• Volume 79, Issue 5

November 2012,   pages  941-1344

• Recent neutrino oscillation results from T2K

The Tokai-to-Kamioka (T2K) experiment studies neutrino oscillations in a $\sim 600$ MeV muon neutrino beam sent at 295 km from the Japan Proton Accelerator Complex (J-PARC) to the Super Kamiokande (SK) detector in Kamioka. The primary goals of T2K are to search for the appearance of electron neutrinos at SK resulting from $\theta_{13} &gt; 0$ and to precisely measure $\theta_{23}$ and $\Delta m_{32}^{2}$ via $\nu_{\mu}$ disappearance. We report on T2K results obtained from neutrino data taken in 2010 and 2011.

• Long-baseline experiments, now and soon!

The new results available this year from a number of neutrino experiments bring into stronger focus the details in the `Standard Model' of neutrino oscillations described by the PMNS mixing matrix. However, the parameters are still not known to very high precision. The next few years look bright for accelerator neutrino experiments, with much action occurring in the near future. We still have to wait a little longer, however, to be sure, but making educated guesses is needed to make plans for the future.

• Towards a $\theta_{13}$ measurement

Reactor-based antineutrino experiments hold the promise of providing an unambiguous determination of the neutrino mixing angle $\theta_{13}$. At present, Daya Bay, Double Chooz and RENO are such experiments being set up for this purpose. In this paper, the status and prospects of these three initiatives are presented.

• Neutrino mass and mixing – status

The status of neutrino oscillations from global data are summarized. An update on the three-flavour picture and recent developments are discussed with regard to the measurement of the mixing angle $\theta_{13}$. Global data currently provide an indication at $3\sigma$ that $\theta_{13}$ is non-zero. Furthermore, the status of sterile neutrino oscillation interpretations of the LSND anomaly in the light of MiniBooNE results and a recent re-evaluation of the neutrino fluxes from nuclear reactors are discussed. Despite several hints for sterile neutrinos at the eV scale, there is severe tension in the global data and no consistent description of all data is possible.

• Whither colliders after the Large Hadron Collider?

This paper presents options for high-energy colliders at the energy frontier for the years to come. The immediate plans include the exploitation of the LHC at its design luminosity and energy as well as upgrades to the LHC (luminosity and energy) and to its injectors. This may be complemented by a linear electron–positron collider, based on the technology being developed by the Compact Linear Collider and by the International Linear Collider, by a high-energy electron– proton machine, the LHeC, and/or by a muon collider. This contribution describes the various future directions, all of which have a unique value to add to experimental particle physics, and concludes by outlining the key messages for the way forward.

• India-based Neutrino Observatory

The current status of the India-based Neutrino Observatory (INO) is summarized. The main physics goals are described followed by the motivation for building a magnetized iron calorimetric (ICAL) detector. The charge identification capability of ICAL would make it complementary to large water Cerenkov and other detectors worldwide. The status of the design of the 50 kt magnet, the construction of a prototype ICAL detector, the experience with resistive plate chambers which will be the active elements in ICAL and the status of the associated electronics and data acquisition system are discussed.

• Indirect searches for dark matter

The current status of indirect searches for dark matter has been reviewed in a schematic way here. The main relevant experimental results of the recent years have been listed and the excitements and disappointments that their phenomenological interpretations in terms of almost-standard annihilating dark matter have brought along have been discussed. The main sources of uncertainties that affect this kind of searches are also listed.

[Report number: Saclay T11/206, CERN-PH-TH/2011-257, extended version in arXiv:1202.1454], [Prepared for the Proceedings of Lepton–Photon 2011, Mumbai, India, 22–27 Aug. 2011].

• Review of dark matter direct detection experiments

Matter, as we know it, makes up less than 5% of the Universe. Various astrophysical observations have confirmed that one quarter of the Universe and most of the matter content in the Universe is made up of dark matter. The nature of dark matter is yet to be discovered and is one of the biggest questions in physics. Particle physics combined with astrophysical measurements of the abundance gives rise to a dark matter candidate called weakly interacting massive particle (WIMP). The low density of WIMPs in the galaxies and the extremely weak nature of the interaction with ordinary matter make detection of the WIMP an extraordinarily challenging task, with abundant fakes from various radioactive and cosmogenic backgrounds with much stronger electromagnetic interaction. The extremely weak nature of the WIMP interaction dictates detectors that have extremely low naturally occurring radioactive background, a large active volume (mass) of sensitive detector material to maximize statistics, a highly efficient detector-based rejection mechanism for the dominant electromagnetic background and sophisticated analysis techniques to reject any residual background. This paper reviews currently available major technologies being pursued by various collaborations, with special emphasis on the cryogenic Ge detector technology used by the Cryogenic Dark Matter Search Collaboration (CDMS).

