Line: 1 to 1  

Analysis of Single Top Polarization using Parton Level Atlas samples  
Line: 55 to 55  
TevatronTo get an idea why the polarization distribution looks the way it does let us take a look at the Tevatron first (ONETOP sample) and what happens when I guess the direction of the incoming d quark wrong.  
Changed:  
< <  
> >  
In the left graph we assumed the antiquark would have the same direction as the incoming antiproton, the middle graph assumes an antiquark coming in the proton direction. The histogram on the right hand side is the sum of the two other histograms.  
Line: 86 to 86  
LHCWhat does all that mean for the LHC?  
Changed:  
< < 
At the LHC half teh time we guess the wrong direction for the antiquark. Therefore the polarization distribution for the schannel should look like the sum of the two graphs, assuming the antiquark comes from the right, respectively from the left. That is it should look like the right histogram in the upper graph.  
> > 
At the LHC half the time we guess the wrong direction for the antiquark. Therefore the polarization distribution for the schannel should look like the sum of the two graphs, assuming the antiquark comes from the right, respectively from the left. That is it should look like the right histogram in the upper graph.  
Changed:  
< < 
The polarization dsitribution schannel (AcerMCfor Atlas with the beamline chosen as basis:  
> > 
The polarization dsitribution schannel (AcerMC) for Atlas with the beamline chosen as basis:  
The "Degree of Polarization" is:  
Line: 107 to 107  
 
Added:  
> > 

Line: 1 to 1  

Analysis of Single Top Polarization using Parton Level Atlas samples  
Line: 62 to 62  
If I consider the fact that we expect a 100% polarized top quark in the schannel, the offset in the first histogram must be due to a wrong assumption of the direction of the incoming antiquark. It makes sense that we see this offset, as a certain percentage of the antiquarks do not come from the antiproton but from the quark sea of the incoming proton. The question is now: Does guessing the wrong side just give me the opposite polarization for the top quark? When we look at the second graph, the answer is no, as in that case we would see exactly the same offset in both the first and the second graph.  
Changed:  
< <  %Br% This can be explained by the fact that the polarization is measured not in the restframe of the incoming quarks (which would mean it should be symmetric in exchanging the directions of the antiquark) but in the top quark restframe.  
> > 
This can be explained by the fact that the polarization is measured not in the restframe of the incoming quarks (which would mean it should be symmetric in exchanging the directions of the quark and the antiquark) but in the top quark restframe.  
If we assume the top to be produced at rest (which can be achieved by putting a cut onto the top PT), we therefore expect that guessing the wrong side just means opposite polarization for the top quark. As a consequence our offset would give us directly the number of antiquark whose direction we guessed wrong and therefore directly the percentage of antiquarks coming from the quark sea of the proton. Furthermore we would expect the two left graphs to have the same offset and the sum to be a horizontal line.  
Changed:  
< <  On the other hand by applying a minimum cut on the top PT we expect the effect to be bigger.  
> > 
On the other hand by applying a minimum cut on the top PT we expect the assymetry between the two left graphs to be bigger and therefore the sum to show a steeper curve, a larger "Degree of Polarization".  
Here we put a PT cut on the top quark, Px>100 GeV. If we compare the "Degree of Polarization" of the sum without and the sum with the cut, we get:  
Changed:  
< < 
D(without cut)=0.102  
> >  D(without cut)=0.102  
D(with cut)=0.55 So how does the momentum of the topquark effect the polarization measurement? 
Line: 1 to 1  

