Cross section e + e - -> wp 0 -> p 0 p + p - p 0

A.De Santis Radiative Meeting 28/04/06

Cross section ee

Antonio De Santis

Simona Giovannella

A.De Santis - Radiative Meeting 28/04/06 2

Amplitude: how to measure BR()

2

0 1

D

mZEE

EPD

mA

D

m

f

g

EE f

2

'

2'

22

3

2

0

4

’

mEBE m 100

contribution in cross section could be represented as interference with continuum process Interference is parametrized by term (Z) at -resonace peak.

A.De Santis - Radiative Meeting 28/04/06 3

Amplitude: MC generatorAll term which differs for exchange between two 0’s or different charge must be summed. Resulting matrix element (M) could be expressed as modulus squared of current composed by two term(0’s permutation) each composed by tree terms ( charge)

20020M

J

(p2)

(p4)

(p1)

(p3)

)(),,,(),,,(),,,( 3241323412314200

0 pppppptpppptpppptGJ

)()()()(

)()(

)(),,,(

31441324133142214334

431

12

4321

ppppppppppppppp

ppDpPD

pPFppppt

Reference: hep-ex/9904024 v2

A.De Santis - Radiative Meeting 28/04/06 4

Analisys strategy

• Acceptance– One vertex at Interaction Point (IP)– Two tracks connected at vertex– Four neutral cluster with:

• Eclu grater than 10 MeV

• ToF compatible with prompt • |cos()| < 0.93

• Kinematic Fit• Fine selection:

– 2 < 50

– m/m

• Slice dataset in function of ECM

• Signal events counting (fit via HMCMLL) • Cross section fit

A.De Santis - Radiative Meeting 28/04/06 5

Data vs MC: 0 recoil mass

)(0 MeVM recoil

)(0 MeVM recoil

old MC

new test MC

)(0 MeVM recoil

Left side: data(2001+2002) fitted with old self-made MC production.Right side: data(2002) compared with new MC test production (100pb-1 all_phys LSF 0.2)

A.De Santis - Radiative Meeting 28/04/06 6

Data vs MC: cos()

][)cos( 0 inclusive

][)cos( 0 inclusive

][)cos( 0 inclusive

old MC

new test MC

Left side: data(2001+2002) fitted with old self-made MC production.Right side: data(2002) compared with new MC test production (100pb-1 all_phys LSF 0.2)

A.De Santis - Radiative Meeting 28/04/06 7

Data vs MC: cos(±)

)cos( )cos(

old MC

new test MC

Left side: data(2001+2002) fitted with old self-made MC production.Right side: data(2002) compared with new MC test production (100pb-1 all_phys LSF 0.2)

A.De Santis - Radiative Meeting 28/04/06 8

Data vs MC: M()old M

C

new test MC

Left side: data(2001+2002) fitted with old self-made MC production.Right side: data(2002) compared with new MC test production (100pb-1 all_phys LSF 0.2)

)()( MeVM )()( MeVM

A.De Santis - Radiative Meeting 28/04/06 9

Analysis Efficiency (MC)

ToTFineAcc 0.472 ± 0.005 0.894 ± 0.003 0.422 ± 0.006

A.De Santis - Radiative Meeting 28/04/06 10

Systematic errors: counting contribution

Source Weight (10-2)

L 0.5

Trg 0.4

Clu 0.7

Acc 0.3

ToT 1.0

Prelim

inar

y

Possible source of systematic error in counting:• Luminosity factor;• Trigger efficiency;• Clustering efficiency;• Resolution effect on acceptance cut.

All these effects are summed with counting fit error.

A.De Santis - Radiative Meeting 28/04/06 11

Cross section fit

Preliminary

0073.00948.0)(

011.0103.0)(

11.068.80

Z

Z

mFit result:

Radiative correction for the cross section are calculated through convolution with radiator function at fit level.

2

0 11

D

mZmEBE m

tot

count

L

N

intexp

A.De Santis - Radiative Meeting 28/04/06 12

Systematic errors: impact of fine cut and counting variable

sysstat

sysstat

sysstatm

Z

Z

006.0008.0095.0)(

004.0011.0103.0)(

08.011.068.80

Systematic errors are evaluated as r.m.s. of fit-parameter distribution

obtained varying value for angular coefficient B in cross section function

and varying counting-fit distribution.

A.De Santis - Radiative Meeting 28/04/06 13

• SPARE

A.De Santis - Radiative Meeting 28/04/06 14

Amplitude current term

Form factor

Inverse propagator

)()(

)()(

)()(

)(),,,(

3144132

4133142214334

431

12

4321

pppppp

ppppppppp

ppDpPD

pPFppppt