CMS Group publishes new study on Lepton flavor in Higgs boson decays

a cylindrical shape made up of blue lines has a cone of red lines emanating from its center within the cylinder, like it's heading toward exiting out the base of the cylinder

Neutrinos mix and transform from one flavor to the other. So do quarks. However, electron and its heavier cousins, the muon and the tau, seem to conserve their flavor identity. This accidental conservation of charged lepton flavor must have a profound reason, or low-levels of violation of that conservation principle should occur at high energy scales. However, evidence for any charged lepton flavor violation remains elusive.

The CMS group recently published a new study on Lepton flavor in Higgs boson decays. At UW–Madison, the effort was led by Sridhara Dasu and postdoctoral researcher Varun Sharma, building off of work done by former postdoctoral researcher Maria Cepeda and former graduate student Aaron Levine.

The international CMS collaboration recently published a news story about this new study. Please read the full story here.

a cylindrical shape made up of blue lines has a cone of red lines emanating from its center within the cylinder, like it's heading toward exiting out the base of the cylinder
An event similar to the lepton flavor violating decay of the Higgs boson, produced with the gluon fusion production mechanism. The red track corresponds to a muon, while the red cone along with its corresponding calorimeter deposits is the tau lepton. | CMS Collaboration

IceCube detection of a high-energy particle proves 60-year-old theory

a colorized simulation of the detection event indicating where energies took place and were transferred

On Dec. 8, 2016, a high-energy particle hurtled to Earth from outer space at close to the speed of light. The particle, an electron antineutrino, smashed into an electron deep inside the ice sheet at the South Pole. This collision produced a particle that quickly decayed into a shower of secondary particles, triggering the sensors of the IceCube Neutrino Observatory, a massive telescope buried in the Antarctic glacier.

IceCube had seen a Glashow resonance event, a phenomenon predicted by Nobel laureate physicist Sheldon Glashow in 1960. With this detection, scientists provided another confirmation of the Standard Model of particle physics. It also further demonstrated the ability of IceCube, which detects nearly massless particles called neutrinos using thousands of sensors embedded in the Antarctic ice, to do fundamental physics. The result was published March 10 in Nature.

For the full story, please visit: https://news.wisc.edu/icecube-detection-of-high-energy-particle-proves-60-year-old-physics-theory/

For the study, please visit: https://www.nature.com/articles/s41586-021-03256-1

Scientists Say Farewell to Daya Bay Site

The Daya Bay Reactor Neutrino Experiment collaboration – which made a precise measurement of an important neutrino property eight years ago, setting the stage for a new round of experiments and discoveries about these hard-to-study particles – has finished taking data. Though the experiment is formally shutting down, the collaboration will continue to analyze its complete dataset to improve upon the precision of findings based on earlier measurements.

The detectors for the Daya Bay experiment were built at UW–Madison by the Physical Sciences Laboratory, and detailed in a 2012 news release.

Says PSL’s Jeff Cherwinka, U.S. chief project engineer for Daya Bay:

The University of Wisconsin Physics Department and the Physical Sciences Lab were very involved in the design, fabrication and installation of the anti-neutrino detectors for the Daya Bay Experiment.  It was a great opportunity for faculty, staff, and students to participate in an important scientific measurement, while learning about another country and culture.  There were many trips and man years of effort in China by UW physicists, engineers and technicians to construct the experiment and many more for operations and data taking.  This international collaboration took a lot of effort, and in the end produced great results.

The chief experimentalist at UW–Madison was Karsten Heeger who has since left for Yale. At present, Prof. Baha Balantekin is the only one remaining at UW–Madison in the Daya Bay Collaboration.

A completion ceremony will be held Friday, December 11from 7:30-8:3opm CST. Video stream options and the full story can be found at Berkeley Lab’s website.