• The information paradox: Conflicts and resolutions

Many relativists have been long convinced that black hole evaporation leads to information loss or remnants. String theorists have however not been too worried about the issue, largely due to a belief that the Hawking argument for information loss is flawed in its details. A recently derived inequality shows that the Hawking argument for black holes with horizon can in fact be made rigorous. What happens instead is that in string theory, black hole microstates have no horizons. Thus the evolution of radiation quanta with $E \sim kT$ is modified by order unity at the horizon, and we resolve the information paradox.

• Applications of the AdS/CFT correspondence

In this writeup of a talk delivered at the Lepton Photon Conference 2011, applications of the AdS/CFT correspondence in diverse areas of physics are reviewed.

• Overview of the Cabibbo–Kobayashi–Maskawa matrix†

The current status of the determination of the elements of the Cabibbo–Kobayashi–Maskawa quark-mixing matrix is reviewed. Tensions in the global fits are highlighted. Particular attention is paid to the progress in, and prospects for, measurements of CP violation effects.

• 𝐵-physics results from the Large Hadron Collider

An overview of the first 𝐵-physics results from the LHC is presented, among which are various aspects of 𝑏 production, rare 𝐵 decays and CP violation.

• Some theoretical issues in heavy flavour physics

Some of the recent developments in heavy flavour physics will be reviewed. This will include an update on some of the Standard Model predictions, and a summary of recent measurements that may indicate the presence of new physics (NP). The focus will be on selected models of NP that are indicated by the anomalies in the current data. Observables that can potentially yield signatures of specific physics beyond the Standard Model will be pointed out.

• Charged-lepton flavour physics

This write-up on a talk at the 2011 Lepton–Photon symposium in Mumbai, India, summarizes recent results in the charged-lepton flavour sector. Searches for charged-lepton flavour violation, lepton electric dipole moments and flavour-conserving CP violation are reviewed here. Recent progress in 𝜏 -lepton physics and in the Standard Model prediction of the muon anomalous magnetic moment is also discussed.

• Summary of Lepton–Photon 2011

In this paper, developments presented at the Lepton–Photon 2011 Conference are summarized and a perspective on the current situation in high-energy physics is given.

• Search with the ATLAS detector for new physics with significant missing transverse energy and two isolated leptons

Results of searches for supersymmetry in events with significant missing transverse energy and two isolated leptons with the ATLAS experiment at the LHC are presented. Three analyses are presented here, the first two are analyses with leptons of opposite charge and same charge, respectively. The third one is an analysis that searches for an excess of same-flavour oppositecharge lepton pairs over those of different-flavour. Data corresponding to an integrated luminosity of 1 fb-1 are analysed.

• Search for anomalous $W \;tb$ couplings in single top quark production at D0

The large mass of the top quark, close to the electroweak symmetry-breaking scale, makes it a good candidate for probing physics beyond the Standard Model, including possible anomalous couplings. D0 has made measurements of single top quark production using 5.4 fb-1 of integrated luminosity. The data are examined to study the Lorentz structure of the $W tb$ coupling. It is found that the data prefer the left-handed vector coupling and set upper limits on the anomalous couplings.

• Measurement of single top production in $pp$ collisions at 7 TeV with the CMS detector

The measurement of 𝑡-channel single top cross-section in proton–proton collisions at the Large Hadron Collider (LHC) at a centre-of-mass energy of 7 TeV, using data collected with the Compact Muon Solenoid (CMS) experiment during the year 2010 is presented. Both the electronneutrino and muon-neutrino decay channels of 𝑊 boson from top decay are considered. Two complementary multivariate analysis methods to separate signal and background and to extract the cross-section for the single top produced in 𝑡-channel are explored. The result is compared with the most precise Standard Model theory predictions.

