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CERN Document Server latest documents in Physics (PH)enWed, 04 Mar 2015 20:20:36 GMTInvenio 1.1.3.1106-62468cds.support@cern.ch36041174125https://cds.cern.ch/img/site_logo_rss.pngCERN Document Server
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Gauge-invariant signatures of spontaneous gauge symmetry breaking by the Hosotani mechanism
https://cds.cern.ch/record/1996449
The Hosotani mechanism claims to achieve gauge-symmetry breaking, for instance $SU(3) \to SU(2)\times U(1)$. To verify this claim, we propose to monitor the stability of a topological defect stable under a gauge subgroup but not under the whole gauge group, like a $U(1)$ flux state or monopole in the case above. We use gauge invariant operators to probe the presence of the topological defect to avoid any ambiguity introduced by gauge fixing. Our method also applies to an ordinary gauge-Higgs system.Akerlund, OscarWed, 04 Mar 2015 06:42:56 GMThttps://cds.cern.ch/record/1996449On jet substructure methods for signal jets
https://cds.cern.ch/record/1996443
We carry out simple analytical calculations and Monte Carlo studies to better understand the impact of QCD radiation on some well-known jet substructure methods for jets arising from the decay of boosted Higgs bosons. Understanding differences between taggers for these signal jets assumes particular significance in situations where they perform similarly on QCD background jets. As an explicit example of this we compare the Y-splitter method to the more recently proposed Y-pruning technique. We demonstrate how the insight we gain can be used to significantly improve the performance of Y-splitter by combining it with trimming and show that this combination outperforms the other taggers studied here, at high $p_T$. We also make analytical estimates for optimal parameter values, for a range of methods and compare to results from Monte Carlo studies.Dasgupta, MrinalWed, 04 Mar 2015 06:40:25 GMThttps://cds.cern.ch/record/1996443Universality of radiative corrections to gauge couplings for strings with spontaneously broken supersymmetry
https://cds.cern.ch/record/1995142
I review recent work on computing radiative corrections to non-abelian gauge couplings in four-dimensional heterotic vacua with spontaneously broken supersymmetry. The prototype models can be considered as K3 surfaces with additional Scherk-Schwarz fluxes inducing the spontaneous $\mathcal{N}=2 \to \mathcal{N}=0$ breaking. Remarkably, although the gauge thresholds are no longer BPS protected and receive contributions also from the excitations of the RNS sector, their difference is still exactly computable and universal. Based on a talk presented at the DISCRETE 2014 conference at King's College London.Florakis, IoannisSat, 28 Feb 2015 07:51:05 GMThttps://cds.cern.ch/record/1995142Two-particle Bose--Einstein correlations in $pp$ collisions at $\mathbf {\sqrt{s} =}$ 0.9 and 7 TeV measured with the ATLAS detector
https://cds.cern.ch/record/1994986
The paper presents studies of Bose--Einstein Correlations (BEC) for pairs of like-sign charged particles measured in the kinematic range $p_{\rm T} >$ 100 MeV and $|\eta|<$ 2.5 in proton--proton collisions at centre-of-mass energies of 0.9 and 7 TeV with the ATLAS detector at the CERN Large Hadron Collider. The integrated luminosities are approximately 7 $\mu$b$^{-1}$, 190 $\mu$b$^{-1}$ and 12.4 nb$^{-1}$ for 0.9 TeV, 7 TeV minimum-bias and 7 TeV high-multiplicity data samples, respectively. The multiplicity dependence of the BEC parameters characterizing the correlation strength and the correlation source size are investigated for charged-particle multiplicities of up to 240. A saturation effect in the multiplicity dependence of the correlation source size is observed using the high-multiplicity 7 TeV data sample. The dependence of the BEC parameters on the average transverse momentum of the particle pair is also investigated.Aad, GeorgesFri, 27 Feb 2015 10:10:22 GMThttps://cds.cern.ch/record/1994986A search for high-mass resonances decaying to $\tau^{+}\tau^{-}$ in $pp$ collisions at $\sqrt{s}=8$ TeV with the ATLAS detector
