simulation status - D. Lawrence - JLab 1

Simulation/Reconstruction for CPP Experiment

David Lawrence JLabSept. 27, 2013

9/27/13

simulation status - D. Lawrence - JLab 2

The GlueX Detector in Hall-D

9/27/13

CPP Experiment will use GlueX detector in Hall-D:• Linearly polarized photon source (~9GeV for GlueX)• 2T solenoidal magnetic field (dp/p = few %)• Drift chambers• High resolution Time-of-flight detector• FCAL segmented lead-glass calorimeter

Modifications to standard GlueX setup:• Replace LH2 target with thin Sn target• Move target upstream to improve low-angle acceptance• Remove start-counter• Add muon/pion detector• Move coherent peak to 6GeV

simulation status - D. Lawrence - JLab 3

Experimental Setup

FDC

Solenoid

TOF FCALTarget

Signal reaction

Beam polarization

• All occur via the Primakoff effect (interaction with the Coulomb field of nucleus)

• All result in very forward going particles

• Low t (-t < 0.005 GeV2)

9/27/13

Muon Detector

Normalization

simulation status - D. Lawrence - JLab 4

Motivation for geometery changes in target region

With start counterWithout start counter

9/27/13

• Smaller z values = target is further upstream• GlueX LH2 target extends from z=50cm to z=80cm

simulation status - D. Lawrence - JLab 5

Start Counter is in the way

9/27/13

Location: (X, Y, Z) = (2.3, 0, 96.6)=============================================== Volume: STRC material: Scintillator density: 1.032 g/cm^3rad. length: 42.1442 cm A: 11.0618 Z: 5.56867 ancestory: STRC -> STRT -> LASS -> HALL -> SITE

Nose angle=17.5o

Trajectory=1.4o

Material=3mm/sin(18.9o) = 9.3mm or 0.022 rad. lengths

simulation status - D. Lawrence - JLab 6

GlueX Simulation Tool Chain

Generators(pythia, genr8, …)

hdgeant(hddsGeant3.F)

mcsmearhdgeant.hddm

hdgeant_smeared.hddm

generated.hddm

reconstruction

Multiple generators exist including:• bggen (pythia + low energy reactions)• genr8 (isobar t-channel configurable)• coherent bremstrahlung photons

GEANT3-based simulation engine:• detailed geometry defined• partial hit digitization

Final stage smearing:• cumulative-level smearing done• dark hits/noise hits added• future: dead-channel removal

HDDS XMLCentralDC_HDDS.xmlForwardTOF_HDDS.xml…

Simulation geometry defined in XML

9/27/13

simulation status - D. Lawrence - JLab 79/27/13

simulation status - D. Lawrence - JLab 89/27/13

Without Vertex Constraint

simulation status - D. Lawrence - JLab 9

With Vertex Constraint

9/27/13

simulation status - D. Lawrence - JLab 10

Kinematics of Experiment

9/27/13

ypp is angle between pp scattering plane and polarization vector in helicity frame

fpp is angle between pp system and incident photon polarization vector in CM frame

simulation status - D. Lawrence - JLab 11

Primakoff + ro

Primakoff only

Wpp(GeV/c2)

Linear Polarization of incident photon beam helps distinguish Primakoff from coherent ro production

9/27/13

fpp ypp

(invariant mass of p+p- system) (invariant mass of p+p- system)

simulation status - D. Lawrence - JLab 12

Extracting the Cross Section(sort of)

9/27/13

• Generated (not simulated) events representing 10 days of running with 70% polarization and r background only

• Fits done for different W bins to extract Primakoff and coherent r contributions

Black: MARK-II dataRed: Statistical errors (from fits)Curves: Theory

simulation status - D. Lawrence - JLab 13

Beam Polarization via po Primakoff

9/27/13

q

f

Use asymmetry between vertical and horizontal polarization data to extract polarization

Plots by Alexander Mushkarenkov

Exercise done with 100% polarization and no backgrounds

simulation status - D. Lawrence - JLab 14

Software Level-1 Event filter

A. Somov GlueX-doc-1043

• Event is kept if either L1a_fired or L1b_fired is true

• Roughly 50% of hadronic events should be accepted by L1 trigger

• Some tuning of FCAL cut will be needed

• Trigger implemented in TRIGGER library (DMCTrigger objects)⎯ hd_eventfilter

Nominal goal for L3 is to discard 90% of L1-accepted events

9/27/13

simulation status - D. Lawrence - JLab 15

Energy deposition in FCAL

1 GeV

2 GeV

9/27/13

p+

m+

m/p detector FCAL

GEANT3 simulation by Lubomir Pentchev

GEANT3GEANT4

• Trigger depends strongly on FCAL response

• Particle ID depends on BOTH FCAL and m/p detector response

• Currently have limited ability to simulate FCAL response to hadronic showers

simulation status - D. Lawrence - JLab 16

Some ideas on what is needed next …

• Implement muon detector in HDDS and test with hdgeant4– Devise code management system to maintain CPP specific geometry while keeping aligned with geometry

shared with GlueX (e.g. FDC)

• Simulations of m/p separation with refined muon/pion detector design

• Tracking in m/p detector ?

