Chapter 162 David Gross's Guidance

"Junior brother, this experiment is over, why are you still analyzing the data?"

At the desk, Xu Chuan raised his head after hearing the voice and saw Senior Brother Qi Xishao standing beside him.

"Senior Brother Qi."

Xu Chuan greeted him and then said, "No, the arrangements with the tutor have been completed. I am working on my own things here, not looking for Yukawa coupling data."

Hearing this, Qi Xishao was slightly stunned and asked curiously, "Hmm? What are you analyzing?"

He thought Xu Chuan was trying to continue looking for traces of Yukawa coupling between Higgs and third-generation heavy quarks, but he didn't expect it to be the case.

"Do an analysis to see if we can infer the ideal search channel for the most likely decay of the Higgs boson from these data."

Xu Chuan said casually, his eyes fell on the Dalitz diagram again.

Perhaps he should change his thinking, first analyze from the original perspective, and then use mathematical methods to verify, so that he may find something.

He is not a very stubborn person. When one method does not work, a short-term abandonment and starting from another method or perspective can sometimes have a completely different effect.

Scientific research and academic research require a spirit of being meticulous, but actual actions cannot be meticulous.

"Looking for the ideal search channel where the Higgs boson is most likely to decay?"

Qi Xishao looked at Xu Chuan with a strange expression, and then said: "Are you referring to the Yukawa coupling energy level of the Higgs and the third-generation heavy quarks?"

"If this is it, the standard model has already made a prediction for it. In experiments below the collision energy level of 13Tev, it will be about 34fb~56fb at the proton-proton center of mass energy, and the llbb decay final state transverse dynamic equilibrium system makes a restrictive fit to"

"You should know these things, right?"

Qi Xishao looked at Xu Chuan and briefly described the standard model's prediction of the decay of the Higgs particle.

As a physics researcher, and a particle physics researcher, there is no reason not to know this.

Xu Chuan stared at the Dalitz diagram and said without turning his head: "I know these, but from the prediction of the standard model, its prediction range is a bit large. I wonder if these things can be narrowed down."

"This will make it more efficient to find the Yukawa coupling between the Higgs and the third-generation heavy quarks. If we can lock the most ideal decay channel, we can find it in the next collision experiment."

Hearing this, Qi Xishao shook his head and advised: "It's up to you, but I suggest you give up."

"This work has been done before, but no one has ever been able to narrow the prediction of the standard model. It's too difficult."

"And even if you do it, you won't get any big rewards. At most, it will shorten the time to discover the Yukawa coupling phenomenon between the Higgs and the third-generation heavy quarks."

"Although this may save CERN millions or tens of millions of gold in collision funds, CERN will not give you a special award for this."

After knowing that Xu Chuan was not continuing to study the data for the Yukawa coupling between the Higgs and the third-generation heavy quarks, Qi Xishao's worries were put down.

However, he was not optimistic about Xu Chuan's attempt to lock the most ideal decay channel for Yukawa coupling between Higgs and third-generation heavy quarks.

As he said before, this work is too difficult.

CERN has also studied this aspect before, after all, it can save a lot of money, but no one has ever been able to do it.

However, as long as this junior brother does not get stuck in a dead end and fall into a state of being hit, other things don't matter.

Let him study if he wants to, anyway, he will naturally give up if there is no result in the end.

Qi Xishao left, and Xu Chuan didn't care. His attention was still on the Daritz diagram in front of him.

After thinking for a while, he picked up the ballpoint pen from the table and started working on the manuscript paper.

It will be difficult to sort out these things from a mathematical perspective in a short period of time, but he can sort them out from a physical perspective first.

