Radphi Signals Analysis Logbook

Mihajlo Kornicer
Richard Jones
started Dec 8, 2003
last modified

This logbook is designated to follow the search for the interesting physics signals from the Radphi experiment, performed by the UConn group. The search should be the part of the prospectus for the M. Kornicer Ph.D. dissertation. The link to the paragraph of the ongoing NIM article related to the LGD resolution, that is going to be extracted from the tech-note is also given here.

The first signal to be considered is η' -> ωγ production in 4γ channel. There is also η' -> γγ reaction that can be seen in 2γ channel. The number of produced η' in 4γ channel from 2000 run is estimated to be 60,000, based on 0.2µb cross-section for the η' production on proton target. Corresponding number in 2γ channel is around 400,000. The details of estimate can be found here (PS). The acceptance is to be checked from MC simulation.


 
Table of Contents
  1. MC analysis of η' production and possible background
  2. Check the usefulness of the fiducial cut on the LGD signal
  3. The BSD signal significance in selecting events that has true LGD-trigger coincidence
  4. What are characteristics of split-off and merged clusters in MC
  5. What is the pTy distribution
  6. What is the beam halo contribution on π°γ continuum
  7. How to use BGV effectively?
  8. Cuts efficiency and ω yield
  9. Tagging analysis
  10. MC acceptance
  11. t-distribution
[MK] 23. Dec. 2003 The first question is what is the acceptance in the case of η' production

    To answer this question I generated 600 events in η' -> ωγ, ω -> π° γ, channel and 4000 η' -> γγ channel. These numbers correspond to 1e6 events per µb.

    η' -> ωγ simulation

    • reconstructed photon multiplicity: out of 600 there are around 150 events reconstructed in 4γ channel.
    • 4γ invariant mass: the mass distribution was fitted with a Gaussian and 2-nd order polynomial background. Approximately 100 η's are under the peak, which is 50 MeV below its nominal value.

    η' -> γγ simulation

    • reconstructed photon multiplicity: out of 4000 there are around 1000 events reconstructed in 2γ channel.
    • 2γ invariant mass: Approximately 900 η's are under the peak, which is 30 MeV below its nominal value.

    Conclusion:

    • the main background in the case of 4γ reconstruction comes from broken b1 events. The b1 production is almost 3 orders of magnitude larger than η' -> ωγ, and the b1 leakage into the 4γ channel gives the yield of 2 order of magnitudes larger then the signal from η'.
    • in the case of 2γ reconstruction the acceptance is rather high, 25%. However η' is not visible in the real data 2;gamma; invariant mass plot (4.3M events sample). One explanation would be that the cluster cleanup has not been applied which will reduce the acceptance. In addition the split-off reclamation procedure pushes ω into the 2γ channel. This can be deduced from the bump in the above plot around ω mass, as well as from the surface and corresponding dot plots of mean energy vs. pair opening angle.
    • without split-off reclamation and fiducial cut, the FULLY_CONTAINED_FORWARD 2γ sample shows some signs of η'(2γ) besides broken ω. The plot is obtained for Dγγ greater then 45cm and minimum Eγ of 1.0GeV. The most right shoulder in the surface plot and corresponding dot plot with &etap;' mass hyperbola support the claim.

    The main conclusion is that we need to use BGV to increase acceptance and probably the BSD and CPV more efficiently, before we analyze such weak signals.

[MK] 24 Dec. 2003 What is the influence of split-off reclamation and cluster cleanup procedure in MC?

    The influence of these two methods can be seen by comparing photon multiplicity before and after they have been applied to η' -> ωγ reconstruction. In the 4γ channel the reconstruction efficiency is reduced from 26% to approximately 16%. The 5 and 6 multiplicities have been suppressed almost completely, however, some fraction of 4 and 3 clusters are transferred to lower multiplicities. As a result the number of 3 and 2 γ's is not changed significantly.

    Acceptance of η' in the case of 2γ channel before and after cluster reclamation and fiducial cut. The mass before and after cluster reclaim and cleanup. It seems that acceptance improves because of cluster reclaim. The role of the fiducial cut on η' acceptance in the case o 2γ channel has yet to be determined.

