Pseudorapidity (η) distributions of charged particles produced in proton-proton collisions at a centre-of-mass energy of 8 TeV are measured in the ranges |η| < 2.2 and 5.3 < |η| < 6.4 covered by the CMS and TOTEM detectors, respectively. The data correspond to an integrated luminosity of L = 45 µb −1 . Measurements are presented for three event categories. The most inclusive category is sensitive to 91-96 % of the total inelastic proton-proton cross section. The other two categories are disjoint subsets of the inclusive sample that are either enhanced or depleted in single diffractive dissociation events. The data are compared to models used to describe high-energy hadronic interactions. None of the models considered provide a consistent description of the measured distributions.

The CMS muon detector system, muon reconstruction software, and high-level trigger underwent significant changes in 2013-2014 in preparation for running at higher LHC collision energy and instantaneous luminosity. The performance of the modified system is studied using proton-proton collision data at center-of-mass energy √ s = 13 TeV, collected at the LHC in 2015 and 2016. The measured performance parameters, including spatial resolution, efficiency, and timing, are found to meet all design specifications and are well reproduced by simulation. Despite the more challenging running conditions, the modified muon system is found to perform as well as, and in many aspects better than, previously. We dedicate this paper to the memory of Prof. Alberto Benvenuti, whose work was fundamental for the CMS muon detector.

The Vertex Locator (VELO) is a silicon microstrip detector that surrounds the protonproton interaction region in the LHCb experiment. The performance of the detector during the first years of its physics operation is reviewed. The system is operated in vacuum, uses a bi-phase CO 2 cooling system, and the sensors are moved to 7 mm from the LHC beam for physics data taking. The performance and stability of these characteristic features of the detector are described, and details of the material budget are given. The calibration of the timing and the data processing algorithms that are implemented in FPGAs are described. The system performance is fully characterised. The sensors have a signal to noise ratio of approximately 20 and a best hit resolution of 4 µm is achieved at the optimal track angle. The typical detector occupancy for minimum bias events in standard operating conditions in 2011 is around 0.5%, and the detector has less than 1% of faulty strips. The proximity of the detector to the beam means that the inner regions of the n + -on-n sensors have undergone space-charge sign inversion due to radiation damage. The VELO performance parameters that drive the experiment's physics sensitivity are also given. The track finding efficiency of the VELO is typically above 98% and the modules have been aligned to a precision of 1 µm for translations in the plane transverse to the beam. A primary vertex resolution of 13 µm in the transverse plane and 71 µm along the beam axis is achieved for vertices with 25 tracks. An impact parameter resolution of less than 35 µm is achieved for particles with transverse momentum greater than 1 GeV/c.

Study of the underlying event at forward rapidity in pp collisions at √ s = 0.9, 2.76, and 7 TeVThe CMS collaboration E-mail: cms-publication-committee-chair@cern.chAbstract: The underlying event activity in proton-proton collisions at forward pseudorapidity (−6.6 < η < −5.2) is studied with the CMS detector at the LHC, using a novel observable: the ratio of the forward energy density, dE/dη, for events with a chargedparticle jet produced at central pseudorapidity (|η jet | < 2) to the forward energy density for inclusive events. This forward energy density ratio is measured as a function of the central jet transverse momentum, p T , at three different pp centre-of-mass energies ( √ s = 0.9, 2.76, and 7 TeV). In addition, the √ s evolution of the forward energy density is studied in inclusive events and in events with a central jet. The results are compared to those of Monte Carlo event generators for pp collisions and are discussed in terms of the underlying event. Whereas the dependence of the forward energy density ratio on jet p T at each √ s separately can be well reproduced by some models, all models fail to simultaneously describe the increase of the forward energy density with √ s in both inclusive events and in events with a central jet.

region at a hadron collider. This document discusses the implications of these first measurements on classes of extensions to the Standard Model, bearing in mind the interplay with the results of searches for on-shell production of new particles at ATLAS and CMS. The physics potential of an upgrade to the LHCb detector, which would allow an order of magnitude more data to be collected, is emphasised.

The LHCb Vertex Locator (VELO) is a silicon strip detector designed to reconstruct charged particle trajectories and vertices produced at the LHCb interaction region. During the first two years of data collection, the 84 VELO sensors have been exposed to a range of fluences up to a maximum value of approximately 45 × 10 12 1 MeV neutron equivalent (1 MeV n eq ). At the operational sensor temperature of approximately −7 • C, the average rate of sensor current increase is 18 µA per fb −1 , in excellent agreement with predictions. The silicon effective bandgap has been determined using current versus temperature scan data after irradiation, with an average value of E g = 1.16 ± 0.03 ± 0.04 eV obtained. The first observation of n + -on-n sensor type inversion at the LHC has been made, occurring at a fluence of around 15 × 10 12 of 1 MeV n eq . The only n + -on-p sensors in use at the LHC have also been studied. With an initial fluence of approximately 3 × 10 12 1 MeV n eq , a decrease in the Effective Depletion Voltage (EDV) of around 25 V is observed. Following this initial decrease, the EDV increases at a comparable rate to the type inverted n + -on-n type sensors, with rates of (1.43 ± 0.16) × 10 −12 V/ 1 MeV n eq and (1.35 ± 0.25) × 10 −12 V/ 1 MeV n eq measured for n + -on-p and n + -on-n type sensors, respectively. A reduction in the charge collection efficiency due to an unexpected effect involving the second metal layer readout lines is observed.

Precise knowledge of the location of the material in the LHCb vertex locator (VELO) is essential to reducing background in searches for long-lived exotic particles, and in identifying jets that originate from beauty and charm quarks. Secondary interactions of hadrons produced in beam-gas collisions are used to map the location of material in the VELO. Using this material map, along with properties of a reconstructed secondary vertex and its constituent tracks, a p-value can be assigned to the hypothesis that the secondary vertex originates from a material interaction. A validation of this procedure is presented using photon conversions to dimuons.

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