1. 27/02/2014 INSTR14 S.Filippov1 First Years of Running for the LHCb Calorimeter System Sergey Filippov (Institute for Nuclear Research of RAS, Moscow) on behalf of the LHCb collaboration

2. 27/02/2014 INSTR14 S.Filippov2 LHCb experiment - Single arm forward spectrometer: 1.9 < η < 4.9 - Impact parameter resolution 20 μm for P t > 2 GeV/c - dP/P from 0.4% at 5GeV/c to 0.6% at 100 GeV/c - Invariant mass resolution: ~22 MeV/c 2 for two-body B decays JINST 3 S08005 (2008) Main subsystems: - Vertex detector – Si strips - RICH1 – aerogel, C4F10 - Tracking stations – Si strips - Warm magnet - Inner tracker – Si - Outer tracker – straw tubes - RICH2 – CF4 - Calorimeter – ECAL, HCAL, preshower - Muon stations – MWPC, GEM Purpose: CP violation and rare decays study

3. 27/02/2014 INSTR14 S.Filippov3 LHCb calorimeters Data from the calorimeters are especially important in physics analyses of: radiative decays B  K*γ, B S  φγ, …; decays with π 0 /η: B  πππ 0, J/ψη, D 0  Kππ 0, …; decays with electrons: B  K*e + e - … The calorimeter system includes: - Scintillator Pad Detector (SPD): - 2.5X 0 lead converter; - Preshower (PS): - Electromagnetic Calorimeter (ECAL): - Hadronic Calorimeter (HCAL): It provides: L0 trigger on high E T h, e ±, γ Precise measurement of e ±, γ energies Offline particle identification

4. 27/02/2014 INSTR14 S.Filippov4 SPD & PS design SPD PS Lead Multi Anode PMT: HAMAMATSU R7600 64 channels, 2x2 mm 2 VFE board One layer of scintillator pads each. ~6 x 8 meters, 6016 x 2 channels. Light collection with embedded WLS fibers. Light yield ~25 ph.el. per MIP. Inner Middle Outer Inner Middle Segmentation: three zones - Inner – pad size 40x40x15 mm 3 - Middle – 60x60x15 mm 3 - Outer – 120x120x15 mm 3 Projectivity between SPD, PS and ECAL

5. 27/02/2014 INSTR14 S.Filippov5 ECAL design Shashlik technology: 4 mm thick scintillator tiles interleaved with 2 mm thick lead plates; Volume ratio Pb:Sc 2:4 Moliere radius ~ 35 mm; Length ~25 X 0 (1.1 λ i ); Module size 121.2 x 121.2 mm 2 ; Photodetector PMT HAMAMATSU R-7899-20. Test beam data: - Light yield: ~3000 ph.el./GeV - Energy resolution: Segmentation: - Inner, Middle and Outer zones; - Total of 3312 modules, 6016 cells; ECAL resolution Test beam data

6. 27/02/2014 INSTR14 S.Filippov6 HCAL design ATLAS TileCal technology: - Iron/scintillator plates parallel to the beam direction; - The volume ratio Fe:Sc ~ 16:3; - Instrumented depth: 1.2 m, 6 tile rows; - ~5.6λ i – used as a trigger device; - PMT HAMAMATSU R-7899, same as for ECAL Segmentation: - 2 zones; - Inner (cells 13x13 cm 2 ); - Outer (26x26 cm 2 ). Total of 1488 cells, ~8.3x6.7 m 2 Test beam data: light yield 105±10 ph.el./GeV energy resolution

7. 27/02/2014 INSTR14 S.Filippov7 Readout electronics - Large fluctuation of signals → maximal integration time within 25 ns slot; - VFE board: two integrators per r/o channel alternating each 25 ns; - 100 Front-End Boards (FEBs): - Combines 64 ch SPD + 64 ch PS; SPD: 1 bit signal (yes/no, 0.5 MIP thr) PS: 10-bit ADC 40 MHz – Parameters for pedestal subtraction, corrections for pile-up and gains; – Digital pipe-line to store data until L0 decision – Trigger block: production of data for L0 trigger. SPD/PS - PMT signal clipping to eliminate a tail beyond 25 ns; - 192 Ecal + 54 Hcal FEBs; - FEB: 32 ch, same for ECAL and HCAL; –12-bit ADC 40 MHz (80 pC full range); – Pedestal subtraction; – Digital pipe-line to store data until L0 decision; – Trigger block: production of data for L0 trigger. ECAL/HCAL

8. 27/02/2014 INSTR14 S.Filippov8 SPD & PS calibration Calibration of SPD is done via threshold scan: the nominal threshold corresponds to ~0.5 MIP; precision on correction factors ~3% for MIPs; efficiency after calibration ~95% with 3% r.m.s. Nominal sensitivity is set to ~ 300 MeV max. the inter-calibration of cells is based on the position of the MIP peak; precision ~5%. The calibration is performed using tracks pointing to a given cell.

