Measurement of Bc in CDF Ilsung Cho Yonsei University, Seoul
Korea
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The 1 st day of Universe In the beginning God created the
heaven and the earth. And God said: 'Let there be light.' And there
was light. - Genesis chapter 1 ? ? ? ? ?
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4 What is the world made of? What holds the world together?
Where did we come from?
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5 Standard Model Particle physics field has been tremendously
successful in creating and establishing Standard Model of Particle
Physics answering what the universe is made of and how it works.
Answers themselves led to even more questions
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6 top quark anti-top quark Z W +, W -.. e e - u d s c b gluons
Elementary Particles Elementary Particles e e + u d s c b - - - - (
Mass proportional to area shown: proton mass = ) Are they the
smallest things? Why are there so many? Where does mass come
from?
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7 Everything is made of electrons, u quarks and d quarks Dark
Matter ??? Galaxies are held together by mass far bigger (x5) than
all stars combined.
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8 1. Are there undiscovered principles of nature: New
symmetries, new physical laws? 2. How can we solve the mystery of
dark energy? 3. Are there extra dimensions of space? 4. Do all the
forces become one? 5. Why are there so many kinds of particles? 6.
What is dark matter? How can we make it in the laboratory? 7. What
are neutrinos telling us? 8. How did the universe come to be? 9.
What happened to the antimatter? Questions remained unsolved yet .
Origin of Mass Unification Energy Frontier Colliders
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9 Hadron Collider
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10 Collider Parameters : Energy Total E 2 : CM frame : Energy
limit : Synchrotron radiation Boost factor
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11 Collider Parameters : Luminosity The number of particles
passing each other unit area x unit time x unit transverse area
Defined as 1year ~ x10 7 sec time to operate ~1year/
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36 proton and antiproton bunches 396 ns bunch crossing 2.5Mhz
The Worlds highest energy hadron collider Instantaneous Luminosity
: 1.2 x 10 32 cm -2 s -1
14 Our EYE : Detector Z R Z direction : normally choose beam
direction Use cylindrical coordinate Pseudo rapidity 45 degree =1
=-1
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15 Our EYE : Collider detector Particle detection is based on
its interactions with matter of the detectors Modern multipurpose
collider detector Stable particle( interacting particle) : P, e, K,
,
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Silicon vertex detector Central Outer Tracker Time of Flight
Solenoid coil Calorimeter Muon chamber Inherited from Run I Central
Calorimeter (||
39 Cross section We choose to use pT(Bc)>4, |y(Bc)|
40 ratio =0.282 0.038(stat.) 0.035(yield) 0.065(acceptance) R K
: Kinematics acceptance ratio = 4.42 0.08(stat.) 1.02(syst.) R :
Electron reconstruction ratio = 1/ (eID) 1/(63%) N(B + )=2872 59
Cross section ratio is defined within our kinematical limits p T
(B) > 4.0GeV, |y(B)| < 1.0 Cross section
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41 Lifetime measurement Proton Anti proton Lxy Muon Electron
neutrino electron Primary vertex Secondary vertex Because of
undetectable neutrino we cannt calculate Bc momentum directly Use
MC simulation and the reconstructed momentum of J/ e pair to
estimate Bc momentum (K-factor) Where a is the angle between the
vector of pT(J/ +e) and pT(Bc) Pseudo-proper decay length
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42 Fake electron : J/ +track with electron fake rates Fake J/ :
Sideband in J/ +track candidates Residual conversion : J/ +tagged
conv. electron with conversion finding efficiency b-bbar : PYTHIA
MC but with change of GS/FE/FC for systematic error Prompt : Assume
to be a resolution function Background shape determination
44 Lifetime fitting result c (Bc) = 139.0 + 22.1/-19.5 (stat.)
10.8 (syst.) m (Bc) = 0.463 +0.073/-0.065(stat.) 0.036(syst.)
ps
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45 Hadronic decay channel bcbc cccc e, , u, e, , d, J/
BcBc
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46 Bc J/ , J/ channel : 3 track topology Precise mass
measurement possible Proton Anti proton Bc decays in the beam pipe
line Muon Muon detector + Tracker Tracker Need aggressive 2 nd
vertex resolution to reduce backgrounds Muon system J/ trigger
Calorimeter Electron ID Tracking system (COT) High efficiency
tracking dE/dx for electron ID Tracking system (Silicon) Good
vertex resolution Which information is needed ? Which information
is needed ?
