Future Exclusive Measurements at HERMES › conference › qcdn06 › TALKS › Thursday 15 › Kaiser.pdfRecoil Detector Event END VIEW LOOKING DOWNSTREAM y x Pd SciFi Si Target Event

Future Exclusive Measurements at HERMES

Ralf Kaiser, University of Glasgowon behalf of the HERMES Collaboration

The Recoil Detector Upgrade

Data Taking in 2006/7

Projections for Exclusive Measurements

– p.1/26

HERMES Physics

Development from inclusive over semi-inclusive toexclusive measurements over decade 1995 - 2005.

Physics emphasis moved from polarised structurefunctions to quark helicities and transversity to GPDs.

Upgrades/changes to the experimental apparatus:RICH detector for semi-inclusive measurements,transverse target for transversity

The final step is the recoil detector upgrade forexclusive measurements, the focus of the final yearof HERMES data taking.

Recent exclusive HERMES results:C.Hadjidakis (overview), A.Rostomyan, Z.Ye.

R.Kaiser - HERMES Future – p.2/26

HERMES with Recoil Detector

RecoilProton

1

0

2

−1

−2

m

LUMINOSITY

CHAMBERSDRIFT

FC 1/2

DVC

MC 1−3MONITOR

BC 1/2

BC 3/4

PROP.CHAMBERS

FIELD CLAMPS

PRESHOWER (H2)

CALORIMETER

DRIFT CHAMBERS

TRIGGER HODOSCOPE H1

0 1 2 3 4 5 6 7 8 9

MAGNET

STEEL PLATE

TARGETCELL

HODOSCOPE H0

27.5 GeV

e+

m

TRD

e

γ

RICH

▽R.Kaiser - HERMES Future – p.3/26

HERMES with Recoil Detector

RecoilProton

−1

−2

1

0

2

RICH

e

γ

m

LUMINOSITY

CHAMBERSDRIFT

FC 1/2

DVC

MC 1−3MONITOR

BC 1/2

BC 3/4

PROP.CHAMBERS

FIELD CLAMPS

PRESHOWER (H2)

CALORIMETER

DRIFT CHAMBERS

TRIGGER HODOSCOPE H1

0 1 2 3 4 5 6 7 8 9

MAGNET

STEEL PLATE

HODOSCOPE H0

27.5 GeV

e+

m

TRD

DETECTORRECOIL


HERMES Recoil Detector - 3D CAD


Goals of the Recoil Detector

Resonances

DVCS+BHsemi-incl.

Detection of all reaction products over theentire momentum range to guarantee theexclusivity of the reaction:

Recoil protons

Pions and protons from backgroundprocesses e.g. ∆+-production withbremsstrahlung

Photons from π0 → γγ

Sufficient t-resolution to allow binning in t.

Si-detector: low t, SciFi detector: higher t

Improved systematics due to removal ofbackground (see left).

Improved statistics due to high densityunpolarised target.


Exclusivity

0

0.02

0.04

0.06

0.08

0.1

0.12

0 20 40Mx2 [GeV

2]

rate Without Recoil Detector

0

0.01

0.02

0.03

0.04

0.05

0.06

0 20 40Mx2 [GeV

2]ra

te

MC totalBH/DVCSBH/DVCS with ∆exclusive π0

semi-inclusive / VMs

With Recoil Detectorand all Cuts

Coplanarity cut, pion suppression, photon detection; efficiency ∼50%(MC simulation)

Reduction of the non-exclusive background:

semi-incl.: 5%→≪1%

associated prod.: 11%→∼1%


Recoil Detector - Complete Setup


Recoil Detector EventEND VIEW LOOKING DOWNSTREAM

y

x

Pd

SciFi

Si

Target

Event number:

Input file:

Event number:

Input file:

Pd

SciFi

Si

Target

y

x

Event number:

Input file:

Pd

SciFi

Si

Target

y

x

Event number:

Input file:

END VIEW LOOKING DOWNSTREAMy

x

Pd

SciFi

Si

Target

Pd

SciFi

Si

Target

y

x

Event number:

Input file:

Pd

SciFi

Si

Target

y

x

Event number:

Input file:

Pd

SciFi

Si

Target

y

x

Event number:

Input file:

Pd

SciFi

Si

Target

y

x

Event number:

Input file:

Pd

SciFi

Si

Target

y

x

Event number:

Input file:

Pd

SciFi

Si

Target

y

x

Event number:

Input file:

Pd

SciFi

Si

Target

y

x

Event number:

Input file:

Pd

SciFi

Si

Target

y

x

Event number:

Input file:

Pd

SciFi

Si

Target

y

x

Event number:

Input file:

Pd

SciFi

Si

Target

y

x

Event number:

Input file:

Pd

SciFi

Si

Target

y

x

Event number:

Input file:

Pd

SciFi

Si

Target

y

x

Event number:

Input file:

Pd

SciFi

Si

Target

y

x

Event number:

Input file:

Pd

SciFi

Si

Target

y

x

Event number:

Input file:

Pd

SciFi

Si

Target

y

x

Event number:

Input file:

Pd

SciFi

Si

Target

y

x

Event number:

Input file:

Pd

SciFi

Si

Target

y

x

Event number:

Input file:

Pd

SciFi

Si

Target

y

x

Event number:

Input file:

Pd

SciFi

Si

Target

y

x

Event number:

Input file:

Pd

SciFi

Si

Target

y

x

Event number:

Input file:

Pd

SciFi

Si

Target

y

x

Event number:

Input file:

Pd

SciFi

Si

Target

y

x

Event number:

Input file:

Pd

SciFi

Si

Target

y

x

Event number:

Input file:

Pd

SciFi

Si

Target

y

x

Event number:

Input file:

Pd

SciFi

Si

Target

y

x

Event number:

Input file:

Pd

SciFi

Si

Target

y

x

Event number:

Input file:

Pd

SciFi

Si

Target

y

x

Event number:

Input file:

Pd

SciFi

Si

Target

y

x

Event number:

Input file:

Pd

SciFi

Si

Target

y

x

Event number:

Input file:

Pd

SciFi

Si

Target

y

x

Event number:

Input file:

Pd

SciFi

Si

Target

y

x

Event number:

Input file:

Pd

SciFi

Si

Target

y

x

Event number:

Input file:

Pd

SciFi

Si

Target

y

x

Event number:

Input file:

Pd

SciFi

Si

Target

y

x

Event number:

Input file:

Pd

SciFi

Si

Target

y

x

Event number:

Input file:

Pd

SciFi

Si

Target

y

x

Event number:

Input file:

Pd

SciFi

Si

Target

y

x

Event number:

Input file:

Pd

SciFi

Si

Target

y

x

Event number:

Input file:

Pd

SciFi

Si

Target

y

x

Event number:

Input file:

SFT (SciFi) DETECTOR UNFOLDED

[angle is measured w.r.t. y axis, clockwise; SFT shift O=-10.1721 / I=-20.0891 deg.]

-20.0891 159.9109 339.9109

-10.1721 169.8279 349.8279

INNER SciFi

OUTER SciFi

SFI1 SFI2 SFI3 SFI4 SFO1 SFO3Thresholds ON

Pd

SciFi

Si

Target

SFI1 SFI2 SFI3 SFI4 SFO1 SFO3

2

1 4

3Si Z

y

x

Event number: 2874310

Date: Wed Mar 29 14:11:18 MEST 2006

Input file: /tmp/xtc2ed.5442.pipe

51115161720212426313233464752535455616263646970717273747576777879808182838485868788899091929394969798105106

79 7928313839727374757677788687122

91515202129498586878889901132838626364656667707172737475767778798081828384858788899099100101102103104105106107108

91105106107 6581828384851021081091101111121131141151221920216466107116

8310310511111551117182045757677828485104110123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100101102103104105106107108109110111112113114115116117118119120121122123124125126127128

971213141516171819202223242527283031333436373839404142439899 24252829313234363739404243454648495152535455565758596061636466676970727376787980828890919394969799100102103105106108109119123

3637303133344344454647484950515253545561626364656667767879808182838485869091929394959697105123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100101102103104105106107108109110111112113114115116117118119120121122123124125126127128

18192022272829303132333435363738394041424344454647484950515254555663646667697076777879808182838485117118121122127 11512712131819204951525472787981828384858687888990919394969799100102103114116122

1920103105106

106105134135

80 99

6

Event with single track in SFT and photon detector.