[RJ] Feb 23, 2004 Justifying the usefulness of fiducial cut on LGD clusters
    The best thing to start from is a good ω signal. I analyzed the sample of 3γ events that have been reconstructed with the FULLY_CONTAINED_FORWARD feature of ntuplet (npix=1., Nbgv=0, Ncpvt2). The reclaim of split-off clusters has not be performed.
    • the invariant mass plots with and without fiducial cut. Apart from the statistics fiducial cut has more influence on the low mass.
    • if we require exactly one pair with mass within one σ of π° peak there is almost no difference in ω signal with and without fiducial cut.

[MK] Feb 2004 What is the BSD signal significance in selecting events that has true LGD-trigger correlation.

    I started with the forward-pixel difference, Δφ distribution.

    • the plot of azimuth difference is normalized to the maximum and centered at zero. The dashed line that corresponds to the requirements of one π plus the total mass within ω (0.7-0.9 GeV) window shows that angular resolution for the "signal" is slightly better.
    • the total BSD pixel energy normalized to the maximum for two different samples. The same for the one chosen pixel Ipix=3, Spix=40 There is a clear difference in mean and RMS between "ω's" and off-angle pixels. However there is a long tail of off-angle pixels with high deposition. They might be coming from nuclear resonance production.
    • with one π° in the sample, cutting on pixel energy and δφ clears the ω signal at the cost of reduced statistics.

    From the flat portion of the Δφ distribution an estimate is that approximately 80% of the FULLY_CONTAINED_FORWARD events are in the real connection with the trigger. The bottom of the peak of the distribution is much wider then the pixel resolution because of Fermi motion and in-target scattering. This has to be compared to MC ω production.

    More from MC ω production: invariant mass for different multiplicities.

[MK] March 17, 2004 What are characteristics of split-off and merged clusters in MC
    The main goal in answering this question is to refine the the present reclamation procedure by an improved algorithm that will take into account energy and spatial relations between split clusters. This should extend the limit for merging close clusters, which is currently set to 6cm at the face of the LGD, and help in suppressing over-merging of near by clusters. In order to achieve these goals the following steps will be performed:
    • select a sample of split forward-generated photons
    • measure split-off probability for the specific set of angles and energies of generated particles depending on the relative coordinates of two showers (u,v) with respect to their center of gravity (the impact point of the generated photon in the LGD plane - see transformation rules
    • propose the way of implementing the best solution.

    Two reactions for this study have been proposed: γp -> p ω(π°γ) and γp -> p b1;(ωπ°). Fig. 1a shows photon multiplicity as a function of number of generated photons (nF) with polar angle defined by fiducial cut (4° = θ =25°), for b1 reaction. Fig. 1b shows photon multiplicity distribution after cluster reclamation has been applied, for the same reaction.

    For training purposes, we decided to start with single-shower Monte Carlo and look at the cluster multiplicity. Single showers are generated into the first quadrant of the LGD with energy up to 5 GeV and polar angle from 5-25° approximately 15% of them are found to have 2 showers reconstructed

    • Energy and polar angle of split forward-generated particles.
    • The energy sum of split showers vs. polar angle of generated particle shows that most split-offs occur in the kinematic region of large angle and large energy which is relatively rare in real reactions, especially for higher multiplicities.
    • Energy of reconstructed singles (black histogram) shows that the cluster finder has an effective threshold around 250 MeV for reconstructing single-showers (the generated spectrum is flat in energy and starts at zero).
    At first this last point was a puzzle to us, in view of the 50 MeV minimum seed energy supplied to the cluster finder. The reason for this threshold is that the clusterizer operates in two passes, first with a 150 MeV seed threshold and then with a 50 MeV threshold. If the first search turns up nothing then the algorithm never continues to pass 2. This can be seen in the plot of reconstruction efficiency for different first-seed thresholds. For this reason we decided that single-shower events are not a good way to study the clusterizer because its behavior on a low-energy shower is fundamentally different depending on whether the shower is accompanied by other larger showers elsewhere in the LGD or not. For this reason we turn from single-cluster Monte Carlo to looking at omega(783) photo-production.

