HERMES Recoil Detector

Roberto Francisco Pérez Benito

Exclusive Reactions at High Momentum TransferMay 21-24, 2007

Jefferson Lab, Newport News, VA USA

On behalf the HERMES Collaboration

2

OutlineOutlineOutlineMotivation

Spin of the NucleonGeneral Parton Distribution (GPD)DVCS & BH

HERMES Hermes Recoil DetectorDesign Requirement

Recoil Detector (RD) Silicon Strip Detector (SSD)Scintillating Fiber Tracker (SFT) Photon Detector (PD)

Performance

3

Spin of the nucleonSpin of the nucleonSpin of the nucleon

Spin of quarks

Spin of gluonsexpected to be small

Orbital angular momentum of quarks

Orbital angular momentum of gluons

~ 30% !

How to access ?

A. Airapetian et al, Phys. Rev. D75(2007)012007

.)evol(028.0.)(exp025.0.)theo(011.0330.0 ±±±=ΔΣHERMES:

4

Generalized Parton DistributionsGeneralized Parton DistributionsGeneralized Parton Distributions

qqqq E~,H~,E,HGeneralized Parton Distributions

possible access toorbital angular momentum

from DISHERMES

Study of hard exclusive processesleads to a new class of PDF’s

GPDs can be accessed in Deeply Virtual Compton Scattering (DVCS)

( )

qq

0t

1

1

qqq

L21J

EHxdx21J

+ΔΣ=

⎟⎠⎞⎜

⎝⎛ +=

→−∫´ Ji´s sumrule [hep-ph/9603249]

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DVCS at HERMESDVCS at HERMESDVCS at HERMES

( )* 2 2*~ | | | |BH DVCS DVC BS HB DVCSHd τ τ + τ τσ + τ + τ

two experimentally undistinguishable processes:Same initial and final state

BH dominates at HERMES kinematics

The DVCS can be measured through azimuthal asymmetries

Deeply Virtual Compton Scattering Bethe-Heitler

6

HERMES in Hamburg - GermanyHERMES in Hamburg HERMES in Hamburg -- GermanyGermanyHERMES is a fixed target experiment in HERA

Long. Polarized beam 27.6 GeV e ±

7

p

e´

HERMES Detector HERMES Detector HERMES Detector

γ

Green PID detectorsRed track detectors

95 - 05 exclusivty through missing mass cut06 - 07 Recoil detector installed to identify the recoiling proton

8

RD - Design RequirementsRD RD -- Design RequirementsDesign Requirements

Improve ExclusivityDetect recoiling protonBackground suppression

semi-incl. : 5%→<<1%BH with resonace excitation: 11%→~1%

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Recoil DetectorRecoil DetectorRecoil Detector Photon Detector3 layers of Tungsten/ScintillatorPID for higher momentumdetects Δ+ pπ0

1 Tesla Superconducting Solenoid

Scintillating Fiber Detector2 Barrels2 Parallel- and 2 Stereo-Layers in each barrel10° Stereo AngleMomentum reconstruction & PID

Silicon Detector16 double-sides sensors perpendicular with respect to each other 97×97 mm2 active area each2 layersInside HERA vacuumMomentum reconstruction &PID

Target Cell

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Target CellTarget CellTarget Cell

Target cell inside beam pipe

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Silicon Strip Detector (SSD)Silicon Strip Detector (SSD)Silicon Strip Detector (SSD)2 layers of double sided TIGRE sensors16 TIGRE sensors operate in beam vacuum few cm close to the beamSize 97mmΧ 97mm, thickness=300μm128 strips per side, perpendicular w.r.t. each other, pitch=758μmHELIX chips are ADC and running under same conditionThe high and low gain yield s from charge sharing

8192 channels in total

Proton momentum 135-500 MeV/c

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Silicon Strip Detector (SSD)Silicon Strip Detector (SSD)Silicon Strip Detector (SSD)2 layers of double sided TIGRE sensors16 TIGRE sensors operate in beam vacuum few cm close to the beamSize 97mmΧ 97mm, thickness=300μm128 strips per side , perpendicular w.r.t. each other, pitch=758μmHELIX chips are ADC and running under same conditionThe high and low gain yield s from charge sharing

8192 channels in total

Proton momentum 135-500 MeV/c

13Low Gain [ADC Channels]

0 100 200 300 400 500 600

Hig

h G

ain

[AD

C C

hann

els]

0

100

200

300

400

500

600

700

Silicon Strip Detector (SSD)Silicon Strip Detector (SSD)Silicon Strip Detector (SSD)2 layers of double sided TIGRE sensors16 TIGRE sensors operate in beam vacuum few cm close to the beamSize 97mmΧ 97mm, thickness=300μm128 strips per side , perpendicular w.r.t. each other, pitch=758μmHELIX chips are ADC and running under same conditionThe high and low gain yield s from charge sharing

