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2017-02-22
08:09
Results (and future prospects) of the CMS experiment in photon-induced interactions in p-Pb collisions / Bylinkin, Alexander (Moscow, MIPT ; Moscow Phys. Eng. Inst.)
Exclusive vector meson photoproduction is studied in ultra-peripheral pPb collisions at p sNN = 5:02 TeV with the CMS experiment at the LHC. [...]
CMS-CR-2016-346.
- 6 p.
Full text

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2017-02-22
06:42
Dichroic subjettiness ratios to distinguish colour flows in boosted boson tagging / Salam, Gavin P (CERN) ; Schunk, Lais (IPhT, Saclay) ; Soyez, Gregory (IPhT, Saclay)
$N$-subjettiness ratios are in wide use for tagging heavy boosted objects, in particular the ratio of 2-subjettiness to 1-subjettiness for tagging boosted electroweak bosons. [...]
arXiv:1612.03917.
- 2016. - 42 p.
00022 Same as figure as \ref{fig:distribs-mass} and \ref{fig:distribs-tau21} now obtained from our analytic calculation instead of Monte-Carlo simulations. In the right-hand plot, for clarity, the $\delta$-function that appears at $\tauDG=1$ (dijets) has been represented with finite width and scaled down by a factor of $5$. - 00023 Same as figure as \ref{fig:distribs-mass} and \ref{fig:distribs-tau21} now obtained from our analytic calculation instead of Monte-Carlo simulations. In the right-hand plot, for clarity, the $\delta$-function that appears at $\tauDG=1$ (dijets) has been represented with finite width and scaled down by a factor of $5$. - 00016 Signal significance plotted versus the non-perturbative effects for the QCD background (defined as the ratio between the background ``fake'' tagging rate at hadron and parton level). Different curves correspond to different combinations indicated in the legend. For the solid curves, a SoftDrop ($\beta=2$ and $\zetacut=0.05$) grooming is applied, while no grooming is applied for the dashed curves. In the left-hand plot, we impose a 2~TeV $p_t$ cut on the initial jet. The symbols on each curve then correspond to a signal efficiency (computed at hadron level) ranging from 0.05 upwards in steps of 0.05, with the large symbol on each line corresponding to $\varepsilon_S=0.5$ and the efficiency at the right-hand extremity explicitly labelled. In the right-hand plot, the signal efficiency (computed at hadron level) is fixed to be 0.5 and the $p_t$ cut on the jet is varied between 500~GeV and 3~TeV (in steps of 500~GeV, labelled explicitly for the groomed dichroic ratio), with the large symbol on each line corresponding to a 3~TeV cut. - 00018 Signal significance and non-perturbative effects for background, for jet $p_t$ cuts ranging from $500\GeV$ to $3\TeV$ in steps of $500\GeV$, as in Fig.~\ref{fig:np-effects}(right). The $3\TeV$ point is always labelled with a larger symbol. The plots compare $\tauDG$ ($\beta_\tau=2$) with a range of other tools, including Y$_\text{m}$-splitter (left) and $\beta_\tau=1$ dichroic subjettiness ratios (right). Where the $\beta_\tau$ value is not explicitly labelled, it is equal to $2$. Note that the default signal-efficiency working point for the dichroic subjettiness ratios is $0.4$ here rather than the $0.5$ chosen in Fig.~\ref{fig:np-effects}. The signal efficiencies for other cases are given in Table~\ref{tab:efficiencies}. - 00025 ROC curves providing a comparison between different $N$-subjettiness ratios for $\beta_\tau=1$ (dashed lines) and $\beta_\tau=2$ (solid lines). The same 4 variants as in Figs.~\ref{fig:roc-parton} and~\ref{fig:roc-full} are included. The left (right) column corresponds to \fulljet (SD-groomed) jets. The top (bottom) row corresponds to parton-level (hadron-level) events. - 00012 $\tau_{21}$ distributions for jets in dijet (solid lines) and $WW$ (dashed lines) events again imposing $p_t>2$~TeV and including SoftDrop grooming. Different colours correspond to different combinations of jets used for the computation of the jet mass, $\tau_1$ and $\tau_2$ as indicated in the legend, our new dichroic combination being plotted in black. We have selected jets with a mass is between 60 and 100~GeV. The cross-section used for normalisation, $\sigma$, is defined after the jet $p_t$ and mass cut, so that all curves integrate to one. - 00017 Signal efficiency plotted as a function of the cut $\taucut$ on $\tau_{21}$ for all the combinations considered in Figs.