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HPS and beam polarization

This presentation discusses the motivation and potential for beam polarization in the HPS collaboration. It explores the sensitivity of spin observables and the potential for detecting A' amplitudes. The speaker also discusses the challenges of integrating over multiple kinematic variables and offers possible solutions.

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HPS and beam polarization

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  1. HPS and beampolarization HPS collaboration meeting 17/06/2014 Michel Guidal IPN Orsay

  2. Motivation The JLabbeamcomespolarized to a highdegree for (almost) free The QED (trident) background amplitudeispurelyreal => No sensitivity to beam spin The A’ amplitude has an imaginary part (width) • Throughinterferencewith the trident amplitude, Any perspective for HPS ? • thereshouldbe a beam spin asymmetry (BSA) • In principle, any non-zeroasymmetrywouldsign an A’ • Spin observables are well-known to be sensitive to smalleffects • An asymmetry (ratio) doesn’tneed the perfectknowledge • of the normalization and shape of the QED background • s +- s - s ++s -

  3. Tree-leveldiagrams for ep->epe+e- fromT. Beranekand M. VanderhaeghenarXiv:1303.2540 [hep-ph] (Relation to M. Guidaland M. Vanderhaeghen(Double DVCS) Phys.Rev.Lett. 90 (2003) 012001) (withantisymmetrization) V = g or A’(onlytimelike)

  4. Kinematics fe’ fA’ Atfixedbeamenergy, there are 8 independent variables: Ee’, qe’ , fe’ , qA’ , fA’ , Me+e-, qcm , qcm

  5. Theoreticalbeam spin asymmetries qcm=0 deg, fcm=0 deg NO ANTISYMMETRIZATION qcm=20 deg, fcm=70 deg qcm=70 deg, fcm=170 deg qcm=170 deg, fcm=250 deg Ebeam=2.2 GeV, qe=0.5 deg, Ee’=1 GeV, qA’=2 deg, Me+e-=50 MeV MA’=50 MeV, e=10-2 (a’/a=10-4) fA’ (deg.)

  6. Theoreticalbeam spin asymmetries qcm=0 deg, fcm=0 deg WITH ANTISYMMETRIZATION qcm=20 deg, fcm=70 deg qcm=70 deg, fcm=170 deg qcm=170 deg, fcm=250 deg Ebeam=2.2, GeVqe=0.5 deg, Ee’=1 GeV, qA’=2 deg, Me+e-=50 MeV MA’=50 MeV, e=10-2 (a’/a=10-4) fA’ (deg.)

  7. Whathappens to the BSA when one integrates over the 8 kinematic variables ? Complicatednumericalproblem: 8 variables, structures and peaks,… Monte-Carlo integration, ~stable resultswith1011events (around mA’ ; lessif onlybackground), 24 hourswith use of IN2P3 grid

  8. y .06 (rad) qv (« vertical » angle) .015 (rad) .05(rad) x -.05(rad) fh (« horizontal » angle) -.015 (rad) -.06 (rad) In the following, wewill use the 8 independent variables: qe’ , fe’ , Me+e- , Ee+ , qv(e+), fh(e+), qv(e-), fh(e-),

  9. MA’=50 MeV, e=10-2 G ~ 10 eV (a’/a=10-4)

  10. Integrating over: qe’ [0,p](rad) fe’[0,2p](rad) Me+e- 1 keV around MA’ Ee+[300,2000] (MeV) qv (e-) [-.06,-.015]+ [.015,.06](rad) fh (e-) [-.05,.05] (rad) qv (e+) [.015,.06] (rad) fh (e+) [-.05,.05](rad)

  11. y qv (« vertical » angle) qv (e+) [.015,.06] x fh (« horizontal » angle) A «bit more» (~3/1000) e+ on the leftsidethan on the right side

  12. Count rates/Statistics • If one takes the fh (e+) binwhere BSA peaks(i.e. fh (e+) ~2 deg.): • N(A’)~4.1011 (arb. unitsproportional to cross section) • N(backgr)~1.5 1011 (arb. unitsproportional to cross section) • DN(A’)~ 8.108 BSA ~ 8.108/4.1011 ~ 2/1000

  13. A’ backgr

  14. Count rates/Statistics • If one takes the fh (e+) binwhere BSA peaks(i.e. fh (e+) ~2 deg.): • N(A’)~4.1011 (arb. unitsproportional to cross section) • N(backgr)~1.5 1011 (arb. unitsproportional to cross section) • DN(A’)~ 8.108 BSA ~ 8.108/4.1011 ~ 2/1000 This all over a DMe+e=1 keV bin !

  15. Count rates/Statistics • If one takes the fh (e+) binwhere BSA peaks(i.e. fh (e+) ~2 deg.): • N(A’)~4.1011 (arb. unitsproportional to cross section) • N(backgr)~1.5 1011 (arb. unitsproportional to cross section) • DN(A’)~ 8.108 BSA ~ 8.108/4.1011 ~ 2/1000 This all over a DMe+e=1 keV bin ! • If one scales over a DMe+e=1 MeV bin: • N(A’)~4.1011 (arb. unitsproportional to cross section) • N(backgr)~1.5 1011 X 103(arb. unitsproportional to cross section) • DN(A’)~ 8.108 BSA ~ 8.108/1.5 1014 ~ 5/106

  16. Count rates/Statistics • If one takes the fh (e+) binwhere BSA peaks(i.e. fh (e+) ~2 deg.): • N(A’)~4.1011 (arb. unitsproportional to cross section) • N(backgr)~1.5 1011 (arb. unitsproportional to cross section) • DN(A’)~ 8.108 BSA ~ 8.108/4.1011 ~ 2/1000 This all over a DMe+e=1 keV bin ! • If one scales over a DMe+e=1 MeV bin: • N(A’)~4.1011 (arb. unitsproportional to cross section) • N(backgr)~1.5 1011 X 103(arb. unitsproportional to cross section) • DN(A’)~ 8.108 BSA ~ 8.108/1.5 1014 ~ 5/106 • And weexpect 107events in a 1 MeV bin for HPS…

  17. Doesn’t look too good… But maybestillsomehope: Instead of integrating over all 8 variables and all HPS acceptance, identify a particular corner of the phase spacewhere BSA is of the order of the percent and, if doingso, one goesfrom 107 to 104events… (one canalwaysdream) Staytuned !

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