# Lunchtime Seminars

## September 15, 2015

Deepali Sharma, Stony Brook University

Studying heavy flavor (charm and bottom) production via dielectrons in p+p and d+Au collisions.

The dielectron mass spectrum is a unique probe to directly access the different stages of a heavy-ion collision. The low mass region (me+e− < 1 GeV/c2) reflects the Quark Gluon Plasma (QGP) temperature and thermalization phase, while the low vector meson resonancesprobechiralsymmetryrestoration.Theintermediate(1<me+e− <3GeV/c2) and high (4 < me+e− < 8 GeV/c2) mass regions are dominated by semi-leptonic decays of open charm and beauty respectively and so provide information about the heavy flavor dynamics.

The PHENIX experiment at RHIC collected a large data set of p+p and d+Au collisons in 2006 and 2008 respectively, reaching to high mass (me+e− < 14 GeV/c2) and high transverse momentum (pT < 8 GeV/c). The large range in mass and pT covers the phase space dominated by heavy flavor thus allowing to extract the heavy flavor cross-section. We show a precise determination of the bottom cross section using the pT and mass- dependence of e+e− pairs in the mass range from 1 < me+e− < 8 GeV/c2. Exploring the mass and pT phase simultaneously provides the access to the regions where either charm or bottom dominates. The talk will also discuss the model dependence on the extracted cross-sections.

time:    Noon
place:   Kolker Room (26-414)

(Lunch will be served.)

September 22, 2015

Jan Balewski, MIT

Potential of Virtualization for Scientific Workloads

In recent years, Cloud computing has become a very attractive and popular model for accessing distributed resources, and has emerged as the next big trend after the "grid computing" approach. In this talk I will discuss how a Virtual Machine (VM) framework has been successfully applied in several particle physics experiments. I will demonstrate how one can adapt physics analysis algorithms and data workflow to leverage remote cloud computing resources.

I will talk about reconstruction of W-boson decays to electrons produced at STAR in polarized p+p collisions at RHIC at sqrt(s) of 500 GeV, which provided crucial information about sea quark polarization. For this experiment run in 2011, we extended STAR computing resources of about 3000 CPU slots by an additional 1000 slots for the near real time reconstruction, using opportunistic resources from pilot DOE/Magellan and DOE/Nimbus projects.

I will discuss the advantages of applying virtualization throughout a future experiment such as DarkLight where intense electron beam of LERF at JLab interacts with the hydrogen gas target. DarkLight will attempt to produce a heavy photon A', believed to be responsible for the interaction of the dark matter. We encapsulated all experiment-specific simulations and analysis software in a VM. The DarkLight VM is periodically updated and redistributed to all collaborating institutions to assure homogeneity of the results despite diverse hardware and varied expertise in system administration across the collaboration.

Finally, the benefits and challenges of running a private cloud will be illustrated using the case of the "Reuse" OpenStack cluster of 260 cores at MIT/LNS. I will present typical-use cases; benchmarking; integration with virtual PXE-boot, virtual Ganglia monitoring, and a license server; extension to multi-cloud computing using Phantom; and use of Dropbox as persistent storage.

time:    Noon
place:   Kolker Room (26-414)

(Lunch will be served.)

September 29, 2015

Ted Kolberg, University of Maryland

Searches for natural supersymmetry in the 1- and 2-lepton final states with the CMS detector at the LHC

SUSY models where the partner of the top quark is near the electroweak scale can offer a natural solution to the heirarchy problem while evading the strong LHC limits on more generic models. During the LHC Run I, CMS and ATLAS both had a extensive programs to develop dedicated search strategies for such models. Signatures with leptons in the final state are of particular interest due to the excellent detector performance for electrons and muons. Results of searches for a relatively light top partner in the 1- and 2-lepton final states are presented and interpreted in terms of several different simplified models.

time:    Noon
place:   Kolker Room (26-414)

(Lunch will be served.)

## October 6, 2015

No talk this week

## October 13, 2015

Ivica Friščić, University of Zagreb

Measurement of the p(e,e’π+pi^2)n reaction with the short-orbit spectrometer at Q2 = 0.078 (GeV/c)2

The precise measurement of the cross section for the p(e,e’π+)n reaction at certain kinematics, allows one to separate the cross section into the terms, which carry the information about the nucleon structure. Since the data at low four-momentum transfer Q2 and close to the reaction threshold are not known with an intended precision, the A1 collaboration (at MAMI) has performed a new measurement at Q2 = 0.078 (GeV/c)2 and at an invariant mass of W = 1094 MeV - approximately 15 MeV above the reaction threshold. For five different kinematical settings, the scattered electron was detected in the standard spectrometer A and the produced charged pion was detected in the new short-orbit spectrometer (SOS), which is equipped with a detector system specialized for a detection of low-energy pions. For the first time, the complete analysis of the p(e,e’π+)n reaction data measured with the SOS was performed. New SOS-specific correction methods were developed to ensure a consistent data analysis. From the obtained cross sections, the transverse and longitudinal cross sections terms were separated using the Rosenbluth method and the transverse-longitudinal interference term has been determined from the left-right asymmetry. The results for the cross section terms, which contain the information about the nucleon structure, were compared with calculations of three models: DMT2001, MAID2007 and MAID.

time:    Noon
place:   Kolker Room (26-414)

(Lunch will be served.)

