Trillions of collisions show the W boson is more massive than expected. What does it mean for the Standard Model?
A decade-long experiment produced the most accurate measurement yet for the mass of W bosons, the particles responsible for the weak force. The result provides even more evidence for undiscovered physics.
By John Conway, The Conversation | Published: Wednesday, April 20, 2022
RELATED TOPICS: PARTICLE PHYSICS | STANDARD MODEL
wboson
Measuring the mass of W bosons took 10 years — and the result was not what physicists expected.
sakkmesterke/Shutterstock
“You can do it quickly, you can do it cheaply, or you can do it right. We did it right.” These were some of the opening remarks from David Toback, leader of the Collider Detector at Fermilab, as he announced the results of a decadelong experiment to measure the mass of a particle called the W boson.
I am a high energy particle physicist, and I am part of the team of hundreds of scientists that built and ran the Collider Detector at Fermilab in Illinois – known as CDF.
After trillions of collisions and years of data collection and number crunching, the CDF team found that the W boson has slightly more mass than expected. Though the discrepancy is tiny, the results, described in a paper published in Science on April 7, 2022, have electrified the particle physics world. If the measurement is correct, it is yet another strong signal that there are missing pieces to the physics puzzle of how the universe works.
standardmodeltable
The Standard Model of particle physics describes the particles that make up the mass and forces of the universe.
MissMJ/WikimediaCommons
The Standard Model of particle physics is science’s current best framework for the basic laws of the universe and describes three basic forces: the electromagnetic force, the weak force and the strong force.
The strong force holds atomic nuclei together. But some nuclei are unstable and undergo radioactive decay, slowly releasing energy by emitting particles. This process is driven by the weak force, and since the early 1900s, physicists sought an explanation for why and how atoms decay.
According to the Standard Model, forces are transmitted by particles. In the 1960s, a series of theoretical and experimental breakthroughs proposed that the weak force is transmitted by particles called W and Z bosons. It also postulated that a third particle, the Higgs boson, is what gives all other particles – including W and Z bosons – mass.
Since the advent of the Standard Model in the 1960s, scientists have been working their way down the list of predicted yet undiscovered particles and measuring their properties. In 1983, two experiments at CERN in Geneva, Switzerland, captured the first evidence of the existence of the W boson. It appeared to have the mass of roughly a medium-sized atom such as bromine.
By the 2000s, there was just one piece missing to complete the Standard Model and tie everything together: the Higgs boson. I helped search for the Higgs boson on three successive experiments, and at last we discovered it in 2012 at the Large Hadron Collider at CERN.
The Standard Model was complete, and all the measurements we made hung together beautifully with the predictions.
particleaccelerator
The Collider Detector at Fermilab collected data from trillions of collisions that produced millions of W bosons.
Bodhita/WikimediaCommons
Measuring W bosons
Testing the Standard Model is fun – you just smash particles together at very high energies. These collisions briefly produce heavier particles that then decay back into lighter ones. Physicists use huge and very sensitive detectors at places like Fermilab and CERN to measure the properties and interactions of the particles produced in these collisions.
In CDF, W bosons are produced about one out of every 10 million times when a proton and an antiproton collide. Antiprotons are the antimatter version of protons, with exactly the same mass but opposite charge. Protons are made of smaller fundamental particles called quarks, and antiprotons are made of antiquarks. It is the collision between quarks and antiquarks that create W bosons. W bosons decay so fast that they are impossible to measure directly. So physicists track the energy produced from their decay to measure the mass of W bosons.
In the 40 years since scientists first detected evidence of the W boson, successive experiments have attained ever more precise measurements of its mass. But it is only since the measurement of the Higgs boson – since it gives mass to all other particles – that researchers could check the measured mass of W bosons against the mass predicted by the Standard Model. The prediction and the experiments always matched up – until now.
wbosonmass
The new measurement of the W boson (red circle) is much farther from the mass predicted by the Standard Model (purple line) and also greater than the preliminary measurement from the experiment.
CDF Collaboration via Science Magazine
Unexpectedly heavy
The CDF detector at Fermilab is excellent at accurately measuring W bosons. From 2001 to 2011, the accelerator collided protons with antiprotons trillions of times, producing millions of W bosons and recording as much data as possible from each collision.