Analysis of Single Top Polarization using Parton Level Atlas samples  
Line: 7 to 7  
1. AbstractI looked at polarization distributions of Atlas parton level samples in the Optimal/Spectator basis for the schannel and the tchannel.  
Changed:  
< <  Trying to do this I ran into missing information and had to reconstruct quarks. This effects the polarization distributions, in a way that is described below.  
> >  Trying to do this I ran into missing information and had to reconstruct quarks.  
2. Parton Level Samples  
Line: 31 to 31  
4. Optimal basis/ Spectator basis  
Added:  
> > 
For the Spectator basis in the tchannel use spectator quark and the antilepton in the CM frame of the top quark.  
For the Optimal basis (schannel) you have to take the incoming antiquark and the antilepton in the CMframe of the top quark.
The Optimal Basis in the schannel corresponds to the Spectator basis in the tchannel.  
Deleted:  
< < 
For the Spectator basis in the tchannel use spectator quark and the antilepton in the CM frame of the top quark.  
1. The tchannel  
Changed:  
< <  For the tchannel we need the spectator quark, which isn't given in the Truth tree, either. So we have to use its jets to get information about the original direction of the spectator quark. The jets have a pdgid of 0 or 5, where 5 stands for the btagged jets. We use only events that contain two jets and use the one with a pdgid of 0. If we condider the fact that electrons can be misinterpreted as jets, we should use events with three jets and use the first jet that fullfills our requirements.  
> >  For the tchannel we need the spectator quark, which isn't given in the Truth tree. So we have to use its jets to get information about the original direction of the spectator quark. The jets have a pdgid of 0 or 5, where 5 stands for the btagged jets. We use only events that contain two jets and use the one with a pdgid of 0. If we condider the fact that electrons can be misinterpreted as jets, we should use events with three jets and use the first jet that fullfills our requirements.  
Here is the result for the tchannel, spectator basis.  
Line: 59 to 59  
In the left graph we assumed the antiquark would have the same direction as the incoming antiproton, the middle graph assumes an antiquark coming in the proton direction. The histogram on the right hand side is the sum of the two other histograms.  
Changed:  
< <  If I consider the fact that we expect a 100% polarized top quark in the schannel, the offset in the first histogram must be due to a wrong assumption of the direction of the incoming antiquark. It makes sense, that we see this offset, as a certain percentage of the antiquarks do not come from the antiproton but from the quark sea of the incoming proton.  
> >  If I consider the fact that we expect a 100% polarized top quark in the schannel, the offset in the first histogram must be due to a wrong assumption of the direction of the incoming antiquark. It makes sense that we see this offset, as a certain percentage of the antiquarks do not come from the antiproton but from the quark sea of the incoming proton.  
The question is now: Does guessing the wrong side just give me the opposite polarization for the top quark? When we look at the second graph, the answer is no, as in that case we would see exactly the same offset in both the first and the second graph. %Br% This can be explained by the fact that the polarization is measured not in the restframe of the incoming quarks (which would mean it should be symmetric in exchanging the directions of the antiquark) but in the top quark restframe. 
Line: 1 to 1  

Analysis of Single Top Polarization using Parton Level Atlas samples  
Line: 47 to 47  
2. The schannel  
Deleted:  
< <  
For the Optimal basis, schannel, we need the direction of the incoming antiquark (the d quark). At the Tevatron we collide protons and antiprotons. Therefore the guess that the antiquark has the same direction as the antiproton is right in most cases, but not in all as there is a certain percentage of events in which the antiquark has its origins in the quark sea of the proton.  
Line: 72 to 71  
Changed:  
< <  Here we put a PT cut on the top quark, PT>100 GeV.  
> >  Here we put a PT cut on the top quark, Px>100 GeV.  
If we compare the "Degree of Polarization" of the sum without and the sum with the cut, we get:
D(without cut)=0.102  
Line: 95 to 94  
The "Degree of Polarization" is:
D=0.63 +/ 0.02  
Changed:  
< <  Here we see a much higher "degree of polarization" than in the graphs above. This means we have a greater assymetry between guessing the right direction for the antitop and guessing the wrong direction for the antitop. An explanation for this could be a higher top PT, which makes sense, as the Atlas samples in contrast to the ONETOP samples have cuts on the minimum PT.  
> >  The high "degree of polarization" means we have a big assymetry between guessing the direction of the incoming antiquark right/ wrong. This means we have a high top PT, which makes sense, as the Atlas samples in contrast to the ONETOP samples have cuts on the minimum PT.  
 SarahHeim  10 Mar 2008  
Line: 103 to 102  
 
