THE BGO‐OD EXPERIMENT (BONN) Rachele Di Salvo Roma “Tor … · 2014-07-08 · R. Di Salvo - Trento - 30/06/2014 BGO-OpenDipole Collaboration ⇒ A collaboration has been established

R. Di Salvo - Trento - 30/06/2014

THE BGO‐OD EXPERIMENT (BONN)

Rachele Di Salvo

Roma “Tor Vergata”

The physics program The BGO-OD Detector Particle reconstruction in central and forward detectors Results from commissioning


BGO-OpenDipole Collaboration

⇒ A collaboration has been established in 2009-2010 (∼ 60 collaborators, Germany, Italy, Great Britain, Russia, Switzerland) - LoI signed and accepted at the PAC Mainz-Bonn 2009, June 25th-26th- MoU signed on 2010, March 9th

Location: S-BeamlineELSA Accelerator in Bonn

Beam: polarized and tagged photon beam in the energy range 0.2-3. GeV

Spokespersons: H. Schmieden, P. Levi Sandri

Responsabile Nazionale: R. Di Salvo

S-BEAMLINE

E-BEAMLINE


BGO-OD: Main physics goals

Systematic investigation of the photoproduction of mesons off the nucleon for the study of the excitation spectrum of the nucleon. The underlying mechanisms must still be considered as poorly understood. Improved experiments will shed new light on the low-energy hadronic aspects of the strong interaction. In particular asymmetry observables can help to disentangle the contribution of the different resonances.

γ N→Nη γ N→Nη’ pseudoscalar mesons

γ N→Nω γ Ν→Νφ vector mesons

γ N→ KΛ (Σ) strange mesons

Joint PAC of MAMI and ELSA 2012, Dec. 6th-7th


η, η', ω = ISOSPIN FILTERS

Isoscalar mesons allow to access only N*(I=1/2) resonances and this simplifies the interpretation of the data.

From B.Krusche, Prog. Part. Nucl. Phys. 51 (2003), 399-485


P. Levi Sandri G. Mandaglio

ETHR

= 1.447 GeV

Data from CLAS (2006-2009) (ETHR

÷ 2.84 GeV) Total and Diff. Cross-sections

η' → π+ π− η → π+ π− π+ π− π0

Data from CB-ELSA (2009) (ETHR

÷ 2.84 GeV) Total and Diff. Cross-sections

η' → π0 π0 η → 6γ Main coupling to S

11 (1535) and P

11(1710) (minor contributions from P13 (1720)

and D13 (1520) +NEW Data from GRAAL (2014) two energy bins at E

THR Beam Asymmetry

See G. Mandaglio's talk η' → γγ, π0π0η, π+π−η


η ' PHOTOPRODUCTION

Inclusion of different set of resonances in the models provides similar predictions for cross-sect. but very different for the beam asym. Σ will be measured at BGO-OD.

● Data from: M. Dugger et al., Phys. Rev. Lett. 96, 062001 (2006)● Curves from: Nakayama and H. Haberzettl, PRC73, 045211 (2006)● I = P11 , S11 , P13 and D13

II= inclusion of an extra D13 (2085) III= inclusion of higher mass P11 and S11 IV=P13 is removed from the fitV=all resonances (W,Γ from PDG)

P. LeviSandri, G. Mandaglio, Proposal PAC2012


A. Fantini A. Braghieri

Extensive campaign of data taking in the last 15 years.

ETHR

= 0.707 (with no F.M.)

GRAAL on the proton (ETHR

÷1.5GeV) Diff. Cross-sections and Beam Asymmetry

GRAAL on the neutron (ETHR

÷1.5GeV) Beam Asymmetry

LNS(Sendai) on proton and neutron (ETHR

÷1.1GeV) Cross Sections

CB-ELSA (Bonn) on proton and neutron (ETHR

÷2.5GeV) Cross Sections

MAMI (Mainz) on proton and neutron (ETHR

÷1.4GeV) Cross Sections Main coupling to S

11 (1535), minor contributions from D

13(1520), F

15(1675)


GRAAL EPJA 33, 169–184 (2007)PLB, 528, 215-220 (2002)PRL, 81, 1797-1800 (1998)Curves: MAID (Dashed Line), CQM (Dot-dashed), Coupled-channel Bonn-Gatchina (solid)

γ p → η p

Low energy: Σ=0 if only S11

(1535) contributes

Interf S11(1535)-D13(1520) (sin2 θηcm behav.)

γ n(p) → η n(p) vs. γ p(n) → η p(n)

= MAID-2001 (q.f.neutrons)= reggeized model (q.f. neutrons)

GRAAL PRC 78, 015203 (2008)

Higher multipoles expansion cosθ(E3-,+M3-)

High energy: interference S11

(1535)-F15(1680)

(peak at forward angles)

Σ=−qCM

2 kγCM

3 sin2 θ Re [E0+ (E2-+ M2- ) ] ( dσ /d Ω)UNP


GRAAL, C. Schaerf, AIP Conf. Proc. 1056(2008), Trieste

GRAAL, C. Schaerf, Proc. NSTAR2005, Tallahasse (Fl)

CBELSA/TAPS EPJA47, 89 (2011)CBELSA/TAPS PRL 100 (2008), 252002 D. Werthmuller, PhD Thesis (2013)

Eγ (GeV)Eγ (GeV)

Eγ (GeV) Eγ (GeV)

W(GeV) W(GeV)

W(GeV)W(GeV)

γ n(p) → η n(p) vs. γ p(n) → η p(n)


S-Beamline.... 4-5 years ago


Daniel Elsner

BGO-OD


Central region and tagger system

D.Elsner


Forward region

D.Elsner


Detector is optimized for:- forward region: charged particle identification and good momentum resolution

- central region: photon detection with good energy and angular resolution; charged particle tracking and identification; energy measurement for protons; neutron detection

- mixed charged and neutral final state detection

- has trigger capabilities (trigger on the energy sum deposited in BGO in coincidence with a signal in the tagger)

- open trigger (many channels can simultaneously be acquired)

BGO-OD Detector Features


PHOTON TAGGER

Photon tagger

A. Bella-F. Messi


Siebke, G. Design of the BGO-OD Tagging System and Test of a Detector Prototype, Physikalisches Institut Bonn, 2010

● High energy e- (→low en. γ): focal plane is not accessible split into 54 horizontal scint. (10-32% E

0) and 66 vertical

ones (32-90% E0)

● trigger on double and triple coincidences

● Commissioning of the full detector completed (2012-2013) => time structure of the bunches of the beamand good results in missing mass spectra (see after)

TAGGER DESIGN

A. Bella-F. Messi

● 120 Channels (covering 0.1-0.9 E0)

● Energy resolution: 10-40 MeV (0.55%E

0-2.15%E

0)

● Beam Intensity: 5 ×107 s-1


LH2/LD2 CRYOGENIC TARGET Commissioning completed Feb. 27th- March 5th 2012; June 20128h to fill the target starting from room temperatureTo take data on empty target → increase the temperature for evaporation and then 2h to go back from gas to liquid

M. Romaniuk – G. Vitali – M. Iannilli – M.Lucentini


CENTRAL DETECTORS


barrel of 32 plastic scintillators (NE102A)

Large solid angle calorimeter optimized for photon detection (with good energy resolution), good efficiency for neutrons and good response also for protons (energy and angles) and charged pions (angles).

Cylindrical MWPC's

480 BGO crystals (15 in ϑ and 32 in ϕ) divided into 24 baskets in Carbon fiber.

Each crystal has a 24 cm length (corresponding to 21 r.l.), is wrapped inside a thin aluminized reflecting mylar foil and is optically coupled to a PM.

BGO CALORIMETER


BGO DETECTOR

G.Nobili- S.Colilli-M.Lucentini-G.Vitali-M.Iannilli-R.Fratoni


BGO Calorimeter + MOMO Detector + SciFi + DIPOLE MAGNET

G.Nobili- S.Colilli-M.Lucentini-G.Vitali-M.Iannilli-R.Fratoni


R. Di Salvo- A. Fantini

BGO Acquisition SystemEquipped with new electronics: Sampling ADC W-Ie-Ne-R (160 MHz):1) Extraction of the main characteristics of the signal:- start time of the rising edge- time and amplitude of the first maximum and of all maxima (same for minima)- total and partial integrals- optional: sampling raw data transmission

2) Declared Time resolution: 1.5 ns

3) Options: baseline height, width of all integration and sampling windows, sampling raw data transmission

4) External or internal trigger (located before or after the signal)

5) Synchronization between modules (master + slaves)


Slow BGO decay time

Fast rising edge ≈ 30-35 ns

Sampled BGO signal in a 1000 ns window during data taking

SAMPLING OF A BGO SIGNAL DURING DATA TAKING

F. Curciarello – V. De Leo – R. Di Salvo – A. Fantini


Crystals are equalized at the beginning of the data taking with a 22Na (1.275 MeV)Calibration (without moving the HV) is performed twice per day

EQUALIZATION OF THE BGO

Blue squares: equal. 2012, Feb 15thRed triangles: calib. 2012, March 1stBlack stars: calib. 2012, March 5th