【Fitted values ​​of the Higgs boson signal intensity parameter μ VHbb for mH=125 GeV, for WH and ZH processes and their combinations. The values ​​of the individual μVHbb (W/Z)H processes are obtained by simultaneously fitting the signal intensities of the independently floating WH and ZH processes, from which the compatibility of the individual signal intensities can be calculated to be 84%. 】

【.】

【The influence of the systematic uncertainty of the fitted Higgs boson signal intensity parameter μ for the nominal MVA analysis of the 13 TeV data. The systematic uncertainties are arranged in descending order of their influence on μ. The boxes represent the changes in μ; refer to the top x-axis, when the corresponding individual interference parameter θ is fixed to】

【Expected and observed significance values ​​(standard deviation) for independently fitting the H→ bb channel and its combination using 7 TeV, 8 TeV and 13 TeV data sets】

It took two days for Xu Chuan to finish sorting out the Dalitz diagrams in his hand.

The Dalitz diagrams and the corresponding information were saved in the computer and projected on the display.

Xu Chuan flipped through them in an orderly manner.

".Overview of systematic uncertainties in modeling the DiBoson production background. PS/UE denote partial subshower/potential event. When only shape uncertainty is evaluated, S notation is used."

"When determining the signal intensity of (W/Z)Z double boson production, the normalization uncertainty is eliminated because the normalization is unconstrained. If the size of the accepted system uncertainty varies from region to region, a range is displayed."

"If this range can be determined, it may be possible to find the fitting value H→ bb of the Higgs boson signal intensity parameter μ, as well as the VH, ttH and ggF+VBF analysis data used in Run 1 and Run 2, and their combination."

"If this step can be achieved, at least the most ideal search decay channel for the Yukawa coupling of the Higgs and the third-generation heavy quarks can be greatly narrowed down."

"But how should I do it?"

Staring at the information on the display, Xu Chuan fell into deep thought again.

From the perspective of particle physics, he has determined that there is indeed a range that can be used to find the fitting value H→ bb of the Higgs boson signal intensity parameter μ.

But he still has no idea how to calculate this range mathematically.

Of course, this is normal.

If it were really that easy to do, these works would have been done long ago.

For CERN physicists, it is better to optimize the calculation method rather than study how to narrow the most ideal search decay channel.

Efficient calculation methods can eliminate complex QCD background interference, obtain relatively pure signals, and thus increase the probability of finding useful signals.

As for studying how to narrow the most ideal search decay channel? It would be easier to find a way to ask the member states for more money and conduct more collision experiments.

Staring at the information on the display screen, Xu Chuan pinched his nose bridge, got up and left the office.

If you can't find inspiration in the office, you might as well go out and relax.

"Strange, you actually came out of the office."

On the lawn outside the CERN work area, Xu Chuan sat on a long wooden chair, and heard a surprised voice.

Turning his head, it was Senior Brother Qi Xishao, who came over with a plastic bag in his hand, sat down on the bench, and took out a bag of snacks from the bag and handed it to Xu Chuan.

Xu Chuan took it and looked at it, a bag of spicy "Jinzai Xiaoyu".

"Where did you buy this?" Xu Chuan asked curiously. This was obviously made in China, and there was no Chinatown in Geneva.

"I drove to Zurich to buy it."

Qi Xishao lazily lay on the bench, unpacked a bag of snacks and ate while basking in the sun.

"So? You drove for several hours to Zurich just for a few bags of snacks?" Xu Chuan stared at the plastic on the bench and was a little dumbfounded.

Qi Xishao shrugged: "This is my only hobby. I may not be able to go back to China twice a year. It's good to be able to eat things from my hometown."

"By the way, how is your research going?"

Xu Chuan unpacked the Jinzai fish, took a bite, and replied: "There is not much progress. I encountered some troubles."

"It's normal. The thing you are studying is extremely difficult. It not only requires a deep foundation in physics, but also requires strong mathematical ability. There are not many people in the entire particle physics community who are capable of studying this thing."

Qi Xishao understood the result clearly and was not surprised at all.

"Instead of studying this, to be honest, you might as well study the calculation method. At least this is much easier, and excellent calculation methods can eliminate scattering background and calculation interference, which can greatly increase the probability of finding useful information."

"As for finding the Yukawa coupling energy level of the Higgs and the third-generation heavy quarks, just leave it to the collider under our feet."