Added:  
> > 
 

Line: 1 to 1  

Analysis of Single Top Polarization using Parton Level Atlas samples  
Line: 53 to 53  
At the LHC protons are collided with protons, which means that there is no preferred direction for the antiquark. The guess that the antiquark comes, let's say from the right, should lead to the correct result in 50% of all events.  
Added:  
> > 
Tevatron  
To get an idea why the polarization distribution looks the way it does let us take a look at the Tevatron first (ONETOP sample) and what happens when I guess the direction of the incoming d quark wrong.  
Line: 67 to 68  
If we assume the top to be produced at rest (which can be achieved by putting a cut onto the top PT), we therefore expect that guessing the wrong side just means opposite polarization for the top quark. As a consequence our offset would give us directly the number of antiquark whose direction we guessed wrong and therefore directly the percentage of antiquarks coming from the quark sea of the proton. Furthermore we would expect the two left graphs to have the same offset and the sum to be a horizontal line.  
Added:  
> >  On the other hand by applying a minimum cut on the top PT we expect the effect to be bigger.  
Changed:  
< <  
> >  
Changed:  
< <  Here we put an energy cut on the top quark, of 197 GeV. If we compare the "Degree of Polarization" of the sum without and the sum with the cut, we get:  
> >  Here we put a PT cut on the top quark, PT>100 GeV. If we compare the "Degree of Polarization" of the sum without and the sum with the cut, we get:  
Changed:  
< < 
D(without cut)=0.102 +/ 0.010 D(with cut)=0.192 +/ 0.011 This is a small effect, but visible.  
> > 
D(without cut)=0.102 D(with cut)=0.55  
So how does the momentum of the topquark effect the polarization measurement? For the Optimal basis the angle between the incoming antiquark and the decay lepton is measured in the top quark restframe.  
Line: 83 to 85  
Thus our basis is not optimal any more and we cannot expect to see full polarization.  
Changed:  
< <  What does all that mean for Atlas?  
> > 
LHCWhat does all that mean for the LHC?At the LHC half teh time we guess the wrong direction for the antiquark. Therefore the polarization distribution for the schannel should look like the sum of the two graphs, assuming the antiquark comes from the right, respectively from the left. That is it should look like the right histogram in the upper graph.  
Changed:  
< < 
The polarization dsitribution schannel for Atlas with the beamline chosen as basis:  
> > 
The polarization dsitribution schannel (AcerMCfor Atlas with the beamline chosen as basis:  
Added:  
> > 
The "Degree of Polarization" is:
D=0.63 +/ 0.02 Here we see a much higher "degree of polarization" than in the graphs above. This means we have a greater assymetry between guessing the right direction for the antitop and guessing the wrong direction for the antitop. An explanation for this could be a higher top PT, which makes sense, as the Atlas samples in contrast to the ONETOP samples have cuts on the minimum PT.  
 SarahHeim  10 Mar 2008
 
Deleted:  
< < 
 

Line: 1 to 1  

Analysis of Single Top Polarization using Parton Level Atlas samples  
Line: 80 to 81  
Guessing the wrong direction for the antiquark doesn't affect our distribution as long as the topquark is close to rest, as then we have a totally symmetric situation and simply get the opposite polarization for the top quark. If our top quark has PT momentum and we guess the wrong direction, the situation is not symmetric any more but the chosen reference axis (which is the direction of the antiquark) is off by a certain angle compared to the direction of the optimal reference axis which is the direction of the quark.  
Changed:  
< <  %Br%Thus our basis is not optimal any more and we cannot expect to see full polarization.  
> > 
Thus our basis is not optimal any more and we cannot expect to see full polarization. What does all that mean for Atlas? The polarization dsitribution schannel for Atlas with the beamline chosen as basis:  
 SarahHeim  10 Mar 2008 
Line: 1 to 1  