8192 channels in total

Proton momentum 135-500 MeV/c

14Energy Deposit Outer [keV]

0 1000 2000 3000 4000 5000 6000 7000

Ene

rgy

Dep

osit

Inne

r [k

eV]

0

1000

2000

3000

4000

5000

6000

7000

Silicon Strip Detector (SSD)Silicon Strip Detector (SSD)Silicon Strip Detector (SSD)

<SRIM>Protons

2 layers of double sided TIGRE sensors16 TIGRE sensors operate in beam vacuum few cm close to the beamSize 97mmΧ 97mm, thickness=300μm128 strips per side , perpendicular w.r.t. each other, pitch=758μmHELIX chips are ADC and running under same conditionThe high and low gain yield s from charge sharing

8192 channels in total

Proton momentum 135-500 MeV/c

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Scintillating Fiber Tracker Scintillating Fiber Tracker Scintillating Fiber Tracker 2 cylinders of 2Χ2 layers,

10° stereo angle1mm Kuraray fibers, mirrored ends and double claddingPMT Hamamatsu 64 channels

5120 channels in total

Proton momentum250-1200 MeV/c

16

Scintillating Fiber Tracker Scintillating Fiber Tracker Scintillating Fiber Tracker Calibration data (blue LED pulser) fitted with Poisson & GaußOne Photon Electron peak

17

Scintillating Fiber Tracker Scintillating Fiber Tracker Scintillating Fiber Tracker reasonable energy reponse of the SFTMC and cosmics data agree

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3 layers of Tungsten/ScintillatorA layer parallel to beam line,B and C layer stereo under +45°/-45°

Strips: 2x1x28cm³same PMTs as for SFT are usedMain purpose

1γ from π° decay Reconstruct π° if 2 γ‘s detected

Photon DetectorPhoton DetectorPhoton Detector

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Data-MonteCarlo comparison:Minimum 1 lepton track in spectrometerSelect exactly 1 hit per layer

MC and data agree

Photon DetectorPhoton DetectorPhoton Detector

DataMonte Carlo

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Recoil DetectorRecoil DetectorRecoil Detector

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Recoil detector AlignmentRecoil detector AlignmentRecoil detector Alignment5 GeV electron test beam was used with Si Reference systemX/Y reconstruction < 100μmParameterizes fibers with polynoms O(4)

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Recoil detector AlignmentRecoil detector AlignmentRecoil detector AlignmentSix parameters (three translations and three rotations) which are common for all tracks are fittedResiduals and dependence of residuals on coordinates used as a tool to check alignment procedure

σ=0.28mm

SFT Paralleltop

Si

Si alignment respect SFT with tracks

Next step is Recoil-Hermes alignment using e-p elastic

σ=0.26 strip

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e – p elastic scattering e e –– p elastic scattering p elastic scattering

We can observe clear correlation. Selection of single tracks protons by making cuts on the momentum of the lepton detected by the forward spectrometer.Only SFT tracking.

24Momentum [GeV/c]

-1.5 -1 -0.5 0 0.5 1 1.5

Ene

rgy

Dep

osit

Inne

r S

ilico

n [k

eV]

0

200

400

600

800

1000

1200

1400

1600

TrackingTrackingTracking

Full tracking including alignment is in production Efficiency of the tracking algorithm studied on MC and found to be above 98%Starting to study the efficiencies, residuals and ghost tracks

pπ- π+

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DIS 2007 (vs. day)

2007/04/30 21.29

0

200

400

600

800

1000

1200

x 10 4

0 20 40 60 80 100 120Day of Data Taking

Nu

mb

er o

f D

IS e

ven

ts

all H

H (Recoil Mag. on)

H (High density)

12672846

12671358

3632226

all D

D (Recoil Mag. on)

D (High density)

3348691

3348691

1273

e+

DIS 2006 (vs. day)

2007/03/24 00.48

0

250

500

750

1000

1250

1500

1750

2000

x 10 4

0 25 50 75 100 125 150 175 200Day of Data Taking

Nu

mb

er o

f D

IS e

ven

ts

all H 7384690

H (Recoil Mag. on) 7208763

H (High density) 1834379

20151104

20117192

6410368

all D 1447585

D (Recoil Mag. on) 1037918

D (High density) 113779

5123846

5123300

232555

e- e+

7M e- 200620M e+ 200613M e+ 2007

maybe 20M until JulyIn total 47M DIS for the

unpol. run

RunningRunningRunning

SFT was working for large set of e- data Si working since September

2006

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Recoil Detector: installed January 2006Fully commissioned in September 2006 and taking data until the end of HERA – July 2007

DVCS and other hard exclusive reactions can be precisely measured with the recoil detector

Conclusion Conclusion Conclusion