[Show abstract][Hide abstract] ABSTRACT: The Compact Muon Solenoid (CMS) detector is described. The detector operates at the Large Hadron Collider (LHC) at CERN. It was conceived to study proton-proton (and lead-lead) collisions at a centre-of-mass energy of 14 TeV (5.5 TeV nucleon-nucleon) and at luminosities up to 1034 cm−2 s−1 (1027 cm−2 s−1). At the core of the CMS detector sits a high-magnetic-field and large-bore superconducting solenoid surrounding an all-silicon pixel and strip tracker, a lead-tungstate scintillating-crystals electromagnetic calorimeter, and a brass-scintillator sampling hadron calorimeter. The iron yoke of the flux-return is instrumented with four stations of muon detectors covering most of the 4π solid angle. Forward sampling calorimeters extend the pseudorapidity coverage to high values (|η| ≤ 5) assuring very good hermeticity. The overall dimensions of the CMS detector are a length of 21.6 m, a diameter of 14.6 m and a total weight of 12500 t.
Journal of Instrumentation 08/2008; 3(08):S08004. DOI:10.1088/1748-0221/3/08/S08004 · 1.40 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: At the Large Hadron Collider at CERN the proton bunches cross at a rate of 40 MHz. At the Compact Muon Solenoid experiment the original collision rate is reduced by a factor of O (1000) using a Level-1 hardware trigger. A subsequent factor of O (1000) data reduction is obtained by a software-implemented high level trigger (HLT) selection that is executed on a multi-processor farm. In this review we present in detail prototype CMS HLT physics selection algorithms, expected trigger rates and trigger performance in terms of both physics efficiency and timing.
European Physical Journal C 06/2006; 46(3-3):605-667. DOI:10.1140/epjc/s2006-02495-8 · 5.08 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: At the Large Hadron Collider at CERN the proton bunches cross at a rate of 40MHz. At the Compact Muon Solenoid experiment the original collision rate is reduced by a factor of O (1000) using a Level-1 hardware trigger. A subsequent factor of O(1000) data reduction is obtained by a software-implemented High Level Trigger (HLT) selection that is executed on a multi-processor farm. In this review we present in detail prototype CMS HLT physics selection algorithms, expected trigger rates and trigger performance in terms of both physics efficiency and timing.
[Show abstract][Hide abstract] ABSTRACT: Deep-inelastic e±p scattering at high squared momentum transfer Q2 up to 30 000 GeV2 is used to search for eq contact interactions associated to scales far beyond the Hera centre of mass energy. The neutral current cross section measurements dσ/dQ2, corresponding to integrated luminosities of 16.4 pb−1 of e−p data and 100.8 pb−1 of e+p data, are well described by the Standard Model and are analysed to set constraints on new phenomena. For conventional contact interactions lower limits are set on compositeness scales Λ ranging between 1.6–5.5 TeV. Couplings and masses of leptoquarks and squarks in R-parity violating supersymmetry are constrained to M/λ>0.3–1.4 TeV. A search for low scale quantum gravity effects in models with large extra dimensions provides limits on the effective Planck scale of MS>0.8 TeV. A form factor analysis yields a bound on the radius of light quarks of Rq<1.0×10−18 m.
Physics Letters B 05/2003; 568:35-47. DOI:10.1016/j.physletb.2003.06.034 · 6.13 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Dijet events in photon-proton collisions in which there is a large pseudorapidity separation, Deltaeta > 2.5 between the two highest E-T jets are studied with the H1 detector at HERA. The inclusive dijet cross sections are measured as functions of the longitudinal momentum fractions of the proton and photon which participate in the production of the jets, x(p)(jets) and x(gamma)(jets) respectively, Deltaeta, the pseudorapidity P separation between the two highest E-T jets, and E-T(gap), the total summed transverse energy between the jets. Rapidity gap events are defined as events in which E-T(gap) is less than E- T(cut), for E-T(cut) varied between jets 0.5 and 2.0 GeV. The fraction of dijet events with a rapidity gap is measured differentially in Deltaeta, x(p)(jets) and x(gamma)(jets). An excess of events with rapidity gaps at low values of E-T(cut) is observed above the expectation from standard photoproduction processes. This excess can be explained by the exchange of a strongly interacting colour singlet object between the jets.