9. 27/02/2014 INSTR14 S.Filippov9 ECAL calibration The L0 trigger decision is based on P t cut so the nominal sensitivity of ECAL cells is set depending on their (x,y) position: E max (θ)=(7+10/sin(θ)) GeV. The ECAL calibration was performed in several steps: 1. Pre-calibration before the startup of LHC. Based on PMT gain measurement with LED monitoring system; precision of ~8%. Overall cell-to-cell intercalibration precision ~13%. Clear π 0 signal was observed right after the LHC startup. 2. “Energy flow” method: for each cell the correction factor is derived from comparison of its average energy deposit per event to that in neighboring cells. Does not require high statistics (~1 M events), was performed shortly after the LHC startup. Precision of ~4-5%. 3. Fine calibration using position of the π 0 peak. 4. E/p calibration with electrons. 133±11

10. 27/02/2014 INSTR14 S.Filippov10 ECAL calibration with π 0 For each cell distribution of the invariant mass of two photons is filled for γγ pairs with centre of one of γ’s cluster at this cell. The correction factor for a cell is determined from the deviation of fitted π 0 mass from the PDG value. Only a subsample of clusters with low energy deposition in PS (<10 MeV) is used at this step. The procedure is iterative, 5-6 iterations. To calibrate all cells, ~100M events is needed. Performed every month, that corresponds to ~200 pb -1 of data. Precision ~1-2%. π 0 decays with converted or non-converted photons are used to find the absolute normalization scale (“β-factor”) for PS. The EM shower energy is calculated off- line as Both α and β being dependent on the shower position and origin (e - or γ). The correction is determined in ECAL + PS calibration by minimizing the π 0 width.

11. 27/02/2014 INSTR14 S.Filippov11 ECAL calibration: E/p Another method to monitor or correct the ECAL cell calibration is through electron E/p. Electrons are identified by estimation of the momentum of the extrapolated tracks and energy of the matching clusters. Used to monitor ageing with applying aging trend corrections every 40 pb -1. Useful when statistics of π 0 is low for mass distribution method. E/p for electrons in ECAL E/p for hadrons in ECAL 2011 data HV corrections Annealing after one month

12. 27/02/2014 INSTR14 S.Filippov12 HCAL calibration Absolute calibration is done with radioactive sources: two 10 mCi 137 Cs sources (one per each detector half) driven by hydraulic system (the same as in ATLAS TileCal) a source propagates consecutively through 26 modules passing each scintillator tile. PMT anode currents are measured every 5 ms with dedicated integrators installed at the back of each phototube; the response of each individual tile can be determined from analysis of currents. The average current of all the tiles of a cell is proportional to the cell’s sensitivity to hadrons; the absolute scale was determined at beam tests before the LHC startup, and then verified with data; precision is 3-4% r.m.s.; calibration is performed on the regular basis (every 1÷3 months) during technical stops. LED monitoring system is used to control HCAL response during data taking.

13. 27/02/2014 INSTR14 S.Filippov13 Particle identification Photon ID. Based on the following observables: energy deposition in PS; track matching χ 2 (there should be no track pointing to the Calo cluster) clusters with and without SPD hits in front are treated separately. Photon/merged π 0 separation. At high p T (>3 GeV/c) ECAL energy depositions of both γ’s from π 0 decay merge into a single cluster. The separation is based on cluster shape different for single and merged photons. Electron ID. Combined likelihood fully based on real data distributions. Clean reference samples are available in data: pure electron/positron sample: photon conversion γ  e + e - ; pure hadron sample: decay D 0  Kπ E/p E PS (MeV ) ___ electrons in ECAL ___ hadrons in ECAL Track – ECAL cluster matching Performance on data: ~4% misidentification rate at 90% efficiency

14. 27/02/2014 INSTR14 S.Filippov14 LHCb Detector Operation LHCb is running at a lower luminosity than ATLAS and CMS (4·10 32 cm -2 s -1 in 2012) using luminosity leveling technique. 2010 2011 2012 TDR, 14TeV: L=2.x10³² cm ⁻ ² s ⁻ ¹ with average number of interactions per event μ = 0.4 2012, 8 TeV: L=4.x10³² cm ⁻ ² s ⁻ ¹ with μ<=1.8

15. 27/02/2014 INSTR14 S.Filippov15 Aging of ECAL  0 mass variation as a function of time (luminosity) observed: The effect is cured by calibrating of ECAL: - changing of PMT HV; - fine calibration of each ECAL cell using  0 and adjusting its mass on a short period of data taking; - on top of fine-calibrated data trending coefficients are applied: If  0 statistic not high enough to follow closely the changes make use of photon conversion and look at E/p Two sources of degradation: - radiation demage of scintillator tiles and WLS fibers (~0.25 Mrad /year); - PMT sensitivity loss.

