1. Detector integration @HERMES
Delia Hasch
outline:
physics goals & experimental design
– a brief history
physics achievements & lessons from HERMES
– a few examples
Common ENC/EIC workshop at GSI, Darmstadt, Germany, May 2009

2. HERMES: physics scope Technical Design Report July 1993 spin puzzle
EMC 1988:
DS=0.12±0.17

3. HERMES: physics scope  inclusive & semi-inclusive DIS
Technical Design Report July 1993
 inclusive & semi-inclusive DIS
- g1 and g2 the proton and neutron
- tensor structure fct
- flavour dependence of quark helicity distribution
EMC 1988:
DS=0.12±0.17
- dV/uV from F2n/F2p
- sea quark distributions

4. HERMES: physics scope  inclusive & semi-inclusive DIS
Technical Design Report July 1993
 inclusive & semi-inclusive DIS
- g1 and g2 the proton and neutron
- tensor structure fct
- flavour dependence of quark helicity distribution
- dV/uV from F2n/F2p
- sea quark distributions
EMC 1988:
DS=0.12±0.17
polarised high energy lepton beam
polarised proton and neutron targets
spectrometer with good PID

5. HERMES: choice of technologies
polarised high energy lepton beam
polarised proton and neutron targets
spectrometer with good PID
 statistical precision:
f: target dilution factor
f=1 gas targets f~0.02 solid targets

6. HERMES: choice of technologies
polarised high energy lepton beam
polarised proton and neutron targets
spectrometer with good PID
 statistical precision:
novel technologies:
 gas target in a storage cell
f=1
rapid polarisation reversal
very thin exit window
f: target dilution factor
f=1 gas targets f~0.02 solid targets
 polarised e- or e+ of HERA storage ring
fast polarisation build up (~30’)
polarisation reversal

7. HERMES: choice of technologies
lepton polarisation at HERA <Pb>~45-55%

8. HERMES: choice of technologies
HERMES integration

9. HERMES: choice of technologies
HERMES integration
target section:
beam live time requirement: ~45h
upper limit for target density:
1015 atoms/cm2

10. HERMES: choice of technologies
spectrometer
P (GeV)
cumulative rate (s-1sr-1GeV-1) p
clear identification of electrons for DIS event ID:
(large p bg from g-production)
calorimeter + TRD: HRF~103 e

11. HERMES: choice of technologies
spectrometer
particle ID: lepton ID with e ~ 98%, hadron contamination <1%
RICH: p, K, p ID within 2<Eh<15 GeV (p from 1 GeV)
resolution: dp/p ~ 1.5%, dq < 0.6 mrad (slightly worse with RICH)

12. HERMES angular acceptance
effect of septum plate
polar angle
azimuthal angle

13. physics scope & achievements
inclusive & semi-inclusive DIS
- g1 and g2 the proton and neutron
- tensor structure fct
- flavour dependence of quark helicity distribution
- dV/uV from F2n/F2p
- sea quark distributions
inclusive & semi-incl. & exclusive DIS
- g1 for p, n and d
- tensor structure fct
first 5-flavour separation of Dq, Ds
first gluon polarisation
- first SSA in sidis: AUL , AUT
first DVCS with polarised beam/target
and two lepton charges
flavour asymmetry of light sea
hadron multiplicities
- nuclear effects in incl.+semi-incl. DIS
- exclusive VM production, polarised SDMEs
- exclusive 1 and 2 pion production
lambda polarisation
exotic states …

14. - GPD&TMD physics program -
lessons from HERMES
- GPD&TMD physics program -
~ hermetic spectrometer
 full event reconstruction
 full kinematic coverage
good e/h separation & hadron ID over whole momentum range
lumi determination for measurement of absolute cross section (differences)
both lepton beam charges desirable

15. lesson 1: full event reconstruction
example:
deeply virtual Compton scattering & GPDs

16. lesson 1: full event reconstruction
example:
deeply virtual Compton scattering & GPDs
HERMES till 2005 g
e+, p
e-, e

