in 1997 peter dornan was elected spokesman of aleph

1Peter Dornan celebration 18-09-2009


In 1997 Peter Dornan was elected Spokesman of ALEPH

After 7 fantastic years spent exploring the Z peak (around 91.1872 GeV/c2) measuring the number of neutrinos (3), the Z width and asymmetries and predicting the top quark mass, not to mention discovering Bs, b and doing wonderful physics…

We had started exploring higher energies, thanks to the adjunction of superconducting RF cavities in LEP.

LEPII physics had several characteristics: 1. Event numbers counted in thousands and no longer in millions.

Most of it was boson pair production (, Z, WW, ZZ…. and HZ) 2. We began to perform kinematic fits using “jets” as particles

3. ALEPH was already built and running and many important and “experienced” physicists started eying on LHC for the continuation of their careers. It was thus important to retain the best, young and fit!

To this effect PJD reorganized the analysis groups by nominating TWO ‘less experienced ’ conveners for each group. This worked very well in *most* cases. 4. and he asked me to be the “physics coordinator”. THANKS!


Most events were still Zs!


WW pair event


Unclaimed discovery:observation of events with 2 jets, a tau and a massless missing momentum was clearand very clean direct discovery of the tau neutrino!!!


The HIGGS Boson

Arguably the strangest and most exciting beast in the Standard Model.

1. While all the known (observed) elementary particles have spin 1 or ½ the famous boson is afflicted with spin 0. No spinning and no dancing. theorists blame on infinite loops that a) it must be heavy b) there should be supersymmetry … otherwise there will be no light Higgs boson to play with. thereby Supersymmetry is very popular model of physics beyond.

(did I miss something?)

2. The Higgs boson generates considerable eagerness and lust among particle physicists and there was no exception in ALEPH:

3. Two groups worked very hard and VERY competitively at LEPI which the Higgs boson limit was around 60 GeV (Z-> HZ*).

Since the process for Higgs production is e+e- HZ starting around Ecm> Mz+60 + =160 we would be hunting for the Higgs again.

And hunt we did.


New particle searches had always been taken very seriously in ALEPH, and in particular by the Orsay group (and friends) on one hand and the Wisconsin group on the other. We published more than ~200 papers on searches of new particles.

In hindsight it is not a surprise that some unexpected searches turned out to give positive signals.

Among them most famously the ll V analysis at LEP I, and the “four jet events” a.k.a. ‘lapino’ (from Jeanneau (Janot) Lapin, french child’s book character) at LEP 1.5.

These ‘false alarms’ were very trying on the collaboration and the spokesman…

The proponents (O or W) of a new effect were extremely excited, had worked very hard, and had “scandinavia dreams”. (PJD expression). At the same time they were vigoroulsy criticized by the other (W or O) group.

Some talked too much when we wanted them to be quiet, ….and the others would not even talk to us, except in writing.

On searches


The ONLINE analysis

At Xmas 1998 an email storm culminated in a downright abusive message to Peter. (I think the subject had to do with ‘whose analysis would be chosen and on which criterion) this was a looow point.

After letting things settle for a couple months Peter and I decided to let both teams have their analysis published (one was ‘CUTS based’ and one ‘NN based’),

But in exchange we requested the analyses to be run ONLINE: -- all details (cuts, estimators etc…) were to be fixed and locked before data taking resumed in 1999. -- a well defined set of data quality checks were to be processed and shown to the collaboration.-- the analysis would run automatically online and the result would be published on a web page available to the collaboration on a daily basis

This motivating plan settled the internal controversies.

The analyses were extremely sophisticated, being based on the calculation for each event of the probability of either ‘only background’ or “background + Higgs signal” as function of MH would give an event more ‘signal like’ than the one observed. Many variables were used for each Higgs channel and the probabilities were estimated using massive amounts of MonteCarlo and toy MonteCarlos.


1999


The rumors had picked on this:

But the online code also calculated the significanceAnd it was only 1.15 …

1999


2000

The ALEPH Experience, http://aleph.web.cern.ch/aleph/alpub/draft/AlephHistory.pdf


2000 was to be the last year of LEP.

(in 1997 it had been decided in the high spheres of CERN to remove LEP from the LEP/LHC tunnel to install LHC (instead of building LHC on top of LEP as originally foreseen. I have to admit that I did not realize this at the time, and it certainly was not publicized among the LEP community. So the removal would be final).

LEP run was entirely focused on the Higgs boson discovery. Patrick Janot was the LEP coordinator. Given that the maximum accessible beam energy was a function of the beam intensity we had devised a ‘miniramp’ system that would keep increasing the beam energy during the two hours of a LEP fill.

The ONLINE Higgs-hunt web site was being looked at every day with fever….

This was not a BLIND analysis at all … but rather an unbiased EYES WIDE OPEN analysis… with no human control.

We had fixed that no result would be communicated apart from pre-fixed dates: -- LEPC, summer conferences, end of run.

2000


Detector performance

Detector working very well, data quality is high

DAQ efficiency = 95.4%

Background conditions are good

Results based on 92.7 pb-1 @ 203-208 GeV

61.5 pb-1 @ 204.9 GeV 31.2 pb-1 @ 206.7 GeV

All results are PRELIMINARY

Gary Taylor, LEPC 20 July 2000


SM Higgs

exp)GeV/ 3.112( GeV/ 1.111M 22H cc

84 observed c/w 82.7 expected

SM

Excess

Deficit

Cb= 0.02100 pb-1


SM Higgs bbqq candidate


SM Higgs bbqq candidate - vertex region

2H /GeV114M c

GeV7.206S


As Gary was speaking a second event showed up and sent the no-signal probability CLb

down to a few 10-3

If someone had plotted the time development of CLb it would have looked like this:

1

10-1

10-2

10-3

10-4

10-5

10-6

CLb

Heavily dominated by the appearance of very significant qqbb events. On my return from vacation August 18 2000 I found CLb at 7 10-6 or so… i.e. more than 4 sigmas. …emotions!

Integrated luminosity

LEPC

LEPC End of LEP


LEPC Sept 5, 2000 D. SchlatterLEPC Sept 5, 2000 D. Schlatter


Online Higgs AnalysesTwo independent streams: NN(19 variables) and Cuts

mrecon=m12+m34-91.2

Ent

ries

/(4

GeV

/c2 )


CL for Background Hypothesis, Cb

NN analyses CUT analyses

Min.: ~ 6 10-5 @ 115.5 GeV

Four Jets alone: min(1-Cb) = 3 10-5 @ 114.5 GeV all others: min(1-Cb) = 0.03


Significance of Excess

NN CUT

3.9 @ 115.5

3.8 @ 115.5

The peak is dominated by 4 jet candidates!


SM Higgs: Likelihood Ratio

bkg onlymedian exp.

observeds+b hypo.

Significance s+b hypo.

NN

Min.@ 113.5

LEPC Sept 5, 2000 D. SchlatterLEPC Sept 5, 2000 D. Schlatter


The rest of the story is well known:

The other LEP experiments also had candidates, but of lesser significance. Some were rejected after the fact (reconstruction or visual inspection). The four LEP experiments (NB spokesperson’s meeting was intitiated by PJD in 1999) agreed, requested and obtained two run extensions in 2000,

But the significance of the effect kept decreasing slowly (as it should, really) and the combined LEP result is less than 2 sigmas.

In Fine the ALEPH excess never really went away; the final publication including all data still describes a positive search with a final significance of more than 3 sigmafor a Higgs boson of ~115 GeV/c2.

The SPC (of which PJD became member in 2003) had special meetings arranged to discuss the matter but it was felt that with LHC in 2005, the significance was not strong enough to delay the CERN flagship project. CERN decided to close LEP operations definitively.

The Higgs flag has been taken up by Tevatron but it will take a long time to know whether our observation was the first harbinger of the Higgs Boson. 115 GeV is still the likeliest place for it to be found....


According to these early sensitivity studies, mH< 130 should be nearly Excluded by now

No VTX upgrade+very difficult region

Will require more analysis time!


Situation will be similar at LHC: low mass Higgs is very difficult. In particular 115 GeV Higgs (LEP ‘hint’/limit) will take a very long time to confirm/exclude

115 GeV/c2


From Heavy Flavours to the lightest Flavours

PJD was always a man of flavour. Very soon after neutrino flavour changes were established by SuperK in 1998,it became clear that there was a new and rich domain of Physics leading eventuallyto leptonic CP violation and, via leptogenesis, a possible solution to the matter-antimatter asymmetry in the universe.

Peter as director of Imperial and influent member of the UK particle physics community gave great support to the development of -- neutrino factory studies in UK and in particular the approval and funding of MICE-- was the first MICE collaboration board chair and wrote the MICE collaboration charter -- Supported the International Scoping study, which he chaired He is now member of the CERN SPC Neutrino panel who should give recommendations on CERN role in the European strategy for (accelerator based) neutrino physics


Incoming muon beam

VariableDiffuser

Beam PIDTOF 0, TOF 1

Cherenkovs

Trackers 1 & 2

Liquid Hydrogen absorbers 1,2,3

Downstreamparticle ID: TOF 2, KL

SW Calorimeter

RF cavities RF power

Spectrometer solenoid 1

Spectrometer solenoid 2

Coupling Coils 1&2

Focus coils

Muon Ionization Cooling Eexperiment (MICE) Collaboration


Overall comparisons from ISS

sign m2

CP phase

More range = more precision

NuFACT does it all…(+ univ. test etc…)but when can it do it and at what cost?


Final quote:

As everyone who has organized a large […] meeting knows, it is not the quality of the talks,the seating or audiovisuals of the lecture halls thateveryone remembers. It is the dinner.

PJD in ‘The ALEPH experience’

in 1997 peter dornan was elected spokesman of aleph

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