Analysis of Single Top Polarization using Parton Level Atlas samples  
Line: 71 to 71  
Here we put an energy cut on the top quark, of 197 GeV. If we compare the "Degree of Polarization" of the sum without and the sum with the cut, we get:  
Changed:  
< <  D(without cut)=0.102 +/ 0.010 D(with cut)=0.192 +/ 0.011 This is a small effect, but visible.  
> > 
D(without cut)=0.102 +/ 0.010 D(with cut)=0.192 +/ 0.011 This is a small effect, but visible.  
So how does the momentum of the topquark effect the polarization measurement? For the Optimal basis the angle between the incoming antiquark and the decay lepton is measured in the top quark restframe. Guessing the wrong direction for the antiquark doesn't affect our distribution as long as the topquark is close to rest, as then we have a totally symmetric situation and simply get the opposite polarization for the top quark. If our top quark has PT momentum and we guess the wrong direction, the situation is not symmetric any more but the chosen reference axis (which is the direction of the antiquark) is off by a certain angle compared to the direction of the optimal reference axis which is the direction of the quark.  
Changed:  
< <  Thus our basis is not optimal any more and we cannot expect to see full polarization.  
> >  %Br%Thus our basis is not optimal any more and we cannot expect to see full polarization.  
 SarahHeim  10 Mar 2008  
Added:  
> > 
 
 
Added:  
> > 
 
 
Deleted:  
< < 

Line: 1 to 1  

Analysis of Single Top Polarization using Parton Level Atlas samples  
Line: 13 to 13  
The used parton samples are generated by AcerMC for the Atlas Single Top analysis. The parton level samples can be found in the Truth tree. This truth tree doesn't contain the initial particles, nor the spectator quark for the tchannel. This complicates things, as explained in the following.  
Changed:  
< < 
3. Optimal basis/ Spectator basis  
> > 
3. Degree of PolarizationThe degree of polarization is defined as D=(N_{}N_{+})/(N_{}+N_{+}) where N_{} is the number of events with a negative polarized top and N_{+} is the number of events with a positive polarized top. There are two ways to get the N_{} and the N_{+} from the histogram: The first method means you just take the number of events at the left and right corner of the histogram (cos(θ)=1 and cos(θ)=1 respectively). In the second method you actually count events and plug the total number of events with negative/positive polarized tops. This requires a fit. The first method works as D is a ratio and using the actual number of N_{}/N_{+} we can simplify it by cancelling, so that we end up with the values at cos(θ)=1 and cos(θ)=1. Although half of the time we use the wrong direction of the antiquark, it is interesting to look at the schannel and see the degree of polarization as a function of the number of jets in our event.4. Optimal basis/ Spectator basis  
For the Optimal basis (schannel) you have to take the incoming antiquark and the antilepton in the CMframe of the top quark.
The Optimal Basis in the schannel corresponds to the Spectator basis in the tchannel.  
Line: 38 to 55  
To get an idea why the polarization distribution looks the way it does let us take a look at the Tevatron first (ONETOP sample) and what happens when I guess the direction of the incoming d quark wrong.  
Changed:  
< <  
> >  
In the left graph we assumed the antiquark would have the same direction as the incoming antiproton, the middle graph assumes an antiquark coming in the proton direction. The histogram on the right hand side is the sum of the two other histograms.  
Line: 47 to 64  
The question is now: Does guessing the wrong side just give me the opposite polarization for the top quark? When we look at the second graph, the answer is no, as in that case we would see exactly the same offset in both the first and the second graph. %Br% This can be explained by the fact that the polarization is measured not in the restframe of the incoming quarks (which would mean it should be symmetric in exchanging the directions of the antiquark) but in the top quark restframe.  
Changed:  
< < 
If we assume the top to be produced at rest (which can be achieved by putting a cut onto the top PT), we therefore expect the two left graphs to have the same offset and the sum to be a horizontal line.
4. Degree of PolarizationThe degree of polarization is defined as D=(N_{}N_{+})/(N_{}+N_{+}) where N_{} is the number of events with a negative polarized top and N_{+} is the number of events with a positive polarized top. There are two ways to get the N_{} and the N_{+} from the histogram: The first method means you just take the number of events at the left and right corner of the histogram (cos(θ)=1 and cos(θ)=1 respectively). In the second method you actually count events and plug the total number of events with negative/positive polarized tops. This requires a fit. The first method works as D is a ratio and using the actual number of N_{}/N_{+} we can simplify it by cancelling, so that we end up with the values at cos(θ)=1 and cos(θ)=1. Although half of the time we use the wrong direction of the antiquark, it is interesting to look at the schannel and see the degree of polarization as a function of the number of jets in our event.  
> >  If we assume the top to be produced at rest (which can be achieved by putting a cut onto the top PT), we therefore expect that guessing the wrong side just means opposite polarization for the top quark. As a consequence our offset would give us directly the number of antiquark whose direction we guessed wrong and therefore directly the percentage of antiquarks coming from the quark sea of the proton. Furthermore we would expect the two left graphs to have the same offset and the sum to be a horizontal line. Here we put an energy cut on the top quark, of 197 GeV. If we compare the "Degree of Polarization" of the sum without and the sum with the cut, we get: D(without cut)=0.102 +/ 0.010 D(with cut)=0.192 +/ 0.011 This is a small effect, but visible. So how does the momentum of the topquark effect the polarization measurement? For the Optimal basis the angle between the incoming antiquark and the decay lepton is measured in the top quark restframe. Guessing the wrong direction for the antiquark doesn't affect our distribution as long as the topquark is close to rest, as then we have a totally symmetric situation and simply get the opposite polarization for the top quark. If our top quark has PT momentum and we guess the wrong direction, the situation is not symmetric any more but the chosen reference axis (which is the direction of the antiquark) is off by a certain angle compared to the direction of the optimal reference axis which is the direction of the quark. Thus our basis is not optimal any more and we cannot expect to see full polarization.  
 SarahHeim  10 Mar 2008
 