• $W^{\pm} Z$ production in $pp$ collisions at 7 TeV with ATLAS

The measurement of the $W^{\pm} Z$ production cross-section in proton–proton interactions at $\sqrt{s} = 7$ TeV is reported from the ATLAS experiment at the Large Hadron Collider using 1.02 fb-1 of data. The measurement is derived from events with leptonically decaying bosons with electrons, muons, and missing energy in the final state. Limits on anomalous triple gauge boson couplings are derived.

• Neutral current cross-section measurement at low $Q^{2}$ and high 𝑦 with the ZEUS detector at HERA

The measurements of the reduced cross-sections for $e^{+} p$ deep inelastic scattering at high inelasticities 𝑦 for three different centre-of-mass energies, 318, 251 and 225 GeV have been extended to lower momentum transferred squared, $Q^{2}$. The analysis of satellite vertex events allows one to extend the cross-section measurement at high y down to $Q^{2} = 4.5$ GeV2, substantially lower that the previously published cross-section measurement from which the longitudinal structure function, $F_{L}$, was extracted.

• Tau reconstruction and identification algorithm

CMS has developed sophisticated tau identification algorithms for tau hadronic decay modes. Production of tau lepton decaying to hadrons are studied at 7 TeV centre-of-mass energy with 2011 collision data collected by CMS detector and has been used to measure the performance of tau identification algorithms by measuring identification efficiency and misidentification rates from electrons, muons and hadronic jets. These algorithms enable extended reach for the searches for MSSM Higgs, 𝑍 and other exotic particles.

• ATLAS fast physics monitoring

The ATLAS experiment at the Large Hadron Collider is recording data from proton–proton collisions at a centre-of-mass energy of 7 TeV since the spring of 2010. The integrated luminosity has grown nearly exponentially since then and continues to rise fast. The ATLAS Collaboration has set up a framework to automatically process the rapidly growing dataset and produce performance and physics plots for the most interesting analyses. The system is designed to give fast feedback. The histograms are produced within hours of data reconstruction (2–3 days after data taking). Hints of potentially interesting physics signals obtained this way are followed up by physics groups.

• Main injector particle production experiment at Fermilab

The main injector particle production (MIPP) experiment at Fermilab uses particle beams of charged pions, kaons, proton and antiproton with beam momenta of 5–90 GeV/c to measure particle production cross-sections of various nuclei including liquid hydrogen, MINOS target and thin targets of beryllium, carbon, bismuth and uranium. The physics motivation to perform such cross-section measurements is described here. Recent results on the analysis of NuMI target and forward neutron cross-sections are presented here. Preliminary cross-section measurements for 58 GeV/c proton on liquid hydrogen target are also presented. A new method is described to correct for low multiplicity inefficiencies in the trigger using KNO scaling.

• Single 𝑊 production in $e^{-} \gamma$ collisions through the decay lepton spectrum to probe $\gamma W W$ couplings

The effect of an anomalous $\gamma W W$ coupling in the $e^{-} \gamma \rightarrow \nu_{e} W^{-}$ process through the angular and energy spectrum of the secondary leptons is investigated. Within the narrowwidth-approximation (NWA), a semianalytical study of the secondary lepton energy angle double distribution is considered. Different observables constructed using this distribution are expected to be very effective to probe the anomalous coupling at a typical International Linear Collider machine. Further, suitable combinations of these observables could be used to disentangle the effect of contributions from different terms in the effective Lagrangian.

• 𝐵 decays to baryons

From inclusive measurements, it is known that about $7$% of all 𝐵 mesons decay into final states with baryons. In these decays, some striking features become visible compared to mesonic decays. The largest branching fractions come with quite moderate multiplicities of 3–4 hadrons. We note that two-body decays to baryons are suppressed relative to three- and four-body decays. In most of these analyses, the invariant baryon–antibaryon mass shows an enhancement near the threshold. We propose a phenomenological interpretation of this quite common feature of hadronization to baryons.

