Simulated CLAS12 Neutron Detection Efficiency in the Forward Time-of-Flight System

Transcription

1 Simulated CLAS12 Neutro Detectio Efficiecy i the Forward Time-of-Flight System G.P. Gilfoyle 1, M.Ugaro 2, J. Carboeau 1, M. Moog 1, ad C. Musalo 1 1 Uiversity of Richmod, Richmod, VA 2 Uiversity of Coecticut, Storrs, CT August 9, 211 Abstract We have simulated the productio of quasi-elastically (QE) scattered electros ad eutros i CLAS12 with the physics-based, CLAS12 simulatio package gemc. The electro evets were recostructed with Socrat. We have studied the properties of the deposited eergy ad efficiecy of the CLAS12 FTOF system to establish a baselie for the future measuremet of the eutro magetic form factor i Experimet E We have simulated the extractio of the eutro detectio efficiecy usig QE eutros ad foud a efficiecy of 16% for paels P1A ad P1B combied together ad a value of 8% for pael P2B. A compariso of the simulated efficiecy usig oly paels P1A ad P2B (that are beig reused from CLAS6) with the measured values from the E5 ru (usig the p(e,e π + ) reactio) shows good agreemet.

2 CLAS-NOTE 211-Draft - August 9, Itroductio I this CLAS-Note we preset the results of a study of the efficiecy for detectig quasielastic eutros i the CLAS12 time-of-flight (TOF) system. We are preparig for experimet E etitled Measuremet of the Neutro Magetic Form Factor at High Q 2 Usig the Ratio Method o Deuterium where the ratio of quasielastic (QE) e to e p scatterig is measured ad the eutro magetic form factor G M is extracted [1]. The QE e scatterig will be measured with the CLAS12 forward TOF system (FTOF) ad the eutro detectio efficiecy (NDE) must be accurately determied to meet the experimetal goals of systematic ucertaities of 3% or less. We will also compare the simulated results foud here with those measuremets of the NDE performed for a earlier CLAS6 measuremet of G M durig the E5 ru. This compariso will be particularly relevat because some of the CLAS12 FTOF scitillators will be the same as the oes used i the E5 measuremet. Experimet E was origially approved by PAC32 ad reviewed by PAC35 to allocate beam time. Thirty days of ruig were awarded by PAC35 alog with a A ratig. The format of this paper is the followig. (1) The motivatio for the experimet will be preseted ad (2) alog with a descriptio of the ratio method). (3) The results from a physics-based simulatio (GEat4 MoteCarlo gemc) of the scitillator respose to the passage of electros ad eutros will be preseted [2]. (4) The iputs ad results will be show from the gemc simulatio of elastic e scatterig ad recostructio with the Rootbased code Socrat [2, 3]. (5) Last we will preset the post-recostructio aalysis used to extract the eutro detectio efficiecy i the FTOF. 2 The CLAS12 G M Experimet (E12-7-4) I JLab Experimet E we ited to dramatically exted the reach of our uderstadig of a fudametal feature of the eutro; its magetic form factor G M. The elastic electromagetic form factors(eeffs) describe the distributio of charge ad magetizatio iside the ucleo at low Q 2 ad probe the quark structure at higher Q 2. This experimet is part of a broad program at JLab to measure the EEFFs, map the iteral ladscape of the ucleo, ad test o-perturbative Quatum Chromodyamics (QCD) ad QCD-ispired models of the ucleo (see NSAC Log-Rage Pla [4]). The measuremet will cover the rage Q 2 = GeV 2 with systematic ucertaities less tha 3%. Statistical ucertaities will be about 3% i the highest Q 2 bi i this rage ad sigificatly less at lower Q 2. The aticipated rage ad statistical ucertaities of the experimet are show i Figure 1. The reduced magetic form factor G M /(µ G D ) is plotted versus Q 2 where µ is the eutro magetic momet ad G D = 1/(1 + Q 2 /Λ 2 ) 2 is the dipole form factor with Λ 2 =.71 GeV 2. We used the recet parameterizatio of the world s data o G M i Ref [13] to predict the reduced form factor. Also show are selected world s data for G M icludig the recet CLAS6 results (blue, ope circles)[5]. The proposed CLAS12 experimet (black, closed squares) will early triple the upper limit of the previous CLAS6 measuremet ad provide precise data well past ay existig measuremet.

3 CLAS-NOTE 211-Draft - August 9, The Ratio Method To measure G M we will use the ratio of quasielastic e to quasielastic e p scatterig o deuterium which has bee used by us i CLAS6 [5] ad others [9, 17, 18, 19, 2] to measure G M (see Figure 1). The ratio method is less vulerable to systematic ucertaities tha previous methods ad we will have cosistecy checks betwee differet detector compoets of CLAS12 (the FTOF ad the CLAS12 electromagetic calorimeter (EC)) ad a overlap with our previous CLAS6 measuremets. A liquid-hydroge/liquid-deuterium, dual target will be used to make i situ measuremets of the eutro ad proto detectio efficiecies. We take advatage of the large acceptace of CLAS12 ad veto evets with additioal particles (beyod e ad e p coicideces) to reduce the ielastic backgroud. We expect to limit the systematic ucertaities to 3% or less [21]. This experimet ca be doe with the base equipmet for CLAS12 ad was approved by PAC32. The method is based o the ratio of e to e p scatterig ( ) σmott (G 2 E + τ ε G 2 1 M ) 1+τ R = dσ dω (2 H(e, e ) QE ) dσ dω (2 H(e, e p) QE ) = a(q2 ) dσ dω (1 H(e, e )p) for quasielastic (QE) kiematics. The right-had side is writte i terms of the free ucleo form factors ad where τ = Q 2 /4M 2 ad ǫ = 1/[1+2(1+τ) ta 2 (θ/2)]. Deviatios from this free ratio assumptio are parameterized by the factor a(q 2 ) which ca be calculated from deutero models ad is close to uity at large Q 2. The results of other measuremets of the (1) /µ M G D G Blue - CLAS6 Gree - Previous World Data Black - CLAS12 aticipated Aticipated Statistical ucertaities oly Miller Guidal et al. Cloet et al :19:52 Q (GeV ) 2 2 Figure 1: Selected data [5, 6, 7, 8, 9,, 11, 12] ad aticipated results for G M (black, filled squares) i uits of µ G D as a fuctio of Q 2. The aticipated CLAS12 results follow a fit to the world data o G M that icludes the recet CLAS6 G M results [13]. The blue, ope circles are the CLAS6 results [5]. The curves are from Miller (blue, dashed,[14]), Guidal et al. (blue, dotted,[15]), ad Cloët at al. (red,[16]).

4 CLAS-NOTE 211-Draft - August 9, proto cross sectio ad the eutro electric form factor are used to extract G M. The ratio R is isesitive to the lumiosity, electro acceptace, electro recostructio efficiecy, trigger efficiecy, the deutero wave fuctio used i a(q 2 ), ad radiative correctios [5, 22]. A essetial aspect of the eutro measuremet i the TOF ad EC systems is measurig the eutro detectio efficiecy. I the experimet we will use the p(e, e π + ) reactio as a source of tagged eutros. Electros ad π + s will be detected i CLAS12 ad missig mass used to select cadidate eutros (foud eutros). We the predict the positio of the eutro i CLAS12 ad search for it. If a eutro is foud we call these recostructed eutros. The ratio of recostructed to foud evets gives us the detectio efficiecy. This will be doe i CLAS12 with a uique, dual target. Co-liear, liquid hydroge ad deuterium cells will provide productio ad calibratio evets simultaeously ad uder the same coditios (i situ). This reduces our vulerability to variatios i detector gais, beam properties, etc. The same method was used i the CLAS6 measuremet durig the E5 ru period. The results for the NDE measuremet at two differet beam eergies is show i Figure 2. Neutro Efficiecy GeV 4.2 GeV Neutro Mometum (GeV) Figure 2: Neutro detectio efficiecy measured with the e, e π + ) reactio for the CLAS6 G M measuremet. For this study we do ot yet have a appropriate simulatio of the p(e, e π + ) reactio so we will start with a simulatio of elastic scatterig from a simulated eutro target as a first step to uderstadig the eutro detectio efficiecy. The method we will use is aalogous to the oe proposed for E ad used i Ref [5]. Scattered electros are simulated i CLAS12 ad the electro iformatio is used to predict the positio of the eutro assumig that elastic scatterig has occurred. If the predicted positio of the eutro is withi the active area of the FTOF we call this a foud eutro. We the search the simulatio results for a eutro i regio of the foud eutro. If a eutro is foud withi a agular coe aroud the predicted positio of the foud eutro, the we have a recostructed eutro.

5 CLAS-NOTE 211-Draft - August 9, The NDE is the ratio of recostructed to foud eutros. 4 Simulatio of FTOF Scitillator Respose to Electros The passage of electros ad eutros through the scitillator material of the FTOF was simulated with gemc. The gemc code is a physics-based simulatio usig the Geat4 package from CERN [23]. It is a object-orieted, C ++ -based code that reads detector iformatio from a exteral, mysql database. Hits i detector compoets are built by a factory method at ru time, ad the output baks are dyamic. Qt4 is used for a graphical user iterface [24]. The geometry of the FTOF is show i Fig. 3 icludig the three FTOF paels i each sector labeled P1A, P1B, P2B. Most of the CLAS12 compoets have bee removed to P2B P1A P1B Soleoid Torus Figure 3: Geometry of the FTOF system. make the FTOF system more visible. The CLAS12 torus ad soleoid are show to oriet the reader. The layer labeled P1A (pik strips i Figure 3) cosists of 23 strips that are each 15. cm wide ad 5.8 cm thick. These are the same strips used i the curret CLAS6 detector. The layer labeled P1B (bright gree strips i Figure 3) just i frot of the P1A pael i each sector cosist of 58 strips that are each 6. cm wide ad 6. cm thick. These scitillators will be ew i CLAS12. The last FTOF pael i each sector is labeled P2B i Figure 3 ad has scitillators that are 22 cm cm wide ad 5.8 cm thick. These scitillators are also beig reused from CLAS6. See the CLAS Techical Desig Report for more details [25]. The gemc code was ru for electros at mometa that covered the rage expected for quasielastic evets i that pael. Each electro struck oe of the strips perpedicular to the

