Deep learning for inferring cause of data anomalies

Daily operation of a large-scale experiment is a resource consuming task, particularly from perspectives of routine data quality monitoring. Typically, data comes from different sub-detectors and the global quality of data depends on the combinatorial performance of each of them. In this paper, the problem of identifying channels in which anomalies occurred is considered. We introduce a generic deep learning model and prove that, under reasonable assumptions, the model learns to identify 'channels' which are affected by an anomaly. Such model could be used for data quality manager cross-check and assistance and identifying good channels in anomalous data samples. The main novelty of the method is that the model does not require ground truth labels for each channel, only global flag is used. This effectively distinguishes the model from classical classification methods. Being applied to CMS data collected in the year 2010, this approach proves its ability to decompose anomaly by separate channels.Comment: Presented at ACAT 2017 conference, Seattle, US

Constraints on parton distribution functions and extraction of the strong coupling constant from the inclusive jet cross section in pp collisions at √s = 7 TeV

The inclusive jet cross section for proton–proton collisions at a centre-of-mass energy of 7 TeV was measured by the CMS Collaboration at the LHC with data corresponding to an integrated luminosity of 5.0 fb^(−1). The measurement covers a phase space up to 2 TeV in jet transverse momentum and 2.5 in absolute jet rapidity. The statistical precision of these data leads to stringent constraints on the parton distribution functions of the proton. The data provide important input for the gluon density at high fractions of the proton momentum and for the strong coupling constant at large energy scales. Using predictions from perturbative quantum chromodynamics at next-to-leading order, complemented with electroweak corrections, the constraining power of these data is investigated and the strong coupling constant at the Z boson mass M_Z is determined to be α_S (M_Z) = 0.1185 ± 0.0019(exp)^(+0.0060)_(−0.0037)(theo) , which is in agreement with the world average

Search for new phenomena in monophoton final states in proton–proton collisions at √s = 8 TeV

Results are presented from a search for new physics in final states containing a photon and missing transverse momentum. The data correspond to an integrated luminosity of 19.6 fb^(−1) collected in proton–proton collisions at √s = 8 TeV with the CMS experiment at the LHC. No deviation from the standard model predictions is observed for these final states. New, improved limits are set on dark matter production and on parameters of models with large extra dimensions. In particular, the first limits from the LHC on branon production are found and significantly extend previous limits from LEP and the Tevatron. An upper limit of 14.0 fb on the cross section is set at the 95% confidence level for events with a monophoton final state with photon transverse momentum greater than 145 GeV and missing transverse momentum greater than 140 GeV

Measurement of the inclusive 3-jet production differential cross section in proton–proton collisions at 7 TeV and determination of the strong coupling constant in the TeV range

This paper presents a measurement of the inclusive 3-jet production differential cross section at a proton–proton centre-of-mass energy of 7 TeV using data corresponding to an integrated luminosity of 5fb^(−1) collected with the CMS detector. The analysis is based on the three jets with the highest transverse momenta. The cross section is measured as a function of the invariant mass of the three jets in a range of 445–3270 GeV and in two bins of the maximum rapidity of the jets up to a value of 2. A comparison between the measurement and the prediction from perturbative QCD at next-to-leading order is performed. Within uncertainties, data and theory are in agreement. The sensitivity of the observable to the strong coupling constant α_S is studied. A fit to all data points with 3-jet masses larger than 664 GeV gives a value of the strong coupling constant of α_S (M Z )=0.1171±0.0013(exp) ^(+0.0073)_(−0.0047)(theo)

Search for a standard model-like Higgs boson in the μ^+μ^−and e^+e^−decay channels at the LHC

A search is presented for a standard model-like Higgs boson decaying to the μ^+μ^- or e^+e^− final states based on proton–proton collisions recorded by the CMS experiment at the CERN LHC. The data correspond to integrated luminosities of 5.0 fb^(−1) at a centre-of-mass energy of 7 TeV and 19.7 fb^(−1) at 8 TeV for the μ^+μ^− search, and of 19.7 fb^(−1) at 8 TeV for the e^+e^− search. Upper limits on the production cross section times branching fraction at the 95% confidence level are reported for Higgs boson masses in the range from 120 to 150 GeV. For a Higgs boson with a mass of 125 GeV decaying to μ^+μ^−, the observed (expected) upper limit on the production rate is found to be 7.4 6.5_(−1.9)^(+2.8)) times the standard model value. This corresponds to an upper limit on the branching fraction of 0.0016. Similarly, for e^+e^−, an upper limit of 0.0019 is placed on the branching fraction, which is ≈3.7×10^5 times the standard model value. These results, together with recent evidence of the 125 GeV boson coupling to τ-leptons with a larger branching fraction consistent with the standard model, confirm that the leptonic couplings of the new boson are not flavour-universal

Measurement of the W boson helicity in events with a single reconstructed top quark in pp collisions at √s = 8 TeV

A measurement of the W boson helicity is presented, where the W boson originates from the decay of a top quark produced in pp collisions. The event selection, optimized for reconstructing a single top quark in the final state, requires exactly one isolated lepton (muon or electron) and exactly two jets, one of which is likely to originate from the hadronization of a bottom quark. The analysis is performed using data recorded at a center-of-mass energy of 8 TeV with the CMS detector at the CERN LHC in 2012. The data sample corresponds to an integrated luminosity of 19.7 fb^(−1). The measured helicity fractions are F_L = 0.298 ± 0.028 (stat) ± 0.032(syst), F_0 = 0.720 ± 0.039 (stat) ± 0.037(syst), and F_R = −0.018 ± 0.019 (stat) ± 0.011(syst). These results are used to set limits on the real part of the tWb anomalous couplings, g_L and g_R

Coherent J/ψ photoproduction in ultra-peripheral PbPb collisions at √s_NN = 2.76 TeV with the CMS experiment

The cross section for coherent J/ψ photoproduction accompanied by at least one neutron on one side of the interaction point and no neutron activity on the other side, X_(n)0_(n), is measured with the CMS experiment in ultra-peripheral PbPb collisions at √s_NN = 2.76 TeV. The analysis is based on a data sample corresponding to an integrated luminosity of 159 μb^(−1), collected during the 2011 PbPb run. The J/ψ mesons are reconstructed in the dimuon decay channel, while neutrons are detected using zero degree calorimeters. The measured cross section is dσ^(coh)_(X_(n)0_(n))/dy(J/ψ) = 0.36 ± 0.04 (stat) ± 0.04 (syst) mb in the rapidity interval 1.8 < |y| < 2.3. Using a model for the relative rate of coherent photoproduction processes, this X_(n)0_(n) measurement gives a total coherent photoproduction cross section of dσ^(coh)/dy(J/ψ) = 1.82 ± 0.22 (stat) ± 0.20 (syst) ± 0.19 (theo) mb. The data strongly disfavor the impulse approximation model prediction, indicating that nuclear effects are needed to describe coherent J/ψ photoproduction in γ+Pb interactions. The data are found to be consistent with the leading twist approximation, which includes nuclear gluon shadowing

Search for new physics with the M_(T2) variable in all-jets final states produced in pp collisions at √s = 13 TeV

A search for new physics is performed using events that contain one or more jets, no isolated leptons, and a large transverse momentum imbalance, as measured through the M_(T2) variable, which is an extension of the transverse mass in events with two invisible particles. The results are based on a sample of proton-proton collisions collected at a center-of-mass energy of 13 TeV with the CMS detector at the LHC, and that corresponds to an integrated luminosity of 2.3 fb^(−1). The observed event yields in the data are consistent with predictions for the standard model backgrounds. The results are interpreted using simplified models of supersymmetry and are expressed in terms of limits on the masses of potential new colored particles. Assuming that the lightest neutralino is stable and has a mass less than about 500 GeV, gluino masses up to 1550-1750 GeV are excluded at 95% confidence level, depending on the gluino decay mechanism. For the scenario of direct production of squark-antisquark pairs, top squarks with masses up to 800 GeV are excluded, assuming a 100% branching fraction for the decay to a top quark and neutralino. Similarly, bottom squark masses are excluded up to 880 GeV, and masses of light-flavor squarks are excluded up to 600-1260 GeV, depending on the degree of degeneracy of the squark masses

Measurement of the ratio of the production cross sections times branching fractions of B^±_c → J/ψπ^± and B^± → J/ψK^± and B(B^±_c → J/ψπ^±π^±π^∓)/B(B^±_c → J/ψπ^±) in pp collisions at √s = 7 TeV

The ratio of the production cross sections times branching fractions (σ(B±c)B(B^±_c → J/ψπ^±))σ(B±)B(B± → J/ψK^±)) is studied in proton-proton collisions at a center-of-mass energy of 7TeV with the CMS detector at the LHC. The kinematic region investigated requires B^±_c and B^± mesons with transverse momentum p_T > 15 GeV and rapidity |y| < 1.6. The data sample corresponds to an integrated luminosity of 5.1 fb^(−1). The ratio is determined to be [0.48 ± 0.05 (stat) ± 0.03 (syst) ± 0.05 (T_B_c)]%. The B^±_c → J/ψπ^±π^±π^∓ decay is also observed in the same data sample. Using a model-independent method developed to measure the efficiency given the presence of resonant behaviour in the three-pion system, the ratio of the branching fractions B(B^±_c → J/ψπ^±π^±π^∓)/B(B^±_c → J/ψπ^±) is measured to be 2.55±0.80 (stat)±0.33 (syst)^(+0.04)_(−0.01) (T_B_c ), consistent with the previous LHCb result