~\ref{fig:roc-parton} and \ref{fig:roc-full}. Solid curves correspond to hadron-level results while dashed curves are obtained at parton level. The left plot is obtained starting from the \fulljet jet, while for the right plot, a SoftDrop grooming has been applied. - 00015 Signal significance plotted versus the non-perturbative effects for the QCD background (defined as the ratio between the background ``fake'' tagging rate at hadron and parton level). Different curves correspond to different combinations indicated in the legend. For the solid curves, a SoftDrop ($\beta=2$ and $\zetacut=0.05$) grooming is applied, while no grooming is applied for the dashed curves. In the left-hand plot, we impose a 2~TeV $p_t$ cut on the initial jet. The symbols on each curve then correspond to a signal efficiency (computed at hadron level) ranging from 0.05 upwards in steps of 0.05, with the large symbol on each line corresponding to $\varepsilon_S=0.5$ and the efficiency at the right-hand extremity explicitly labelled. In the right-hand plot, the signal efficiency (computed at hadron level) is fixed to be 0.5 and the $p_t$ cut on the jet is varied between 500~GeV and 3~TeV (in steps of 500~GeV, labelled explicitly for the groomed dichroic ratio), with the large symbol on each line corresponding to a 3~TeV cut. - 00001 Lund diagram representation for the phasespace regions relevant to the \fulljet jet mass (left) and the mMDT mass (right). The solid black point corresponds to the emission dominating the jet mass and can be anywhere along the solid red line. It gives the prefactor in the jet mass distribution. The shaded red area corresponds to the vetoed region yielding the Sudakov exponent. - 00019 Lund diagrams associated with various analytic calculations. Left: the basic building block $T_\alpha$, Eq.~(\ref{eq:basic-analytic-block}), used to write all Sudakov exponents. Centre: representation of the \fulljet jet Sudakov $R_{\text{\fulljet}}(\rho,\taucut,z)$, Eq.~(\ref{eq:finalRplain}), including secondary emissions. Right: representation of the \fulljet jet Sudakov $R_{\text{SD}}(\rho,\taucut,z)$, Eq.~(\ref{eq:finalRsd}), including secondary emissions. For both the centre and right plots, the dot indicated by $z$ corresponds to the emission dominating the jet mass and we will integrate over allowed values of its momentum fraction $z$. - 00002 Lund diagram representation for the phasespace regions relevant to the \fulljet jet mass (left) and the mMDT mass (right). The solid black point corresponds to the emission dominating the jet mass and can be anywhere along the solid red line. It gives the prefactor in the jet mass distribution. The shaded red area corresponds to the vetoed region yielding the Sudakov exponent. - 00008 - 00010 Caption not extracted - 00011 Phasespace constraints on QCD jets obtained from our new combination including grooming: we first groom the jet, \eg with SoftDrop (SD). We then compute both the jet mass and $\tau_1$ on the tagged jet (here using the mMDT), yielding the solid red line prefactor and the shaded red region (A) for the Sudakov exponent. We then impose a cut on the $\tau_{21}$ ratio with $\tau_2$ computed on the SD jet, leading to the extra shaded blue and green regions (B and C) for the Sudakov exponent. - 00007 Schematic representation of three possible kinematic configurations for the combination of $\tau_{21}$ with mMDT/SD (shown specifically for mMDT or SD with $\beta=0$). In each Lund diagram, emission ``a'' corresponds to the emission that dominates the mMDT/SD jet mass. This defines three regions: region A (red) is vetoed by mMDT, region B (blue) contains the constituents of the mMDT/SD jet and region C (blue) is the difference between the mMDT/SD jet and the \fulljet jet. Emissions ``b'' and ``c'' are respectively in regions B and C, and the three plots correspond to three different orderings of $z_c\theta_c^2$ compared to $z_a\theta_a^2$ and $z_b\theta_b^2$. The table below the plots shows the corresponding value of $\tau_{21}$ for both the QCD background (where all three regions have to be included) and the signal (where only regions A and B are present). For simplicity, ``b/a'' stands for $(z_b\theta_b^2)/(z_a\theta_a^2)$, and so forth. - 00005 Schematic representation of three possible kinematic configurations for the combination of $\tau_{21}$ with mMDT/SD (shown specifically for mMDT or SD with $\beta=0$). In each Lund diagram, emission ``a'' corresponds to the emission that dominates the mMDT/SD jet mass. This defines three regions: region A (red) is vetoed by mMDT, region B (blue) contains the constituents of the mMDT/SD jet and region C (blue) is the difference between the mMDT/SD jet and the \fulljet jet. Emissions ``b'' and ``c'' are respectively in regions B and C, and the three plots correspond to three different orderings of $z_c\theta_c^2$ compared to $z_a\theta_a^2$ and $z_b\theta_b^2$. The table below the plots shows the corresponding value of $\tau_{21}$ for both the QCD background (where all three regions have to be included) and the signal (where only regions A and B are present). For simplicity, ``b/a'' stands for $(z_b\theta_b^2)/(z_a\theta_a^2)$, and so forth. - 00006 Schematic representation of three possible kinematic configurations for the combination of $\tau_{21}$ with mMDT/SD (shown specifically for mMDT or SD with $\beta=0$). In each Lund diagram, emission ``a'' corresponds to the emission that dominates the mMDT/SD jet mass. This defines three regions: region A (red) is vetoed by mMDT, region B (blue) contains the constituents of the mMDT/SD jet and region C (blue) is the difference between the mMDT/SD jet and the \fulljet jet. Emissions ``b'' and ``c'' are respectively in regions B and C, and the three plots correspond to three different orderings of $z_c\theta_c^2$ compared to $z_a\theta_a^2$ and $z_b\theta_b^2$. The table below the plots shows the corresponding value of $\tau_{21}$ for both the QCD background (where all three regions have to be included) and the signal (where only regions A and B are present). For simplicity, ``b/a'' stands for $(z_b\theta_b^2)/(z_a\theta_a^2)$, and so forth. - 00009 Regions where real emissions are vetoed when combining a mMDT/SD tagger with a cut on $\tau_{21}$. See text for details. - 00020 Lund diagrams associated with various analytic calculations. Left: the basic building block $T_\alpha$, Eq.~(\ref{eq:basic-analytic-block}), used to write all Sudakov exponents. Centre: representation of the \fulljet jet Sudakov $R_{\text{\fulljet}}(\rho,\taucut,z)$, Eq.~(\ref{eq:finalRplain}), including secondary emissions. Right: representation of the \fulljet jet Sudakov $R_{\text{SD}}(\rho,\taucut,z)$, Eq.~(\ref{eq:finalRsd}), including secondary emissions. For both the centre and right plots, the dot indicated by $z$ corresponds to the emission dominating the jet mass and we will integrate over allowed values of its momentum fraction $z$. - 00000 Lund diagram representing the phasespace available for an emission from the jet initial parton at an angle $\theta$ and carrying a momentum fraction $z$. The diagram shows a given emission (the solid dot) as well as lines with the same momentum fraction, $k_t$ and mass scales. - 00003 Lund diagram for QCD background jets (left) and signal jets (right) corresponding to the requirement of a given \fulljet jet mass with a cut on the $N$-subjettiness ratio $\tau_{21}$. The red shaded region (present only in the background case) corresponds to the Sudakov vetoed region for the mass, as in Fig.~\ref{fig:lund-masses}, together with the prefactor for having an emission on the solid red line. The blue shaded region corresponds to the additional veto coming from the cut on $N$-subjettiness. The dashed/dotted red line for the signal case represents the fact that, for signal jets, small-$z$ configurations are exponentially suppressed. The region that emerges from the plane is referred to as a ``leaf'' and in the left-hand diagram represents secondary emissions from emission $1$, while in the right-hand diagram it represents emissions from the softer of the two prongs of the decay. - 00021 Lund diagrams associated with various analytic calculations. Left: the basic building block $T_\alpha$, Eq.~(\ref{eq:basic-analytic-block}), used to write all Sudakov exponents. Centre: representation of the \fulljet jet Sudakov $R_{\text{\fulljet}}(\rho,\taucut,z)$, Eq.~(\ref{eq:finalRplain}), including secondary emissions. Right: representation of the \fulljet jet Sudakov $R_{\text{SD}}(\rho,\taucut,z)$, Eq.~(\ref{eq:finalRsd}), including secondary emissions. For both the centre and right plots, the dot indicated by $z$ corresponds to the emission dominating the jet mass and we will integrate over allowed values of its momentum fraction $z$. - 00004 Lund diagram for QCD background jets (left) and signal jets (right) corresponding to the requirement of a given \fulljet jet mass with a cut on the $N$-subjettiness ratio $\tau_{21}$. The red shaded region (present only in the background case) corresponds to the Sudakov vetoed region for the mass, as in Fig.~\ref{fig:lund-masses}, together with the prefactor for having an emission on the solid red line. The blue shaded region corresponds to the additional veto coming from the cut on $N$-subjettiness. The dashed/dotted red line for the signal case represents the fact that, for signal jets, small-$z$ configurations are exponentially suppressed. The region that emerges from the plane is referred to as a ``leaf'' and in the left-hand diagram represents secondary emissions from emission $1$, while in the right-hand diagram it represents emissions from the softer of the two prongs of the decay. - 00014 ROC curves for various $\tau_{21}$ combinations, \ie background versus signal efficiency, at parton level. The left plot is obtained starting from the \fulljet jet, while for the right plot, a SoftDrop grooming step has been applied. The ROC curves are obtained by varying the cut on the $\tau_{21}$ ratio. In all cases, we considered anti-$k_t$($R=1$) jets with $p_t>2$~TeV.Same as figure as \ref{fig:roc-parton}, now for hadron level (including the Underlying Event). - 00024 Same as figure as \ref{fig:roc-parton} now obtained from our analytic calculation instead of Monte-Carlo simulations. - 00013 Mass distribution for QCD jets with $p_t>2$~TeV (anti-$k_t$, $R=1$) at parton level, including SoftDrop grooming. The dashed lines, in red for the SD-groomed jet and in blue for the mMDT-tagged jet, are the mass distributions with no constraint on $N$-subjettiness. The solid lines have an additional cut $\tau_{21}<0.3$ with different combinations of jets used for the computation of the jet mass, $\tau_1$ and $\tau_2$ as indicated in the legend, our dichroic combination being plotted using a solid black line. The cross section used for normalisation, $\sigma$ is that for jets above the $p_t$ cut. - Full text

