Plots for the Top Decay in 1000 TTbar events generated by Pythia

I have generated using the following pythia parameters:

'MSEL=0                  ! User defined processes',
'MSUB(81) = 1            ! qqbar to QQbar',
'MSUB(82) = 1            ! gg to QQbar',
'MSTP(7) = 6             ! flavour = top',
'PMAS(6,1) = 175.        ! top quark mass',

• Signal Process I.D. for the TTbar generation.:
  
  

How many t's did we get?

I ran on 1000 TTbar events and I got 2000 t (or t_bar) quarks:

• The number of t's per event.:
  
  

Each with 1000 t⁺ and 1000 t^- (pdgId = 6 and -6, respectively):

• The I.D. of t's per event.:
  
  

What do the t's decay to?

The daughters of the TTbar events:
1 = d quark,  2 = u quark,  3 = s quark,  4 = c quark,  5 = b quark,  6 = t quark
21 = gluon,  22 = photon,  23 = Z,  and 24 = W+

• The daughters of the t's:
  
• the daughters of the t⁺'s (absolute value):
  
• the daughters of the t^-'s (absolute value):
  
  

We expected t → Wb to lowest order. When I require only two daughters, I get 915 out of 1000 events with 1830 W's, 1825 b's, and 5 s's.

• t's with only two daughters:
  

How many W's do we get?

In all cases, the t → W+X.

• The number of times a t has a W as a daughter. (absolute value):
  * P_T of leptons from W boson decays:
  

How many b's do we get?

I expected

• The number of daughters that are b's.:
  

If I require only one b quark in the final state I get 1994 of the 2000 t decays:

• t's with 1 b's in the final state:
  

If I require zero b's in the final state I get 5 of the 2000 t decays:

• t's with no b's in the final state:
  

If I require ≥ three b's in the final state I get 1 of the 2000 t decays:

• t's with 3 b's in the final state:
  

Other quarks in the final state.

In a few TTbar events, we get qq(bar) pairs in the final state. Luckily they always come in pairs (even numbers). 6 events with u's in the final state.

• t's with u's in the final state:
  

8 events with d's in the final state.

• t's with d's in the final state:
  

3 events with s's in the final state.

• t's with s's in the final state:
  

3 events with c's in the final state.

• t's with c's in the final state:
  

What do the b's decay to?

The b quarks quickly hadronize into B mesons or Λ, Σ, or Ξ baryons. Here are the total number of b-type meson/baryons in the event (no attempt to associate them in a decay chain):

• The b-type meson/baryons.:
  

The B mesons only:

pdgId	Meson Type	quark content	J	Γi / Γ to decay to lνl + anything (%)
511	B0	db(bar)	0	10.4
521	B+	ub(bar)	0	10.9
531	Bs	sb(bar)	0	7.9
513	B0*	db(bar)	1
523	B+*	ub(bar)	1
533	Bs*	sb(bar)	1

• The b-type meson.:
  

The Λ, Σ, or Ξ baryons only:

pdgId	Baryon Type	quark content	J
5112	Σb-	ddb	1/2
5114	Σb-*	ddb	3/2
5122	Λb0	bdu	1/2
5132	Ξb-	bds	1/2
5232	Ξb0	bsu	1/2
5212	Σb0	bud	1/2
5214	Σb0*	bud	3/2
5222	Σb+	buu	1/2
5224	Σb+*	buu	3/2
5232	Ξb0	bsu	1/2
5312	Ξb-	bsd	1/2
5314	Ξb-*	bsd	3/2
5322	Ξb0	bsu	1/2
5324	Ξb0*	bsu	3/2

• The b-type baryons.:
  

The number of lowest energy b-type mesons/baryons

I have a total of 2079 B meson/baryons in the lowest lying energy state. This number seems high. I would have expected 1997 based on the number of generated b-quarks.

• The lowest engery b-type meson/baryons:
  
• The lowest engery b-type mesons:
  
• The lowest energy b-type baryons:
  

How many of these lowest energy b-type mesons/baryons decay leptonically?

• The b-type mesons/baryons that decay leptonically:
  
• The b-type mesons that decay leptonically:
  
• The b-type baryons that decay leptonically:
  

This seems to be consistent with the PGD:
# of B's that decay leptonically / # of lowest energy B's  =  423 / 2079 = 0.2035
PDG value for B hadron to e/μ decays is ≅ 0.205

What's going on with the C's?

Another significant source of leptons is from the semi-leptonic decay of C-type hardrons. To see this, we find the number of lowest lying energy C-hadrons (hadrons that are not excited such as D*+).

• The lowest energy C hadrons:
  
• The lowest energy C meson:
  
• The lowest energy C baryons:
  

We compare them to the number of C hadrons that have al least one charged lepton in the final state (in this case, I only consider the e and μ case).

How many of the lowest energy b-type hadrons decay to c-type hadron?

• The number of B hadrons the decay to C hadrons + stuff:
  

Of these c-type hadrons, how many decay leptonically?

• The number of C hadrons that decay semileptonically:
  
• The number of C mesons that decay semileptonically:
  
• The number of C baryons that decay semileptonically:
  

As a cross check, how many of the e/μ's in the final state have a C hadron mother? The plot below shows that we seem to be off by 2 leptons (507 C hadrons from the above plot but 509 e/μ's from the plot below).

• The number of leptons with a C hadron mother.:
  

If we look at the lowest lying C meson plot more closely, we see one state that is a lowest lying energy C hadron. We have four leptons that decayed from a ccbar bound state with j = 1 (pdgId = 443). We can see that the ccbar states annihilated to form a j = 1 photon (so the ccbar hadron must be in the j = 1 state to do this) and then pair creates into a lepton pair. It does this twice so instead of these two ccbar pairs decaying into a lepton and lepton neutrinio, we have the fully leptonically decay leaving us with two e/μ pair. This give is an extra two leptons in the lepton collection than naively expected.

• The number of leptons that have a c cbar pair mother.:
  

This seems to be consistent with the PGD:
# of C's that decay leptonically / # of lowest energy C's  =  507 / 2668 = 0.190
PDG value for C hadron to e/μ decays is ≅ 0.175

p_T distribution of the two type of leptons

Here we plot the e/μ's pt distribution from B hadron decays, C hadron decays, and B hadrons decaying to C hadrons decaying to leptons.

• P_T of leptons from B hadron decays:
  
• P_T of leptons from C hadron decays:
  
• P_T of leptons from B and C hadron decays:
  

-- RyanKelley - 21 Jan 2008