European Physical Journal C 09/2002; 24:517-527. · 5.08 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A search for contributions from odderon - photon fusion to exclusive single pi0 production via ep --> epi0N* in the photoproduction regime at HERA, at an average photon - proton centre-of-mass energy = 210 GeV, and for photon virtualities of Q2 < 0.01 GeV2 is reported. The measurement proceeded via detection of the pi0 decay photons, the leading neutron from the N* decay, and the scattered electron. No indication for an odderon contribution was found. An upper limit is presented for the cross section integrated in the "visible" range 0.02 GeV2 < -t < 0.3 GeV2. It was derived as sigma(gammap --> pi0N*) < 39 nb at 95 % CL. This excludes an odderon - photon fusion cross section of 400 nb as predicted by theory.
Physics Letters B 09/2002; 544:35-43. · 6.13 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Results on diffractive photoproduction of psi(2S) mesons are presented using data collected between 1996 and 2000 with the H1 detector at the HERA ep collider. The data correspond to an integrated luminosity of 77 pb(-1). The energy dependence of the diffractive psi(2S) cross section is found to be similar to or possibly somewhat steeper than that for J/psi mesons. The dependences of the elastic and proton dissociative psi(2S) photoproduction cross sections on the squared momentum transfer t at the proton vertex are measured. The t-dependence of the elastic channel, parametrised as e(bt), yields b(el)(psi(2S)) = (4.31 +/- 0.57 +/- 0.46) GeV-2, compatible with that of the J/psi. For the proton dissociative channel the result b(pd)(psi(2S)) = (0.59 +/- 0.13 +/- 0.12) GeV-2 is 2.3 standard deviations smaller than that measured for the J/psi. With proper account of the individual wavefunctions theoretical predictions based on perturbative QCD are found to describe the measurements well. (C) 2002 Elsevier Science B.V. All rights reserved.
Physics Letters B 09/2002; 541:251-264. DOI:10.1016/S0370-2693(02)02275-X · 6.13 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Dijet cross sections as functions of several jet observables are measured in photoproduction using the HI detector at HERA. The data sample comprises e(+)p data with an integrated luminosity of 319 pb(-1). Jets are selected using the inclusive k(perpendicular to) algorithm with a minimum transverse energy of 25 GeV for the leading jet. The phase space covers longitudinal proton momentum fraction x(p) and photon longitudinal momentum fraction x(gamma) in the ranges 0.05 < x(p) < 0.6 and 0.1 < x(gamma) < 1. The predict ions of next-to- leading order perturbative QCD, including recent photon and proton parton densities, are found to be compatible with the data in a wide kinematical range.
European Physical Journal C 09/2002; 25:13-23. · 5.08 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A measurement of inclusive jet cross-sections in deep-inelastic ep scattering at HERA is presented based on data with an integrated luminosity of 21.1 pb(-1). The measurement is performed for photon virtualities Q(2) between 5 and 100 GeV2, differentially in Q(2), in the jet transverse energy E-T, in E- T(2)/Q(2) and in the pseudorapidity eta(lab). With the renormalization scale mu(R) = E-T, perturbative QCD calculations in next-to-leading order (NLO) give a good description of the data in most of the phase space. Significant discrepancies are observed only for jets in the proton beam direction with ET below 20 GeV and Q2 below 20 GeV2. This corresponds to the region in which NLO corrections are largest and further improvement of the calculations is thus of particular interest. (C) 2002 Elsevier Science B.V. All rights reserved.
Physics Letters B 07/2002; 542(3-4). DOI:10.1016/S0370-2693(02)02375-4 · 6.13 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The helicity structure of the diffractive electroproduction of rho mesons, e + p --> e + rho + Y, is studied in a previously unexplored region of large four-momentum transfer squared at the proton vertex, t: 0 < t' < 3 GeV2, where t' = \t\ - \t\ min. The data used are collected with the HI detector at HERA in the kinematic domain 2.5 < Q(2) < 60 GeV2, 40 < W < 120 GeV No t dependence of the r(00)(04) spin density matrix element is found. A significant t dependent helicity non-conservation from the virtual photon to the rho meson is observed for the spin density matrix element combinations r(00)(5) + 2r(11)(5) and r(00)(1) + 2r(11)(1). These t dependences are consistently described by a perturbative QCD model based on the exchange of two gluons. (C) 2002 Elsevier Science B.V. All rights reserved.
Physics Letters B 07/2002; 539:25-39. DOI:10.1016/S0370-2693(02)02035-X · 6.13 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A search for contributions to the reaction ep→eπ0N∗ from photon–odderon fusion in the photoproduction regime at HERA is reported, at an average photon–proton centre-of-mass energy 〈W〉=215 GeV. The measurement proceeds via detection of the π0 decay photons, a leading neutron from the N∗ decay, and the scattered electron. No π0 signal is observed and an upper limit on the cross section for the photon–odderon fusion process of σ(γp→π0N∗)<49 nb at the 95% confidence level is derived, integrated over the experimentally accessible range of the squared four-momentum transfer at the nucleon vertex 0.02<|t|<0.3 GeV2. This excludes a recent prediction from a calculation based on a non-perturbative QCD model of a photon–odderon fusion cross section above 200 nb.
Physics Letters B 06/2002; 544:35-43. DOI:10.1016/S0370-2693(02)02479-6 · 6.13 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Deep-inelastic scattering data in the range 150 < Q(2) < 35000 GeV2 are used to investigate the minimum jet separation necessary to allow accurate description of the rate of dijet production using next-to-leading order perturbative QCD calculations. The required jet separation is found to be small, allowing about 1/3 of DIS data to be classified as dijet, as opposed to approximately 1/10 with more typical jet analyses. A number of precision measurements made using this dijet sample are well described by the calculations. The data are also described by the combination of leading order matrix elements and parton showers, as implemented in the QCD based Monte Carlo model RAPGAP.
European Physical Journal C 05/2002; 24:33-41. DOI:10.1007/s100520100888 · 5.08 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The inclusive production of mesons in deep-inelastic scattering is studied with the H1 detector at HERA. In the kinematic region 1<Q2<100 GeV2 and 0.05<y<0.7 an e+p cross section for inclusive meson production of 8.50±0.42(stat.)+1.21−1.00(syst.) nb is measured in the visible range GeV and . Single and double differential inclusive meson cross sections are compared to perturbative QCD calculations in two different evolution schemes. The charm contribution to the proton structure, F2c(x,Q2), is determined by extrapolating the visible charm cross section to the full phase space. This contribution is found to rise from about 10% at Q2=1.5 GeV2 to more than 25% at Q2=60 GeV2 corresponding to x values ranging from 5×10−5 to 3×10−3.
Physics Letters B 03/2002; B528(3-4):199-214. DOI:10.1016/S0370-2693(02)01195-4 · 6.13 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We present a search for excited neutrinos using e−p data taken by the H1 experiment at HERA at a center-of-mass energy of 318 GeV with an integrated luminosity of 15 pb−1. No evidence for excited neutrino production is found. Mass dependent exclusion limits are determined for the ratio of the coupling to the compositeness scale, f/Λ, independently of the relative couplings to the SU(2) and U(1) gauge bosons. These limits extend the excluded region to higher masses than has been possible in previous searches at other colliders.
Physics Letters B 01/2002; 525:9-16. DOI:10.1016/S0370-2693(01)01410-1 · 6.13 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Signals of QCD instanton-induced processes are searched for in deep-inelastic scattering (DIS) at the electron-proton collider HERA in a kinematic region defined by the Bjorken-scaling variables x > 10(-3), 0.1 < y < 0.6 and photon virtualities 10 less than or similar to Q(2) < 100 GeV2. Several observables characterising hadronic final state properties of QCD instanton-induced events are exploited to identify a potentially instanton-enriched domain. While an excess of events with instanton-like topology is observed it cannot be claimed significant given the uncertainty of the standard DIS background simulation. Upper limits on the cross-section for instanton-induced processes of between 60 pb and 1000 pb are set dependent on the kinematic domain considered. The data do not exclude the cross-section predicted by instanton perturbation theory for small instanton sizes. At large instanton sizes a naive extrapolation of instanton perturbation theory yields a cross-section in the range of sensitivity of this study. Such a cross-section is not observed, in agreement with non-perturbative lattice simulations of the QCD vacuum.
[Show abstract][Hide abstract] ABSTRACT: The leptoproduction of J/psi mesons is studied in inelastic reactions for four momentum transfers 2<Q^2<100GeV^2. The data were taken with the H1 detector at the electron proton collider HERA and correspond to an integrated luminosity of 77 pb-1. Single differential and double differential cross sections are measured with increased precision compared with previous analyses. New leading order calculations within the non-relativistic QCD factorisation approach including colour octet and colour singlet contributions are compared with the data and are found to give a reasonable description of most distributions. An exception is the shape of the distribution in the J/psi fractional energy, z, which deviates significantly from that of the data. Comparisons with photoproduction are made and the polarisation of the produced J/psi meson is analysed. Paper: PostScript, PDF, or Other formats
[Show abstract][Hide abstract] ABSTRACT: An analysis of inelastic photoproduction of J/Psi mesons is presented using data collected at the ep collider HERA corresponding to an integrated luminosity of above 80pb-1. Differential and double differential cross sections are measured in a wide kinematic region: 60<W_gammap<260 GeV, 1<p_t^2< 60 GeV^2 and 0.05<z<0.9, where z is the fraction of the energy of the exchanged photon transferred to the J/Psi meson in the rest frame of the target proton. Cross sections at z<0.3 are presented for the first time. Theoretical calculations within the Colour Singlet Model at NLO for direct photon processes are shown to give a good description of the data in the medium z region (0.3<z<0.9) up to the highest p_t^2 values. A calculation using a k_t factorisation approach in LO in the Colour Singlet Model is also able to describe these data. The data in the full z range are also compared to LO calculations within a non-relativistic QCD framework including color octet and colour singlet contributions for direct and resolved photons. It seems possible to reconcile data and theory with modest contributions from colour octet processes. The polarisation of the J/Psi meson is measured as a function of z and p_t,psi and is reasonably described by the theoretical predictions.
[Show abstract][Hide abstract] ABSTRACT: The total cross section for the photoproduction process with a leading proton in the final state has been measured at yp centre-of-mass energies W of 91, 181 and 231 GeV. The measured cross sections apply to the kinematic range with the transverse momentum of the scattered proton restricted to P-T less than or equal to 0.2 GeV and 0.68 less than or equal to z less than or equal to 0.88, where z = E'(p)/E-p is the scattered proton energy normalised to the beam energy. The cross section d sigma (gammap-->Xp')(W, z)/dz is observed to be independent of W and z within the measurement errors and amounts to (8.05 +/- 0.06 (stat) +/- 0.89 (syst)) Pb on average. The data are well described by a Triple Regge model in which the process is mediated by a mixture of exchanges with an effective Regge trajectory of intercept alpha (i)(0) = 0.33 +/- 0.04 (stat) +/- 0.04 (syst). The total cross section for the interaction of the photon with this mixture (gamma alpha (i) --> X) can be described by an effective trajectory of intercept alpha (k) (0) = 0.99 +/- 0.01 (stat) +/- 0.05 (syst). Predictions based on previous triple Regge analyses of pp --> pX data assuming vertex factorisation are broadly consistent with the yp data. The measured cross sections are compared with deep inelastic scattering leading proton data in the same region of z and p(T) for photon virtuality Q(2) > 2.5 GeV2. The ratio of the cross section for leading proton production to the total cross section is found to rise with Q(2). (C) 2001 Elsevier Science B.V. All rights reserved.
Nuclear Physics B 12/2001; 619:3-21. DOI:10.1016/S0550-3213(01)00544-2 · 3.93 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A measurement is presented of the cross section for D∗± meson production in diffractive deep-inelastic scattering for the first time at HERA. The cross section is given for the process ep→eXY, where the system X contains at least one D∗± meson and is separated by a large rapidity gap from a low mass proton remnant system Y. The cross section is presented in the diffractive deep-inelastic region defined by 2<Q2<100 GeV2, 0.05<y<0.7, , MY<1.6 GeV and |t|<1 GeV2. The D∗± mesons are restricted to the range GeV and . The cross section is found to be 246±54±56 pb and forms about 6% of the corresponding inclusive D∗± cross section. The cross section is presented as a function of various kinematic variables, including which is an estimate of the fraction of the momentum of the diffractive exchange carried by the parton entering the hard-subprocess. The data show a large component of the cross section at low where the contribution of the boson–gluon-fusion process is expected to dominate. The data are compared with several QCD-based calculations.
Physics Letters B 09/2001; 520:191-203. DOI:10.1016/S0370-2693(01)01155-8 · 6.13 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A measurement of the derivative (∂ lnF2/∂ lnx)Q2≡−λ(x,Q2) of the proton structure function F2 is presented in the low x domain of deeply inelastic positron–proton scattering. For 5×10−5⩽x⩽0.01 and , λ(x,Q2) is found to be independent of x and to increase linearly with lnQ2.
Physics Letters B 08/2001; 520:183-190. DOI:10.1016/S0370-2693(01)01074-7 · 6.13 Impact Factor