6 CLAS-NOTE 211-Draft - August 9, plae of the pael. All of the other CLAS12 compoets betwee the target ad the FTOF pael were removed i the simulatio so those compoets would ot alter the properties of the electros strikig the pael. The CLAS12 magetic field was also tured off. The gemc commad is show below. gemc -USE_QT= -OUTPUT=p1a.gcard -N=5 -PRINT_EVENT=2 -HALL_MATERIAL=Vacuum -gcard=$gcard -USE_PHYSICSL=gemc -BEAM_P="e-, 9.25*GeV, 25*deg, *deg" -SPREAD_P=".*GeV, *deg, *deg" -LUMI_EVENT=",*s,2*s" -NO_FIELD=all The eergy deposited for electros i the P1A scitillator pael is show i Figures 4 for electro mometa of 9.25 GeV/c ad 3.5 GeV/c respectively. The left-had pael of Fig. 4 Couts/N-MeV -1-2 p = 9.25 GeV/c electros e TOF pael P1A Black - all evets Red - E > 8 MeV Blue - E < 8 MeV GeV/c electros TOF pael P1A E Figure 4: Eergy deposited ad particle eergy i the FTOF scitillators for electros of mometum p e = 9.25 GeV for FTOF pael P1A. The vertical axis i the left-had pael is the umber of evets from the Mote Carlo, gemc calculatio divided by the bi size ad the umber of throw evets. The histogram i the right-had pael is the umber of evets divided by the umber of throw evets. shows the distributio of for all particles that deposit ay eergy i the scitillator (black curve largely obscured by the other histograms). Electros were simulated of mometum 9.25 GeV, icidet at oe poit ear the ceter of the scitillator, ad ormal to the surface. The spectra i Fig. 4 are for all particles, but early all (98%) are electros. The peak created by miimum-ioizig particles (MIPs) is visible at 9 MeV. This is the expected positio sice MIPs deposit about 2 MeV of eergy per cm of scitillator material. There is also a sigificat umber of evets at eergies below the MIP peak. To uderstad the low- features cosider the right-had pael of Fig. 4 which shows a two-dimesioal histogram of versus E where E is the eergy (kow i simulatio) of the particle as it eters the volume (the P1A scitillator pael here). The threshold at 8 MeV is the low- edge of the MIP peak. Electros passig through the

7 CLAS-NOTE 211-Draft - August 9, scitillator are ot expected to deposit eergy less tha this amout. There are arrow peaks at E = 9.25 GeV i the right-had pael of Fig. 4 (correspodig to the icidet electro eergy) ad at E = MeV. The log, E tail below E = 9.25 GeV is due to primary electros that have emitted a bremsstrahlug photo before reachig the P1A scitillator. At E = 9.25 GeV ad < 8 MeV i the right-had pael of Fig. 4 there is a low- tail below the eergy of a miimum-ioizig particle. These evets are due to full-eergy electros that eter the scitillator ad emit a bremsstrahlug photo that carries away early all of the icidet electro eergy. The remaiig, ow low-eergy electros will stop i the scitillator ad deposit less tha the MIP eergy all the way dow to zero. Aother explaatio for this high-e, low- tail is from backscattered electros, but the cross sectio for bremsstrahlug is orders of magitude greater tha the backscatter oe. This low-, high-e feature ca be see i the red histogram i the left-had pael of Fig. 4 where the spectrum is extracted for evets with E > 8 MeV; the miimum eergy deposited for MIPs ad the threshold visible i the right-had pael. The red histogram almost completely overlaps the MIP peak ad has the low- tail. The blue histogram i the left-had pael is for evets with E < 8 MeV ad correspods to the peak ear E = MeV i the right-had pael. These are low-e, secodary electros produced whe the primary electro passed through the scitillator. The thickess of the P1A scitillator (5.8 cm) correspods to the rage of electros with eergies of about MeV so electros with eergies up to MeV will stop i the scitillator (uless they are produced ear the back surface of the pael so they ca escape). Oce the eergy of the secodary electros exceeds MeV they will pass through the scitillator ad deposit the MIP eergy (uless they have a mometum that carries them alog the log-axis of the scitillator paddle through a larger amout of the material). I the Edep E distributio there is also a hit of protos that deposited eergy i the scitillator at E 1 GeV. There protos were produced by reactios i the scitillator. We ow cosider the effect of lower icidet mometum electros o the FTOF respose. Fig. 5 shows the results from the aalysis of the same study illustrated i Fig. 4, but at a lower primary electro mometum correspodig to the mometum of quasielastic electros ear the large-agle edge of the FTOF pael P1A. The commad used to geerate the evet file with gemc was the same used above with oly the icidet electro mometum chaged. The left-had pael of Fig. 5 shows the same distributio except ow the icidet electro mometum is 3.5 GeV. The overall shape of the distributio ad its breakdow ito compoets above ad below the MIP threshold are early idetical. The right-had pael i Fig. 5 shows versus E distributio as i Fig. 4, but with the reduced icidet electro mometum. The oly differece is the reduced E rage due to the lower icidet mometum. For the rage of electro mometa we have studied here the respose of the FTOF system to electros is largely idepedet of the icidet eutro mometum. The respose of the FTOF pael P1B is show i Figs 6-7. These paels are mouted i frot of pael P1A (see Fig. 3), cover about the same agular rage, ad are thicker (6. cm versus 5.1 cm). As i the previous study simulated, icidet electros at two mometa (3.5 GeV/c ad 9.25 GeV/c) struck the ceter of the pael ormal to the surface. Comparig Figs. 4 ad 6 (9.25 GeV/c) the distributios are very similar. The oly differece is the threshold for the miimum ioizig particles is higher i pael P1B tha i pael P1A (9 MeV versus 8 MeV) because P1B is thicker. The same features ca be see comparig

8 CLAS-NOTE 211-Draft - August 9, Couts/N-MeV -1-2 p = 3.5 GeV/c electros e TOF pael P1A Black - all evets Red - E > 8 MeV Blue - E < 8 MeV GeV/c electros TOF pael P1A E Figure 5: Eergy deposited ad particle eergy i the FTOF scitillators for electros of mometum p e = 3.5 GeV for FTOF pael P1A. The vertical axis i the left-had pael is the umber of evets from the Mote Carlo, gemc calculatio divided by the bi size ad the umber of throw evets. The histogram i the right-had pael is the umber of evets divided by the umber of throw evets. Couts/N-MeV -1-2 p = 9.25 GeV/c electros e TOF pael P1B Black - all evets Red - E > 9 MeV Blue - E < 9 MeV GeV/c electros TOF pael P1B E Figure 6: Eergy deposited ad particle eergy i the FTOF scitillators for electros of mometum E = 9.25 GeV/c for FTOF pael P1B. The vertical axis i the left-had pael is the umber of evets from the Mote Carlo, gemc calculatio divided by the bi size ad the umber of throw evets. The histogram i the right-had pael is the umber of evets divided by the umber of throw evets. Figs. 5 ad 7 (3.5 GeV/c).

