A Quantum Diaries Survivor

Congratulations to D0, which produced a conference note for ICHEP describing their observation of a Z–>bb signal in D0 Run II data. I was quite happy to find the note today while browsing through D0’s web site. You can get a pdf version of the preliminary note in http://www-d0.fnal.gov/Run2Physics/WWW/results/prelim/HIGGS/H22/H22.pdf .

The D0 signal is extracted from events with two jets, both tagged, back-to-back in azimuth, with a methodology already used ten years ago by yours truly. Indeed, their note does contain a reference to my “First observation” paper (http://xxx.lanl.gov/PS_cache/hep-ex/pdf/9806/9806022.pdf), but the text does not point to it, curiously. Anyway, kudos to D0, whose 1200+-250 event signal is shown below, background-subtracted. 

After congratulations, a bit of self-promotion. Of course it makes me happy to see that the signal I have found in 1998 -and the means to extract it, which have basically stayed unchanged- is now becoming a standard. The signal is becoming not only an established “standard candle” with which to calibrate the jet energy scale from b-quark jets, but also a testing ground of algorithms aimed at reducing the b-jet energy resolution, as hinted by the D0 paper itself.

Maybe a bit of history (which is, as is well known, always written by the winners) helps here, for those of you who have read this deep in the post.

When I undertook my search for Z->bb decays as a grad student in 1996, people were discouraging me - the signal was too small in the hadronic environment. But when two years later I blessed my result (a 90-event peak), and produced a conference note for ICHEP 98 in Vancouver, it became clear that the signal could actually become useful with larger statistics. A group of physicists from Chicago (Shochet, Culbertson) and Pisa (Leone, Bigongiari, Menzione) designed a dedicated trigger using primitives from the newly designed Silicon Vertex Tracker, and we got ready for Run II data.

At the start of Run II, I first believed I could find evidence for a second time with the very first few inverse picobarns of data collected by CDF, but it soon became clear that things were going to be tough - the trigger was very hard to understand both in rate and -what’s worse- in the biases it produced on the jet-jet mass spectrum where the tiny signal should be seen. 

A group of interested researchers in CDF (from Harvard, Padova, Berkeley, Chicago, Geneva) was formed and led by myself in 2003 to investigate and search for the signal. The group was tough to manage, because people were interested but not overly willing to work overtime on it… And pieces started to drop off soon. We made slow progress, and it took us three years to get to a first solid result, the one you see below: a 3300-event signal of Z decays in 330 pb-1 of data, blessed in February last year by my collaboration.

Now Julien is finalizing our analysis of 700 pb-1 of data, containing about 7000 signal events, and with which we plan to measure the b-jet energy scale to better than 2%. You will hear about it very soon here.

Today’s electronic edition of the italian newspaper La Repubblica (www.repubblica.it) has a collection of astonishing pictures of vegetable pornography - that is, plants mimicking sexual parts of humans or even sexual acts altogether.

I found some of the pictures really intriguing. Here is a sample:

I have been in the CDF experiment, an O(500) physicists endeavour at Fermilab, for over fourteen years now. However, it was only a couple of years ago that I was brought to realize, by my friend Paolo Giromini, that ours is practically a “whites only” community.

Quite strange to have spent so much time at physics meetings, in trailer corridors, in detector enclosures, control room, assembly hall… and failed to notice the almost perfect absence of blacks! Sure, we do have a strong asian component in CDF, several hispanics, and an unreasonable number of italians … But, as far as I remember, we sport probably not more than two or three niggers african americans; one of them, my friend Ayana Holloway, graduated not long ago at Harvard.

I was reminded of this odd fact while erratically reading some of Michael Moore’s “Stupid White Men” the other day. In a hilarious chapter that begins with a description of his fear of male whites - who, contrarily to popular beliefs, are more dangerous to Michael than blacks (he has a list of all the evil he received in his life, all perpetrated by whites) - he takes on a discussion of the way a racist America who stained itself with slavery a century ago grew smarter, and apparently allowed integration, while making the separation subtler but not a bit less stark.

( By the way, I could not restrain from laughing when Moore explains the move to the suburbs of the white dominant class (”of course you can have your kids come and study in our schools - we were moving out anyway“)… But I do not wish to marry Michael Moore’s opinions as a block here - better stated, I do not wish to take the pains to defend them. Let’s go back to CDF.)

So is the observation of <3 blacks in a 500 people community a signal that something is going on ? Of course. As a scientist, let me take it to the statistics board. 13.4% of the US population is black. 50% of the CDF members are US citizens. That makes for an expectation of 33 blacks in CDF. If I see two, is that a statistical fluke ? Nope.

The difference between 33 expected and two observed blacks has a ridiculously low probability of being due to a fluctuation. So the cause is systematic. Given the simple assumptions, here are possible causes of systematics:

• Wrong counting - I might have counted wrongly the number of blacks
• Wrong input data - 13.4% might be slightly off (took it from the web with a 30-second search), 50% is probably off too but not too much so, 500 is an approximate figure
• Blacks have fewer chances of ending up as members of CDF than whites - maybe they do not like Physics, maybe they are banned from CDF, maybe they fail to qualify, maybe they do not populate 13.4% of the population of researchers, scholars, and students of top notch Universities participating in HEP. 

I may for sure have met not all of the members of CDF, or forgot some, so the counting could indeed be wrong. But alas, I think the main cause of the observed deficit is the third listed above.

Of course. To many of us, this is kicking down an open door. Now, I do not want to open a debate here on the causes. Or maybe I do.  Do blacks avoid HEP ? Do top notch Universities avoid blacks ? Do they fail to qualify ? It is not individual Universities who are at fault, I think. It is the whole system. By selecting students - and ultimately, personnel - on the basis of census, the private school system maintains a cultural apartheid.

Now, there is more to it, I think. Because if the figures are the ones above, one could take them bottoms up and compute what is the average fraction of black physics researchers in the US from the 2/250 ratio: 0.8% ? Sounds too low. If it is too low, it means that there are additional systematics causes that work together to make CDF a “whites only” experiment… After all, I think D0, our brother experiment at the Tevatron, has (very roughly) the same kind of US/foreign institution mixture, has a similar number of members, and has definitely more than two african americans in it.

Any hints ? Are brazilians in D0 which I mistook for african americans the cause ? Or the slightly less than five-starred Universities participating in D0 ?