINHAC++. This is a new, object-oriented version of the Monte Carlo generator WINHAC written in Fortran, which is used to model the charged-current Drell–Yan processes, taking into account the radiative corrections by exclusive Yennie–Frautschi–Suura exponentiation. At present, the Born level and the final-state radiation (FSR) has been included into the latest stable release. The correctness of the implementation has been confirmed by a series of numerical tests. The current stage of the development includes the implementation of standard event records and the integration with parton shower and hadronization generators, such as Pythia.

abstract

AFP is a project to extend the diffractive physics programme of the ATLAS experiment by installing new detectors that will be able to tag forward protons scattered at very small angles. This will allow us to study Single Diffraction, Double Pomeron Exchange, Central Exclusive Production and photon–photon processes. This note presents the physics case for the AFP project and briefly describes the proposed detector system.

abstract

An overview of more than 25 years of the Tevatron Collider program at Fermi National Accelerator Laboratory in Batavia, near Chicago, Illinois, USA, is presented. The physics goals of the program itself, the Tevatron accelerator design characteristics and some of its achievements are described. A selected set of the past and ongoing physics analyses and measurements performed by CDF and D0 collaborations are summarized. Also, in view of the modified plans and schedule of the Large Hadron Collider (LHC) at CERN, the future of the Tevatron program is discussed.

abstract

This paper describes the performance of low energy electron reconstruction and identification at ATLAS with proton–proton collisions at a centre of mass energy of 7 TeV produced by the Large Hadron Collider. This study was performed with a sample collected from April to June 2010, corresponding to an integrated luminosity of 78 \(\textrm {nb}^{-1}\). We present the reconstruction of prompt \(J/\psi \) mesons decaying into \(e^+e^-\) pairs. These electrons can be used to study the detector performance at low energy, as a complement of higher energy electrons coming from \(W\) and \(Z\) decays. A sample of \(\sim 220\) \(J/\psi \) events can be selected. Their mass values reconstructed with different inputs agree with the values expected from the initial calibration of the ATLAS detector. The kinematics and shower shape distributions (used for identification purpose) have been extracted from the \(J/\psi \) data sample and show a good agreement with the simulation.

abstract

Quarkonia and open heavy flavour production are crucial to study the properties of the nuclear matter at high energy densities and of the Quark Gluon Plasma (QGP). In proton–proton collisions at LHC, the measurement of their production cross-section will allow to test perturbative QCD calculations in a new energy regime and provide the baseline for measurements in heavy ion collisions. In the latter, as they experience the full evolution of the collision, heavy quarks are ideal probes to study the property of the system. During the 2010 campaign of the LHC, ALICE took proton–proton data at \(\sqrt {s}=7\) TeV and Pb–Pb data at \(\sqrt {s_{nn}}=2.76\) TeV. The first physics results on heavy flavors production in \(p\)–\(p\) collisions are presented combining hadronic and (semi-)leptonic channels, both at central and forward rapidity.

abstract

We discuss the new era of precision QCD as it relates to the physics requirements of the LHC for both the signal and background type processes. Some attention is paid to the issue of the theoretical error associated with any given theoretical prediction. In the cases considered, we present where the theory precision is at this writing and where it needs to go in order that it not impede the discovery potential of the LHC physics program. To complete the discussion, we also discuss possible paradigms the latter program may help us understand and some new developments that may play a role in achieving that respective understanding.

abstract

The status of Monte Carlo system for the simulation of bremsstrahlung in arbitrary decays and for the decay itself of \(\tau \)-lepton is reviewed. During the last \(\tau \)-lepton conference in 2010 several developments of the last two years have been presented: (i) For the TAUOLA Monte Carlo generator of \(\tau \)-lepton decays, automated and simultaneous use of many versions of form-factors for the calculation of optional weights for fits was developed and checked to work in Belle and BaBar software environment. On-going work on alternative parameterizations of hadronic decays is presented too. (ii) The TAUOLA universal interface based on HepMC (the C++ event record) is now public. A similar interface for PHOTOS is now also public. (iii) Extension of PHOTOS Monte Carlo for QED bremsstrahlung in decays featuring kernels based on complete first order matrix element are gradually becoming widely available thanks to properties of the new, HepMC based interface. (iv) Tests of the programs systematized with the help of MC-TESTER are now available for FORTRAN and C++ users. Since then, further progress has been achieved. In particular, first order matrix element for \(Z\) decay is now installed into publicly available version of PHOTOS Monte Carlo. New parameterizations of hadronic \(\tau \) decay currents, can now be confronted with the data. The programs found their first use for LHC applications too. Results presented here illustrate the status of the projects performed in collaboration with Nadia Davidson, Piotr Golonka, Gizo Nanava, Tomasz Przedziński, Olga Shekhovtsova, Elżbieta Richter-Wąs, Pablo Roig, Qingjun Xu and others.

abstract

Tau leptons provide a useful signature in searches for new physics phenomena in the ATLAS experiment, like Higgs bosons or supersymmetry. The Standard Model processes with tau leptons are important backgrounds in such searches and also can be used to calibrate the detector and demonstrate the performance of tau identification. The data collected at centre-of-mass energy of \(\sqrt {s} = 7\) TeV with the ATLAS detector are used to study the reconstruction and identification algorithms for hadronic tau decays. Their performance in data and Monte Carlo simulations is compared in dijet sample and good agreement is observed. The first observation of \(W \rightarrow \tau \nu \) decays in ATLAS is also presented. The observed yield over the total background is compatible with Standard Model signal expectation.

abstract

In 2010 the CMS experiment has collected about 40/pb of proton–proton collision data at \(\sqrt s=7\) TeV. This allowed us to perform several searches for physics beyond Standard Model. No significant excess has been found in any of these. As a result, limits extending previous experimental constraints has been set. Some of them are the most stringent to date. Representative subset of these searches is presented.

abstract

The reconstruction and identification of \(\tau \) leptons are important in physics analysis of Standard Model (SM) processes and searches for new phenomena. In this paper the comparison of distributions of identification variables between data and Monte Carlo samples is done, using the initial dataset collected by the ATLAS detector at a centre-of-mass energy of \(\sqrt {s} = 7\) TeV, corresponding to an integrated luminosity of 244 nb\(^{-1}\). As the number of recorded \(\tau \) leptons is small, the background jets reconstructed as \(\tau \)-lepton candidates can be used to check the algorithm performance. The background efficiency suppression is tested on a QCD dijet data sample using cut-based \(\tau \) identification criteria. Multivariate methods, such as boosted decision trees and projective likelihood, are also tested to check their background rejection performance.

abstract

The Large Hadron Collider accelerates and collides both proton beams and lead beams to the highest energies available in the laboratory. One of the most important global characteristics of such collisions is the multiplicity of produced particles. The ATLAS detector registers passage of charged particles using silicon detectors over a pseudorapidity range of about 5 pseudorapidity units. Several methods of reconstruction of the charged particle multiplicity and angular distribution were developed. These methods range from the full reconstruction of particles and their momenta to an estimate of the number of charged particles based on counting hits registered in a single layer of the Pixel detector. First results obtained from experimental data for \(p+p\) interactions and performance studies for heavy ion collisions based on Monte Carlo simulations are discussed.