Added:  
> > 
 
 
Changed:  
< < 
 
> > 

Line: 1 to 1  

Analysis of Single Top Polarization using Parton Level Atlas samples  
Line: 36 to 36  
At the LHC protons are collided with protons, which means that there is no preferred direction for the antiquark. The guess that the antiquark comes, let's say from the right, should lead to the correct result in 50% of all events.  
Changed:  
< <  To get an idea why the polarization distribution looks the way it does let us take a look at the Tevatron first and what happens when I guess the direction of the incoming d quark wrong.  
> >  To get an idea why the polarization distribution looks the way it does let us take a look at the Tevatron first (ONETOP sample) and what happens when I guess the direction of the incoming d quark wrong.  
Added:  
> >  In the left graph we assumed the antiquark would have the same direction as the incoming antiproton, the middle graph assumes an antiquark coming in the proton direction. The histogram on the right hand side is the sum of the two other histograms.  
Added:  
> >  If I consider the fact that we expect a 100% polarized top quark in the schannel, the offset in the first histogram must be due to a wrong assumption of the direction of the incoming antiquark. It makes sense, that we see this offset, as a certain percentage of the antiquarks do not come from the antiproton but from the quark sea of the incoming proton. The question is now: Does guessing the wrong side just give me the opposite polarization for the top quark? When we look at the second graph, the answer is no, as in that case we would see exactly the same offset in both the first and the second graph. %Br% This can be explained by the fact that the polarization is measured not in the restframe of the incoming quarks (which would mean it should be symmetric in exchanging the directions of the antiquark) but in the top quark restframe. If we assume the top to be produced at rest (which can be achieved by putting a cut onto the top PT), we therefore expect the two left graphs to have the same offset and the sum to be a horizontal line.  
Line: 71 to 78  
 
Changed:  
< < 
 
> > 

Line: 1 to 1  

Analysis of Single Top Polarization using Parton Level Atlas samples  
Line: 30 to 30  
2. The schannel  
Changed:  
< <  
> >  
For the Optimal basis, schannel, we need the direction of the incoming antiquark (the d quark). At the Tevatron we collide protons and antiprotons. Therefore the guess that the antiquark has the same direction as the antiproton is right in most cases, but not in all as there is a certain percentage of events in which the antiquark has its origins in the quark sea of the proton. At the LHC protons are collided with protons, which means that there is no preferred direction for the antiquark. The guess that the antiquark comes, let's say from the right, should lead to the correct result in 50% of all events.  
Changed:  
< <  To get an idea why our  
> >  To get an idea why the polarization distribution looks the way it does let us take a look at the Tevatron first and what happens when I guess the direction of the incoming d quark wrong.  
Line: 67 to 71  
 
