Colin Bernet

A bstract The discovery by the ATLAS and CMS experiments of a new boson with mass around 125 GeV and with measured properties compatible with those of a Standard-Model Higgs boson, coupled with the absence of discoveries of phenomena beyond the Standard Model at the TeV scale, has triggered interest in ideas for future Higgs factories. A new circular e + e − collider hosted in a 80 to 100 km tunnel, TLEP, is among the most attractive solutions proposed so far. It has a clean experimental environment, produces high luminosity for top-quark, Higgs boson, W and Z studies, accommodates multiple detectors, and can reach energies up to the $$ \mathrm{t}\overline{\mathrm{t}} $$ threshold and beyond. It will enable measurements of the Higgs boson properties and of Electroweak Symmetry-Breaking (EWSB) parameters with unequalled precision, offering exploration of physics beyond the Standard Model in the multi-TeV range. Moreover, being the natural precursor of the VHE-LHC, a 100 TeV hadron machine in the same tunnel, it builds up a long-term vision for particle physics. Altogether, the combination of TLEP and the VHE-LHC offers, for a great cost effectiveness, the best precision and the best search reach of all options presently on the market. This paper presents a first appraisal of the salient features of the TLEP physics potential, to serve as a baseline for a more extensive design study.

First measurements of the Collins and Sivers asymmetries of charged hadrons produced in deep-inelastic scattering of muons on a transversely polarized 6-LiD target are presented. The data were taken in 2002 with the COMPASS spectrometer using the muon beam of the CERN SPS at 160 GeV/c. The Collins asymmetry turns out to be compatible with zero, as does the measured Sivers asymmetry within the present statistical errors.

We present a measurement of the deuteron spin-dependent structure function g1d based on the data collected by the COMPASS experiment at CERN during the years 2002–2004. The data provide an accurate evaluation for Γ1d, the first moment of g1d(x), and for the matrix element of the singlet axial current, a0. The results of QCD fits in the next to leading order (NLO) on all g1 deep inelastic scattering data are also presented. They provide two solutions with the gluon spin distribution function ΔG positive or negative, which describe the data equally well. In both cases, at Q2=3(GeV/c)2 the first moment of ΔG(x) is found to be of the order of 0.2–0.3 in absolute value.

The measurements of the Collins and Sivers asymmetries of identified hadrons produced in deep-inelastic scattering of 160 GeV/c muons on a transversely polarised 6LiD target at COMPASS are presented. The results for charged pions and charged and neutral kaons correspond to all data available, which were collected from 2002 to 2004. For all final state particles both, the Collins and Sivers asymmetries turn out to be small, compatible with zero within the statistical errors, in line with the previously published results for not identified charged hadrons, and with the expected cancellation between the u- and d-quark contributions.

New high precision measurements of the Collins and Sivers asymmetries of charged hadrons produced in deep-inelastic scattering of muons on a transversely polarised 6LiD target are presented. The data were taken in 2003 and 2004 with the COMPASS spectrometer using the muon beam of the CERN SPS at 160 GeV/c. Both the Collins and Sivers asymmetries turn out to be compatible with zero, within the present statistical errors, which are more than a factor of 2 smaller than those of the published COMPASS results from the 2002 data. The final results from the 2002, 2003 and 2004 runs are compared with naive expectations and with existing model calculations.

We report the first measurement using a solid polarized target of the neutron electric form factor G(n)(E) via d-->(e-->,e(')n)p. G(n)(E) was determined from the beam-target asymmetry in the scattering of longitudinally polarized electrons from polarized deuterated ammonia ( 15ND3). The measurement was performed in Hall C at Thomas Jefferson National Accelerator Facility in quasifree kinematics with the target polarization perpendicular to the momentum transfer. The electrons were detected in a magnetic spectrometer in coincidence with neutrons in a large solid angle segmented detector. We find G(n)(E) = 0.04632+/-0.00616(stat)+/-0.00341(syst) at Q2 = 0.495 (GeV/c)(2).