17. exclusivity via missing mass3%
‘exclusive sample’
 BH&DVCS + intermediate nucleon resonance production

18. 1 out of 17 DVCS observables
 model independent extraction of CFF HIm, HRe
[M. Guidal, H. Moutarde, ]
fraction of associated
 full event reconstruction with 2006/07

19. HERMES06/07 with recoil

20. HERMES06/07 with recoil D production full event reconstr.,
PID capabilities:
ID of intermediate
D production

21. lesson 1&2: full kinematic coverage & PID
example-I :
semi-inclusive 2 hadron production: transversity from IFF
incomplete angular coverage
restricted momentum range for PID
example-II :
semi-inclusive 1 hadron production: transversity&friends
incomplete pT coverage

22. 2-hadron production: only relative momentum of hadron pair relevant
lesson 1&2: example-I
2-hadron production:
interference fragmentation function between pions in s-wave and p-wave
only relative momentum of hadron pair relevant
!collinear factorisation!  relativ. momentum: R=(Pp++Pp-)/2  can have transv. component even when integrating over PT of the pair
 integration over transverse momentum of hadron pair simplifies factorisation (collinear!) and Q2 evolution
however cross section becomes very complicated (depends on 9! variables)
 sensitive to detector acceptance effects

23. (1)2-hadron production (f) - inclompete angular coverage -
lesson 1&2: example-I
(1)2-hadron production
[thesis P. van der Nat, Vrije Universiteit Amsterdam 2007]
- inclompete angular coverage -
(f)

24. (1)2-hadron production (f) - inclompete angular coverage -
lesson 1&2: example-I
(1)2-hadron production
[thesis P. van der Nat, Vrije Universiteit Amsterdam 2007]
- inclompete angular coverage -
(f)
resolve acceptance effects:
… and preferably even more kinematic variables

25. 2-hadron production - restricted momentum range -
lesson 1&2: example-I
[thesis P. van der Nat, Vrije Universiteit Amsterdam 2007]
2-hadron production
- restricted momentum range -
…facilitate interpretation
q integration

26. 2-hadron production q acceptance is momentum dependent:
lesson 1&2: example-I
[thesis P. van der Nat, Vrije Universiteit Amsterdam 2007]
2-hadron production
- restricted momentum range -
…facilitate interpretation
q integration
q acceptance is momentum dependent:
full acceptance

27. 2-hadron production q acceptance is momentum dependent:
lesson 1&2: example-I
[thesis P. van der Nat, Vrije Universiteit Amsterdam 2007]
2-hadron production
- restricted momentum range -
…facilitate interpretation
q integration
q acceptance is momentum dependent:
full acceptance

28. 2-hadron production - restricted momentum range - binning also in q
lesson 1&2: example-I
[thesis P. van der Nat, Vrije Universiteit Amsterdam 2007]
2-hadron production
- restricted momentum range -
binning also in q

29. lesson 1&2: full kinematic coverage & PID
example-I :
semi-inclusive 2 hadron production: transversity from IFF
incomplete angular coverage:
need to evaluate AUT instead of sUT  complicates
interpretation
restricted momentum range for PID
need to fit also polar angular dependence  highly
non-linear fits

30. lesson 1&2: example-II
1-hadron production:
Collins effect:

31. 1-hadron production: Collins effect:
lesson 1&2: example-II
1-hadron production:
Collins effect:
convolution integral over initial (pT) and final (kT) quark transverse momenta
for a model independent extraction:
evaluate PhT weighted asymmetries
 product of dqH1 instead of convolution integral

32. lesson 1&2: example-II
[L. Pappalardo, PhD Thesis University Ferrara]
acceptance studies:
Monte Carlo: gmc_trans: generator for transversity + TMDs
simulates full kinematic dependences of observables
Collins asymmetries
unweighted

33. lesson 1&2: example-II
[L. Pappalardo, PhD Thesis University Ferrara]
acceptance studies:
Monte Carlo: gmc_trans: generator for transversity + TMDs
simulates full kinematic dependences of observables
Collins asymmetries
weighted
 large acceptance effects