• Model unspecific search for new physics in $pp$ collision at $\sqrt{s} = 7$ TeV

We present the results of a model-independent analysis, which systematically scans the data taken by CMS for deviations from the Standard Model (SM) predictions. Due to the minimal theoretical bias, this approach is sensitive to a variety of models for new physics. Events with at least one electron or muon are classified according to their content of reconstructed objects (muons, electrons, photons, jets and missing transverse energy). A broad scan of three kinematic distributions in those classes is performed by identifying deviations from SM expectations, accounting for systematic uncertainties. In this particular search, no significant discrepancies have been observed in data taken by CMS in 2010 and corresponding to an integrated luminosity of 36.1 pb-1.

• Model-independent search for new physics at D0 experiment

Finding the evidence of new physics beyond the Standard Model is one of the primary goals of RunII of the Tevatron. Many dedicated searches for new physics are ongoing at the Tevatron but in order to broaden the scope and maximize the chances of finding the new physics, we also search in a model-independent way. The results of such searches for indications of new physics at the electroweak scale are presented using data collected using the D0 detector from $p\bar{p}$-interactions at $\sqrt{s} = 1.96$ TeV.

• Search for the Higgs boson in $H \rightarrow W W \rightarrow 2l2\nu$ mode with the CMS detector

A search is reported for the Higgs boson decaying to $W^{+} W^{−}$ in pp collisions at $\sqrt{s} = 7$ TeV. The analysis is performed using LHC data recorded by the CMS detector, corresponding to an integrated luminosity of 1.55 fb-1. No significant excess above the Standard Model background expectation is observed, and upper limits on Higgs boson production are derived, excluding the presence of a Higgs boson with a mass in the range of 147–194 GeV/c2 at the 95% confidence level (CL) using the CLs approach.

• Angular distribution of cosmic muons using INO–ICAL prototype detector at TIFR

The India-based Neutrino Observatory Collaboration is planning to set up a magnetized 50 kt iron calorimeter (ICAL) with resistive plate chambers (RPC) as active detectors to study neutrino oscillations and precisely measure its parameters. A prototype detector stack is set up at TIFR ($18^{\circ}54'$N, $72^{\circ}48'$E) to track cosmic ray muons. Using the muon data, angular distribution of cosmic ray muons at the sea level is studied here.

• Radiative see-saw formula in nonsupersymmetric $SO(10)$ with dark matter

In $SO(10)$, the type-I and type-II see-saw scales $\geqq 10^{12}$ GeV are far away from being probed by direct experimental tests. In the absence of supersymmetry, we show how experimentally verifiable radiative see-saw formula of Ma type is realized in non-SUSY $SO(10)$ while fulfilling the twin objectives: precision gauge coupling unification and dark matter. This model is expected to have a dramatic impact on neutrino physics, dark matter and all fermion masses and mixings.

• Top-spin analysis of new scalar and tensor interactions in $e^{+} e^{-}$ collisions with transverse beam polarization

The top polarization at the International Linear Collider (ILC) with transverse beam polarization is utilized in the $e^{+} e^{-} \rightarrow t\bar{t}$ process to probe interactions of the scalar and tensor type beyond the Standard Model and to disentangle their individual contributions. Confidence level limits of 90% are presented on the interactions with realistic integrated luminosity and are found to improve by an order of magnitude compared to the case when the spin of the top quark is not measured. Sensitivities of the order of a few times $10^{−3}$ TeV-2 for real and imaginary parts of both scalar and tensor couplings at $\sqrt{s} = 500$ and 800 GeV with an integrated luminosity of 500 fb-1 and completely polarized beams are shown to be possible.

• $B_{s}$ data at Tevatron and possible new physics

The new physics (NP) is parametrized with four model-independent quantities: the magnitudes and phases of the dispersive part $M_{12}$ and the absorptive part $\Gamma_{12}$ of the NP contribution to the effective Hamiltonian. We constrain these parameters using the four observables $\Delta M_{\text{s}}$, $\Delta \Gamma_{\text{s}}$, the mixing phase $\beta_{\text{s}}^{J/\psi \phi}$ and $A_{\text{sl}}^{b}$. This formalism is extended to include charge-parity-time reversal (CPT) violation, and it is shown that CPT violation by itself, or even in the presence of CPTconserving NP without an absorptive part, helps only marginally in the simultaneous resolution of these anomalies.

• $W/Z +$jet(s) production in pp collisions at $\sqrt{s} = 7$ TeV

The measurements of the cross-sections are presented for the production of jets in association with 𝑊 and 𝑍 bosons reconstructed in their decays to electrons and muons. The results are based on 36 pb-1 of $pp$ collisions at $\sqrt{s} = 7$ TeV collected by the CMS Collaboration. Jets are reconstructed with the CMS particle flow algorithm and must pass a transverse momentum threshold of 30 GeV. The study presents the ratios $\sigma (V + \geq n-{\text{jet}})/\sigma (V)$ and $\sigma (V + \geq n-{\text{jet}})/\sigma(V + \geq (n - 1)-{\text{jet}}).$ The comparison between the data and the Monte Carlo prediction is also showed.

• Search for a SM Higgs boson in dilepton plus missing transverse energy final state with the DØ detector at $\sqrt{s} = 1.96$ TeV

A search is presented for the Standard Model (SM) Higgs boson optimized in the decay channel $H \rightarrow W^{+} W^{−}$, where both 𝑊 bosons decay leptonically. The final state considered contains dileptons and missing transverse energy from the neutrinos. A multivariate analysis is used to suppress the background. No significant excess above the SM background has been observed and limits set on the Higgs boson production cross-section $∗$ the branching ratio for $m_{H} = 115–200$ GeV are computed. Results using 8.1 fb$^{−1} of data are presented. • Anomalous top magnetic couplings The real and imaginary parts of the one-loop electroweak contributions to the left and right tensorial anomalous couplings of the$tbW$vertex in the Standard Model (SM) are computed. • Top polarization and exploration of$t\bar{t}$forward–backward asymmetry The large forward–backward asymmetry in top pair-production observed at the Tevatron has generated much excitement in recent times.Many different models have been proposed as possible explanations for this anomaly. We discuss how the measurement of the polarization of the top quark can be used to establish the role of new physics in generating the observed asymmetry and to characterize and discriminate among various models. • Quantifying uncertainties in the high-energy neutrino cross-section The predictions for high-energy neutrino and antineutrino deep inelastic scattering cross-sections are compared within the conventional DGLAP formalism of next-to-leading order QCD, using the latest parton distribution functions (PDF) such as CT10, HERAPDF1.5 and MSTW08 and taking account of PDF uncertainties. From this, a benchmark cross-section and uncertainty are derived which is consistent with the results obtained earlier using the ZEUS-S PDFs. The use of this is advocated for analysing data from neutrino telescopes, in order to facilitate comparison between their results. • Triggering on hadronic tau decays: ATLAS meets the challenge Hadronic tau decays play a crucial role in taking Standard Model (SM) measurements as well as in the search for physics beyond the SM. However, hadronic tau decays are difficult to identify and trigger on due to their resemblance to QCD jets. Given the large production crosssection of QCD processes, designing and operating a trigger system to efficiently select hadronic tau decays, while maintaining the rate within the bandwidth limits, is a difficult challenge. This contribution will summarize the status and performance of the ATLAS tau trigger system during the 2010–2011 data taking period. Different methods that have been explored to obtain the trigger efficiency curves from data will be shown. Finally, the status of the measurements, which include hadronic tau decays in the final state, will be summarized. In light of the vast statistics collected in 2011, future prospects for triggering on hadronic tau decays in this exciting new period of increased instantaneous luminosity will be presented. • Event shape variables in supersymmetry searches at 7 TeV LHC Supersymmetry (SUSY) signatures are probed at the Large Hadron Collider with 7 TeV energy in the framework of CMSSM with a new set of cuts based on event shapes and jet energy scales. It is showed that with our cuts, it is possible to probe a large portion of CMSSM parameter space in situations, where the SUSY cascade decay chain produces hard multijets + missing energy. We also extend our analysis to include other supersymmetries which produce hard multijets + missing energy. • The pion form factor from analyticity and unitarity Analyticity and unitarity techniques are employed to estimate Taylor coefficients of the pion electromagnetic form factor at$t = 0$by exploiting the recently evaluated two-pion contribution to the muon$(g − 2)$and the phase of the pion electromagnetic form factor in the elastic region, known from$\pi \pi$scattering