V. Brigljević

The CMS detector at the CERN LHC features a silicon pixel detector as its innermost subdetector. The original CMS pixel detector has been replaced with an upgraded pixel system (CMS Phase-1 pixel detector) in the extended year-end technical stop of the LHC in 2016/2017. The upgraded CMS pixel detector is designed to cope with the higher instantaneous luminosities that have been achieved by the LHC after the upgrades to the accelerator during the first long shutdown in 2013–2014. Compared to the original pixel detector, the upgraded detector has a better tracking performance and lower mass with four barrel layers and three endcap disks on each side to provide hit coverage up to an absolute value of pseudorapidity of 2.5. This paper describes the design and construction of the CMS Phase-1 pixel detector as well as its performance from commissioning to early operation in collision data-taking.

The formation of the η′ in the reaction e+e−→e+e−η′→e+e−π+π−γ has been measured by the L3 detector at a centre-of-mass energy of 91GeV. The radiative width of the η′ has been found to be Γγγ=4.17±0.10(stat.)±0.27(sys.)keV. The Q2 dependence of the η′ formation cross section has been measured for Q2≤10GeV2 and the η′ electromagnetic transition form factor has been determined. The form factor can be parametrised by a pole form with Λ=0.900±0.046(stat.)±0.022(sys.)GeV. It is also consistent with recent non-perturbative QCD calculations.

We analyse e+e−→ττγ events using 100pb−1 of data collected by the L3 experiment during the 1991-1995 LEP runs at the Z pole. From the energy of the photons and their isolation from the tau decay products, we determine the anomalous magnetic and electric dipole moments of the tau to be, respectively: aτ=0.004±0.027±0.023;dτ=(0.0±1.5±1.3)×10−16e·cm.This is a direct measurement of these τ form factors at q2=0.

The paper presents the dose mapping of the panoramic 60Co gamma irradiation facility at the Ruđer Bošković Institute in Croatia. Both experimental (using ionisation chamber) and simulation (using the Geant4 Monte Carlo code) studies have been performed and compared. Measured and simulation dose rates are found to be in very good agreement and can be used for the absorbed dose determination in the irradiation chamber in everyday work. In order to get a complete description of the dose distribution in the facility, the transit dose, which has to be taken into consideration at low doses, was also experimentally determined.

Using a data sample of 1 475 000 Z → qq̄(γ) events collected during 1994 with the L3 detector at LEP, we have studied the purely leptonic decays of heavy flavour mesons, Ds− → τ−ντ and B− → τ−ντ. A signal is observed in the invariant mass distribution M(γDs−) corresponding to the decay sequence D∗− → γDs−, Ds− → τ−ντ, τ− → l−νlντ. The branching fraction for Ds− → τ−ντ decays is measured to be β(Ds− → τ−ντ) = 0.074 ± 0.028(stat) ± 0.016(syst) ± 0.018(norm). No signal of B− → τ−ντ decays is observed in the data, corresponding to an upper limit on the branching franction β(B− → τ−ντ) < 5.7 × 10−4 at 90% CL.

The measurements of hadron and lepton-pair production cross sections and leptonic forward–backward asymmetries performed with the L3 detector at centre-of-mass energies between 130 GeV and 189 GeV are used to search for new physics phenomena such as: contact interactions, exchange of virtual leptoquarks, scalar quarks and scalar neutrinos, effects of TeV strings in models of quantum gravity with large extra dimensions and non-zero sizes of the fermions. No evidence for these phenomena is found and new limits on their parameters are set.

We report the result of a search for charginos and neutralinos, in e+e− collisions at 189 GeV centre-of-mass energy at LEP. No evidence for such particles is found in a data sample of 176 pb−1. Improved upper limits for these particles are set on the production cross sections. New exclusion contours in the parameter space of the Minimal Supersymmetric Standard Model are derived, as well as new lower limits on the masses of these supersymmetric particles. Under the assumptions of common gaugino and scalar masses at the GUT scale, we set an absolute lower limit on the mass of the lightest neutralino of 32.5 GeV, and a limit on the mass of the lightest chargino of 67.7 GeV for M2<2TeV.

We present a study of the inclusive production of π0, η, Ks0 and Λ based on 929,000 hadronic Z decays recorded with the L3 detector at LEP. The measured inclusive momentum distributions have been compared with predictions from parton shower models as well as an analytical Quantum Chromodynamics calculation. Comparing to low energy e+e- data, we find that QCD describes the energy evolution of the hadron spectrum.

We report on the measurement of the leptonic and hadronic cross sections and leptonic forward-backward asymmetries at theZ peak with the L3 detector at LEP. The total luminosity of 40.8 pb−1 collected in the years 1990, 1991 and 1992 corresponds to 1.09·106 hadronic and 0.98·105 leptonicZ decays observed. These data allow us to determine the electroweak parameters. From the cross sections we derive the properties of theZ boson: $$\begin{gathered} M_Z = 91195 \pm 9MeV\Gamma _{\rm Z} = 2494 \pm 10MeV \hfill \\ \Gamma _{had} = 1748 \pm 10MeV\Gamma _\ell = 83.49 \pm 0.46MeV \hfill \\ \end{gathered} $$ assuming lepton universality. We obtain an invisible width of Γinv=496.5±7.9 MeV which, in the Standard Model, corresponds to a number of light neutrino species ofN v=2.981±0.050. Using also the three leptonic forward-backward asymmetries and the average tau polarization, we determine the effective vector and axial-vector coupling constants of the neutral weak current to charged leptons to be: $$\bar g^\ell v = - 0.0378_{ - 0.0042}^{ + 0.0045} \bar g^\ell _A = - 0.4998 \pm 0.0014.$$ Within the framework of the Standard Model, and including our measurements of the $$Z \to b\bar b$$ forward-backward asymmetry and partial decay width, we derive an effective electroweak mixing angle of $$sin^2 \bar \theta _W = 0.2326 \pm 0.0012$$ . We obtain an estimate for the strong coupling constant, αS=0.142 ± 0.013 and for the top-quark mass,m t =158 −40 +32 ±19(Higgs) GeV, where the second error arises due to the uncertainty in the Higgs-boson mass.

The results of the searches for neutral Higgs boson production in the process e+e− → Z∗ H0 are reported, focusing on Higgs boson masses below 70 GeV. The data sample consists of three million hadronic Z0 decays collected by the L3 experiment at LEP from 1991 through 1994. No signal is found leading to a lower limit on the mass of the Standard Model Higgs boson of 60.2 GeV at 95% C.L. These results are also interpreted in the framework of the General Two Doublet Model and limits on the nonstandard Higgs boson production through the process e+e− → Z∗h0 are set. A lower limit of 66.7 GeV at 95% C.L. is obtained for the case where the Higgs decays into an invisible final state.

Recent theories propose that quantum gravity effects may be observable at LEP energies via gravitons that couple to Standard Model particles and propagate into extra spatial dimensions. The associated production of a graviton and a photon is searched for as well as the effects of virtual graviton exchange in the processes: e+e- -> gamma gamma, ZZ, WW, mu mu, tau tau, qq and ee No evidence for this new interaction is found in the data sample collected by the L3 detector at LEP at centre-of-mass energies up to 183 GeV. Limits close to 1 TeV on the scale of this new scenario of quantum gravity are set.

The hadronic photon structure function Fγ2 is studied in the reaction e+e−→e+e−hadrons at LEP with the L3 detector. The data, collected from 1991 to 1995 at a centre-of-mass energy s≃91 GeV, correspond to an integrated luminosity of 140 pb−1. The photon structure function Fγ2 is measured in the Q2 interval 1.2 GeV2 ≤Q2≤9.0 GeV2 and the x interval 0.002<x<0.2. Fγ2 shows a linear growth with lnQ2. The value of the slope α−1dFγ2(Q2)/dlnQ2 is measured to be 0.079±0.011±0.009.