"As long as it is started enough times, it will be found one day."

Xu Chuan smiled and said, "Maybe, but I still want to try."

Seeing that Xu Chuan still didn't want to give up, Qi Xishao shook his head slightly and said, "Then I suggest you go find your mentor Edward Witten."

"If there is anyone who can help you in this regard, it may be him."

Hearing this, Xu Chuan's eyes suddenly lit up.

Maybe someone can really help him in this regard.

Of course, this person is not Edward Witten. Witten specializes in quantum field theory, string theory and related topology and geometry, but his research on particle physics is not so in-depth.

But there is a person related to Witten who is quite good at research in this area.

That is Edward Witten's mentor, or his master, David Gross.

David Gross is the current chairman of the CERN Council and one of the founders of quantum chromodynamics, particle physics and string theory.

He has conducted in-depth research in gauge field theory, particle physics and superstring theory.

In 2004, he won the Nobel Prize in Physics for discovering the "asymptotic freedom of quarks" and is a top physics expert.

According to statistics, he is now an academician of at least ten countries, including China. He was elected as a foreign academician of the Chinese Academy of Sciences in 2011.

It can be seen how awesome this guy is.

However, he is not very familiar with David Gross now. If he wants to ask him for help, the best way is to go through his mentor Edward Witten.

After saying "thank you" to Senior Brother Qi, Xu Chuan ate the Jinzai fish in his hand in two bites, then returned to his hotel room and sent an email to Edward Witten, who had returned to the Institute for Advanced Study in Princeton, asking him to help introduce David Gross.

Maybe Professor Witten was in front of the computer? Or maybe his email was set to follow. Anyway, this time, he received a reply not long after waiting.

"I have contacted Professor Gross. He will wait for you in his office at 2 pm tomorrow, but you don't have much time, only one hour."

"You can sort out the questions you need to consult first and send them to him by email first, so as to avoid wasting time. Professor Gross's email address is."

For Xu Chuan's request, Professor Witten did not delay at all. After receiving the email, he contacted David Gross for him.

Of course, this is not a big deal.

After all, in name, David Gross is still Xu Chuan's ancestor.

"Thank you, mentor. I will sort out the questions first."

After receiving Witten's reply, Xu Chuan quickly sorted out his research and data analysis results in recent days, and then packaged and compressed them into files and sent them to Professor David Gross.

The next day, at 2 pm, Xu Chuan came to the Nuclear Research Center Building of CERN.

As the chairman of the CERN Council, David Gross basically works here all year round.

According to the location in his memory, Xu Chuan successfully found David Gross's office.

He knocked on the wooden door, and a voice came from inside immediately.

"Come in."

Xu Chuan pushed the door open and walked in. In the office, an old man wearing rimless glasses was looking at him with a smile.

"Welcome to you. The report you hosted in the past two months was quite exciting."

As he spoke, David Gross stood up with a smile, made a cup of tea for Xu Chuan, and said: "I heard that Chinese people all drink tea. I just happen to have some tea leaves sent by others."

"Thank you." Xu Chuan hurriedly took the teacup with both hands.

After making a cup of tea for Xu Chuan and a cup of coffee for himself, David Gross looked at Xu Chuan and slowly said:

"Sit down, I don't have much time, and there will be a meeting later."

"I have read the email you sent me last night. I have to say that your idea is very unique. It may be difficult to achieve it, but I have some ideas here, maybe you can refer to it."

Seeing that he was getting to the point, Xu Chuan also became serious and listened carefully.

After chatting for a while, David Gross looked at Xu Chuan and said, "I don't know how to use mathematics to narrow down the most ideal decay channel for the Yukawa coupling between the Higgs and the third-generation heavy quarks."

"But from the perspective of particle physics, all particles are made up of quarks. Perhaps you can try to study from the two aspects of 'asymptotic freedom of quarks' and 'quark confinement'?"

Study from 'asymptotic freedom of quarks' and 'quark confinement'?

Hearing the old man's words, Xu Chuan fell into deep thought.