Ž. Antunović

This work summarizes and puts in an overall perspective studies done within the compact muon solenoid (CMS) concerning the discovery potential for squarks and gluinos, sleptons, charginos and neutralinos, supersymmetric (SUSY) dark matter, lightest Higgs, sparticle mass determination methods and the detector design optimization in view of SUSY searches. It represents the status of our understanding of these subjects as of summer 1997. As a benchmark we used the minimal supergravity-inspired supersymmetric standard model (mSUGRA) with a stable lightest supersymmetric particle (LSP). Discovery of supersymmetry at the large hadron collider should be relatively straightforward. It may occur through the observation of large excesses of events in missing ET plus jets, or with one or more isolated leptons. An excess of trilepton events or isolated dileptons with missing ET, exhibiting a characteristic signature in the l+l− invariant mass distribution, could also be the first manifestation of SUSY production. Squarks and gluinos can be discovered for masses in excess of 2 TeV. Charginos and neutralinos can be discovered from an excess of events in dilepton or trilepton final states. Inclusive searches can give early indications from their copious production in squark and gluino cascade decays. Indirect evidence for sleptons can also be obtained from inclusive dilepton studies. Isolation requirements and a jet veto would allow detection of both the direct chargino/neutralino production and the directly produced sleptons. Squark and gluino production may also represent a copious source of Higgs bosons through cascade decays. The lightest SUSY Higgs h → b may be reconstructed with a signal/background ratio of order 1 thanks to hard cuts on ETmiss justified by escaping LSPs. The LSP of SUSY models with conserved R-parity represents a very good candidate for cosmological dark matter. The region of parameter space where this is true is well covered by our searches, at least for tanβ = 2.

The amplitude of the signal collected from the PbWO4 crystals of the CMS electromagnetic calorimeter is reconstructed by a digital filtering technique. The amplitude reconstruction has been studied with test beam data recorded from a fully equipped barrel supermodule. Issues specific to data taken in the test beam are investigated, and the implementation of the method for CMS data taking is discussed.

The avalanche photodiodes, developed by Hamamatsu Photonics in collaboration with CMS, which are to be used to read out the lead tungstate crystals in the barrel part of the CMS electromagnetic calorimeter, are described. The procedures taken to ensure their long-term reliability in the radiation environment expected in CMS are outlined, as well as the studies made to verify the very high reliability required.

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

Performance tests of some aspects of the CMS ECAL were carried out on modules of the "barrel" sub-system in 2002 and 2003. A brief test with high energy electron beams was made in late 2003 to validate prototypes of the new Very Front End electronics. The final versions of the monitoring and cooling systems, and of the high and low voltage regulation were used in these tests. The results are consistent with the performance targets including those for noise and overall energy resolution, required to fulfil the physics programme of CMS at the LHC.

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

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

The performance of electromagnetic calorimeter modules made of proton-irradiated PbWO4 crystals has been studied in beam tests. The modules, similar to those used in the Endcaps of the CMS electromagnetic calorimeter (ECAL), were formed from 5×5 matrices of PbWO4 crystals, which had previously been exposed to 24 GeV protons up to integrated fluences between 2.1× 1013 and 1.3× 1014 cm−2. These correspond to the predicted charged-hadron fluences in the ECAL Endcaps at pseudorapidity η = 2.6 after about 500 fb−1 and 3000 fb−1 respectively, corresponding to the end of the LHC and High Luminosity LHC operation periods. The irradiated crystals have a lower light transmission for wavelengths corresponding to the scintillation light, and a correspondingly reduced light output. A comparison with four crystals irradiated in situ in CMS showed no significant rate dependence of hadron-induced damage. A degradation of the energy resolution and a non-linear response to electron showers are observed in damaged crystals. Direct measurements of the light output from the crystals show the amplitude decreasing and pulse becoming faster as the fluence increases. The latter is interpreted, through comparison with simulation, as a side-effect of the degradation in light transmission. The experimental results obtained can be used to estimate the long term performance of the CMS ECAL.

We evaluated the effects on the absorbed dose to thyroid follicular cells of self-absorption of (131)I radiation (specifically, beta-rays) in the follicular colloid.Thyroid follicles were modeled as colloid-filled spheres, containing a uniform concentration of (131)I and surrounded by a concentric monolayer of cells. Assuming close packing of identical follicles, we used Monte Carlo simulation to assess the absorbed dose to follicular cells.Because of beta-ray self-absorption in colloidal spheres with radii larger than 50 mum, the absorbed dose to follicular cells is less than the average thyroid absorbed dose.For the same thyroid mass, radioiodine thyroid uptake, and effective half-life, patients with follicles with colloidal sphere radii of 100, 200, 300, and 400 microm should be administered 9%, 15%, 21%, and 30% more (131)I, respectively, than patients with colloidal sphere radii of less than 50 microm, to yield the same absorbed dose to follicular cells.

