The experimental discovery of charm quarks

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1 The experimental discovery of charm quarks Jacek Otwinowski GSI-armstadt

2 Content: Charm before 1974 Theory predictions imuon measurements by L. Lederman et al. The R - ratio November Revolution J/ψ discovery J resonance at AGS/BNL (S. Ting et al.) psion family at SPEAR/SLAC (B. Richter et al.) J/ψ properties From J/ψ to charm Summary 08/11/2007 TU armstadt, Jacek Otwinowski 2

3 Theory predictions Year 1974 The first speculations about charm J.. Bjorken and S.L. Glashow, Phys. Lett. 11 (1964) 255 Massive lepton-pair production in h-h collisions S.. rell and T-M Yan, Phys. Rev. Lett. 25 (1970) 316 Weak interactions with Lepton-Hadron symmetry S.L. Glashow, J. Iliopoulos and L. Maiani, Phys. Rev. (1970) 1285 (GIM model) In April 1974 S.L. Glashow said There are just three possibilities: 1. Charm is not found and I eat my hat 2. Charm is found by hadron spectroscopy, and we celebrate 3. Charm is found by outlanders, and you eat your hats. (International Conference on Experimental Meson Spectroscopy, 2-27 April 1974 Boston) source: Fermilab-Conf97/432-E (story by John Yon for the E288 collaboration) 08/11/2007 TU armstadt, Jacek Otwinowski 3

4 imuon measurements at AGS/BNL Fixed target experiment (no B field!): (J.H. Christenson et al. Phys. Rev. 8 (1973) 2016) 1 m Concrete Steal ense U target (20 seg.) Pion/Kaon absorbtion µ 1 Steal/Concrete Absorbers p > 6 GeV/c p t > 450 MeV/c Steal θ 12 µ 2 Angle hodoscopes µ angle measurement Momentum hodoscopes Initial p µ measurement imuon signal = difference between in-time and delayed coincidences! p+u µ + µ - + X T p = 22, 25, 28.5, 29.5 GeV M = 2 p p2[1 cos 12] µµ 1 θ 08/11/2007 TU armstadt, Jacek Otwinowski 4

5 imuon measurements at AGS/BNL Phys. Rev. 8 (1973) nb Muon pairs with effective masses 1 GeV/c 2 and 6.5 GeV/c 2 have been observed in the collisions of 30-GeV protons with a uranium target. The production cross section was seen to vary smoothly with mass exhibiting no resonant structure.?? imuon spectra σ M /M ~25% at 3 GeV/c 2 4% of in-time data sample (from 2% at 1.5 GeV/c 2 to 40% at 5 GeV/c 2 ) small signal-to-noise ratio data sensitive to subtraction procedure p+u µ + µ - + X T p = 29.5 GeV 1 pb A year later S.Ting group completed e+e- pair spectrometer at AGS/BNL 08/11/2007 TU armstadt, Jacek Otwinowski 5

6 The R ratio Quark model: The R ratio (July 1974) R + σ ( e e hadrons) + + σ ( e e µ µ ) = for u,d,s quarks R=2! = 3 q 2 Q q Measured R grows with energy! is quark model OK? a new quark? irect motivation for B. Richter to measure the R ratio at SPEAR/SLAC 08/11/2007 TU armstadt, Jacek Otwinowski 6

7 November Revolution - J/ψ discovery J.J. Auber et al. PRL 33 (1974) 1404 BNL J.J. Augustin et al. PRL 33 (1974) 1406 SLAC e + e - hadrons p+be e + e - + X T p = 30 GeV e + e - e + e - M J =3.1 GeV σ M 20 MeV e + e - µ - µ +, π + π -, K + K - Particle ata Book (2007): M J/ψ = ±0.011 MeV Γ J/ψ = 93.4±2.1 kev M ψ =3.1±0.003 GeV FWHM 1.3 MeV 08/11/2007 TU armstadt, Jacek Otwinowski 7