9 CLAS-NOTE 211-Draft - August 9, Couts/N-MeV -1-2 p = 3.5 GeV/c electros e TOF pael P1B Black - all evets Red - E > 9 MeV Blue - E < 9 MeV GeV/c electros TOF pael P1B E Figure 7: Eergy deposited ad particle eergy i the FTOF scitillators for electros of mometum E = 3.5 GeV/c for FTOF pael P1B. The vertical axis i the left-had pael is the umber of evets from the Mote Carlo, gemc calculatio divided by the bi size ad the umber of throw evets. The histogram i the right-had pael is the umber of evets divided by the umber of throw evets. Couts/N-MeV -1-2 p = 2.5 GeV/c electros e TOF pael P2B Black - all evets Red - E > 8 MeV Blue - E < 8 MeV GeV/c electros TOF pael P2B E Figure 8: Eergy deposited ad particle eergy i the FTOF scitillators for electros of mometum E = 2.5 GeV/c for FTOF pael P2B. The vertical axis i the left-had pael is the umber of evets from the Mote Carlo, gemc calculatio divided by the bi size ad the umber of throw evets. The histogram i the right-had pael is the umber of evets divided by the umber of throw evets. The respose of the FTOF pael P2B is show i Fig. 8. This pael is mouted i at

10 CLAS-NOTE 211-Draft - August 9, 211 larger agles relative to pael P1A (see Fig. 3), covers the agular rage θ =???, ad has the same thickess as the P1A paels (5.1 cm). The scitillators will be reused from CLAS6. Simulated, icidet electros at mometum 2.5 GeV/c struck the ceter of the pael ormal to the surface. We oly used a sigle mometum here sice the agular rage ad, hece, the mometum rage for quasielastic electros is arrow. Comparig Fig. 8 with the other paels shows that the miimum ioizig peak is much the same as the oe for pael P1A which has the same thickess of scitillator. The shape of the spectrum chages little with icidet electro beam eergy as see i comparig the left-had paels i Figs I the two-dimesioal plots of versus E, they all have similar features; the oly differece is the positio of the peak from the icidet electros. 5 Simulatio of FTOF Scitillator Respose to Neutros The gemc code was ru for eutros strikig oe of the strips i each pael perpedicular to the plae of the pael over the rage p = GeV/c. For each pael all of the other CLAS12 compoets betwee the target ad the TOF pael were removed so those compoets would ot alter the properties of the electros strikig the pael. The gemc commad is show below. It is much the same as the oe above except for the choice of particle ad mometum. gemc -USE_QT= -OUTPUT=eutros.ev -N=5 -PRINT_EVENT=2 -HALL_MATERIAL=Vacuum -gcard=p1a.gcard -USE_PHYSICSL=gemc -BEAM_P="eutro, 8.*GeV, 25*deg, *deg" -SPREAD_P="*GeV, *deg, *deg" -LUMI_EVENT=",*s,2*s" -NO_FIELD=all The eergy deposited for eutros i the scitillator is show i Figs The left-had pael of Fig. 9 shows the distributio of deposited eergy for all eutral particles (black histogram largely obscured by the red oe) from primary eutros with p = 8. GeV/c icidet o pael P1A ad perpedicular to the face of the pael. The distributio is broad; stretchig out to a eergy E 5 MeV where E is the eergy (kow i simulatio) of the particle as it eters the volume (the P1A scitillator pael here). The distributio is domiated by eutros (7%) with the remaider composed mostly of photos produced by eutro reactios i the scitillator. The other importat feature is the scale is much smaller tha the comparable mometum for electros (see Fig 4) reflectig the much lower detectio efficiecy of the scitillators for eutros tha electros. The right-had pael of Fig. 9 shows the distributio of versus E. The arrow ridge at E = 8. GeV is produced by the primary eutros ad there is smaller group ear E = 1 GeV from secodary eutros produced by reactios i the scitillator. Similar distributios are show i Fig. for a lower icidet, primary eutro mometum p = 3.1 GeV/c. The deposited eergy distributio for eutros i the left-had pael is softer; it does ot exted to as high a eergy as the higher-mometum eutros i Fig.. O the other had, the photo spectrum, which is produced by reactios i the material of the scitillator, is about the same i Figs. 9 ad. The E spectrum i