The ground-state properties of 3He and 4He dimers and trimers in infinite carbon nanotubes are studied. The ground state eigen-functions of a helium atom in tubes of different radii are obtained numerically and then fitted by analytic expressions. Total wave function is assumed to be a product of Jastrow–Feenberg pair correlation and one particle functions. After extensive Monte Carlo (MC) calculation in two successive stages, simple variational MC and diffusion MC it is found that binding depends on the tube radius and it has the maximum for a certain tube width. This radius is between 5 and 7Å, and the average distance between atoms in such tubes is ranges from 5 to 10Å. The difference in binding between bosons and fermions disappears for R→0.

Abstract Helium dimers and trimers in infinite carbon nanotubes are described by wave function constructed as a product of Jastrow–Feenberg (JF) pair correlation and one-particle functions. One-particle functions are the ground state eigenfunctions of one helium atom in the tube; their analytic form is derived by fitting the corresponding numerical solution. Using this function in the Monte Carlo (MC) calculations in two successive stages, VMC (simple variational MC) and DMC (diffusion MC), it is found that binding strongly depends on the tube radius. Among armchair nanotubes binding is the strongest for the (7,7) nanotube. In that case the average distance between helium atoms in dimers and trimers is between 5 and 10 A . For larger radii the energies of 3 He dimers and trimers are the same within the errorbars, indicating the possible dimerized structure. In the (5,5) nanotube, the binding energies of boson 4 He 3 and fictitious fermion trimer, which has the same mass as 4 He 3 and spin 1 2 , are within the errorbars.

The photodetectors which read out the scintillation light generated in the lead tungstate crystals in the barrel part of the Compact Muon Solenoid (CMS) electromagnetic calorimeter are avalanche photodiodes (APDs). Scanning the APD's active area with a collimated light spot, the spatial uniformity of their quantum efficiency and gain has been measured at four different operating gains. Details of the APD surface structure are examined by scanning with a fine light spot. These details help to explain the difference between the bias voltage for a given gain when the full APD area is illuminated and when only the central part is illuminated.

The problem of the participation of young drivers in trafficaccidents is constantly present and represents a significant socialproblem. In complex and dynamic conditions of moderntraffic flows, the young drivers are exposed to various and unforeseenhazard situations and events which they had not experiencedduring the basic training. Therefore, they should be providedwith the possibility of acquiring additional experiences insolving typical hazard situations in traffic. This is possible bythe system of advanced training which places the course participantin the situation of facing possible hazards, with the aim ofincreasing the awareness of risk in driving and behaviour at thesteering wheel. Advanced driver training is based on the specificprogram and training the drivers to acquire additional experiencesin solving dangerous traffic situations.

The ground state of the helium 4 dimer is considered using the Monte Carlo technique. In a cylinder with a hard core wall, binding depends on its radius. For a small radius binding occurs as in the one-dimensional case. With an increase of the radius, the binding becomes stronger, reaches its maximum value, and then slowly diminishes. In conical geometry, that may be realized as a generalization of a cylindrical one, this dependence of the binding energy on the radius might lead to an effective force which tends to move the molecule toward the region of minimal energy. Thus, in channels, with nonhomogeneous cross-sections, the particles move easier in dimer form. In addition, the square of the momentum and of the particle separation along the cylinder axis and in the plane perpendicular to it are calculated as well.

We show that a suitably ansatzed form of coherent states leads to infrared finite coherent state amplitudes in QEMD.

We investigate the possibility of searching for squarks and gluinos in the [Formula: see text] + jets final states within the SUGRA framework. With the chosen set of model parameters, A 0 = 0, tan β=2, and with μ both negative and positive, for an integrated luminosity of 10 fb -1 the CMS detector would probe squarks and a gluino mass range of up to ≈ 1 TeV.

We evaluate the maximal reach of the CMS detector for the discovery of squarks and gluinos at large tan β=35 in [Formula: see text] final states during the initial low luminosity phase of LHC. For an integrated luminosity of 1 fb -1 a signal should be observed if squarks and gluinos have masses not exceeding ≈1.3 TeV.

A generalized Lagrangian BRST formalism is used to study the quantum structure of the simple supergravity, whose classical gauge algebra is not closed. It is shown that in this approach one can naturally introduce a set of auxiliary fields as certain combinations of ghosts and antifields, so that the resulting theory has the closed classical gauge algebra.

The CMS Collaboration presents the first measurement of the differential cross section of jets from charm quarks produced in proton-lead (pPb) collisions at a nucleon-nucleon center-of-mass energy of sqrt(s[NN]) = 5.02 TeV, as well as results from charm quark jets in proton-proton (pp) collisions at sqrt(s) = 2.76 and 5.02 TeV. By comparing the yields of the pPb and pp collision systems at the same energy, a nuclear modification factor for charm jets from 55 to 400 GeV/c in pPb collisions at sqrt(s[NN]) = 5.02 TeV of R[pA] = 0.92 +/- 0.07 (stat) +/- 0.11 (syst) is obtained. This is consistent with an absence of final-state energy loss for charm quarks in pPb collisions. In addition, the fraction of jets coming from charm quarks is found to be consistent with that predicted by PYTHIA 6 for pp collisions at sqrt(s)= 2.76 and 5.02 TeV, and is independent of the jet transverse momentum from 55 to 400 GeV/c.

The light from the lead tungstate crystals of the barrel part of the CMS ECAL will be measured using avalanche photodiodes developed for the purpose by Hamamatsu Photonics in collaboration with CMS.The requirements for the diodes are described, and the performance achieved is summarised, with emphasis on the long-term reliability in the difficult high radiation conditions at CMS.

Na CERN-u su u toku zadnje pripreme za pustanje u pogon LHCa. Na tom sudarivacu ce se proucavati sudari protona na energiji centra mase od 14 TeV. Eksperimentalni program LHC obuhvaca siroki spektar otvorenih pitanja u fizici elementarnih cestica: porijeklo masa bozona i fermiona, potraga za kandidatima tamne tvari, kvarkgluonska plazma, simetrija materija-antimaterija, itd. Visegodisnja faza razvoja i izgradnje LHC detektora zavrsila je 2008. godine i 4 velika detektora ALICE, ATLAS, CMS i LHCb su danas spremna za snimanje prvih sudara. U protekloj godini su LHC detektori snimili vecu kolicinu kozmickih zraka, pomocu kojih su se mogle testirati performanse raznih podsustava detektora i sustava prikupljanja podataka, kao i razne metode kalibracije detektora. Također su se proucile karakteristike spektra kozmickih miona. Na jesen 2009. se ocekuju prva mjerenja proton-proton sudara. Predavanje ce se uz navedeno osvrnuti i na mjerenja koja se ocekuju u ranoj fazi LHC-a, od provjera standardnog modela do prvih potraga za novom fizikom.

Rezultati kolaboracije MAGIC (Major Atmospheric Gamma-ray Imaging Cherenkov) su otkrice pulsne emisije gama-zraka iz okoline pulsara u podrucju Rakove maglice, sto iskljucuje model polarne kape, te detekcija visokoenergijskih gama-zraka iz aktivne galakticke jezgre 3C 279 udaljene vise od 5 milijardi svjetlosnih godina, sto ukazuje na vecu transparentnost svemira. Hrvatska grupa u kolaboraciji MAGIC radi na poboljsanju metode gama/hadron separacije na niskim energijama, analizi visokoenergijskog gama-zracenja iz aktivnih galaktickih jezgri i pulsara. Prvi projekt iz podrucja astrocesticne fizike koji ce financirati ASPERA (mreža nacionalih agencija za finaciranje projekata iz astrocesticne fizike) je projekt CTA (Cherenkov Telescope Array), opservatorij visokoenergijskog gamazracenja kojeg ce ciniti dvjestotinjak teleskopa razlicitih velicina.

Opažanje aktivnih galaktickih jezgri (AGN) u podrucju gama–zraka može omoguciti bolje razumijevanje relativistickih mlazova supermasivnih crnih rupa, a time i mehanizama nastanka visokoenergijskih cestica pri akreciji tvari u crnu rupu. Galaksija M87 je za sada jedina radio galaksija koja ne pripada skupiti blazara u cijem su spektru opažene visokoenergijske gama–zrake. Kolaboracija MAGIC vec niz godina prati i istražuje ponasanje M87 u podrucju visokih energija. MAGIC (Major Atmospheric Gamma Imaging Cherenkov) teleskop je optimiziran za opažanje i bilježenje Cerenkovljevog zracenja u Zemljinoj atmosferi koje stvara gama–zracenje iz svemira. U ovom radu predstavljen je MAGIC teleskop, te postupak i rezultati analize opažanja M87.