    In the study of omega(3γ) events, we find that the Event utility is useful in analyzing the topology of split-offs. There are several types of events that we were able to identify. The first one that we call type 0 represents the well-reconstructed events that comprised 72±5% of total reconstructions. Examples of this kind of event are type 0a, type 0b and type 0c. In addition there are 4 different types of split-offs:

    • beam-hole split where a low angle shower leaks into the beam hole and deposits energy in the blocks adjacent to the hole. These events occur at a 5±2% rate. Examples of type 1 events are 1a and 1b.
    • large-angle split when modest energy shower is spread over several blocks in the radial direction of the incoming photon. These events occur at a 11±3% rate. Examples of type 2 events are 2a and 2b.
    • split at mid-angle of a large-energy cluster, when the block at the cluster edge produces a new cluster at least 2 blocks away from the initial shower. The new cluster has random direction in respect to the radial direction of the main part of the shower. These events occur at a 9±3% rate. Examples of type 3 events are 3a, 3a and 3c.
    • trivial split when far-away blocks have enough energy to form a new cluster but it is constructed close to the initial cluster. It happens frequently when two clusters are 2-4 blocks apart and share some energy. This case is handled with the present reclaim procedure. Type 4 events occur at a 4±2% rate. Examples are 4a, 4b and 4c.

    After studying events by Event display utility the idea to measure split-off probability by selecting isolated clusters is abandoned. The procedure involves choosing a window around the impact point of generated photons. By making a window to small the clusters from neighboring generated photons might be counted as splits. The split-offs occur up to the 15-16 cm from the impact point. By making a window to wide some parts of the detector are preferred more than others, which makes the split-off probability measure unreliable. This can be seen in the radial distribution of isolated generated photons with one (solid) and two (dot) showers inside the 20 cm window set by the impact point.

    The qualitative analysis of events lead to the following proposal:

    • type 4 is very sensitive to the choice of seeds. Since those splits are hard to classify, we propose to prevent the forming by increasing the seeds to the (250,75) MeV.
    • for other types form a special cluster clean-up that will do the following:
      • Type 1: showers near the edge of the hole and energy ≤ 200 MeV merge with the closest shower with the seed block at the hole edge and energy above 1GeV (most of the beam hole splits are from high energy showers).
      • Type 3: showers less than 200 MeV merge with the clusters above 1.5 GeV and less than 15-16 cm apart.
      • Type 2: use statistical method to determine whether the two clusters with the radial distance from the beam line greater than 30 cm are coming from one source.
    • The current procedure uses one level3 (levelOne(150),levlTwo,levelOne(50)) step. An alternative would be to do the clustering in two steps.
      • level2 and 300 MeV seed (levelOne(300), levelTwo) search.
      • level3 and 150,50 MeV seeds (levelOne(150),levelTwo,levelOne(50)

    The analysis of the split-offs resulted in the design of new clusterizer at UConn.

[RTJ] Oct 25, 2004 What is the pTy distribution?
    The out-of-plane momentum is transverse momentum projected perpendicularly to the reaction plane (pTy). The reaction plane is defined by the beam axis and direction of the recoil. Thus pTy = -sin(φ)pNx + cos(φ)pNy, where pN is total lab momentum of N-γ system.
    • the pTy distributions from 3γ sample. Distributions for different cuts are normalized to maximum bin for comparison.
    • the 2-Gaussian fit of tagged neutral distribution. It is much wider than its MC equivalent from ω simulation.
    • with ω mass window (0.68-0.98 GeV) cut, pTy fit gives 70 MeV narrower second Gaussian. The tail of this distribution vanishes at 1 GeV, compared to 1.4 GeV without ω mass cut.
    • the background suppression reduces width of the second Gaussian by 20 MeV and it's contribution to 0.22% (compared to 0.28% from cut 0.68-0.98). The suppression has been performed by subtracting the scaled black distribution, shown in pTy figure, from the red one. The scaling factor was estimated from the ratio of the background under the ω signal for two different mass windows. The mass plot was obtained with CPV veto and π°γ cuts without tagging.
    • a severe fiducial cut (6-22°) did not have significant impact on the background subtraction in the pTy distribution.
    The difference is attributed to unaccounted nuclear motion inside the nucleus. After new Fermi generator is applied in the MC simulation the pTy MC distribution from ω simulation looks more like one from real data. The difference between generated and measured pTy distributions is bigger by 2 MeV than before.

    The impact of this change on acceptance before and after the new generator has been applied was not huge!.

    pTy distribution from MC without Fermi motion and corresponding ΔpTy. The measured pT distribution.

    Accounting for yields from 2000 run.

