HASPECT in action: CLAS12 analysis of Development of an analysis framework for the MesonEx experiment A. Celentano (INFN Genova and Genova University)
Outline The MesonEx experiment at JLab@12 GeV in Hall B Development of the analysis framework for the experiment The framework in action: study of the reaction Conclusions and future perspectives
MesonEx: mesons spectroscopy with quasi real photoproduction Meson spectroscopy program searching for exotics and rare qq states. Technique: electron scattering at very low Q2 on a proton target (<Q2> ~ 0.1 GeV2) Quasi-real photons are produced by the electron scattering at low angle on a proton target. Kinematics and polarization of the quasi real photon are defined event by event measuring the scattered electron. MesonEx (JLab Hall B) Quasi real photo-production of mesons. Final state hadrons measured with the CLAS12 detector Scattered electron measured with the new Forward Tagger detector Forward Tagger eforward Tagger * ep CLAS12 P μγ =P μe Pμe '
MesonEx analysis framework: requirements and purposes Goal: develop a framework to perform Partial Wave Analysis of a given final state, with amplitudes defined by the user. Input: experimental data or pseudo-data (Monte-Carlo generated according to a given amplitude). Analysis: PWA of the final state. The intensity of the reaction is parametrized as a coherent sum of user-defined amplitudes. Free parameters are determined trough a maximum likehood unbinned fit. Output: fit parameters, errors, likehood pre- and post-fit. Framework flow-chart: Detector Response Data Phase-Space MonteCarlo Events Detector Simulation PWA-Fit Data Reconstruction Reconstruction Pseudo Data Detector MonteCarlo Events
MesonEx analysis framework: components The developed framework is basically a set of different softwares, each performing a specif operation, interconnected trough a set of common definitions, like event and data formats. Phase Space MonteCarlo Events: generated trough the TGenPhaseSpace ROOT class. Detector Simulation: currently trough FASTMC effective MonteCarlo, GEMC in the final version. Reconstruction: currently trough a stand-alone code, CLAS12 software in the final version. Pseudo-Data: AmpTools, trough hit or miss method. PWA: AmpTools, trough maximum likehood fit. AmpTools: software to handle complex amplitudes for a given reaction, and to combine them in coherent or incoherent sums to obtain the intensity. The program includes the possibility to perform maximum likehood fits to the data, handling normalization and taking into account detector efficiency (calculated trough MonteCarlo simulations).
MesonEx analysis framework: production amplitudes Final state particles for interesting events in MesonEx: Scattered electron within the FT Recoil proton X mesons Production amplitude in the OPE approximation (i.e. first perturbative order for the electron scattering): Using Ward identity to explicit sum over virtual photon polarization: Resulting amplitude is the product of two terms: Emission of a quasi-real photon (m ~ 0) by the electron Photoproduction on the proton of the final state px
MesonEx analysis framework: production amplitudes in AmpTools The leptonic vertex in the production amplitude is the same for all reactions and it is handled by the framework. The user has to code the specific photoproduction amplitude. 12 amplitudes: 3 x polarization, 2 x target polarization, 2 x recoil polarization. The sum over the polarization is handled by the framework. Pratically: a new amplitude class is derived from AmpTools Amplitude Clas12PhotonAmplitude:public Amplitude... Clas12PhotonAmplitude::CalcAmplitude(GDouble **P4){ return Spin variables for electron (beam: s, scattered: s') and proton (target: h, recoil: h') are handled trough a incoherent sum } Quasi-real photon emission amplitude, known and hard-coded Photoproduction amplitude, user specified. With this method the same amplitudes for real photoproduction can be used in the framework without any major change.
The framework in action: study of the channel Feasibility study of this channel in MesonEx trough MonteCarlo simulations. Resons for the choice of this particular channel: The defined C-parity of state (C=+1) helps in the search for exotic quantum numbers (i.e. a signal in the JP= 1- wave would be automatically exotic). Past experiments (VES, Crystal Barrel, E852) have seen hints for an exotic signal in this channel but there is not a definite answer. a2(1320) 1-+ exotic wave (Some) results from E852 experiment.
The framework in action: study of the channel Pseudo MonteCarlo data has been generated according to the production amplitude calculate by theoreticians colleagues (A. Szczepaniak and V. Mathieu) The response of the detector to this final state has been studied trough FASTMC program, for the specific case of the decay of both mesons in The stand-alone reconstruction code for the reaction has been developed Currently, I am dealing with the PWA fits: fit with the production amplitudes and check that they can be retrieved. X Photoproduction amplitudes for the final state: signal + background (double Regge mechanism). Signal: resonance X decaying in Currently X is a2 (1320) Background: doubleregge exchange
The framework in action: study of the channel Pseudo-Data generation trough hit-or-miss technique (Ebeam = 11 GeV) PHASE SPACE Phase Space Dalitz plot is not flat, s changes event by event for the sub-reaction PHYSICS
The framework in action: study of the channel Pseudo-Data generation trough hit-or-miss technique (Ebeam = 11 GeV) PhaseSpace Events PhaseSpace Events a2(1320) Physics Events Physics Events
The framework in action: study of the channel Electron momentum resolution (FASTMC) Photons energy resolution (FASTMC) from and in CLAS12 Electrons in the FT (electrons have been generated up to 4 Gev/c) CLAS12 Acceptance (FASTMC) for Black: counting only the measured photons. Red: requiring that also the recoil proton is measured.
Conclusions MesonEx experiment (JLab, Hall B) will perform a Meson Spectroscopy program, searching for exotics and rare qq states, trough quasi-real photoproduction: electron scattering at very low Q2 An analysis framework for this experiment has been designed and developed. It consists of several programs, each performing a specific task, interconnected trough common rules and definitions. The framework let the user perform a PWA of a given reaction trough a set of arbitrary amplitudes. AmpTools software, developed at Indiana University, is the core of this framework. Some programs are still in a preliminary version and will be upgraded in the near future. This framework has been tested with the reaction involving the p final state, that has been studied trough MonteCarlo simulations. The production amplitude for this final state has been developed (sum of signal + double-regge background). Pseudo-MonteCarlo data has been generated and projected into CLAS12+FT detector. A stand-alone reconstruction software has been written. Currently PWA is being performed, with the first objective to retrieve production amplitudes from the data.
Backup Slides
Leptonic vertex contribution in the quasi real photoproduction amplitudes Leptonic vertex: * emission The calculation is performed projecting the electron spin on the helicity base and working on the GJ frame ( * moving along z axis)
Pseudo data generation: Hit or Miss technique Hit or Miss : technique used to generate pseudo-data (MonteCarlo) for a certain reaction according to a given production amplitude. Generate a large set of phase-space events (i.e. no dynamics, only kinematics) Various generators on the market, root TGenPhaseSpace is a good choice Calculate the intensity Ii of each event according to the given amplitude Imax is the maximum intensity For each event, trow a random number r uniformly distributed between 0 and Imax If r < Ii keep the event, otherwise discharge it Physically, the Phase Space for the given reaction is modulated with the given production amplitude.
Photoproduction amplitudes for X Signal: peripheral photoproduction of a X resonance, decaying in V. Mathieu A. Szczepaniak
Photoproduction amplitudes for Background: double Regge exchange. V. Mathieu A. Szczepaniak
Pseudo-Data generation trough hit-or-miss technique (Ebeam = 11 GeV) 7 7.25 GeV 7.25 7.5 GeV 7.5 7.75 GeV 7.75 8 GeV PhaseSpace Events 10 10.25 GeV 10.25 10.5Spectroscopy GeV at Events binned respect to quasi-real photon energy (7-10.5 GeV) 12 =250 GeV: Working MeV Together
Pseudo-Data generation trough hit-or-miss technique (Ebeam = 11 GeV) 7 7.25 GeV 7.25 7.5 GeV 7.5 7.75 GeV 7.75 8 GeV Physics Events 10 10.25 GeV 10.25 10.5Spectroscopy GeV at Events binned respect to quasi-real photon energy (7-10.5 GeV) 12 =250 GeV: Working MeV Together
The dependence of the production intensity on the azimuthal angle of the in the GJ frame, after summing over the helicities of the electron (beam, scattered), is on the form: