Preliminary Results from the pp2pp Engineering Run

1
Preliminary Results from the pp2pp Engineering Run
Stephen Bültmann Brookhaven National
Laboratory
RHIC
Spin Discussion, February 4, 2003
For the pp2pp Collaboration

• Introduction
• Experimental Setup
• Preliminary Results from the 2002 Engineering Run
• Conclusions Outlook

2
List of Collaborators
Stephen Bültmann BNL

RHIC Spin Discussion, February
4, 2003
3
Observables in Elastic Scattering

• Measurement of Differential Cross Section to
  obtain
• Total cross section stot need to know
  luminosity L ? normalize by measuring
  in Coulomb region
• ? parameter in CNI region

• Slope parameter B

in nuclear region
Stephen Bültmann BNL

RHIC Spin Discussion, February
4, 2003
4
Differential Elastic Cross Section
Nuclear Term
Combined Term
Coulomb Term
DF Coulomb Phase
GE Proton Electric Form Factor
Interference Term
Stephen Bültmann BNL

RHIC Spin Discussion, February
4, 2003
5
Overview of Elastic Scattering Data
Highest Energy so far in pp 63 GeV (ISR) pp 1.8
TeV (Tevatron) pp2pp Energy Range 50 GeV ? ?s ?
500 GeV pp2pp t -range (at ?s 500
GeV) 4104 GeV2 ? t ? 1.3 GeV2
Stephen Bültmann BNL

RHIC Spin Discussion, February
4, 2003
6
Spin Physics with pp2pp
Single spin asymmetry AN arises in CNI region
from interference of hadronic non-flip amplitude
with electromagnetic spin-flip amplitude
pp2pp Measure t- and ?-dependence later
also s-dependence
for small t
Statistical Precision ?AN ? 0.02 (with 2002 data
set)
pp2pp 2002
N.H. Buttimore, B.Z. Kopeliovich, E. Leader, J.
Soffer, T.L. Trueman, The Spin Dependence of
High-Energy Proton Scattering, PRD 59, 114010
(1999)
Data from E704 (1993)
Stephen Bültmann BNL

RHIC Spin Discussion, February
4, 2003
7
Principle of Measurement

Elastically forward scattered protons have very
small scattering angle ? Beam transport magnets
determine trajectory of beam and scattered
protons Detector position along beam axis is
where the scattered protons are well separated
from the beam protons Need Roman Pot to measure
scattered protons close to beam
Beam transport equations relate measured
position at detector to scattering angle
x a11 x0 Leff ?x ? Optimize so
that a11 small and Leff large ?x
a12 x0 a22 ?x ? x0 can be calculated
by measuring ?x (2nd RP)


Similar equations for y-coordinate Neglect terms
mixing x- and y-coordinate in above equations
Stephen Bültmann BNL

RHIC Spin Discussion, February
4, 2003
8
Beam Transport
S. Tepikian
pp2pp RP Position
Stephen Bültmann BNL
RHIC Spin
Discussion, February 4, 2003
9
Experimental Setup at IR 2

• One Roman Pot station equipped with detector
  packages, placed
• downstream of interaction point (IP) on either
  side
• ( Detectors arranged vertically above and below
  beam )
• 4 planes of inelastic scintillation counters on
  either side of IP
• ( Kinematic coverage 2.4 ? ? ? 5.3 )

Accelerator magnets ensure that scattered protons
have beam momentum
Stephen Bültmann BNL

RHIC Spin Discussion, February
4, 2003
10
Roman Pot Stations at RHIC
Station 1
Detector Package consists of 2 x-silicon
planes 2 y-silicon planes 1 trigger
scintillator Active area of silicon covers 7.5 x
4.5 cm²
Bellows
Station 2
Two Roman Pot Stations installed in each
Sector One Station was equipped with a detector
package in top and bottom Roman Pot
Stephen Bültmann BNL

RHIC Spin Discussion, February
4, 2003
11
Silicon Microstrip Detector Efficiency
First order efficiency calculated for combination
of two x- or y-planes inside any given Roman Pot
14 out of 16 total silicon detectors have an
average efficiency gt 0.98 Detection efficiency
for elastic arm A is almost 100
Arm A
Stephen Bültmann BNL

