In 2017 a new pixel detector was installed in the CMS detector. This so-called Phase-1 pixel detector features four barrel layers in the central region and three disks per end in the forward regions. The upgraded pixel detector requires an upgraded data acquisition (DAQ) system to accept a new data format and larger event sizes. A new DAQ and control system has been developed based on a combination of custom and commercial microTCA parts. Custom mezzanine cards on standard carrier cards provide a front-end driver for readout, and two types of front-end controller for configuration and the distribution of clock and trigger signals. Before the installation of the detector the DAQ system underwent a series of integration tests, including readout of the pilot pixel detector, which was constructed with prototype Phase-1 electronics and operated in CMS from 2015 to 2016, quality assurance of the CMS Phase-1 detector during its assembly, and testing with the CMS Central DAQ. This paper describes the Phase-1 pixel DAQ and control system, along with the integration tests and results. A description of the operational experience and performance in data taking is included.

A new CMS Tracker is under development for operation at the High Luminosity LHC from 2026 onwards. It includes an outer tracker based on dedicated modules that will reconstruct short track segments, called stubs, using spatially coincident clusters in two closely spaced silicon sensor layers. These modules allow the rejection of low transverse momentum track hits and reduce the data volume before transmission to the first level trigger. The inclusion of tracking information in the trigger decision is essential to limit the first level trigger accept rate. A customized front-end readout chip, the CMS Binary Chip (CBC), containing stub finding logic has been designed for this purpose. A prototype module, equipped with the CBC chip, has been constructed and operated for the first time in a 4 GeV/c positron beam at DESY. The behaviour of the stub finding was studied for different angles of beam incidence on a module, which allows an estimate of the sensitivity to transverse momentum within the future CMS detector. A sharp transverse momentum threshold around 2 GeV/c was demonstrated, which meets the requirement to reject a large fraction of low momentum tracks present in the LHC environment on-detector. This is the first realistic demonstration of a silicon tracking module that is able to select data, based on the particle's transverse momentum, for use in a first level trigger at the LHC . The results from this test are described here.

The high luminosity upgrade of the Large Hadron Collider, foreseen for 2026, necessitates the replacement of the CMS experiment’s silicon tracker. The innermost layer of the new pixel detector will be exposed to severe radiation, corresponding to a 1 MeV neutron equivalent fluence of up to \(\Phi _{eq} = 2 \times 10^{16}\) cm\(^{-2}\), and an ionising dose of \({\approx } 5\) MGy after an integrated luminosity of 3000 fb\(^{-1}\). Thin, planar silicon sensors are good candidates for this application, since the degradation of the signal produced by traversing particles is less severe than for thicker devices. In this paper, the results obtained from the characterisation of 100 and 200 \(\upmu \)m thick p-bulk pad diodes and strip sensors irradiated up to fluences of \(\Phi _{eq} = 1.3 \times 10^{16}\) cm\(^{-2}\) are shown.

The upgrade of the LHC to the High-Luminosity LHC (HL-LHC) is expected to increase the LHC design luminosity by an order of magnitude. This will require silicon tracking detectors with a significantly higher radiation hardness. The CMS Tracker Collaboration has conducted an irradiation and measurement campaign to identify suitable silicon sensor materials and strip designs for the future outer tracker at the CMS experiment. Based on these results, the collaboration has chosen to use n-in-p type silicon sensors and focus further investigations on the optimization of that sensor type. This paper describes the main measurement results and conclusions that motivated this decision.

The degradation of signal in silicon sensors is studied under conditions expected at the CERN High-Luminosity LHC. 200 μm thick n-type silicon sensors are irradiated with protons of different energies to fluences of up to 3 · 1015 neq/cm2. Pulsed red laser light with a wavelength of 672 nm is used to generate electron-hole pairs in the sensors. The induced signals are used to determine the charge collection efficiencies separately for electrons and holes drifting through the sensor. The effective trapping rates are extracted by comparing the results to simulation. The electric field is simulated using Synopsys device simulation assuming two effective defects. The generation and drift of charge carriers are simulated in an independent simulation based on PixelAV. The effective trapping rates are determined from the measured charge collection efficiencies and the simulated and measured time-resolved current pulses are compared. The effective trapping rates determined for both electrons and holes are about 50% smaller than those obtained using standard extrapolations of studies at low fluences and suggest an improved tracker performance over initial expectations.

Jet multiplicity distributions in top quark pair () events are measured in pp collisions at a centre-of-mass energy of 8 TeV with the CMS detector at the LHC using a data set corresponding to an integrated luminosity of 19.7. The measurement is performed in the dilepton decay channels (, , and ). The absolute and normalized differential cross sections for production are measured as a function of the jet multiplicity in the event for different jet transverse momentum thresholds and the kinematic properties of the leading additional jets. The differential and cross sections are presented for the first time as a function of the kinematic properties of the leading additional jets. Furthermore, the fraction of events without additional jets above a threshold is measured as a function of the transverse momenta of the leading additional jets and the scalar sum of the transverse momenta of all additional jets. The data are compared and found to be consistent with predictions from several perturbative quantum chromodynamics event generators and a next-to-leading order calculation.

Inclusive jet production in pPb collisions at a nucleon-nucleon (NN) center-of-mass energy of [Formula: see text] is studied with the CMS detector at the LHC. A data sample corresponding to an integrated luminosity of 30.1 nb[Formula: see text] is analyzed. The jet transverse momentum spectra are studied in seven pseudorapidity intervals covering the range [Formula: see text] in the NN center-of-mass frame. The jet production yields at forward and backward pseudorapidity are compared and no significant asymmetry about [Formula: see text] is observed in the measured kinematic range. The measurements in the pPb system are compared to reference jet spectra obtained by extrapolation from previous measurements in pp collisions at [Formula: see text]. In all pseudorapidity ranges, nuclear modifications in inclusive jet production are found to be small, as predicted by next-to-leading order perturbative QCD calculations that incorporate nuclear effects in the parton distribution functions.

The response of n(+)p silicon strip sensors to electrons from a Sr-90 source was measured using a multi-channel read-out system with 25 ns sampling time. The measurements were performed over a period of several weeks, during which the operating conditions were varied. The sensors were fabricated by Hamamatsu Photonics on 200 im thick float-zone and magnetic-Czochralski silicon. Their pitch was 80 ifm, and both p-stop and p-spray isolation of the n strips were studied. The electrons from the Sr-90 source were collimated to a spot with a full-width-at-half-maximum of 2 mm at the sensor surface, and the dose rate in the SiO2 at the maximum was about 50 Gy(SiO2)/d. After only a few hours of making measurements, significant changes in charge collection and charge sharing were observed. Annealing studies, with temperatures up to 80 degrees C and annealing times of 18 h showed that the changes can only be partially annealed. The observations can be qualitatively explained by the increase of the positive oxidecharge density due to the ionization of the SiO2 by the radiation from the 13 source. TCAD simulations of the electric field in the sensor for different oxide-charge densities and different boundary conditions at the sensor surface support this explanation. The relevance of the measurements for the design of n'p strip sensors is discussed. (C) 2015 Elsevier B.V.

In the last few years there has been a significant experimental progress in quark and lepton flavor physics. In the quark sector, the validity of the Standard Model (SM) has been substantially reinforced by a series of high-precision measurements in the Bs and Bd systems. Most notably, a significant fraction of the parameter space of well-motivated SM extensions has been ruled out by the precise determination of the Bs mixing phase at LHCb [1], and by the strong bounds on B(Bs ! μ+μ ) set by CDF [2] first and more recently by ATLAS, CMS, and LHCb [3–5]. Similarly, in the lepton sector strong bounds on possible SM extensions have been set by the improved bounds on B(μ! e ) obtained the MEG experiment at PSI [6]. Alltogether, the SM works remarkably well: the Cabibbo-Kobayashi-Maskawa (CKM) mechanism of quark-flavor mixing has been tested in various processes (although in many interesting cases with limited accuracy) and no flavor-violating effects are observed in the charged-lepton sector. Despite this progress, the origin of flavor remains a mystery. Our “ignorance” can be summarized by the following two open questions: i) what determines the observed pattern of masses and mixing angles of quarks and leptons? ii) Which are the sources of flavor symmetry breaking accessible at low energies? Is there anything else beside quark and lepton mass matrices? Answering the first of these question is not easy: the energy scale where the flavor structures observed at low energies are originated may well be above any realistic experimental reach. On the other hand, answering the second question is mainly a question of precision, both on the theory and on the experimental side: this is the direction of research along which we can expect significant progress in the near future. Observing new sources of flavor mixing (i.e. flavor violating couplings not related to quark and lepton mass matrices) is a natural expectation for any extension of the SM with new degrees of freedom not far from the TeV scale. While direct searches of new particles at high energies provide a direct information on the mass spectrum of the possible new degrees of freedom, the indirect information from low-energy flavor-changing processes translates into unique constraints on their couplings. The present bounds on possible deviations from the SM in flavor-violating processes already set stringent limits on the flavor structure of physics beyond the SM, and this provides a key information for model-building. However, several options are still open, and the quality of this information could be substantially improved with improved studies of selected flavor-violating observables.

A search for supersymmetry or other new physics resulting in similar final states is presented using a data sample of 4.73 fb−1 of pp collisions collected at \( \sqrt{s}=7 \) TeV with the CMS detector at the LHC. Fully hadronic final states are selected based on the variable M T2, an extension of the transverse mass in events with two invisible particles. Two complementary studies are performed. The first targets the region of parameter space with medium to high squark and gluino masses, in which the signal can be separated from the standard model backgrounds by a tight requirement on M T2. The second is optimized to be sensitive to events with a light gluino and heavy squarks. In this case, the M T2 requirement is relaxed, but a higher jet multiplicity and at least one b-tagged jet are required. No significant excess of events over the standard model expectations is observed. Exclusion limits are derived for the parameter space of the constrained minimal supersymmetric extension of the standard model, as well as on a variety of simplified model spectra.