Added:  
> > 

Line: 1 to 1  

Analysis of Single Top Polarization using Parton Level Atlas samples  
Line: 7 to 7  
1. AbstractI looked at polarization distributions of Atlas parton level samples in the Optimal/Spectator basis for the schannel and the tchannel.  
Changed:  
< <  Trying to do this I ran into missing information and had to reconstruct quarks. This effects the polarization distributions, that is, it increases the offset, in a way that I haven't looked at quantitatively so far.  
> >  Trying to do this I ran into missing information and had to reconstruct quarks. This effects the polarization distributions, in a way that is described below.  
2. Parton Level Samples  
Line: 20 to 20  
For the Spectator basis in the tchannel use spectator quark and the antilepton in the CM frame of the top quark.  
Added:  
> > 
1. The tchannel  
Changed:  
< < 
1. The schannelAt the LHC protons are collided with protons (unlike the Tevatron which collides protons and antiprotons). That means at the LHC we have a totally symmetric situation, that is the probability for our incoming antiquark to come in positive zdirection is as big as the probability to come in negative zdirection.  
> >  For the tchannel we need the spectator quark, which isn't given in the Truth tree, either. So we have to use its jets to get information about the original direction of the spectator quark. The jets have a pdgid of 0 or 5, where 5 stands for the btagged jets. We use only events that contain two jets and use the one with a pdgid of 0. If we condider the fact that electrons can be misinterpreted as jets, we should use events with three jets and use the first jet that fullfills our requirements.  
Changed:  
< <  As we don't have information about the incoming antiquark we have to use the beamline as reference axis. This means have of the time, we assume the wrong direction, so we cannot expect to see a total polarization any more.  
> >  Here is the result for the tchannel, spectator basis.  
Changed:  
< <  Here is the result for the schannel, with a messed up Optimal basis that is effectively a beamline basis now and therefore not optimal any more.  
> > 
2. The schannelFor the Optimal basis, schannel, we need the direction of the incoming antiquark (the d quark). At the Tevatron we collide protons and antiprotons. Therefore the guess that the antiquark has the same direction as the antiproton is right in most cases, but not in all as there is a certain percentage of events in which the antiquark has its origins in the quark sea of the proton. At the LHC protons are collided with protons, which means that there is no preferred direction for the antiquark. The guess that the antiquark comes, let's say from the right, should lead to the correct result in 50% of all events. To get an idea why our  
Deleted:  
< < 
2. The tchannel  
Deleted:  
< <  For the tchannel we need the spectator quark, which isn't given in the Truth tree, either. So we have to use its jets to get information about the original direction of the spectator quark. The jets have a pdgid of 0 or 5, where 5 stands for the btagged jets. We use only events that contain two jets and use the one with a pdgid of 0. If we condider the fact that electrons can be misinterpreted as jets, we should use events with three jets and use the first jet that fullfills our requirements.  
Deleted:  
< <  Here is the result for the tchannel, spectator basis.  
Deleted:  
< <  
4. Degree of PolarizationThe degree of polarization is defined as D=(N_{}N_{+})/(N_{}+N_{+})  
Line: 53 to 58  
Although half of the time we use the wrong direction of the antiquark, it is interesting to look at the schannel and see the degree of polarization as a function of the number of jets in our event.  
Deleted:  
< < 
5. ONETOPsamplesUsing ONETOP samples for the schannel that had been generated with the updated LHCcode, there was no information about incoming particles either, so that we get an offset here, too, which can simply be explained by the fact that half the time we guess the direction of the incoming antiquark wrong. This was tested by using the updated code, but with Tevatron setting. Here no offset was seen.  
 SarahHeim  10 Mar 2008 
Line: 1 to 1  

Analysis of Single Top Polarization using Parton Level Atlas samples  
Line: 22 to 22  
1. The schannel  
Changed:  
< <  At the LHC we collide protons with protons (unlike the Tevatron which collides protons and antiprotons). That means at the LHC we have a totally symmetric situation, that is the probability for our incoming antiquark to come in positive zdirection is as big as the probability to come in negative zdirection.  
> >  At the LHC protons are collided with protons (unlike the Tevatron which collides protons and antiprotons). That means at the LHC we have a totally symmetric situation, that is the probability for our incoming antiquark to come in positive zdirection is as big as the probability to come in negative zdirection.  
As we don't have information about the incoming antiquark we have to use the beamline as reference axis. This means have of the time, we assume the wrong direction, so we cannot expect to see a total polarization any more.  
Line: 55 to 55  
5. ONETOPsamples  
Changed:  
< <  Using ONETOP samples for the schannel that had been generated with the updated LHCcode, there was no information about incoming particles either, so that we get an offset here, too, which can simply be explained by the fact that half the time we guess the direction of the incoming antiquark wrong. IThis was tested by using the updated code, but with Tevatron setting. Here no offset was seen.  
> >  Using ONETOP samples for the schannel that had been generated with the updated LHCcode, there was no information about incoming particles either, so that we get an offset here, too, which can simply be explained by the fact that half the time we guess the direction of the incoming antiquark wrong. This was tested by using the updated code, but with Tevatron setting. Here no offset was seen.  
 SarahHeim  10 Mar 2008  
Line: 64 to 64  
 