34. pT weighted asymmetries:
lesson 1&2: example-II
[U. Elschenbroich, PhD Thesis University Erlangen]
pT weighted asymmetries:
acceptance depends strongly on pT:
MC distributions:
p+/- p0

35. lesson 1&2: full kinematic coverage & PID
example-II :
semi-inclusive 1 hadron production: transversity&friends
incomplete pT coverage:
pT dependent acceptance biases asymmetry extraction
( way out: multi-D unfolding )

36. lesson 1&2: full kinematic coverage & PID
example-II :
semi-inclusive 1 hadron production: transversity&friends
incomplete pT coverage:
pT dependent acceptance biases asymmetry extraction
( way out: multi-D unfolding )
BUT
“no particle physics experiment has a perfect acceptance”

37. lesson 1&2: full kinematic coverage & PID
example-II :
semi-inclusive 1 hadron production: transversity&friends
incomplete pT coverage:
pT dependent acceptance biases asymmetry extraction
( way out: multi-D unfolding )
BUT
“no particle physics experiment has a perfect acceptance”

38. lesson 1&2: full kinematic coverage & PID
example-II :
semi-inclusive 1 hadron production: transversity&friends
incomplete pT coverage:
pT dependent acceptance biases asymmetry extraction
( way out: multi-D unfolding )
BUT
“no particle physics experiment has a perfect acceptance”
 need the tools (Monte Carlo) to estimate detector effects
 need the tools (e.g. multi-D unfolding) to correct for

39. lesson 3: lumi  cross section (differences)
Lesson from RHIC: measure cross sections for particle production
justify validity of pQCD interpretation of you data
 measure your hadron multiplicities (or better prod. cross section) for ‘own’ (spin-independent) fragmentation fct.s
 get rid of interpretation uncertainties due to denominator in asymmetries
example-I: lepton-beam or virtual-photon asymmetries AUT
example-II: DVCS asymmetries

40. interpretation uncertainties I
lesson 3: example-I
interpretation uncertainties I
SIDIS AUT: lepton-beam or virtual-photon asymmetries
Collins asymmetry:
 account for A(x,y) and B(y) to get virtual-photon asymmetries
BUT: need RSIDIS
this is an !

41. interpretation uncertainties II
lesson 3: example-II
interpretation uncertainties II
DVCS: e.g. beam-charge asymmetry …
wanted: interference term
gets admixture of Fourier coefficients related to BH and DVCS squared terms
 need to be accounted for in fitting procedure

42. lesson 4: both lepton beam charges desirable

43. lesson 4: both lepton beam charges desirable
DVCS: charge asymmetry
CFF Re (GPDs)
contribution of ‘D-term’

44. lesson 4: both lepton beam charges desirable
DVCS: charge asymmetry & separation of interference and DVCS squared terms
CFF Re (GPDs)
contribution of ‘D-term’

45. the end of the story ?
1:09:56 am T

46. the end of the story ?
1:09:56 am T
more to come:
EIC/ENC

47. conclusion  lessons from HERMES many pioneering measurements
~ hermetic spectrometer
 full event reconstruction
 full kinematic coverage
good e/h separation & hadron ID over whole momentum range
lumi determination for measurement of absolute cross section (differences)
both lepton beam charges desirable

48. backup slides

49. HERA fills and bunch structure
typical beam history for HERA p and e beams:
Typical fill~15h (electron scale absent), ‘end of run’ HD  lifetime: 15h  2h
high density ‘end of fill run’
beam live time: ~15  2h allowed target densities up to 1017 atoms/cm2

50. HERA fills and bunch structure
Typical fill~15h (electron scale absent), ‘end of run’ HD  lifetime: 15h  2h

51. good particle ID identify DIS events:
HERMES
P (GeV)
cumulative rate (s-1sr-1GeV-1)
identify DIS events:
good e/h separation over wide momentum range and espec. at low momenta
most modern PID:
ALICE: P ~ (0.5 – 100) GeV