Mircho Rodozov

Bulgarian Academy of Sciences | BAS · High Energy Physics

The CERN Compact Muon Solenoid (CMS) RPC system phase-2 upgrade project is in good progress. It covers the replacement of the off-detector electronics for the present Resistive Plate Chambers (RPC), known as ‘‘link system’’, and includes the renovation of the legacy slow controller with brand new electronics, called RPC backend electronics. The sco...

The muon system of the CERN Compact Muon Solenoid (CMS) experiment includes more than a thousand Resistive Plate Chambers (RPC). They are gaseous detectors operated in the hostile environment of the CMS underground cavern on the Large Hadron Collider where pp luminosities of up to $2\times 10^{34}$ $\text{cm}^{-2}\text{s}^{-1}$ are routinely achiev...

With the HL-LHC upgrade of the LHC machine, an increase of the instantaneous luminosity by a factor of five is expected and the current detection systems need to be validated for such working conditions to ensure stable data taking. At the CERN Gamma Irradiation Facility (GIF++) many muon detectors undergo such studies, but the high gamma backgroun...

PurposeThe Large Hadron Collider (LHC) at European Organization for Nuclear Research is planned to be upgraded to the high luminosity LHC. Increasing the luminosity makes muon triggering reliable and offline reconstruction very challenging. To enhance the redundancy of the Compact Muon Solenoid (CMS) Muon system and resolve the ambiguity of track r...

During the upcoming High Luminosity phase of the Large Hadron Collider (HL-LHC), the integrated luminosity of the accelerator will increase to 3000 fb ⁻¹ . The expected experimental conditions in that period in terms of background rates, event pileup, and the probable aging of the current detectors present a challenge for all the existing experimen...

During the upcoming High Luminosity phase of the Large Hadron Collider (HL-LHC), the integrated luminosity of the accelerator will increase to 3000 fb$^{-1}$. The expected experimental conditions in that period in terms of background rates, event pileup, and the probable aging of the current detectors present a challenge for all the existing experi...

The present RPC Link System has been servicing as one of the CMS subsystems since installation in 2008. Although the current Link System has been functioning well for the past 13 years, the aging of its electronic components and lack of radiation hard ASICs could present problems for future operations. Additionally, the needs to have a more robust...

The expected radiation background in the CMS RPC system has been studied using the MC prediction with the CMS FLUKA simulation of the detector and the cavern. The MC geometry used in the analysis describes very accurately the present RPC system but still does not include the complete description of the RPC upgrade region with pseudorapidity 1.9 < |...

A new generation of resistive plate chambers, capable of withstanding high particle fluxes (up to 2000 Hz · cm ⁻² ) and instrumented with precise timing readout electronics is proposed to equip two of the four high pseudorapidity stations of the CMS muon system. Double-gap RPC detectors, with each gap made of two 1.4 mm High Pressure Laminate elect...

PurposeTo complement and ensure redundancy in the endcap muon system of the Compact Muon Solenoid (CMS) detector and to extend the Resistive Plate Chamber (RPC) system coverage, improved RPCs (iRPCs) with either orthogonal layer strips with one-end electronics or single layer strips with two-end electronics providing more precise time measurement w...

As part of the Compact Muon Solenoid experiment Phase-II upgrade program, new resistive plate chambers will be installed in the region at low angle with respect to the beam collision axis, in order to improve the detection of muons with a low transverse momentum. High background conditions are expected in this region during the high-luminosity phas...

During Phase-2 of the LHC, known as the High Luminosity LHC (HL-LHC), the accelerator will increase its instantaneous luminosity to 5 x 10(34) cm(-2) s(-1), delivering an integrated luminosity of 3000 fb(-1) over 10 years of operation starting from 2027. In view of the HL-LHC, the CMS muon system will be upgraded to sustain efficient muon triggerin...

The CMS experiment implements a two-level triggering system composed of Level-1, instrumented by custom-design hardware boards, and a software High Level Trigger. To cope with the more challenging luminosity conditions, a new Level-1 architecture has been deployed during run II. This new architecture exploits in a better way the redundancy and comp...

Resistive Plate Chambers have a very important role for muon triggering both in the barrel and in the endcap regions of the CMS experiment at the Large Hadron Collider (LHC). In order to optimize their performance, it is of primary importance to tune the electronic threshold of the front-end boards reading the signals from these detectors. In this...