Added:  
> > 
 

Line: 1 to 1  

Analysis of Single Top Polarization using Parton Level Atlas samples  
Line: 52 to 52  
Although half of the time we use the wrong direction of the antiquark, it is interesting to look at the schannel and see the degree of polarization as a function of the number of jets in our event.  
Changed:  
< <  
> >  
5. ONETOPsamples  
Added:  
> >  Using ONETOP samples for the schannel that had been generated with the updated LHCcode, there was no information about incoming particles either, so that we get an offset here, too, which can simply be explained by the fact that half the time we guess the direction of the incoming antiquark wrong. IThis was tested by using the updated code, but with Tevatron setting. Here no offset was seen.  
 SarahHeim  10 Mar 2008
 
Added:  
> > 
 
 
Deleted:  
< < 
 

Line: 1 to 1  

Analysis of Single Top Polarization using Parton Level Atlas samples1. Abstract  
Added:  
> >  I looked at polarization distributions of Atlas parton level samples in the Optimal/Spectator basis for the schannel and the tchannel. Trying to do this I ran into missing information and had to reconstruct quarks. This effects the polarization distributions, that is, it increases the offset, in a way that I haven't looked at quantitatively so far.  
2. Parton Level SamplesThe used parton samples are generated by AcerMC for the Atlas Single Top analysis. The parton level samples can be found in the Truth tree. This truth tree doesn't contain the initial particles, nor the spectator quark for the tchannel. This complicates things, as explained in the following.  
Line: 46 to 50  
The first method works as D is a ratio and using the actual number of N_{}/N_{+} we can simplify it by cancelling, so that we end up with the values at cos(θ)=1 and cos(θ)=1.  
Added:  
> >  Although half of the time we use the wrong direction of the antiquark, it is interesting to look at the schannel and see the degree of polarization as a function of the number of jets in our event.  
5. ONETOPsamples SarahHeim  10 Mar 2008
 