RHIC Spin Discussion, February
4, 2003
12
Running Conditions in 2002
Running conditions during a pp2pp, 14 hour
dedicated run Beam momentum
p 100 GeV/c Number of bunches per beam NB
55 used 35 bunches Beam scraped to
emittance e ? 12 p 10-6 m
and intensity I ? 51011 protons
in each beam Beam tune used
ß 10 m Beam polarization (working )
Pb 0.24 ? 0.02 Closest approach of first
detector strip to beam about 15 mm ?
15 sbeam ? tmin -410-3 GeV2 Collected 1
million triggers of which gt30 are elastic events
O. Jinnouchi
Stephen Bültmann BNL

RHIC Spin Discussion, February
4, 2003
13
Data Sample with Cuts
Cut Events Fraction Total triggers for Run
11 116.8 k After bunch number cut
89.5 k Elastic triggers 49.4 k
Elastic triggers in Arm A 24.7 k
1.00 Silicon Analysis Elastic trigger with
reconstructed track 20.8 k 0.84
Elastic trigger after x-y-correlation-cut (4s)
20.0 k 0.81 Elastic trigger with ? 6
planes (of 8) with track info 19.9 k
0.81 Elastic trigger with ? 2 planes with
multiple hits 19.3 k 0.78
Stephen Bültmann BNL

RHIC Spin Discussion, February
4, 2003
14
Collinearity Plots
Correlation plots of x- and y-coordinates using
elastic triggers with reconstructed tracks of
scattered protons
Stephen Bültmann BNL

RHIC Spin Discussion, February
4, 2003
15
Beam Angular Divergence
Good agreement between width of ?x and ?y
distributions for measured and simulated events
with emittance of e 12 p 10-6 m ??x
? 150 µrad ??y ? 70 µrad
??y
??x
N. Öztürk
N. Öztürk
Stephen Bültmann BNL

RHIC Spin Discussion, February
4, 2003
16
Correlation Cut
Correlation of x- and y-coordinates for
reconstructed events
Outside of the 3s-cut elastic events are visible
4s-cut leads to uniform background distribution
Stephen Bültmann BNL

RHIC Spin Discussion, February
4, 2003
17
Elastic Hit Pattern
Hit distribution of scattered protons within
3s-correlation cut reconstructed using the
nominal beam transport (Run 011)
Stephen Bültmann BNL

RHIC Spin Discussion, February
4, 2003
18
Comparison with MC Simulation
Simulated hit distribution in sector 2 using the
beam transport matrix, which includes the
quadrupole roll
Hit distribution in sector 2
N. Öztürk
Stephen Bültmann BNL

RHIC Spin Discussion, February
4, 2003
19
Beam Transport Correction
Distribution of y- vs. x-coordinate in sector 2
and ?y vs. ?x calculated using the beam
transport, which includes the quadrupole roll
Stephen Bültmann BNL

RHIC Spin Discussion, February
4, 2003
20
t -?-Acceptance
Find region in t - and ?-space with full
acceptance coverage and high statistics
Stephen Bültmann BNL

RHIC Spin Discussion, February
4, 2003
21
Efficiency Corrected Acceptance from Simulation
Stephen Bültmann BNL

RHIC Spin Discussion, February
4, 2003
22
Elastic t -Distribution
Event Sample 159,250 events ( 0 lt f lt 180º
) 122,437 events ( 45º lt f lt 135º ) 58,511
events ( 45º lt f lt 135º 0.010 GeV2 ? t ?
0.020 GeV2 )
Stephen Bültmann BNL

RHIC Spin Discussion, February
4, 2003
23
Extracting B from t -Distribution
Fit t -distribution with
4 p ( a GE 2 ) 2
Preliminary

C

t2



fixing stot 52 mb and r 0.13 and keeping B
as a free parameter in range 0.010 GeV2 ? t
? 0.019 GeV2 results in B ( 16.4 ?
1.6 ) GeV-2
Stephen Bültmann BNL

RHIC Spin Discussion, February
4, 2003
24
Systematic Studies

• Apply different cuts in f and t
• 0.010 GeV2 ? t ?
  0.019 GeV2 0.011 GeV2 ? t
  ? 0.019 GeV2
• 45º lt f lt 135º B ( 16.4 ? 1.6 ) GeV-2
  B ( 16.6 ? 2.3 ) GeV-2
• 50º lt f lt 130º B ( 17.0 ? 1.8 ) GeV-2
  B ( 16.7 ? 2.4 ) GeV-2
• 55º lt f lt 125º B ( 16.5 ? 1.9 ) GeV-2
  B ( 16.7 ? 2.6 ) GeV-2
• Studied sensitivity to stot and r
• Dstot 4mb ? DB
  0.2 GeV-2
• Dr 0.02 ? DB
  0.4 GeV-2
• indicating small correlation with B