Researchers awarded Department of Energy Quantum Information Science Grant

Three UW–Madison physics professors and their colleagues have been awarded a U.S. Department of Energy (DOE) High Energy Physics Quantum Information Science award for an interdisciplinary collaboration between theoretical and experimental physicists and experts on quantum algorithms.

The grant, entitled “Detection of dark matter and neutrinos enhanced through quantum information,” will bring a total of $2.3 million directly to UW-Madison. Physics faculty include principal investigator Baha Balantekin as well as Mark Saffman, and Sue Coppersmith. Collaborators on the grant include Kim Palladino at the University of Oxford, Peter Love at Tufts University, and Calvin Johnson at San Diego State University.

With the funding, the researchers plan to use a quantum simulator to calculate the detector response to dark matter particles and neutrinos. The simulator to be used is an array of 121 neutral atom qubits currently being developed by Saffman’s group. Much of the research plan is to understand and mitigate the behavior of the neutral atom array so that high accuracy and precision calculations can be performed. The primary goal of this project is to apply lessons from the quantum information theory in high energy physics, while a secondary goal is to contribute to the development of quantum information theory itself.

Kevin Black named co-coordinator of LHC Physics Center at Fermilab

Professor Kevin Black has been named one of the next co-coordinators of the LHC (Large Hadron Collider) Physics Center at Fermilab (LPC at FNAL), LPC announced recently. His initial appointment starts on September 1st, 2020 and lasts for two years.

Prof. Kevin Black

As co-coordinator, Black’s roles will include leading the several hundred physicists who are residents or visit the LPC for research on CMS, managing the distinguished research program, and leading the training of students and young physicists at FNAL.

According to their website, LPC at FNAL is a regional center of the Compact Muon Solenoid (CMS) Collaboration. It serves as a resource and physics analysis hub primarily for the seven hundred US physicists in the CMS collaboration. The LPC offers a vibrant community of CMS scientists from the US and overseas who play leading roles in analysis of data, in the definition and refinement of physics objects, in detector commissioning, and in the design and development of the detector upgrade.

Black joined the CMS experiment in 2018 when he joined the UW–Madison physics faculty after 13 years on CMS’s companion experiment, ATLAS. Since that time, he has been involved in the forward muon upgrade project — which will install GEM (Gas Electron Multiplier) detectors — as manager of the U.S. component of the electronic readout project. He has also served as deputy run coordinator of the GEM system, and his group is focusing on the data-acquisition development for that system. Additionally, his students and post-docs are working on a variety of physics analysis ranging from searches for new physics with the top quark, flavor anomalies in bottom quark decays, and searches for pair-production of Higgs bosons.

“I am excited for this important leadership opportunity to play a crucial role in facilitating U.S. participation in cutting edge particle physics research at a unique facility,” Black says. It will allow me to continue the excellent tradition of the LPC and bring my own ideas and initiatives to the center.”

As LPC at FNAL co-coodinator, Black will also serve as co-Chair of the LPC Management Board. He will be working with Dr. Sergo Jindariani, a senior scientist at FNAL, and succeed Prof. Cecilia Gerber from the University of Illinois at Chicago.

Particle collider experiment CMS — and UW physicists who contribute — celebrate 1000th publication

1000 boxes laid out to make an image of the CMS detector at CERN, and spells "1000 papers"

In June 2020, The Compact Muon Solenoid (CMS) collaboration announced the submission of its 1000th scientific publication since the experiment began a decade ago. With multiple University of Wisconsin–Madison physics faculty involved in CMS over the years, the physics department wanted to use this milestone to celebrate their achievements.

CMS is an international collaboration of over 4000 scientists at CERN’s Large Hadron Collider, which churns out data that have contributed immensely to our understanding of particle physics and pointing directions to moving beyond the Standard Model. Amongst its achievements, CMS announced in 2012 the discovery of the Higgs boson, along with ATLAS collaboration.

