SoLID Background Update Zhiwen Zhao UVa 2013/11/08 1

Outline Intro – Estimation – Method PVDIS – Baffle update SIDIS – target collimator, target widow, etc Todo list 2

Estimation PVDISSIDIS He3JPsi Beam50uA15uA3uA TargetLD2 40cm10amg He3 40cmLH2 15cm WindowAl 2*100umGlass 2*120umAl 2*100um Radiation length (target) 5.4e-20.8e-31.7e-2 Radiation length (window) 2.25e-33.4e-32.25e-3 Radiation length (total) 5.6e-24.2e-31.9e-2 Luminosity (target)1.27e393e361.2e37 Luminosity (window) 1e373.7e366e35 Luminosity (total)1.27e396.7e361.2e37 Commentbaffle target window collimator 3

Method EM background – Build all parts with realistic material in GEMC, turn on general Geant4 physics list “QGSP_BERT_HP”, throw electrons into SoLID targets – Results dominated by low energy photons and electrons. EM process should be fairly accurate – Hadrons produced also, but not used for later study because Geant4 doesn’t have all necessary crosssections – Neutrons including low energy ones produced also, hasn’t been used for study yet. (Lorenzo showed Geant4 has similar results with FLUKA) 4

Method Hadron background – pi/K/p generated from Wiser fit, more accurate at DIS region, but extends to low energy region also – With a distribution according to crossection and no “weight” factor (by Yuxiang Zhao’s modified “eicRate” code), they are thrown into SoLID from their simulated vertices – SoLID has realistic material in GEMC and physics list “QGSP_BERT_HP” is turned on. It’s the same condition like in EM background study. – A lot of secondary hadrons are produced. Also many low energy photons, electrons and neutrons – The primary particle “kind” always dominates unless it decays like pi0 or Ks where decay products donimates 5

Method e(DIS) and e(ES) – e(DIS) generated from CTEQ fit by code “eicRate” – e(ES) generated from formula by code “eicRate” – Only have even distribution with a “weight” factor. Doesn’t have distribution same as crosssection and no “weight” factor yet – Don’t expect it as a big source of background – But it’s need for energy loss and radiation correction study 6

Code and Result Code – ckground ckground Result – sim/background 7

PVDIS, baffle design What we have learned – It’s not easy to have code automatically optimize to let high x e(DIS) pass, block position pions and straight photons at same time – 6 baffle planes is not enough to reduce secondary pion background to the level trigger can take, 11+1 planes works – 1 st baffle inner radius needs to be large to reduce background like moller electron. We use 5cm now – Beamline at downstream should have as large opening angle as position 8

Baffle Design Method 1. Study phi turning from eDIS events at every baffle plate front face. Allow 96% (2-98% of phi change) of rate weighted events with GeV to pass through. This define the opening for a very narrow phi slice of eDIS events from the target 9 Rate VS phi turning At 20 blocks of 1 st baffle plane

Baffle Design Method 2. Enlarge this opening by 5 o where positive leaks start to appear, expect 40%=5/12 acceptance for these eDIS events 10 Example of 11 baffle planes

3. Further block photons (pi0) by adding more blocking At the last (11 th ) baffle, negative and neutral mixes with each other at low phi where high x and high P events are. Block photon here will harm eDIS acceptance at high x At EC, negative and neutral split well from each other due to the additional flight path. Photon block at EC works better. 11 Baffle Design Method

EC photon block EC coverage R(110,265)cm EC photon block – 30 of them – R( )cm – 5cm(8*X 0 ) thick lead, reduce photon energy by 1 order – We have 19cm in Z between Cherenkov and EC for the photon block and 2 GEM planes 12 Illustration only

Err_Apv(%) x Baffle in pCDR Baffle new EC R(110,250)cm nominal acceptanceAssume 50uA, 40cm LD2 Pol_beam 85%, 120 days No trig cut New baffle 0.55x 5deg 5cm, 5555 baffle Background needs to be re-evaluated Similar level is expected from its blocking ability

SIDIS He3 A pair of Tungsten collimators are optimized to block hadrons from target windows into forward angle detectors The acceptance shown with and without the collimator is similar to the SIDIS proposal A full background study is done EC performance is under study. Single trigger rate will be checked 14

SIDIS He3, pi-/e- ratio at detector 15 No backgroud (HGCC) Full backgroud (HGCC) No backgroud (FAEC) Full backgroud (FAEC)

Todo list Next iteration of PVDIS: background with new baffle SIDIS He3: figure of merit check to further optimize the target collimator SIDIS proton: study sheet of flame and its impact on detectors JPsi: full background study 16

backup 17

source Z(-10,30)cm R(0,3.536)mm for 5x5mm raster neutral negative positive Acceptance, Baffle 0.55x5degblock 18 EC module R(110,265)cm EC photon block (“baffle 3.5degblock”) 30 of them R( )cm Start from 2.8 degree and width 4 degree. 5cm(8*X 0 ) thick lead, hope to reduce photon energy by 1 order

eDIS acceptance comparison at EC “0.55x 5deg” and “0.55x 5deg block” has best acceptance at high x 19

eDIS rate comparison at EC 20 “0.55x 5deg” and “0.55x 5deg block” has no low mom leak which could leads to high trig rate