Presentation on theme: "THE NOVEMBER 1974 REVOLUTION THE J/ DISCOVERY VIEWED FROM FRASCATI Giorgio Bellettini A personal recollection of that historical event LNF, May 21 st,"— Presentation transcript:
THE NOVEMBER 1974 REVOLUTION THE J/ DISCOVERY VIEWED FROM FRASCATI Giorgio Bellettini A personal recollection of that historical event LNF, May 21 st, 2004
ADONE The design top energy of ADONE was 3.0 GeV. Operation at high energy was typically around 2.8 GeV.
The “Boson” detector The “Boson” detector was covered with a cosmic muon shield.
The detector A representative ADONE detector: two telescopes of trigger counters and tracking detectors, with limited solid angle coverage.
Picture of the BCF detector The Bologna- CERN-Frascati detector featured two telescopes at large angle.
A telephone call received on November 11 th, 1974 From an excited Sau Lan Wu calling from BNL: “We have found a new particle!” “What is so special about it?” “It is very heavy and very narrow! It decays into e + e – ” “How heavy?” “About 3.1 GeV.” In the conversation it was soon understood that the Adone energy could possibly be stretched up to that value.
7 days from hearing to publishing Telephone call by S.L.Wu: November 11 th Resonance found at ADONE: November 13 th Data collected, paper written: November 17 th Paper-by-phone: night of November 17 th Paper received by P.R.L: November 18 th. The amazing spelling mistakes in the PRL author list.
The Frascati early result C.Bacci et al., Phys.Rev.Lett. 33, 1408, 1974 This plot is from the group. The MEA group and the B- Bbar groups reported in the PRL paper a similar evidence.
The detector The detector employed telescopes of optical spark chambers and of wire chambers interleaved with absorber plates, set orthogonal to the beams.
Bhabha scattering In the ADONE energy range Bhabha scattering depended on energy precisely as expected in QED. e + e – e + e – BCF e + e – e + e – e + e – e + e –
e + e – + – / e + e – e + e – Also e + e – + – depended on energy as expected in QED. e + e – + – BCF + – /e + e – BCF
e + e - into hadrons Naïve expectation in the quark model: R= (e + e – hadrons)/ (e + e – + – ) = 3 Q q 2 = 2 for u,d,s quarks
R= h / around 3 GeV before the discovery However, annihilation into hadrons was messy in the Adone energy range. In summer 1974 the MARK1 detector at the SPEAR e + e – collider had started a closer inspection of the energy region above 3 GeV, where the annihilation cross section into hadrons was showing a mysterious rise.
The -pair spectrum of J.H.Christenson et al. Phys RevD8,2016,1973 An interesting anomaly in the muon pair spectrum observed in a rudimentary experiment at BNL was around since over one year.
J.H.Christenson et al.after background subtraction After subtracting the large background (mostly accidentals).
The high resolution e-pair spectrometer at BNL S.C.C. Ting and collaborators understood that that spectrum deserved a much closer look, and built a high resolution electron-pair spectrometer at BNL.
The rumor was around since a while What I learned later (too late!) A peak in the pair mass spectrum was evident in the BNL experiment since summer 1974. A number of BNL physicists not belonging to the group had heard about it (but had not seen the data). The information was given during the week of October 13 to a number of physicists outside the group, who were requested to keep silent. The information was not made public in the hope to be able to understand first what the new particle was. On October 22 nd Melvin Schwartz, a distinguished Stanford physicist, had heard about the peak and went to BNL to interrogate the group but did not succeed in getting a confirmation.
Getting public eventually On November 11 th the leader of the BNL group, Sam Ting, was at SLAC and the discovery by his group and by the MARK1 group led by Burton Richter on the SPEAR e + e – collider was jointly announced.
Discovery of the J particle The J discovery spectrum was presented publicly on November 11, 1974.
SPEAR SPEAR could operate from ~2.5 to ~8.0 GeV.
The Mark1 detector MARK1 was the only experiment on SPEAR.
Discovery of the particle The new resonance could be clearly seen also in the leptonic channels.
Mark1 energy scan Soon the ` was also discovered.
Early charmonium spectrum Later more hidden and open charm states could be found.
FINAL REMARK My years at Frascati as the lab Director were years of great social turbulence. Pure research was under serious attack. In 1976 an INFN sector was split and made independent of the CNEN (now ENEA) lab. Out of the 820 employees of the original LNF, only 82 moved to INFN. I suspect the the concern and confusion created by those criticisms and attacks, ending with that traumatic split have greatly contributed to make us overlook a major scientific discovery which was at hand.
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