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47 Prompt J/ + track from PV Search range : 6.4 +- 2 s 5.6 to
7.2 GeV Backgrounds : Key elements for Bc analysis B-Bbar
background Muon B+ B0 Muon Cut optimization : Signal from MC and
background from data, choose max significant point Tight vertex
requirements
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48 Bc J/ reconstruction Num(events) FIT = 38.9 sig 26.1 bkg
between 6.24-6.3 Significance > 6 over search area 0.36 fb -1
~0.8 fb -1 ~0.7 fb -1 ~0.6 fb -1 ~0.5 fb -1 Mass = 6275.2
4.3(stat.) 2.3(syst.) MeV/c 2
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49 Cross section ratio between B c + J/ e + and B + J/ K + for
p T (B)>4GeV, |y(B)|
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50 Do we need more physics ???
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51 e + e - superparticle ~ e spin 1/2 spin 0 M e M e Symmetry
between fermions (matter) and bosons (forces) Undiscovered new
symmetry SUSY solves Standard Model problems: Origin of Mass Origin
of Mass : Higgs mass calculation Unification Dark Matter SUSY
provides a candidate particle for Dark Matter Laws of Nature will
be much more elegant at high energy. ~ e SUSY
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52 SUSY Supersymmetry contains squarks and sleptons. Squark
mass matrixes contain information on SUSY breaking mechanisms
&/or GUT scale interactions. Quark flavor changing neutral
current processes, e.g. B S or D 0 mixing, are sensitive to the
off-diagonal elements of the squark mass matrix
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53 MSSM Measurements Contributions to B s mixing ~10 x SM CP
asymmetry 0.1sin cos sin( m s t), ~10 x SM Asym =(M W /m squark ) 2
sin( ), ~0 in SM Contributions to direct CP violing decay B - K -
vs B + K + b sss
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54 Bs (FCNC decay) From Okada ICHEP 2006
71 Kinematical limit on cross section = x-section for B meson
certain kinematical range We choose to use pT(Bc)>4,
|y(Bc)|
73 ratio =0.282 0.038(stat.) 0.035(yield) 0.065(acceptance) R K
: Kinematics acceptance ratio = 4.42 0.08(stat.) 1.02(syst.) R :
Electron reconstruction ratio = 1/ (eID) 1/(63%) N(B + )=2872 59
Cross section ratio is defined within our kinematical limits p T
(B) > 4.0GeV, |y(B)| < 1.0 Cross section
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74 Lifetime measurement Proton Anti proton Lxy Muon Electron
neutrino electron Primary vertex Secondary vertex Because of
undetectable neutrino we cannt calculate Bc momentum directly Use
MC simulation and the reconstructed momentum of J/ e pair to
estimate Bc momentum (K-factor) Where a is the angle between the
vector of pT(J/ +e) and pT(Bc) Pseudo-proper decay length
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75 Strategy for lifetime measurement Fake electron, Residual
conversion, bbBAR and fake J/ K-factor estimation Do the maximum
likelihood fitting No L xy cut fake J/ 164.0 9.1 fake electron
110.2 19.0 conversion electron 67.4 34.8 bb 63.0 18.5 observed J/ e
+ pairs 783
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76 K factor Calculate using Monte Carlo simulation Divide K
factor with J/ +e mass bin
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77 Likelihood definition Construct likelihood function
including signal and all backgrounds
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78 Lifetime fitting result c (Bc) = 139.0 + 22.1/-19.5 (stat.)
