The U.S. particle physics community is proud to host the 38th ICHEP in Chicago from the 3rd to the 10th August 2016. ICHEP is a focal point of the field of particle physics, bringing together experimentalists and theorists of the world. It was first held in 1950, and is biennial since 1960.
| Dates: | from 3 August 2016 17:00 to 10 August 2016 17:50 |
|---|---|
| Timezone: | US/Central |
| Location: |
Sheraton Grand Chicago |
| Address: | 301 East North Water Street Chicago IL 60611 USA |
A search for new physics is performed based on multijet events with large missing transverse momentum produced in 13 TeV proton-proton collisions. The data sample, corresponding to an integrated luminosity of 2.2 fb-1, was collected with the CMS detector at Run 2 of the CERN LHC. The data are examined in search regions of jet multiplicity, bottom-quark jet multiplicity, missing transverse momentum, and the scalar sum of jet transverse momenta. Exclusion limits are presented for simplified supersymmetric models of gluino pair production.These results significantly extend the limits from LHC Run 1.
Results are reported from a search for supersymmetric particles in pp collisions in the final state with a single, high pT lepton; multiple jets, including at least one btagged jet; and large missing transverse momentum. The data sample corresponds to 2.1 fb-1 recorded by the CMS experiment at ps = 13 TeV. The search focuses on processes leading to high jet multiplicities, such as gluino pair production with the gluino decaying to top quarks. The quantity MJ, defined as the sum of the masses of the large-radius jets in the event, is used in conjunction with other kinematic variables to provide discrimination between signal and backgrounds and as a key part of the background estimation method. Competitive exclusion limits are obtained.
We present a search for new physics in events with one or two low-momentum leptons and missing transverse energy, based on the first proton-proton integrated luminosity recorded with the CMS detector at 13 TeV. The final state can be the phenomenology of SUSY models foreseeing a small mass splitting between the lightest supersymmetric particle and e.g. the top squark or chargino, in the so called compressed mass spectra scenario. The event selection and kinematics, together with methods for estimating the standard model backgrounds are presented. Results are interpreted in terms on SUSY models where a compressed mass scenario is foreseen.
We study detector performance of Higgs boson identification variables at very high energy proton colliders. We study Higgs bosons decaying to bottom quarks with transverse momentum in the multi-TeV range. Detectors are benchmarked in various configurations in order to understand the impact of granularity and resolution on boosted Higgs boson discrimination.
Current experiments measuring CP asymmetries in $D$ meson decays approach a sensitivity which is comparable to the tiny Standard-Model (SM) predictions for these quantities. However, the errors of the SM predictions, which essentially all rely on the approximate SU(3) flavour symmetry, make the search for new physics in $D$-meson CP asymmetries difficult. I present new calculations which control the dominant hadronic uncertainties up to linear order in SU(3) breaking. I further discuss the potentially large CP asymmetry in $D^0 \to K_S K_S$.
Precision measurements are presented of the top-quark pair inclusive production cross section in proton-proton collisions at the LHC at centre-of-mass energies of 7, 8 and 13 TeV. The data are collected with the CMS experiment during the years 2011, 2012, and 2015. The analyses profit from different top quark final states and make use of events with two, one or no reconstructed charged leptons. In most analyses b-jet identification is used to increase the purity of the selection. The backgrounds are determined using data-driven techniques. The results are combined with each other and compared with theory predictions. Indirect constraints on both the top quark mass and alpha_s are obtained through their relation to the inclusive cross section.
Differential top quark pair production cross sections are measured in proton-proton collisions at the LHC at centre-of-mass energies of 7, 8, and 13 TeV, using data collected by the CMS experiment in the years 2011, 2012, and 2015. The differential cross sections are measured as functions of various kinematic observables, including the transverse momentum and rapidity of the (anti)top quark and the top-antitop system and the jets and leptons of the event final state. Multiplicity and kinematic distributions of the jets produced in addition to the top pair are investigated. Measurements of the associate production of top quark pairs with additional b-quarks, and a search for four-top production are also presented.
State-of-the-art theoretical predictions accurate to next-to-leading order QCD interfaced with Pythia8 and Herwig++ event generators are tested by comparing the unfolded ttbar differential data collected with the CMS detector at 8 TeV. These predictions are also compared with the underlying event activity distributions in ttbar events using CMS proton-proton data collected in 2015 at a center of mass energy of 13 TeV.
Training session for volunteers for library program. Stop by for 30 minutes when you have time to learn about your presentation.
Searches for the direct electroweak production of supersymmetric charginos and neutralinos in topologies containing leptons and W, Z, and Higgs bosons are presented.
A search for direct top squark pair production in the hadronic final state is presented. The data used are 2.3 fb-1 of pp collision data at 13 TeV taken with the CMS detector in 2015.
Naturalness arguments for weak-scale supersymmetry favour supersymmetric partners of the third generation quarks with masses not too far from those of their Standard Model counterparts. Top or bottom squarks with masses of a few hundred GeV can also give rise to large direct pair production rates at the LHC. The recent increase in the center of mass energy of the proton-proton collisions gives a unique opportunity to extend the sensitivity to production of supersymmetric particles at the Large Hadron Collider. The talk presents recent ATLAS results from searches for direct stop and sbottom pair production, with emphasis on those obtained using proton-proton collisions at a centre-of-mass energy of 13 TeV.
Charmless hadronic B decays constitute a powerful probe to search for new physics beyond the standard model and provide constraints of various CP violation parameters. We report the final measurements from Belle of the branching fraction and CP asymmetry for a variety of charmless decays -- $B^0 \to \pi^0\pi^0$, $B^+ \to K^+ K^- \pi^+$, $B\to \phi \phi K$, and $B^+ \to K_S^0 K_S^0 h^+$ $(h=K,\pi)$ -- as well as a search for the $B^0 \to \eta\eta$ decay. All investigations employ the full dataset at $\Upsilon(4S)$ delivered by the KEKB $e^+ e^-$ collider. The $B^0 \to \pi^0 \pi^0$ measurement enables improved constraints on the CKM unitarity triangle $\phi_2$. For $B^+ \to K^+ K^- \pi^+$ we measure CP asymmetry as a function of the invariant mass of the $K^+ K^-$ system, where LHCb has earlier reported an unexpectedly strong enhancement at low mass. The three-body decays $B^+ \to K_S^0 K_S^0 h^+$ $(h=K,\pi)$ and $B\to \phi \phi K$ both proceed predominantly via flavor-changin!
g neutral current transitions and hence are sensitive to potential new physics effects. The $B^0 \to \eta\eta$ decays could play an important role in understanding the $B$ decay dynamics and improving the deviation boundary of $\sin 2\phi_1$ measured in $b\to s c\bar{c}$ and $b\to s q\bar{q}$ decays.
Charmless $B_s$ decays are studied using a data sample of 121 fb−1 collected at the Υ(10860) resonance ($\sqrt{s} = 10.87$ GeV) at Belle. We present the branching fraction of $B_s \to K^0 \bar{K}^0$, which is the first observation of a charmless two-body $B_s$ decays involving only neutral hadrons in the final state. Also presented is the first search for $B_s \to \eta\eta$ decay.
Knowledge on the angles of the Unitarity Triangle provides stringent tests on the Standard Model of electroweak interactions and enables one to constrain potential effects of the physics beyond. The parameter $\sin (2\beta) = \sin (2\phi_1)$ has been precisely measured by the B factory experiments BaBar and Belle using $b \to c \bar{c} s$ transitions such as the golden mode $B^0 \to J/\psi K_S^0$. In terms of the angle $\beta = \phi_1$, the value smaller than $\pi/2$ is favored between two possible solutions, however the discrimination is not evident yet at current experimental status. By reconstructing the neutral $D$ meson decays in self-conjugated multi-body final states, a time-dependent Dalitz analysis in $B^0 \to D^{(*)} h^0$ decays provide a theoretically clean probe to constrain $\cos(2\beta) = \cos(2\phi_1)$. We present a time-dependent Dalitz analysis of $B^0 \to D^{(*)} h^0$ decays followed by the $D$ meson decays to $K_S^0 \pi^+ \pi^-$ where the $h^0$ is a $\pi i^0$, $\eta$ or $\omega$ meson. The measurement is performed by combining the final data samples of $471 \times 10^6$ $B\overline{B}$ pairs and $772 \times 10^6$ $B\overline{B}$ pairs recorded by the BaBar and the Belle experiments, respectively.
Measurements are presented of the properties of top quarks in pair production from proton-proton collisions at the LHC. The data were collected at pp centre-of-mass energies of 7 and 8 TeV by the CMS experiment during the years 2011 and 2012. The charge asymmetry is measured using the difference of the absolute rapidities of the reconstructed top and anti-top kinematics, as well as from distributions of the top quark decay products. The measurements are performed in the decay channels of the ttbar pair into both one and two leptons in the final state. The results, obtained differentially in several kinematic variables of the ttbar-system, are discussed in the context of the forward-backard asymmetry measurements at Tevatron. The polarization of top quarks is measured from the decay angular distributions. Ttbar spin correlation and asymmetries are measured from the angular distributions of the top quark decay products. These measurements are used to search for new physics. TTbar spin correlation is also measured using a matrix element method. Measurements of the associate production of top quark pairs with vector bosons (photons, W and Z) are also presented. The results are compared with standard model predictions.
Several measurements of top quark properties in top quark decays are presented using data collected by the CMS experiment during the years 2011 and 2012. The polarization of W bosons in top quark decays is measured. The W-boson helicity fractions and angular asymmetries are extracted and limits on anomalous contributions to the Wtb vertex are determined. Furthermore, searches for flavor-changing neutral currents in top quark decays are presented using samples of top-quark pair event candidates decaying via Wb and Zq into lνb and llq events, or decaying via Hq into 3 b-quarks. The flavor contents in top-quark pair events are measured using the fraction of top quarks decaying into a W-boson and a b-quark relative to all top quark decays, R=BR(t->Wb)/Sum(BR(t->Wq)), and the result is used to determine the CKM matrix element Vtb as well as the width of the top quark resonance. The top-quark charge is measured, using the charge correlations between high-pT muons from W boson decays and soft muons from B-hadron decays in b jets. We also report on searches for CP violation effects in ttbar.
The integration of HPC resources into the standard computing toolkit of HEP experiments is becoming important as traditional resources are being outpaced by the needs of the experiments. We will describe solutions that address some of the difficulty in running data-intensive pipelines on HPC systems. Users of NERSC HPCs are benefiting from a newly developed package called "Shifter" that creates docker-like images and the deployment of the new "Burst Buffers" NVRAM file system designed to offer extreme I/O performance, supporting terabyte-per-second bandwidth and 10s of millions of IO operations per second. These tools have enabled particle physicists from multiple experiments routinely run their entire multi-TB sized CVMFS software stacks across tens of thousands of compute cores. In addition, an Edge Service has been developed to provide a uniform interface for HEP job management systems to access supercomputer sites. It is based on the Python Django framework and is composed of two processes, of which one runs inside the supercomputing environment and one runs outside. It has been used to run over 100 million core-hours of LHC experiment jobs on the Mira supercomputer at the Argonne Leadership Computing Facility and on the Edison supercomputer at NERSC for LHC experiments.
A variety of vector boson measurements has been performed with Run 1 LHCb data, including inclusive Z/W cross-sections, the Z forward-backward asymmetry, Z plus charm, Z/W production with jets (including heavy flavor), and top production. Additionally, new inclusive Z/W cross-sections have been measured with Run 2 data. A summary of the most relevant results will be presented.
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We present a search for supersymmetry in diphoton plus jets plus missing transverse energy final states. The analysis uses data collected with the CMS detector at a center-of-mass energy of 13 TeV.
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The Belle II experiment aims to record 50 ab$^{-1}$ data with the high
luminosity to be provided by the SuperKEKB energy-asymmetric $e^+e^-$
collider. The anticipated high statistics data enables us to perform
studies of $B$ decays involving $\tau$ leptons such as
$B^+ \to \tau^+ \nu_{\tau}$ and $B \to D^{(*)} \tau^+ \nu_{\tau}$ modes.
The precise measurements of branching fraction as well as the $\tau$
lepton polarization in these $B$ decays provide a very sensitive indirect
search for a charged Higgs boson. Belle IIs's sensitivity for the charged
Higgs is complementary to direct searches at ATLAS and CMS.
Measurements are presented of t-channel single top quark production in proton-proton collisions at the LHC at centre-of-mass energies of 7, 8 and 13 TeV, using data collected with the CMS experiment during the years 2011, 2012 and 2015. The analyses consider leptonic decay channels of the W from the top decays, and makes use of kinematic characteristics of electroweak single top production for the separation of signal from backgrounds using multivariate methods. The measurement is used to constrain the Vtb CKM matrix element. The results are compared with the most precise standard model theory predictions. The inclusive fiducial cross section is also measured. Measurements of top/antitop cross section ratio and of various differential single top quark production cross sections are also presented.
Measurements of single top quark production in the tW-channel in pp collisions are presented. In the tW-channel a top quark is produced in association with a W boson. The data were collected in the years 2011 and 2012 at centre-of-mass energies of 7 and 8 TeV. The experimental signature is similar to top pair production, and there is interference at higher orders between the two processes. The measurements are performed using final states in which the associated W boson as well as the one originating from the top quark decay leptonically. Multivariate methods are used to extract the cross section. The result is compared with current standard model theory predictions. The measurement is used to constrain the Vtb CKM matrix element. Furthermore, a search for s-channel single top production at 8 TeV is presented.
Early-career scientists from Fermilab will discuss physics, life and career with students attending the ASP.
We consider a dark sector with SU(3)C×U(1)Y×U(1)X and three families of dark fermions that are chiral under dark U(1)X gauge symmetry, whereas scalar dark matter X is the SM singlet. U(1)X dark symmetry is spontaneously broken by nonzero VEV of dark Higgs field ⟨Φ⟩, generating the masses of dark fermions and dark photon Z′. The resulting dark Higgs boson ϕ can be produced at the LHC by dark quark loop (involving 3 generation) and will decay into a pair of photon through charged dark fermion loop. Its decay width can be easily ∼45 GeV due to its possible decays into a pair of dark photon, which is not strongly constrained by the current LHC searches pp→ϕ→Z′Z′ followed by Z′ decays into the SM fermion pairs. The scalar DM can achieve thermal relic density without conflict with direct detection bound or the invisible ϕ decay into a pair of DM.
Merged abstract
Our understanding of the transition from partons to hadrons in QCD has been challenged in recent years. In particular for high-multiplicity minimum-bias events at the LHC, novel experimentation techniques have revealed tantalising indications of non-trivial and possibly collective phenomena. A new wave of model building efforts has ensued, including ideas of colour reconnections, colour ropes, interacting strings, and hydrodynamics. It is essential to develop further sensitive probes of the mechanisms underpinning this fundamental aspect of QCD, to find answers to key questions such as if and how jet universality is broken and whether thermalisation is relevant in pp collisions. The answers will not only be of fundamental interest but will also impact precision studies that rely on hadronisation models, as well as the interpretation of heavy-ion results that use pp collisions as a reference. Using strangeness and baryons as tracers, we propose an extension of minimum-bias studies adapted to the environment of the underlying event which show substantial discriminatory power between several alternative models of soft physics. The applicability of this and related works to improve soft physics modelling at the LHC is explored.