CMS (Compact Muon Solenoid) je detektor opce namjene za mjerenje fizikalnih događaja u sudarima protona na LHC-u (Large Hadron Collider). Optimiziran je za potragu za Higgsovim bozonom u relevantnom podrucju masa, od donje granice od 114, 4 GeV/c2, postavlje direktnim mjerenjima na LEP-u (Large Electron Positron Collider), pa sve do mase od oko 1 TeV/c2. U ovom radu bit ce prezentiran potencijal CMS detektora za pronalazak Higgsovog bozona, s naglaskom na potragu kroz raspad H → ZZ(*)→ l+l− l+l− (l predstavlja elektrone, mione i njihove anticestice). Rezultati pokazuju da ce se Higgsov bozon moci pronaci kroz ovaj kanal raspada vec pri integriranom luminozitetu od 3 fb-1, ako je njegova masa oko 150 GeV/c2 ili veca od oko 190 GeV/c2. U drugom dijelu rada bit ce prezentiran potencijal CMS detektora za mjerenje proizvodnje dvaju baždarnih bozona (ZZ i WZ), kroz njihove leptonske raspade, te ce biti pokazano da se ovaj signal može mjeriti u ranoj fazi eksperimenta, pri integriranom luminozitetu manjem od 1 fb-1. Svi rezultati prikazani u ovom radu dobiveni su koristeci potpunu Monte Carlo simulaciju CMS detektora i novo razvijene algoritme za rekonstrukciju elektrona i miona te realisticnu procjenu sistematskih efekata.

A search for resonance like structures in the B0sπ± 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 B0s mesons are reconstructed in the decay chain B0s→J/ψϕ, with J/ψ→μ+μ− and ϕ→K+K−. The B0sπ± invariant mass distribution shows no statistically significant peaks for different selection requirements on the reconstructed B0s and π± candidates. Upper limits are set on the relative production rates of the X(5568) and B0s states times the branching fraction of the decay X(5568)±→B0sπ±. In addition, upper limits are obtained as a function of the mass and the natural width of possible exotic states decaying into B0sπ±.

The massive superparticle in D = 9 is covariantly quantized by using a generalized lagrangian BRST formalism. The method is based on the structure of the classical gauge algebra, and ensures the off-shell nilpotency of the BRST symmetry of the gauge-fixed action by introducing a set of auxilliary fields with non-vanishing ghost numbers.

The Compact Muon Solenoid is one of two general purpose detectors currently being constructed for the Large Hadron Collider at CERN foreseen to begin data taking in 2007. Avalanche Photo Diodes (APDs) have been chosen to detect the scintillation light of the 61 200 lead tungstate crystals in the barrel part of the electromagnetic calorimeter of CMS. After a 8 years long R&D work Hamamatsu Photonics produces now APDs with a structure that is basically radiation resistant. Since a reliability of 99.9% is required, a method to detect weak APDs before they are built into the detector had to be developed. The described screening method is a combination of an irradiation with 60Co and annealing under bias of all APDs and on a sampling basis only an irradiation with hadrons.

We discuss the current status of the Large Hadron Collider (LHC) machine, the progress on the construction of the CMS detector and some expectations for physics studies and searches at the LHC.

Specially developed vacuum phototriodes (VPTs) will be used to detect scintillation light produced in the lead tungstate (PbWO4) crystals in the end-cap sub-system of the electromagnetic calorimeter (ECAL) of the Compact Muon Solenoid (CMS) detector. The spatial uniformity of the VPT's photocathode quantum efficiency was measured by scanning their photosensitive area with collimated light source.

The lead tungstate crystals of the barrel part of the CMS electromagnetic calorimetar (ECAL) will be read out using avalanche photodiodes (APDs). To maintain performance of the CMS ECAL, the APDs must operate with a very high reliability for at least ten years in an extremely hostile environment. By measuring the dark current of APDs every 30 minutes over 72 days the stability of carefully selected APDs has been studied.

The observability of the light neutral Higgs boson h in the final state is investigated and shown to be possible in a large region of the supersymmetric parameter space with reasonable requirements on the calorimeter resolution. This channel significantly extends the search of the basic channel to lower and down to GeV with . Although less demanding on calorimeter resolution, this mode of detection does require largest available statistics, at least .

We show that it is possible to search for the Standard Model Higgs bosons in the H - ZZ - 4l channel at LHC using Z^0 polarization. This will strengthen the conclusivity of detection by the primary method based on the reconstruction of 4l invariant mass and provide information about Higgs boson polarization.

We investigate the possibility to search for squarks and gluinos in the 4 l + E(miss) + jets final state within the mSUGRA framework.

Abstract The infrared problem of the quantum field theory of electric and magnetic charges is resolved by using functional methods, without recourse to perturbation theory.

The topological spinning particle is quantized using a generalized Lagrangian BRST formalism based on the analysis of the constraint structure of the classical gauge algebra.