• Complete implementation of relevant reactions in GlueX ANALYSIS package– gp -> pp+p-

– gp -> ppo

• Full-scale simulation and extraction of signal reaction with all relevant backgrounds– s meson– Incoherent p+p- ?

• Simulate Polarization measurement using Primakoff asymmetry with:– 70% polarization– Realistic trigger– Backgrounds

9/27/13

simulation status - D. Lawrence - JLab 17

Backup Slides

9/27/13

simulation status - D. Lawrence - JLab 18

Backgrounds• Experiment will measure reaction:

g Pb -> Pb p+p-

• Primary background will be coherent ro production followed by r->pp decay– Will use angular distributions to separate Primakoff from

coherent ro production (see later slides)

• Currently gathering list of other potentially relevant backgrounds including:– s meson production (angular distributions same as Primakoff)

– incoherent p+p- production– …

9/27/13

simulation status - D. Lawrence - JLab 19

Relating cross-section to ap-bp

9/27/13

Figure 5. from Pasquini et al. Phys. Rev. C 77, 065211 (2008)

Cross-section for gg -> p+p- calculated based on two values of ap-bp:

ap-bp = 13.0 x 10-4 fm3 (top, dotted line)

ap-bp = 5.7 x 10-4 fm3 (solid and dashed lines)

Cross-section varies by ~10% for factor of 2 variation in ap-bp

Need measurement of s(gg -> p+p- ) at few percent level

gg -> p+p-

dotted: subtracted DR calculation with ap-bp = 13.0dashed: subtracted DR calculation with ap-bp = 5.7solid: unsubtracted DR calculation with ap-bp = 5.7

Invariant mass of p+p-

ap-bp = 13.0

ap-bp = 5.7

(Data points from MARK-II)

simulation status - D. Lawrence - JLab 20

Detector Rates/Acceptance

• 107 tagged photons/second on 5% radiation length Pb target

• 500 hours of running• Wpp acceptance down to ~320 MeV/c2

(working to improve acceptance to even lower Wpp)

• Estimated ~36k* Primakoff events(contrast this with the ~400 events in the acceptance of the MARK-II measurement)

9/27/13

* before detector acceptance

simulation status - D. Lawrence - JLab 21

Charged Particle Tracking

Source code is checked out and built via nightly cron job on 3 platforms

Twice a week cron jobs automatically simulate and reconstruct single track events and multi-track b1p events

Plots from 5/4/12 semi-weekly single track tests

o Tracking code development began in 2004

o Tracking is done in multiple stages:• Track Finding• Wire-based fitting (wire positions only)• Time-based fitting (drift times used)

o Fitting done using a Kalman Filter (replaced original least-squares fitter)

9/27/13

simulation status - D. Lawrence - JLab 22

Charged Particle Tracking

Plots from 5/7/12 semi-weekly b1p tests

Results of recent semi-weekly test doing full reconstruction of b1p events

Final state: p p+ p+ p- p- gg(5 charged tracks)

Some mis-identification of p+ and proton exists

>60% reconstruction efficiency of “X” meson

9/27/13

simulation status - D. Lawrence - JLab 23

Calorimetry

FCALCode developed based on experience with Rad-f experiment in Hall-B• Full reconstruction (GlueX-doc-823)• Depth corrections (GlueX-doc-1093)• Calibration procedure established

BCALo 1st generation Code developed copied from

KLOE and adapted to GlueXo 2nd generation currently under

development by GlueX• Improved angular resolution• Better error estimation• Increased po reconstruction efficiency

(61%->73% 11/28/11 report)

FCAL reconstruction efficiencyRed: minblocks= 1

Black: minblocks= 2

BCAL reconstructed energy resolution

9/27/13

simulation status - D. Lawrence - JLab9/27/13 24

pp invariant mass

w/ vertex constraint

w/ vertex constraint

w/o vertex constraint

w/o vertex constraint