Supersymmetry (SUSY) is an exciting and beautiful theory that answers some of the open questions in particle physics. It predicts that all known particles have a “superpartner” with somewhat different properties. For example, the heaviest quark of the Standard Model, the top quark, would have a superpartner called the top squark, or simply the “stop.”

In 2021 the CMS collaboration analyzed the entire set of collision data collected from 2016 to 2018 and found features suggesting that it might contain stop particles. In that case, “might” meant that there was less than a 5% chance that data containing only known particles could look like what was observed.

Instead of waiting many years to collect more data with the hope of reproducing this behavior, the CMS collaboration decided to reanalyze the same data with upgraded analysis techniques.

The new analysis looks for the simultaneous production of pairs of stops. Each stop decays into a top quark accompanied by several lighter quarks or gluons, which then form bound states known as hadrons, ultimately creating clusters of particles reconstructed in the detector as “jets.” The signal footprint is therefore two top quarks and multiple jets.

What makes the analysis challenging is that a very similar footprint is produced by one of the most common Standard Model processes in the LHC: the pair production of top quarks. Top quark production with many accompanying jets is a process that is difficult to accurately simulate, so to have a reliable determination of this background, it must be estimated from observed data.

A commonly used method of estimating backgrounds from data is called the “ABCD method.” It requires two uncorrelated observables that can discriminate between signal and background. The data set can then be divided into four regions (A, B, C and D) depending on the value of each observable being “signal-like” or “background-like.”

The subdivision then provides a region dominated by the signal, a region dominated by backgrounds and two intermediate regions. The key feature of the ABCD method is that, following the mathematics of probabilities for independent events, one can estimate the background in the signal-dominated region using only the information from the other regions.

The problem with using this method for the stop search is that all simple variables are correlated in this search, making the method invalid. To overcome this issue, CMS physicists have implemented an innovative approach based on advanced machine-learning techniques to determine two variables with a minimal level of correlation. These two variables are then used to divide the data into the four aforementioned regions.

The figure below shows the correlation between the two variables for the signal and the background and demonstrates that the signal mostly lies in region “A.”

Using this novel method, the CMS collaboration was able to accurately predict the dominant background in this analysis from observed data, without relying on simulations with large uncertainties associated with the modeling of the jet multiplicity distribution.

This resulted in a large gain in analysis sensitivity. If the signal hinted at by the 2021 analysis was real, it would now have been observed without any doubt. The fact that a signal was not seen in this analysis implies that, in specific SUSY scenarios, a stop decaying ultimately to top quarks and jets must have a mass greater than 700 GeV.

With a much more sensitive analysis method in place, the physicists are now eagerly looking forward to analyzing the data of the ongoing LHC Run 3 to go even further and to find where Nature hides its answers.

Boeing launched astronauts for the first time Wednesday, belatedly joining SpaceX as a second taxi service for NASA.

A pair of NASA test pilots blasted off aboard Boeing’s Starliner capsule for the International Space Station, the first to fly the new spacecraft.

The trip by Butch Wilmore and Suni Williams was expected to take 25 hours, with an arrival Thursday. They will spend just over a week at the orbiting lab before climbing back into Starliner for a remote desert touchdown in the western U.S. on June 14.

“Let’s get going!” Wilmore called out a few minutes before liftoff.

Half an hour later, he and Williams were safely in orbit and giving chase to the space station. Back at Cape Canaveral, the relieved launch controllers stood and applauded. After all the trouble leading up to Wednesday’s launch, including two scrapped countdowns, everything seemed to go smoothly before and during liftoff.

Years late because of spacecraft flaws, Starliner’s crew debut comes as the company struggles with unrelated safety issues on its airplane side.

Wilmore and Williams—retired Navy captains and former space station residents—stressed repeatedly before the launch that they had full confidence in Boeing’s ability to get it right with this test flight. Crippled by bad software, Starliner’s initial test flight in 2019 without a crew had to be repeated before NASA would let its astronauts strap in. The 2022 do-over went much better, but parachute problems later cropped up and flammable tape had to be removed from the capsule.

Wednesday’s launch was the third attempt with astronauts since early May, coming after a pair of rocket-related problems, most recently last weekend. A small helium leak in the spacecraft’s propulsion system also caused delays, but managers decided the leak was manageable and not a safety issue.

“I know it’s been a long road to get here,” NASA’s commercial crew program manager Steve Stich said before the weekend delay.

Boeing was hired alongside Elon Musk’s SpaceX a decade ago to ferry NASA’s astronauts to and from the space station. The space agency wanted two competing U.S. companies for the job in the wake of the space shuttles’ retirement, paying $4.2 billion to Boeing and just over half that to SpaceX, which refashioned the capsule it was using to deliver station supplies.

SpaceX launched astronauts into orbit in 2020, becoming the first private business to achieve what only three countries—Russia, the U.S. and China—had mastered. It has taken nine crews to the space station for NASA and three private groups for a Houston company that charters flights.

The liftoff from Cape Canaveral Space Force Station was the 100th of an Atlas V for rocket maker United Launch Alliance. It was the first ride for astronauts on an Atlas rocket since John Glenn’s Mercury era more than 60 years ago; the rocket usually launches satellites and other spacecraft.

Despite the Atlas V’s perfect record, the human presence cranked up the tension for the scores of NASA and Boeing employees gathered at Cape Canaveral and Mission Control in Houston.

Boeing’s Starliner and SpaceX’s Dragon are designed to be fully autonomous and reusable. Wilmore and Williams occasionally will take manual control of Starliner on their way to the space station, to check out its systems.

If the mission goes well, NASA will alternate between SpaceX and Boeing for taxi flights, beginning next year. The backup pilot for this test flight, Mike Fincke, will strap in for Starliner’s next trip.

“This is exciting. We built up to this moment for years and years, and it finally happened,” Fincke said from neighboring Kennedy Space Center. “I feel like the whole planet was cheering for them.”

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