Stefano Di Falco & Achim Denig Universität Karlsruhe The new pp g(g) Montecarlo and Report on the luminosity measurement KLOE Workshop Conca Specchiulla,

Stefano Di Falco & Achim DenigUniversität Karlsruhe

The new Montecarlo

and

Report on the luminosity measurement

KLOE Workshop

Conca Specchiulla, June 10th- 12th, 2002

S. Di Falco & A. Denig – Conca Specchiulla, June 10th -12th, 2002

2

selection for small angle

• Trigger

• FILFO/par=5

• PPGTAG (tracks, vertex, MTRACK,…)

• Pion fiducial volume: 40o < < 140o New!!

• Photon fiducial volume: 0o < < 15o New!!

• E >10 MeV (in fact cut on E)

• Likelihood

• MTRACK

DATA…MC


3

HADR and Montecarlo generators

The hadronic cross section measurements needs MC help in more steps:

• acceptance: is determined using the angular distribution and ‘’

• correlations between selection efficiencies (mainly FILFO)

• MTRACK cut: cuts on the tail due to the radiation of one or more ISR

Furthermore:

•Final state radiation and ISR-FSR interference: needs to be know only with

rough approximation in the small angle analysis

• Radiation Function: used to extract the pion form factor F from the M2

• Luminosity determination (BABAYAGA)


4

Montecarlo generators

ISR FSR me precision

EVA*(J.Kühn et al.)

+coll.rad. pointlike 0 ~2%

PHOKHARA*o

(J.Kühn et al.) NO 0 ~0.5%

AFRODITE*(F.Jegerlehner et al.)

pointlike F

0 ?

KKMC (e+eff+n)(S.Jadach et al.)

CEEX NO 0 (<0.2%)

* Interfaced with Geanfi oModified to impose cuts on the pp system instead of the s


5

Comparison Eva-Phokhara:

EVA doesn’t give the correct cross section for < 0.1o:

min= 0o now available! Higher , lower background, no smearing problems !


6

Comparison Eva-Phokhara: Q2

EVA was generating too many events at small angle, nonetheless the Q2 spectrum shape was correct:


7

Comparison Eva-Phokhara: smearing

Nonetheless the cut >5o was causing troubles especially at large Q2

because of the resolution on :

+10%

-10%

The discrepancy was due to the EVA, with PHOKHARA it’s no more present:

EVA

PHOKHARA+10%

-10%


8

Comparison Eva-Phokhara: TOT

ISR in EVA doesn’t include the vacuum polarizationand O(2) terms

The global effecton for large

is ~2% (flat in Q2)


9

Contamination from FSR

ISR radiation (PHOKHARA)TOT= 14.3 nb

FSR radiation (EVA) TOT= 0.03 nb

(~0.2%)

FSR

ISR+FSR

M2

%

• ISR photons are mostly emitted collinear to the e+e- beams (small angle) while the FSR ones prefer the pion direction.

At leading order = and then the cut: < 15o or > 165o

suppresses FSR when 40o < < 140o

(also +-0 background is suppressed)


10

Summary & Outlook on generators

A new Montecarlo, PHOKHARA, with O(2) ISR, is available and has been adapted to our experimental cuts and interfaced with Geanfi. It allows to lower to 0 the lower cut on the missing momentum (‘’) resolving the smearing problems and decreasing the impact of FSR and background

The work to include FSR in Phokhara is going on.

Results are waited also from Afrodite (Berlin-Cracow group) and KKMC (work not yet started) to evaluate the systematics as discrepancies of the different theoretical calculations.

A realistic multiphoton generator including FSR will be very important to perform the measurement at large angle needed to cover the low M

2 region.