8 J resonance at BNL Two arms e + e - spectrometer S. Ting - Nobel Lecture 1976 e- Tracking M 0, M 1, M 2 dipol magnets A 0, A, B, C MWPCs σ M 20 MeV C b B PI detectors a, b hodoscopes (tof) S el. mag. shower counters C b, C 0, C e Ĉerenkov counters hadron pair rejection factor >>10 8 p+be e + e - + X T p = 30 GeV J particle ecoupled measurement of momentum and angles. e+ M 2 2 = me + me+ + 2 [ Ee Ee+ pe pe+ cosθe e + ] 08/11/2007 TU armstadt, Jacek Otwinowski 8

9 SPEAR the e + e - storage ring at SLAC The SPEAR parameters SLAC linac min. filling time 2 h data taking GeV c.m. e+e- energy collision volume (σ x x σ y x σ z = 0.1 x 0.01 x 5 cm 3 ) e- e+ 08/11/2007 TU armstadt, Jacek Otwinowski 9

10 MARK I magnetic detector at SPEAR/SLAC MARK I exploded view The psion family was discovered at SPEAR by using MARK I detector! MARK I beam s eye view e Tracking Cylindrical magnet (5 KG / 20 m 3 ) 16 cylindrical wire chambers PI detectors Trigger chambers (tof) Shower counters (e identification) Muon wire chambers µ R.F. Schwitters et al., Ann. Rev. Nucl. Sci. 26 (1976) 89 h 08/11/2007 TU armstadt, Jacek Otwinowski 10

11 ψ resonance at SPEAR/SLAC ψ production in e+e- collisions e- e+ γ* ψ h,µ,e ψ intermediate qq (J PC =1 -- ) hadron state decaying into leptons and hadrons. σ σ de i Γ ( Γ i M Breit - Wigner ψ i e ) - partial, Γ ψ 2 2π (2 J + 1) = M, J 2 ψ - mass, widths cross total ΓiΓ Γ to section the width i(e) Fit results (MARK I data): M ψ = 3.095±0.004 GeV Γ ψ = 69±13 kev (long lived resonance!) (A.M. Boyarski et al., Phys. Rev. Lett. 34 (1975) 1357) PG(2007): M J/ψ = ±0.011 MeV Γ J/ψ = 93.4±2.1 kev ψ e and for e channels spin + e - of ψ ψ i B. Richter- Nobel Lecture 1976 Γ h Γ µ Γ e B-W cross section + beam spread (Gauss) + radiative effects 08/11/2007 TU armstadt, Jacek Otwinowski 11

12 ψ resonance at SPEAR/SLAC (10 days after ψ) MARK I (SPEAR) event display B. Richter- Nobel Lecture 1976 ψ ψ + π + π -, followed by ψ e+e- At MARK I: M ψ =3.695 ± GeV FWHM < 2.7 GeV (G.S. Abrams et al., Phys. Rev. Lett. 33 (1974) 1453) Fit results (MARK I data) M ψ =3.684 ± GeV Γ ψ = 225±56 kev (V. Lüth et al., Phys. Rev. Lett. 35 (1975) 1124) pattern = name! 08/11/2007 TU armstadt, Jacek Otwinowski 12

13 Radiative transitions ψ or ψ γ + intermediate state Search methods: B. Richter- Nobel Lecture 1976 oris (ESY) SPEAR (SLAC) Energy levels remainds positronium atom! ψ is a bound state of cc ( charmonium ) 08/11/2007 TU armstadt, Jacek Otwinowski 13

14 The R-ratio measurement at SPEAR/SLAC B. Richter- Nobel Lecture 1976 The R ratio (E c.m. = GeV) ψ, ψ reconance peaks removed! ~2.5 ~5 R + σ ( e e hadrons) + + σ ( e e µ µ ) = = 3 q 2 Q q for u,d,s,c quarks R=10/3 Not enough?! (recent data: M.R. Whalley, J. Phys. G: Nucl. Part. Phys. 29 (2003) A1-A133) A new members of psion family The broad ψ-like states at 3.95, 4.1, 4.4 GeV (much broader than ψ(3.684)): mass limit for the lightest charm particle M ψ(3.684) /2 < m < M ψ(3.950) /2 08/11/2007 TU armstadt, Jacek Otwinowski 14

15 J/ψ properties (1976) Heavy and long lived resonance M = 3.095±0.004 GeV, Γ J/ψ J/ψ = 69±13 kev irect production in e+e- collisions J PC =1 -- (A.M. Boyarski et al., Phys. Rev. Lett. 34 (1975) 1357) Hadronic decays: even number of pions (consistent with 2nd order electromagnetic decays) odd numbers of pions (enhanced) G parity conservation (J/ψ is a hadron) (π + π - π 0, pp, ΛΛ) I=0 Radiative transitions ( positronium like spectrum ) cc bound state ( charmonium ) The R ratio > 2 evidence for a new quark Enough to get the Nobel Prize! 08/11/2007 TU armstadt, Jacek Otwinowski 15

16 S. Ting and B. Richter and S.L. Glashow were celebrating! The Nobel Prize in Physics 1976 for their pioneering work in the discovery of a heavy elementary particle of a new kind Burton Richter Samuel Chao Chung Ting 08/11/2007 TU armstadt, Jacek Otwinowski 16

17 iscovery of charmed neutral mesons at SPEAR/SLAC e e + X at E c.m. = 3.9, 4.6 GeV G. Goldhaber et al., Phys. Rev. Lett. 37(1976) 265 mesons decays: 0 + K π 0 + K π K π π π K π π π At MARK I: M = ± 15 MeV Γ < 40 MeV PG(2007): 0 ( cu), 0 ( cu) M = 1864 ± 0.5 MeV τ = (410.3 ± 1.5) s 08/11/2007 TU armstadt, Jacek Otwinowski 17

18 iscovery of charmed charged mesons at SPEAR/SLAC + + e e + X at E c.m. = 4.03 GeV mesons decays: I. Peruzzi et al., Phys. Rev. Lett. 37(1976) 569 m K π ± π ± + K K + + π π π π ecay modes : not seen + m K + π π m * + 0 π + At MARK I: M = ± 15 MeV Γ < 40 MeV m K π + π PG(2007): + ( cd), ( cd ) M = ± 0.5 MeV τ = (1040 ± 7) s 08/11/2007 TU armstadt, Jacek Otwinowski 18

19 iscovery of charmed *+ mesons at SPEAR/SLAC + * + e e + X at E c.m. = 4.03 GeV mesons decays: * + K π π π G. J. Feldman et al., Phys. Rev. Lett. 37(1977) m K π ± π ± At MARK I: M = 2010 ± 20 MeV Γ < 2 MeV PG(2007): * + ( cd), ( cd ) M = 2010 ± 0.4 MeV M M * * (2010) (2010) + + * M M + 0 = ± 0.10 MeV = ± 0.10 MeV m K π + π 08/11/2007 TU armstadt, Jacek Otwinowski 19

20 Summary The discovery of charm was a pivotal event for particle physics. It established the reality of the quark structure of matter and provided enormous evidence for the SM. SU(4) F - multiplets PG(2007): c + 1 P I( J ) = 0 2 Mass m = 1.15 to1.35 GeV 2 Charge q = e 3 Charm = /11/2007 TU armstadt, Jacek Otwinowski 20

21 Bibliography 1. B. Richter Nobel Lecture S. C.C. Ting - Nobel Lecture R.F. Schwitters and K. Strauch, Ann. Rev. Nucl. Sci. 26 (1976) P. Braun-Munzinger Lectures, TU armstadt J.. Bjorken and S.L. Glashow, Phys. Lett. 11 (1964) S.. rell and T-M Yan, Phys. Rev. Lett. 25 (1970) S.L. Glashow, J. Iliopoulos and L. Maiani, Phys. Rev. (1970) J.H. Christenson et al. Phys. Rev. 8 (1973) J.J. Auber et al. PRL 33 (1974) J.J. Augustin et al. PRL 33 (1974) A.M. Boyarski et al., Phys. Rev. Lett. 34 (1975) G.S. Abrams et al., Phys. Rev. Lett. 33 (1974) V. Lüth et al., Phys. Rev. Lett. 35 (1975) M.R. Whalley, J. Phys. G: Nucl. Part. Phys. 29 (2003) A1-A G. Goldhaber et al., Phys. Rev. Lett. 37(1976) I. Peruzzi et al., Phys. Rev. Lett. 37(1976) G. J. Feldman et al., Phys. Rev. Lett. 37(1977) 08/11/2007 TU armstadt, Jacek Otwinowski 21

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