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2017-02-21
16:11
A General Method for Motion Compensation in X-ray Computed Tomography / Hancock, Steven (CERN) ; Biguri, Ander (Bath U.) ; Dosanjh, Manjit (CERN) ; Soleimani, Manuchehr (Bath U.)
Motion during data acquisition is a known source of error in medical tomography, resulting in blur artefacts in the regions that move. [...]
CERN-OPEN-2017-018.
- 2017. - 22 p.
Preprint

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2017-02-21
14:13
Observation of the suppressed decay $\Lambda^0_b \to p \pi^- \mu^+ \mu^-$
The suppressed decay $\Lambda^0_b \to p\pi^- \mu^+ \mu^-$ , excluding the $J/\psi$ and $\psi (2S) \to \mu^+ \mu^-$ resonances, is observed for the first time with a significance of $5.5$ standard deviations. [...]
CERN-EP-2016-312 ; LHCB-PAPER-2016-049.
- 2017.
Fulltext - Previous draft version - Related data file(s)

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2017-02-21
13:05
Performance of the ATLAS Transition Radiation Tracker in Run 1 of the LHC: tracker properties
The tracking performance parameters of the ATLAS Transition Radiation Tracker (TRT) as part of the ATLAS inner detector are described in this paper for different data-taking conditions in proton--proton, proton--lead and lead--lead collisions at the Large Hadron Collider (LHC). [...]
CERN-EP-2016-311.
- 2017.
Fulltext - Previous draft version

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2017-02-21
12:51
Measurements of the production cross section of a $Z$ boson in association with jets in pp collisions at $\sqrt{s} = 13$ TeV with the ATLAS detector
Measurements of the production cross section of a $Z$ boson in association with jets in proton-proton collisions at $\sqrt{s} = 13$ TeV are presented, using data corresponding to an integrated luminosity of 3.16 fb$^{-1}$ collected by the ATLAS experiment at the CERN Large Hadron Collider in 2015. [...]
CERN-EP-2016-297.
- 2017.
Fulltext - Previous draft version

