One and a half years ago ATLAS produced measurements for the Higgs boson mass using their selected sample of H->gamma gamma and H->ZZ*-> 4-lepton decay candidates, based on data collected in 2011 and 2012. That preliminary measurement was rather surprising as the two independent determinations appeared to disagree with one another at the 2.5-sigma level. The matter even spurred some online debate (see e.g. my blog entry) and a few gambling addicts waged $100 on the fact that those might be two distinct particle states.
On the matter you of course know well my opinion: as CMS has been measuring two very consistent mass values for the two Higgs boson decay modes, with accuracy superior to that of ATLAS and with combined mass right in the middle of the two ATLAS determinations, the 2.5 sigma effect is certainly just a fluke or some unknown systematical bias affecting the ATLAS results.
While we wait for more data to decide the issue of whether we are in presence of two distinct resonances or not - we will be collecting more Higgs bosons in 2015 than we have in our hands so far - it is nice to see a reanalysis of the ATLAS Higgs samples, which is the experiment's final word on the mass of the Higgs boson based on the 7- and 8-TeV proton-proton collisions collected until 2012. This has appeared as a preprint two days ago. I should be precise and say that it is not just a reanalysis: ATLAS has added some 33% more statistics in this measurement, coming from the latter part of the 2012 run.
The bottomline of the complex and very detailed measurements made by ATLAS is summarized graphically in the figure below, which shows 1- and 2-sigma contours on the mass versus signal rate plane. You clearly see that the ATLAS data insist on finding two distinct minima for the two datasets, although they have gotten a bit closer than they used to be.
The two mass measurements are quoted as follows in the paper:
You can see that the discrepancy is almost exactly at the 2-sigma level today. One interesting thing to notice is that while in the past ATLAS result the H->gamma gamma rate measurement was higher than the H->ZZ one, now it is the opposite. The reanalysis anyway finds results compatible with the old ones, if a bit more precise due to increased statistics.
So is it one particle or two particles ? Well, of course it is just one particle ! But the funny twin peaks of ATLAS will live on for another year or two, I suppose. If the 2015 data will insist in showing a difference between the determinations using the two final states, the conclusions we will be forced to draw is that there is a well-hidden, nasty systematical effect that spoils the energy scale of the ATLAS detector (either the photons or the leptons) at the level of 1%... But we are not there yet!
- PHYSICAL SCIENCES
- EARTH SCIENCES
- LIFE SCIENCES
- SOCIAL SCIENCES
Subscribe to the newsletter
Stay in touch with the scientific world!
Know Science And Want To Write?
- Highlights From ICNFP 2015
- Most Idiotic Rejection Of Course From Philosopher Of Science Not Grasping Relativity
- Artificial Intelligence: It's Time To Talk About What Emotions We Want AI To Have
- Supertranslations And Eternal Ghosts: Black Holes No Closer To Being Understood
- Innate GMO Potato Deregulated By USDA
- Lettuces Now, What Next - Could Astronauts Get All Their Oxygen And Food From Algae Or Plants?
- Brain Size Matters When It Comes To Remembering
- "I wouldn't take it too hard buddy. Suppose they did publish it- then what, 20 more people might..."
- "I had some problems with Dr. Vongehr's short essay. One of them is the broken English. Now I am..."
- "Carney3 - when Columbus sailed to America - his boat was the results of several millennia of development..."
- "The ISS being used to do even more unnecessary human-factors research is a waste of time and money..."
- "I have a friend who has 2 Ph.D., one in nuclear physics and one in philosophy. His general observation..."
- “Shock Therapy” – Not a Cuckoo’s Nest, a Valid Depression Rx
- Innate: Simplot genetically engineered potato gets USDA nod for deregulation
- Sorry, AIDS Deniers, It’s Only a Headline
- Mission Not Yet Accomplished on Vaccines
- Cigarettes, Now With An Organic Health Halo
- Bee Wary of Tales of the ‘Beepocalypse’
- Pollution and weather influence heart attack outcomes?
- Fish oil diet versus gut microbes
- Naps linked to reduced blood pressure and fewer medications
- Why girls are less interested in computer science: Classrooms are too 'geeky'
- Frogs make irrational choices - and what means for understanding animal mating