We have searched for neutralinos produced via the reactions e+e− → χχ′ and e+e−→ χ′χ′, where the next-to lightest neutralino, χ′, decays into the lightest neutralino, χ, and either a photon or a fermion pair. Based on 1.8 × 106 hadronic Z decays collected with the L3 detector at LEP, no signal has been observed. We present upper limits of a few times 10−5 on the branching ratios Z → χχ′ and Z → χ′χ′. In the framework of the Minimial Supersymmetric Standard Model, we exclude a lightest χ with mχ less than 18 GeV, if either tan β > 2 or the gluino mass m≈g > 100 GeV.

We present a study of the structure of hadronic events recorded by the L3 detector at center-of-mass energies of 130 and 136 GeV. The data sample corresponds to an integrated luminosity of 5 pb−1 collected during the high energy run of 1995. The shapes of the event shape distributions and the energy dependence of their mean values are well reproduced by QCD models. From a comparison of the data with resummed O(αs2) QCD calculations, we determine the strong coupling constant to be αs(133 GeV) = 0.107 ± 0.005(exp) ± 0.006(theor).

Extra spatial dimensions are proposed by recent theories that postulate the scale of gravity to be of the same order as the electroweak scale. A sizeable interaction between gravitons and Standard Model particles is then predicted. Effects of these new interactions in boson and fermion pair production are searched for in the data sample collected at centre-of-mass energies above the Z pole by the L3 detector at LEP. In addition, the direct production of a graviton associated with a Z boson is investigated. No statistically significant hints for the existence of these effects are found and lower limits in excess of 1 TeV are derived on the scale of this new theory of gravity.

The reaction e+e− → e+e−γ∗γ∗ → e+e− hadrons is analysed using data collected by the L3 detector during the LEP runs at s = 130−140 GeV and s = 161 GeV. The cross sections σ(e+e− → e+e− hadrons) and σ(γγ → hadrons) are measured in the interval 5 ≤ Wγγ ≤ 75 GeV. The energy dependence of the σ(γγ → hadrons) cross section is consistent with the universal Regge behaviour of total hadronic cross sections.

Single and multi-photon events with missing energy are analysed using data collected with the L3 detector at LEP at a centre-of-mass energy of 189 GeV, for a total of 176 pb^{-1} of integrated luminosity. The cross section of the process e+e- -> nu nu gamma (gamma) is measured and the number of light neutrino flavours is determined to be N_\nu = 3.011 +/- 0.077 including lower energy data. Upper limits on cross sections of supersymmetric processes are set and interpretations in supersymmetric models provide improved limits on the masses of the lightest neutralino and the gravitino. Graviton-photon production in low scale gravity models with extra dimensions is searched for and limits on the energy scale of the model are set exceeding 1 TeV for two extra dimensions.

Measurements of the two-photon interaction e+e− → e+e− + hadrons at s≃ 91GeV and s≃ 183GeV are presented. The double-tag events, collected with the L3 detector, correspond to interated luminosities of 140 pb−1 at 91 GeV and 52 pb−1 at 183 GeV. The cross-section of γ∗γ∗ collisions has been measured at 〈Q2〉 = 3.5 GeV2 and 〈Q2〉 = 14 GeV2. The data agree well with predictions based on perturbative QCD, while the Quark Parton Model alone is insufficient to describe the data.

We report on the measurement of W-boson pair-production with the L3 detector at LEP at a centre-of-mass energy of 161.34 GeV. In a data sample corresponding to a total luminosity of 11 pb−1, we select four-fermion events with high invariant masses of pairs of hadronic jets or leptons. Combining all final states, the measured total cross section for W-pair production is: sigmaWW = 2.89−0.70+0.81(stat.) ± 0.14 (syst.) pb. Within the Standard Model, this corresponds to a mass of the W boson of: MW = 80.80−0.42+0.48 (exp.) ± 0.03 (LEP) GeV. Limits on anomalous triple-vector-boson couplings are derived.

A search for the Standard Model Higgs boson has been performed with the L3 detector at LEP. The data sample was collected at three centre-of-mass energies, 161.3, 170.3 and 172.3 GeV with integrated luminosities of 10.8, 1.0 and 9.2 pb, respectively. No Higgs signal is observed. In combination with previous data taken at the Z resonance, a lower Higgs mass limit, MH > 69.5 GeV, is obtained at 95% confidence level.

We measure Bose-Einstein correlations between like-sign charged pion pairs in hadronic Z decays with the L3 detector at LEP. The analysis is performed in three dimensions in the longitudinal center-of-mass system. The pion source is found to be elongated along the thrust axis with a ratio of transverse to longitudinal radius of $0.81\pm 0.02 ^{+0.03}_{-0.19}$.

Total and differential cross sections for the process e+e− → γγ(γ), and the total cross section for the process e+e− → γγγ, are measured at energies around 91 GeV using the data collected with the L3 detector from 1991 to 1993. We set lower limits, at 95% CL, on a contact interaction energy scale parameter Λ > 602 GeV, on the mass of an excited electron me∗>146GeV and on the QED cut-off parameters Λ+ > 149 GeV and Λ_ > 143 GeV. Upper limits are also set o branching fractions of Z decaying into γγ, π° and ηγ of 5.2 × 10−5, 5.2 × 10−5 and 7.6 × 10−5 respectively. The reactions e+e− → ℓ+ℓ−nγ (ℓ = e, μ, τ) are studied using the data collected from 1990 to 1994. The data are consistent with the QED expectations.

A measurement of the inclusive charmless semileptonic branching fraction of beauty hadrons, b→Xuℓν, has been performed using almost two million hadronic Z decays collected by the L3 experiment at LEP, yielding the result: Br(b→Xuℓν)=(3.3±1.0±1.7)×10−3. The first uncertainty is statistical and the second is systematic. The modulus of the Cabibbo-Kobayashi-Maskawa matrix element Vub extracted from this measurement is: |Vub|=(6.0+0.8−1.0+1.4−1.9±0.2)×10−3, where the uncertainties are statistical, systematic and theoretical, respectively.

We present a study of the structure of hadronic events recorded by the L3 detector at LEP at the center of mass energies of 161 and 172 GeV. The data sample corresponds to an integrated luminosity of 21.25 pb−1 collected during the high energy runs of 1996. The distributions of event shape variables and the energy dependence of their mean values are well reproduced by QCD models. From a comparison of the data with resummed O(αs2) QCD calculations, we determine the strong coupling constant at the two energies. Combining this with our earlier measurements we find that the strong coupling constant decreases with increasing energy as expected in QCD.

With a data sample of 86 000 Z → τ+τ−(γ) events collected in 1990 through 1993 we have measured the polarization of τ-leptons as a function of the production polar angle using the following 1-prong τ decay modes: τ−→e−vevτ, τ−→π−(K−)vτ, τ−→ϱ−vτandτ−→a1−vτ. We obtain for the ratio vector to axial-vector weak neutral couplings for electrons gVe/gAe=0.0791±0.0099(stat)±0.0025 (syst) and taus gVτ/gAτ=0.0752±0.0063 (stat)±0.0045 (syst) consistent with the hypothesis of e - τ universality. Assuming universality of the e - τ neutral current we determine the effective electroweak mixing angle to be sin2 θeffw = 0.2309 ± 0.0016.