Average hit multiplicity per SFT layer ∼3.


HERMES Data Taking HERA Run II

2002-5 transverse target 2006-7 unpol. targete− March-June 06


Target Cell AccidentMarch: damage probablydue to accidental beam loss

May: radiation damage tosilicon detector due tosecond incident

Si detector removed forrepair, re-installation end ofJune

DVCS BCA affected most,lose recoil protons at small t

SciFi detector available forpart of the e− data, MC stu-dies under way.


HERMES Statistics Overview (pb−1)

HERA-I (1996-2000) H D 4He N2 Ne Kr Xee− 11 50 - - - - -e+ 240 320 30 50 86 30 -

HERA-II (2002-2007)e− 250 150 - - - 50 50e+ 820 200 - - - 55 30

of which e+ with RD 750 200 - - - - -

DVCS BCA: Published 10 pb−1 e−. Expect to have 250 pb−1 e−.

Total cross section for VM and PSM production on hydrogen: 1.3 fb−1.

2006/7 running: 23M → 56M DIS events on (unpolarised) hydrogen

Average beam polarisation only ∼35% for HERA-II, while ≥50% for HERA-I.


Exclusive Processes to Constrain GPDs

Quantum number of final state

selects GPD.

DVCS e⇆

p → epγ H

(BSA/BCA) e± → epγ

Vector ep → epρ0 H,EMesons ep → epφ0

Pseudoscalar ep → enπ+∼

H,∼

E

Mesons

HERMES measures many different final statessimultaneously with the same spectrometer !


Exclusive Measurements at HERMESProcess Comments Learn about GPDs Recoil Detector Can Do

DVCS BCA unique ! D-term desirable (but n/a) ++

DVCS BSA vs xB , t constrain Hu desirable ++

∆DVCS first measurement N → ∆ GPDs required ?

σL(ρ0, φ0) vs Q2 quarks/gluons not necessary ++

σL(ω0, ρ+) vs Q2 quarks/gluons not necessary +

ρ : ω : φ cross.sec. ratio H, E flavours not necessary +

ρ0, φ0 SDME vs t comp. GPD model not necessary ++

σL(π+) vs xB

∼

Hu −∼

Hd not necessary ++

π+ : π0 : η cross.sec. ratio∼

H,∼

E flavours not necessary +

K+Λ0 transv. asym. AK+Λ∼

Hp→Λ

,∼

Ep→Λ

required ?

π∆ vs xB N → ∆ GPDs required ?


DVCS Beam Charge Asymmetry

GPD H dominates,∼

H and E suppressed[Goeke et al. PPNP 47(2001)401]

t-dependence candistinguish different GPDmodel versions.

More background in highert-bins.

25x e−1 statistics !

A-D Curves from code byVGG for HERMES kinema-tics.


DVCS Beam Spin AsymmetryHu(x = ξ, ξ, t) (modeldepedent)

GPD modelsdistinguishable viat-dependence

1996-2000: PB ≈ 55%2002-2007: PB ≈ 35%

Statistics marginal for2-dim dependences.

A-E Curves from code byVGG for HERMES kinema-tics.


ρ0 Spin Density Matrix Elements

0 decay plane0ρlepton scattering

plane

Φ

π-π+

0 ρ

0 ρ

’N

e

φ

’γ*

production planeρ

π+

-

ρ

θ

N

Rest Frame

π’

e

φ

Photon-Nucleon CMS

N

SDMEs from maximumlikelihood fit minimisingdifference between 3-dim.(cos Θ, φ,Φ) decay anglematrix and fullyreconstructed high statisticsMonte Carlo data set.

15 ’unpolarised’ SDMEs,8 ’polarised’ SDMEs(require beam polarisation)

For SDME definitions see[Schilling,Wolf Nucl.Phys.B61(1973)381].


Spin Density Matrix Elements for ρ0/φ0


SDMEs t-Dependence

0.4

0.6

0.8

0 0.25

0

0.05

0 0.25

-0.1

0

0 0.25

-0.1

0

0 0.25

-0.1

0

0.1

0 0.25

-0.05

0

0 0.25

0.2

0.4

0 0.25

0

0.05

0.1

0 0.25

-0.3

-0.2

-0.1

0 0.25

-0.025

0

0.025

0 0.250

0.1

0.2

0 0.25

0.1

0.2

0 0.25

0

0.02

0 0.25

-0.15

-0.1

0 0.25

-0.025

0

0.025

0 0.25

GPD-based modelfor t-dependence[Goloskokov,Kroll,

EPJ C 42 (2005) 02298]

Model for Q2 > 3GeV2, 2-gluonexchange only.

2-quark exchangebeing incorporated.

ProjectionsA.Borissov.


Exclusive π+-Cross-Section

)2 (GeV2Q0 2 4 6 8 10

cros

s se

ctio

n (n

b)

1

10

210

0.02

Summary

HERMES is playing a pioneering role exploring thepotential of exclusive photon/meson production in thecontext of Generalised Parton Distributions.

The new Recoil Detector, combined with anunpolarised target, is expected to lead to significantimprovements of both statistics and systematics inexclusive measurements at HERMES.

In the last year of data taking 2006/7 HERMES isexpecting to take about as much data as in the 10years before.


Additional Slides


Recoil Detector - Kinematics

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0 0.2 0.4 0.6 0.8 1 1.2 1.4θ [rad ]

p [G

eV/c

]

SciFiSciFi

SiliconSilicon

Silicon(positiononly)


DVCS Asymmetries

Beam Spin ALU (φ) =dσ↑(φ)−dσ↓(φ)dσ↑(φ)+dσ↓(φ) ∝ sin φ ⇒ Im(H)

Beam Charge Ach(φ) =dσ+(φ)−dσ−(φ)dσ+(φ)+dσ−(φ) ∝ cos φ ⇒ Re(H)

x

y

z φ

~pγ

~k

~k′

~q

uli


SDMEs t-Dependence: r500

0

0.05

0.1

0.15

0.2

0.25

-0.05 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4


Q2-Dependence of R = σL/σT

10-1

1

10-1

1 10

Q2 [GeV2]

R=σ

L/σ

T

HERMES PRELIMINARY 〈W〉=5 GeVprotonprojection for2002-2007 1.3 fb-1

CLAS 〈W〉=2.1 GeVDESY 〈W〉=2.6 GeV

CORNELL 〈W〉=3.5 GeV

NMC 〈W〉=14 GeV

COMPASS PREL.〈W〉=14 GeVE665 〈W〉=18 GeV

ZEUS 〈W〉=50 GeVH1 〈W〉=75 GeV


Exclusive Pion-Pair Production

0.2 0.4 0.6 0.8 1 1.2 1.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

0.5

Hydrogen

mππ [ GeV ]

R.Fabbri


sf �lue {hspace *{-1cm}Future Exclusive Measurements at HERMES}sf �lue {HERMES Physics}sf �lue {HERMES with Recoil Detector}sf �lue {HERMES Recoil Detector - 3D CAD}sf �lue {Goals of the Recoil Detector}sf �lue {Exclusivity}sf �lue {Recoil Detector - Complete Setup}sf �lue {Recoil Detector Event}sf �lue {HERMES Data Taking HERA Run II}sf �lue {Target Cell Accident}sf �lue {HERMES Statistics Overview (pb$^{-1}$)}sf �lue {Exclusive Processes to Constrain GPDs}sf �lue {Exclusive Measurements at HERMES}sf �lue {DVCS Beam Charge Asymmetry}sf �lue {DVCS Beam Spin Asymmetry}sf �lue {$ho ^0$ Spin Density Matrix Elements}sf �lue {hspace *{-0.5cm} Spin Density Matrix Elements for $ho ^0$/$phi ^0$}sf �lue {SDMEs $t$-Dependence}sf �lue {Exclusive $pi ^+$-Cross-Section}sf �lue {Summary}sf �lue {Additional Slides}sf �lue {Recoil Detector - Kinematics}sf �lue {DVCS Asymmetries}sf �lue {SDMEs $t$-Dependence: r$_{00}^5$}sf �lue {$Q^2$-Dependence of R = $sigma _L/sigma _T$}sf �lue {Exclusive Pion-Pair Production}

Documents

Future Exclusive Measurements at HERMES › conference › qcdn06 › TALKS › Thursday 15 › Kaiser.pdfRecoil Detector Event END VIEW LOOKING DOWNSTREAM y x Pd SciFi Si Target Event