A Reconstruction Algorithm for a RICH detector for CLAS12 Ahmed El Alaoui RICH Workchop, Jefferson Lab, newport News, VA November th 2011

Outline  Motivation  Detector Design  Reconstruction algorithm  Unfolding  Conclusion 2 Ahmed El Alaoui RICH Workshop, Jefferson Lab, Newport News, VA 11/16/2011

Motivation 3  The feasibility of the Jlab physics programs dealing with kaons in the final state requires a good detection system capable of identifying kaons with high efficiency and low contamination in a broad momentum range.  Particle Identification system used by CLAS12 (TOF, LTCC, HTCC) does not allow for a good identification/separation between π/K/p in the whole GeV/c momentum range - Reliable kaon identification is only possible for momentum up to 2.5 GeV - For momentum range GeV/c kaon identification depends on LTCC performance - In the momentum region 4-8 GeV/c it is not possible to separate between kaons and protons RICH detector is needed to improve CLAS12 PID

RICH performance 4 Ahmed El Alaoui RICH Workshop, Jefferson Lab, Newport News, VA 11/16/2011 General rule: minimize   C and maximize N pe The separating power: Usually N o between ~ 20 and 100 The number of photo-electrons N pe : The angular resolution per photon:, N 0 = N∫(QTR)dE

RICH simulation 5 Ahmed El Alaoui RICH Workshop, Jefferson Lab, Newport News, VA 11/16/2011 Requirements: - Fit inside the available Area (124 cm) -Operate in a high rate environment and in the presence of a Magnetic field - Reasonable cost - Low material budget to minimize impact on CLAS12 performance A full simulation was developed in order to optimize: - the aerogel thickness - the aerogel refractive index - the gap length - the detector pixel (pad) size Outcome of the simulation: - Separation power (N σ ) - Number of photoelectrons (N pe ) Upstream viewDownstream view

RICH detector design 6 Ahmed El Alaoui RICH Workshop, Jefferson Lab, Newport News, VA 11/16/2011 ComponentDimensions in cm x 2, x 1, y, z Material Rich Body360, 40, 420, 124Aluminum Radiator320, 60, 380, 3Aerogel Gap340, 46, x400, 90Air Planar Mirror150, 36, 120, 2SiO2 + Aluminum Ellipsoidal Mirror370, 370, 440 (semi axis)SiO2 + Aluminum Photon Detector5.2x5.2x2.8 MAPMT H8500-C PMT plane180, 62, 120, 12.8 x1x1 x2x2 z y Roughly 650 PMTs are needed to cover one sector

RICH detector components 7 Ahmed El Alaoui RICH Workshop, Jefferson Lab, Newport News, VA 11/16/2011 Material: Aluminum+SiO2 Reflectivity: > nm Data from Knight Optics company BW : nm, 30% 400 nm, packing factor: 89% New technique “Pinhole drying (PD)” method allow the production of aerogel with high refractive index (n> 1.05) and high transparency

Dual mirror system 8 Ahmed El Alaoui RICH Workshop, Jefferson Lab, Newport News, VA 11/16/ Angular coverage: - Direct: 5-12 deg. - w/ Reflections: deg. - Reduce the number of PMTs by a factor of 3 - PMTs close to the beam line may be subject to radiation damage Inward reflection + Direct detection Aerogel Planar mirror Ellipsoidal mirror charged track Photon detector Beam line One RICH sector must span over 6 m 2 in order to cover the whole acceptance.  (~2000 PMTs)  (very high cost)  use of a dual mirror system is necessary in order to reduce the detector cost.

Views of RICH detector from GEMC 9 Ahmed El Alaoui RICH Workshop, Jefferson Lab, Newport News, VA 11/16/2011 Aerogel Planar mirror Ellipsoidal mirror PMTs plane Gap upstream viewdownstream viewside view

Reconstruction Algorithm 10 Ahmed El Alaoui RICH Workshop, Jefferson Lab, Newport News, VA 11/16/2011 The objective of this algorithm is to determine the type of the particle that produce a ring in the RICH detector plane. The probability to hit the i th PMT - Generate a number of Cerenkov photons around the track. - Propagate these photons and find where they hit the photon detector plane (DRT) T: Track table H: Hypothesis table For each track t (having a momentum p) and for each mass hypothesis h “hit probability distribution”. - Determine the number of photons that hit the i th PMT A realistic probability should take into account the detector efficiency, geometry,…

Reconstruction Algorithm 11 Ahmed El Alaoui RICH Workshop, Jefferson Lab, Newport News, VA 11/16/2011 C PMT (i) is 1(0) if the i th PMT did(did not) respond in the observed hit pattern (GEMC) Where n h,t is the total number of photoelectrons expected for the (h,t) ring and is the mean number of photoelectrons in the i th PMT The hypothesis which maximizes the likelihood L h,t will be considered as the true particle. Assuming a Poisson distribution of the photoelectrons the probability that the i th PMT will respond can be evaluated as: and finally the probability that the hypothesis h is true can be estimated as

Pythia+GEMC - Run pythia to produce real events and use them as input to GEMC to generate the real hit pattern (“Experimental data”). Reconstruction code - Generate a large number of photons for each mass hypothesis. - Propagate them towards the PMT plane - Directly in case of no mirror option or for charged track with angular momentum less than 12 degree - Two inward reflections (photons must go twice through the radiator) - Transform hit position into a PMT Construct the reconstructed hit pattern. - Compare the reconstructed hit to the real hit PMT pattern (from GEMC) to get the C PMT coefficients. - Assign a likelihood to each mass hypothesis as function of the particle momentum. The true particle type will be the one who maximized the likelihood function. Reconstruction Algorithm 12 Ahmed El Alaoui RICH Workshop, Jefferson Lab, Newport News, VA 11/16/2011

Reconstruction Algorithm 13 Ahmed El Alaoui RICH Workshop, Jefferson Lab, Newport News, VA 11/16/2011 Aerogel Planar mirror Ellipsoidal mirror charged track Photon detector Beam line E D

Cerenkov angle for a 4 GeV kaon 14 Ahmed El Alaoui RICH Workshop, Jefferson Lab, Newport News, VA 11/16/2011

Number of photoelectrons 15 Ahmed El Alaoui RICH Workshop, Jefferson Lab, Newport News, VA 11/16/2011 Almost a factor of 4 drop in the number of photoelectrons is observed due to mirror reflectivity (2x88%) and Aerogel opacity (2x60%)

Direct detection 16 Ahmed El Alaoui RICH Workshop, Jefferson Lab, Newport News, VA 11/16/2011

Inward reflection (central track) 17 Ahmed El Alaoui RICH Workshop, Jefferson Lab, Newport News, VA 11/16/2011

Inward reflection (edge track) 18 Ahmed El Alaoui RICH Workshop, Jefferson Lab, Newport News, VA 11/16/2011

Unfolding 19 Ahmed El Alaoui RICH Workshop, Jefferson Lab, Newport News, VA 11/16/2011 The unfolding is the extraction of the true hadron types from the measured ones. I h are the identified particles N h are the unfolded true particles P is the efficiency matrix obtained from Monte Carlo

Conclusion 20 Ahmed El Alaoui RICH Workshop, Jefferson Lab, Newport News, VA 11/16/2011  Simulation showed that a dual mirror, 3cm thick Aerogel with a refractive index of n=1.06, an 80 cm length gap and a pixel size less than 8x8 mm 2 offers an acceptable performance  The Reconstruction Algorithm based on DRT and likelihood approach works very well for the direct detection case. It can also be applied to the inward reflection case with some exceptions (tracks close to sector edge have to be treated carefully).  An unfolding procedure to extract the true particle type from the measured hadron spectra is under development.

Backup slide Ahmed El Alaoui RICH Workshop, Jefferson Lab, Newport News, VA 11/16/

Ahmed El Alaoui RICH Workshop, Jefferson Lab, Newport News, VA 11/16/ momentum and angular distributions of kaons from pythia event generator. Q 2 >1GeV 2, W 2 >4GeV 2, y<0.85, pdf cteq6m, CLAS12 acc. Kaon distributions

23 Ahmed El Alaoui RICH Workshop, Jefferson Lab, Newport News, VA 11/16/2011 Freon+UV-light detection does not provide enough discrimination power in the 2-8 GeV/c momentum range Use of Aerogel is mandatory to separate hadrons in the 2-8 GeV/c momentum range  collection of visible Cherenkov light  use of PMTs Geant3 versus Geant4 codes