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ELEMENTARY PARTICLES

ELEMENTARY PARTICLES. Until 1932, the “ elementary ” particles were the electrons, protons and neutrons. Now, we know that leptons ( like e - ) and fractionally charged quarks are really the “ elementary ” particles. STANDARD MODEL. CHARGE +2/3 -1/3 0 -1. QUARKS LEPTONS.

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ELEMENTARY PARTICLES

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  1. ELEMENTARY PARTICLES Until 1932, the “elementary” particles were the electrons, protons and neutrons. Now, we know that leptons ( like e-) and fractionally charged quarks are really the “elementary” particles.

  2. STANDARD MODEL CHARGE +2/3 -1/3 0 -1 QUARKS LEPTONS CHARGED NEUTRAL ALL STRONG E.M. WEAK

  3. FUNDAMENTAL INTERACTIONS REALITY STEW Info: color-charge neutral hadrons

  4. CP VIOLATION – WHAT IS IT? In 1964, James Cronin, Val Fitchand collaboraters discovered that the decays of neutral kaons did not respect the symmetry known as CP, the combination of particle- anti-particle (charge-conjugation C) and mirror (parity P) symmetry. This was the first evidence of the CP violation in weak decays. Currently, high energy experimentalists at KEK, Japan and SLAC, U.S.A. are working on finding similar signature in the B-meson sector. Kaon decay channelat NA48 expt.. at CERN, Switzerland

  5. CP VIOLATION - WHY DOES IT MATTER AT ALL? CP violation helps understand the elementary particles and the Big Bang origin of the universe. -> Nature’s forces wereindistinguishable. Equal amount of matter and anti-matter existed. -> Strong force became distinct from e.m. and weak forces.A tiny excess of matter over anti-matter began to develop. -> E.m. and weak forces separated.Protons, neutrons and mesons formed.Anti-matter started to disappear.

  6. -> Proton and neutron building continued.Remaining anti-matter disappeared. -> Light atomic nuclei formed. ->First atoms formed. -> Galaxy formation started. Stars and planets formed. -> Life forms emerge on earth.

  7. CP VIOLATION IN STANDARD MODEL Weak interaction eigen-states are not the same as the physical mass eigen-states of the quarks. Weak eigenstates are related to the mass eigen states by a 33 matrix, called Cabibbo-Kobayashi-Maskawa(CKM)matrix. d'Vud Vus Vubd s' = Vcd Vcs Vcbs b'Vtd Vts Vtbb CKM matrix is unitary. This leads to relationships between the matrix elements. One such relation is: Vud Vub * +Vcd Vcb *+Vtd Vtb *= 0. This can be represented as a triangle in the complex plane, called ”unitary triangle”. UNITARY TRIANGLE

  8. SEARCH FOR B+-> D*+P0 • B0 : bd , B+: bu • b -> c or b -> u by emission of W- boson • B-meson decay rates are used to determine coupling of third generation • quarks to lighter quarks, |Vcb|, |Vub|, |Vts|, |Vtd|. • The Cabibbo- suppressed B+ -> D*+P0 decay has same amplitude as • that of the doubly Cabibbo- suppressed B0 -> D*+P- mode. • Interference in B0(B0) -> D*+/- P+/- • =>arg(-Vub*VcdVtd*Vtb/VcbVud*VtdVtb*) • = sin(2f1 + f2) • AIM OF ANALYSIS: • B+->D*+P0 B0->D*-P+ • | | • D0 P+ D0 P- • Determination of the ratio of branching • fractions of B+->D*+P0 andB0->D*-P+ • decays. FEYNMAN DIAGRAM OF B+->D*+P0

  9. B-MESON PRODUCTION U(upsilon) is a bound state of b,b. mU (4S) ~ 10.58 GeV ; mB ~ 5.279 GeV. U(4S) has enough energy to create a light quark anti-quark pair ; thus producing B-mesons. m U (4S) – mB ~ 20 MeV. => B-mesons are produced nearly at rest in the U(4S) centre-of-mass. At KEK (Tsukuba, Japan), there is one such B-factory. The detector used for particle identification is BELLE detector.

