Converted photons efficiency Edwige LAPP 18/12/2014

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-INT2013-051: 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-2014-012: Study of VELO material description with hadronic interactions LHCb note 2007-025: Estimation of the material budget of the LHCb detector (M.Needham, T. Ruf) Problem of SPD multiplicity: are the secondary interactions not well modeled?

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 !!

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 Ks vertexing: D/MC~0.85-0.8 0.7

Material before magnet LHCb note 2007-025: Uses DC06 description Update in LHCb note 2008-054 No big changes Material up to z=270cm Material up to z=270cm DC06 July 2008

Selection All: acceptance cuts , SPD multiplicity 2.25<  <4.5 Remove most inner region for cleaner sample: (abs(gamma_PX/gamma_PZ)>0.03 || abs(gamma_PY/gamma_PZ)>0.025) Remove plane y=0 and outer edge to remove electron background: abs(gamma_PY/gamma_PE)>0.02 && abs(gamma_PY/gamma_PE)<0.2 && abs(gamma_PX/gamma_PE)<0.2 nSPDhits<600 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

DD vs LL: MC study Conversion in first part of Velo DD LL true Z <500mm DD LL Low : not enough hits to be reconstructed as Long, (especially if late conversion) => Downstream pairs High : the number of Velo hits is less dependent on the z of conversion => still LL pairs at end of Velo Conversion in 2nd part of Velo 500< true Z <900mm DD LL

DD vs LL Radiation length ( -  plane) (LHCb-2007-025) Conversion after Velo true Z >900mm DD LL VELO to RICH interface RICH

ee selection: LL MC 2011 LL pairs MC 2011 LL true gamma Fraction of events rejected by this cut: 13% in MC - 17% in data Background: combinatorics including misID (e) and 0ee ~55% are rejected by this cut

ee LL invariant mass: data/MC Distributions agree well 30% more pairs rejected by Mee vs Z_vertex cut in data Background: combinatorics inc misID (e) and 0ee 55% are rejected by Mee vs Z_vertex cut Remaining bkg in MC ~ 4%  5% in data Removed by Meevs Z_vertex cut -data -MC

ee DD invariant mass: data/MC Agreement less good than for LL: magnetic field uncertainties? Fraction of events rejected: 10% in MC 12 % in data Efficiency and background estimated with chi_c data Rejected by Mee vs Z cut -data -MC

Efficiencies: ee DD Efficiency of cut Mee-0.04*ENDVERTEX_Z<20 mm measured using c sample: inefficiency MC Data 600<pT<1300 : 1.9 +/-0.3% 1.3+/-0.3% 1300<pT<4000 : 2.2 +/-0.2% 1.8+/-0.3% Not passing cut With cut Data 600<pT<1300 Data 1300<pT<4000

Background in ee DD sample Cannot rely on MC truth information to check photon real ID: check on c MC In about 50% of the conversions 1 of the e+/- has TRUEID==0 Not good matching due to energy loss  worse Eres but good conversions TRUEID!= 11 or 0  negligible (0.3%) Gamma TRUEID==22 Gamma TRUEID==0 e+ TRUEID==11 , e- ==0 e+ and e- TRUEID==0 Check fraction of events in upper mass sidebands: - only real photons for TRUEID==22 - mix of real photons and background for TRUEID==0 Background fraction = 13% of the TRUEID==0 3.40.5% of the full sample No dependance with energy observed Gamma TRUEID==22 Gamma TRUEID==0 M(ee) (MeV)

DD vs LL Ratio of number of DD to LL conversions in Data and MC The agreement is pretty good except in 2 regions: LL -> DD migration due to Velo inefficiency badly reproduced in MC for late conversions? ? Velo-> RICH interface Slightly less material in MC?

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 300000000 - 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)

Efficiencies: CALO Efficiency of isNotH cut (MC) Background fraction Electrons others 5% 3% pT pT isNotH: data less peaked at 0 and 1 Matching region ~0.4 =>Photon inneficiency underestimated by ~20% Mostafa: D/MC agreement for cut isNotH>0.3 for pT>2.5GeV Seems to be ~10% less background in data but tail might be different Data MC MC: true gamma isNotH distribution

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

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

 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

 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

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

3.25 <  < 3.5 3.5 <  < 3.75 3.75 <  < 4.0 4.0 <  < 4.25

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

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

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

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?

50<nVeloTracks<80 2.75 <  < 3.0 3.0 <  < 3.25 3.25 <  < 3.5 3.75 <  < 4.0 4.0 <  < 4.25 3.5 <  < 3.75