11 CLAS-NOTE 211-Draft - August 9, Couts/N-MeV -2 p = 8 GeV TOF pael P1A Black - All eutrals Red - eutros Blue - photos N = p = 8 GeV/c eutros TOF pael P1A :17: E Figure 9: Eergy deposited ad particle eergy i the FTOF scitillators for eutros of mometum p = 8. GeV/c for FTOF pael P1A. The vertical axis i the left-had pael is the umber of evets from the Mote Carlo, gemc calculatio divided by the bi size ad the umber of throw evets. The histogram i the right-had pael is the umber of evets divided by the umber of throw evets ad the bi size. Couts/N-MeV -2 p = 3.1 GeV TOF pael P1A Black - All eutrals Red - eutros Blue - photos N = p = 3.1 GeV/c eutros TOF pael P1A :19: E Figure : Eergy deposited ad particle eergy i the FTOF scitillators for eutros of mometum p = 3.1 GeV/c for FTOF pael P1A. The vertical axis i the left-had pael is the umber of evets from the Mote Carlo, gemc calculatio divided by the bi size ad the umber of throw evets. The histogram i the right-had pael is the umber of evets divided by the umber of throw evets ad the bi size. the right-had pael of Fig. has much the same features as the higher-mometum oe i

12 CLAS-NOTE 211-Draft - August 9, Fig. 9 except the ridge from the primary eutro is shifted to lower E. The results for paels P1B ad P2B (see Fig. 3) are show i Figures The Couts/N-MeV -1-2 p = 8. GeV TOF pael P1B Black - All eutrals Red - eutros Blue - photos N = 5 Couts/N-MeV -1-2 p = 3.1 GeV TOF pael P1B Black - All eutrals Red - eutros Blue - photos N = :52: Figure 11: Eergy deposited ad particle eergy i the FTOF scitillators for eutros of mometum p = 8. GeV/c (left-had pael) ad p = 3.1 GeV/c (right-had pael) for FTOF pael P1B. The vertical axis o each plot is the umber of evets from the Mote Carlo, gemc calculatio divided by the bi size ad the umber of throw evets. Couts/N-MeV -1-2 p = 9.2 GeV TOF pael P2B Black - All eutrals Red - eutros Blue - photos N = Figure 12: Eergy deposited ad particle eergy i the FTOF scitillators for eutros of mometum p = 9.1 GeV/c for FTOF pael P2B. The vertical axis o each plot is the umber of evets from the Mote Carlo, gemc calculatio divided by the bi size ad the umber of throw evets. deposited eergy has the same features see above. (1) The eutro spectrum is harder

13 CLAS-NOTE 211-Draft - August 9, for higher-mometum icidet eutros ad (2) the photo distributio chages little with icidet eutro mometum. 6 Simulatio of Neutro Detectio Efficiecy for Quasielastic e Evets We ow study the simulatio of the quasielastic scatterig of electros from eutros to extract the eutro scatterig efficiecy (NDE); a essetial compoet of the G M measuremet described above. This study will provide a baselie of uderstadig of the NDE i preparatio for the experimet. Quasielastic e evets were simulated assumig (1) a statioary eutro target ad (2) a isotropic agular distributio. The first assumptio provides a startig poit for a future study of the NDE with a more realistic simulatio of the Fermi motio of the eutro i deuterium. The secod oe eables us to obtai a adequate umber of Mote Carlo evets at large agles i a shorter period of time. These evets were the used as iput to gemc [2] usig the followig commad. gemc -USE_QT= -OUTPUT="evio,gemc_results1.ev" -N=5 -INPUT_GEN_FILE="LUND, Iput1.dat" -PRINT_EVENT=2 -HALL_MATERIAL=Vacuum -gcard=de.gcard -USE_PHYSICSL=gemc -SCALE_FIELD=1 -SAVE_ALL_MOTHERS=1 -HALL_FIELD=srr-soleoid -ENERGYCUT="*MeV" Electros were recostructed with the code Socrat described i Ref. [3]. Recostructio parameters ca be foud i Appedices A-B. A cut o the ratio p/p was required. Fig. 13 shows the distributio of p/p. The differece p was extracted betwee the recostructed Couts 5 CLAS12 electro mometum resolutio χ 2 / df 3.92 / 14 p 514 ± 27.2 p ±.759 p ±.12 4 gemc/socrat E = 11 GeV p/p Figure 13: Distributio of p/p usig the mometum from the Socrat recostructio with the mometum calculated from the recostructed electro agle ad assumig quasielastic scatterig. electro mometum from Socrat ad the mometum calculated from the measured polar