https://cds.cern.ch/record/1994408
A search for high-mass resonances decaying into $\tau^{+}\tau^{-}$ final states using proton-proton collisions at $\sqrt{s}= 8$ TeV produced by the Large Hadron Collider is presented. The data were recorded with the ATLAS detector and correspond to an integrated luminosity of 19.5-20.3 fb$^{-1}$. No statistically significant excess above the Standard Model expectation is observed; 95% credibility upper limits are set on the cross section times branching fraction of $Z^{\prime}$ resonances decaying into $\tau^+\tau^-$ pairs as a function of the resonance mass. As a result, $Z^{\prime}$ bosons of the Sequential Standard Model with masses less than 2.02 TeV are excluded at 95% credibility. The impact of the fermionic couplings on the $Z^{\prime}$ acceptance is investigated and limits are also placed on a $Z^{\prime}$ model that exhibits enhanced couplings to third-generation fermions.Aad, GeorgesWed, 25 Feb 2015 14:20:51 GMThttps://cds.cern.ch/record/1994408Differential top--antitop cross-section measurements as a function of observables constructed from final-state particles using pp collisions at $\sqrt{s}=7$ TeV in the ATLAS detector
https://cds.cern.ch/record/1993530
Various differential cross-sections are measured in top-quark pair ($t\bar{t}$) events produced in proton--proton collisions at a centre-of-mass energy of $\sqrt{s} = 7$ TeV at the LHC with the ATLAS detector. These differential cross-sections are presented in a data set corresponding to an integrated luminosity of $4.6$ fb$^{-1}$. The differential cross-sections are presented in terms of kinematic variables of a top-quark proxy referred to as the pseudo-top-quark whose dependence on theoretical models is minimal. The pseudo-top-quark can be defined in terms of either reconstructed detector objects or stable particles in an analogous way. The measurements are performed on $t\bar{t}$ events in the lepton+jets channel, requiring exactly one charged lepton and at least four jets with at least two of them tagged as originating from a $b$-quark. The hadronic and leptonic pseudo-top-quarks are defined via the leptonic or hadronic decay mode of the $W$ boson produced by the top-quark decay in events with a single charged lepton.The cross-section is measured as a function of the transverse momentum and rapidity of both the hadronic and leptonic pseudo-top-quark as well as the transverse momentum, rapidity and invariant mass of the pseudo-top-quark pair system. The measurements are corrected for detector effects and are presented within a kinematic range that closely matches the detector acceptance. Differential cross-section measurements of the pseudo-top-quark variables are compared with several Monte Carlo models that implement next-to-leading order or leading-order multi-leg matrix-element calculations.Aad, GeorgesFri, 20 Feb 2015 14:09:38 GMThttps://cds.cern.ch/record/1993530Emerging Jets
https://cds.cern.ch/record/1993313
In this work, we propose a novel search strategy for new physics at the LHC that utilizes calorimeter jets that (i) are composed dominantly of displaced tracks and (ii) have many different vertices within the jet cone. Such emerging jet signatures are smoking guns for models with a composite dark sector where a parton shower in the dark sector is followed by displaced decays of dark pions back to SM jets. No current LHC searches are sensitive to this type of phenomenology. We perform a detailed simulation for a benchmark signal with two regular and two emerging jets, and present and implement strategies to suppress QCD backgrounds by up to six orders of magnitude. At the 14 TeV LHC, this signature can be probed with mediator masses as large as 1.5 TeV for a range of dark pion lifetimes, and the reach is increased further at the high-luminosity LHC. The emerging jet search is also sensitive to a broad class of long-lived phenomena, and we show this for a supersymmetric model with R-parity violation. Possibilities for discovery at LHCb are also discussed.Schwaller, PedroFri, 20 Feb 2015 08:33:38 GMThttps://cds.cern.ch/record/1993313Search for massive supersymmetric particles decaying to many jets using the ATLAS detector in $pp$ collisions at $\sqrt{s} = 8$TeV