by Fermi–Watson theorem and the values of the form factor at several points in the space-like region. Regions in the complex 𝑡-plane are isolated where the form factor cannot have zeros. • Search for the Standard Model Higgs boson in the decay channel$H \rightarrow ZZ^{(∗)} \rightarrow 4l$at CMS A search for the Standard Model (SM) Higgs boson in the decay channel$H \rightarrow ZZ^{(∗)} \rightarrow 4l$with each 𝑍 boson decaying to an electron or muon pair is presented using$pp$collisions from the LHC at$\sqrt{s} = 7$TeV. The data analysed correspond to an integrated luminosity of$1.66 \pm 0.07$fb-1 recorded by the CMS detector in 2010 and 2011. The search covers Higgs boson mass$(m_{\text{H}})$hypotheses of$110 &lt; m_{\text{H}} &lt; 600$GeV/c2. Twenty-one events are observed, while$21.2 \pm 0.8$events are expected from Standard Model (SM) background processes. The events are not clustered in mass excluding interpretation as the SM Higgs boson and its$(4l)$mass distribution is consistent with the expectation of SM continuum production of$ZZ^{(∗)}$pairs. Upper limits at 95% CL on the cross-section × branching ratio for a SM Higgs boson with SM like decays exclude cross-sections from about once to twice the expected SM cross-section for masses in the range of$150 &lt; m_{\text{H}}&lt; 420$GeV/c2. • Measurement of neutral current cross-sections at high Bjorken-𝑥 with the ZEUS detector at HERA A new method is employed to measure the neutral current cross-section up to Bjorken 𝑥 values of 1 with the ZEUS detector at HERA using an integrated luminosity of 187 pb-1 of electron–proton collisions and 142 pb-1 of positron–proton collisions, at a centre-of-mass energy of 318 GeV. Cross-sections have been extracted for$Q^{2}$&gt; 575 GeV2. A much improved precision with respect to the previous ZEUS publication, which used only 16.7 pb-1 of electron–proton collisions and 65.1 pb-1 of positron–proton collisions, is achieved, owing to the large data sample and improved kinematic reconstruction methods. The measurement is well-described by different theory predictions. • Low-energy neutrino and dark matter physics with sub-keV germanium detectors The TEXONO-CDEX Collaboration (Taiwan experiment on neutrino–China dark matter experiment) explores high-purity germanium (HPGe) detection technology to develop a sub-keV threshold detector for pursuing studies on low mass weakly interacting massive particles (WIMPs), properties of neutrino and the possibilities of neutrino-nucleus coherent scattering observation. This article will introduce the facilities of newly established China Jing-Ping Underground Laboratory (CJPL), preliminary result of cosmic ray background studies at CJPL, the dark matter studies pursued at Kuo-Sheng Neutrino Laboratory (KSNL) and research efforts to accomplish our physics goals. • Tau reconstruction, energy calibration and identification at ATLAS Tau leptons play a central role in the LHC physics programme, in particular as an important signature in many Higgs boson and supersymmetry searches. They are further used in Standard Model electroweak measurements, as well as detector-related studies like the determination of the missing transverse energy scale. Copious backgrounds from QCD processes call for both efficient identification of hadronically decaying tau leptons, as well as large suppression of fake candidates. A solid understanding of the combined performance of the calorimeter and tracking detectors is also required. We present the current status of the tau reconstruction, energy calibration and identification with the ATLAS detector at the LHC. Identification efficiencies are measured in$W \rightarrow \tau \nu$events in data and compared with predictions from Monte Carlo simulations, whereas the misidentification probabilities of QCD jets and electrons are determined from various jet-enriched data samples and from$Z \rightarrow ee$events, respectively. The tau energy scale calibration is described and systematic uncertainties on both energy scale and identification efficiencies discussed. • Search for a Higgs boson decaying into two photons in the CMS detector A search for a Higgs boson decaying into two photons in$pp\$ collisions at the LHC at a centre-of-mass energy of 7 TeV is presented. The analysis is performed on a dataset corresponding to 1.66 fb-1 of data recorded in 2011 by the CMS experiment. Limits are set on the cross-section of a Standard Model Higgs boson decaying into two photons, and on the cross-section of a fermiophobic Higgs boson decaying into two photons.

• # Pramana – Journal of Physics

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• # Editorial Note on Continuous Article Publication

Posted on July 25, 2019