1. Physics with the LHCb calorimeter
Sergey Barsuk
Laboratoire de l’Accélérateur Linéaire, Orsay
on behalf of the LHCb calorimeter group
KIPT
The LHCb calorimeter comprises the scintillator pad detector (SPD), preshower (PS), electromagnetic Shashlyk type (ECAL) and hadronic Tile (HCAL) calorimeters, arranged in pseudo-projective geometry. All the four detectors follow the general principle of reading the light from scintillator tiles with wave-length shifting fibers, and transporting the light towards photomultipliers (25 ns R/O).
Scintillator pad detector and preshower consist of a 2.5 Xo layer of lead sandwiched between two planes of identical detectors, SPD and PS, 15 mm each. SPD/PS comprises a total of 2x6016 detector cells/R-O channels
Electromagnetic calorimeter employs Shashlik technology, has the volume ratio Pb:Sc = 2:4 (mm), and has a 25 Xo (1.1 λI) depth ECAL comprises a total of 6016 detector cells/R-O channels
Hadronic calorimeter is a Fe-Sc tile calorimeter, 5.6 λI depth, comprises 1468 detector cells/R-O channels
Scintillator tile
WLS fiber loops
End-cover
Lead plate
Scintillator
TYVEK
Front-cover
Scintillator + coiled fiber
Light from the tile is read-out by the WLS fiber curled in 3.5 loops in the deep groove of the tile
Inner Middle + Outer Modules
~48 cm
144 tile cells tile cells tile cells
WLS fibers of HCAL run along the tile edges. To improve LY, an Al mirror is made on the fiber end at the front side. The ECAL fibers penetrate the Sc/Pb stack perpendicularly and form a loop at the front side, thus maximizing LY.
SPD/PS and HCAL tiles are wrapped in the TYVEK paper. The ECAL tiles are sandwiched between TYVEK sheets; in addition tile edges are chemically treated, thus providing a high efficiency internal diffusive reflection.
Inner
module
16 cells
0.98 fibers/cm2 PS
SPD
Middle
module
The LHCb calorimeter has been installed in the LHCb experiment. Commissioning is ongoing.
HCAL
Outer
module
Lead
~12 cm
4 cells
0.98 fibers/cm2
1 cell
0.44 fibers/cm2
The calorimeter cells have been tested and pre-calibrated before the installation.
Aglobal= ( 0.46  )%
Alocal = ( 0.39  0.01 )%
Lateral uniformity from scan with 50 GeV e- X mm
ADC channels
Spread over the cell (Max.-to-Min.):
1.3% for e-beam parallel to module axis
0.6% for e-beam at 200 mrad
ECAL cell
SPD/PS light yield measured with cosmic particles: <LY> = 24 ph.e./MIP
ECAL Outer cell energy resolution: e- beam  E
SPD E
 (0.83  0.02)% 
 ((145  13) MeV)/E
(9.40.2)%
Pulse shape on 30 GeV e-beam for different layers in depth of HCAL
outer
middle
inner 1 2 3 4 5 6 E
GeV
25 ns pulse shaping
Response of all ECAL cells to cosmic particles is equal, cell-to-cell spread <8% (r.m.s.)
Cosmic data allow ECAL pre-calibration to 3% precision < 0.3% of cells rejected (outside 3σ)
6-th layer PS t
r.m.s. = 8.0%
r.m.s. = 5.3%
r.m.s. = 6.7% IN
MID
OUT
outer
LY = 3100 ph.e./GeV
LY = 3500 ph.e./GeV
LY = 2600 ph.e./GeV
middle
1-st layer
inner
Longitudinal scan with electron beam
±0.5%
24 hours
PMT stability corrected with pin diode
MIP position, ADC channels
HCAL
N ph.e.
Pre-calibration done with cosmic particles for SPD/PS and ECAL, and with 137Cs source for HCAL, x-checked using e/h TestBeam. Final calibration achieved with physics data, methods in preparation use ET flow, MIPs, electrons, πo iterative and analytical procedures. Goal is to achieve 1% ECAL mis-calibration at the start of LHCb.
Calorimeters will use LED light during empty LHC bunches to monitor the stability of the R/O chain during data taking. ECAL and HCAL use pin diodes to monitor LED stability. HCAL will also use 137Cs source driven through each tile center.
The LHCb calorimeter provides high ET hadron, electron, photon and πo candidates for the first level trigger, provides electron identification essential for the flavour tagging, and gives access to studies of B-meson decays with πo and prompt photons.
Combined electron identification from Calo (+ Cerenkov detector) information: efficiency ~95%, misidentification rate < 3%
γ reconstruction: 70% Xo before Calo => ~40% conversions before Calo: reconstruct convertion if<Magnet with tracker, if>Magnet as single cluster tagged by SPD hit
High energy πos are often seen as single ECAL clusters.
Prompt photons from radiative b->s(d)γ transitions:
CP-asymmetries, photon polarisations, … => NP in penguin loops
|Vtd|/|Vts| measurement:
Measurement of the angle  of the Bd unitarity triangle
Bo-> K*oγ,
Bos-> φγ,
ρo(ω)γ; 16 12 8 4
= ξ
Γ(Bo->ρo(ω)γ)
Γ(Bo->K*oγ)
Vtd 2
Vts
2 clusters
/o separation is essential
1 cluster
With 2 fb-1 (1 nominal year) of LHCb data:
time-dependent Dalitz analysis of 14k Bd -> π+π-πo events, S/B ~1
(probability of mirror solution ~15%,
for 10 fb-1 <1%)
ET(πo) (GeV/c)
Dedicated shower shape analysis allows to identify single cluster (merged) πos
Bd -> π+π-πo events
σ(MB) ~65 MeV/c²
<ε> = 53%
 = (97 )o +6 -4
merged, ~40%
resolved, ~60% BR
Events selected/2 fb-1
90% CL
Bo -> K*o γ
4 x 10-5
4 x 104
> 1.4
Bso -> φ γ
9 x 103
> 0.4
Bo -> ω γ
5 x 10-7 40
> 0.3