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1st look at Forward Backward Asymmetry in Z ee Toy MC

1st look at Forward Backward Asymmetry in Z ee Toy MC. Samir Ferrag. electron. In Z* center of Mass. q*. q. qbar. positron. Introduction: FB asymmetry in EW interaction. Asymmetric distribution. Dilution at P-P collider. No access to the incoming quark direction

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1st look at Forward Backward Asymmetry in Z ee Toy MC

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  1. 1st look at Forward BackwardAsymmetry in ZeeToy MC Samir Ferrag

  2. electron In Z* center of Mass q* q qbar positron Introduction: FB asymmetry in EW interaction Asymmetric distribution

  3. Dilution at P-P collider No access to the incoming quark direction Assumption: The quark direction is the one of the Z boson (lep-lep pair) Fraction of the events with wrong q-direction Fraction of the events with wrong q-direction Mass dependence of the wrong assignment distribution because of PDFs Built Likelihood function in ROOT: L1D:  g=3/8(1+cos(theta)*cos(theta))+Afb*cos(theta). L2D:  g=3/8(1+cos(theta)*cos(theta))+Afb*(1-2*W(eta))*cos(theta)

  4. Check the Likelihood the first check is the fit routine: **************************************************** ************     Output of tarte.C     ************* Generated number of events:.........10000 Consider Wrong quark direction is:..FALSE Consider Cos(Theta*) cut is:........FALSE Consider the Eta cut is:............FALSE Number of events after cuts:........10000 perform a 2D fit (eta,theta*):......FALSE Generated Asymmetry Value = 0.6 Fitted Asymmetry Value    = 0.595675  ±   0.00877341 ****************************************************

  5. Dilution effect **************************************************** ************     Output of tarte.C     ************* Generated number of events:.........10000 Consider Wrong quark direction is:..< TRUE > Consider Cos(Theta*) cut is:........FALSE Consider the Eta cut is:............FALSE Number of events after cuts:........10000 perform a 2D fit (eta,theta*):......FALSE Generated Asymmetry Value = 0.6 Fitted Asymmetry Value    = 0.375652  ±   0.0117288 **************************************************** the fake quark direction introduce a dilution (or bias) of ~40% of the real asymmetry value.

  6. Correct by cut over rapidity I keep only the events above eta=0.8, **************************************************** ************     Output of tarte.C     ************* Generated number of events:.........10000 Consider Wrong quark direction is:..< TRUE > Consider Cos(Theta*) cut is:........FALSE Consider the Eta cut is:............< TRUE > Number of events after cuts:........5368perform a 2D fit (eta,theta*):......FALSE Generated Asymmetry Value = 0.6 Fitted Asymmetry Value    = 0.523719  ±   0.0136739 **************************************************** ~12% of dilution.

  7. Correct by cut over Cos(Theta*) cut at cos(theta*)=0.9 **************************************************** ************     Output of tarte.C     ************* Generated number of events:.........10000 Consider Wrong quark direction is:..< TRUE > Consider Cos(Theta*) cut is:........< TRUE > Consider the Eta cut is:............< TRUE > Number of events after cuts:........4573 perform a 2D fit (eta,theta*):......FALSE Generated Asymmetry Value = 0.6 Fitted Asymmetry Value    = 0.519499  ±   0.0159087 **************************************************** • no changed. • acceptance function is symmetric over cos(theta). (symmetric response of the detector in reconstruction of l+ and l-). • Likelihood normalisation independent of factor: NO NEED TO CUT OVER COS(THETA*). 

  8. 2D fit I try the 2D fit witout any cut: **************************************************** ************     Output of tarte.C     ************* Generated number of events:.........10000 Consider Wrong quark direction is:..< TRUE > Consider Cos(Theta*) cut is:........FALSE Consider the Eta cut is:............FALSE Number of events after cuts:........10000 perform a 2D fit (eta,theta*):......< TRUE > Generated Asymmetry Value = 0.6 Fitted Asymmetry Value    = 0.598073  ±   0.0144405 **************************************************** the dilution of the asymmetry is concelled and the result is not biaised.

  9. Likelihood accuracy 1D fit accuracy for 10, 100, 1000 events 2D fit accuracy for 10, 100, 1000 events

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