Results of dN/dt Elastic
Scattering
Jorge Molina
ELASTIC EVENTS
FPD LAYOUTFPD LAYOUT
D SQ4 Q3 Q2S A1A2 P1 P2
p p
z (m)
D2 D1 A2Q2 Q3 Q4
59 57 33 23 0 23 33
ELASTIC TRIGGER GIVEN BYELASTIC TRIGGER GIVEN BY
P1D·P2D·A1U·A2U·(EAU + EPD + VT + LM)
A2U A1U
P2DP1D
P
Halo Early Hits LM
VC
Halo In time Hits
PP-P-
FPD Detector SetupFPD Detector Setup
● 6 layers per detector in 3 planes and a trigger scintillator
● U and V at 45 degrees to X, 90 degrees to each other
● U and V planes have 20 fibers, X planes have 16 fibers
● Layers in a plane offset by ~2/3 fiber
● Each channel filled with four fibers
● 2 detectors in a spectrometer
0.8 mm
3.2 mm
1 mm
17
.39 m
m
17.39 mm
UU’
XX’
VV’
Trigger
PLANE (U, V, X) : Two layers of parallel fibers offset by 1/3 fiber width
Bottom view
of the detector
16 + 16 fibers = 63 possible
SEGMENT values with 0.27 mm
resolution
1 2 3 4 ...
SEGMENT CONCEPTSEGMENT CONCEPT
Segment Numbers
SEGMENT : Coincidence of fibers hits in the two layes of each PLANE
HIT RESOLUTION IN YHIT RESOLUTION IN Y
The hit resolution is given by the difference y_ux - y_vu, where:● y_ux is the y value constructed by the intersection of segments u and x, and● y_vu is the y value constructed by the intersection of segments u and v.
y
0
v segment
u segment
x segment
Exaggerated: just to give the idea.
SPATIAL RESOLUTION SPATIAL RESOLUTION
P1D = 136 m P2D = 155 m
The value of the resolution was obtained dividing the standard deviation of the distribution y_ux - y_uv by 2. For both detectors we found:
ACCEPTANCEACCEPTANCE
Note that the probability of receive any particle with |t| 1.7 GeV2 is negligible. We will restrict to the region |t| < 1.7 GeV2.
The geometrical acceptances were calculated by an event generator at the operational pot positions
The program generates tracks at the IP and propagates them through the Tevatron lattice until they reach the pots P1D and P2D in their operational positions.Dead channels are taking into account
RESULTSRESULTSThe sample analysed consisted of 31 runs taken at:
P1D = 17.05 mm (8.98 ) and P2D = 13.80 mm (8.70 )The distribution after the reconstruction of events
found in all runs considered are:
Note the diffractive contamination due to particles with |t| 0.04. This effect obligated us to introduce new cuts to
certify that we have only elastic events
● The y1-y2 distribution shows a huge contamination of high t particles that we have to clean up● The x1-x2 correlation shows a lot of events off the axis
Comparing the distribution of x1-x2 and y1-y2 with the event simulation we find:
STUDYING THE HIT CORRELATION STUDYING THE HIT CORRELATION
To cut the diffractive particles we based on the MC distributions. We will analyse only the particles that
hits the areas enclosed by the lines:
BACKGROUND CUTSBACKGROUND CUTS
FINAL SAMPLEFINAL SAMPLEThe final events considered are the ones that survived all the 6 cuts:
• Multiplicity 1: One or zero hits in each of 12 planes (6 x detector)
• Multiplicity 2: One segment per plane
• Segment cut: must exist 3 reconstructed segments per detector, ie: all 6 segments must be nonzero
• Fiducial cut: The distance yux-yuv between intersections of segments should not exceed in 2 of the gaussian distribution
• Background cuts: events too far from the MC simulations are not considered
• Acceptance cut: only the events that reaches the region allowed by simulation were considered
EFFICIENCY OF THE CUTSEFFICIENCY OF THE CUTS
The table shows the efficiency of each cut:
Note that most of the events registered were cleaned by the multiplicity cuts, this can indicate that spray of
particles reached the detectors.
1001308734-
1.317724Acceptance
1.418569Noise
1.621287Fiducial
2.026428Segments
2.229285Multiplicity 2
5.978095Multiplicity 1
% of total# of evts that survived the cuts
Cut
FINAL RESULTSFINAL RESULTSThe events that survived all the six cuts have the
distribution:
Events are peaked at zero as expected with a resolution of = 0.019
The events that survived all the six cuts presents the |t distribution:
|t| DISTRIBUTION|t| DISTRIBUTION
There’s an extra peak around |t|~1.4 GeV2 that is not expected and that we will try to subtract
Events without any cut
HALO BACKGROUND SUBTRACTIONHALO BACKGROUND SUBTRACTION
The events that survived to all cuts still have a contamination due to halo and diffractive particles
The halo events were simulated by the BD. It takes into account beam gas scattering and were simulated with the four pots at operational positions.