We present a new measurement of the longitudinal spin asymmetry A1d and the spin-dependent structure function g1d of the deuteron in the range 1<Q2<100GeV2 and 0.004<x<0.7. The data were obtained by the COMPASS experiment at CERN using a 160 GeV polarised muon beam and a large polarised 6LiD target. The results are in agreement with those from previous experiments and improve considerably the statistical accuracy in the region 0.004<x<0.03.

The semi-inclusive difference asymmetry Ah+−h− for hadrons of opposite charge has been measured by the COMPASS experiment at CERN. The data were collected in the years 2002–2004 using a 160 GeV polarised muon beam scattered off a large polarised 6LiD target in the kinematic range 0.006<x<0.7 and 1<Q2<100(GeV/c)2. In leading order QCD (LO) the deuteron asymmetry Ah+−h− measures the valence quark polarisation and provides an evaluation of the first moment of Δuv+Δdv which is found to be equal to 0.40±0.07(stat.)±0.06(syst.) over the measured range of x at Q2=10(GeV/c)2. When combined with the first moment of g1d previously measured on the same data, this result favours a non-symmetric polarisation of light quarks Δu¯=−Δd¯ at a confidence level of two standard deviations, in contrast to the often assumed symmetric scenario Δu¯=Δd¯=Δs¯=Δs.

The charge asymmetry in the production of top quark and antiquark pairs is measured in proton-proton collisions at a center-of-mass energy of 8 TeV. The data, corresponding to an integrated luminosity of 19.6 inverse femtobarns, were collected by the CMS experiment at the LHC. Events with a single isolated electron or muon, and four or more jets, at least one of which is likely to have originated from hadronization of a bottom quark, are selected. A template technique is used to measure the asymmetry in the distribution of differences in the top quark and antiquark absolute rapidities. The measured asymmetry is A[c,y] = [0.33 +/- 0.26 (stat) +/- 0.33 (syst)]%, which is the most precise result to date. The results are compared to calculations based on the standard model and on several beyond-the-standard-model scenarios.

We present a precise measurement of the deuteron longitudinal spin asymmetry A1d and of the deuteron spin-dependent structure function g1d at Q2<1(GeV/c)2 and 4×10−5<x<2.5×10−2 based on the data collected by the COMPASS experiment at CERN during the years 2002 and 2003. The statistical precision is tenfold better than that of the previous measurement in this region. The measured A1d and g1d are found to be consistent with zero in the whole range of x.

Recent results on the gaseous microstrip detector Micromegas which will be used to track particles in the COMPASS experiment at CERN are presented. Developments concerning its mechanical and electrical design, associated readout electronics and gas mixture were carried out. Particular attention was paid to the discharge phenomenon which affects this type of microstrip detector. The adequacy of the options finally retained, especially the SFE16 readout and the use of a Ne–C2H6–CF4 gas mixture, was demonstrated in a set of beam tests performed on a 26×36cm2 prototype. Operating at a gain of ∼6400, full efficiency is reached along with a spatial resolution of ∼50μm and a timing accuracy of 8.5ns. Discharges are kept at a low rate, less than one per SPS spill in a COMPASS-like environment. Via a decoupling of the strips through individual capacitors their impact is greatly reduced. They generate a dead time on the full detector of ∼3ms, affecting marginally the detection efficiency given their rate. The probability of discharge, at a given value of efficiency, is found to decrease with the mean value of the gas mixture atomic number. In view of these results, the commissioning of Micromegas for COMPASS is foreseen in the near future.

The response of the CMS barrel calorimeter (electromagnetic plus hadronic) to hadrons, electrons and muons over a wide momentum range from 2 to 350 GeV/c has been measured. To our knowledge, this is the widest range of momenta in which any calorimeter system has been studied. These tests, carried out at the H2 beam-line at CERN, provide a wealth of information, especially at low energies. The analysis of the differences in calorimeter response to charged pions, kaons, protons and antiprotons and a detailed discussion of the underlying phenomena are presented. We also show techniques that apply corrections to the signals from the considerably different electromagnetic (EB) and hadronic (HB) barrel calorimeters in reconstructing the energies of hadrons. Above 5 GeV/c, these corrections improve the energy resolution of the combined system where the stochastic term equals 84.7±1.6% and the constant term is 7.4±0.8%. The corrected mean response remains constant within 1.3% rms.

The measurements in the COMPASS experiment at CERN require high-resolution tracking detectors, with low radiation length and high-rate capability. For this purpose we have developed and optimized a gaseous microstrip detector `Micromegas'. Twelve planes with 1024 strips each, assembled in 3 stations of 4 views XYUV, are now being operated with success in the COMPASS environment. We describe here the performances and results obtained.

Calibration of the relative response of the individual channels of the barrel electromagnetic calorimeter of the CMS detector was accomplished, before installation, with cosmic ray muons and test beams. One fourth of the calorimeter was exposed to a beam of high energy electrons and the relative calibration of the channels, the intercalibration, was found to be reproducible to a precision of about 0.3%. Additionally, data were collected with cosmic rays for the entire ECAL barrel during the commissioning phase. By comparing the intercalibration constants obtained with the electron beam data with those from the cosmic ray data, it is demonstrated that the latter provide an intercalibration precision of 1.5% over most of the barrel ECAL. The best intercalibration precision is expected to come from the analysis of events collected in situ during the LHC operation. Using data collected with both electrons and pion beams, several aspects of the intercalibration procedures based on electrons or neutral pions were investigated.

The longitudinal double spin asymmetry A1 ρ for exclusive leptoproduction of ρ0 mesons, μ+N→μ+N+ρ, is studied using the COMPASS 2002 and 2003 data. The measured reaction is incoherent exclusive ρ0 production on polarised deuterons. The Q2 and x dependence of A1 ρ is presented in a wide kinematical range, 3×10-3<Q2< 7 (GeV/c)2 and 5×10-5<x<0.05. The results presented are the first measurements of A1 ρ at small Q2 (Q2< 0.1 (GeV/c)2) and small x (x<3×10-3). The asymmetry is in general compatible with zero in the whole kinematical range.

Ensuring the radiation hardness of PbWO4 crystals was one of the main priorities during the construction of the electromagnetic calorimeter of the CMS experiment at CERN. The production on an industrial scale of radiation hard crystals and their certification over a period of several years represented a difficult challenge both for CMS and for the crystal suppliers. The present article reviews the related scientific and technological problems encountered.

The trigger system of the COMPASS experiment at the CERN polarized muon beam is presented. It detects muon scattering events on (polarized) nucleons with a relative energy loss exceeding a selectable value ymin independent of the four-momentum transfer. The requirement of a minimum energy deposit in a hadron calorimeter rejects background events like scattering on electrons, elastic and quasi-elastic radiative events as well as events from beam halo tracks. The trigger system which can be considered as a tagger for quasi-real photon events is now, along with larger trigger hodoscope system for deep inelastic scattering events, in regular use for the measurement of the gluon polarisation ΔG/G.

The measurements foreseen in the COMPASS experiment at CERN, require high resolution tracking detectors, with low radiation length and high rate capability. For this purpose we have developed and optimized a gaseous microstrip detector ‘Micromegas’. Twelve planes with 1024 strips each, assembled in 3 stations of 4 views XYUV, have been operated with success in the summer of 2002 in the COMPASS environment. We describe here the performances and results obtained.

A gas-chromatography-olfactometric detection (GCO) using a direct estimation of odor intensities with the finger span (FSCM) was used to establish aroma profiles of three wines of gewürztraminer from different ‘terroirs’ of the Alsace region. The GCO-FSCM analyses of their hydroalcoholic wine extracts were performed using a group of untrained assessors. Forty-four olfactory signals were perceived by at least four assessors out of six and their intensities were scored in triplicate in each of the three wine extracts, amongst which ten of them were found discriminant between wines. The reliability of each assessor was studied on the basis of the finger span estimation repeatability, from the number of discriminant variables and the mean finger span values found for the assessor. These untrained assessors appear to be able to achieve self-calibration from odor intensities without using any internal of external quantitative reference. The results suggest that GCO-FSCM may be performed by naive assessors to analyse and compare odor profiles of complex extracts without time-consuming training periods.

On July 4, 2012, the discovery of a new boson, with mass around 125 GeV/c2 and with properties compatible with those of a standard-model Higgs boson, was announced at CERN. In this context, a high-luminosity electron-positron collider ring, operating in the LHC tunnel at a centre-of-mass energy of 240 GeV and called LEP3, becomes an attractive opportunity both from financial and scientific point of views. The performance and the suitability of the CMS detector are evaluated, with emphasis on an accurate measurement of the Higgs boson properties. The precision expected for the Higgs boson couplings is found to be significantly better than that predicted by Linear Collider studies.

A search is performed for the production of a massive W′ boson decaying to a top and a bottom quark. The data analysed correspond to an integrated luminosity of 19.7 fb−1 collected with the CMS detector at the LHC in proton-proton collisions at $$ \sqrt{s}=8 $$ TeV. The hadronic decay products of the top quark with high Lorentz boost from the W′ boson decay are detected as a single top flavoured jet. The use of jet substructure algorithms allows the top quark jet to be distinguished from standard model QCD background. Limits on the production cross section of a right-handed W′ boson are obtained, together with constraints on the left-handed and right-handed couplings of the W′ boson to quarks. The production of a right-handed W′ boson with a mass below 2.02 TeV decaying to a hadronic final state is excluded at 95% confidence level. This mass limit increases to 2.15 TeV when both hadronic and leptonic decays are considered, and is the most stringent lower mass limit to date in the tb decay mode.

Between 2002 and 2006, the COMPASS high-rate experiment at CERN has been successful using the Micromegas technique to reach high performances in particle detection. The twelve 40 cm times 40 cm Micromegas planes, the largest gaseous micro-pattern detectors ever used to date in a high energy experiment, provide an excellent tracking device in the hottest part of the spectrometer, even with the use of hadron beams. The detectors see a total flux of 30 MHz, with rates reaching 5 kHz/mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> in the region close to the beam. So far, they have accumulated more than 1 mC/mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> in their central region without experiencing any damage.

We present the first measurement of the gluon polarisation in the nucleon based on the photon-gluon fusion process tagged by charmed meson production and decay to charged K and pi. The data were collected in polarised muon scattering off a polarised deuteron target by the COMPASS collaboration at CERN during 2002-2004. The result of this LO analysis is _x = -0.47 +- 0.44 (stat) +- 0.15 (syst) at ~= 0.11 and a scale mu^2 ~ 13 (GeV/c)^2.

We have developed and built 12 planes of large-size (40/spl times/40 cm/sup 2/) MICROMEGAS detectors. These detectors were installed at CERN and successfully operated during the first year of the COMPASS data taking. All important detector parameters: space and time resolutions, discharge probabilities, noise figure and experimental efficiencies were found to agree with the design values.

Searches for supersymmetry were conducted using the 35 pb-1 of data collected by the CMS experiment at the LHC in 2010, at a centre-of-mass energy of 7 TeV. A wide variety of final states featuring jets and missing transverse energy, possibly with leptons, were investigated. The data, consistent with the standard-model hypothesis, allow us to set limits on the existence of new physics, extending those previously obtained at the Tevatron and LEP.

The COMPASS experiment will determine the gluon polarization in the nucleon $\Delta G/G$ from the double helicity asymmetry measured in the scattering of a 160 GeV muon beam on a longitudinally polarized deuteron target, by selecting the photon-gluon fusion reaction. This reaction can be tagged either by the production of open charm, or by the production of high $p_T$ hadron pairs. The first asymmetry obtained with the latter method is presented.

