The discovery of Top quarkGraduate Seminar PHY 599

Fall 2015

Mukul Vinayak Sholapurkar

Advisor:Prof. Robert MccarthyStony Brook University

October 26, 2015

Mukul Vinayak Sholapurkar The discovery of Top quark

Outline of the seminar

Brief history and theoretical background

Experimental details

Relation to Higgs and other recent developments

Mukul Vinayak Sholapurkar The discovery of Top quark

What is a top quark ?

The heaviest elementary particle

A third generation quark

Has an extremely short lifetime (0.4 × 10−24 seconds)

Generally gets produced in top-antitop pairs via stronginteraction but can also be generated as a single particle viaweak interaction.

Decays via weak interaction

Mukul Vinayak Sholapurkar The discovery of Top quark

Introduction into the standard model

Prof. Kobayashi and Prof. Maskawa in 2008

The Kobayashi-Maskawa theory

In 1973, Kobayashi and Maskawa predicted the existence of athird generation of quarks (top and bottom) to explain CPviolation in kaon decay.

In 1977, bottom quark was found at Fermilab.

Mukul Vinayak Sholapurkar The discovery of Top quark

Attempts to find the top

No conclusive evidence was found till 1995 with SLAC(Stanford Linear Accelerator Center), DESY(German ElectronSynchrotron at Hamburg), CERN, CDF (Collider detector atFermilab), D0 collaboration in the hunt.

Improvements along the way

Progression of the observed lower limit on the mass of the top :

CERN : 41 GeV/c2

CERN : 77 GeV/c2

D0 : 131 GeV/c2

Mukul Vinayak Sholapurkar The discovery of Top quark

Success

In March 1995, the D0 collaboration reported the observationof top quark.

In April 1995, the CDF collaboration also reported theobservation of the top.

Mukul Vinayak Sholapurkar The discovery of Top quark

General experimental methodology

Identifying the dominant production and decay modes

Background estimation and optimizing selection criteria

Fixing the signature

Data collection

Deriving conclusion by correlating with the expected results

Mukul Vinayak Sholapurkar The discovery of Top quark

Top quark production

Dominant modes of production :

Mukul Vinayak Sholapurkar The discovery of Top quark

Decay modes

Dominant decay modes:

Mukul Vinayak Sholapurkar The discovery of Top quark

The channels

Dilepton modes :

The ee mode : tt̄ →W (eν)W (eν)bb̄

The µµ mode : tt̄ →W (µν)W (µν)bb̄

The eµ mode : tt̄ →W (eν)W (µν)bb̄

Untagged single lepton modes :

The e + jets mode : tt̄ →W (eν)W (qq̄)bb̄

The µ + jets mode : tt̄ →W (µν)W (qq̄)bb̄

Tagged single lepton modes :

The e + jets/µ mode : tt̄ →W (eν)W (qq̄)b(µ)b̄

The µ + jets/µ mode : tt̄ →W (µν)W (qq̄)b(µ)b̄

Mukul Vinayak Sholapurkar The discovery of Top quark

The parameters

The parameters which were observed and used in the selectioncriteria were :

Transverse energy ET

Transverse momentum pT

HT : Scalar sum of transverse energies ET of the jets(for thesingle lepton and µµ + jets channels) or the scalar sum of theET ’s of the leading electron and the jets(for the eµ + jets andee + jets channels).

Missing transverse energy

Aplanarity

Mukul Vinayak Sholapurkar The discovery of Top quark

Significance of HT

Mukul Vinayak Sholapurkar The discovery of Top quark

Selection criteria and signature summarized

Mukul Vinayak Sholapurkar The discovery of Top quark

Data

The actual data collected by the D0 collaboration in pp̄ collisionsat√s = 1.8 TeV alongwith the expected numbers:

Mukul Vinayak Sholapurkar The discovery of Top quark

Correlation

Mukul Vinayak Sholapurkar The discovery of Top quark

Conclusion

The D0 collaboration reported the observation of top quarkwith mass 199+19

−21(stat.)± 22(syst.) GeV /c2.

The CDF collaboration then also observed the top quark witha mass of 176 ± 8(stat.) ± 10(syst.) GeV /c2.

Implications of the discovery

A major confirmation of the validity of the standard model

A new dimension to the search for Higgs boson.

Mukul Vinayak Sholapurkar The discovery of Top quark

Current status

Current value for the mass of the top quark : 173.34 ± 0.27(stat.) ± 0.71 (syst.) GeV /c2.

Satisfies the constraining relation between the masses of theHiggs boson, the W boson and the top quark with the currentvalues of the masses of the Higgs and the W being :

mHiggs = 125.09 ± 0.21 (stat.) ± 0.11 (syst.) GeV /c2

mW = 80.385 ± 0.015 GeV /c2

Mukul Vinayak Sholapurkar The discovery of Top quark

Looking forward

Open areas of study regarding the top :

Further fine-tuning of the top mass as it greatly affects ourunderstanding of the Higgs field, radioactive decay and therate of energy production in the sun.

The role of the top quark in cosmology.

Mukul Vinayak Sholapurkar The discovery of Top quark

References

F. Abe, et al. (CDF collaboration), Phys. Rev. Lett. 74,2626(1995)

S.Abachi, et al. (D0 collaboration), Phys. Rev. Lett. 74,2632(1995)

S. Abachi et al. (D0 collaboration), Phys. Rev. Lett. 72,2138 (1994)

S. Abachi et al. (D0 collaboration), Fermilab-Pub-94/354-E,1994

Chris Quigg, Discovery of the Top quark,http://lutece.fnal.gov/Papers/PhysNews95.html

Mukul Vinayak Sholapurkar The discovery of Top quark