The simulation gave the position and the angle at P1D
The process consisted in propagate the particles until P2D, then convert the positions into fibers to reconstruct as usual data
Same amount of halo inside and outside
NORMALIZATION USEDNORMALIZATION USED
Cut # of evts that survived the
cuts
% of total
- 1308734 100
Mult 1 78095 5.9
Mult 2 29285 2.2
Segments 26428 2.0
Fiducial 21287 1.6
Noise 18569 1.4
Acceptance 17724 1.3
0.12821287
18569)(21287
goodbckg
(removed)bckg
The normalization concept used to scale the halo distribution is based in the background cuts
After dividing by acceptance and scale at 13% we have:
It cannot reproduce the data at high values of |t|, where we suppose it’s mainly halo
There’s no peak at |t|~1.4 GeV2 that we can subtract in the bckg file
It was decided to fit between bins 4 ± 1 to bin 12 ± 1 and take the average
FITTING RANGEFITTING RANGE
The |t| distribution found after subtracting the halo Spectra is:
UNSMEARINGUNSMEARING
The dN/dt spectra obtained with the events that survived all cuts and that were subtracted must be corrected by the factor that takes into account the resolution of the detector: fres = f(t)ideal/f(t)measured
To obtain this factor a exponential function were used as ansatz, that was convolute with a linear function that describes the variation of the resolution in |t|
FIT RESULTSFIT RESULTS
Bin range -bdata -bbckg -bsubt -bunsm -bnorm -bpeak
3:11 3.10 1.90 3.21 3.20 3.38 3.51
3:12 3.23 1.88 3.36 3.35 3.55 3.52
3:13 3.20 1.83 3.35 3.34 3.55 3.56
4:11 3.27 2.02 3.40 3.39 3.58 3.70
4:12 3.40 1.98 3.54 3.54 3.75 3.68
4:13 3.34 1.89 3.50 3.49 3.72 3.71
5:11 3.53 2.47 3.66 3.64 3.81 3.74
5:12 3.63 2.32 3.79 3.78 3.99 3.70
5:13 3.52 2.15 3.70 3.68 3.92 3.74
Average 3.34 2.04 3.45 3.47 3.68 3.64
2
2
/1
)/(
ii
iiix
b
ii )/1(
12
2
Is not an statistical effect because all the other runs that shows the peak have less events
Both set of runs presents flat distribution after |t|~1.3 GeV2
Runs 138-141Runs 176-180
2376 evts 3709 evts
DIFFERENT RUNSDIFFERENT RUNS
Systematic errors due to the vertical position of the Systematic errors due to the vertical position of the detectorsdetectors
The error in the vertical position y were determined changing the position of the pots in +0.5 mm in the calculation of the acceptance. The dN/dt spectra measured then were divided by this value of the acceptance, obtaining the error + . The value obtained using the acceptance in –0.5 mm is the same
The error in the vertical position were calculated through
a = (|A+|+|A-|)/2
Then this value was added in squared with the statistical error to obtain the systematic error in the vertical position:
y = (2est + 2
a )1/2
Systematic errors due to the halo background Systematic errors due to the halo background subtractionsubtraction
The errors due to the halo subtration were obtained through the subtraction of the slopes found before and after the subtraction: subt = bdata - bsubt
Systematic errors due to the diffractive contaminationSystematic errors due to the diffractive contamination
The uncertainties introduced by the remanent diffractive events in the final sample were estimated to contribute in the amount that the halo background: subt = diff
The errors due to the halo subtration were obtained through the subtraction of the slopes found before and after the unsmearing: uns = buns - bsubt
Systematic errors due to the unsmearing processSystematic errors due to the unsmearing process
The final error in the slope b is calculated through:
Final error in the slope bFinal error in the slope b
37.02222 unsdiffhaloy
Where each term contributes to the final error in:
Uncertainty Contribution (%)
y 88.1
halo 5.8
diff 5.8
uns 0.3Finally the slope found is:
237.047.3 GeVb
COMPARISON WITH OTHER EXPERIMENTS COMPARISON WITH OTHER EXPERIMENTS The points corrected by the unsmearing procedure were
normalized by the points obtained by the E710 experiment (which agrees with CDF for dN/dt in the determination of
the slope b at low |t|).
The results are in excellent agreement with the model of M. Block showed in the figure
Still need to understand why the error bars are so little In progress
1) Proton antiproton elastic scattering was measured by the D0 Roman Pots.
2) Elastic data samples contain diffractive and halo backgrounds, most of which were removed by simple cuts.
3) The halo remaining after the cuts were subtracted using a MC simulation normalized according to the background cuts assumption
4) The four momentum transfer range considered in the analysis were limited to the region
0.87 < |t| < 1.34 GeV2
5) The final result for the slope were obtained taking the average of different fit ranges around the limit imposed by the acceptance uncertainty at low |t| and the abnormal behavior of the accelerator at high |t|
CONCLUSIONSCONCLUSIONS
6) The first measurement of the dN/dt slope in the region analysed, at c.m.s. energy of s = 1.96 TeV gave the result:
b = -3.47 0.37 GeV-2
7) The error in the measurement are mostly dominated by the uncertainty in the determination of the vertical position of the detectors
8) The result of the slope found is in good agreement with the phenomenological model of M. Bloch based in measurements made by experiments E710 and CDF at
s = 1.8 TeV.