  10. BELLE DETECTOR

  11. BELLE DETECTOR SVD:Tracks low momentum particles together with CDC. CDC:Measures transverse momentum of charged particles from the curvature of the track traversing the magnetic field. ACC:Distinguishes K+/- from P+/- in the momentum range 1.2 GeV/c to 4.0 GeV/c. ToF: Distinguishes low momentum (up to 1.2 GeV/c) K+/- from P+/- by the timing of plastic scintillation counters. CsI: Measures energy of electrons and protons via detection of scintillation light from electro-magnetic showers. KLM:Detects high momentum(>600 MeV/c) kaons and muons Superconducting Solenoid:Generates a 1.5 T magnetic field which causes charged particles to have curved tracks.

  12. PARTIAL RECONSTRUCTION TECHNIQUE • B+ -> D*+P0 mB+=5.279 GeV • | mD* =2.010 GeV • D0P- mD0 =1.864 GeV • mB+ -mD* =3.269 GeV => P0 : hard pion (high energy) • mD* - mD0 =0.146 GeV => P- : soft pion (low energy) • B-mesons are produced nearly at rest in the U(4S) centre- • of-mass frame. • => D*+ and P0 are monochromatic and anti-collinear in momentum. • PARTIAL RECONSTRUCTION • Only momentaof hard and soft pions are used. • D-candidates are not reconstructed from its decay products. • =>Gain in efficiency of a factor of about 20 expected over modes • where D0 -> K-P+ is used.

  13. Mass difference between D* and D0 ~ 0.146 GeV =>Small energy release in D*+ -> D0P- decay =>Ps travels almost in the direction of D*+ =>Ph andPs are almost back-to-back. This is the signature of the decay. DECAY FORM OF B+-> D*+ P0

  14. B+-> D*+ P0 ANALYSIS In the U(4S) frame, pPh + pD* = pB ~ 0 Energy conservation => ED* = EB+ - EP0 =>| pD*| = sqrt (E D*2 – m D*2) p Ph – p D* = (diff) < pB ~ 0.39 GeV Partially reconstructed D* frame: Constructed using ED* and pD* , along - p Ph. All charged pions are boosted into this frame. Parallel component of pPs along opposite direction of pPh( ppar) Transverse component of pPs along opposite direction of pPh(pperp) Event track Display for B0-> D* -P+

  15. DATA SAMPLE Data taken with Belle Detector at KEKB asymmetric e+e- collider. Luminosity used currently = 8.2 fb-1 ~ 8.2 × 10 6 BB pairs. Total luminosity to be used= 100 fb-1. SELECTION CRITERIA For Monte – Carlo study, track selection was done using the following criteria: |pPh | > 2.1 GeV,| p Ps |< 0.25 GeV,| diff | < 0.4 GeV, | ppar| < 0.05 GeV,| pperp| < 0.1 GeV. BACKGROUND STUDY Possible background decays are: B0-> D*- r+,D*- -> D0 P - decay chain, Generic B-decays with P s generated from D*, Other generic B- decays, Continuum jet-like events. SIGNAL MONTE CARLO STUDY Two - dimensional plots of “ppar”vs. “ pperp” shows signal in the signal Monte- Carlo plots of B+-> D*+P0 whenthe hard pion is a P0, but no signal when hard pion is P-. ppar pperp ppar vs. pperp SIGNAL MC CONTINUUM EVENT

  16. SUMMARY • Two- dimensional plots of “ppar” vs.”pperp” to be • further analyzed • B0-> D*+ P- signal to be used to develop further • strategies • Event parameter cuts to be employed • Fisher discriminant method to be used

  17. SEARCH FOR B+-> D*+P0 DECAY BY PARTIAL RECONSTRUCTION

  18. Seema Bahinipati

  19. ppar ppar pperp pperp B+ -> D*+P0 Signal Monte - Carlo B0 -> D*+P- Signal Monte - Carlo

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