We report the observation of $823\ifmmode\pm\else\textpm\fi{}57$ ${B}^{0}$ and $970\ifmmode\pm\else\textpm\fi{}65$ ${B}^{+}$ decays to doubly charmed final states ${D}^{(*)}{D}^{(*)}K,$ where ${D}^{(*)}$ and ${D}^{(*)}$ are fully reconstructed and K is either a ${K}^{\ifmmode\pm\else\textpm\fi{}}$ or a ${K}^{0}.$ We use a sample of $82.3\ifmmode\pm\else\textpm\fi{}0.9$ million $B\overline{B}$ events collected between 1999 and 2002 with the BABAR detector at the PEP-II storage ring at the Stanford Linear Accelerator Center. The 22 possible B decays to ${D}^{(*)}{D}^{(*)}K$ are reconstructed exclusively and the corresponding branching fractions or limits are determined. The branching fractions of the ${B}^{0}$ and of the ${B}^{+}$ to ${D}^{(*)}{D}^{(*)}K$ are found to be $\mathcal{B}{(B}^{0}\ensuremath{\rightarrow}{D}^{(*)}{D}^{(*)}K)=[4.3\ifmmode\pm\else\textpm\fi{}0.3(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}0.6(\mathrm{syst})]%,$ $\mathcal{B}{(B}^{+}\ensuremath{\rightarrow}{D}^{(*)}{D}^{(*)}K)=[3.5\ifmmode\pm\else\textpm\fi{}0.3(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}0.5(\mathrm{syst})]%.$ A search for decays to orbitally excited ${D}_{s}$ states, $\stackrel{\ensuremath{\rightarrow}}{B}{D}^{(*)}{D}_{\mathrm{sJ}}^{+}$ ${(D}_{\mathrm{sJ}}^{+}\ensuremath{\rightarrow}{D}^{(*)0}{K}^{+}),$ is also performed. No statistically significant contributions from ${D}_{s1}^{+}(2536)\ensuremath{\rightarrow}{D}^{*0}{K}^{+}$ and ${D}_{\mathrm{sJ}}^{+}(2573)\ensuremath{\rightarrow}{D}^{0}{K}^{+}$ to the ${D}^{(*)}{D}^{(*)0}{K}^{+}$ final state are found and we set 90% C.L. limits on their production rates.

We report on measurements of the triple-gauge-boson couplings of the W boson in e+e− collisions with the L3 detector at LEP. W-pair, single-W and single-photon events are analysed in a data sample corresponding to a total luminosity of 76.7 pb−1 collected at centre-of-mass energies between 161GeV and 183GeV. CP-conserving as well as both C- and P-conserving triple-gauge-boson couplings are determined. The results, in good agreement with the Standard-Model expectations, confirm the existence of the self coupling among the electroweak gauge bosons and constrain its structure.

We describe the sample of energetic single-photon events (Eγ > 15 GeV) collected by L3 in the 1991–1993 LEP runs. The event distributions agree with expectations from the Standard Model. The data are used to constrain the ZZγ coupling and to set an upper limit of 4.1 × 10−6, μB (90% C.L.) on the the magnetic moment of the τ neutrino.

The production of B∗ mesons in Z decays has been measured at LEP with the L3 detector. A sample of Z → bb events was obtained by tagging muons in 1.6 million hadronic Z decays collected in 1991, 1992 and 1993. A signal with a peak value of Eγ = 46.3 ± 1.9 (stat) MeV in the B rest frame energy spectrum was interpreted to come from the decay B∗ → γB. The inclusive production ratio of B∗ mesons relative to B mesons was determined from a fit to the spectrum to be NB∗(NB∗+ NB)= 0.76 ± 0.08 ± 0.06, where the first error is statistical and the second is systematic.

We measure the masses, decay widths and relative production rate of orbitally excited B mesons using 1.25 million hadronic Z decays recorded by the L3 detector. B-meson candidates are inclusively reconstructed and combined with charged pions produced at the primary event vertex. An excess of events above the expected background in the B\pi mass spectrum in the region 5.6-5.8 GeV is interpreted as resulting from the decay B_u,d^** -> B^(*)\pi, where B_u,d^** denotes a mixture of l=1 B-meson states containing a u or a d quark. A fit to the mass spectrum yields the masses and decay widths of the B_1^* and B_2^* spin states, as well as the branching fraction for the combination of l=1 states. In addition, evidence is presented for the existence of an excited B-meson state or mixture of states in the region 5.9-6.0 GeV.

We report on the first measurements of e+e− annihilations into hadrons and lepton pairs at centre-of-mass energies between 130 GeV and 140 GeV. In a total luminosity of 5 pb−1 collected with the L3 detector at LEP we select 1577 hadronic and 401 lepton-pair events. The measured cross sections and leptonic forward-backward asymmetries agree well with the Standard Model predictions.

The BaBar experiment at PEPII relies on the instrumentation of the flux return (IFR) for both muon identification and KL detection. The active detector is composed of resistive plate chambers (RPCs) operated in streamer mode. Since the start of operation the RPCs have suffered persistent efficiency deterioration and dark current increase problems. The “autopsy” of bad BaBar RPCs revealed that in many cases uncured linseed oil droplets had formed on the inner surface of the Bakelite plates, leading to current paths from oil “stalagmites” bridging the 2 mm gap. In this paper, a possible model of this “stalagmite” formation and its effect on the dark current and efficiency of RPC chambers is presented. Laboratory test results strongly support this model. Based upon this model we are searching for solutions to eliminate the unfavorable effect of the oil stalagmites. The lab tests show that the stalagmite resistivity increases dramatically if exposed to the air, an observation that points to a possible way to remedy the damage and increase the efficiency. We have seen that flowing an oxygen gas mixture into the chamber helps to polymerize the uncured linseed oil. Consequently, the resistivity of the bridged oil stalagmites increases, as does that of the oil coating on the frame edges and spacers, significantly reducing the RPC dark currents and low-efficiency regions. We have tested this idea on two chambers removed from BaBar because of their low efficiency and high dark current. These test results are reported in the paper, and two other remediation methods also mentioned. We continue to study this problem, and try to find new treatments with permanent improvement.

Using the L3 detector, the branching ratio BR(b → πνX) has been measured using a sample of Z → bb events tagged by high momentum and high transverse momentum leptons in one hemisphere and with missing energy in the opposite hemisphere. From a sample of 948 000 hadronic events we find BR(b → πνX) = (2.4 ± 0.7 (stat.) ± 0.8 (syst.))%.

A search for rare charmless decays of Bd0 and Bs0 mesons has been performed in the exclusive channels Bd(s)0 →ηη, Bd(s)0 →ηπ0 and Bd(s)0 →π0π0. The data sample consisted of three million hadronic Z decays collected by the L3 experiment at LEP from 1991 through 1994. No candidate event has been observed and the following upper limits at 90% confidence level on the branching ratios have been set: Br(B()d→ηη) <4.1 x 10−4, Br(B()s→ηη) < 1.5 x 10−3, Br(B()d→ηφ()) < 2.5 x 10−4, Br(B()s→ηphi;()) < 1.0 x 10−3, Br(B()d→phi;()phi;()) < 6.0 x 10−5, Br(B()s→phi;()phi;()) < 2.1 x 10−4. These are the first experimental limits on Bd0→ηη and on the Bs0 neutral charmless modes.

We report on measurements of the mass and total decay width of the W boson with the L3 detector at LEP. W-pair events produced in $\mathrm{e^+e^-}$ interactions between 161 GeV and 183 GeV centre-of-mass energy are selected in a data sample corresponding to a total luminosity of 76.7 pb$^{-1}$. Combining all final states in W-pair production, the mass and total decay width of the W boson are determined to be $\mathrm{M_W}=80.61\pm0.15$ GeV and $\Gamma_{\mathrm{W}}=1.97\pm0.38$ GeV, respectively.

We present results obtained from a study of the structure of hadronic events recorded by the L3 detector at various centre-of-mass energies. The distributions of event shape variables and the energy dependence of their mean values are measured from 30GeV to 189GeV and compared with various QCD models. The energy dependence of the moments of event shape variables is used to test a power law ansatz for the non-perturbative component. We obtain a universal value of the non-perturbative parameter alpha_0 = 0.537 +/- 0.073. From a comparison with resummed O(alpha_s^2) QCD calculations, we determine the strong coupling constant at each of the selected energies. The measurements demonstrate the running of alpha_s as expected in QCD with a value of alpha_s(m_Z) = 0.1215 +/- 0.0012 (exp) +/- 0.0061 (th).

The structure functions of real and virtual photons are derived from cross section measurements of the reaction e+e−→e+e−+ hadrons at LEP. The reaction is studied at s≃91GeV with the L3 detector. One of the final state electrons is detected at a large angle relative to the beam direction, leading to Q2 values between 40 GeV2 and 500 GeV2. The other final state electron is either undetected or it is detected at a four-momentum transfer squared P2 between 1 GeV2 and 8 GeV2. These measurements are compared with predictions of the Quark Parton Model and other QCD based models.

A new CMS tracker detector will be installed for operation at the High Luminosity LHC (HL-LHC). This detector comprises modules with two closely spaced parallel sensor plates and front-end ASICs capable of transmitting tracking information to the CMS Level-1 (L1) trigger at the 40 MHz beam crossing rate. The inclusion of tracking information in the L1 trigger decision will be essential for selecting events of interest efficiently at the HL-LHC. The CMS Binary Chip (CBC) has been designed to read out and correlate hits from pairs of tracker sensors, forming so-called track stubs. For the first time, a prototype irradiated module and a full-sized module, both equipped with the version 2 of the CBC, have been operated in test beam facilities. The efficiency of the stub finding logic of the modules for various angles of incidence has been studied. The ability of the modules to reject tracks with transverse momentum less than 2 GeV has been demonstrated. For modules built with irradiated sensors, no significant drop in the stub finding performance has been observed. Results from the beam tests are described in this paper.

To cope with the challenging environment of the planned high luminosity upgrade of the Large Hadron Collider (HL-LHC), scheduled to start operation in 2029, CMS will replace its entire tracking system. The requirements for the tracker are largely determined by the long operation time of 10 years with an instantaneous peak luminosity of up to 7.5 × 1034 cm−2 s−1 in the ultimate performance scenario. Depending on the radial distance from the interaction point, the silicon sensors will receive a particle fluence corresponding to a non-ionising energy loss of up to Φeq= 3.5 × 1016 cm−2. This paper focuses on planar pixel sensor design and qualification up to a fluence of Φeq = 1.4 × 1016 cm−2.For the development of appropriate planar pixel sensors an R&D program was initiated, which includes n+-p sensors on 150 mm (6”) wafers with an active thickness of 150 µm with pixel sizes of 100×25 µm2 and 50×50 µm2 manufactured by Hamamatsu Photonics K.K. (HPK). Single chip modules with ROC4Sens and RD53A readout chips were made. Irradiation with protons and neutrons, as well was an extensive test beam campaign at DESY were carried out. This paper presents the investigation of various assemblies mainly with ROC4Sens readout chips. It demonstrates that multiple designs fulfil the requirements in terms of breakdown voltage, leakage current and efficiency. The single point resolution for 50×50 µm2 pixels is measured as 4.0 µm for non-irradiated samples, and 6.3 µm after irradiation to Φeq = 7.2 × 1015 cm−2.

Abstract The Large Hadron Collider at CERN will undergo an upgrade in order to increase its luminosity to 7.5 × 10 34 cm -2 s -1 . The increased luminosity during this High-Luminosity running phase, starting around 2029, means a higher rate of proton-proton interactions, hence a larger ionizing dose and particle fluence for the detectors. The current tracking system of the CMS experiment will be fully replaced in order to cope with the new operating conditions. Prototype planar pixel sensors for the CMS Inner Tracker with square 50 μm × 50 μm and rectangular 100 μm × 25 μm pixels read out by the RD53A chip were characterized in the lab and at the DESY-II testbeam facility in order to identify designs that meet the requirements of CMS during the High-Luminosity running phase. A spatial resolution of approximately 3.4 μm (2 μm) is obtained using the modules with 50 μm × 50 μm (100 μm × 25 μm) pixels at the optimal angle of incidence before irradiation. After irradiation to a 1 MeV neutron equivalent fluence of Φ eq = 5.3 × 10 15 cm -2 , a resolution of 9.4 μm is achieved at a bias voltage of 800 V using a module with 50 μm × 50 μm pixel size. All modules retain a hit efficiency in excess of 99% after irradiation to fluences up to 2.1 × 10 16 cm -2 . Further studies of the electrical properties of the modules, especially crosstalk, are also presented in this paper.

A search for single and multi-photon events with missing energy is performed using data collected at centre-of-mass energies between 161 GeV and 172 GeV for a total of 20.9 pb−1 of integrated luminosity. The results obtained are used to derive the value for the ννγ(γ) cross section as well as upper limits on new physics processes.

The two-photon width Γγγ of the ηc meson has been measured with the L3 detector at LEP. The ηc is studied in the decay modes π+π−π+π−, π+π−K+K−, K0sK±π∓, K+K−π0, π+π−η, π+π−η′, and ρ+ρ− using an integrated luminosity of 140 pb−1 at s≃91 GeV and of 52 pb−1 at s≃183 GeV. The result is Γγγ(ηc)=6.9±1.7stat±0.8sys±2.0(BR) keV. The Q2 dependence of the ηc cross section is studied for Q2<9 GeV2. It is found to be better described by a Vector Meson Dominance model form factor with a J-pole than with a ρ-pole. In addition, a signal of 29±11 events is observed at the χc0 mass. Upper limits for the two-photon widths of the χc0, χc2, and ηc′ are also given.

The pair production of Z bosons is studied using the data collected by the L3 detector at LEP in 1998 in e+e- collisions at a centre-of-mass energy of 189 GeV. All the visible final states are considered and the cross section of this process is measured to be 0.74 +0.15 -0.14 (stat.) +/- 0.04 (syst.) pb. Final states containing b quarks are enhanced by a dedicated selection and their production cross section is found to be 0.18 +0.09 -0.07 (stat.) +/- 0.02 (syst.) pb. Both results are in agreement with the Standard Model predictions. Limits on anomalous couplings between neutral gauge bosons are derived from these measurements.

A study of resonance formation is presented in the π+π−π0 final state in two-photon collisions at LEP. The a2(1320) radiative width is measured to be Λγγ = 0.98 ± 0.05 ± 0.09 keV. The helicity 2 production is dominant. Exclusive π+π−π0 production has also been studied in the mass region above the a2 in the ϱπ and f2π channels. This region is dominated by a JP = 2+ helicity 2 wave.

Bhabha scattering data recorded at \sqrt{s}=189 GeV by the L3 detector at LEP are used to measure the running of the effective fine-structure constant for spacelike momentum transfers. The results are alpha^-1(-2.1 GeV^2) - alpha^-1(-6.25 GeV^2) = 0.78 +/- 0.26 alpha^-1(-12.25 GeV^2) - alpha^-1(-3434 GeV^2) = 3.80 +/- 1.29, in agreement with theoretical predictions.

Two-photon formation of the charmonium resonance χc2 has been studied with the L3 detector at LEP. The χc2 is identified through its decay χc2→γJ/ψ, with a subsequent decay J/ψ→e+e− or J/ψ→μ+μ−. With an integrated luminosity of 140 pb−1 at s≃ 91 GeV and 52 pb−1 at s≃ 183 GeV, we measure the two-photon width of the χc2 to be Γγγ(χc2)=1.02±0.40(stat.)±0.15(sys.)±0.09(BR.)keV.

A study of neutral-current four-fermion processes is performed using a data sample corresponding to 55.3 pb−1 of integrated luminosity collected by the L3 detector at LEP at an average centre-of-mass energy of 183 GeV. The neutral-current four-fermion cross sections for final states with a pair of charged leptons plus jets and with four charged leptons are measured to be consistent with the Standard Model predictions. Events with fermion pair masses close to the Z boson mass are selected in all observable final states and the ZZ production cross section is measured to be σZZ=0.30+0.22+0.07−0.16−0.03 pb, in agreement with the Standard Model expectation. No evidence for the existence of anomalous triple gauge boson ZZZ and ZZγ couplings is found and limits on these couplings are set.