## October 20, 2015

Nathan Jurik, Syracuse University

Observation of J/psi p resonances consistent with pentaquark states in Lambda b to J/psi p K- decays

It has now been over 50 years since the inception of the quark model. The original papers by Gell-Mann and Zweig included the description of the now well known three-quark baryons and quark-antiquark mesons. They also included the possibility of "exotic" hadrons, such as mesons containing two quarks and two antiquarks (tetraquarks), or four quarks and an antiquark (pentaquarks). There is no clear reason why such exotic combinations of quarks should not exist. Indeed, in recent years strong tetraquark candidates have been discovered. However, until recently the observation of any lasting pentaquark candidates had eluded all searches. Using the LHCb Run 1 dataset, two J/ψp resonances consistent with pentaquark states have been observed in Λb→J/ψpK- decays. I will describe a full amplitude analysis which was performed in order to be most sensitive to the underlying physics and best study the resonant nature of these states. These states are overwhelmingly significant, and mark the first convincing observation of pentaquark candidates.

time:    Noon
place:   Kolker Room (26-414)

(Lunch will be served.)

## October 27, 2015

Markus Klute, MIT

Exploiting the LHC Physics Potential

The current LHC schedule foresees colliding beams till 2038. To reach a total luminosity of more than 3000/fb an increase in intensity is scheduled in 2026 to 5 to 7 times the nominal LHC luminosity. The instantaneous luminosity translates to 140 to 200 simultaneous proton-proton collisions. About 90% of the LHC data will be accumulated with these challenging conditions. In addition, aging and radiation damage will take a toll on the detectors. The ATLAS and CMS collaborations developed a coherent plan to meet these challenges. In this talk I will discuss the long term physics program of the LHC and the challenges and opportunities of operating detectors in the high luminosity LHC environment.

time:    Noon
place:   Kolker Room (26-414)

(Lunch will be served.)

## November 3, 2015

No Talk This Week

November 10, 2015

Sinead Farrington, University of Warwick

Results on the Standard-Model-like Higgs Boson at LHC Run I

I will review the current state of knowledge of the SM-like Higgs boson discovered at the LHC Run I. An indisputable observation has been made in boson and fermion decay channels, in several production mechanisms. I will review the strength of these observations and the associated coupling measurements they yield and motivate the sensitivity needed in future such measurements. Further, I will analyse the properties measurements that have so far been made of this boson, including spin, CP and width/lifetime.

time:    Noon
place:   Kolker Room (26-414)

(Lunch will be served.)

## November 17, 2015

Charles Epstein, MIT

DarkLight Phase 1: Opportunities with Intense Electron Beams

The DarkLight experiment aims to search for a massive "dark photon" that would mediate forces between particles of Dark Matter in an analogous fashion to that of the photon in the Standard Model. DarkLight aims to search for such a dark photon by studying electron-proton collisions at Jefferson Lab's Energy-Recovering Linear Accelerator. By directing this megawatt electron beam onto a dense hydrogen gas target and studying the process in which an additional electron-positron pair is created, a dark photon could be observed. While this is currently a topic receiving much attention, DarkLight aims to approach the measurement in a novel way. The first phase of DarkLight is being prepared in which we will address a number of unique technical challenges and will make new, precise measurements of related Standard Model physics such as radiative Moller scattering. The opportunities for technical advancement will be described and the status of these new measurements presented.

time:    Noon
place:   Kolker Room (26-414)

(Lunch will be served.)

## November 24, 2015

Philip Ilten, MIT

Physics with forward heavy-flavor jets

The LHCb experiment, designed for b-hadron physics, has expanded its physics program to include jet measurements that are complementary to results from more central-rapidity detectors. An inclusive c and b-jet tagging algorithm, developed to utilize the excellent secondary vertex reconstruction of LHCb, will be described. By measuring W + c and W + b-jet production ratios the s-quark and intrinsic b-quark content of the proton is probed. Top production measurements will help constrain high momentum fraction gluon content of the proton, and also provide important limits on axi-gluon production. Possible future measurements investigating the intrinsic c-quark content of the proton and their subsequent impact on measuring Higgs couplings to second generation fermions, will also be presented.

time:    Noon
place:   Kolker Room (26-414)

(Lunch will be served.)

## December 1, 2015

Sadia Kahlil, Kansas State University

Searches for Vector-like quarks at CMS experiment, at the LHC

I will present results of searches for massive top and bottom quark partners using proton-proton collision data collected with the CMS detector at the CERN LHC at a center-of-mass energy of 8 TeV. These fourth-generation vector-like quarks are postulated to solve the Hierarchy problem and stabilize the Higgs mass, while escaping constraints on the Higgs cross section measurement. The vector-like quark decays result in a variety of final states, containing top and bottom quarks, gauge and Higgs bosons. I will present searches using several categories of reconstructed objects, from multi-leptonic to fully hadronic final states. At 8 TeV, we set exclusion limits on both the vector-like quark mass and pair-production cross sections, for combinations of the vector-like quark branching ratios. I will also present these searches using 13 TeV collision data.

time:    Noon
place:   Kolker Room (26-414)

(Lunch will be served.)

## December 8, 2015

Carlos Arguelles, MIT

Results from the Search for eV-Sterile Neutrinos with IceCube-86

The IceCube neutrino telescope at the South Pole has measured the atmospheric muon neutrino spectrum as a function of zenith angle and energy. Using IceCube's full detector configuration we have performed a search for eV-scale sterile neutrinos. Such a sterile neutrino, motivated by the anomalies in short-baseline experiments, is expected to have a significant effect on the $\bar{\nu_\mu}$ survival probability due to matter induced resonant effects for energies of order 1 TeV. This effect makes this search unique and sensitive to small sterile mixings. In this talk, I will present the results of the IceCube sterile neutrino search.

time:    Noon
place:   Kolker Room (26-414)

(Lunch will be served.)