The Fermilab team published initial results using a fraction of the data in 2012. We found the mass to be slightly off, but close to the prediction. The team then spent a decade painstakingly analyzing the full data set. The process included numerous internal cross-checks and required years of computer simulations. To avoid any bias creeping into the analysis, nobody could see any results until the full calculation was complete.
When the physics world finally saw the result on April 7, 2022, we were all surprised. Physicists measure elementary particle masses in units of millions of electron volts – shortened to MeV. The W boson’s mass came out to be 80,433 MeV – 70 MeV higher than what the Standard Model predicts it should be. This may seem like a tiny excess, but the measurement is accurate to within 9 MeV. This is a deviation of nearly eight times the margin of error. When my colleagues and I saw the result, our reaction was a resounding “wow!”
What this means for the Standard Model
The fact that the measured mass of the W boson doesn’t match the predicted mass within the Standard Model could mean three things. Either the math is wrong, the measurement is wrong or there is something missing from the Standard Model.
First, the math. In order to calculate the W boson’s mass, physicists use the mass of the Higgs boson. CERN experiments have allowed physicists to measure the Higgs boson mass to within a quarter-percent. Additionally, theoretical physicists have been working on the W boson mass calculations for decades. While the math is sophisticated, the prediction is solid and not likely to change.
The next possibility is a flaw in the experiment or analysis. Physicists all over the world are already reviewing the result to try to poke holes in it. Additionally, future experiments at CERN may eventually achieve a more precise result that will either confirm or refute the Fermilab mass. But in my opinion, the experiment is as good a measurement as is currently possible.
That leaves the last option: There are unexplained particles or forces causing the upward shift in the W boson’s mass. Even before this measurement, some theorists had proposed potential new particles or forces that would result in the observed deviation. In the coming months and years, I expect a raft of new papers seeking to explain the puzzling mass of W bosons.
As a particle physicist, I am confident in saying that there must be more physics waiting to be discovered beyond the Standard Model. If this new result holds up, it will be the latest in a series of findings showing that the Standard Model and real-world measurements often don’t quite match. It is these mysteries that give physicists new clues and new reasons to keep searching for fuller understanding of matter, energy, space and time.
John Conway, Professor of Physics, University of California, Davis
This article is republished from The Conversation under a Creative Commons license. Read the original article.
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多倫多大學 工程科學系 (加拿大)https://engsci.utoronto.ca