https://cds.cern.ch/record/1993236
Results of a search for decays of massive particles to fully hadronic final states are presented. This search uses 20.3 fb$^{-1}$ of data collected by the ATLAS detector in $\sqrt{s} = 8$TeV proton--proton collisions at the LHC. Signatures based on high jet multiplicities without requirements on the missing transverse momentum are used to search for $R$-parity-violating supersymmetric gluino pair production with subsequent decays to quarks. The analysis is performed using a requirement on the number of jets, in combination with separate requirements on the number of $b$-tagged jets, as well as a topological observable formed from the scalar sum of the mass values of large-radius jets in the event. Results are interpreted in the context of all possible branching ratios of direct gluino decays to various quark flavors. No significant deviation is observed from the expected Standard Model backgrounds estimated using jet-counting as well as data-driven templates of the total-jet-mass spectra. Gluino pair decays to ten or more quarks via intermediate neutralinos are excluded for a gluino with mass $m_{\tilde{g}} < 1$TeV for a neutralino mass $m_{\tilde{\chi}^0_1} = 500$GeV. Direct gluino decays to six quarks are excluded for $m_{\tilde{g}} < 917$GeV for light-flavor final states, and results for various flavor hypotheses are presented.Aad, GeorgesThu, 19 Feb 2015 20:21:21 GMThttps://cds.cern.ch/record/1993236Towards the physical point hadronic vacuum polarisation from Moebius DWF
https://cds.cern.ch/record/1992983
We present steps towards the computation of the leading-order hadronic contribution to the muon anomalous magnetic moment on RBC/UKQCD physical point DWF ensembles. We discuss several methods for controlling and reducing uncertainties associated to the determination of the HVP form factor.Marinkovic, MarinaThu, 19 Feb 2015 06:53:17 GMThttps://cds.cern.ch/record/1992983Fundamental Composite Electroweak Dynamics: Status at the LHC
https://cds.cern.ch/record/1992768
We determine the current status of the fundamental composite electroweak dynamics paradigm after the discovery of the Higgs boson at the Large Hadron Collider experiments. Our analysis serves as universal and minimal template for a wide class of models with the two limits in parameter space being composite Goldstone Higgs models and Technicolor. This is possible because of the existence of a unified description, both at the effective and fundamental Lagrangian levels, of models of composite Higgs dynamics where the Higgs boson itself can emerge, depending on the way the electroweak symmetry is embedded, either as a pseudo-Goldstone boson or as a massive excitation of the condensate. We constrain the available parameter space at the effective Lagrangian level. We show that a wide class of models of fundamental composite electroweak dynamics, including Technicolor, are compatible with experiments. The results are relevant for future searches of a fundamental composite nature of the Higgs mechanism at the Large Hadron Collider.Arbey, AlexandreWed, 18 Feb 2015 06:43:44 GMThttps://cds.cern.ch/record/1992768Robust collider limits on heavy-mediator Dark Matter
https://cds.cern.ch/record/1992767
We discuss how to consistently use Effective Field Theories (EFTs) to set universal bounds on heavy-mediator Dark Matter at colliders, without prejudice on the model underlying a given effective interaction. We illustrate the method for a Majorana fermion, universally coupled to the Standard Model quarks via a dimension-6 axial-axial four-fermion operator. We recast the ATLAS mono-jet analysis and show that a considerable fraction of the parameter space, seemingly excluded by a na\"ive EFT interpretation, is actually still unexplored. Consistently set EFT limits can be reinterpreted in any specific underlying model. We provide two explicit examples for the chosen operator and compare the reach of our model-independent method with that obtainable by dedicated analyses.Racco, DavideWed, 18 Feb 2015 06:43:42 GMThttps://cds.cern.ch/record/1992767Black Hole Solutions in $R^2$ Gravity
https://cds.cern.ch/record/1992512
We find static spherically symmetric solutions of scale invariant $R^2$ gravity. The latter has been shown to be equivalent to General Relativity with a positive cosmological constant and a scalar mode. Therefore, one expects that solutions of the $R^2$ theory will be identical to that of Einstein theory. Indeed, we find that the solutions of $R^2$ gravity are in one-to-one correspondence with solutions of General Relativity in the case of non-vanishing Ricci scalar. However, scalar-flat $R=0$ solutions are global minima of the $R^2$ action and they cannot in general be mapped to solutions of the Einstein theory. As we will discuss, the $R=0$ solutions arise in Einstein gravity as solutions in the tensionless, strong coupling limit $M_P\rightarrow 0$. As a further result, there is no corresponding Birkhoff theorem and the Schwarzschild black hole is by no means unique in this framework. In fact, $R^2$ gravity has a rich structure of vacuum static spherically symmetric solutions partially uncovered here. We also find charged static spherically symmetric backgrounds coupled to a $U(1)$ field. Finally, we provide the entropy and energy formulas for the $R^2$ theory and we find that entropy and energy vanish for scalar-flat backgrounds.Kehagias, AlexTue, 17 Feb 2015 06:33:49 GMThttps://cds.cern.ch/record/1992512Search for a CP-odd Higgs boson decaying to $Zh$ in $pp$ collisions at $\sqrt{s} = 8$ TeV with the ATLAS detector
https://cds.cern.ch/record/1989793
A search for a heavy, CP-odd Higgs boson, $A$, decaying into a $Z$ boson and a 125 GeV Higgs boson, $h$, with the ATLAS detector at the LHC is presented. The search uses proton--proton collision data at a centre-of-mass energy of 8 TeV corresponding to an integrated luminosity of 20.3 fb$^{-1}$. Decays of CP-even $h$ bosons to $\tau\tau$ or $bb$ pairs with the $Z$ boson decaying to electron or muon pairs are considered, as well as $h \rightarrow bb$ decays with the $Z$ boson decaying to neutrinos. No evidence for the production of an $A$ boson in these channels is found and the 95% confidence level upper limits derived for $\sigma (gg\rightarrow A) \times \mbox{BR}(A\rightarrow Zh) \times \mbox{BR}(h\rightarrow f\bar{f})$ are 0.098--0.013 pb for $f=\tau$ and 0.57--0.014 pb for $f=b$ in a range of $m_A =$ 220--1000 GeV. The results are combined and interpreted in the context of two-Higgs-doublet models.Aad, GeorgesMon, 16 Feb 2015 07:47:13 GMThttps://cds.cern.ch/record/1989793$D^6 R^4$ amplitudes in various dimensions
https://cds.cern.ch/record/1989347
Four-graviton couplings in the low energy effective action of type II string vacua compactified on tori are strongly constrained by supersymmetry and U-duality. While the $R^4$ and $D^4 R^4$ couplings are known exactly in terms of Langlands-Eisenstein series of the U-duality group, the $D^6 R^4$ couplings are not nearly as well understood. Exploiting the coincidence of the U-duality group in $D=6$ with the T-duality group in $D=5$, we propose an exact formula for the $D^6 R^4$ couplings in type II string theory compactified on $T^4$, in terms of a genus-two modular integral plus a suitable Eisenstein series. The same modular integral computes the two-loop correction to $D^6 R^4$ in 5 dimensions, but here provides the non-perturbative completion of the known perturbative terms in $D=6$. This proposal hinges on a systematic re-analysis of the weak coupling and large radius of the $D^6 R^4$ in all dimensions $D\geq 3$, which fills in some gaps and resolves some inconsistencies in earlier studies.Pioline, BorisFri, 13 Feb 2015 06:37:29 GMThttps://cds.cern.ch/record/1989347Non-minimally flavour violating dark matter
https://cds.cern.ch/record/1989328
Flavour symmetries provide an appealing mechanism to stabilize the dark matter particle. I present a simple model of quark flavoured dark matter that goes beyond the framework of minimal flavour violation. I discuss the phenomenological implications for direct and indirect dark matter detection experiments, high energy collider searches as well as flavour violating precision data.Blanke, MonikaFri, 13 Feb 2015 06:36:59 GMThttps://cds.cern.ch/record/1989328Generalized Metric Formulation of Double Field Theory on Group Manifolds
https://cds.cern.ch/record/1987944
We rewrite the recently derived cubic action of Double Field Theory on group manifolds [arXiv:1410.6374] in terms of a generalized metric and extrapolate it to all orders in the fields. For the resulting action, we derive the field equations and state them in terms of a generalized curvature scalar and a generalized Ricci tensor. Compared to the generalized metric formulation of DFT derived from tori, all these quantities receive additional contributions related to the non-trivial background. It is shown that the action is invariant under its generalized diffeomorphisms and 2D-diffeomorphisms. Imposing additional constraints relating the background and fluctuations around it, the precise relation between the proposed generalized metric formulation of DFT${}_\mathrm{WZW}$ and of original DFT from tori is clarified. Furthermore we show how to relate DFT${}_\mathrm{WZW}$ of the WZW background with the flux formulation of original DFT.Blumenhagen, RalphTue, 10 Feb 2015 07:07:43 GMThttps://cds.cern.ch/record/1987944Precise measurements of the properties of the $B_1(5721)^{0,+}$ and $B^\ast_2(5747)^{0,+}$ states and observation of $B^{+,0}\pi^{-,+}$ mass structures
https://cds.cern.ch/record/1987883
Invariant mass distributions of $B^+\pi^-$ and $B^0\pi^+$ combinations are investigated in order to study excited B mesons. The analysis is based on a data sample corresponding to $3.0 fb^{-1}$ of $pp$ collision data, recorded by the LHCb detector at centre-of-mass energies of 7 and 8 TeV. Precise measurements of the masses and widths of the $B_1(5721)^{0,+}$ and $B_2^*(5747)^{0,+}$ states are reported. Clear enhancements, particularly prominent at high pion transverse momentum, are seen over background in the mass range $5850$-$6000$ MeV in both $B^+\pi^-$ and $B^0\pi^+$ combinations. The structures are consistent with the presence of four excited B mesons, labelled $B_J(5840)^{0,+}$ and $B_J(5960)^{0,+}$, whose masses and widths are obtained under different hypotheses for their quantum numbers.Aaij, RoelTue, 10 Feb 2015 07:06:46 GMThttps://cds.cern.ch/record/1987883Spot the stop with a b-tag
https://cds.cern.ch/record/1987870
The LHC searches for light compressed stop squarks have resulted in considerable bounds in the case where the stop decays to a neutralino and a charm quark. However, in the case where the stop decays to a neutralino, a bottom quark and two fermions via an off-shell W-boson, there is currently a significant unconstrained region in the stop-neutralino mass plane, still allowing for stop masses in the range 90-140 GeV. In this paper we propose a new monojet-like search for light stops, optimized for the four-body decay mode, in which at least one b-tagged jet is required. We show that, already by using the existing 8 TeV LHC data set, such a search would cover the entire unconstrained region. Moreover, in the process of validating our tools against an ATLAS monojet search, we show that the existing limit can be extended to exclude also stop masses below 100 GeV.Ferretti, GabrieleTue, 10 Feb 2015 07:06:43 GMThttps://cds.cern.ch/record/1987870Search for a standard model Higgs boson produced in association with a top-quark pair and decaying to bottom quarks using a matrix element method
https://cds.cern.ch/record/1987629