Calibration constants must be corrected if different integration windows are used for calibration and acquisition:

c.c.WINDCORR=c.c.MEAS∗

RCAL

RACQ

QTOTMEAS,CAL

=RCAL QTOTTRUE.CAL

c.c.MEAS=1.275 MeV

QTOTMEAS,CAL

c.c.CORR=1.275 MeV

QTOTTRUE,CAL =

1.275 MeV

QTOTMEAS,CAL ∗RCAL=c.c.MEAS∗RCAL

QTOTTRUE,ACQ=

QTOTMEAS,ACQ

RACQ


Linearity Tests@BTF (LNF, Frascati)Electron beam at fixed energy (6 settings) and variable multiplicity

EMEAS−ENOM

ENOM



Resolution Tests@BTF (LNF, Frascati)Electron beam at fixed energy (6 settings) and variable multiplicity



Time Measurements at BTF

Central Crystal in the matrix Trigger is provided by this crystal most of the timeTypical Time Resolution < 2ns

PM ∅51mm

Lateral Crystal in the matrix Typical Time Resolution < 5-6ns

PM ∅38mm → electron transit time about 11ns smaller than the other PM (37ns vs. 48ns)

Mean value is closer to trigger



BGO BALL COMMISSIONING

June 2012-May2014: Commissioning of barrel detector=> Very good results in the 2γ invariant mass! (see after)

Since 2012, the trigger on BGO in coincidence with Tagger represents the main trigger for collecting physics eventsIn December data have been collected with half value of the magnetic field and with a suitable equalization (at higher channel values), good results have been obtained also in the forward crowns

On the basis of simulation a shielding has been constructed and installed last week

Feb.-March 2012: Successful Commissioning of the BGO calorimeterTests on synchronization between the ADC, calibration, energy and time response, mapping of the response of the detector=> Very good results in the 2γ invariant mass! (see after)


Two cylindrical MWPCs. Each chamber is made of: - two coaxial cylindrical cathodes segmented into strips, wrapped helicoidally into opposite directions (±45°) around the beam axis (gas gap≈8mm, strip width≈4.5mm, ∆z≈300µm, ∆θ≈1°);- an anode array of equally spaced wires stretched parallel to the cathode axis in the middle of the gas gap (wire pitch 2mm, ∅ 20µm, ∆ϕ≈2°).Installed in March-May 2014, tested with cosmics, will be tested on beam in July 2014

CYLINDRICAL MWPCs

A. Braghieri – P. Pedroni


SCINTILLATOR BARREL

32 Scintillator bars (BC440 high temperature resistant: Soft. Point = 99°, light output 60% Anthracene, λ max. emission = 434 nm, τ

dec = 3.3 ns, attenuation

length=400cm, n=1.58)

Read-out Hamamatsu PM3164

(dE/dx)BARREL

% EBGO

pion/proton identification

Neutral/charged discrimination

F. Ghio – G. Nobili – S. Colilli

F. Ghio – R. Di Salvo – T.Jude

RECONSTRUCTION IN THE CENTRAL DETECTORS Periods with no barrelMultipl. ≥ 3 crystals => candidate photon Multipl. < 3 crystals => candidate proton

Periods with barrelSignal in BGO withAzimuthal/Time Correlation BGO-barrel => candidate protonNo Azimuthal/Time correlation BGO-barrel => candidate photon

Time Diff BGO-BarrelAzimuthal Angle Diff BGO-Barrel


γ + p → π0 + p γ + p → η + p 2γ 2γ

2 neutral clusters + 1 charged cluster in BGO + θMiss,part

> 25°

From 2 neutral clusters → Meson Invariant Mass, Energy, AnglesFrom Eγ

and Meson Energy and Momenta →Missing Particle X

γ + p →Meson + X

If θMiss,part

> 25° ==> Missing Particle in BGOReaction is overdetermined and we cut on

Coplanarity Meson-Charged Clus

θMiss,part

– θcharg, clus


L. Magnisi, R. Di Salvo, A. Fantini, BGO-OD Int. Note

2γ Invariant Mass Missing Mass from 2γ

2γ Inv. Mass vs. Miss Mass from 2γ Before and After Cuts


Missing Mass from Proton

2γ Invariant Mass Missing Mass from 2γ 2γ Inv. Mass vs.

Miss. Mass from 2γ 2γ Invariant Mass

L. Magnisi, Laurea Thesis

From Eγ and Proton Energy and Momenta →Missing Meson X'

γ + p →p + X'


2γ Invariant Mass 2γ Inv. Mass vs. Miss Mass After Cuts

Zoom on η


γ + p → π0 + p γ + p → η + p 2γ 2γ

2 neutral clusters in BGO + θMiss,part

< 25°If θ

Miss,part < 25° ==> Missing Particle in Forward Direction

We look for a track in the forward detectors ==> θfront,track

ϕfront,track

Reaction is overdetermined

θMiss,part

– θfront,track

ϕMiss,part

– ϕfront,track

2γ Invariant Mass



1 Track in Front Detectors 1 Track in Front Detectors+Kin cuts

2γ Invariant Mass

2γ Invariant Mass vs. Missing Mass

θMiss,part

<12° 800<MissMass<1030 MeV


2γ Invariant Mass


γ + p → π0 + p γ + p → η + p 2γ 2γ

2 neutral clusters + 1 “charged cluster” in BGO + θMiss,part

< 25°

“Charged cluster” = Noise in BGO

ENoise

θNoise

EProton

θProton


ϕfront,track


γ + p → π0 + p γ + p → η + p 2γ 2γ

2 neutral clusters + 1 “charged cluster” in BGO + θMiss,part

< 25°

“Charged cluster” = Noise in BGO

ENoise

θNoise

EProton

θProton


ϕfront,track

2γ Invariant Mass

2γ Invariant Mass After Kin. Cuts

2γ Invariant Mass

Missing Mass


Clusters from a photon

µ = (-8.3±1.5)×10-2 (ns)σ = 2.39 ± 0.01 (ns)

µ = (9.1±0.1)×10-1 (ns)σ = 1.57 ± 0.01 (ns)

For selected π0 events

For not selected events

Time Distribution of clusters in BGO

Clusters from a proton

For selected π0 events

For not selected events

Absolute Cross Section

γ + p → π0 + p


Blue - Time distribution all crystalsRed – Time Difference between members of the same cluster

Time Difference between members of the same cluster

T. Jude, D. Elsner, Proposal PAC2012


FORWARD SPECTROMETER


FORWARD SPECTROMETER: BEFORE DIPOLE

MOMO

Scintillation fiber detector (∅44cm)672 total channels3 layers of 2x112 parallel fibers (∅2.5mm, ∆x=1.5mm)Each layer rotated of 60° w.r.t. each otherRead-out 16 channel PMCentral hole (∅5cm) for the passage of beam

Successful commissioning with beam tests in Feb.-March 2012 and June 2012

SciFi2

Scintillation fiber detector (66cmx51cm)640 total channels2 double layers x/y (352 and 288 rot. 90°)Each single layer consists of two fiber arrays (2.0mm track length for crossing particles)Read-out 16 channel PMCentral hole (∅4cm) for the passage of beam

D. Bayalov-S. Boese



DRIFT CHAMBERS

Two sets of 4 double layers X(vert.), Y(90°), U(+9°), V(-9°) Sensitive area 1.2 x 2.4 m2

X = horizontalY = verticalU = 99° w.r.t. XV = 81° w.r.t. XHexagonally shaped drift cells (inner radius 8.5mm) Distance from target = 3.8 m÷4.5 mGas mixture: 70% Ar, 30% Co

2

Central insensitivity spot (5x5cm2)

PNPI- Gatchina

FORWARD SPECTROMETER: AFTER DIPOLE

TOF WALLS

PNPI- Gatchina O. Jahn – V. Vegna





All charged tracks in the forward spectrometerWith a π0 in the BGO Ball

Missing Mass from Charged Tracks in Forward Spectrometer


Missing Mass from Protons Detected in the Forward Spectrometer

N.B. pproton

> 400 MeV/c in order to suppress π0 photoproduction

mη η → 3π 0,π+π−π0

mω ω → π+π−π0

First Tests with Linearly Polarized Gamma Beam

Polarization Degree from simulation

Intensity of polarized beam with respectto the unpolarized one (a.u.)

J. Hannappel, V.Vegna, BGO-OD Int. Note

Neglecting the polar angle dependence of the terms and assuming the asymmetry Σ of π0 photoproduction in this energy range ≈ 0.5, we can estimate the polarization degree in the three bins and compare it with simulation.

J. Hannappel, V.Vegna, BGO-OD Int. Note


CONCLUSIONS AND FUTURE PROGRAMS

The BGO-OD Detector has been constructed in Bonn. It will work in the energy gamma region 0.3-3.GeV.

2012-2013 → Successful commissioning of:

- liquid H2 target- BGO calorimeter- scintillator barrel- Tagging Detector

- MOMO detector- SciFi2 - Drift chambers- 2 TOF Walls- Flux Detectors

Good results on particle reconstruction in the central and forward regions and channel identification (π0 and η photoproduction)

Next months: commissioning of MWPC, beam polarization studies, commissioning of the 2 additional TOF walls and end of construction of MRPC

BEFORE END 2014: first data taking with the whole apparatus


THANK YOU!!

THE BGO‐OD EXPERIMENT (BONN) Rachele Di Salvo Roma “Tor … · 2014-07-08 · R. Di Salvo - Trento - 30/06/2014 BGO-OpenDipole Collaboration ⇒ A collaboration has been established

Documents