INSTR14 S.Filippov

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First Years of Running for the LHCb Calorimeter System

Sergey Filippov(Institute for Nuclear Research of RAS, Moscow)

on behalf of the LHCb collaboration

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LHCb experiment

- Single arm forward spectrometer: 1.9 < η < 4.9- Impact parameter resolution 20 μm for Pt> 2 GeV/c- dP/P from 0.4% at 5GeV/c to 0.6% at 100 GeV/c- Invariant mass resolution: ~22 MeV/c2 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

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LHCb calorimeters

Data from the calorimeters are especially important in physics analyses of:

radiative decays BK*γ, BSφγ, …;

decays with π0/η: Bπππ0, J/ψη, D0Kππ0, …;

decays with electrons: BK*e+e-…

The calorimeter system includes:

- Scintillator Pad Detector (SPD):

- 2.5X0 lead converter;

- Preshower (PS):

- Electromagnetic Calorimeter (ECAL):

- Hadronic Calorimeter (HCAL):

It provides:

• L0 trigger on high ET h, e±, γ

• Precise measurement of e±, γ energies

• Offline particle identification

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SPD & PS design

SPD

PS

Lead

Multi Anode PMT:

HAMAMATSU R7600 64 channels, 2x2 mm2

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

Outer

Inner

Middle

Segmentation: three zones- Inner – pad size 40x40x15 mm3

- Middle – 60x60x15 mm3

- Outer – 120x120x15 mm3

Projectivity between SPD, PS and ECAL

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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 X0 (1.1 λi);

• Module size 121.2 x 121.2 mm2;

• Photodetector PMT HAMAMATSU R-7899-20.

Test beam data:

- Light yield: ~3000 ph.el./GeV

- Energy resolution:

%9.0)(

)%108( GeVEE

E

Segmentation: - Inner, Middle and Outer zones;- Total of 3312 modules, 6016 cells;

ECAL resolutionTest beam data

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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;

- ~5.6λi – used as a trigger device;

- PMT HAMAMATSU R-7899, same as for ECAL

Segmentation: - 2 zones; - Inner (cells 13x13 cm2); - Outer (26x26 cm2). Total of 1488 cells, ~8.3x6.7 m2

Test beam data:

• light yield 105±10 ph.el./GeV

• energy resolution

)%(E

)%(Eσ 29

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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

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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.

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ECAL calibration The L0 trigger decision is based on Pt cut so the nominal sensitivity of ECAL cells is set depending on their (x,y) position: Emax(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 π0 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 π0 peak.

4. E/p calibration with electrons.

133±11

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ECAL calibration with π0

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 π0 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%.

π0 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 π0 width.

PSECALEM EEE

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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 π0 is low for mass distribution method.

E/p for electrons in ECALE/p for hadrons in ECAL2011 data

HV corrections

Annealingafter one month

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HCAL calibration

Absolute calibration is done with radioactive sources:• two 10 mCi 137Cs 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.

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Particle identification

Photon ID. Based on the following observables:

• energy deposition in PS;

• track matching χ2 (there should be no track pointing to the Calo cluster)

• clusters with and without SPD hits in front are treated separately.

Photon/merged π0 separation. At high pT (>3 GeV/c) ECAL energy depositions of both γ’s from π0 decay merge into a single cluster. The separation is based on cluster shape different for single and merged photons.

Mass resolution for resolved π0 – 8 MeV/c2, merged – 20 MeV/c2.

Electron ID. Combined likelihood fully based on real data distributions. Clean reference samples are available in data:

• pure electron/positron sample: photon conversion γe+e-;

• pure hadron sample: decay D0KπE/p EPS(MeV)

___ electrons in ECAL___ hadrons in ECAL

Track – ECAL cluster matching

Performance on data: ~4% misidentification rate at 90% efficiency

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LHCb Detector Operation

LHCb is running at a lower luminosity than ATLAS and CMS 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

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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 changesmake 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.

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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.

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Physics performance: Radiative decays

Nucl. Phys. B 867 (2013) 1-18

Measurement of the ratio of branching fractions B(B0→K 0∗ γ )/B(B0s→φγ)

Proceed through electromagnetic transitions b->sγ. Sensitive to extensions of SM.

Invariant-mass distributions of the (a) B0 → K 0∗ γ and (b) B0 →K 0∗ γ decay candidates.

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Physics performance: B0→J/ψω

Nucl. Phys. B 867 (2013) 547-566

First evidence of the B0→J/ψω decay (1.0 fb−1 @ √s = 7 TeV):

Invariant mass distribution for selected B0→J/ψω candidates.

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Physics performance: B0s→J/ψη(‘)

Nucl. Phys. B 867 (2013) 547-566

The ratio of the branching fractions of B0s→J/ψη and B0

s →J/ψη’ decays is measured to be

Invariant mass distributions for selected B0s→J/ψη(‘) candidates. The thin solid

orange lines show the signal B0s contributions and the orange dot-dashed lines

correspond to the B0 contributions.

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LHCb calorimeter upgradeIn 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)·1033 @√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.

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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.

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Thank you!

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BACK UP

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LHCb Trigger Organization

Hardware Level-0 trigger SPD multiplicity CALORIMETRY search for a highest ET object:

• ET (e±/γ) > 2.7 GeV; CALORIMETRY

• ET (hadron) > 3.6 GeV; CALORIMETRY

• pT (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.

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.