Added:  
> > 
 

Line: 1 to 1  

Analysis of Single Top Polarization using Parton Level Atlas samples  
Line: 7 to 7  
1. Abstract2. Parton Level Samples  
Changed:  
< <  The used parton samples are generated by AcerMC for the Atlas Single Top analysis. The parton level samples can be found in the Truth tree. This truth tree doesn't contain the initial particles, nor the spectator quark for the tchannel. This complicates things, as explained in the following.  
> >  The used parton samples are generated by AcerMC for the Atlas Single Top analysis. The parton level samples can be found in the Truth tree. This truth tree doesn't contain the initial particles, nor the spectator quark for the tchannel. This complicates things, as explained in the following.  
3. Optimal basis/ Spectator basis  
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Here is the result for the schannel, with a messed up Optimal basis that is effectively a beamline basis now and therefore not optimal any more.  
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2. The tchannelFor the tchannel we need the spectator quark, which isn't given in the Truth tree, either. So we have to use its jets to get information about the original direction of the spectator quark. The jets have a pdgid of 0 or 5, where 5 stands for the btagged jets. We use only events that contain two jets and use the one with a pdgid of 0. If we condider the fact that electrons can be misinterpreted as jets, we should use events with three jets and use the first jet that fullfills our requirements. Here is the result for the tchannel, spectator basis.  
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4. Degree of PolarizationThe degree of polarization is defined as D=(N_{}N_{+})/(N_{}+N_{+})  
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 SarahHeim  10 Mar 2008  
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Analysis of Single Top Polarization using Parton Level Atlas samples  
> > 
Analysis of Single Top Polarization using Parton Level Atlas samples  
1. Abstract2. Parton Level Samples  
Added:  
> >  The used parton samples are generated by AcerMC for the Atlas Single Top analysis. The parton level samples can be found in the Truth tree. This truth tree doesn't contain the initial particles, nor the spectator quark for the tchannel. This complicates things, as explained in the following.  
3. Optimal basis/ Spectator basisFor the Optimal basis (schannel) you have to take the incoming antiquark and the antilepton in the CMframe of the top quark.  
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For the Optimal basis (schannel) you have to take the incoming antiquark and the antilepton in the CMframe of the top quark.
The Optimal Basis in the schannel corresponds to the Spectator basis in the tchannel.  
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For the Spectator basis in the tchannel use spectator quark and the antilepton in the CM frame of the top quark.  
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1. The schannelAt the LHC we collide protons with protons (unlike the Tevatron which collides protons and antiprotons). That means at the LHC we have a totally symmetric situation, that is the probability for our incoming antiquark to come in positive zdirection is as big as the probability to come in negative zdirection. As we don't have information about the incoming antiquark we have to use the beamline as reference axis. This means have of the time, we assume the wrong direction, so we cannot expect to see a total polarization any more. Here is the result for the schannel, with a messed up Optimal basis that is effectively a beamline basis now and therefore not optimal any more.2. The tchannelFor the tchannel we need the spectator quark, which isn't given in the Truth tree, either. So we have to use its jets to get information about the original direction of the spectator quark. The jets have a pdgid of 0 or 5, where 5 stands for the btagged jets. We use only events that contain two jets and use the one with a pdgid of 0. If we condider the fact that electrons can be misinterpreted as jets, we should use events with three jets and use the first jet that fullfills our requirements. Here is the result for the tchannel, spectator basis.  
4. Degree of PolarizationThe degree of polarization is defined as D=(N_{}N_{+})/(N_{}+N_{+}) 
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Analysis of Single Top Polarization using Parton Level Atlas samples  
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< <  The first method means you just take the number of events at the left and right corner of the histogram (cos(&sigma)=1 and cos(&sigma)=1 respectively).  
> >  The first method means you just take the number of events at the left and right corner of the histogram (cos(θ)=1 and cos(θ)=1 respectively). In the second method you actually count events and plug the total number of events with negative/positive polarized tops. This requires a fit. The first method works as D is a ratio and using the actual number of N_{}/N_{+} we can simplify it by cancelling, so that we end up with the values at cos(θ)=1 and cos(θ)=1.  
5. ONETOPsamples 
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Analysis of Single Top Polarization using Parton Level Atlas samples  
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4. Degree of Polarization  
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< <  The degree of polarization is defined as  
> >  The degree of polarization is defined as D=(N_{}N_{+})/(N_{}+N_{+}) where N_{} is the number of events with a negative polarized top and N_{+} is the number of events with a positive polarized top.  
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< <  D=(N_{N+<\SUB>)}  
> >  There are two ways to get the N_{} and the N_{+} from the histogram:  
Added:  
> >  The first method means you just take the number of events at the left and right corner of the histogram (cos(&sigma)=1 and cos(&sigma)=1 respectively).  
5. ONETOPsamples SarahHeim  10 Mar 2008 
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Analysis of Single Top Polarization using Parton Level Atlas samples  
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For the Spectator basis in the tchannel use spectator quark and the antilepton in the CM frame of the top quark. 4. Degree of Polarization  
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5. ONETOPsamples SarahHeim  10 Mar 2008  
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Analysis of Single Top Polarization using Parton Level Atlas samples  
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1. Abstract2. Parton Level Samples3. Optimal basis/ Spectator basisFor the Optimal basis (schannel) you have to take the incoming antiquark and the antilepton in the CMframe of the top quark.The Optimal Basis in the schannel corresponds to the Spectator basis in the tchannel. For the Spectator basis in the tchannel use spectator quark and the antilepton in the CM frame of the top quark. 4. Degree of Polarization5. ONETOPsamples  
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Analysis of Single Top Polarization using Parton Level Atlas samples  
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