UW–Madison’s Professor Emeritus Don Reeder, Professor Emeritus Wesley H. Smith, Emeritus Distinguished Scientist Richard Loveless and Professor and current department chair Sridhara Dasu are amongst the founding members of CMS. The team later expanded to include Professor Matt Herndon and Senior Scientists Dr. Sascha Savin and Dr. Armando Lanaro. In 2018, Professor Kevin Black and Professor Tulika Bose joined the physics department.

1000 boxes laid out to make an image of the CMS detector at CERN, and spells "1000 papers"
Image from CERN. The original image can be found at https://cms.cern/news/cms-collaboration-celebrates-1000th-paper

“It’s a proud moment for CMS in general and for the UW CMS group to see our work over the years culminate in this historic milestone!” says Bose, who currently serves as the Deputy U.S. CMS Software and Computing Operations program manager. “We are looking forward to more with the upcoming run and with the High-Luminosity LHC upgrade.”

Of the current UW­–Madison physics faculty involved:

  • Sridhara Dasu currently leads the UW–Madison High Energy Physics group. On CMS, his focus is in better understanding the Higgs boson, searching for its partners, and possible new physics connections, especially to dark matter. He helped design the CMS calorimeter trigger system and continues to dabble in designing its upgrades.
  • Matthew Herndon is involved in the ongoing upgrade of the CSC (cathode strip chamber) forward muon system and well as detailed studies of the performance of the CSC system. He studies the physics of multiple gauge boson interactions and associated new physics phenomena involving multiple gauge bosons.
  • Tulika Bose previously served as the Physics Co-coordinator (PC) of the CMS Experiment during 2017-2019 and as the CMS Trigger Co-coordinator (2014-2016). In addition to her current program manager role, she is involved in physics studies that cover both precision measurements of Standard Model processes as well as direct searches for new physics including dark matter and top quark partners.
  • Kevin Black joined CMS when he joined the UW–Madison physics department in 2018, after 13 years on the CMS companion experiment ATLAS. Since then, he has been involved in the forward muon upgrade project — which will install GEM (Gas Electron Multiplier) detectors — as manager of the U.S. component of the electronic readout project and as deputy run coordinator of the GEM system. His group is focusing on the data-acquisition development for that system.

“I am especially proud of our eighteen PhD graduates who have contributed about two papers each to this set of thousand; one on a search for new physics channel and another on a carefully made measurement,” Dasu says.

Adds Herndon, “It’s an amazing milestone and a testament to the scientific productivity of the CMS experiment!  UW personnel, especially our students, have been a major part of that achievement contributing to nearly 100 of those papers.”

In collaboration with the Physical Sciences Laboratory, the UW Physics team helped design the steel structures and other mechanical systems of the CMS experiment, especially leading the installation, commissioning and operations of the endcap muon system. The UW Physics team has also helped design, build, install and operate the electronics and data acquisition systems, in particular the calorimeter trigger system, and began collecting data from day one of LHC operations. They also collaborated with the HT Condor group of the Department of Computer Science to design and build the Worldwide LHC Computing Grid (WLCG), hosting one of the productive Tier-2 computing centers in Chamberlin.

The UW–Madison group was a key player in the discovery of Higgs boson in 4-lepton decay mode and establishing its coupling to fermions. The group has also searched for new physics especially looking for evidence of beyond the standard model in the form of heavy Higgs bosons that decay to tau-pairs. The group also upgraded the calorimeter trigger system and completed the endcap muon chamber system for the second higher energy run of the LHC. Searches continue for new Higgs partners, rare decays of the SM-like Higgs boson, and searches for new particles. They have added to our repertoire a series of searches for anomalous production of single high energy objects that are indicative of dark matter production in the LHC collisions.

The abundant production of papers proclaiming discoveries or the best measurements to date were possible in large part because of numerous UW–Madison electronics and computing personnel.

“The publication of the 1000th paper of the CMS collaboration is a significant milestone capping the achievement of thousands of physicists worldwide on a wide range of topics that can only be made at this unique instrument and facility,” Black says.