Some discoveries
- ttbar correlation: 0 means flat in cosine distribution of the 2 angles. but combk means flat in angle distribution, so that not flat in cosine plne, but symmetry
Consideration 4 for non-bias
- The signal and the background mix with a fixed ratio in fast and full simulation in AcerMC 73%(576/788) and 74.8%(510/682). But not the same ratio in MCNLO 113.8%(2364./2078) and 105.3% (1883/1788)
- With MCNLO sample, the background effect doesn't make bias. The reason is background (combk and non-ttbar events) doesn't have correlation information and should have the same shape as MCNLO sample, so the different ratio of S/B should not affect
- A similar S/B in AcerMC should not bring effects from background.
Bias on measurement of A code
- As seen, using the correction function obtained in atlfast to apply on full simulation, the measurement on A is biased of around
.
- There are 3 type of calculation:
- dataI, based on truth infomation: no detector and cut effects
- dataII, based on atlfast measurement: ideal detector and cuts effects
- dataIII, based on atlfull measurement: realistic detector and cuts effects
- How to understand the bias and what makes the bias.
- cuts introduced
- resolution introduced
- statistics
- Considerations
- correlation between 2 measurements needs more statistics?
- other method for measuring?
- at least using correction function from full simulation for real measurement
- why effects are larger for product of 2 variables?
- correlation measurement need how good a resolution? When the resolution is worsen than a limit, the correlation will not be measured? Can I have
- If a large
need a large statistics for precise measurement of A. Can I have have
- Checks and conclusions
- divide the atlfast data into 2 part. Use the correction function got from part 1 on part 2. Check the bias, if no bias, means not statistical problem; if bias, means statistical problem.
the truth A=0.405, error 0.03 consistent with SM (with Mttba<550G)
use data "eventnumber even" to get the correction function and measurement with data "eventnumber odd":
A=0.48, error 0.23 (change to quality cut specially for atlfast, A=0.29, error 0.24 )
change the 2 parts of data:
A=0.43, error 0.22
means the correction function inside atlfast works well, the bias is not from statisticas only.
-
- the same can be done to atlfull
It's fairly bad, before correction, "eventnumber odd" A=-0.01, "eventnumber even" A=0.51
use data "eventnumber even" to get the correction function and measurement with data "eventnumber odd":
A=-0.84, error 0.23
change the 2 parts of data:
A=1.10 error 0.23
Means statistical problem in full simulation data.....?
More checks is done to distribution of reconstructed -9/0.51*cos\theta1*cos\theta2 for 2 parts of atlfull data directly without any correction.
The means are -0.02 and 0.51 respectively, error 0.21 for both.
If checks is done to their corresponding truth:
The means are 0.46 and 0.37 respectively, error are similar.
That means: for the small statistics, .
-
- Use dataI , for the truth cuts and atlfast reconstructed cuts, to check whether the resolution bias the cuts much. If yes, change to atlfull reconstructed cuts to see whether larger bias?
- Artificially put different resolution to truth (dataI), and different statistics, to see whether the correlation disappear without cuts and detector effects? how the angle resolution propogate to the final measurement, and makes needing more statistics. How the resolution bring errors on the final measurement? the resolution may be affect much collaberating with correction function.
- The correction function from atlfast may bring large uncertainty due to low statistics. The fact is the old correction function is from old atlfast with good statistics, means small uncertainty due to statistics. So the bias should not be from atlfast statistics.
- The atlfull data may have different composition in least energy jet (different ratio of quarks flavors), so different spin analyzer power , but the fact is there is no effect on Ad, so the effect should be not the reason of the bias.
- The fact that there is a slope on the ratio between the distribution of full and fast for different data, means the background is not the reason of the bias. but the slope is the reason, what makes the slope?
- the e event and muon events ratio are different for atlfast and atlfull. As known the e event and muon event have different results(not know why), this may be the reason of the bias. also atlfull has more jets means more combk?
this is not the reason.
1. we give a weight to e and mu events, to adjust them to the same ratio in atlfast as in atlfull. the measure still gives in atlfull A=0.84.
2. We have tried to correct efficiency function using the fact that reco efficiency for atlfast and atlfull are different, and the correction doesn't work at all to A.
* atlfull has more jets means more combk?
* should use different quality cut for atlfast and atlfull, to decrease the bias, because the event reonstruction (mass distribution) are different for them
Use MCNLO data,
1. which has no ttbar spin correlation, to see the

and

in 2D histogram, which has 2x2 bins. The results is the bin closed to (-1,-1) has events 45200 and the other 3 bins have 45900 events each.
2. To look at

, which is the mean of the distribution, in truth, it gives 0.005.
3. Use the correction function obtained from atlfast in the reconstruction level, the bias is 0.26.
4. If I take the cuts officially defined for T7 note and corresponding correction function, the bias is 0.36. The bias is same as study with
AcerMC data.
- MCNLO data (T7CSCnot selection) corrected with AcerMC atlfast corr_func red atlfast:
- correction with 2D efficiency::
- correction with from 2 angle efficiencies:
- efficiencies of the 2 anlges:
- 2D efficiency for full and fast:
- resoultion effects on distribution of angle 1D:
- resoultion effects on distribution of angle 2D:
*
AcerMC data (selection
T7CSCnote) corrected with it's corr_func from atlfast, red atlfast:
* to look at the ratio of distribution of

between full sim data and atlfast data. the data used are 3 types: semiemu; semiemu*goodlnb; semiemu*goodlnb*goodjjb and the distribution of ratios are similar and the bias on measurement of A is even larger. It means the background (tau events and cmbk) is not the reason of the bias.
-
- full over fast for costheta1costheta2 for 3 different data : semiemu. semiemu*goodlng, semiemu*goodlnb*goodjjb:
-
- without quality cut, full over fast for costheta1costheta2 for 3 different data : semiemu. semiemu*goodlng, semiemu*goodlnb*goodjjb::
- for truth
, the events are reserved only if on the reconstruction level, the event is reconstructed. This is to remove the resolution effect. we see that
- the bias is very small <0.05
- if we cut the \|Mwjj-Mw\|<20000, we got bias of 0.15. To change Mw to as measured 80.5 for atlfast and 83.5 for full sim, then the bias is smaller as 0.08. which means the cut result in different events for atlfast ans atlfull, resulting in bias.
- if we cut the \|Mlnb-Mt\|<35000, we got bias of 0.12. To change Mt as measured 172 for atlfast and 173.3 for atlfull. bias doesn't change.
- if we cut the \|Mjjb-Mt\|<35000, we got bias of 0.07. To change Mt as measured 172 for atlfast and 177 for atlfull. bias is 0.06
- if we cut the pt_n/pt_miss>0.99, we got bias of 0.26. if cut pt_n/pt_miss>0.9, bias 0.29, if cut pt_n/pt_miss>0.6, bias 0.03. This cut makes big difference as in the following plot
- et shrink when reconstructing wln:
- cut effect to costheta1*costheta2:
- cut effects on costheta1_true*costheta2_true:
- correction with 2D efficiency:
- correction with from 2 angle efficiencies:
- efficiencies of the 2 anlges:
- 2D efficiency for full and fast:
- resoultion effects on distribution of angle 1D:
- resoultion effects on distribution of angle 2D: