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W and Z Bosons and the 3 Neutrino Families
Sedat Altinpinar
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Theorie/Prediction of Neutrinos
-Prediction of “a“ Neutrino Pauli, ß-decay
eepn
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Experimental Discovery of the Neutrinos
Cross Section for Neutrino reactions
• Cowan and Reines 1959
24310 cm
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Discovery of the µ Neutrino
• Until the end of the '50s : Only one Generation of Neutrinos
• Bruno Pontecorvo (1913-1993): Why doesn't annihilate the Neutrino and Antineutrino which at the µ- Decay arise?
• The solution could be that the Neutrinos are different
e
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The first HE Neutrino Experiment
• Melvin Schwartz (*1932) was researching about Neutrinos• He was interested in the ratio
e
e
For the case, there is only one type of Neutrinos,the ratio should be 10-4
• This value could already at that time be excluded (< 10-8 )
• Schwartz had the same idea like Pontecorvo
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Spark Chamber
• The neutrinos react with the Neutrons of the Aluminium
• The arrised charged particles leave tracks of ionised Neons.
• A Scintillator is triggering the High Voltage
• The tracks are visible as a row of sparks
)(
epn
pn
The Brookhaven Experiment at 1960
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Distinction between e- und µ-
CharakteristicTrack
e- loose more energy
µ- are radiating less due to theirhigher mass
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Result
• 1014 Neutrinos traversed the detector
• 29 Neutrino reactions were measured
• All produced are Muons
•If there would exist only one generation of Neutrinos there should arrise in equal amount electrons and muons
e
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Discovery of the Tau Neutrino
• Discovery of the Tau Lepton 1975
• Postulation of the Tau Neutrino
• Discovery of the Tau Neutrino in 2000 with DONUT (Direct Observation of NU Tau) at Fermilab
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Why is it so difficult to discover the ?
• Neutrinos appear through their charged Lepton partner
• Lifetime of τ is 300 fs
• 's are rare: From 1013 Neutrinos only 103 have reacted, 4 from them were
pn
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Results from DONUT
• Es wurden 4 Tau Neutrinos nachgewiesen!
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Prediction of W Z Bosons
Glashow-Weinberg-Salam Modell: Electroweak force is mediated by the
W+, W-, Z0 bosons.
Prediction of mass
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Discovery at CERN
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W+ /W- /Z0: Where and how shall one search?
Measurements with charged and neutral currents (i.e. Muon decay, Neutrino scattering) ergeben Abschätzungen für die Massen für das W± bzw. Z0:
MW ≈ 80GeV und MZ ≈ 90GeV
In particle collisions it can be produced new particles up to a mass of M =
Production in e+ e- - collisions? (LEP in Planning)
but: e+ + e- → Z0 → ... ✔aber: e+ + e- → W+ + W- → ... ✘
(Schwerpunktsenergie von ≈ 160GeV notwendig)
s
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Am CERN bereits vorhanden: Protonenbeschleuniger SPS mit fixem Target
Protonen werden dort auf eine Energie von EP ≈ 300 GeV beschleunigt ≈ 25 GeV
Neue Idee: Protonen und Antiprotonen aufeinander schießenVorteile:
• Antiquark als Valenzquark im Antiproton vorhanden• Nur ein Beschleunigungsring nötig
Problem: Woher Antiprotonen?
Erzeugung durch Beschuss eines Targets mit Protonen:sehr ineffizient! ( N anti-P ≈ 10-6 ∙ N P)
s
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Daher: Notwendigkeit der Speicherung der Antiprotonen um sie zu sammeln
neues Problem: Antiprotonen sind „heiß“ (haben große Impulsverteilung)
Idee von Simon van der Meer:stochastische Kühlung
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Stochastic Cooling
Pickup
Kicker
---- ----
++++++++-
Ein Teilchen, das nicht auf der Sollbahn liegt,
influenziert auf dem Pickup ein Signal
Dieses Signal wird im Kicker zur Korrektur der
Teilchenbahn verwandt
S.v.d.Meer, 1972
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Principle of stochastic cooling
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Nachweis von W±→e±+ νe
•Das W zerfällt in zwei Teilchen, ein hochenergetisches e±(oderMyon) und ein Neutrino. Zerfall back to back im Schwerpunktssystem des W.
•Da das Neutrino nicht detektiert wird, benutzt man “missing pT” (Impuls!) alsSignatur.
Der fehlendeTransversalimpuls ist betragsmäßig gleich dem des e±
und hat das umgekehrte Vorzeichen =>Man muß den (transversal-) Impuls/Energie allerTeilchen bestimmen
•Zerfälle des W in du,...quark treten häufiger auf, sind aber schwer vom QCD Untergrund zu trennen.