14 CLAS-NOTE 211-Draft - August 9, agle (also from Socrat) ad assumig elastic scatterig. This quatity was divided by the mometum from Socrat. This ratio was calculated evet-by-evet ad required to be withi ±.5 of the origi. This limit is larger tha the expected resolutio of CLAS12 of.1% [26]. A secod cut o was also required. The miimum value for the deposited eergy i CLAS6 ( >.5 MeV) was estimated from Ref. [27] ad applied to all FTOF sigals i gemc. Quasielastic eutros were recostructed i the followig way. (1) Usig oly the recostructed electro iformatio ad assumig elastic scatterig off the eutro, the directio of the scattered eutro was calculated ad the expected CLAS12 sector the eutro would strike was determied. The struck sector was determied solely from the calculated directio of the eutro extracted from the measured electro iformatio. (2) A eutro track was geerated assumig the electro vertex as the startig poit ad usig the calculated eutro 3-mometum to determie the directio from that vertex. (3) The itersectio poit of the eutro track ad the plae of each FTOF pael i the expected CLAS12 sector was calculated. This task was doe usig the three poits at the corers of the active area of the FTOF P1A ad P1B paels to defie a triagular plae, calculatig the itersectio poit, ad usig a theorem from aalytical geometry to determie if the itersectio poit lay iside this triagle [28]. If the itersectio poit lay withi the FTOF pael active area, this eutro was classified as foud. If the itersectio poit lay outside the active area, the evet was rejected. For the P2B pael a similar approach was used. The trapezoidal shape of the pael was used to form the bottom portio of a ew triagle, i.e. the base ad the two equivalet agles of a isosceles triagle. The itersectio of the eutro track with this ew triagle was calculated ad tested to see if it lay iside the triagle. If that was true, the the itersectio poit was required to lie close to the base of the isosceles triagle ad withi the active area of the P2B pael. (4) The FTOF data was scaed to see if oe of the hits i the FTOF matched the expected positio of the foud eutro. A ray was draw from the vertex of the electro track to the positio of a hit o the face of the FTOF pael ad the agle γ was calculated betwee this ray ad the oe represetig the directio of the 3-mometum of the foud eutro. If this agle was less tha, the eutro recostructio was deemed a success. If the agle was greater tha, the evet was rejected. If more tha oe FTOF hit lay withi this agular coe aroud the foud eutro 3-mometum, the the hit with the smallest agle γ was selected. Fig. 14 shows the opeig agle γ betwee the directio of the foud eutro 3- mometum ad the ray goig from the electro track vertex ad the FTOF hits i pael P1B. The black histogram shows γ for all FTOF hits i the pael. There is a rapid, expoetial drop from the peak at γ = out to. Beyod that rage, the distributio is early flat ad the drops rapidly agai beyod 4 to zero. The red histogram shows the same distributio for all FTOF hits that lay i the sector of the foud eutro. It closely follows the black histogram for all FTOF hits out to γ = ad the diverges; cotiuig to fall rapidly to zero. The dashed lie i Fig. 14 marks the positio of the cut o γ used to select recostructed eutros. This value for the γ cut (γ = ) was origially used i the CLAS6 G M aalysis ad it ca be see here that the cut excludes the regio where backgroud hits i other sectors start to become sigificat. About 99% of the evets i the red histogram fall withi the cut.

15 CLAS-NOTE 211-Draft - August 9, E = 11 GeV, E >.5 MeV dep Black - all P1B hits Red - P1B hits i foud eutro sector γ (deg) Figure 14: Opeig agle betwee foud eutro ad TOF hit i pael P1B which lies i frot of pael P1A. The vertical lie shows positio of cut to select eutros. The eutro detectio efficiecy (NDE) ca ow be extracted from the simulatio. It is the ratio of recostructed eutros to foud eutros. Fig. 15 shows the mometum distributio of foud (black) ad recostructed (red) eutros i the left-had pael. The mometum distributio of foud eutros is peaked at higher mometum. This abudace Couts 25 2 Red - Recostructed eutros Black - Foud eutros E = 11 GeV >.5 MeV NDE E = 11 GeV, gemc simulatio Neutro detectio efficiecy >.5 MeV p (GeV/c) p (GeV/c) Figure 15: Histograms of foud (black) ad recostructed (red) eutros detected i FTOF are show i the left-had pael. The eutro detectio efficiecy derived from these results is show i the right-had pael.

16 CLAS-NOTE 211-Draft - August 9, of high-mometum eutros ca be explaied sice it is associated with low-mometum, large-agle electros i quasielastic scatterig. These large-agle electros are scattered ito a regio where CLAS12 has larger acceptace because it is away from the regio at forward agles where the cryostat for the torus coils is mergig ad reducig the acceptace. The red histogram for the recostructed eutros has much the same shape, but reduced i size by about a factor of te. The right-had pael i Fig. 15 shows the NDE extracted from the distributios show i the left-had pael. The simulated NDE (blue poits) is largely flat over most of the mometum rage ad drops off rapidly at the limits of the acceptace. The drop i the efficiecy at p 3 GeV/c is due to edge of the P1B pael. Quasielastic eutros at higher mometum ad more forward agles have to pass through both P1B ad P1A paels. At larger eutro agle (ad lower mometum for QE eutros), the particles oly ecouter the P2B pael which has lower efficiecy tha the combied P1A+P1B paels. The respose of the eutro detectio efficiecy to chages i the threshold was studied. As metioed above the value used here was the CLAS6 value take from Ref. [27]. The results of chagig this miimum value for are show i Fig. 16. The average NDE E = 11 GeV FTOF eutro detectio efficiecy Threshold Figure 16: Depedece of the eutro detectio efficiecy (NDE) for quasielastic eutros as a fuctio of the miimum deposited eergy is show. NDE for the P1A+P2B paels is 15.6 ±.2% at the omial CLAS6 threshold ad rises to a maximum of 17.6 ±.2% whe the threshold is reduced to zero. Turig the threshold up has oly a modest effect o the eutro detectio efficiecy. The detectio efficiecy for quasielastic eutros was measured i the E5 ru period ad presets a opportuity to challege our simulatios here with data. Durig the E5 ru the p(e, e π + ) reactio provided a source of tagged or foud eutros where the eutro mometum was kow from the electro ad pio kiematics. The foud eutros were the matched with hits i the CLAS6 time-of-flight system. The P1A ad P2B paels to be

