A more realistic photon simulation in Geanfi

Capri 24-5-03, Kloe Phys Workshop III

Motivations:• A better description of shower simulation for photons and a “standard” recipe to recover the data-MC discrepancy needed to : - attain a 0.1% error on Ks 00

- measure rare Ks decays in neutral channels - parametrize response /resolution for Kinematic Fitting • Four main tasks : - selection of Machine background events - insertion of Machine background events in MC data - survey of existing data-MC discrepancy - correction-adjustment of MC simulation

By: C.Bloise, M.Martini, S.Miscetti, M.Moulson, T.Spadaro ...

S.Miscetti @ KPW3

Differences with last year bkg simulation (ACCELE + MBCKADD) Use a unique selection sample ( ee from FILFO) for evaluation of DCH, EMC, QCAL machine background ( bias found in mbckadd where the usage of L3BHA events was providing events already cleaned of out of time clusters ! )

Study side-bands (early/late) of T-R/c to measure rate of accidental events but extend the selection to the whole time spectrum & inserting hits for the 3 detectors at the same time. All correlations preserved. Closely follow the rate dependence along the run by selecting events of “same machine activity” in groups of few pb-1. The background is inserted in MC on a run by run basis.

Finally ... • BGG stream created! • Insertion in MC weighted with the effective cross section of BGG selector.

SELBKG & INSERT: basic ideas

S.Miscetti @ KPW3

Two clusters inthe barrel with: TW ( 5 T, 1 ns) Ecl > 480 MeV Etot > 960 MeV * cuts z cuts Vclu cut Etot (1+2) (MeV)

T (ns)

Still a lot ofmess in the“IN TIME”window

SELBKG : selection of golden events

S.Miscetti @ KPW3

T (ns)

R(cm)

Once “clean” clusters have been selected welook for all “residual”ones looking at allcombinations of DRijvs DTij between the“clean” and “residual”clusters.

() Flying clusters (shower fragments) splitted clusters

3 categories

SELBKG : looking for the machine bkg events

S.Miscetti @ KPW3

Fiducial region

After golden clusters selection & restricting the search to the fiducial region:

pieces of collision remain in the c0,c1,c2 bands for single hits.

comparing the E vs cos plot for early band and cj bands a set of 2D weights is found.

Nice agreement found in all distributions after applying these 2D weights

SELBKG : survey distributions after weighting tecnique

1 hit

1 hit

Early Times c0 c1 c2 bands

S.Miscetti @ KPW3

SELBKG : survey distributions after weighting tecnique II

S.Miscetti @ KPW3solid line (early-band) black dots (Cj bands)

C0

C0

C1

C2 C0,C1,C2

C1

C2C0,C1,C2

INSERT:two bugs found in TSKT &SmearT0 fixed last week: now times can be negativecorrection for att in EMC and space2time relation for DCH close to reality. overlap between accidental and MC hits tested at first order both for tracking &clustering

INSERT: inserting BGG events inside MC events• SELBKG technique applied to groups of few pb-1 to follow closely the machine activity along the run. • BGG stream DONE!

S.Miscetti @ KPW3

Tests of insert bgg done with MC PRE-Production• T-R/c behaviour with /without t0_finder:• enhancement 0 for bgg satisfying t0_finder !• otherwise correctly bunched

Tests to be done for post-production are:• energy slope • hits multeplicity• effects on Filfo • effect on rec.efficiency

INSERT: inserting BGG events inside MC events

S.Miscetti @ KPW3

EMC geometry closer to the real one (Barrel moved down inY of 1 cm) Survey of existing data-MC discrepancy done! Most of the checks based on sample. Other tests in progress with & Bhabha’s samples. A lot of differences data-MC found. Scale and Resolutions: - Energy resolution - Timing resolution - Non linearity of response - behaviour along cracks ( barrel , X EndCaps) - behaviour along Y ( attenuation lengths EndCaps) Shower shape - X0 simulation Light Yield - Ea/Eb - Efficiency ?

Toward a more realistic MC description of EMC

S.Miscetti @ KPW3

Energy response and resolution vs E

Data MC

5.7%/(E/GeV) 5.0%/(E/GeV)

Energy scale is set better in data than in MC. Still contained below 1% Non linearity better in data than MC (clufixene effect) Stoc.term in resolution much better in MC

S.Miscetti @ KPW3

DATA MC

Energy response vs

• Data show clear -cracks + calib error around = 0 S.Miscetti @ KPW3

Energy response vs MOD(,15)

• crack effect much more visible if shown vs mod(,15)S.Miscetti @ KPW3

Energy response & resolution: no crack vs crack zone

• As shown by profile there is a lowering in response in the crack. Integrating 1 degree around the crack the effect is of –2% in response (some energy dependence ?)• slightly worse resolution!