The CMS experiment recorded 177.75 fb −1 of proton-proton collision data during the RUN-1 and RUN-2 data taking period. Successful data taking at increasing instantaneous lumi-nosities with the evolving detector configuration was a big achievement of the collaboration. The CMS RPC system provided redundant information for the robust muon triggering...

The CMS experiment has 1054 RPCs in its muon system. Monitoring their currents is the first essential step towards maintaining the stability of the CMS RPC detector performance. The current depends on several parameters such as applied voltage, luminosity, environmental conditions, etc. Knowing the influence of these parameters on the RPC current i...

The Muon Upgrade Phase II of the Compact Muon Solenoid (CMS) aims to guarantee the optimal conditions of the present system and extend the eta coverage to ensure a reliable system for the High Luminosity Large Hadron Collider (HL-LHC) period. The Resistive Plate Chambers (RPCs) system will upgrade the off-detector electronics (called link system) o...

on behalf of the CMS collaboration A : The second LHC long shutdown period (LS2) is an important opportunity for the CMS Resistive Plate Chambers (RPC) to complete their consolidation and upgrade projects. The consolidation includes detector maintenance for gas tightness, HV (high voltage), LV (low voltage) and slow control operation. All services...

The expected radiation background in the CMS RPC system has been studied using the MC prediction with the CMS FLUKA simulation of the detector and the cavern. The MC geometry used in the analysis describes very accurately the present RPC system but still does not include the complete description of the RPC upgrade region with pseudorapidity $1.9 <...

C++ Modules come in C++20 to fix the long-standing build scalability problems in the language. They provide an io-efficient, on-disk representation capable to reduce build times and peak memory usage. ROOT employs the C++ modules technology further in the ROOT dictionary system to improve its performance and reduce the memory footprint. ROOT with C...

In the High Luminosity Large Hadron Collider (HL-LHC) program, during the next years, the instantaneous luminosity will increase up to 5 × 10 34 cm −2 s −1 which means a factor five higher than the nominal LHC luminosity. In that period, the present CMS Resistive Plate Chambers (RPC) system will be subjected to background rates higher than those fo...

C++ Modules, one of the new features of C++20, aim to fix the long-standing build scalability problems in the language. They provide an IOefficient, on-disk representation capable to reduce build times and peak memory usage. ROOT already employs the C++ modules technology in its dictionary system to improve performance and reduce the memory footpri...

Several theoretical models inspired by the idea of supersymmetry (SUSY) accommodate the possibility of Heavy Stable Charged Particles (HSCPs). The Phase II upgrade of the CMS-RPC system will allow the trigger and identification of this kind of particles exploiting the Time-of-Flight Technique with the improved time resolution that a new Data Acquis...

The CMS experiment, located at the Large Hadron Collider (LHC) in CERN, has a redundant muon system composed by three different gaseous detector technologies: Cathode Strip Chambers (in the forward regions), Drift Tubes (in the central region), and Resistive Plate Chambers (both its central and forward regions). All three are used for muon reconstr...

Based on previous experience and attempt, a real-size mosaic Multi-gap Resistive Plate Chamber (MRPC) has been developed within the framework of the CMS muon upgrade efforts. The chamber is a 5-gap with plates made each of 6 pieces of low resistive glass. Cosmic ray test at CERN 904 shows that its efficiency can reach above 95% with a gas mixture o...

The High Luminosity LHC (HL-LHC) phase is designed to increase by an order of magnitude the amount of data to be collected by the LHC experiments. The foreseen gradual increase of the instantaneous luminosity of up to more than twice its nominal value of 10 x 10(34) cm(-1) s(-2) during Phase I and Phase II of the LHC running, presents special chall...

The high pseudorapidity (eta) region of the Compact Muon Solenoid (CMS) muon system is covered by Cathode Strip Chambers only and lacks redundant coverage despite the fact that it is a challenging region for muons in terms of backgrounds and momentum resolution. During the annual Year-End Technical Stops 2022 & 2023, two new layers of improved Resi...

We measure the efficiency of CMS Resistive Plate Chamber (RPC) detectors in proton-proton collisions at the centre-of-mass energy of 13 TeV using the tag-and-probe method. A muon from a Z(0) boson decay is selected as a probe of efficiency measurement, reconstructed using the CMS inner tracker and the rest of CMS muon systems. The overall efficienc...