[RTJ] Oct 25, 2004 What is the beam halo contribution to π°γ continuum?
    In order to address this question the distribution of pair mass vs bachelor polar angle has been formed from 3γ sample. The cut off on π° with bachelor less than 6° away from beam axis has significant impact on overall mass distribution. This is the impact of the above cut on tagged neutral π°γ selection, compared with different fiducial cuts. Impression is that the bachelor cut does not clear the continuum background significantly, but pushes up the ω mass peak.

    It was proposed to look at energy-angle showers distribution to see is there any way to use 2-d cut to improve our ω signal

    A 2D cut in E-Θ plane (distribution obtained by applying CP veto, π°γ selection and M(3γ) ≤0.4 GeV) is shown by two straight lines. The first line represents a low energy cut-off (0.15 GeV) while the other one goes through E-Θ points (0.1,7.0) - (0.5,4.0). After this cut a very nice ω signal was produced. It seems that this gives better signal than simple fiducial (6-24°) cut. Both fits in previous mass plots were performed with the Gaussian and 3-rd polynomial background. Here is the invariant mass comparison from two line cuts in E-Θ plane: black curve is from cut above (0.1,7.0) - (0.5,4.0) line, and the red one is with E≥0.15 GeV in addition.

    A 2D cut revision with two cut-off regions defined by (0.1,7.0) - (0.5,4.0) line and Θ≥24°, Eγ<0.2 GeV box. Here is the resulting mass plot fit, compared to distribution obtained with fiducial cut (6,24) (dot line) Note: spectra were not tagged.

[RTJ] Nov 16, 2004 How to use BGV effectively?
    In the previous analysis we used the sample of Fully Contained Forward (FCF) events that has been obtained by applying, among other cuts, a cut in the BGD: no hits in the BGD unrelated to the recoil. The cut does not take into account hits energy and time in respect to the recoil. In order to make the cut less restrictive the energy and time information in the BGD should be used. However, correlation between energy spectra of upstream and downstream ends is not obvious:
    • energy spectra of hits behind recoil UP, DOWN (recoil hits from now on). There is a clear MIP in the upstream spectra of recoil hits. The peak is present in the downstream spectra, but it appears at 20 MeV instead of 80 MeV. In addition, the tail of the background for the downstream and is much higher than the tail for the upstream end. This indicates that the gain in the downstream is approximately four times less, and that recoil goes through scintillator guide at the downstream end.
      • there is no significant dependence on pixel position in the upstream energy, except that MIP moves up by few MeV, as expected.
      • Downstream energy shows a growing tail as a function of the pixel position (for single recoil - single pixel events). Since the peak does not move with pixel it is unlikely that the peak is associated with the recoil MIP.
      • UP-DOWN time difference for downstream hits above 300 MeV shows two peaks (ipix=1). Early peak (negative) moves towards second peak and disappears after ipix=3 pix 0-6 ( pix 0-2 comparison). There is third peak visible only in pix 3 and 4 (
      • Eup for downstream hits above 300 MeV, all pixels.
      • Down vs Up energy (dot plot) and corresponding box plot, for recoil hits.
    • energy spectra of hits not associated to recoil UP, DOWN (non-recoil hits) show a sign of MIP in the upstream end, and very prominent peak in the downstream end at the same position (16-18 MeV) seen from recoil hits. However, the tail of the background under the peak on the downstream side is very different than the tail of recoil hits. It is possible that the upstream MIP is associated with broken pixels when one layer in the BSD is missing. A hypothesis that the downstream peak might be related to the back splash from the LGD is ruled out by examining relation between BGD downstream spectra and showers angle. The peak for both recoil and non-recoil hits is insensitive to the maximum allowed shower polar angle (18, 22, 25°)
    • raw adc spectra for recoil and non- recoil hits show the same characteristics as energy spectra.
    • raw spectra vs run number: adc UP, adc DOWN, tdc UP, tdc DOWN. Runs after 8050.
    • Comparison between channel 9 and 19 adc UP and adc DOWN.
    • Logarithm of adc ratio (Up/Down) vs (Up-Down) time difference channel 3, channel 9, channel 19, channel 22, when all hits (adcUp, adc Down, tdc Up, tdc Down) in the channel are non zero. The spectra of both upstream adc and downstream adc are affected by this requirement.

    New BGD veto applied to 3γ gives 1,285,779 ω , compared to 526,506 previous use of bgveto.

    In conclusion, we established a set of simple rules for a hit in the BGD to be included in the veto counting. The AND of the following conditions forms a valid non-recoil hit:

    • the presence of both upstream and downstream energy (i.e. Eup>0, Edwn>0)
    • the differences of upstream and downstream times in respect to the recoil to be inside (-10,10 ns) window.