17 CLAS-NOTE 211-Draft - August 9, used i CLAS12 gemc were origially part of the CLAS6 time-of-flight system. To compare the gemc simulatio ad the E5 NDE measuremet we focus oly o the P1A ad P2B paels. The P1B pael i frot of P1A was tured off i the simulatio. The results are show i Fig. 17. The left-had pael shows the mometum spectra for Couts 25 2 Red - Recostructed eutros Black - Foud eutros E = 11 GeV >.5 MeV o P1B pael NDE E = 11 GeV, gemc simulatio Neutro detectio efficiecy with P1B removed >.5 MeV p (GeV/c) p (GeV/c) Figure 17: Histograms of foud (back) ad recostructed (red) eutros detected i FTOF paels P1A ad P2B oly are show i the left-had pael. The eutro detectio efficiecy derived from these results is show i the right-had pael (blue poits) alog with the NDE measured at E = 4.2 GeV i CLAS6 durig the E5 ruig period (black poits). foud ad recostructed eutros. The shapes are qualitatively similar to the oes i the left-had pael of Fig. 15. The right-had pael i Fig. 17 shows the NDE extracted from the mometum spectra (blue poits). For p > 4 GeV/c the eutros were detected i pael P1A ad have a roughly costat efficiecy of about 8%. There is a dip i the efficiecy at p 3 GeV/c where the QE eutros fall ito a gap betwee paels P1A ad P2B. This gap is covered by the P1B pael i the full CLAS12 detector. At the lowest eutro mometa, the efficiecy returs to about 8% where the eutros are strikig pael P2B. The E5 measuremet of the NDE is show as the black poits i Fig. 17. The measured NDE rises rapidly from zero ad reaches a plateau at p 2GeV/c ad at a efficiecy of about 8%. There is good agreemet withi the experimetal ucertaity betwee the measured NDE ad the simulated oe. It bears emphasizig that the simulated ad measured results agree eve though two differet reactios are used. We ow summarize the work described i this CLAS-Note. We have simulated the productio ad recostructio of quasi-elastically scattered electros ad eutros i CLAS12 with gemc [2] ad Socrat [3]. We have studied the properties of the deposited eergy ad efficiecy of the CLAS12 FTOF system to establish a baselie for the future. We have simulated the extractio of the eutro detectio efficiecy usig QE eutros ad foud a efficiecy of 16% for paels P1A ad P1B combied together ad a value of 8% for pael

18 CLAS-NOTE 211-Draft - August 9, P2B. A compariso of the simulated efficiecy usig oly paels P1A ad P2B (that are beig reused from CLAS6) with the measured values from the E5 ru (usig the p(e, e π + ) reactio) shows good agreemet. For future work to prepare for the CLAS12 G M measuremet we will add the effects of Fermi motio to the target eutro ad develop a simulatio of the p(e, e π + ) reactio that will be used to extract the eutro detectio efficiecy i the CLAS12 G M experimet (E12-7-4). This work is supported by US Departmet of Eergy grat DE-FG2-96ER498 ad Jefferso Sciece Associates. Refereces [1] G.P. Gilfoyle et al. Experimet E12-7-4, Jefferso Lab, Newport News, VA, 27. [2] M. Ugaro. gemc - geat4 motecarlo. Techical report, Jefferso Lab, 211. [3] S. Procureur. Socrat: a software for clas12 recostructio ad trackig. CLAS-Note 28-15, Jefferso Lab, 28. [4] Nuclear Sciece Advisory Committee. The Frotiers of Nuclear Sciece. US Departmet of Eergy, 27. [5] J. Lachiet, A. Afaasev, H. Arehövel, W. K. Brooks, G. P. Gilfoyle, D. Higibotham, S. Jeschoek, B. Qui, M. F. Vieyard, et al. Precise Measuremet of the Neutro Magetic Form Factor G M i the Few-GeV2 Regio. Phys. Rev. Lett., 2(19):1921, 29. [6] W. Bartel et al. Nucl. Phys. B, 58:429, [7] G. Kubo et al. Phys. Lett. B, 524:26 32, 22. [8] A. Lug et al. Phys. Rev. Lett., 7(6): , Feb [9] H. Akli et al. Phys. Lett. B, 428: , [] B. Aderso et al. Phys. Rev. C, 75:343, 27. [11] R. G. Arold et al. Measuremets of trasverse quasielastic electro scatterig from the deutero at high mometum trasfers. Phys. Rev. Lett., 61(7):86 89, Aug [12] S. Rock et al. Measuremet of Elastic Electro-Neutro Cross Sectios up to Q 2 = (GeV/c) 2. Phys. Rev. Lett., 49(16): , Oct [13] W. M. Alberico, S. M. Bileky, C. Giuti, ad K. M. Graczyk. Electromagetic form factors of the ucleo: New fit ad aalysis of ucertaities. Phys. Rev. C (Nuclear Physics), 79(6):6524, 29. [14] G.A. Miller. Phys. Rev. C, 66:3221, 22.

