Okamura Yusuke Shibata lab.

1. Physics Colloquium July 7th, 2008 ― √ s “Experimental Observation of Isolated Large Transverse Energy Electrons with Associated Missing Energy at = 540 GeV” G. Arnison et al., UA1 Collaboration Phys. Lett. 122B (1983) 103 Contents: 1.Introduction 2. Experimental Method 3. Analysis 4. Summary Okamura Yusuke Shibata lab.

2. 1. Introduction p n － － ‐ ‐ ν ν ν ν e e Weak Interaction e e e e Fermi made a theory of β-decay in 1930's . The interaction was a contact interaction . ( no intermediate particle ) β-decay Fermi’s Model Weinberg-Salam’s Model Weinberg and Salam made a theory for ElectroWeak Interaction in 1960's . The ElectroWeak Interaction is a combined framework for Electromagnetic Interaction and Weak Interaction . β-decay p n ‐ charged current The intermediate particles of Weak Interaction are W and Z .The mass of W and Z are large . The range of interaction is short . W ± p p neutral current Z ± Experimental discovery of W and Z is important to establish ElectroWeak Theory .

3. 2. Experimental Method E We look for the following event ； p - ± p + p → W + X ± (－) - ν e + ν e － u p - - collision u d - Accelerator p u u p d CERN SPS Proton-Antiproton Collider + W : proton and antiproton collisions at = 540 GeV ― √ s two-body decay p + e E = 270 GeV = 270 GeV － p

4. Detector The name of experimental group is UA1 ① In cross section ② ◎ Hadronic Calorimeter 　 ・ energymeasurement of hadrons The UA1 detector 25° ③ ± 155° ④ beam axis ⑤ ◎ Electromagnetic (EM) Calorimeter ( consists of two parts ) 　 ・ energy measurement of e and 0° ⑥ beam crossing point ⑦ ◎ Drift Chamber ( in magnetic field ) 　 ・ measurement of charged tracks and momenta

5. ± (－) Event Selections ± Search for W　 → e + ν ± This experiment was carried in a 30-day period . (－) ﾆｭｰﾄﾘﾉはこうやって測定した - - ◎Expected number of p-p collisionin this period 5 ◎Recorded events ・ Electron was measured with drift chamber and electromagnetic calorimeter. ・ Neutrino was not measured . Momentum of neutrino wasdetermined by momentum imbalance using the electromagnetic calorimeter andhadronic calorimeter. 9 ：10 5 ：9.75×10 ± e conditions: 　・large transverse energy of electron 　・large missing transverse energy(neutrino) 　・no hadron jet (－) ν 1行開ける ：5events ± ◎Candidateevents of W Electron

6. 3. Analysis Detailed Investigation of the electron-neutrino events 5 candidates events are carefully investigated . Following figures are data ofone event . electromagnetic calorimeter electron track E max 23.7 GeV T charged tracks in the detector beam axis φ 270° Energy depositions in the calorimeters θ φ angle +1.4 particle track ・φ is angle of spherical coordinate beam crossing point －90° Pseudo-rapidity η －1.4 hadronic calorimeter E max 0.5 GeV T ・Pseudo-rapidity η is a function of θ Φ angle Pseudo-rapidity θ= 28° ～ 90 ～ 152 ( η ＝ -1.4 ～ 0 ～ 1.4 ) 270° φ angle +1.4 Pseudo-rapidity η －1.4 －90° Pseudo-rapidityη is the function of θ, like the following table .

7. Momentum balance between electron and neutrino This figure shows the correlation between transverse electron energy and the missing transverse energy . E E E E These two energies are proportional. T T T T ← 40 GeV ± This result shows two-body decay of W . Missing transverse energy Events with large transverse energy Events with small transverse energy ← 20 40 GeV ± ± 20 e e ↓ ↓ beam axis 4 2 0 ＃ of events 2 (－) (－) 1 ＃ of events ν ν beam crossing point 0 Transverse electron energy m is determined as by correcting for the transverse motion of W . W m = 81 ±5 GeV/c 2 W ±

8. 4. Summary ± - ・W and Z are intermediate particles of weak interaction . ・ pand p collision at high center-of-mass energy can produce W . ・ Experiment was carried out by UA1 collaboration at CERN-SPS . ・ W decays to electron and neutrino (missing energy) back-to-back . ・ 5 events are consistent with two-body decay of W . ・ m ＝ 81 ±5 GeV/c ・ It agrees with the Weinberg-Salam model ± － ± ± 2 W Z was also discovered by UA1 collaboration in 1983 . The physics Nobel prize 1984 was awarded to this discovery .

10. Energy flow vector

11. Energy flow vector ・Neglecting particle masses ・With an ideal calorimeter response ・With ideal solid-angle coverage ⇒　∑ΔE = 0

12. Event Selections 9 9 10 Expected number of p-p collisions in a 30-day period： events trigger conditions and other conditions for good data selection ： Requirement of Three trigger conditions 5 9.75 × 10 ・with large transverse energy ・with undetected muon tracks 5 1.4 × 10 the electron trigger 28000 ＞15 GeV of transverse energy 2125 with a good quality , vertex-associated charged track 1106 The fast track must hit a pair of adjacent EM calorimeter modules 276 p of other tracks entering the same modules ≧ 2 GeV/c . T 167 TheΦ information agree with the impact of the track . 72 The energy deposition in the hadronic calorimeters ≦ 600 MeV 39 The energy match the momentum with no jets activity 5 events

13. Particle Identification ① ◎ e Identification 　・ By their charged tracks 　 ・ By the lack of penetrationin the hadron calorimeter ② ③ ◎ ν Identification 　 ・ Only by transverse energy imbalance ( missing transverse energy ) ④ ⇒・ Now , we define an energy flow vector ΔE , which is 0 in ideal conditions . ⇒ ・ By using this technique , we detect the missing transverse energy , namely ν . ⑤ Events without jets Events with jets Transverse to electron Missing transverse energy Missing transverse energy Parallel to electron Electron direction Parallel to electron Missing transverse energy normal to electron Electron transverse energy

14. Background evaluations ① ② Backgrounds to the electron signature for no jets events (1) a high-p charged pion ( hadron ) misidentified as an electron or overlapping with π 　　　　　　⇒ negligible (2) high-p π , η or γconverted to an e e pair with one leg missed 　　　　　　⇒ negligible (3) heavy quark associated production followed by pathological fragmentation and decay configuration 　　　　　　⇒ negligible ③ ④

15. 3. Analysis Search for electron candidates We require conditions ； ( i ) three conditions on the track forisolated tracks ( 2125 events → 167 events ) ( ii ) two conditions to enhance its electromagnetic nature ( 167 events → 39 events ) ⇒ 　(1) with no jet activity ( 5 events ) (2) with a jet opposite to the track (11 events ) (3) with two jets or clear e e conversion pairs ( 23 events ) + ‐ Now , we find that , ・events with a jet have no missing energy ・events with no jets show missing energy ( Fig.2,3 ) Fig.3 Fig.2

16. Search for events with energetic neutrinos ① Events without jets Taking 2125 events again , we operate conditions. ② ( i ) two conditions of a high missing transverse energyand the candidate track not part of a jet ③ ( 2125 events → 70 events ) ④ ( ii ) removing undetectable events ⑤ ( 70 events → 31 events ) ⑥ ⇒　　(1) E ＞ 0.01 E ( 21 events ) (2) E ＜ 0.01 E ( 10 events ) ⑦ ⑧ ( iii ) with no high-p track in the small-θcone Events with jets ( 31 events → 18 events ) ⇒　　(1) E ≠ 0 ( 10 events ) (2) E =0 (8 events ) ⇒　　(1) without jet ( 7 events ) (2) with jet opposite to the track (11 events ) These events with jet are likely to be hadrons , and without jet electrons . ( Fig.4 ) These jetless events include previous 5 events. ( electron candidates) Fig.4

17. m (e,ν) = (|p

18. 1. Introduction Discovery of W ± － ‐ ν e e n p ① W ( Intermediate Vector Bosons of weak interaction ) 　　 ： cf.) Z also of weak interaction , of electromagnetic interaction , g of strong interaction ・ mediating the β-decay ( Fig.1 ) ・ of very large masses about 80 GeV － W ± ② - ν e ③ u - ④ Fig.1 β-decay - collision u d - p u u p ⑤ d + W ◎ We look for the following event ； two-body decay - ± p + p → W + X ± (－) e + ν + e