Performance of the CLEO-III RICH Detector

Performance of the CLEO-III RICH Detector Syracuse University RICH 2004 Radia Sia For the CLEO-III RICH Group • Outline: • The CLEO-III RICH Detector • Physics Requirements • CLEO-III RICH at work…

CLEO-III Detector • Designed to study the decays of b and c quarks, τ leptons and Y mesons produced in e+e-collisions near 10 GeV cm energy. • CsI imposed hard • outer radial limit. • Excellent charged • particle tracking • imposed a lower • limit. • Low mass RICH: • ~13% of X0 at • normal incidence • SILICON Detector • Double sided, • r and z strips

LiF-TEA CLEO-III RICH

LiF-TEA CLEO-III RICH Consists of 3 components: • radiators: LiF radiator • expansion volume: Use pure N2 volume, 15.6cm thick to allow the Cherenkov angle to expand • expansion gap (15.7cm) • photon detectors: • MWPC: CH4+TEA as VUV photosensor (135-165 nm) • Charge induced on cathode pads, analog readout to measure photon position. • CaF2 windows Methane-TEA MWPC LiF radiator g CaF2 windows K/p g N2 expansion gap

Crystal radiators • Array of planar LiF crystals • Large refraction index (n=1.5 at 150 nm) ---> number of photons are internally reflected ---> “sawtooth” radiators implemented in the 4 central raws Flat Sawtooth Flat

Photon detectors Detection sequence: • g passes through thin UV transparent CaF2 window • Converted to single e by ionizing a TEA molecule. • single Photo-e drifts towards, then avalanches near the 20 um ø Au-W anode wires. • induces a charge signal on the cathode pads • Metallized traces at CaF2 window to act as electrodes

Physics Requirements on CLEO III RICH Design • Require>3σπ/K separation at 2.8 GeV/c from RICH (we will also get ~2σ from dE/dx above 2.2 GeV/c to give ~4σ total PID) • At 2.8 GeV/c:(θp-θK)=12.8 mrad • need σθtrk = 4 mrad per track • use multiple p-e per track, so σθtrk = σθpe /(Npe) • Design benchmarks: •  σθpe = 14 mrad, Npe = 12 pe/trk 1/2

Event Analysis • Look for photon hits within ±3s of the expected angle for each of 5 mass hypotheses (e, m, p, K, p) for every track • For each track find the most likely mass hypothesis • Do not allow photons which belong to the most likely mass hypothesis to be used by any other track • Recalculate PID quantities • Performance plots for hadrons are obtained on kaons identified kinematically via D*+D0p+, D0K-p+ • Combinatorial background subtracted by fitting D0 mass peak

Single Photon Resolution (Bhabhas) Flat Sawtooth Flat Sawtooth Radiators Flat Radiators Electrons P=5.2 GeV s=12.2 mrad s=14.7 mrad

Single Photon Resolution (hadrons) Sawtooth Radiators Flat Radiators Background 12.8% Background 8.4% s=13.2 mrad s=15.1 mrad Averaged over kaons with P>0.7 GeV

Photon Yield Sawtooth Radiators Flat Radiators Bhabhas) Bhabhas) Mean after Background subtraction 11.9 10.6 Hadrons Hadrons Mean after Background subtraction 11.8 9.6

Per Track Resolution Sawtooth Radiators Flat Radiators Bhabhas s = 3.6 mrad s = 4.7 mrad Hadrons s=3.7 mrad s = 4.9 mrad

Resolution per track: decomposition Sawtooth Flat Flat Measured Expected Tracking error Chromatic error Photon position error Emission point error

PID Likelihoods • There are some optical path ambiguities for Cherenkov photon (from the sawtooth radiator and from a track passing two radiators)  we chose the closest to the expected one when calculating per track Cherenkov angle There is some loss of information in this approach. use likelihood method to perform PIdentification. • The likelihood method weights each possible path by its optical probability Poptical: • which includes the refraction probability and the length of radiation path • Psignal is a Gaussian like function with asymmetric high tail (CBL) as seen before. • The likelihood folds in Cherenkov photon yield with Cerenkov angle measurements • for each hypothesis • The distribution of -2ln(Lp/LK) is expected to have the same behavior as c2K – c2p

PID Likelihoods: example • Log-likelihood-ratio distributionsfor1.0-1.5 GeVK’s and p’sidentified viaD*+a D0p+,D0a K-p+ K p

Integral K/π Separation & Efficiency vs fakes study At 90% efficiency, fake rate is 7% Kaons Pions

PID performance (1) Kaon efficiency = 0.80 = 0.85 = 0.90 B physics Pion Fake Rate CLEO-c

PID performance (2) Ds invariant mass from the Y(4S)data Without PID This year, we used The Ds meson yield, reconstructed through the decay mode: Ds  π,  KK from the Y(5S) and the Y(4S) data collected with the CLEO III detector to measure the: Br(Y(5S) Bs(*) Bs(*) ) which has never been measured before… D π # of Events / 2MeV Ds  π With PID Ds invariant mass (GeV)

RICH at CLEO-c Era e+ e-(3770) Tagged Side D+ D- D0 D0 Through hadronic channel -> Need particle ID to keep background low Signal Side, ex: Leptonic: D-> m n Semileptonic: Need electron ID, RICH is useful .. DATA K-p+ p+

Summary • CLEO LiF-TEARICH is providing us with excellent particle identification for all momenta relevant to the past beauty threshold data and present charm threshold CLEO–c data. • It was operating successfully for over 4 years (we made and are making extensive studies of the Upsilon, B and Bs decays). • Since last year, we used the detector for the CLEO-c program which is providing us with the Charm factory data to study decays of charm mesons and charmonium decays. The results went already for publication…

Backup slides

Efficiency vs fakes study K  K  mD0(GeV)/c2 2K 2 2K 2 x • cut on 2K2 • fit m(D0)

Efficiency vs fake rate For example at 85% efficiency, fake rate is ~13%

Momentum dependence line solid dashed dotted red 0.7-0.9 0.9-1.1 1.1-1.3 blue 1.3 1.5 1.5 1.7 1.7 1.9 line solid dashed dotted green 1.9 2.1 2.1 2.3 2.3 2.5 black 2.5 2.7 2.7 2.9 2.9 3.1

Momentum dependence Momenta 0.6-1.1GeV(red) 2.5-2.7GeV(blue)

Performance of the CLEO-III RICH Detector