Stephen Bültmann BNL

RHIC Spin Discussion, February
4, 2003
25
Systematic Studies (2)
Beam transport uncertainties were evaluated by
changing the roll and field strength of
quadrupole magnets, using typical uncertainties
in those values (roll 0.1 mrad, strength
0.0001 m-2). Use altered transport for the
reconstruction Original B (
16.4 ? 1.6 ) GeV-2 Altered transport B (
16.6 ? 1.6 ) GeV-2 We are now using the MC
simulation to evaluate systematic errors due to
the transport
Stephen Bültmann BNL

RHIC Spin Discussion, February
4, 2003
26
Result Forward Cone Slope B Value
B ( 16.4 ? 1.6 ) GeV-2
Correlation error with stot and r is of the
order of 0.4 GeV-2 Systematic error due to the
beam transport and beam vertex uncertainty is
under study
Stephen Bültmann BNL

RHIC Spin Discussion, February
4, 2003
27
Bunch Interaction Pattern
Two beams of 55 bunches each Bunches filled with
transversely polarized protons Polarization
state, up or down, was selected on Bunch-By-Bunch
basis for each beam separately
Bunch interaction patterns ?? ?? ?? ??
?0 ? ?
Crossings with empty bunches were used for
background estimates Bunch dependent inelastic
count rate can potentially be used for relative
normalization of elastic count rate in asymmetry
calculation
Stephen Bültmann BNL

RHIC Spin Discussion, February
4, 2003
28
Analyzing Power AN
Combine analyzing powers for the two polarized
proton beams and also double-spin asymmetry to
obtain
The assumption that ANN Pblue Pyellow
cos2? is small leads to
Stephen Bültmann BNL

RHIC Spin Discussion, February
4, 2003
29
Analyzing Power AN (2)
Use Square-Root-Formula to cancel acceptance and
luminosity dependence of count rates and obtain
Fit ?N / cos ? ( Pblue Pyellow )
AN in the kinematic range 0.010 GeV2 ? t
? 0.020 GeV2
Stephen Bültmann BNL

RHIC Spin Discussion, February
4, 2003
30
Raw Asymmetry ?N
Result of fit gives ?N / cos ? 0.017
0.014 Assuming Pblue Pyellow 0.24
0.10 leads to AN 0.035 0.033
Stephen Bültmann BNL

RHIC Spin Discussion, February
4, 2003
31
False Asymmetries ?f
Result of fit gives ?f / cos ? -0.001
0.014
Preliminary
Stephen Bültmann BNL

RHIC Spin Discussion, February
4, 2003
32
False Asymmetries ?f (2)
Assign polarization of interacting bunches
according to a random number and treat resulting
polarization sorted count rates like the raw
asymmetry ?N Fit results in ?f / cos ?
0.001 0.014
Preliminary
Stephen Bültmann BNL

RHIC Spin Discussion, February
4, 2003
33
t -Dependent Raw Asymmetry ?N
Split data sample into two regions in t Low
t 0.0100 GeV2 ? t lt 0.0145 GeV2 High
t 0.0145 GeV2 ? t ? 0.0200 GeV2 Fits
to both data samples gives the same result for ?N
/ cos ?
Preliminary
Stephen Bültmann BNL

RHIC Spin Discussion, February
4, 2003
34
Conclusions

• We had a successful engineering run in 2002
• Beam was set up efficiently for pp2pp running
  conditions
• Detectors and trigger were efficient
• MC Simulation reproduces features of the data
• We made the first measurement of the forward
  slope value B 16.41.6 GeV-2 in proton-proton
  elastic scattering at ?s 200 GeV for 0.010 GeV2
  ? t ? 0.019 GeV2
• We measured the raw asymmetry eN for
  proton-proton elastic scattering in the range
  0.010 GeV2 ? t ? 0.020 GeV2 to be eN 0.017
  0.014

Stephen Bültmann BNL

RHIC Spin Discussion, February
4, 2003
35
Steps to be taken for run in 2003

• Install detector packages in two remaining Roman
  Pot Stations not to depend on vertex position (
  in x0 and y0 ) in calculation of scattering
  angles and increase of detection redundancy
• Measure beam tune under pp2pp running conditions
  to reduce systematic uncertainty in beam
  transport calculation
• Include Van der Meer beam scans for luminosity
  determination
• Run longer to improve statistics in view of
  physics goals (and also systematic uncertainties)

Stephen Bültmann BNL

RHIC Spin Discussion, February
4, 2003