light jet energy scale determination with top events after rome workshop status

Light jet energy scale determination with Top

eventsAfter Rome Workshop status

D. PALLIN 15/12/05

D. Pallin TOP meeting DEc 2005 2

Rome Workshop Extract the light jet energy scale E parton -> E jet MC -> E jet recons no hypothesis on calib funtion jets > 40 GeV ; W sample from top sample 85%purity

Calibration function (Ejet) = Eparton / EjetAOD

Cone 04

EPa

rt /

E E

An example: Rome AOD (Ejet) = 1. to 1.1 ‘cone 04’


Rome Workshop Ingredients Constraint 1 Rq: angle well reproduced if jet masses used Constraint 2 : 1 and 2 have the same dependance in function of E ( f(E) ) give the correlation between all W mass reconstructed => Build MW distributions in function of E to keep correlation

each MW distrib gives <MW> (E)

<MW> (E) depends on calib

jeti

parti

iRECW

PDGW

EE

withEEMEEM )(),( 212121

MW

E


Rome Workshop Methods Use MW distributions in function of E Find best 1 and 2 such that <MW> (E) = MW

PDG(E)

=> 1/ 2 FIT <MW> (E) = MWPDG(E)

=> 2/ iterative method without fit


Iterative Method to extract the E scale Constraint R=1

compute R for k bins in E apply k factors on R and recompute R n times =>

jeti

parti

iWPDGW E

EwithMMR 21/

1 2k j j True nk k

n

R

E

AODW Recons.

No comb BKG


Iterative Method to extract the E scale

compute R for k bins in E apply k factors on MW and recompute R n times =>

jeti

parti

iWPDGW E

EwithMMR 21/

1 2k j j True nk k

n

E

EPa

rt /

E

E

EPa

rt /

E


Method1 Results after recalibration

Function found with any

‘a priori’ hypothesis

EPa

rt /

E

E

before

after

AOD4000 W Recons.No comb BKG

Mw


After Rome Workshop

Reduce known systematics

Try to get calibration below 40 GeV

try to explain the connections existing between the know systematics on calibration method and the observed Mtop dependence in function of Pt


Systematic 1 E_jet / E_part % E_parton MC calib=1


Systematic 1 E_jet / E_part % E_jet MC calib=1

!! No more calibrated ???

Bias is within 1% above 40 GeV

But need to be corrected

huge effect below 40 GeV


Systematic 1 Why ?

E_jet

E_parti i+1i-1

j

Ej=ai Epi overestimated

(E/Ep)j = Ej / (ai Epi) underestimated


Systematic 1 How to correct? origine of bias : purely statistical from : E shape+ E

resolution negligeable if resolution(E)<<E important when resolution(E)~E

Need to know shape and resolution Use full Top MC to extract bias Compute statistical function = corr_det

1;)1(

)(

*),0(1

j

i

i

ji

j

jj

binj

binj iiji

EpEpa

EpE

EpE

nGa


Systematic 1 E_part / E_jet % E_jet after bias correction E_jet =E_jet X corr_det

Corr_det Works for any generated resolution and E shape

Shape taken as the observed E shape


Effects on Mw MW

REC-cor = MWREC X sqrt(corr_det (E1) )

BUT additionnal effect (effect 2)

Mw MC calib=1Mw=79.93 ±0.08 GeV ;

470 MeV from the generated W mass


Effects on Mw (effet 2) Mw MC calib=1

)1)(1()cos1(2 2121rrMEEM PDG

jjW

• 1+r1+r2 almost gaussian, centered on 1

• r1r2 not linear, introduce a bias

• effect seen in SM group (Z resonnance) and computed recently by Kramner. Same as our result

• depends on E

• Alreaydy known effect but negligeable (0.5%) for our purpose

MeVM

Bias EW 4808

12


Effects on Mw (effect 1) Mw % E_parton MC calib=1


Effects on Mw (systematic 1) Mw % E MC calib=1

Meth1 on AOD: Calibration obtained is a convolution of calib X corr_det MW%Ejet , Ejet/Ep%Ejet distrib are flat MW%Ep , Ejet/Ep%Ep distrib no more flat

Same effect as on

Ejet/Epart

Same correction apply

MWrec

x corr-det is

flat in function of E

=> Same type of correction apply to correct MW in function of Pt cut

EPa

rt /

E

MW

Ejet

Ejet


Method 1 remove systematics Energy resolution and distribution needed

Good estimate of the shape given by Ejet shape E Resolution could be given by MW resolution

OR/AND from outside ( Z+jets) Suppose resolution and shape known :

Correct bias with fonction corr-det Apply method1 as previously result OK for E>40GeV Correlation found between calib and corr-det below

40GeV.


E resolution f rom MW width

MW /MW do not depend on calib use MW distributions for different Energy bins => Measure MW /MW in function of E Extract E/E from the constraint :

result is enough precise to be used in coor_det

2222

1

1 )()22

()2(

W

W

W

W

MM

EE

EE

MM


Conclusion for calib

to calibrate jets below 40 GeV, knowledge of E and E distributions are needed

Still possible to extract jet energy scale without using MC or calib function hypothesis

OR use MC apply E and calibration on partons find the best E and calibration reproducing the observed

MW %E and E distribution.


Mw and Mtop in function of pt cut

for the same reasons (effets from E and E distributions) Mw or Mtop % Pt cut are flat . No dependence Mw or Mtop % Ptjet cut are no flat. Huge effect on Mtop

Easy to handle for MW. Tricky for Mtop Mtop : use MC to get the Mtop value for a given Ecut

use measurement of E and calibration from MW for light jets find the best E and calibration for bjets reproducing the observed Mtop

%ptcut and ptb distributions. This


Mw and Mtop in function of pt cut

for the same reasons (effets from E and E distributions) Mw or Mtop % Pt cut are flat . No dependence Mw or Mtop % Ptjet cut are no flat. Huge effect on Mtop

Easy to handle for MW. Tricky for Mtop Mtop : use MC to get the Mtop value for a given Ecut To be tested

use measurement of E and calibration from MW for light jets find the best E and calibration for bjets reproducing the observed Mtop

%ptcut and ptb distributions. How sensible is the dependence to the b jet calib. Could we calib also b

jets form the Top ?

light jet energy scale determination with top events after rome workshop status

Documents

e epart e e epart

observed e

e shapeshape

e alreaydy

e mc calib

function of e fe

bias correction e

calib mw