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Ricardo Vázquez Gómez (UB/ICC) on behalf of the LHCb calorimeter group

Commissioning of the Scintillator Pad Detector of LHCb with cosmic rays and first LHC collisions. Ricardo Vázquez Gómez (UB/ICC) on behalf of the LHCb calorimeter group. Outline. Introduction : the LHCb calorimeter SPD commissioning Time alignment Calibration Conclusions.

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Ricardo Vázquez Gómez (UB/ICC) on behalf of the LHCb calorimeter group

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  1. Commissioning of theScintillatorPad Detector of LHCbwithcosmicrays and first LHC collisions Ricardo Vázquez Gómez (UB/ICC) onbehalf of theLHCbcalorimetergroup

  2. Outline • Introduction: theLHCbcalorimeter • SPD commissioning • Time alignment • Calibration • Conclusions CALOR 2010, May 10-14, IHEP, Beijing

  3. Introduction: theLHCbexperiment • Single-arm forward spectrometer • Acceptance 10-250 mrad (V)/ 10-300 mrad (H) 1.6 < η < 4.9 PID RICH-1, RICH-2 Calorimeter SPD, PS, ECAL, HCAL Muon chambers Interactionpoint VELO Tracking system TT+IT+OT CALOR 2010, May 10-14, IHEP, Beijing

  4. TheLHCbcalorimeter • ScintillatorPad Detector (SPD): • Contributestothefirstlevel of trigger (L0 at 40 MHz) by: • Photon/Electronseparation • Multiplicity veto • Multiplicityused in 2009 & 2010 collisions as minimumbiastrigger. • PreShower Detector (PS): • Separation of electrons, photons and π0 fromhadrons at the L0trigger • Offline PID forelectron and photon X ~ 7m Y ~ 8.5m HCAL SPD/PS γ ECAL e+/e- Scintillator lead 2.5 X0 ECAL&HCAL: talkby Irina Machikhiliyan PS: talkbyValentinNiess CALOR 2010, May 10-14, IHEP, Beijing

  5. The SPD detector • Layer of 6016 scintillatingplasticcells. • 1.5 cm thickness. • 3 regionswithdifferentgranularity at differentdistancestobeam line. • Read-outby 100 64-channel MAPMT coupledto a single Very Front End (VFE). • Electronicsapply a binarydiscriminationnon standardenergy-basedcalibration and time alignment. • Pre-calibration of thresholdbasedoncosmicrays and test bench (offset, nphe, electronicsgain, HV gain). Energy deposition: log scale! MIP peak Threshold Background CALOR 2010, May 10-14, IHEP, Beijing

  6. Time alignment CALOR 2010, May 10-14, IHEP, Beijing

  7. Objective and method • Findthedelaythatmaximizesthenumber of hits in thecollisionbunchcrossing (T0) and has nothingbefore (Prev1). • Delaysonlyappliedbygroups of 64 channels (VFE). • LHCbtriggerallowstoreadoutconsecutivebunchcrossings. LHCbpreliminary Prev1 T0 Next1 CALOR 2010, May 10-14, IHEP, Beijing

  8. Cosmicrays • AlthoughLHCb has NOT theoptimalshapetotakecosmic data more than 1.5M eventswererecorded. • Usingtheenergydeposited, we can define a trackonlywiththecalorimeter. Cosmic track CALOR 2010, May 10-14, IHEP, Beijing

  9. Results With 7 TeV collisions With cosmics • Cosmic results provided an excellent starting point. SPD used as Minimum bias trigger. • Minimum bias trigger. • Timing is wrt LHC beam. • Half of SPD kept as trigger while scanning with different delays the other half. • Triggering on ECAL & HCAL coincidence. • Arrival time wrt integration provided by ECAL & HCAL. LHCbpreliminary Statisticalprecision of ~0.5 nswith 1M cosmicevents. Delaysimplemented in October 2009. Statisticalprecision of ~0.5 nswith 1M cosmicevents. Delaysimplemented in April 2010. CALOR 2010, May 10-14, IHEP, Beijing

  10. Calibration CALOR 2010, May 10-14, IHEP, Beijing

  11. Calibrationstrategy • SPD efficiencytodetectchargedparticlesis a function of thethreshold. • Can bemeasured as: • Studytheefficiency as a function of thethresholdvalueforallcells. Compare withthetheoreticalexpectation. • Electronicresolutionforsettingthevalue of thethresholdvalueis5% of EMIP. This sets ourobjectiveresolution. ε = # hits with a track in a cell / # total tracks in thecell Theoreticalefficiency ε = Landau x Poisson Fluctuations of nphe at photocathode. Energyloss CALOR 2010, May 10-14, IHEP, Beijing

  12. Cosmicrays • Cosmicselectioncriteriabasedon ECAL and HCAL signal: • Cosmicarrival time centered in theintegration time window. • Selectonlylowangletrackswrtto perpendicular toavoidexcessiveionization. • Take data at thresholdvalue of 1 EMIP . • Duetolimitedstatistics, onlyanefficiency per VFE wasextracted. • Cells in thesame VFE share HV valuesame global correction. • Averagedeviationshowedthat pre-calibrationwascorrect up to 15%. CALOR 2010, May 10-14, IHEP, Beijing

  13. LHC collisions • Cellbycellcalibration can beachieved. • Take data at differentthresholdvalues (from pre-calibration) values and compare withthetheoretical curve. • Correctionsextractedfromfittingtheobservedefficiency vs thresholdtothetheoreticalexpectation. • Efficiency at 0.3MIP measuresplateauefficiency (convoluteseffects of misalignment and ghosttracks). LHCbpreliminary Experimental efficiency for a typical cell CALOR 2010, May 10-14, IHEP, Beijing

  14. Results • Using ~12M ppcollisions at √s = 7TeV fromApril 2010. • Currentfittedvalues show a dispersion of 9.7% and central value shows no significantbias. • Verypreliminaryresults. Includecellsnotyet in theefficiencyplateau. • Thiscorrectionswillbeapplied in the hardware forfuture data taking. LHCbpreliminary CALOR 2010, May 10-14, IHEP, Beijing

  15. Conclusions • The SPD detector isfullyoperational. • Cosmicraysprovided a goodstartingpointfor time alignment and definedthestrategyforcalibration. • Fine time alignment has beenachievedwithcollision data with a precision of 0.5 ns. • The SPD cellintercalibrationis as good as < 10%. • Final correctionswillbesoonappliedtoachievedtheoptimal performance. CALOR 2010, May 10-14, IHEP, Beijing

  16. BACK-UP CALOR 2010, May 10-14, IHEP, Beijing

  17. Time alignmentasymmetry Zerocrossingpointgivesthedelaythat has tobeapplied in theelectronics CALOR 2010, May 10-14, IHEP, Beijing

  18. Calibration: trackdefinition • Collisions • Use LHCb tracking system • Cosmics • Use ECAL & HCAL deposits: • Selectlowanglewrt perpendicular CALOR 2010, May 10-14, IHEP, Beijing

  19. Calibrationcosmic vs collisions Efficiencies at 1MIP are compatible betweencosmics and collisions. 10-15% dispersionwrtperfectcalibration. CALOR 2010, May 10-14, IHEP, Beijing

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