1. Converted photons efficiency
Edwige
LAPP 18/12/2014

2. Introduction
The fraction of reconstructed converted photons depends on
The detector material
The reconstruction efficiency
In this study: focus on conversions from Downstream tracks
Downstream tracking
Depends on Velo tracks multiplicity
LHCb-INT : Reconstruction efficiency of DD K0s mesons (P.Owen, T.Blake)
Tracking meeting 6/11/2014: Data driven reconstruction efficiency of K0S (Eluned Smith)
Material description:
LHCb-INT : Study of VELO material description with hadronic interactions
LHCb note : Estimation of the material budget of the LHCb detector (M.Needham, T. Ruf)
Problem of SPD multiplicity: are the secondary interactions not well modeled?

3. Downstream tracking LHCb-INT2013-051 :
Ratio of DD/LL Ks depends on nVELO tracks:
Due to Dwonstream tracks wrongly upgraded to Long
Downstream efficiency measured with KS with
reweighting according to nVeloTracks
 Data/MC~0.95 (raw) – Data/MC=1 (with reweighting)
!! KS vertexing is responsible for most
of Data/MC disagreement !!

4. K0S reconstruction efficiency
Tracking meeting 6/11/2014: Data driven reconstruction efficiency of K0S (Eluned Smith)
10<P<20, 2.0<  <3.2
20<P<40, 3.2<  <5.0
0.7

5. Material before magnet
LHCb note :
Uses DC06 description
Material up to z=930cm

6. Principle of the measurement
Measure the ratio of number ee to the number of CALO
 measure of conversion probability x reconstruction efficiency as a function of pT and 
(pT,)=N(ee )/N(CALO)
Compare data to MC using minimum bias events – 2011 data
MC: Event type Sim08c – Reco 14 stripping20r1
Data: Reco14 stripping 20r1
Trigger: Hlt1L0AnyRateLimitedDecision and use only L0DiMuon,L0Muon trigger and L0Hadron to avoid bias from CALO clusters (trigger independant of our signal)

7. Selection All: acceptance cuts 2.25<  <4.5
Remove inner and outer edges for cleaner sample:
(abs(gamma_PX/gamma_PZ)> || abs(gamma_PY/gamma_PZ)>0.025) && abs(gamma_PX/gamma_PE)< && abs(gamma_PY/gamma_PE)<0.24
Remove plane y=0 and outer edge to remove electron background:
abs(gamma_PY/gamma_PE)> &&
abs(gamma_PY/gamma_PE)<0.2 && abs(gamma_PX/gamma_PE)<0.2
Conversions:
Use here only Downstream pairs
Standard ee reconstruction and selection
combDLLe>0, gamma_IPCHI2_OWNPV<200,
Mee<100MeV/c and Mee-0.04*ENDVERTEX_Z<20 mm
CALO photons:
isNotH>0.3 (no cut on isNotE as bad agreement data/MC)
No / separation: most photons come from pi0 so better keep also merged pi0s + better efficiency

8. Efficiencies: CALO Efficiency of isNotH cut Background fraction
Electrons
others 5% 3% pT pT
isNotH cut distribution
isNotH: data less peaked at 0 and 1
Matching region ~0.4 =>Photon inneficiency underestimated by ~20%
Seems to be ~10% less background in data but tail might be different
Data MC
MC: true gamma

9. Efficiencies: ee
Efficiency of cut Mee-0.04*ENDVERTEX_Z<20 mm measured using c sample:
MC: /-0.5 % for all pT
Data: 600<pT<3000 : 2.3+/-0.5%

10. pT distributions Data vs MC: harder photons in data pT ee pT CALO
Resolution: does not affect the distribution for ee but does for CALO
 better do some unfolding
pT ee
- Data
- MC
pT CALO
- Data
- MC
pT ee
- MC true pT
- MC rec pT
pT CALO
- MC true pT
- MC rec pT

11. Unfolding pT CALO true pT CALO +MC rec unfolded + MC rec raw
- MC true
CALO
+data unfolded
- Data rec raw
rec pT

12.  distributions Example for 1300<pT<1700  ee  CALO - Data
- MC
 ee
- Data
- MC
Material budget for z<930cm from DC06
N(ee)/N(CALO)
- Data
- MC

13.  distributions Example for 1700<pT<2300  CALO - Data - MC
 ee
- Data
- MC
N(ee)/N(CALO)
- Data
- MC
Material budget for z<930cm from DC06

14. Efficiency results: (pT,)=N(ee )/N(CALO)
For nVeloTracks <60 and nSPDHits<600
2.25 <  < 2.5
2.5 <  < 2.75 MC
Data
2.75 <  < 3.0
3.0 <  < 3.25

15. 3.25 <  < 3.5
3.5 <  < 3.75
3.75 <  < 4.0
4.0 <  < 4.25

16. Ratio Data/MC 2.25 <  < 2.5 2.5 <  < 2.75
2.75 <  < 3.0
3.25 <  < 3.5
3.5 <  < 3.75
3.0 <  < 3.25

17. Ratio Data/MC 3.75 <  < 4.0 4.25 <  < 4.5
4.0 <  < 4.25

18. Dependance with nVeloTracks
3.0 <  < 3.25
80<nVeloTracks<160
nVeloTracks<80

19. Summary To do: Corrections for efficiency selection
Background subtraction
Improve unfolding to recover true pT distribution
Study dependance of results with multiplicities (nVeloTracks, nSPDHits)
Preliminary results:
Data/MC ~0.9 at low and high 
 consistent with Downstream tracking efficiency ~0.95
Data/MC ~0.82 for 3.0 <  < 3.75
 lack of material in MC in this region?