10.8 (syst.) m (Bc) = 0.463 +0.073/-0.065(stat.) 0.036(syst.)
ps
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79 Mass = 6275.2 4.3(stat.) 2.3(syst.) MeV/c 2 ~0.8 fb -1
Numver of events FIT : Sngnal : 38.9 Backgrounds : 26.1 ( between
6.24-6.3 ) Significance > 6 over search area Bc mass
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80 Recent lattice QCD calculation PRL 94, 172001 (2005) PLB
453, 289 (1999) m Bc = 6287.0 4.8 1.1 MeV hep-ex/0505076 (
theory-exp)= 12 MeV
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81 Lifetime measurement Proton Anti proton Lxy Muon Electron
neutrino electron Primary vertex Secondary vertex Because of
undetectable neutrino we cannt calculate Bc momentum directly Use
MC simulation and the reconstructed momentum of J/ y- e pair to
estimate Bc momentum (K-factor) Where a is the angle between the
vector of pT(J/ y +e) and pT(Bc) Pseudo-proper decay length Play on
r f plane
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82 Lifetime (Semileptoinc Bc J/ e ) c (Bc) = 139.0 + 22.1/-19.5
(stat.) 10.8 (syst.) m (Bc) = 0.463 +0.073/-0.065(stat.)
0.036(syst.) ps V. V. Kiselev, hep-ph/0308214 (2003) : 0.55ps+-
0.15ps
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83 Bc J/ result : Bc Mass Mass = 6275.2 4.3(stat.) 2.3(syst.)
MeV/c 2 ~0.8 fb -1 Significance > 6 s 0.36 fb -1 ~0.8 fb -1 ~0.7
fb -1 ~0.6 fb -1 ~0.5 fb -1
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84 Recent lattice QCD calculation PRL 94, 172001 (2005) PLB
453, 289 (1999) m Bc = 6287.0 4.8 1.1 MeV hep-ex/0505076
(theory-exp)= 12 MeV
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85 The Standard Model Theoretical Background Physical States in
the Standard Model The gauge bosons: W , g & Z o and the Higgs
H o Lagrangian for charged current weak decays Where
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86 The 6 CKM Triangles Best measured in B s decays There are 4
independent phases: ( can be substituted for or as ) Area of each =
A 2 6 , the Jarlskog Invariant
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87 Some B Meson Decay Diagrams a) is dominant, b) is color
suppressed a) & b) are called tree level diagrams
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88 B s : Mixing in the Standard Model Measurement of B s mixing
provides the ratio of V td /V ts which gives the same essential
information as B d mixing alone, but with much better control of
theory parameters |V td | 2 =A 2 4 [(1- ) 2 + 2 ] |V td | 2 / |V ts
| 2 =[(1- ) 2 + 2 ] Circle in ( ) plane centered at (1,0) To relate
constraints on CKM matrix in terms of say r & h need to use
theoretical estimates of =f B s 2 B B s / f B d 2 B B d
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89 Bs for each decay mode
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90 The measured amplitude values and uncertainties versus the
Bs s oscillation frequency, Dms
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91 Observation of Bs Oscillation PRL 97, 242003 2006 Belle PRL
96, 221601 (2006) b d g : |Vtd|/|Vts| = 0.199 +0.026-0.025(exp)
+0.018-0.015(theo)
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92 Physics motivation b s Transitions (Penguins Physics
motivation b s Transitions (Penguins ) In SM t in loop dominates
and CP asymmetry should be equal to that in J/ K s Other objects in
loop, new virtual particles, could interfere So this process is
sensitive to new physics
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93 J/ trigger p T >1.5GeV, | |2GeV, 0.6 8 GeV, e e For
Electron cut study
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94 CPV Measurements in b s We cannot just average these modes,
but.... =sin2 =0.500.06 S = 0.520.05-0.68.03 =-0.16 0.06 Does u
& c parts of Penguin contribute? Yes but S >0, ~0.1 New
Physics???