Measurements of inclusive charged-hadron transverse-momentum and pseudorapidity distributions are presented for proton-proton collisions at \(\sqrt{s} = 0.9 \) and 2.36 TeV. The data were collected with the CMS detector during the LHC commissioning in December 2009. For non-single-diffractive interactions, the average charged-hadron transverse momentum is measured to be 0.46 ± 0.01 (stat.) ± 0.01 (syst.) GeV/c at 0.9 TeV and 0.50 ± 0.01 (stat.) ± 0.01 (syst.) GeV/c at 2.36 TeV, for pseudorapidities between --2.4 and +2.4. At these energies, the measured pseudorapidity densities in the central region, dN ch/dη||η|<0.5, are 3:48 ± 0:02 (stat.) ± 0.13 (syst.) and 4:47 ± 0:04 (stat.) ± 0.16 (syst.), respectively. The results at 0.9 TeV are in agreement with previous measurements and confirm the expectation of near equal hadron production in \( \overline p p \) and pp collisions. The results at 2.36 TeV represent the highest-energy measurements at a particle collider to date.

The Compact Muon Solenoid experiment at the Large Hadron Collider at CERN includes a silicon pixel detector as its innermost component. Its main task is the precise reconstruction of charged particles close to the primary interaction vertex. This paper gives an overview of the mechanical requirements and design choices for the barrel pixel detector. The distribution of material in the detector as well as its description in the Monte Carlo simulation are discussed in detail.

The results of the CMS tracker alignment analysis are presented using the data from cosmic tracks, optical survey information, and the laser alignment system at the Tracker Integration Facility at CERN. During several months of operation in the spring and summer of 2007, about five million cosmic track events were collected with a partially active CMS Tracker. This allowed us to perform first alignment of the active silicon modules with the cosmic tracks using three different statistical approaches; validate the survey and laser alignment system performance; and test the stability of Tracker structures under various stresses and temperatures ranging from +15 °C to −15 °C. Comparison with simulation shows that the achieved alignment precision in the barrel part of the tracker leads to residual distributions similar to those obtained with a random misalignment of 50 (80) μm RMS in the outer (inner) part of the barrel.

The CMS barrel pixel detector is the innermost tracking device, reconstructing the interaction vertices and charged particle trajectories. At the LHC design luminosity, 10 34 cm − 2 s − 1 , there will be 1000 charged particles per bunch crossing every 25 ns. In the innermost layer the pixel sensors will be exposed to a fluence of 3 × 10 14 n eq / cm 2 / yr with consequent degradation of the silicon lattice structure and particle detection performances. Beam tests of irradiated pixel sensors were performed at CERN with the final front end electronics in a 3T magnetic field. We present the measurements of charge collection and radiation hardness, as well as spatial resolution.

In March 2007 the assembly of the Silicon Strip Tracker was completed at the Tracker Integration Facility at CERN. Nearly 15% of the detector was instrumented using cables, fiber optics, power supplies, and electronics intended for the operation at the LHC. A local chiller was used to circulate the coolant for low temperature operation. In order to understand the efficiency and alignment of the strip tracker modules, a cosmic ray trigger was implemented. From March through July 4.5 million triggers were recorded. This period, referred to as the Sector Test, provided practical experience with the operation of the Tracker, especially safety, data acquisition, power, and cooling systems. This paper describes the performance of the strip system during the Sector Test, which consisted of five distinct periods defined by the coolant temperature. Significant emphasis is placed on comparisons between the data and results from Monte Carlo studies.

The subsystems of the CMS silicon strip tracker were integrated and commissioned at the Tracker Integration Facility (TIF) in the period from November 2006 to July 2007. As part of the commissioning, large samples of cosmic ray data were recorded under various running conditions in the absence of a magnetic field. Cosmic rays detected by scintillation counters were used to trigger the readout of up to 15% of the final silicon strip detector, and over 4.7 million events were recorded. This document describes the cosmic track reconstruction and presents results on the performance of track and hit reconstruction as from dedicated analyses.

The CMS experiment at the LHC includes a hybrid silicon pixel detector for the reconstruction of charged tracks and of the interaction vertices. The barrel region consists of n-in-n sensors with 100X150 um^2 cell size processed on diffusion oxygenated float zone silicon. A biasing grid is implemented and pixel isolation is achieved with the moderated p-spray technique. An extensive test program was carried out on the H2 beam line of the CERN SPS. In this paper we describe the sensor layout, the beam test setup and the results obtained with both irradiated and non-irradiated prototype devices. Measurements of charge collection, hit detection efficiency, Lorentz angle and spatial resolution are presented.

We show that doubly peaked electric fields are necessary to describe grazing-angle charge collection measurements of irradiated silicon pixel sensors. A model of irradiated silicon based upon two defect levels with opposite charge states and the trapping of charge carriers can be tuned to produce a good description of the measured charge collection profiles in the fluence range from 0.5×1014 to 5.9×1014neq/cm2. The model correctly predicts the variation in the profiles as the temperature is changed from -10 to -25∘C. The measured charge collection profiles are inconsistent with the linearly varying electric fields predicted by the usual description based upon a uniform effective doping density. This observation calls into question the practice of using effective doping densities to characterize irradiated silicon.