The Resistive Plate Chambers (RPC) are used for muon triggers in the CMS experiment. To calibrate the high voltage working-points (WP) and identify degraded detectors due to radiation or chemical damage, a high voltage scan has been performed using 2017 data from pp collisions at a center-of-mass energy of 13 TeV. In this paper, we present the cali...

The high luminosity expected from the HL-LHC will be a challenge for the CMS detector. The increased rate of particles coming from the collisions and the radioactivity induced in the detector material could cause significant damage and result in a progressive degradation of its performance. Simulation studies are very useful in these scenarios as t...

In the next decades, the Large Hadron Collider (LHC) will run at very high luminosity (HL-LHC) 5×10³⁴ cm⁻²s⁻¹, factor five more than the nominal LHC luminosity. During this period the CMS RPC system will be subjected to high background rates which could affect the performance by inducing aging effects. A dedicated longevity program to qualify the p...

Event-by-event fluctuations in the elliptic-flow coefficient v2 are studied in PbPb collisions at √sNN = 5.02 TeV using the CMS detector at the CERN LHC. Elliptic-flow probability distributions p(v2) for charged particles with transverse momentum 0.3 < pT < 3.0 GeV/c and pseudorapidity |η| < 1.0 are determined for different collision centrality cla...

Searches for resonant and nonresonant pair-produced Higgs bosons (HH) decaying respectively into ℓνℓν, through either W or Z bosons, and \( \mathrm{b}\overline{\mathrm{b}} \) are presented. The analyses are based on a sample of proton-proton collisions at \( \sqrt{s}=13 \) TeV, collected by the CMS experiment at the LHC, corresponding to an integra...

High-sensitivity double-gap phenolic resistive plate chambers (RPCs) are studied for the Phase-2 upgrade of the Compact Muon Solenoid (CMS) muon system at high pseudorapidity η. Whereas the present CMS RPCs have a gas gap thickness of 2 mm, we propose to use thinner gas gaps, which will improve the performance of these RPCs. To validate this propos...

With the increase of the LHC luminosity foreseen in the coming years, many detectors currently used in the different LHC experiments will be dramatically impacted and some need to be replaced or upgraded. The new ones should be capable to provide time information to reduce the data ambiguity due to the expected high pileup. We propose to equip CMS...

A bstract A search is presented for resonances decaying to a Z boson and a photon. The analysis is based on data from proton-proton collisions at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 35.9 fb ⁻¹ , and collected with the CMS detector at the LHC in 2016. Two decay modes of the Z boson are investigated. In the...

Four double-gap CMS resistive plate chambers are being tested at the CERN Gamma Irradiation Facility to determine the performance and aging effects at the expected conditions of the High Luminosity-Large Hadron Collider. Results up to an integrated charge of 290 millicoulomb/cm² are reported.

A search for narrow vector resonances decaying into quark-antiquark pairs is presented. The analysis is based on data collected in proton-proton collisions at \( \sqrt{s}=13 \) TeV with the CMS detector at the LHC, corresponding to an integrated luminosity of 35.9 fb−1. The hypothetical resonance is produced with sufficiently high transverse moment...

Measurements of azimuthal angle and transverse momentum (pT) correlations of isolated photons and associated jets are reported for pp and PbPb collisions at sNN=5.02 TeV. The data were recorded with the CMS detector at the CERN LHC. For events containing a leading isolated photon with pTγ>40 GeV/c and an associated jet with pTjet>30 GeV/c, the phot...

The High Luminosity LHC (HL-LHC) phase is designed to increase by an order of magnitude the amount of data to be collected by the LHC experiments. The foreseen gradual increase of the instantaneous luminosity of up to more than twice its nominal value of $10\times10^{34}\ {\rm cm}^{-1}{\rm s}^{-2}$ during Phase I and Phase II of the LHC running, pr...

A bstract This paper presents a measurement of the underlying event activity in proton-proton collisions at a center-of-mass energy of 13 TeV, performed using inclusive Z boson production events collected with the CMS experiment at the LHC. The analyzed data correspond to an integrated luminosity of 2.1 fb ⁻¹ . The underlying event activity is quan...

Azimuthal correlations between the two jets with the largest transverse momenta \(p_{\mathrm {T}}\) in inclusive 2-, 3-, and 4-jet events are presented for several regions of the leading jet \(p_{\mathrm {T}}\) up to 4\(\,\text {Te}\text {V}\). For 3- and 4-jet scenarios, measurements of the minimum azimuthal angles between any two of the three or...