Using the data collected by the L3 experiment at LEP from 1991 to 1995 at energies around the Z mass, a measurement of the weak anomalous magnetic dipole moment, awτ, and of the weak electric dipole moment, dwτ, of the τ lepton is performed. These quantities are obtained from angular distributions in e+e−→τ+τ−→h+ν̄τh−ντ, where h is a π or a ρ. The results are: Re(awτ)=(0.0±1.6±2.3)×10−3, Im(awτ)=(−1.0±3.6±4.3)×10−3 and Re(dwτ)=(−0.44±0.88±1.33)×10−17e·cm. This is the first direct measurement of awτ.

The three different helicity states of W bosons produced in the reaction e+ e- -> W+ W- -> l nu q q~ at LEP are studied using leptonic and hadronic W decays. Data at centre-of-mass energies \sqrt s = 183-209 GeV are used to measure the polarisation of W bosons, and its dependence on the W boson production angle. The fraction of longitudinally polarised W bosons is measured to be 0.218 \pm 0.027 \pm 0.016 where the first uncertainty is statistical and the second systematic, in agreement with the Standard Model expectation.

We search for anomalous ZZγ and Zγγ couplings with the L3 detector at LEP. The analysis is based on the study of the process e+e+→Zγ at center-of-mass energies in the range 161GeV<s<183GeV. No evidence for anomalous effects is found. Limits at the 95% confidence level are set on the values of the eight possible anomalous couplings. Depending on the type of coupling new physics scales below 213 GeV to 1083 GeV are excluded.

A search for the Standard Model Higgs boson is carried out on 176.4pb−1 of data collected by the L3 detector at a center-of-mass energy of 189 GeV. The data are consistent with the expectations of Standard Model processes and no evidence of a Higgs signal is observed. Combining the results of this search with those at lower center-of-mass energies, a lower limit on the mass of the Standard Model Higgs boson of 95.3 GeV is set at the 95% confidence level.

We report on the observation of single W boson production in a data sample collected by the L3 detector at LEP2. The signal consists of large missing energy final states with a single energetic lepton or two hadronic jets. The cross-section is measured to be 0.61−0.33+0.43 ± 0.05 pb at the centre of mass energy s = 172 GeV, consistent with the Standard Model expectation. From this measurement the following limits on the anomalo γWW gauge couplingsare derived at 95% CL: −3.6 < Δκγ < 1.5 and −3.6 < λγ < 3.6.

We report on the measurement of W-boson pair-production with the L3 detector at LEP. In a data sample corresponding to a total luminosity of 55.47 pb−1 collected at an average centre-of-mass energy of 182.68GeV, we select 824 four-fermion events with pairs of hadronic jets or pairs of leptons with high invariant masses. Branching fractions of W decays into different fermion-antifermion pairs are determined. Assuming charged-current lepton universality, the branching fraction for hadronic W decays is measured to be: B(W→hadrons)=70.1±1.3(stat.)±0.4(syst.)%. Combining all final states the total cross section for W-pair production is measured to be: σWW=16.53±0.67(stat.)±0.26(syst.) pb.

The BaBar experiment uses a big system based on RPC detectors to discriminate muons from pions and to identify neutral hadrons. About 2000m2 of RPC chambers have been working at SLAC since the end of 1998. We report on the performances of the RPC chambers focusing on new problems discovered in the RPC behaviour. These problems started very soon after the installation of the chambers on the detector when the high-ambient temperature triggered an increase of dark currents inside the chambers and a reduction of the efficiency. Careful analysis of the BaBar data and dedicated R&D efforts in the laboratory have helped to identify the main source of the trouble in the linseed oil varnish on the bakelite electrodes.

XDAQ is a generic data acquisition software environment that emerged from a rich set of of use-cases encountered in the CMS experiment. They cover not the deployment for multiple sub-detectors and the operation of different processing and networking equipment as well as a distributed collaboration of users with different needs. The use of the software in various application scenarios demonstrated the viability of the approach. We discuss two applications, the tracker local DAQ system for front-end commissioning and the muon chamber validation system. The description is completed by a brief overview of XDAQ.

Abstract The CMS Inner Tracker, made of silicon pixel modules, will be entirely replaced prior to the start of the High Luminosity LHC period. One of the crucial components of the new Inner Tracker system is the readout chip, being developed by the RD53 Collaboration, and in particular its analogue front-end, which receives the signal from the sensor and digitizes it. Three different analogue front-ends (Synchronous, Linear, and Differential) were designed and implemented in the RD53A demonstrator chip. A dedicated evaluation program was carried out to select the most suitable design to build a radiation tolerant pixel detector able to sustain high particle rates with high efficiency and a small fraction of spurious pixel hits. The test results showed that all three analogue front-ends presented strong points, but also limitations. The Differential front-end demonstrated very low noise, but the threshold tuning became problematic after irradiation. Moreover, a saturation in the preamplifier feedback loop affected the return of the signal to baseline and thus increased the dead time. The Synchronous front-end showed very good timing performance, but also higher noise. For the Linear front-end all of the parameters were within specification, although this design had the largest time walk. This limitation was addressed and mitigated in an improved design. The analysis of the advantages and disadvantages of the three front-ends in the context of the CMS Inner Tracker operation requirements led to the selection of the improved design Linear front-end for integration in the final CMS readout chip.

We report on measurements of e+e− annihilation into hadrons and lepton pairs. The data have been taken with the L3 detector at LEP at center-of-mass energies between 161 GeV and 172 GeV. In a data sample corresponding to 21.2 pb−1 of integrated luminosity 2728 hadronic and 868 lepton-pair events are selected. The measured cross sections and leptonic forward-backward asymmetries agree well with the Standard Model predictions.

We have analyzed one-prong τ decays with neutral kaons using the information from a fine-grained hadron calorimeter. The data sample consists of 43 500 Z → τ+τ−(γ) events collected by the L3 detector at LEP in 1991, 1992 and 1993. The following branching fractions are measured: B(τ− → ντπ−K0) = 0.0095 ± 0.0015(stat) ± 0.0006(syst); B(τ− → ντπ− π0K0) = 0.0041 ± 0.0012(stat) ± 0.0003(syst) and B(τ− → ντπ−K0K0) = 0.0031 ± 0.0012(stat) ± 0.0004(syst).

We have measured the time integrated B0B0 mixing parameter and the forward-backward asymmetry in the process e+e− → bb using hadronic events containing muons or electrons. The data sample corresponds to 1,044,000 hadronic decays of the Z. From a fit to the momentum and transverse momentum distributions for single lepton and dilepton events, we have determined the B0B0 mixing parameter to be χB = 0.123 ± 0.012 (stat.) ± 0.008 (sys.), and the bb forward-backward asymmetry at the effective center-of-mass energy √s = 91.30 GeV to be Abb = 0.087 ± 0.011 (stat.) ± 0.004 (sys.) This measurement corresponds to a value of the effective electroweak mixing angle of sin2θw = 0.2335 ± 0.0021.

The reaction e+e− → e+e−γ∗γ∗ → e+e−KS0KS0 is studied with the L3 detector at LEP and the formation of the f2′(1525) resonance is observed. For an integrated luminosity of 114 pb−1, 31±6 f2′ events are found. Their angular distribution is consistent with a pure helicity two. The radiative width times the branching ratio is measured to be Γγγ(f2′)×Br(f2′ → KK)=(0.093±0.018±0.022) keV. Only three events are found in the f2(1270)−a2(1320) mass region, consistent with destructive f2−a2 interference in the KS0KS0 final state. The mixing angle of the tensor meson nonet is determined to the θ = (29.4−1.6+1.4)°.

A measurement of the Ks0 and Λ inclusive production rates and momentum spectra in two- and three-jet events is presented. On the basis of about 3.1 million Z decays collected with the L3 detector at LEP, we observe that the production of these particles is well modelled by string fragmentation.

We have studied the structure of hadronic events with a hard, isolated photon in the final state (e+e− → Z → hadrons + γ) in the 3.6 million hadronic events collected with the L3 detector at centre-of-mass energies around 91 GeV. The centre-of-mass energy of the hadronic system is in the range 30 GeV to 86 GeV. Event shape variables have been measured at these reduced centre-of-mass energies and have been compared with the predictions of different QCD Monte Carlo programs. The event shape variables and the energy dependence of their mean values are well reproduced by QCD models. We fit distributions of several global event shape variables to resummed O(αs2) calculations to determine the strong coupling constant αs over a wide range of energies. We find that the strong coupling constant αs decreases with increasing energy, as expected from QCD.

The decays Bd0, Bs0 → e+e−, μ+μ−, e±μ∓ are searched for in 3.5 million hadronic Z events, which constitute the full LEP I data sample collected by the L3 detector. No signals are observed, therefore upper limits at the 90% (95%) confidence levels are set on the following branching fractions: Br(B0d→e+e−) < 1.4(1.8) × 10−5; Br(B0s→e+e−) < 5.4(7.0) × 10−5;Br(B0d→μ+μ−) < 1.0(1.4) × 10−5; Br(B0s→μ+μ−) < 3.8(5.1) × 10−5;Br(B0d→e±μ−∓) < 1.6(2.0) × 10−5; Br(B0s→e±e−∓) < 4.1(5.3) × 10−5; The results for Bs0 → e+e− and Bs0 → e±μ∓ are the first limits set on these decay modes.

We present a study of the inclusive ω and η′ production based on 3.1 million hadronic Z decays recorded with the L3 detector at LEP during 1991–1994. The production rates per hadronic Z decay have been measured to be 1.17±0.17 ω mesons and 0.25±0.04 η′ mesons. The production rates and the differential cross sections have been compared with predictions of the JETSET and the HERWIG Monte Carlo models. We have observed that the differential cross sections can be described by an analytical quantum chromodynamics calculation.

The Michel parameters ϱ, η, ξ, and ξδ, the chirality parameter ξh and the τ polarization Pτ are measured using 32012 τ pair decays. Their values are extracted from the energy spectra of leptons and hadrons in τ−→ l−νlντ and τ− → π−ντ decays, the energy and decay angular distributions in τ− → ϱ−ντ decays, and the correlations in the energy spectra and angular distributions of the decay products. Assuming universality in leptonic and semileptonic τ decays, the results are ϱ = 0.794±0.039±0.031, η = 0.25±0.17±0.11, ξ = 0.94±0.21±0.07, ξδ = 0.81±0.14±0.06, ξh = −0.970±0.053±0.011, and Pτ = −0.154±0.018±0.012. The measurement is in agreement with the V-A hypothesis for the weak charged current.

Using the data collected with the L3 detector at LEP between 1990 and 1995, corresponding to an integrated luminosity of 149 pb−1, the τ longitudinal polarisation has been measured as a function of the production polar angle using the τ decays τ−→h−ντ (h=π,ρ,a1) and τ−→ℓ−ν̄ℓντ (ℓ=e,μ). From this measurement the quantities Ae and Aτ, which depend on the couplings of the electron and the τ to the Z, are determined to be Ae=0.1678±0.0127±0.0030 and Aτ=0.1476±0.0088±0.0062, consistent with the hypothesis of e–τ universality. Under this assumption a value of Aℓ=0.1540±0.0074±0.0044 is obtained, yielding the value of the effective weak mixing angle sin2θW=0.2306±0.0011.

We report measurements of the inclusive production of heavy quarkonium states in Z decays based on the analysis of 3.6 million hadronic events collected by the L3 detector at LEP. The measurement of inclusive J production and an improved 95% confidence level upper limit on ϒ production are presented. In addition, two independent measurements of the ratio, fp, of prompt J mesons to those from B decay are made using two different isolation cuts to separate prompt J mesons from J mesons produced in the decays of b hadrons. The results are: Br(Z→J+X)=(3.21±0.21(stat.)+0.19−0.28(sys.))×10−3, Br(Z→ϒ(1S)+X)<4.4×10−5, fp=(7.1±2.1(stat.)±1.2(sys.)+1.5−0.8(theo.))×10−2 .

A search for heavy neutrinos that are isosinglets under the standard SU(2)L gauge group is made at center-of-mass energies 130<s<189 GeV with the L3 detector at LEP. Such heavy neutrinos are expected in many extensions of the Standard Model. The search is performed for the first generation heavy singlet neutrino, Ne, through the decay mode Ne→e+W. We set upper limits on the mixing parameter between the heavy and light neutrino for the heavy neutrino mass range from 80 GeV to 185 GeV.

During the high-luminosity phase of the LHC (HL-LHC), planned to start in 2027, the accelerator is expected to deliver an instantaneous peak luminosity of up to 7.5×1034 cm−2 s−1. A total integrated luminosity of 0300 or even 0400 fb−1 is foreseen to be delivered to the general purpose detectors ATLAS and CMS over a decade, thereby increasing the discovery potential of the LHC experiments significantly. The CMS detector will undergo a major upgrade for the HL-LHC, with entirely new tracking detectors consisting of an Outer Tracker and Inner Tracker. However, the new tracking system will be exposed to a significantly higher radiation than the current tracker, requiring new radiation-hard sensors. CMS initiated an extensive irradiation and measurement campaign starting in 2009 to systematically compare the properties of different silicon materials and design choices for the Outer Tracker sensors. Several test structures and sensors were designed and implemented on 18 different combinations of wafer materials, thicknesses, and production technologies. The devices were electrically characterized before and after irradiation with neutrons, and with protons of different energies, with fluences corresponding to those expected at different radii of the CMS Outer Tracker after 0300 fb−1. The tests performed include studies with β sources, lasers, and beam scans. This paper compares the performance of different options for the HL-LHC silicon sensors with a focus on silicon bulk material and thickness.

The status of the Silicon Microvertex Detector (SMD) and its installation into the LEP-I.3experiment are presented, highiighting novel features and sophisticated techniques.Preliminary results based on 1993 data are given and compared with Monte Carlo predictions, to understand the detector performances and its tracking capabilities.

An upper limit on the lifetime difference of short- and long-lived B0s mesons has been obtained using an inclusive bottom hadron sample from 2 million hadronic Z decays collected by the L3 experiment at LEP. A lifetime fit has been performed on data samples separately enriched in neutral and charged b hadrons. An experimental upper limit on the decay rate difference of short- and long-lived B0s mesons of (|ΔΓ|/Γ)B0s<0.67 (95% C.L.) has been determined. In addition, the lifetimes of B+ and B0d mesons have been measured to be τ(B+)=1.66±0.06±0.03ps and τ(B0d)=1.52±0.06±0.04ps, where the first errors are statistical and the second are systematic.

We report on a study of single W boson production in a data sample collected by the L3 detector at centre-of-mass energies from 130 to 183 GeV. The signal consists of large missing energy final states with a single energetic lepton or two hadronic jets. The measured cross sections at five different centre-of-mass energies are consistent with the Standard Model expectations. The following limits on the anomalous WWγ gauge couplings are derived at 95% CL: −0.46<Δκγ<0.57 and −0.86<λγ<0.75.

A search for the decays Bd,s0 → γγ in 2.95 million hadronic Z decays has been performed using the L3 detector at LEP. No candidates are found in the signal region and upper limits have been set on the branching ratios: Br(Bd0→γ)<3.9×10−5 and Br(Bs0 → γγ) < 14.8 × 10−5 at 90% CL. These are the first limits set on these exclusive rare decays.

We search for anomalous trilinear gauge couplings in the ZZγ and Zγγ vertices using data collected with the L3 detector at LEP at a centre-of-mass energy s=189GeV. No evidence is found and limits on these couplings and on new physics scales are derived from the analysis of the process e+e−→Zγ.

The BaBar Collaboration has operated an instrumented flux return (IFR) system covering over 2000m2 with resistive plate chambers (RPCs) for nearly 3 years. The chambers are constructed of bakelite sheets separated by 2mm. The inner surfaces are coated with linseed oil. This system provides muon and neutral hadron detection for BaBar. Installation and commissioning were completed in 1998, and operation began mid-year 1999. While initial performance of the system reached design, over time, a significant fraction of the RPCs demonstrated significant degradation, marked by increased currents and reduced efficiency. A coordinated effort of investigations have identified many of the elements responsible for the degradation. This article presents our current understanding of the aging process of the BaBar RPCs along with the action plan to combat performance degradation of the IFR system.

V. Brigljevic, G. Bruno, E. Cano, S. Cittolin, A. Csilling, D. Gigi, F. Glege, R. Gomez-Reino, M. Gulmini, J. Gutleber, C. Jacobs, M. Kozlovszky, H. Larsen, I. Magrans, F. Meijers, E. Meschi, S. Murray, A. Oh, L. Orsini, L. Pollet, A. Racz, D. Samyn, P. Scharff-Hansen, C. Schwick, P. Sphicas CERN, European Organization for Nuclear Research, Geneva, Switzerland Also at INFN, Laboratori Nazionali di Legnaro, Legnaro, Italy Also at University of Athens, Greece L. Berti, G. Maron, G. Rorato, N. Toniolo, L. Zangrando INFN, Laboratori Nazionali di Legnaro, Legnaro, Italy M. Bellato, S. Ventura INFN, Sezione di Padova, Padova, Italy S. Erhan University of California, Los Angeles, California, USA

Searches for scalar top and scalar bottom quarks have been performed at center-of-mass energies between 161 GeV and 183 GeV using the L3 detector at LEP. No signal is observed. Model-independent limits on production cross sections are determined for the two decay channels t̃1→cχ̃10 and b̃1→bχ̃10. Within the framework of the Minimal Supersymmetric extension of the Standard Model mass limits are derived. For mass differences between t̃1 and χ̃10 greater than 10 GeV a 95% C.L. limit of 81.5 GeV is set on the mass of the Supersymmetric partner of the left-handed top. A supersymmetric partner of the left-handed bottom with a mass below 80 GeV is excluded at 95% C.L. if the mass difference between b̃1 and χ̃10 is greater than 20 GeV.

The measurements of hadron and lepton-pair production cross sections and lepton-pair forward–backward asymmetries performed with the L3 detector at centre-of-mass energies between 130 GeV and 172 GeV are used to search for new physics phenomena. New physics effects involving four fermion vertices – contact interactions – are looked for in all channels. For hadron production the exchange of virtual leptoquarks and scalar quarks is studied. No evidence for deviations from the Standard Model expectations is found. Lower limits on the scale Λ of contact interactions in the range 1.2–7.1 TeV are obtained at the 95% confidence level for various models. Upper limits on the coupling strengths of leptoquarks and scalar quarks are derived.

Local multiplicity fluctuations in angular phase space intervals are studied using factorial moments measured in hadronic events at s≃91.2GeV, which were collected by the L3 detector at LEP. Parton shower Monte Carlo programs agree well with the data. On the other hand, first-order QCD calculations in the Double Leading Log Approximation and the Modified Leading Log Approximation are found to deviate significantly from the data.

We have studied the process e+e− → nγ (n ≥ 2) at centre-of-mass energies of 161.3 GeV and 172.1 GeV. The analysis is based on a sample of events collected by the L3 detector in 1996 corresponding to total integrated luminosities of 10.7 pb−1 and 10.1 pb−1 respectively. The observed rates of events with two and more photons and the characteristic distributions are in good agreement with the Standard Model expectations. This is used to set lower limits on contact interaction energy scale parameters, on the QED cut-off parameters and on the mass of excited electrons.

The reactions e+e−→ e+e−e+e− and e+e−→ e+e−μ+μ−, in a single tag configuration, are studied at LEP with the L3 detector. The data set corresponds to an integrated luminosity of 93.7 pb−1 at s=91 GeV. Differential cross sections are measured for 1.4GeV2≤Q2≤7.6GeV2. The leptonic photon structure function Fγ2 and azimuthal correlations are measured for e+e−→ e+e−μ+μ−. The related structure functions FγA and FγB, which originate from interference terms of the scattering amplitudes, are determined for the first time.

A search for unstable neutral and charged heavy leptons as well as for stable charged heavy leptons has been made at center-of-mass energies s= 161GeV ands172GeV with the L3 detector at LEP. No evidence for their existence was found. We exclude unstable neutral leptons of Dirac (Majorana) type for masses below 78.0 (66.7), 78.0 (66.7) and 72.2 (58.2) GeV, if the heavy neutrino couples to the electron, muon or tau family, respectively. We exclude unstable charged heavy leptons for masses below 81.0 GeV for a wide mass range of the associated neutral heavy lepton. The production of stable charged heavy leptons with a mass less than 84.2 GeV is also excluded. If the unstable charged heavy lepton decays via mixing into a massless neutrino, we exclude masses below 78.7 GeV.

We have studied the process e+e− → nγ (n ≥ 2) at an average center-of-mass energy of 133 GeV using the L3 detector at LEP. For an integrated luminosity of 4.95 pb−1 we find one γγγγ(γ) final state with only hard photons. The rates of both γγγ and γγ events are consistent with QED expectations. The cross section of the reaction e+e− → γγ(γ) in the polar range 16° < θγ < 164° is measured to be 22.6 ± 2.2 pb. Decays into photons of narrow scalar resonances with masses between 90 and 130 GeV are not observed. The observation of the event with four energetic photons is consistent with QED although the kinematic configuration of the photons is atypical.

The inclusive production of η mesons has been studied using 1.6 million hadronic Z decays collected with the L3 detector. The η multiplicity per event, the multiplicity for two-jet and three-jet events separately, and the multiplicity in each jet have been measured and compared with the predictions of different Monte Carlo programs. The momentum spectra of η in each jet have also been measured. We observe that the measured η momentum spectrum in quark-enriched jets agrees well with the Monte Carlo prediction while in gluon-enriched jets it is harder than that predicted by the Monte Carlo models.

The time-integrated B0B̄0 mixing parameter and the forward-backward charge asymmetry in the process e+e−→bb̄ are measured in hadronic Z events containing prompt muons or electrons, collected by the L3 experiment in the years 1990 to 1995. The total sample of 3.3 milion hadronic Z events with a mean centre-of-mass energy of 91.26 GeV yields: AbFB=0.0960±0.0066(stat.)±0.0033(sys.), χb=0.1192±0.0068(stat.)±0.0051(sys.). This asymmetry measurement together with measurements at energies away from the Z pole energy yield a pole asymmetry and corresponding effective electroweak mixing angle of: A0,bFB=0.1015±0.0064(stat.)±0.0035(sys.), sin2θ̄W=0.2318±0.0013.

Single W boson production in electron-positron collisions is studied with the L3 detector at LEP. The data sample collected at a centre-of-mass energy of \sqrt{s} = 188.7GeV corresponds to an integrated luminosity of 176.4pb^-1. Events with a single energetic lepton or two acoplanar hadronic jets are selected. Within phase-space cuts, the total cross-section is measured to be 0.53 +/- 0.12 +/- 0.03 pb, consistent with the Standard Model expectation. Including our single W boson results obtained at lower \sqrt{s}, the WWgamma gauge couplings kappa_gamma and lambda_gamma are determined to be kappa_gamma = 0.93 +/- 0.16 +/- 0.09 and lambda_gamma = -0.31 +0.68 -0.19 +/- 0.13.