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Der UA1 Detektor
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Zentraldetektor
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Elektromagmetisches Kalorimeter
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Hadronen Kalorimeter
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Magnets
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Myonen Kammern•zwei Ebenen aus je vier Lagen Driftröhren
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eW
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ET>15GeV (1,5 * 106events)
Isolierte e-Spur im DC mit pT> 7GeV (Faktor100 weniger)
Energiedeposition in Hardronen Kalorimeter>600MeV (346 events)
Ereignisse ohne Jets(55 events)
Ereignisse in der Mitte des Detektors(43 events)
43 events wurden von Hand angeschaut und für gut befunden
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Missing energy
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Bestimmung der Masse des W
Messung des Transversalimpulses und Transversalenergie
)cos1(22veT
eTT ppm
Events per [GeV]
2Wm
][GeVpT
Jakobi Peak
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Transversale Masse
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Nachweis von Z0→e++ e-
•Suche nach isolierten e±Spuren: hohe Energie im e/m Kalorimeter (>25GeV) und nur wenig Energie im Hadronen Kalorimeter (<800MeV)
•Ausschluss aller events, wenn alle überigenTeichlenzusammen pT>3GeV
•4 events nach den cuts
Gleiches Schema für µ+µ-liefert insgesamt neun events
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Nachweis von Z0→e++ e-
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Energy Deposition
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Invariante Masse des Z
Bestimmung der Masse des Z zu:mZ = (93,9±2,9) GeV/c2
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Precision Studies at LEP
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What happens in e- e+collisions
• Zu vermessen:– Form der Resonanz – Zerfallsraten für verschiedene
Endzustände
• Was sind nun die möglichen Zerfallskanäle?
• Z “Weglänge” 2 x 10-18 m
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Z Decay Channels:
Z -> e+e- (Bhabha-Scattering)
Z -> m+m-
Z -> t+t-
Z ->
Z -> Quark Anti-Quark
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e+e- : Bhabha_Scattering
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m+m- : Muon Produktion
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t+t- : Tau Production
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t+t- : Tau Production
Pions,Kaons
+
u
dW-
W+
-
+
Z
e+
e-
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Quark-Pair Production
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Quark-Pair Production
10-15 m
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How can we see Neutrinos if they are invisible
total
Hadrons
total
e
ZHadrons M
2
12
The Production Probability for Hadrons =
Hadrons
lll
HadronsZ
ll
leptonhadtotal
RRM
RN
N
312
3
2
= Resonance Width
=2 (from Theory)
Relative Number (Ratio) of leptonic zu hadronic Events
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-> “Counting Experiment” •Count hadronic Events
•Count leptonic Events
0083.09835.2 N
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Precise Measurements
00023.023192.0sin
037.0544.41
/0024.04944.2
/0021.01871.91
2
0
2
2
W
had
Z
Z
nb
cGeV
cGeVM
2
22
222
1sin
sin
Z
WW
W
M
M
eg
...and other observables consistent with the Standard Model
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What for are these precise measurements
Example : Prediction of the Top-Quark Mass
For this we consider again the reaction e+e- -> Hadrons...
e+
e-Quark
Z
Anti-Quark
This is a Quantum - Process
Experimentel precisely
measured…
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Reminding Some Quantum Mechanics The Double Gap - Experiment
Photon - orElektron Source
A1
A2
Inte
rfere
nce-S
tructu
re in
Inte
nsity
Dis
tribu
tion
QM gives Probability Distribution for Aufprallort :
P = | A1 + A2 |2 = |A1|2 + |A2|2 + 2ReA1*A2
Interference!!
Consider all possible ways, |sum their Amplitudes|2
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That's Why...
e+
e-Quark
ZAnti-Quark e+
e-
Z
Quark
Anti-Quark
Top
Anti-top
Z+
A1 A2
e+
e-Quark
Z
Anti-Quark
Higgs
A3
+ + ...
E2 m2 + p2
Sum all possible
Ways, to come to the same final state
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HiggsHiggstoptop
hadtot
mmfAmmfA
AAAAAA
AAAAA
AAAP
log)(
Re2...
...Re2
...
32
2
2*1
2
1
2
3
2
2
2
1
2*1
2
3
2
2
2
1
2
321
If Measurement precision is high -> sensitivity to these Terms -> sensitivity to Top- and even Higgs-Mass
So...
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Mtop = 173.2 +/- 4.5 GeV/c2
Mhiggs = 77 +69 -39 GeV/c2
Direct Discovery at Fermilab :
Mtop = 174.3 +/- 5.1 GeV/c2
RESULT: