Transcript Studies of + and (1520) photoproductions

LEPS Collaboration Meeting in Taiwan, 1 May 2008
Studies of + and (1520) photoproductions
[TN46 and TN47 (will be released soon)]
Norihito Muramatsu
RCNP, Osaka University
4.2 Before/after inclusion of new ntag=1
Fig.16 MMd(,K-p) spectrum in the (1520)
region of the LD2 data with the original
tagger reconstruction.
Fig.17 MMd(,K-p) spectrum in the (1520)
region of the LD2 data with the first
update of tagger reconstruction.
Fig.18 MMd(,K-p) spectrum in the (1520)
region of the LD2 data with the second
update of tagger reconstruction.
So far, tagger reconstruction was updated twice by Kato. First a part of ntag=2 events was saved by tightening true
tagger hit requirement, and statistics of K-p events was increased by 15.7% (1139113179 events). Then, a part of
ntag.ge.3 events was further saved, and the statistics was increased by 2.4% (1317913495 events), which resulted
in18.5% increase in total. Background spectra were simply scaled by these factors, and overlaid to the updated missing
mass spectra as shown in Fig.16-18. Width of the + peak got wider after inclusion of new ntag=1 events. E resolution
was slightly changed from 11.74 MeV to 12.69 MeV after the update of tagger reconstruction, but it is not large as the
observations. (This resolution was re-smeared to the background spectra at the first update, and the individual background was rescaled depending on small change of #events, which passed the same event selection.) Also, it was
confirmed that this width change was not caused by the new photon energy calibration, simultaneously released by
Kato. The increase of the statistics must have forced the peak width wider in direction of the mass resolution. Statistical
significance was not so changed (rather increased a bit) by improving the tagger reconstruction as shown in Table 3.
This is a signal-like behavior of the peak structure, and not likely a fluctuation.
Table 3. Comparison of statistical significances depending on tagger reconstruction.
old
new1
new2
narrow gate S/sqrt(B)=4.75 S/sqrt(S+B)=4.15 S/sqrt(B)=5.04 S/sqrt(S+B)=4.41 S/sqrt(B)=5.24 S/sqrt(S+B)=4.57
wide gate
S/sqrt(B)=3.18 S/sqrt(S+B)=2.97 S/sqrt(B)=3.49 S/sqrt(S+B)=3.25 S/sqrt(B)=4.15 S/sqrt(S+B)=3.83
2
5.1 Photon energy resolution
After adopting the second update of tagger reconstruction, photon energy resolution was re-estimated to be 12.58 MeV
with the same calculation method. (See Fig.28.) Since this value was consistent with the previous estimate, 12.69 MeV
was retained to smear the resolution in the MC simulations. Photon energy resolution for original ntag=1 events and newly
reconstructed events by the two updates were also measured to be 12.31 MeV and 13.41 MeV, respectively. (See Fig.29
-30.) Since the new events do not have too worse resolution, these events are kept in the analysis.
Fig.29 Same as Fig.28, but for events which were
saved by the updated tagger reconstruction.
Fig.28 Difference of tagger energy measurement from photon
energy calculated by assuming MMp(,K-p) gives K+ mass in
the LH2 data, after the second update of tagger reconstruction.
Fig.30 Same as Fig.28, but for events which were
retained from the original tagger reconstruction.
3
4.3 Dependence on gate width of (1520) selection
10 MeV
50 MeV
20 MeV
(standard)
100 MeV
Table 4. Number of signal events and statistical significances depending on
width of  selection cut.
1.51<M(K-p)<1.53 GeV/c2
narrow gate: data= 23815.4 bg= 164.42.7 sig= 73.615.7
s/sqrt(b)=5.74 s/sqrt(s+b)=4.77
wide gate : data= 41520.4 bg= 327.13.9 sig= 87.920.7
s/sqrt(b)=4.86 s/sqrt(s+b)=4.32
1.50<M(K-p)<1.54 GeV/c2
narrow gate: data= 36419.1 bg= 276.93.6 sig= 87.119.4
s/sqrt(b)=5.24 s/sqrt(s+b)=4.57
wide gate : data= 65325.6 bg= 555.25.2 sig= 97.826.1
s/sqrt(b)=4.15 s/sqrt(s+b)=3.83
1.47<M(K-p)<1.57 GeV/c2
narrow gate: data= 72126.9 bg= 567.05.4 sig=154.027.4
s/sqrt(b)=6.47 s/sqrt(s+b)=5.74
wide gate : data=128435.8 bg=1122.37.6 sig=161.736.6
s/sqrt(b)=4.83 s/sqrt(s+b)=4.51
1.42<M(K-p)<1.62 GeV/c2
narrow gate: data=112733.6 bg= 954.17.1 sig=172.934.3
s/sqrt(b)=5.60 s/sqrt(s+b)=5.15
wide gate :data=206945.5 bg=1881.610.0 sig=187.446.6
s/sqrt(b)=4.32 s/sqrt(s+b)=4.12
Fig.19 Distribution of K-p missing mass from a deuteron depending
on width of (1520) selection cut in the LD2 data.
4
Fig.20 K-p invariant mass distribution after tagging +
signal region in the LD2 data. Background estimates
are overlaid with the same selection cuts.
Fig.21 Number of + signals divided by width of (1520)
selection cut depending on the width. Data points
correspond to four panels of Fig.19.
Fig. 19 shows MMd(,K-p) distributions depending on width of (1520) selection cut. A clear peak at the + mass was
observed in all the mass spectra. Table 4 summarizes statistical significances of the 4 different conditions to select
(1520). 5.24 to 6.47 sigmas (4.15 to 4.86 sigmas) of enhancement was observed in the missing mass region of
1.520<MMd(,K-p)<1.545 GeV/c2 (1.510<MMd(,K-p)<1.560 GeV/c2). S/N ratio at the + mass region was increased
by tightening the (1520) selection cut. Fig.20 shows M(K-p) distribution in case that 1.525<MMd(,K-p)<1.540 GeV/c2
is tagged in the LD2 sample. It is clear that the + photoproduction is associated with (1520). Fig. 21 shows #signal
/ [width of (1520) selection cut] as a function of the width. Solid line indicates relative number of events from quasifree (1520) photoproduction with the (1520) selection cut indicated in x axis. The number of events were counted
in the filtered sample of the K(1520) MC, and normalized to the measurement at the standard (1520) selection cut.
Again, (1520) association of the + signals is clear.
5
4.4 + photoproduction in sidebands
Fig.24 MMd(,K-p) spectrum in 1.450<M(K-p)<1.500
GeV/c2 and 1.540<M(K-p)<1.590 GeV/c2. This spectrum
is the same as sum of Fig.22 and Fig.23.
Fig.25 Number of + signals divided by M(K-p) mass range to
count it. Two data points correspond to the standard (1520)
selection (Fig.14) and the sideband selection (Fig.24). A curve
made from quasi-free K(1520) MC was fitted to them.
Table 5. Number of signal events and statistical significances in sidebands.
Narrow gate: data=57624.0 BG=479.15.1 signal=96.924.5
sig/sqrt(bg)=4.43 sig/sqrt(sig+bg)=4.04
Wide gate : data=102732.0 BG=937.87.2 signal=89.232.8
sig/sqrt(bg)=2.91 sig/sqrt(sig+bg)=2.78
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5.3 Unbinned fit to the + mass spectrum
Fig.33 Unbinned fit of a Voigt function to MMd(,K-p) spectrum
over the MC-based background estimate in the LD2 data. Mass
resolution was fixed in the Voigt function.
Fig.34 Unbinned fit of a Gaussian function to MMd(,K-p)
spectrum over the MC-based background estimate in the
LD2 data.
Since usual 2 fitting to a binned histogram is affected by a way of binning incase of limited signal statistics,
unbinned fit was adopted to examine the + peak. The unbinned fit defines a probability density function
with free parameters, and maximizes a product of the probability densities of individual events. A ‘RooFit’
package, which ran on ROOT and was prepared for BABAR experiment, was used to perform the unbinned
fit. (Basic programming scheme for our purpose was prepared by Matsumura.)
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5.4 Probability to observe a peak with sigma=7.3 MeV
5.5 Probability to observe a 5.24 sigma peak
Methods were updated, and number of toy MC trials were increased.
Fig.35  distribution of unbinned Gaussian fits
in 1000 toy MC simulations. The  got below
7.3 MeV (a vertical line) 121 times, which gave
a probability of the downward fluctuation to be
12.10.7 %.
Fig.36 Distribution of statistical significances of the maximum
fluctuation in 25 MeV mass window around the + mass.
Measurement was performed in 1,000,000 MC trials, and two
trials exceeded 5.24 sigma, indicated by a vertical line.
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6. Measurement of differential cross sections
6.1 Luminosity
Number of photons in LEP beam
tagger counts w/ dead time correction depending on filling pattern, DAQ live time, upveto efficiency, and #photon
normalization based on #proton/#photon ratio (See miho:/np1b/v01/mura/leps/ana/temp2/ngamma[lld2/llh2]-corr-[mylist/missing].dat, which was made based on tables from Kohri / Sumihama and TN43.)
LD2: 4.587*1012, LH2: 2.803*1012 w/ all the above corrections
(LD2: 5.142*1012, LH2: 3.205*1012 w/o #photon normalization)
(LD2: 5.01 *1012, LH2: 3.13 *1012 before the above corrections)
transmission : 0.5260.017(0.007[stat]0.016[sys])
(See ~sp8lep/HTMLpub/leps_notes/ana_meeting/2004may28/index.html.)
ntag=1 prob. : LD2: 15954/19677=0.81080.0006 , LH2: 5049/6127=0.82410.0011
Ratio of ntag(the newest reconstruction)=1 was measured by the real data samples selected with K -p detection,
|ytof|>50 mm, vertex requirement, and 1.75<E(calculated backwardly from K-p missing mass=MK+)<2.40 GeV.
tagger reconstruction eff. * Ratio of E >1.75 GeV (See miho:/np1b/v01/mura/leps/ana/temp2/weightcc_
[ld2/llh2]_term*.20.1.50001, which were made based on tables from Sumihama.)
LD2 r24095-r24231: 0.780 (0.60*1012 photons) + r24241-r24398:0.753 (0.43*1012 photons)
+ r24443-r26338: 0.748 (3.99*1012 photons) ---> weighted efficiency: 0.752
Note that there was a tagger SSD problem in r24241-r24398 and that this period was specially treated as
described in the next section.
LH2 r23690-r24058: 0.792 (1.14*1012 photons) + r25453-r25968: 0.747 (1.99*1012 photons)
---> weighted efficiency: 0.763
-----> #photon(LD2) = (1.4710.049)*1012, #photon(LH2) = (0.9270.030)*1012
Number of target particles
density
LD2:0.169 g/cm3, LH2:0.0708 g/cm3
thickness: 16 cm due to pressure difference between target cell and vacuum (The information came from Kohri.)
Avogadro number : 6.022*1023 & mass number LD2 : 2, LH2 : 1
-----> #deuteron = 8.14 * 10-13 /pb, #proton = 6.82 * 10-13 /pb
Luminosity (Its error is dominated by a systematic error of the transmission.)
LD2: #photon * #deuteron = 1.1970.040 /pb LH2: #photon * #proton = 0.6320.020 /pb
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6.3 Differential cross section of + photoproduction
assuming a constant matrix element
As shown in Fig.39, there is no acceptance of + detection in case of
K-p polar angle at d-CMS greater than 35. Therefore, differential
cross section was measured in the polar angle region less than 35.
Table 6 summarizes number of signals and significance in this region.
Number of signals in wide signal gate (1.51<MMd(,K-p)<1.56 GeV/c2)
was used to calculate differential cross section because it covers 2
region of the expected mass resolution with some statistics:
#signal(0-35 degree, wide gate) = 96.626.0 events
& solid angle of 0-35 degree = 1.136 sr
Acceptance was measured by generating d  +(1520) events flatly
at d-CMS. Energy dependence of the yield just followed a E spectrum
of backward Compton scattering of the multi-line UV laser. The event
generation was done by G3LEPS with options of DCAY=1, HADR=1,
LOSS=2, MULS=1, dc_eff.00009. (Note influence by a possible update
of DC efficiency map is discussed in the next page.)
Acc.(E >1.75 GeV, 0-35 degree) = 0.041530.00075
As a result, differential cross section of d+ K- p in 1.50<M(K-p)<1.54
GeV/c2 was calculated to be:
d/d (d+ K- p) = 96.626.0 events / 0.041530.00075
/ (1.1970.040 /pb) / 1.136 sr = 1.710.46 nb/sr
In case of assuming that most of the observed signals
come from d+(1520), total acceptance further includes acceptance
of (1520) resonance within 1.50-1.54 GeV/c2, and branching ratio of
(1520)  K-p decay (0.225) must be also taken into account.
Acc.(E >1.75 GeV, 0-35 degree) = 0.031560.00059
Differential cross section of d+(1520) was calculated to be:
d/d (d+*) = 96.626.0 events / 0.031560.00059 / 0.225
/ (1.1970.040 /pb) / 1.136 sr = 10.002.72 nb/sr
Fig.39 MMd(,K-p) spectra of the LD2 data in K-p polar angle
at d-CMS smaller than 35 degree (upper panel) and larger
than 35 degree (lower panel).
Table 6. Number of signal events and statistical significances
in K-p polar angle smaller than 35 degree at d-CMS.
Narrow gate: data = 36219.0, BG = 275.1 3.6
signal =86.919.4 events
sig/sqrt(bg) = 5.24, sig/sqrt(sig+bg) = 4.57
Wide gate: data = 64725.4, BG = 550.4 5.1
signal = 96.626.0 events
sig/sqrt(bg) = 4.12, sig/sqrt(sig+bg) = 3.80
10
6.4 Differential cross section of + photoproduction
assuming Titov’s theoretical prediction
Instead of the isotropic generation of d+*, another MC set
following Titov’s theoretical differential cross section, shown in
Fig.40, was generated to measure a variation of the acceptance.
This measurement gives a hint of systematic error to the cross
section measurement. Titov’s cross section is peaked around
22 in polar angle of (1520) at d-CMS, where a momentum
of a nucleon reacting with an exchanged kaon becomes the
minimum. + production yield is significantly lower in the other
polar angle region because of a deuteron form factor. This may
explain a negative result in CLAS experiment. The strength in
a region less than 10 degree slightly depends on spin-parity of
+, but the peaking structure is unchanged. A region of 0-35
degree was used for the differential cross section measurement
as done in the previous section:
Acc(d+K-p) = 0.046920.00026 = 1.13 * Acc.(flat)
===> d/d (d+K-p) = 1.510.41 nb/sr
Acc(d+*) = 0.035480.00020 = 1.12 * Acc.(flat)
===> d/d (d+*) = 8.902.41 nb/sr
Fig.40 Titov’s theoretical calculation of differential cross section
for d+(1520) depending on * polar angle at d-CMS.
A calculation for E = 2.0 GeV and spin-parity = 3/2- is shown.
The results are well close to the case with a constant matrix
element, which only differs by ~10%.
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7. Kinematic dependences of the + yield
7.1 Polar angle dependence at d-CMS
Since CLAS have not observed the + peak in their
acceptance region, where extremely forward going K-p
system cannot be covered, polar angle dependence of
the + yield may exist. Interestingly, Titov’s theoretical
calculation of differential cross section (Fig.40) shows
such dependence, which supports + photoproduction
associates with extremely forward going (1520). Fig.47
shows (1520) polar angle at d-CMS vs. missing K+
momentum in the quasi-free K+(1520) MC simulation.
At the polar angle of ~25 degree, the K+ momentum
reaches ~420 MeV/c, which can produce + with a rest
neutron. In the other angle region, a neutron must have
larger Fermi momentum to produce +, and the reaction
rate will decrease by a deuteron form factor. Unfortunately,
LEPS experiment has no acceptance for (1520) polar
angles larger than 35 degree, but peaking behavior around
25 degree was examined by dividing the LD2 sample to two
angle regions (0-15 degree and 15-35 degree). Since
statistics with the standard (1520) selection was not large,
the width of the selection cut was extended to 40 MeV/c2
of the (1520) pole.(d+K-p may be contaminated in the
sample, but it is assumed that reaction mechanism is not so
different.)
Fig.47 (1520) polar angle at d-CMS vs. K+ momentum
in quasi-free pK+(1520) MC simulation.
12
0<d-CMS(K-p)<15
15<d-CMS(K-p)<35
Fig.48 MMd(,K-p) spectra depending on (1520) polar
angle in LD2 data.
Table 7. Number of signal events and statistical significances
depending on K-p polar angle in 1.520<MMd(,K-p)<1.545 GeV/c2.
0<d-CMS(K-p)<15 degree
data= 13511.6 bg=106.12.3 sig=28.911.9
s/sqrt(b)=2.81, s/sqrt(s+b)=2.49
15<d-CMS(K-p)<35 degree
data=46321.5 bg=363.44.3 sig=99.621.9
s/sqrt(b)=5.22, s/sqrt(s+b)=4.63
35<d-CMS(K-p)<90 degree
data= 4 2.0 bg= 3.70.4 sig= 0.3 2.0
s/sqrt(b)=0.16, s/sqrt(s+b)=0.15
Fig.49 Relative yield of d+* depending on
(1520) polar angle at d-CMS.
13
Fig. 48 shows MMd(,K-p) spectra in the two different polar
angle regions with the extended (1520) selection cut.
A clearer + peak was observed in 15<d-CMS(K-p)<35 degree.
Numbers of signal and background events are summarized
in Table 7 with angle region of 35<d-CMS(K-p)<90 degree.
+ yields were compared by correcting number of signals with
K-p detection acceptance and solid angle:
#signal
acceptance
solid angle
0-15 deg 28.911.9 0.08070.0020
0.214
15-35 deg 99.621.9 0.03220.0007
0.922
Number of signals were counted in the narrow signal region
(1.520<MMd(,K-p)<1.545 GeV/c2) since S/N ratio must be
better giving smaller influence of background fluctuation.
The acceptance was measured by using d+(1520) MC
generated in flat phase space. Fig. 49 shows relative + yields
with the above corrections. Enhancement was observed in
(1520) polar angle region of 15-35 degree.
Fig. 50 shows missing mass resolutions for + in the three
polar angle regions described above. The mass resolutions
are consistent in all angle regions. Therefore, the polar angle
dependence of the + yields is not caused by the mass
resolution.
0<d-CMS(K-p)<15
15<d-CMS(K-p)<35
35<d-CMS(K-p)<90
Fig.50 Mass resolutions of + depending on (1520)
polar angle in d+* MC.
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7.2 Photon energy dependence
1.75<E<2.06 GeV
2.06<E GeV
Fig.51 MMd(,K-p) spectra depending on photon energy
in LD2 data.
Fig. 51 shows MMd(,K-p) spectra in two photon energy
region: 1.75<E<2.06 and E>2.06 GeV. In order to increase
statistics, width of the (1520) selection cut was extended
to 40 MeV/c2 of the (1520) pole. + peak was observed
in both energy regions. Numbers of signal and background
events are summarized in Table 8. + yields were compared
by correcting number of signals with acceptance and ratio
of number of photons in the two energy regions:
#signal
acceptance
#photon
1.75-2.06 GeV 73.316.3 0.002550.00010 0.308
2.06-~2.4 GeV 55.619.0 0.004750.00011 0.443
As done in the measurement of polar angle dependence,
number of signals were counted in the narrow signal region
(1.520<MMd(,K-p)<1.545 GeV/c2), and the acceptance
was measured by using d+(1520) MC generated in
flat phase space. Fig.52 shows relative + yields with
the above corrections. Since the acceptance and the number
of photons in the higher energy region are larger, relative +
yield is further enhanced in the lower energy region. This may
be connected with the fact that many high energy experiments
have not observed +.
15
Table 8. Number of signal events and statistical significances
depending on photon energy in 1.520<MMd(,K-p)<1.545
GeV/c2.
1.75<E<2.06 GeV
data=25616.0 bg=182.73.0 sig=73.316.3
s/sqrt(b)=5.42, s/sqrt(s+b)=4.58
2.06<E GeV
data=34618.6 bg=290.43.8 sig=55.619.0
s/sqrt(b)=3.26, s/sqrt(s+b)=2.99
Fig.52 Relative yield of d+* depending on
photon energy.
16
From Nam et. al.,
hep-ph/053149
Note definition of
angle is vice-versa.
Fig.43
Fig.44
As a result, differential cross sections were calculated as follows:
Luminosity=0.6320.020 /pb, BR((1520)K-p)=0.225
0<CMS(K-p)< 30 (0.84 sr) #events=3903.3 275.1 d/d=32.72.5 nb/sr d/dcos=20516 nb
30<CMS(K-p)< 60 (2.30 sr) #events=8279.0 581.5 d/d=25.31.9 nb/sr d/dcos=15912 nb
60<CMS(K-p)< 90 (3.14 sr) #events=7868.61333.8 d/d=17.63.0 nb/sr d/dcos=111 19 nb
Order of the differential cross sections is consistent with Nam’s calculation, which are shown in Fig.43 and 44.
Note that the acceptance measurement may depend on polar angle distribution at t-channel helicity frame,
which is currently studied with Jia-Ye. Updates related with this point will be described in a separate note later.
17
3.2 K- polar angle distribution at t-channel helicity frame
LH2
LD2
18
3.3 Differential cross sections of forward (1520)
photoproduction from proton
Differential cross sections were measured depending on photon energy (2 bins) and (1520) polar angle at CMS (3 bins).
Number of signals were divided by acceptance, branching ratio (BR[(1520)K-p]=0.225), lumnosity in each energy bin,
and solid angle (or cos range). Since K- polar angle distribution at t-channel helicity was consistent with isotropic
generation, acceptances were measured without applying any filters to phase space MC. Therefore, number of signals
and acceptances are basically the same as TN46. (Only re-smearing of photon energy resolution was updated.)
Differential cross sections were evaluated in two photon energy regions, although this energy division was not done in
TN46. In polar angle region less than 60 degree, cross sections became higher in lower energy region. This behavior is
seen in forward (1520) photoproduction of Nam’s theoretical calculation, while not seen in Titov’s calculation. The energy
dependence of (1520) photoproduction would partly explain energy dependence of d+(1520) reaction in TN46.
*** 2.04<Ecms<2.18 GeV (1.75<Eg<2.06 GeV) ***
0-30 degree data:11810.863 BG:21.6520.788 #signal:96.34810.891
Acc.:0.05517170.0015925 d/d:35.814.32 nb/sr d/dcos:224.5527.11 nb
30-60 degree data:19513.964 BG:53.5841.258 #signal:141.41614.021
Acc.:0.03351780.0007592 d/d: 31.603.36 nb/sr d/dcos:198.5721.11 nb
60-90 degree data: 91 9.539 BG:53.4511.237 #signal: 37.549 9.619
Acc.:0.01221380.0003955 d/d: 16.874.39 nb/sr d/dcos:105.9227.55 nb
*** 2.18<Ecms
GeV (2.06<Eg
GeV) ***
0-30 degree data:28316.823 BG:92.5811.616 #signal:190.41916.900
Acc.:0.08817410.0016560 d/d: 30.552.94 nb/sr d/dcos:191.5618.43 nb
30-60 degree data:27516.583 BG:107.4421.741 #signal:167.55816.674
Acc.:0.04133230.0007065 d/d: 20.952.22 nb/sr d/dcos:131.6113.94 nb
60-90 degree data: 69 8.307 BG:31.5560.943 #signal: 37.444 8.360
Acc.:0.00778760.0002662 d/d: 18.204.15 nb/sr d/dcos:114.2826.07 nb
19
3.4 Differential cross sections of forward (1520)
photoproduction from deuteron
*** 2.04<Ecms<2.18 GeV (1.75<Eg<2.06 GeV) ***
0-30 degree data:26116.155 BG:113.2652.558 #signal:147.73516.357
Acc.:0.0448652+-0.0014849 d/d: 35.484.26 nb/sr d/dcos:222.4926.71 nb
30-60 degree data:31317.692 BG:118.7912.590 #signal:194.20917.880
Acc.:0.0188388+-0.0005937 d/d: 40.574.16 nb/sr d/dcos:254.9426.16 nb
*** 2.18<Ecms
GeV (2.06<Eg
GeV) ***
0-30 degree data:59324.352 BG:345.4284.403 #signal:247.57224.746
Acc.:0.07745240.0015879 d/d: 23.962.58 nb/sr d/dcos:150.2016.15 nb
30-60 degree data:31117.635 BG:191.6673.283 #signal:119.33317.938
Acc.:0.01659160.0004650 d/d: 19.693.08 nb/sr d/dcos:123.7019.38 nb
20
7.3 Dependence on MMp(,K-p)
MC simulation of d+*
LD2 data
1.525-1.540 GeV/c2
was tagged.
LD2 data
- BG sum
Fig.54 MMp(,K-p) spectrum of LD2 data by tagging + peak.
Upper panel shows an original spectrum with background
estimates and lower panel shows a spectrum after the subtraction.
K+ mass
Fig.55 MMp(,K-p) spectrum of d+(1520) MC.
Off-shell component of kaon exchange does not look negligible.
21
8.1 LD2 extra events
LD2 data
(KKp x2)
dK-pK+n MC
LD2 data
- BG sum
Fig.56 MMp(,K-p) spectrum of LD2 data by tagging LD2 extra events.
Upper panel shows an original spectrum with background estimates
and lower panel shows a spectrum after the subtraction. Sum of K*,
p, and twice of non-resosnt KKp MCs were taken for BG estimates.
Fig.57 Spectator momentum vs. MMp(,K-p)
of dK-pK+n MC.
As seen in Fig. 11, extra events were observed in higher side of (1520) resonance peak in the LD2 data.
They can not be figured out by non-resonant KKp, K(1520), and p productions, whose kinematics was
extracted from the LH2 data. In order to understand nature of the extra events, M(K-p)>1.54 GeV/c2 region
was tagged in the LD2 data. Fig. 56 shows MMp(,K-p) distribution of the tagged sample. Non-resonant
KKp background spectrum (blue) was scaled twice as in Fig. 11, and it was added to K(1520) and p
background spectra (red). MMp(,K-p) spectrum after subtracting the summed background spectrum is
well peaked at K+ mass. Fig. 57 shows momentum of spectator nucleon vs. MMp(,K-p) in dK-pK+n MC
simulation. It is clear that MMp(,K-p) is peaked at K+ mass when the spectator momentum is close to 0.
The LD2 extra events are likely due to contribution from n photoreaction. That is why background spectrum
for the extra events were estimated by making kinematic filters for non-resonant KKN MC simulation.
22
8.2 1.6 GeV bump
dK+(1520)n MC
LD2 data w/
BG estimates
LD2 data
- BG sum
Fig.63 MMp(,K-p) spectrum of dK+(1520)n MC.
nK(1520) MC
Fig.62 MMp(,K-p) spectrum of LD2 data by tagging 1.6 GeV bump.
Upper panel shows an original spectrum with background estimates
and lower panel shows a spectrum after the subtraction.
dK+(1520)n is not likely a source of the bump structure,
since MMp(,K-p) distribution is skewed toward high mass side
and the maximum of MMd(,K-p) spectrum differs from 1.6 GeV/c2.
By comparing MMp(,K-p) distributions of dK+(1520)n and n
K(1520), the former spectrum is closer to the LD2 spectrum.
Since a ‘shoulder’ of the maximum region in the LD2 spectrum
is slightly lower than the dK+(1520)n MC, momentum of a
spectator nucleon may be soft. Also, a possibility of new particle
states like + cannot be excluded.
Fig.64 MMp(,K-p) spectrum of nK(1520) MC.
23
Appendix A. Background estimation based on sideband method
In order to test existence of + peak, the K(1520) spectrum estimated by the sideband subtraction in the LH2 sample
was fitted to MMd(,K-p)<1.51 GeV/c2 of the LD2 missing mass spectrum over the sideband averaged background
components. Fig. 76 shows the MMd(,K-p) spectra obtained after the fitting. + peak and 1.6 GeV bump were observed
as seen in the filtering method. Number of signals and statistical significances are summarized in Table 10. The statistical
significances were at the same level as the filtering method.
Table 10. Number of signal events and statistical
significances by sideband method.
Fig.76 MMd(,K-p) spectra of LD2 data with background
estimates by sideband method.
Narrow gate:
1.520-1.545 GeV/c2 (5 bins)
~ 1 sigma of mass resolution
data = 364 19.1 events
BG = 279.0 6.9 events
signal = 85.020.3 events
sig/sqrt(bg)
= 5.09
sig/sqrt(sig+bg) = 4.46
Wide gate:
1.510-1.560 GeV/c2 (10 bins)
~ 2 sigma of mass resolution
data = 653 25.6 events
BG = 535.1 9.6 events
signal = 117.927.3 events
sig/sqrt(bg)
= 5.10
sig/sqrt(sig+bg) = 4.61
Note: In calculation of errors in background
estimates, an improvement factor by 10 MeV
smearing (0.4), a normalization factor of
sideband average to the (1520) region (0.4),
and a scaling factor of K(1520) component
(1.336) were used. The improvement factor
came from Nakano’s study.
24
2.2 Results of training by LH2
Fig.1 MMp(,K+) distribution with
M(KK)>cutmkk2(20,egamma) in
LH2 data.
Fig.4 MMp(,K-) distribution with
M(KK)>cutmkk2(20,egamma) in
LH2 data.
25
Fig.7 MMp(,K+K-) distribution without
phi exclusion cut in LH2 data.
Fig.8 M(K+K-) distribution without
phi exclusion cut in LH2 data.
26
Fig.19 K- polar angle distribution at t-channel helicity
frame [KK mode in LH2 data]. sin2 was fitted.
Fig.20 K- polar angle distribution at t-channel helicity
frame [same as Fig.19]. a*sin2+b*(1/3+cos2) was fitted.
Fig.19 and Fig.20 have the same data points, but sin2 and a*sin2+b*(1/3+cos2) were fitted, respectively.
Better 2 was obtained in Fig.20 (2 /ndf=0.3697/1) than Fig.19 (2 /ndf=4.844/2). In Fig.20, ratio of sin2
[a/(a+b)] was calculated to be 0.78290.0943, which resulted in sin2 dominance. In calculations of differential
cross sections described below, the fitting result of Fig.20 was adopted to estimate detector acceptance. (The
observed dependence means K-p pair tends to fly to side direction, and the detector acceptance of KK mode
must be lower than the case with isotropic generation at t-channel helicity frame.) This fit will at least give
a phenomenological correction to the detector acceptance.
27
2.5 Luminosity in K+K- detection mode
Procedure to calculate luminosity is similar to TN46, but a few calculations were updated as indicated blue characters.
Number of photons in LEP beam
tagger counts (same as TN46)
LD2: 4.587*1012, LH2: 2.803*1012
transmission (same as TN46)
0.5260.017(0.007[stat]0.016[sys])
ntag=1 prob. (re-estimated by using real events with K+K- detection)
LD2: 18861/22712=0.83040.0025, LH2: 6408/7668=0.84610.0041
Ratio of ntag(the newest reconstruction)=1 was measured by the real data samples selected with K +K- detection,
|ytof|>50 mm, vertex requirement, and 2.00<E(calculated backwardly from K+K- missing mass=Mp)<2.40 GeV.
Note these probabilities are slightly higher than Kp mode because higher energy region (E>2.0 GeV) is selected.
tagger reconstruction eff. * Ratio of E >2.00 GeV (See miho:/np1b/v01/mura/leps/ana/temp2/weightcc_
[ld2/llh2]_term*.20.1.50001.qfkk, which were made based on tables from Sumihama.)
LD2 r24095-r24231: 0.5328 (0.60*1012 photons) + r24241-r24398:0.5328 (0.43*1012 photons)
+ r24443-r26338: 0.5056 (3.99*1012 photons) ---> weighted efficiency: 0.5112
Note that a tagger SSD problem in r24241-r24398 does not affect this ratio because E>2.0 GeV is required.
LH2 r23690-r24058: 0.5411 (1.14*1012 photons) + r25453-r25968: 0.5068 (1.99*1012 photons)
---> weighted efficiency: 0.5193
-----> #photon(LD2) = (1.02420.0332)*1012, #photon(LH2) = (0.64780.0212)*1012
Number of target particles (same as TN46)
-----> #deuteron = 8.1417 * 10-13 /pb, #proton = 6.8217 * 10-13 /pb
Luminosity
LD2: #photon * #deuteron = 0.83390.0270 /pb
LH2: #photon * #proton = 0.44190.0145 /pb
28
2.6 Differential cross sections of backward
(1520) photoproduction
Fig.21 shows MMp(,K+) distributions depending on K+ polar angle at CMS. Number of (1520) signals were counted
in 1.48<MMp(,K+)<1.56 GeV/c2, and was divided by detector acceptance, branching ratio (BR[(1520)K-p]=0.225),
lumnosity, and solid angle (or cos range) to calculate differential cross sections. The acceptances were measured by
applying 0.7829*sin2+0.2171*(1/3+cos2) dependence to pK+(1520) MC at t-channel helicity frame. Calculations
of differential cross sections are summarized below:
0- 30 degree
Data: 14111.874, BG: 65.310 1.561
#signal: 75.69011.976
Acc.: 0.00760380.0005343
d=0.84179 sr  d/d =118.93 20.96 nb/sr
dcos=0.13397  d/dcos=747.30131.68 nb
30- 60 degree
Data: 20814.422, BG: 151.479 2.249
#signal: 56.52114.597
Acc.: 0.00480830.0002582
d=2.29981 sr  d/d = 51.41 13.67 nb/sr
dcos=0.36603  d/dcos= 322.99 85.86 nb
60- 90 degree
Data: 31 5.568, BG: 22.900 0.845
#signal: 8.100 5.632
Acc.: 0.00040870.0000646
d=3.14159 sr  d/d = 63.45 45.29 nb/sr
Fig.21 MMp(,K+) distributions depending on K+ polar
angle at CMS. Four panels correspond to 0-30, 30dcos=0.50000  d/dcos=398.66284.56 nb
60, 60-90, and 90-180 from upper-left to lower-right.
29