blast: a detector for internal target experiments

U. Kentucky, 31 March 2005

BLAST: A Detector for Internal Target Experiments

Introduction

Overview and status of the Program

Present Results

Outlook

John Calarco, UNH and UT



BLAST COLLABORATION

R. Alarcon, E. Geis, J. Prince, B. Tonguc, A. YoungArizona State University, Tempe, AZ 85287

J. Althouse, C. D’Andrea, A. Goodhue, J. Pavel, T. Smith,

Dartmouth College, Dartmouth, NH

D. Dutta, H. Gao, W. XuDuke University Durham, NC 27708-0305

H. Arenhövel,Johannes Gutenberg-Universität, Mainz, Germany

T. Akdogan, W. Bertozzi, T. Botto, M. Chtangeev, B. Clasie, C. Crawford,

A. Degrush, K. Dow, M. Farkhondeh, W. Franklin, S. Gilad, D. Hasell, E. Ilhoff, J. Kelsey, M. Kohl, H. Kolster, A. Maschinot, J. Matthews, N. Meitanis, R. Milner, R. Redwine,

J. Seely, S. Sobczynski, C. Tschalaer, E. Tsentalovich, W. Turchinetz, Y. Xiao, C. Zhang, V. Ziskin, T. ZwartMassachusetts Institute of Technology, Cambridge, MA 02139

andBates Linear Accelerator Center, Middleton, MA 01949

J. Calarco, W. Hersman, M. Holtrop, O. Filoti, P. Karpius, A. Sindile, T. Lee

University of New Hampshire, Durham, NH 03824

J. RapaportOhio University, Athens, OH 45701

K. McIlhany, A. Mosser

United States Naval Academy, Annapolis, MD 21402

J. F. J. van den Brand, H. J. Bulten, H. R. PoolmanVrije Universitaet and NIKHEF, Amsterdam, The Netherlands

W. Haeberli, T. Wise

University of Wisconsin, Madison, WI 53706


Approved BLAST Scientific Program

Form Factor Measurements: Q2 1.0 (GeV/c)2

Proton Charge and MagnetismElastic Scattering with Polarized Beam and H Target (01-01)

Neutron Charge and Magnetism and Deuteron Electromagnetic Structure

Quasi-elastic Scattering with Polarized Beam and D Target (89-12 and 91-09)

Elastic scattering off Tensor and Vector Polarized Deuterium (00-03

and 03-02)


General Kinematics for Polarized e Scattering on a Polarized Target


Bates Linac

500MeV Linac recirculated to reach up to 1GeV Inject into South Hall Ring Polarization maintained by Siberian snakes Polarization monitored real time by Compton Polarimeter Internal Target located in the ring vacuum


• Left-right symmetric detector– simultaneous parallel and

perpendicular asymmetry determination

• Large acceptance– covers 0.1GeV2 ≤ Q2 ≤ 1GeV2

– out-of-plane measurements

• DRIFT CHAMBERS– momentum determination,

particle identification• CERENKOV COUNTERS

– electron/pion discrimination• SCINTILLATORS

– TOF, particle identification• NEUTRON COUNTERS

– neutron determination• MAGNETIC COILS

– 3.8kG toroidal field

The BLAST Spectrometer

DRIFT CHAMBERS

CERENKOVCOUNTERS

SCINTILLATORSNEUTRON COUNTERS

TARGET

BEAM

BEAM


BLAST: Present Configuration


Detector Performance• All detectors operating at or near designed level

– Drift chambers ~98% efficient per wire– TOF resolution of 300ps

• Clean event selection– Cerenkov counters 85% efficient in

electron/pion discrimination– Neutron counters 10% (25-30%) efficient in

left (right) sectors• To be improved further

• Reconstruction resolutions good but still being improved

current goal

p 3% 2%

0.5° 0.3°

0.5° 0.5º

z 1cm 1cm


ep Elastic Kinematic Correlation


Asymmetries AL and AR


GE/GM from ep Elastic


GE/GM Comparison between BLAST and JLab


Inclusive H(e,e’) Cross Sections TL TT from MC


Inclusive H(e,e’) Cross Sections from Data


Motivation I: Why Deuteron• N-N Interaction• Deuteron as test-bed for N-N interaction models THE 2-nucleon bound state

• D-wave admixture … Tensor force Model predictions vary from 4% to 7%

• Deuteron as neutron target understand Deuteron structure


• Loosely-bound deuterium readily breaks up

electromagnetically into two nucleons

– e + d e’ + p + n

• Most generally, the cross section

can be written as

:

• In the Born approximation,

• vanishes in the L = 0 model for the deuteron (i.e. no L = 2 admixture)

– Measure of L = 2 contribution and thus tensor NN component

– Reaction mechanism effects (MEC, IC, RC) convoluted with tensor contribution

• “There is no direct measure of the tensor component.” -- somebody• provides a measure of reaction mechanisms

• Useful for extraction of Gne

• Beam-vector dilution (h•Pz) gotten from analysis

Deuteron Electrodisintegration

S h,Pz ,Pzz S0 1PzAdV PzzAd

T h Ae PzAedV PzzAed

T

Ae AdV Aed

T 0TdA

AedV

N)Ne',e(d


Beam and Target Performance• Beam fills to 175mA with 25min lifetime, average polarization = 65% ± 4%• Deuterium polarization in tri-state mode

– (Vector, Tensor) :

(-Pz, +Pzz) ( +Pz, +Pzz)

(0, -2Pzz)• Flow = 2.2 1016 atoms/s, Density = 6.0 1013 atoms/cm2

• Luminosity = 4.0 1031 /cm2/s @ 140mA• Target polarizations from data analysis: Pz = 88% ± 4%, Pzz = 65% ± 2%


Motivation II: Why T20

• e-d elastic scattering: GC GM GQ

GQ > D-state > Tensor Force• Rosenbluth Separation

• 3rd Measurement to separate 3 form factors

• Tensor Asymmetry in e-d elastic scattering


e-d Elastic Event Selection

Timing Cuts Coplanarity: =1o

• Need clean e-d elastic sample• e-d Elastic rate ~ 3% of coincident rate by one positive and

one negative charge scattered into either sector.

EverythingColpanarityKinematics

Full cuts


Kinematics:pe

=24MeV d=1o

… …

Mass: timing & trackingBlue: everythingRed: after coplanary cut

Deuterons

Protons

+ ?

e-d Elastic Event Selection

e- left, d+ right

e- right, d+ left


Preliminary T20 Result


From Measurements of the Elastic Vector Asymmetry AV

ed


Deuterium Wave Functions• The NN interaction conserves only total

angular momentum• Spin-1 nucleus lies in an L = 0, 2

admixture ground state:

• A tensor component must be present to allow L = 2

• Fourier transform into momentum space:

• L = 2 component becomes dominant at pM ~ 0.3GeV

(Bonn Potential)

(Bonn Potential)

R0(r) , R2(r)

˜ R 0(p) , ˜ R 2(p)

mdr R0 r Y110

md r R2 r Y112md r

Mnpnp ppp2

1prrr

R0 r ˜ R 0 p , R2 r ˜ R 2 p


Deuteron Density Functions• Calculate the density functions:

• One-to-one correspondence between md and the (PZ,PZZ) polarization states:

• In the absence of a tensor NN component, these plots are spherical and identical• Famous “donut” and “dumbbell” shapes

mdr ' md

r md

r

md 1 1 1 PZ ,PZZ 1,+1 md 0 0 1 PZ ,PZZ 0,- 2

0 r '

'1 r

PZZ

PZ

(-1,+1) (+1,+1)

(0,-2)


Missing Mass• Only the e- and p+ are measured

– actually measure d(e,e’p)X and thus need cuts to ensure that X = n

• Define “missing” energy, momentum, and mass:

• Demanding that mM = mn helps ensure that X = n

• Momentum magnitude corrections greatly improve mM spectra

EM md Ep ,p M

q

p p , mM EM

2 pM2


Missing Momentum

• Good MC agreement up to pM = 0.5GeV/c

Left Sector Electron Right Sector Electron


Beam-Vector Asymmetry


Beam-Vector Asymmetry (cont.)


Tensor Asymmetry Results


Tensor Asymmetry (cont.)


Potential Dependence

• Monte Carlo for Bonn, Paris, and V18 potentials compared to BLAST data

• Potential dependence small compared to MEC and IC contributions


Determination of hPz


D(e,e’n) Kinematic Distribution


Missing Mass from D(e,e’n) QES


GE/GM for the Neutron from D(e,e’n) QES


GnM


GnE from D(e,e’n)


Conclusions and Outlook

• World-class data for GpE/Gp

M , GnE/Gn

M , D(e,e’) elastic T20 , D(e,e’p) QES AV

ed and ATd,, Inclusive H(e,e’)X and

D(e,e’)X

• Analysis still in progress

• Many other channels to be analyzed: H(e,e’p)H(e,e’n) , H(,n) , D(,pn) , … etc.

• Continuing to take data on D until June (?); expect to at least double data set (or more!)

• Shut down and decommission; relocate detectors and remap BLAST field


The BLASTers

blast: a detector for internal target experiments

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