19 CLAS-NOTE 211-Draft - August 9, [15] M. Guidal, M.V. Polyyakov, A.V. Radyushki, ad M. Vaderhaeghe. Phys. Rev. D, 72:5413, 25. [16] I. C. Cloet, G. Eichma, B. El-Beich, T. Klah, ad C. D. Roberts. Survey of ucleo electromagetic form factors. Few Body Syst., 46:1 36, 29. [17] C.E. Hyde-Wright ad K.deJager. Electromagetic Form Factors of the Nucleo ad Compto Scatterig. A. Rev. Nucl. Part. Sci., 54. [18] H. Akli et al. Phys. Lett. B, 336: , [19] G. Kubo et al. Phys. Lett. B, 524:26 32, 22. [2] E. E. W. Bruis et al. Measuremet of the eutro magetic form factor. Phys. Rev. Lett., 75(1):21 24, Jul [21] G.P. Gilfoyle, W.K. Brooks, S. Stepaya, M.F. Vieyard, S.E. Kuh, J.D. Lachiet, L.B. Weistei, K. Hafidi, J. Arrigto, D. Geesama, R. Holt, D. Potterveld, P.E. Reimer, P. Solvigo, M. Holtrop, M. Garco, S. Jeschoek, ad P. Kroll. Measuremet of the Neutro Magetic Form Factor at High Q 2 Usig the Ratio Method o Deuterium. E12-7-4, Jefferso Lab, Newport News, VA, 27. [22] J.D. Lachiet, W.K. Brooks, G.P. Gilfoyle, B. Qui, ad M.F. Vieyard. A high precisio measuremet of the eutro magetic form factor usig the CLAS detector. CLAS Aalysis Note 28, Jefferso Lab, 28. [23] J. Alliso et al. Geat4 developmets ad applicatios. IEEE Trasactios o Nuclear Sciece, 53:27 278, 26. [24] Wikipedia. Qt (framework) wikipedia, the free ecyclopedia, 211. [Olie; accessed 27-Jue-211]. [25] The CLAS12 TDR Editorial Board. The CLAS12 Techical Desig Report. Techical report, Thomas Jefferso Natioal Accelerator Facility, Newport News, VA, 28. [26] The Hall B 12 GeV Upgrade CDR Editorial Board. The Hall B 12 GeV Upgrade Precoceptual Desig Report. Techical report, Thomas Jefferso Natioal Accelerator Facility, Newport News, VA, 25. [27] K. Loukachie. Measuremet of the Polarizatio of the phi(2) i Electroproductio. PhD thesis, Virgiia Polytechic Istitute, 2. [28] Wikipedia. Lie-plae itersectio wikipedia, the free ecyclopedia, 211. [Olie; accessed 26-July-211].

20 CLAS-NOTE 211-Draft - August 9, A Socrat Parameter Iput // This is the optio file to ru the Socrat trackig code // Author: S.Procureur, May 28, v1. //the electro beam eergy i GeV, oly importat for Neutro Trackig Ebeam 11. // ru the eutro trackig code (1) or ot () Neutro Trackig 1 // ru the forward trackig code (1) or ot () Forward Trackig 1 // ru the cetral trackig code (1) or ot () Cetral Trackig // vertex fit o (1) or off () (both cetral ad forward track must be o!) Vertex Fit // Evets from Geat (1) of from iteral Socrat routie () Geat 1 // if Geat mode, specify the path to the Geat output //GFile gemc.root //GFile /home/moog/ec/clas12ec3.root //GFile results.root GFile mmass.root // Mode: batch (1) or iteractive () Mode 1 // Number of evets to process (batch mode oly, without Geat) Evets // Save a DC or BST display of last evet (iteractive mode oly) DispEvet DC 1 DispEvet BST 1 // Do the fial fit or ot (usig Kalma Filter) Kalma Filter 1 // Fill the output root tree (1) or ot () Outtree 1 // Debug mode (more variables i output tree) o (1) or off () Debug // Verbosity, how much do you wat prited to the scree while socrat rus? Verbosity

21 CLAS-NOTE 211-Draft - August 9, // Cut o deposited eergy i DC ad FST (i MeV) DC Edep.1 SVT Edep.2 CTOF Edep 1. // Use liear iterpolatio for torus field estimatio (should be 1!) Liear Iterp 1 // orietatio of first wire i DC: +6 (1) or -6 (-1) DC Firstagle 1 // miistagger i the DC (i micros) DC Miistag 5. // torus polarity (1: electros go back to the beam; -1: opposite) Torus Polarity 1 // Use the Forward Tracker (1) or ot () FST use // fractio of dead chaels i the FST (i %) FST dead. // // if Geat mode is ot used, you eed to specify the phase space for // the iteral track geerator type of charged particle (umberig // scheme from PDG, eg proto is 2212, electro is 11) Cetral Particle 11 Forward Particle 11 // rage i p (GeV/c) Cetral Prage Forward Prage 5 8 // rage i theta (polar agle, i degrees) Cetral Thetarage Forward Thetarage 15 4 // rage i phi (azimuthal agle, i degrees) Cetral Phirage 5 6 Forward Phirage 5 6 // z legth of the target (i m, vertex will be geerated radomly iside it) Target legth. // occupacy i each of the DC regios (i %)

22 CLAS-NOTE 211-Draft - August 9, DC occ // backgroud rate i FST, if used (i MHz/ layer) FST rate // backgroud rate i BST, if used (i MHz/ layer) BST rate // Multiple scatterig o (1) or off() Mult Scat 1 // Prit the hits iformatio Prit Hit // itroduce some misaligmets (i mm ad mrad!) Misalig BST Z Misalig BST R Misalig BST Phi Misalig DC R Misalig DC Tilt Misalig DC Agle1st Misalig FST Z Misalig FST Phi Misalig Soleoid Misalig Torus // Iteral param (chage speed, do t chage if you do t kow it!) Time Accel 4.e-13 5 B Socrat Trackig Parameters // This is the parameter file to ru the Socrat trackig code // Author: S.Procureur, Jue 17th, 28, v1.1 FI2 iteratio 3 KF iteratio 2 DC Dwire FST IterMargi.2 FST Dphi.2 FST DRadius DC LRiter 8 BST IterMargi.1 BST VertexDist.8 BST Prage.1 4. CTOF TimeWidow 6 8 BST Dphi BST distp4.7.1 BST cosp //Torus FieldIt Torus FieldItp Torus FieldItm

23 CLAS-NOTE 211-Draft - August 9, FT CovMat FT CovMat FT CovMatN DCFST Rmatchig.1 FST MultResol 1.. CT CovMat zphi CT CovMat mom BST MultResol 3. VERTEX DistRZ.1.1