16. 27/02/2014 INSTR14 S.Filippov16 Aging of HCAL Light yield degradation can be corrected by -modifying PMT gain (HV) -calibration with Cs source runs + LED Lost of sensitivity for ECAL/HCAL PMTs 0 1 2 3 4 5 HCAL tile row Light yield degradation in the HCAL centre HCAL PMTs anode currents are 5 times more the for ECAL. Integrated anode currents are up to 100C. Gain reduction vs. integrated anode current was studied in the lab.

17. 27/02/2014 INSTR14 S.Filippov17 Physics performance : Radiative decays Nucl. Phys. B 867 (2013) 1-18 Measurement of the ratio of branching fractions B(B 0 →K ∗ 0 γ )/B(B 0 s →φγ) Invariant-mass distributions of the (a) B 0 → K ∗ 0 γ and (b) B 0 →K ∗ 0 γ decay candidates.

18. 27/02/2014 INSTR14 S.Filippov18 Physics performance: B 0 →J/ψω Nucl. Phys. B 867 (2013) 547-566 First evidence of the B 0 →J/ψω decay (1.0 fb −1 @ √s = 7 TeV): Invariant mass distribution for selected B 0 →J/ψω candidates.

19. 27/02/2014 INSTR14 S.Filippov19 Physics performance: B 0 s →J/ψη ( ‘ ) Nucl. Phys. B 867 (2013) 547-566 The ratio of the branching fractions of B 0 s →J/ψη and B 0 s →J/ψη’ decays is measured to be Invariant mass distributions for selected B 0 s →J/ψη (‘) candidates. The thin solid orange lines show the signal B 0 s contributions and the orange dot-dashed lines correspond to the B 0 contributions.

20. 27/02/2014 INSTR14 S.Filippov20 LHCb calorimeter upgrade In 2015-2017, LHCb is expected to take 5-7 fb -1 of data @13 TeV. There is strong physics case to continue the flavor physics programme. This requires running at higher luminosities: (1-2)·10 33 @√s = 14 TeV after 2018. For LHCb calorimeter system PS and SPD shall be eliminated (they mainly contribute to L0 trigger) DAQ @ 40MHz –Change in the readout electronics Lower PMT gain –Higher luminosity –Ageing Possibly replacement of few ECAL modules in hottest areas. LHCb Upgrade LoI: CERN-LHCC-2011-001 LHCb Upgrade Framework TDR: CERN-LHCC-2012-007 With the present trigger organization, 1 MHz L0 limit: for all the hadronic final states, no gain from increasing the luminosity. A fully software trigger is necessary to select desired final states.

21. 27/02/2014 INSTR14 S.Filippov21 Conclusions During the data taking in 2010 – 2012 LHCb collected ~3.2 fb -1 of physics data; The calorimeter system provided photon and electron reconstruction and input information for L0 decision perfectly well; Aging of PMT, scintillators is within expectations. Under control thanks to frequent calibration procedures.

22. 27/02/2014 INSTR14 S.Filippov22 Thank you!

23. 27/02/2014 INSTR14 S.Filippov23 BACK UP

24. 27/02/2014 INSTR14 S.Filippov24 LHCb Trigger Organization  Hardware Level-0 trigger  SPD multiplicity  CALORIMETRY  search for a highest E T object: E T (e ± /γ) > 2.7 GeV;  CALORIMETRY E T (hadron) > 3.6 GeV;  CALORIMETRY p T (μ) > 1.4 GeV/c;  up to 1 MHz output.  Software High Level Trigger (HLT):  ~30000 processes in parallel on ~1500 farm nodes.  Storage rate: 5 kHz.  Efficiency (L0+HLT):  ~90 % for di-muon channels;  ~30 % for multi-body hadronic final states – limitation from hadron trigger.

25. LHCb upgrade: electronics architecture Yu. Guz CHEF 2013 LHCb Calorimeter Upgrade Current: latency-buffer in FE, and zero-suppress after L0 trigger Upgrade: zero-suppress in FE, no trigger decision to FE, LLT in back-end.

26. 27/02/2014 INSTR14 S.Filippov26 B(B0s→J/ψη) B(B0s→J/ψη) = 0.90±0.09(stat)+0.06−0.02(syst).