A search for a standard model Higgs boson produced in association with a top-quark pair and decaying to bottom quarks is presented. Events with hadronic jets and one or two oppositely charged leptons are selected from a data sample corresponding to an integrated luminosity of 19.5 fb$^{-1}$ collected by the CMS experiment at the LHC in pp collisions at a centre-of-mass energy of 8 TeV. In order to separate the signal from the larger $\mathrm{t \bar{t}}$+jets background, this analysis uses a matrix element method that assigns a probability density value to each reconstructed event under signal or background hypotheses. The ratio between the two values is used in a maximum likelihood fit to extract the signal yield. The results are presented in terms of the measured signal strength modifier, $\mu$, relative to the standard model prediction for a Higgs boson mass of 125 GeV. The observed (expected) exclusion limit at a 95% confidence level is $\mu$ lower than 4.2 (3.3), corresponding to a best fit value $\hat{\mu}=1.2^{+1.6}_{-1.5}$.Khachatryan, VardanMon, 09 Feb 2015 14:03:40 GMThttps://cds.cern.ch/record/1987629Massive Born--Infeld and Other Dual Pairs
https://cds.cern.ch/record/1987236
We consider massive dual pairs of p-forms and (D-p-1)-forms described by non-linear Lagrangians, where non-linear curvature terms in one theory translate into non-linear mass-like terms in the dual theory. In particular, for D=2p and p even the two non-linear structures coincide when the non-linear massless theory is self-dual. This state of affairs finds a natural realization in the four-dimensional massive N=1 supersymmetric Born-Infeld action, which describes either a massive vector multiplet or a massive linear (tensor) multiplet with a Born-Infeld mass-like term. These systems should play a role for the massive gravitino multiplet obtained from a partial super-Higgs in N=2 Supergravity.Ferrara, SFri, 06 Feb 2015 06:58:50 GMThttps://cds.cern.ch/record/1987236Regge behavior saves String Theory from causality violations
https://cds.cern.ch/record/1985331
Higher-derivative corrections to the Einstein-Hilbert action are present in bosonic string theory leading to the potential causality violations recently pointed out by Camanho et al. We analyze in detail this question by considering high-energy string-brane collisions at impact parameters $b \le l_s$ (the string-length parameter) with $l_s \gg R_p$ (the characteristic scale of the D$p$-brane geometry). If we keep only the contribution of the massless states causality is violated for a set of initial states whose polarization is suitably chosen with respect to the impact parameter vector. Such violations are instead neatly avoided when the full structure of string theory - and in particular its Regge behavior - is taken into account.D'Appollonio, GiuseppeThu, 05 Feb 2015 06:38:16 GMThttps://cds.cern.ch/record/1985331Search for new phenomena in final states with an energetic jet and large missing transverse momentum in $pp$ collisions at $\sqrt{s}=8~$TeV with the ATLAS detector
https://cds.cern.ch/record/1985260
Results of a search for new phenomena in final states with an energetic jet and large missing transverse momentum are reported. The search uses 20.3 fb${}^{-1}$ of $\sqrt{s}=8$ TeV data collected in 2012 with the ATLAS detector at the LHC. Events are required to have at least one jet with $p_T > 120$ GeV and no leptons. Nine signal regions are considered with increasing missing transverse momentum requirements between $E_{\mathrm{T}}^{\mathrm{miss}} >150$ GeV and $E_{\mathrm{T}}^{\mathrm{miss}} > 700$ GeV. Good agreement is observed between the number of events in data and Standard Model expectations. The results are translated into exclusion limits on models with large extra spatial dimensions, pair production of weakly interacting dark matter candidates, and production of very light gravitinos in a gauge-mediated supersymmetric model. In addition, limits on the production of an invisibly decaying Higgs-like boson leading to similar topologies in the final state are presented.Aad, GeorgesWed, 04 Feb 2015 17:05:00 GMThttps://cds.cern.ch/record/1985260Threshold corrections, generalised prepotentials and Eichler integrals
https://cds.cern.ch/record/1984735
We continue our study of one-loop integrals associated to BPS-saturated amplitudes in $\mathcal{N}=2$ heterotic vacua. We compute their large-volume behaviour, and express them as Fourier series in the complexified volume, with Fourier coefficients given in terms of Niebur-Poincar\'e series in the complex structure modulus. The closure of Niebur-Poincar\'e series under modular derivatives implies that such integrals derive from holomorphic prepotentials $f_n$, generalising the familiar prepotential of $\mathcal{N}=2$ supergravity. These holomorphic prepotentials transform anomalously under T-duality, in a way characteristic of Eichler integrals. We use this observation to compute their quantum monodromies under the duality group. We extend the analysis to modular integrals with respect to Hecke congruence subgroups, which naturally arise in compactifications on non-factorisable tori and freely-acting orbifolds. In this case, we derive new explicit results including closed-form expressions for integrals involving the ${\varGamma}_0(N)$ Hauptmodul, a full characterisation of holomorphic prepotentials including their quantum monodromies, as well as concrete formulae for holomorphic Yukawa couplings.Angelantonj, CarloWed, 04 Feb 2015 06:35:35 GMThttps://cds.cern.ch/record/1984735Observation of top-quark pair production in association with a photon and measurement of the $t\bar{t}\gamma$ production cross section in pp collisions at $\sqrt{s}=7$ TeV using the ATLAS detector
https://cds.cern.ch/record/1984432
A search is performed for top-quark pairs ($t\bar{t}$) produced together with a photon ($\gamma$) with transverse momentum $>20$ GeV using a sample of $t\bar{t}$ candidate events in final states with jets, missing transverse momentum, and one isolated electron or muon. The dataset used corresponds to an integrated luminosity of 4.59 $fb^{-1}$ of proton--proton collisions at a center-of-mass energy of 7 TeV recorded by the ATLAS detector at the CERN Large Hadron Collider. In total 140 and 222 $t\bar{t}\gamma$ candidate events are observed in the electron and muon channels, to be compared to the expectation of $79\pm 26$ and $120\pm 39$ non-$t\bar{t}\gamma$ background events respectively. The production of $t\bar{t}\gamma$ events is observed with a significance of 5.3 standard deviations away from the null hypothesis. The $t\bar{t}\gamma$ production cross section times the branching ratio (BR) of the single-lepton decay channel is measured in a fiducial kinematic region within the ATLAS acceptance. The measured value is $\sigma_{t\bar{t}\gamma}^{fid} = 63 \pm 8 (stat.) ^{+17}_{-13} (syst.) \pm 1 (lumi.)$ fb per lepton flavor, in good agreement with the leading-order theoretical calculation normalized to the next-to-leading-order theoretical prediction of $48\pm 10$ fb.Aad, GeorgesMon, 02 Feb 2015 17:33:04 GMThttps://cds.cern.ch/record/1984432Search for supersymmetry using razor variables in events with b-tagged jets in pp collisions at $\sqrt{s}$ = 8 TeV
https://cds.cern.ch/record/1984165
An inclusive search for supersymmetry in events with at least one bottom-quark jet is performed using proton-proton collision data collected by the CMS experiment in 2012 at a center-of-mass energy of 8 TeV. The data set size corresponds to an integrated luminosity of 19.3 fb$^{-1}$. The two-dimensional event distribution of the razor variables $R^2$ and $M_R$ is studied in events with and without leptons. The data are found to be consistent with the expected background, which is modeled with an empirical function. Exclusion limits on supersymmetric particle masses at a 95% confidence level are derived in several simplified supersymmetric scenarios for several choices of the branching fractions. By combining the likelihoods of a search in events without leptons and a search that requires a single lepton (electron or muon), an improved bound on the top-squark mass is obtained. Assuming the lightest supersymmetric particle to be stable, weakly interacting, and to have a mass of 100 GeV, the branching-fraction-dependent (-independent) production of gluinos is excluded for gluino masses up to 1310 (1175) GeV. The corresponding limit for top-squark pair production is 730 (645) GeV.Khachatryan, VardanSun, 01 Feb 2015 20:05:10 GMThttps://cds.cern.ch/record/1984165