A search for physics beyond the standard model in events with one or more high-momentum Higgs bosons, H, decaying to pairs of b quarks in association with missing transverse momentum is presented. The data, corresponding to an integrated luminosity of 35.9 fb−1, were collected with the CMS detector at the LHC in proton-proton collisions at the cent...

Measurements are presented of the lifetimes of the B0, Bs0, Λb0, and Bc+ hadrons using the decay channels B0→J/ψK∗(892)0, B0→J/ψKS0, Bs0→J/ψπ+π-, Bs0→J/ψϕ(1020), Λb0→J/ψΛ0, and Bc+→J/ψπ+. The data sample, corresponding to an integrated luminosity of 19.7fb-1, was collected by the CMS detector at the LHC in proton–proton collisions at s=8TeV. The B0...

Results are reported from a search for physics beyond the standard model in proton–proton collisions at a center-of-mass energy of s=13TeV. The search uses a signature of a single lepton, large jet and bottom quark jet multiplicities, and high sum of large-radius jet masses, without any requirement on the missing transverse momentum in an event. Th...

The nuclear modification factors of \({\mathrm {J}/\psi }\) and \(\psi \text {(2S)}\) mesons are measured in \(\text {PbPb}\) collisions at a centre-of-mass energy per nucleon pair of \(\sqrt{\smash [b]{s_{_{\text {NN}}}}} = 5.02\,\text {Te}\text {V} \). The analysis is based on \(\text {PbPb}\) and \(\mathrm {p}\mathrm {p}\) data samples collected...

A search for a heavy neutral lepton N of Majorana nature decaying into a W boson and a charged lepton is performed using the CMS detector at the LHC. The targeted signature consists of three prompt charged leptons in any flavor combination of electrons and muons. The data were collected in proton-proton collisions at a center-of-mass energy of 13 T...

A search for resonancelike structures in the Bs0π± invariant mass spectrum is performed using proton-proton collision data collected by the CMS experiment at the LHC at s=8 TeV, corresponding to an integrated luminosity of 19.7 fb−1. The Bs0 mesons are reconstructed in the decay chain Bs0→J/ψϕ, with J/ψ→μ+μ− and ϕ→K+K−. The Bs0π± invariant mass dis...

The prompt D0 meson azimuthal anisotropy coefficients, v2 and v3, are measured at midrapidity (|y|<1.0) in Pb-Pb collisions at a center-of-mass energy sNN=5.02 TeV per nucleon pair with data collected by the CMS experiment. The measurement is performed in the transverse momentum (pT) range of 1 to 40 GeV/c, for central and midcentral collisions. Th...

A search for narrow resonances decaying to bottom quark-antiquark pairs is presented, using a data sample of proton-proton collisions at s=8 TeV corresponding to an integrated luminosity of 19.7 fb−1. The search is extended to masses lower than those reached in typical searches for resonances decaying into jet pairs at the LHC, by taking advantage...

A search for long-lived particles was performed with data corresponding to an integrated luminosity of 2.6 fb^(−1) collected at a center-of-mass energy of 13 TeV by the CMS experiment in 2015. The analysis exploits two customized topological trigger algorithms, and uses the multiplicity of displaced jets to search for the presence of a signal decay...

Many measurements and searches for physics beyond the standard model at the LHC rely on the efficient identification of heavy-flavour jets, i.e. jets originating from bottom or charm quarks. In this paper, the discriminating variables and the algorithms used for heavy-flavour jet identification during the first years of operation of the CMS experim...

A search for supersymmetry (SUSY) is performed in final states comprising one or more jets and missing transverse momentum using data from proton-proton collisions at a centre-of-mass energy of 13 TeV. The data were recorded with the CMS detector at the CERN LHC in 2016 and correspond to an integrated luminosity of 35.9 fb−1. The number of signal e...

Modifications of the properties of jets in PbPb collisions, relative to those in pp collisions, are studied at a nucleon-nucleon center-of-mass energy of \( \sqrt{s_{\mathrm{N}\;\mathrm{N}}}=5.02 \) TeV via correlations of charged particles with the jet axis in relative pseudorapidity (Δη), relative azimuth (Δϕ), and relative angular distance from...

A search for a new heavy particle decaying to a pair of vector bosons (WW or WZ) is presented using data from the CMS detector corresponding to an integrated luminosity of 35.9 fb−1 collected in proton-proton collisions at a centre-of-mass energy of 13 TeV in 2016. One of the bosons is required to be a W boson decaying to eν or μν, while the other...