S.Miscetti @ KPW3

Reconstruction efficiency: no crack vs crack zone

• No effect on efficiency• data MC differ up to 70 MeV S.Miscetti @ KPW3

• Also on Endcaps cracks are visible along X.

• Moreover, there is a miscalibration of response along Y at a level of 3-4 %

Energy response in EndCaps: dependence vs Y

S.Miscetti @ KPW3

Shower Shape: measurement of the decay length (data)

• N(x) = N0 e(-x/) (1) with x the EMC depth.

• The distribution of the first plane fired fit with (1) in bins of as a function of E.

• E dependence of cross section as expected.

• “plateau” region E250 MeV

We derive• = 1.5 cm

• X0 = 7/9 1.2 cm

S.Miscetti @ KPW3

(degrees)

Shower Shape: measurement of the decay length (MC)

Following same description X0 1.5 cm (MC)

MC composition:23 cm with Pb/Sc slabs of0.11 cm (400 m/700m)

X0 = 1.53 cmFs(Mip) = 24%Fs(e.m.) = 14.5%

Same exercize on data: 200 planes of 500 m Pb

S.Miscetti @ KPW3

(degrees)

1/X0 = Fpb/X0pb+Fsc/X0

sc

Great agreement!

X0 = 1.2 cmEMC in MC too light!

Measurement of light yield (MC)

S.Miscetti @ KPW3

Two techniques used to get Npe

Gaussian fit to the distributions:• R = (Ea/Eb)• /S = (Ea-Eb)/(Ea+Eb)for Barrel cells fired @ Z=0.

Assuming fluctuaction tobe dominated by Poissonon Npe v = (2/Npe)

/S method more stable. • we get 1.2 pe/MeV in scint@ calorimeter center.• In agreement with light yield used in MC 25pe*0.145*0.33

(2./(1.2xE/MeV)) 0.11

(2./(1.5xE/MeV)) 0.12

Measurement of light yield (data)

S.Miscetti @ KPW3

Using same technique ondata sample we find Npe = 0.6-0.7/MeVi.e. 600-700 pe/GeV/side

50% of exp. light yield

- 20% drop due to B-field - estimated @ CRS using time resolution and (scint) - effect of light yield on energy resolution small. ( in operation we found less than

extrapolating from CRS and TB )

(2./(0.60xE/MeV)) 0.12

(2./(0.65xE/MeV)) 0.12

S.Miscetti @ KPW3

Measurement of time resolution (data)

• Usual numbers: - stoc. term 57 ps/sqrt(E/GeV) - const.term 140 ps• Stable since 1999• on MC - const.term 0 - stoc.term 50 ps/sqrt(E/GeV)

• much more light in MC still not a factor 2

E (MeV)

T-R/c (ns)

T(ns)

Radiation length on data 1.26 cm ( vs 1.53 cm MC) Light yield 0.6-0.7 pe/MeV (1.2 pe/MeV) Sampling fraction used in MC for showers 14.5 % Stoc.term of energy resolution lower in data than MC (5.7% vs 5.0 %) Not recoverable only with difference in Npe Stoc.term of time resolution 57ps (data) vs 50 ps (MC)

S.Miscetti @ KPW3

Summary review of information in our hands

• missing description of holes and behaviour along Y• reconstruction efficiency data lower than MC

Geanfi simulation was adjusted in many steps varying : 1) X0 lead thickness from 400 to 500 m 2) light yield lowered from 25 to 19 pe/MeV 3) adjusting sampling fraction in rec for each selected X0

4) fastening the Time emission distribution and recalibrating MC T0s for each choice. 5) constant term of 140 ps add

+Two new routines in MC path:• EMCSIMULA: Adding holes• CLUADJUST called in clufixene - fixing calib-hole and attenuation lengths

- flagging clusters to be killed to simulate obs.efficiency (only )

S.Miscetti @ KPW3

Adjustements done in MC and Reconstruction

S.Miscetti @ KPW3

Comparison old vs new MC ( fo ) events

• Barrel• Barrel holes• EndCaps

Resolution OK, holes ok bug found on EndCap .. now fixed

S.Miscetti @ KPW3

Old vs New MC: dependence along

S.Miscetti @ KPW3

Old vs New MC: dependence along X and Y

S.Miscetti @ KPW3

New MC: simulation of cluster efficiency for

MC meeting LNF 23-1-03 S.Miscetti @ KPW3

Conclusions

The new MC follows much more closely the details of cluster reconstruction and shower development in the EMC:

• energy and time resolution OK• Non linearity in response similar.• holes and other small details simulated• shower shape OK• inefficiency still a trouble. Forced imposing measured efficiency.• simulation of mach background OK for all detectors (much more tests expected for post-mc production

Slopes, rates of accidentals )• Much more testing also necessary on masses of neutral objects