We present a preliminary measurement of the gluon polarization ΔG/G in the nucleon, based on the spin asymmetry of quasi‐real photoproduction events for which a pair of large transverse momentum hadrons is produced. The data were obtained by the COMPASS experiment at CERN using a 160 GeV polarized muon beam scattered on a large polarized 6LiD target. The preliminary helicity asymmetry for the selected events is A∥/D = 0.002 ± 0.019(stat.) ± 0.003(exp.syst.). From this value, a leading order analysis based on the model of PYTHIA leads to the gluon polarization in the nucleon ΔG/G(xg = 0.095, μ2 = 3 GeV2) = 0.024 ± 0.089(stat.) ± 0.057(syst.). This value is consistent with parameterizations obtained from QCD fits to the g1 data, with a first moment ΔG ≡ ∫01 ΔG(x)dx ≃ 0.5, at the same scale.

A search for massive resonances decaying to a Z boson and a photon is performed in events with a hadronically decaying Z boson candidate, separately in light-quark and b quark decay modes, identified using jet substructure and advanced b tagging techniques. Results are based on samples of proton-proton collisions collected with the CMS detector at the LHC at center-of-mass energies of 8 and 13 TeV, corresponding to integrated luminosities of 19.7 and 2.7 inverse femtobarns, respectively. The results of the search are combined with those of a similar search in the leptonic decay modes of the Z boson, based on the same data sets. Spin-0 resonances with various widths and with masses in a range between 0.2 and 3.0 TeV are considered. No significant excess is observed either in the individual analyses or the combination. The results are presented in terms of upper limits on the production cross section of such resonances and constitute the most stringent limits to date for a wide range of masses.

The inelastic hadronic cross section in proton-lead collisions at a centre-of-mass energy per nucleon pair of 5.02 TeV is measured with the CMS detector at the LHC. The data sample, corresponding to an integrated luminosity of 12.6 +/- 0.4 inverse nanobarns, has been collected with an unbiased trigger for inclusive particle production. The cross section is obtained from the measured number of proton-lead collisions with hadronic activity produced in the pseudorapidity ranges 3<abs(eta)<5 and/or -5<abs(eta)<-3, corrected for photon-induced contributions, experimental acceptance, and other instrumental effects. The inelastic cross section is measured to be sigma[inel,pPb]=2061 +/- 3 (stat) +/- 34 (syst) +/- 72 (lum) mb. Various Monte Carlo generators, commonly used in heavy ion and cosmic ray physics, are found to reproduce the data within uncertainties. The value of sigma[inel,pPb] is compatible with that expected from the proton-proton cross section at 5.02 TeV scaled up within a simple Glauber approach to account for multiple scatterings in the lead nucleus, indicating that further net nuclear corrections are small.

Searches for supersymmetry were conducted using the 35 pb-1 of data collected by the CMS experiment at the LHC in 2010, at a centre-of-mass energy of 7 TeV. A wide variety of final states featuring jets and missing transverse energy, possibly with leptons, were investigated. The data, consistent with the standard-model hypothesis, allow us to set limits on the existence of new physics, extending those previously obtained at the Tevatron and LEP.

A measurement of the ttbar production cross section at sqrt(s)=13 TeV is presented using proton-proton collisions, corresponding to an integrated luminosity of 2.3 inverse femtobarns, collected with the CMS detector at the LHC. Final states with one isolated charged lepton (electron or muon) and at least one jet are selected and categorized according to the accompanying jet multiplicity. From a likelihood fit to the invariant mass distribution of the isolated lepton and a jet identified as coming from the hadronization of a bottom quark, the cross section is measured to be sigma(ttbar)= 835 +/- 3 (stat) +/- 23 (syst) +/- 23 (lum) pb, in agreement with the standard model prediction. Using the expected dependence of the cross section on the pole mass of the top quark (m[t]), the value of m[t] is found to be 172.7+2.4-2.7 GeV.

The COMPASS experiment will determine the gluon polarization in the nucleon $ΔG/G$ from the double helicity asymmetry measured in the scattering of a 160 GeV muon beam on a longitudinally polarized deuteron target, by selecting the photon-gluon fusion reaction. This reaction can be tagged either by the production of open charm, or by the production of high $p_T$ hadron pairs. The first asymmetry obtained with the latter method is presented.