The total and differential cross sections of the process e+e- -> n gamma with n >= 2 are measured using data collected by the L3 experiment at centre-of-mass energies of \sqrt{s}=183 and 189 GeV. The results are in agreement with the Standard Model expectations. Limits are set on deviations from QED, contact interaction cut-off parameters and masses of excited electrons.

We present evidence for soft gluon interference, as required by QCD. This interference is expected to manifest itself in an angular ordering of the gluons radiated within a jet. Using hadronic decays of the Z boson in the L3 detector at LEP, we compare variables sensitive to such an angular ordering, namely the energy-energy correlation asymmetry and the newly introduced particle-particle correlation asymmetry, with the predictions of various parton shower models. Only those models which incorporate the expected interference agree with the data.

We present a measurement of the average b-hadron lifetime τb at the e+e−collider LEP. Using hadronic Z decays collected in the period from 1991 to 1994, two independent analyses have been performed. In the first one, the b-decay position is reconstructed as a secondary vertex of hadronic b-decay particles. The second analysis is an updated measurement of τb using the impact parameter of leptons with high momentum and high transverse momentum. The combined result isτb=[1549±9(stat)±15(syst)]fs.In addition, we measure the average charged b-decay multiplicity 〈nb〉 and the normalized average b-energy 〈xE〉b at LEP to be〈nb〉=4.90±0.04(stat)±0.11(syst),〈xE〉b=0.709±0.004(stat+syst).

A search for pair-produced charged Higgs bosons is performed with the L3 detector at LEP using data collected at centre-of-mass energies from 130 to 183 GeV, corresponding to an integrated luminosity of 88.3 pb−1. The Higgs decays into a charm and a strange quark or into a tau lepton and its associated neutrino are considered. The observed candidates are consistent with the expectations from Standard Model background processes. A lower limit of 57.5 GeV on the charged Higgs mass is derived at 95% CL, independent of the decay branching ratio Br(H±→τν).

A search for the neutral Higgs boson in the processes e+e− → Z → H0γ → qqγ and e+e− → Z → Z∗H0 → qqγγ has been performed using 2.8 million hadronic Z decays collected with the L3 detector at LEP from 1991 through 1994. No evidence for these processes has been observed. Upper limits at 95% confidence level for the corresponding cross sections have been set and the results have been compared with theoretical predictions beyond the Standard Model.

Time-dependent Bd0-Bd0 mixing is studied using 1.5 million hadronic Z decays collected by L3. Semileptonic B decays are selected by requiring at least one reconstructed lepton in both thrust hemispheres. Charge correlations between the tagged leptons are studied as a function of proper time. The proper time of the b-hadron decay is measured by reconstructing the production and decay vertices using a silicon microvertex detector. The measured Bd0 meson oscillation frequency corresponds to a mass difference Δmd between the two Bd0 mass eigenstates of Δmd = (0.496−0.051+0.055 (stat) ± 0.043 (syst)) ps−1.

We report on a detailed study of the energy and particle flow in the event plane of three-jet events (qqg) and radiative two-jet events (qqγ) in hadronic Z decays recorded with the L3 detector. We find a significant decrease in particle and energy density in the angular region between quark and antiquark jets for qqg events as compared with qqγ events. Several QCD model predictions are compared with the observed effect.

Inclusive production of $\mathrm{D^{*\pm}}$ mesons in two-photon collisions was measured by the L3 experiment at LEP. The data were collected at a centre-of-mass energy $\sqrt{s} = 189$ GeV with an integrated luminosity of $176.4 \mathrm{pb^{-1}}$. Differential cross sections of the process $\mathrm{e^+e^- \to D^{*\pm} X}$ are determined as functions of the transverse momentum and pseudorapidity of the $\mathrm{D^{*\pm}}$ mesons in the kinematic region 1 GeV $< p_{T}^{\mathrm{D^*}} < 5 $ GeV and $\mathrm{|\eta^{D^*}|} < 1.4$. The cross section integrated over this phase space domain is measured to be $132 \pm 22(stat.) \pm 26(syst.)$ pb. The differential cross sections are compared with next-to-leading order perturbative QCD calculations.

A search for excited leptons e∗, μ∗, τ∗ and νe∗ in e+e− collisions at s=161 GeV is performed using the 10.8 pb−1 of data collected by the L3 detector at LEP. No evidence has been found for their existence. From an analysis of the expected ℓ∗ℓ∗ pair production in the channels eeγγ, μμγγ, ττγγ, eeWW, and ννγγ, the lower mass limits at 95% C.L. are 79.7 GeV for e∗, 79.9 GeV for μ∗, 79.3 GeV for τ∗ and 71.2 GeV for νe∗ assuming the same couplings as for standard leptons. From an analysis of the expected ℓℓ∗ single production in channels eeγ, μμγ, ττγ, νeeW and ννγ, the upper limits on the couplings λmℓ∗ up to mℓ∗= 161GeV are determined.

The measurements of Rb=σ(e+e−→bb̄)/σ(e+e−→qq̄) and of the b quark forward–backward charge asymmetry, Afbb, at centre-of-mass energies above the Z pole are described. The measurement of Rb is performed at s between 130 and 189GeV using a b-tagging method that exploits the relatively large decay length of b-hadrons. The measurement of Afbb is performed using the large statistics event sample collected at s=189GeV with a lepton-tag analysis based on the selection of prompt muons and electrons. The results at s=189GeV are Rb=0.163±0.013(stat.)±0.005(syst.), Afbb=0.61±0.18(stat.)±0.09(syst.).

The BaBar Collaboration has operated a system covering over 2000 m/sup 2/ with resistive plate chambers for nearly three years. The chambers are constructed of bakelite sheets separated by 2 mm. The inner surfaces are coated with linseed oil. This system provides muon and neutral hadron detection for BaBar. Installation and commissioning were completed in 1998, and operation began mid-1999. While initial performance of the system reached design, over time, a significant fraction of the resistive plate chambers demonstrated significant degradation, marked by increased currents and reduced efficiency. A coordinated investigative effort has identified many of the elements responsible for the degradation.

The Run Control and Monitor System (RCMS) of the CMS experiment is the set of hardware and software components responsible for controlling and monitoring the experiment during data-taking. It provides users with a "virtual counting room", enabling them to operate the experiment and to monitor detector status and data quality from any point in the world. This paper describes the architecture of the RCMS with particular emphasis on its scalability through a distributed collection of nodes arranged in a tree-based hierarchy. The current implementation of the architecture in a prototype RCMS used in test beam setups, detector validations and DAQ demonstrators is documented. A discussion of the key technologies used, including Web Services, and the results of tests performed with a 128-node system are presented.

The neutrino energy spectrum in semileptonic b-hadron decays with identified energetic electrons and muons has been measured. The observed relative energy sharing between the neutrino and the cahrged lepton is found to be well described with a W± polarization obtained from a free b-quark decay model with a (Vf-A)×(Vf-A) decay structure. The alternative of a (V+A)×(Vf-A) decay structure is excluded with a significance of more than 6 standard deviations. The possibility that hadronic corrections to the b-hadron decay destroy any W± polarization is disfavored by more than 3 standard deviations.

We report on the measurement of W-boson pair-production with the L3 detector at LEP at an average centre-of-mass energy of 172.13 GeV. In a data sample corresponding to a total luminosity of 10.25 pb−1 we select 110 four-fermion events with pairs of hadronic jets or leptons with high invariant masses. Branching fractions of W decays into different fermion-antifermion pairs are determined with and without the assumption of charged-current lepton universality. The branching fraction for hadronic W decays is measured to be: B(W → hadrons) = 64.2−3.8+3.7 (stat.) ± 0.5 (syst.) %. Combining all final states the total cross section for W-pair production is measured to be: σWW = 12.27−1.32+1.41 (stat.) ± 0.23 (syst.) pb. The results are in good agreement with the Standard Model.