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2017-02-21
06:46
Measurement of parameters of scintillating bars with wavelength-shifting fibres and silicon photomultiplier readout for the SHiP Muon Detector / Montanari, A (INFN, Bologna) ; Tosi, N (INFN, Bologna) ; Baldini, W (INFN, Ferrara) ; Calcaterra, A (Frascati) ; Lanfranchi, G (Frascati) ; Saputi, A (Frascati) ; Khotjantsev, A (Moscow, INR) ; Kudenko, Yu (Moscow, MIPT ; Moscow, INR ; Moscow Phys. Eng. Inst.) ; Kurochka, V (Moscow, INR) ; Mefodiev, A (Moscow, INR) et al.
The light yield and the time resolution of different types of 3 m long scintillating bars instrumented with wavelength shifting fibres and read out by different models of silicon photomultipliers have been measured at a test beam at the T9 area at the CERN Proton Synchrotron. [...]
arXiv:1612.01125.
- 2016. - 20 p.
00009 Light yield scan across 3 cm, 5 cm and 10 cm bars (a). Attenuation of scintillating light in the opposite directions from a fibre in the 10 cm bar (b). - 00006 Sum of the light yield measured at each as a function of the beam position along the bar for L2, L1, L4 bar. - 00004 L2 bar: light yield measured at each end (red squares and blue solid circles) and the sum of the light yields measured at both ends (black open circles) as a function of the incident beam position along the bar. - 00003 L1 bar: light yield measured at each end (red squares and blue solid circles) and the sum of the light yields at both ends (black open circles) as a function of the incident beam position along the bar. - 00007 Light yield scan for 3 cm bars U1 (a) and 5 cm bars U2 (b). - 00002 Example of distribution of the sum of the light yield collected at both ends of a 2 cm thick NICADD bar. - 00014 L2 bar time resolution using only SiPM $L$($R$), red circles(blue squares) and both SiPMs (green triangles). - 00013 L1 bar time resolution using only SiPM $L$($R$), red circles(blue squares) and both SiPMs (green triangles). - 00015 L4 bar time resolution using only SiPM $L$($R$), red circles(blue squares) and both SiPMs (green triangles). - 00001 Example of MPPC spectrum used for the calibration of the light yield. - 00008 Light yield scan for 10 cm bars U3 (a) and U4 (b). - 00000 Four types of bars manufactured at UNIPLAST factory. - 00018 Time resolution for 10 cm bars with 2 MPPC readout (a) and 4 MPPC readout (b). - 00017 Time resolution for 3 cm (a) and 5 cm bars (b) vs position along the bars. - 00011 Example of baseline-subtracted waveform for 2 cm thick NICADD bars. - 00010 The inefficiency for 3 and 5 cm wide bars as a function of the charge detection threshold. The events are counted if the charge is over the specified threshold at each bar end. - 00005 L4 bar: light yield measured at each end (red squares and blue solid circles) and the sum of the light yields measured at both ends (black open circles) as a function of the beam position along the bar. - 00016 Fitting of digitized pulse shape to obtain the timing mark. - 00012 Speed of light propagation $v_f$ in L2 fibre, for signals read by SiPM left (red line) and right (blue line); $v_f$ is measured as $(16.0\pm0.1)$ cm/ns. - Full text

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2017-02-20
22:57
Search for standard model production of four top quarks in proton-proton collisions at $ \sqrt{s} = $ 13 TeV
A search for events containing four top quarks (${\mathrm{ t \bar{t} }\mathrm{ t \bar{t} }} $) is reported from proton-proton collisions recorded by the CMS experiment at $\sqrt{s} = $ 13 TeV and corresponding to an integrated luminosity of 2.6 fb$^{-1}$. [...]
CERN-EP-2017-023 ; CMS-TOP-16-016-003.
- 2017.
Additional information for the analysis - CMS AuthorList - Fulltext

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2017-02-16
16:54
Top physics at HL-LHC / Azzi, Patrizia (INFN, Padua) /ATLAS ,CMS and Top Collaborations
A summary of the prospects for top-quark physics at the High Luminosity LHC is given..
CMS-CR-2017-029.- Geneva : CERN, 2017 - 8 p. Fulltext: PDF;
In : 9th International Workshop on Top Quark Physics, Olomouc, Czech Republic, 19 - 29 Sep 2016

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2017-02-16
16:43
Performance of the CMS Event Builder / Andre, Jean-marc Olivier (Fermilab) ; Behrens, Ulf (DESY) ; Branson, James (UC, San Diego) ; Brummer, Philipp Maximilian (CERN) ; Chaze, Olivier (CERN) ; Cittolin, Sergio (UC, San Diego) ; Contescu, Cristian (Fermilab) ; Craigs, Benjamin Gordon (CERN) ; Darlea, Georgiana Lavinia (MIT) ; Deldicque, Christian (CERN) et al.
The data acquisition system (DAQ) of the CMS experiment at the CERN Large Hadron Collider (LHC) assembles events at a rate of 100 kHz. It transports event data at an aggregate throughput of ~100 GB/s to the high-level trigger (HLT) farm. [...]
CMS-CR-2017-034.- Geneva : CERN, 2017 - 9 p. Fulltext: PDF;
In : 22nd International Conference on Computing in High Energy and Nuclear Physics, CHEP 2016, San Francisco, Usa, 10 - 14 Oct 2016

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