劍橋大學 工程學系 (英國)
http://www.eng.cam.ac.uk/
http://www.cs.toronto.edu/songfrompi/
As a Tree Through the Ages
麻薩諸塞理工學院Massachusetts Institute of Technology SONG【https://youtu.be/5hyAe3uMwQY】
吳佳玲 袁天華 通報系統·隱藏要素。伺服器。
https://chinaq.tv/interrogation-room/
https://chinaq.tv/kinkyu-torishirabeshitsu-2/
https://chinaq.tv/jp190411d/
吳佳玲 袁天華 通報系統·隱藏要素。伺服器。
吳佳玲做鼠媽 袁天華做猴媽 皆不做虎媽 哈佛量子系
我來支援瞻"妄"者啦
注意:不是"望"旺，我~並~不~是~屁屁先生屁屁偵探~ Aug 13 Thu 2020
瞻妄評估工具Confusion Assessment Method for the ICU (CAM-ICU-7)
分享: facebook PLURK twitter
先了解定義
譫妄(delirium)指的是病人發生「急性的認知、意識障礙」
可以由CAM-ICU做評估
Confusion Assessment Method for the ICU總分最高七分，簡稱CAM-ICU-7
※整個CAM-ICU-7評估，必須要有特徵1+2+3或1+2+4之一的存在，才能確認有譫妄(delirium)，而總分越高，代表越嚴重(最低3分，最高7分)
特徵1：精神狀態急性發作或改變
如果有以下情形得1分，沒有則0分
= 和病人平常的狀況相較，有證據顯示精神態急性改變嗎？
= (不正常的)行為在過去24小時有變動嗎？嚴重度有增加或減少嗎？
--- 變動的差異可以由鎮靜評估表(例：Richmond Anxiety Sedation Scale (RASS))、Glasgow Coma Scale (GCS)，或與先前的譫妄狀態來評估(資料來源可由床旁重症護士或家屬獲得)。
特徵2：不注意
在以下擇一的測試中，若答對低於3次得2分，答對4~7次得1分，答對8次以上得0分
= 聽覺隨機數字測試
--- 指引：告訴病人：「我會唸給您聽10個數字，當您聽到數字1時，就握住我的手！」
--- 執行：以病人足夠聽到的音量(至少要比周遭環境噪音大聲)，以病人能聽懂的語言(母語，國語、台語、英語、越語…)，以約每秒一個數字的速度唸出下列10個數字：8, 1, 7, 5, 1, 4, 1, 1, 3, 6
--- 記分：當唸到「1」時，如果病人沒有握住，或是當唸到其他數字時握住，則記為錯誤，反之則記為答對
※需要時須調整數字的順序，不然病人可能會把答案背下來，造成低估瞻妄的程度
= 視覺圖片辨認
--- 執行：請病人辨認八張圖片，或是八項可以從床邊取得的一般用品
--- 計分：紀錄答對幾項
特徵3：意識層次的改變
以Richmond Anxiety Sedation Scale (RASS)做評估
若RASS = 0則得0分，若RASS = 1或-1則得1分，若RASS大於2或小於-2則得2分
特徵 4：沒有組織的思考
以下建議題組的題目中，若能答對4題得0分，若能答對2~3題得1分，若只能答對0~1題得2分
= 建議題組A
--- 1.一個石頭可以浮在水面上嗎？
--- 2.海洋中有魚嗎？
--- 3. 1公斤比2公斤重嗎？
--- 4.鐵鎚是用來敲釘子的嗎？
= 建議題組B
--- 1.一片葉子可以浮在水面上嗎？
--- 2.海洋中有大象嗎？
--- 3. 2公斤比1公斤重嗎？
--- 4.鐵鎚是用來切木頭的嗎？
※整個CAM-ICU-7評估，必須要有特徵1+2+3或1+2+4之一的存在，才能確認有譫妄(delirium)，而總分越高，代表越嚴重(最低3分，最高7分)
補充：
里奇蒙躁動鎮靜量表Richmond Agitation-Sedation Scale, RASS
得分
名稱
描述
+4
攻擊性
好鬥或具有暴力行為，當下就對工作人員造成危險
+3
極度躁動
拉扯或拔除身上的管路或導線，行為具有攻擊性
+2
躁動
常常毫無目的的舉動或患者呼吸器不協調
+1
煩躁不安
焦慮或恐懼，但其行為不具攻擊性或不劇烈
0
清醒且平靜
-1
嗜睡
沒有完全清醒，聲音刺激後有眼神接觸超過10秒
-2
輕度鎮靜
聲音刺激僅能短暫維持清醒(眼神接觸低於10秒)
-3
中度鎮靜
對聲音刺激有反應或動作(但無眼神接觸)
-4
深度鎮靜
對聲音刺激毫無反應，但對身體刺激會有動作
-5
無法喚醒
對聲音或身體刺激都沒有反應
評估RASS的步驟：
= 1. 觀察：不具互動性的觀察病人，如果病患對此有警覺，給予相對應的0~+4分，如果病患毫無警覺，則執行聲音刺激
= 2. 言語：大聲叫喚病人的名字並且要求病人看評估者，必要時可以重複1~2次，如果病人對聲音有反應，則給予相對應的-1~-3分，若沒有反應，則執行身體刺激
= 3. 身體：搖晃病人的肩膀，如果仍沒有反應則進行疼痛刺激(如大力的搓揉胸骨)，根據其反應給予對應的-4~-5分
CAMICU.PNG
RASS.PNG
文章標籤
瞻妄
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腦
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ICU
加護病房
老年
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CAM-ICU-7
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醫療
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嚴重
RASS
鎮靜
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混亂
delirium
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每天像被凌遲！死囚崩潰求伏法 法務部：逐步廢死
52
東森新聞
2021年6月23日·2 分鐘 (閱讀時間)
近年死刑的存廢一直都是社會爭論的議題，部分人挺死認為這是還給社會公道的唯一方式；但卻有部分人認為人權、生命相當重要因此反對死刑的存在，不過日前卻有名死刑犯認為，與其在監獄裡關到死，不如讓他早點伏法，因次多次寫信到法務部求死，近期更直接投書媒體，希望訴求能被正視。
根據《聯合報》報導，一名關在高雄第二監獄的死刑犯鄭武松指出，關在監獄的每天就像是被人拿刀凌遲，簡直生不如死「對我呼求不理睬的司法人員，比殺人犯還殘忍」，他不僅多次寫信到法務部求死，也曾親自和前法務部長表達這樣的想法，對他而言關到死比直接執行死刑更為痛苦，不想再拖下去了。
鄭武松認為關到死比死刑還痛苦。（示意圖／pixabay）
鄭武松認為關到死比死刑還痛苦。（示意圖／pixabay）
據了解，鄭武松是名拖吊車司機，2002年11月42歲的鄭武松因想找前妻復合被拒絕，開始懷疑前妻有新歡，並在半夜前往工廠持刀殺死前妻及一名男子，2005年被判處死刑定讞，不過當時政策傾向不執行死刑，因此他已經被關了19年仍遲遲未伏法。
儘管鄭武松13年前就開始在獄中繪畫創作，也會抄心經寫自傳，但對於他來說，在獄中等待死期的每一天都相當煎熬，認為這比殺人還慘忍。對此，法務部也回應，政策是逐步廢死，要執行死刑需要審慎考量各方面，會要求獄方給予更多關懷。
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Trillions of collisions show the W boson is more massive than expected. What does it mean for the Standard Model?
A decade-long experiment produced the most accurate measurement yet for the mass of W bosons, the particles responsible for the weak force. The result provides even more evidence for undiscovered physics.
By John Conway, The Conversation | Published: Wednesday, April 20, 2022
RELATED TOPICS: PARTICLE PHYSICS | STANDARD MODEL
wboson
Measuring the mass of W bosons took 10 years — and the result was not what physicists expected.
sakkmesterke/Shutterstock
“You can do it quickly, you can do it cheaply, or you can do it right. We did it right.” These were some of the opening remarks from David Toback, leader of the Collider Detector at Fermilab, as he announced the results of a decadelong experiment to measure the mass of a particle called the W boson.
I am a high energy particle physicist, and I am part of the team of hundreds of scientists that built and ran the Collider Detector at Fermilab in Illinois – known as CDF.
After trillions of collisions and years of data collection and number crunching, the CDF team found that the W boson has slightly more mass than expected. Though the discrepancy is tiny, the results, described in a paper published in Science on April 7, 2022, have electrified the particle physics world. If the measurement is correct, it is yet another strong signal that there are missing pieces to the physics puzzle of how the universe works.
standardmodeltable
The Standard Model of particle physics describes the particles that make up the mass and forces of the universe.
MissMJ/WikimediaCommons
The Standard Model of particle physics is science’s current best framework for the basic laws of the universe and describes three basic forces: the electromagnetic force, the weak force and the strong force.
The strong force holds atomic nuclei together. But some nuclei are unstable and undergo radioactive decay, slowly releasing energy by emitting particles. This process is driven by the weak force, and since the early 1900s, physicists sought an explanation for why and how atoms decay.
According to the Standard Model, forces are transmitted by particles. In the 1960s, a series of theoretical and experimental breakthroughs proposed that the weak force is transmitted by particles called W and Z bosons. It also postulated that a third particle, the Higgs boson, is what gives all other particles – including W and Z bosons – mass.
Since the advent of the Standard Model in the 1960s, scientists have been working their way down the list of predicted yet undiscovered particles and measuring their properties. In 1983, two experiments at CERN in Geneva, Switzerland, captured the first evidence of the existence of the W boson. It appeared to have the mass of roughly a medium-sized atom such as bromine.
By the 2000s, there was just one piece missing to complete the Standard Model and tie everything together: the Higgs boson. I helped search for the Higgs boson on three successive experiments, and at last we discovered it in 2012 at the Large Hadron Collider at CERN.
The Standard Model was complete, and all the measurements we made hung together beautifully with the predictions.
particleaccelerator
The Collider Detector at Fermilab collected data from trillions of collisions that produced millions of W bosons.
Bodhita/WikimediaCommons
Measuring W bosons
Testing the Standard Model is fun – you just smash particles together at very high energies. These collisions briefly produce heavier particles that then decay back into lighter ones. Physicists use huge and very sensitive detectors at places like Fermilab and CERN to measure the properties and interactions of the particles produced in these collisions.
In CDF, W bosons are produced about one out of every 10 million times when a proton and an antiproton collide. Antiprotons are the antimatter version of protons, with exactly the same mass but opposite charge. Protons are made of smaller fundamental particles called quarks, and antiprotons are made of antiquarks. It is the collision between quarks and antiquarks that create W bosons. W bosons decay so fast that they are impossible to measure directly. So physicists track the energy produced from their decay to measure the mass of W bosons.
In the 40 years since scientists first detected evidence of the W boson, successive experiments have attained ever more precise measurements of its mass. But it is only since the measurement of the Higgs boson – since it gives mass to all other particles – that researchers could check the measured mass of W bosons against the mass predicted by the Standard Model. The prediction and the experiments always matched up – until now.
wbosonmass
The new measurement of the W boson (red circle) is much farther from the mass predicted by the Standard Model (purple line) and also greater than the preliminary measurement from the experiment.
CDF Collaboration via Science Magazine
Unexpectedly heavy
The CDF detector at Fermilab is excellent at accurately measuring W bosons. From 2001 to 2011, the accelerator collided protons with antiprotons trillions of times, producing millions of W bosons and recording as much data as possible from each collision.
The Fermilab team published initial results using a fraction of the data in 2012. We found the mass to be slightly off, but close to the prediction. The team then spent a decade painstakingly analyzing the full data set. The process included numerous internal cross-checks and required years of computer simulations. To avoid any bias creeping into the analysis, nobody could see any results until the full calculation was complete.
When the physics world finally saw the result on April 7, 2022, we were all surprised. Physicists measure elementary particle masses in units of millions of electron volts – shortened to MeV. The W boson’s mass came out to be 80,433 MeV – 70 MeV higher than what the Standard Model predicts it should be. This may seem like a tiny excess, but the measurement is accurate to within 9 MeV. This is a deviation of nearly eight times the margin of error. When my colleagues and I saw the result, our reaction was a resounding “wow!”
What this means for the Standard Model
The fact that the measured mass of the W boson doesn’t match the predicted mass within the Standard Model could mean three things. Either the math is wrong, the measurement is wrong or there is something missing from the Standard Model.
First, the math. In order to calculate the W boson’s mass, physicists use the mass of the Higgs boson. CERN experiments have allowed physicists to measure the Higgs boson mass to within a quarter-percent. Additionally, theoretical physicists have been working on the W boson mass calculations for decades. While the math is sophisticated, the prediction is solid and not likely to change.
The next possibility is a flaw in the experiment or analysis. Physicists all over the world are already reviewing the result to try to poke holes in it. Additionally, future experiments at CERN may eventually achieve a more precise result that will either confirm or refute the Fermilab mass. But in my opinion, the experiment is as good a measurement as is currently possible.
That leaves the last option: There are unexplained particles or forces causing the upward shift in the W boson’s mass. Even before this measurement, some theorists had proposed potential new particles or forces that would result in the observed deviation. In the coming months and years, I expect a raft of new papers seeking to explain the puzzling mass of W bosons.
As a particle physicist, I am confident in saying that there must be more physics waiting to be discovered beyond the Standard Model. If this new result holds up, it will be the latest in a series of findings showing that the Standard Model and real-world measurements often don’t quite match. It is these mysteries that give physicists new clues and new reasons to keep searching for fuller understanding of matter, energy, space and time.
John Conway, Professor of Physics, University of California, Davis
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