A search is presented for the decays of heavy exotic long-lived particles (LLPs) that are produced in proton-proton collisions at a center-of-mass energy of 13 TeV at the CERN LHC and come to rest in the CMS detector. Their decays would be visible during periods of time well separated from proton-proton collisions. Two decay scenarios of stopped LL...

A search is presented for new physics in events with two low-momentum, oppositely charged leptons (electrons or muons) and missing transverse momentum in proton-proton collisions at a centre-of-mass energy of 13 TeV. The data collected using the CMS detector at the LHC correspond to an integrated luminosity of 35.9. The observed event yields are co...

A search for a heavy right-handed W boson (WR) decaying to a heavy right-handed neutrino and a charged lepton in events with two same-flavor leptons (e or μ) and two jets, is presented. The analysis is based on proton-proton collision data, collected by the CMS Collaboration at the LHC in 2016 and corresponding to an integrated luminosity of 35.9 f...

The transverse momentum (pT) spectrum of prompt D⁰ mesons and their antiparticles has been measured via the hadronic decay channels D⁰→K⁻π⁺ and D‾⁰→K⁺π⁻ in pp and PbPb collisions at a centre-of-mass energy of 5.02 TeV per nucleon pair with the CMS detector at the LHC. The measurement is performed in the D⁰ meson pT range of 2–100GeV/c and in the ra...

Charge-dependent azimuthal correlations of same- and opposite-sign pairs with respect to the second- and third-order event planes have been measured in pPb collisions at sNN=8.16TeV and PbPb collisions at 5.02 TeV with the CMS experiment at the LHC. The measurement is motivated by the search for the charge separation phenomenon predicted by the chi...

An analysis of the bottom baryon decay Λb→J/ψ(→μ+μ−)Λ(→pπ−) is performed to measure the Λb polarization and three angular parameters in data from pp collisions at s=7 and 8 TeV, collected by the CMS experiment at the Large Hadron Collider. The Λb polarization is measured to be 0.00±0.06(stat)±0.06(syst) and the parity-violating asymmetry parameter...

A search is presented for heavy vectorlike quarks (VLQs) that couple only to light quarks in proton-proton collisions at s=8 TeV at the LHC. The data were collected by the CMS experiment during 2012 and correspond to an integrated luminosity of 19.7 fb−1. Both single and pair production of VLQs are considered. The single-production search is perfor...

Results are presented from a search in the dijet final state for new massive narrow resonances decaying to pairs of W and Z bosons or to a W/Z boson and a quark. Results are based on data recorded in proton-proton collisions at s=13 TeV with the CMS detector at the CERN LHC. The data correspond to an integrated luminosity of 35.9 fb−1. The mass ran...

Results are presented from a search in the dijet final state for new massive narrow resonances decaying to pairs of W and Z bosons or to a W/Z boson and a quark. Results are based on data recorded in proton-proton collisions at √s=13 TeV with the CMS detector at the CERN LHC. The data correspond to an integrated luminosity of 35.9 fb−1. The mass ra...

Data from heavy ion collisions suggest that the evolution of a parton shower is modified by interactions with the color charges in the dense partonic medium created in these collisions, but it is not known where in the shower evolution the modifications occur. The momentum ratio of the two leading partons, resolved as subjets, provides information...

The relative yields of ϒ mesons produced in pp and Pb-Pb collisions at sNN=5.02 TeV and reconstructed via the dimuon decay channel are measured using data collected by the CMS experiment. Double ratios are formed by comparing the yields of the excited states, ϒ(2S) and ϒ(3S), to the ground state, ϒ(1S), in both Pb-Pb and pp collisions at the same c...

An inclusive search for anomalous Higgs boson production in the diphoton decay channel and in association with at least one jet is presented, using LHC proton–proton collision data collected by the CMS experiment at a center-of-mass energy of 13 TeV and corresponding to an integrated luminosity of 35.9fb−1. The razor variables MR and R2, as well as...

A study of the associated production of a \(\mathrm{Z} \) boson and a charm quark jet (\(\mathrm{Z} + \mathrm{c} \)), and a comparison to production with a \(\mathrm{b} \) quark jet (\(\mathrm{Z} + \mathrm{b} \)), in \(\mathrm {p}\mathrm {p}\) collisions at a centre-of-mass energy of 8\(\,\text {TeV}\) are presented. The analysis uses a data sample...