11

Luminosity counters

Data

Trigger

EmCReconstruction

FILFO

LAB ( >45°)

Golden Bhabha ( > 25° including )

Trigger Luminosity(Bhabhas on Barrel)

DCReconstruction

GGL: > 45°)

DC - Events Selection: 2 Tracks from I.P. with opp. charge

First Hits > 50 cm separated 400 MeV < E+ - < 600 MeV

VLAB > 55°)

B and Energy calibrated

NO

NO

YES

YES

YES

EMC - Events Selection: 300 MeV < E+ - < 800 MeV, | TCL1 - TCL2 | < 4 ns, N Hits DC > 50,

cos( Acoll. (3d) ) < - 0.975

Effective(nb)

~ 800

~5700

~ 119

~ 800

~ 425


12

VLAB systematics

The luminosity is given as usual by: L = N / EFF where EFF is the theoretical cross

section evaluated from MC including the efficiencies for the selection cuts

MC-Data difference in:

1) Acceptance2) Efficiency3) Background contamination

Variations in time due to Running Conditions:

s , p , L-R asymmetries not const.,

Beam position not const. EmC - Calibration (DC?) Machine Background

Monitoring ToolHas been studied in the past: MC and Data distributions agree very well <1% level

The systematics of the measurement are given by :


13

Acceptance (checks)

TOTAL CROSS SECTION (CORNER REGION EFFECT? ): MC

MCDATA

o

o

o

o

o

o

N

N

N

N

N

N

40

55

40

55

40

55

= 0.2 0.5 %

%

e(degrees) e (degrees)

Relative difference


14

Efficiencies

Cluster Inefficiency:

Pmiss > 20 MeV| miss - 90o | < 35o

| Tcl | < 10 ns | Rcl | > 10 cm

additional Ncl = 0

“Tracking Inefficiency”:

Ncl=2Ntr=1

To be refined !

Data-MC: better than 1%

Data-MC: better than 1%

Monitoring…%

%


15

BackgroundLAB - Sample VLAB - Sample

LAB - Sample VLAB - Sample

Removed byE+- > 400 MeVCutAfter Likelihood

Before Likelihood

0.3 %

backgr.


16

Effect of run conditions: s

Suppose s = +1 MeV

Two effects:

• Change in Bhabha cross section:

-0.45 % L / L

• Change of the efficiency (95.65%) for

2 tracks with E + - >400 MeV

0.05 0.05 % L / L

L /

L %

Radiative Tail well described by Theory

BABAYAGA

GEANFI

Data


17

Effect of run conditions: beam position

Effect of a shift z=–1 cm of the interaction point on the cut on Polar Angle of Clusters

Corresponds to a left - right asymmetry = 1%

Variations in single bins reach ~2% but compensate each other…

VLAB(only barrel)

0.03 0.01 % L / L


18

GGLLAB

Additional infos on machine background

Mean value of not associated hits

Mean of Nclu

Mean of ETOT-E1-E2

Accidental rate inside+50 < T< +70 ns( T0= < t-l/c > )


19

Cross check VLAB – and GBHA

VLAB - GGL VLAB - GBH2002 dataRuns > 85nb-1

stat.error @ 100 nb-1: VLAB = 0.5% GGL = 1.0% GBH = 0.1%

= 0.3 %RMS = 1.0 %

= -2.8 %RMS = 0.6 %


20

Summary & Outlook (luminosity)

Error on Luminosity enters in our - cross section measurement as

absolute normalization Precision required: <= 1% ?!

VLAB sample is more stable and reliable than the previous LAB

Systematic error: - theoretical error estimated 0.5%

- no evidence for experimental effects larger than 1%

- agreement - VLAB ~0.3% (similar theoretical uncertainties)

In the latest version VLAB selection includes the monitoring of many variables

useful to determine the quality of the run (and eventually discard the bad ones)

• Works in progress:

• description of hard Bremsstrahlung, ….

• Cross check of Lumi-Bhabha-measurement by looking at - data

Stefano Di Falco & Achim Denig Universität Karlsruhe The new pp g(g) Montecarlo and Report on the luminosity measurement KLOE Workshop Conca Specchiulla,

Documents

denig conca specchiulla

cut q g

p miss

pointlike p

e s likelihood

eva phokhara

q g correlations

s tot isr