[RTJ] Dec 30, 2004 Cuts efficiency and ω yields.
    Effect of cuts in 3 γ events from ω simulation. Out of 300,000 generated events 77,484 ω's were reconstructed (0.26 acceptance). By applying Nrec=1 and CPveto cuts acceptance went down to 0.18. The BGveto did not have significant impact on the ω reconstruction, as expected, while π°γ selection and modified fiducial cut (Energy-angle dependent) reduced acceptance to 0.16. Cuts in E-θ space are defined by lines (0.1,7.0)-(0.5,4.) and (0.1,24.)-(0.5,23). The MC E-θ distribution, as well as the one for M≤0.4 GeV, is similar to the one from the real data, including discrete block-size effects.

    The following table gives ω yield from real data depending on the applied cut. Each cut represented in a column implies presence of previous cuts except for the 5-th column where πγ selection and fiducial cut are applied separately. Consequently, in the last column both of the cuts are used. The last row gives ratio of the height of the background at the 0.8 MeV and the Gaussian height.
    CutNrec=1 and CPvetotaggingBGveto
    • π°γ
    • E-θ
    		E-θ
    Yield 4,821,930 2,227,765
    Background/peak 0.52 0.56 0.35
    • 0.28
    • 0.30
    		 0.25

    The estimate of the leak from 3γ into 4γ. 3γ mass distributions (non-tagged) are obtained when a low-energy shower near the beam hole is removed from the 4γ sample.
    Cutnrec=1 and CPVeto BGVeto
    Yield 723,948 517,288
    Background/peak 0.840.61

    The number of tagged neutral fully contained forward produced ω (1.5M) is factor of 2.5 less than what we would expect based on the known cross-section. Efficiency corrections to the ω yield from various sources:

    • the random acidentals in the CPV have contribution to the CP Veto. The estimate from the ω yield as a function of CP Veto gate width gives factor of 0.7
    • the overlap of the target with the beam estimated from the bremsstrahlung profile and the distance of the tager from the target is 0.93
    • tagger efficiency 0.9
    • recoil detection efficiency vareis from 0.82-0.7 depending on the BSD ring.

    Cross sections for ω production depending on energy:
    Energy [GeV]average4.75.88.2
    σ [µb]2.72.9+-0.42.3+-0.42.0+-0.3
    Yield [M]4.374.693.723.23

    BSD pixel efficiency

    Summary of the accounting for ω production in Radphi:

      Parameters used to obtain integrated luminosity of 100M 1/µb :
    • target tickness of 2.6 cm
    • target density of 1.85 g/cm3
    • live time 430 h
    • photon flux 50M/s
    σ [µb] 2.7 ± 0.4
    branching ratio 0.0898 ± 0.003
    MC acceptance 0.17 ± 0.01
    tagging efficiency 0.95 ± 0.01
    CP veto randoms 0.68 ± 0.01
    target-beam overlap 0.94 ± 0.005
    BSD efficiency 0.70 ± 0.03
    expected yield 1.75 M ± 0.3
    yield in 3γ sample 1.50 M ± 0.08
    yield in 4γ sample 0.23 M ± 0.02
    total observed yield 1.7 M ± 0.2

    φ yield (Gaaussian background)

    σ [µb] 0.4
    branching ratio 0.0051
    MC acceptance 0.12
    tagging efficiency 0.95 ± 0.01
    CP veto randoms 0.68 ± 0.01
    target-beam overlap 0.94 ± 0.005
    BSD efficiency 0.70 ± 0.03
    expected yield 10K

    The sample without π° (m2(1)>0.2 GeV): m2 all pairs, mN vs m2 scater plot, and m2 after 0.9<M(3γ)<1.1 cut.

    Tagged distributions of m2 vs M(3γ) for each pair ordered by its mass. The second row is corresponding projection onto m2 axis.

    box plot, color plot m2,m3 and m2+m3. eta selection

[RTJ] March 1, 2005 Tagging analysis

    Tagging issues:

    1. Trecoil-tag dashed histogram is without tag-cpv inside (-1,5) and dotted is for standard cpv veto (-3,3) recoil-cpv.
    2. Trecoil-cpv , Tcpv-tag .
    3. recoil-tag time for R-cpv and cpv-tag veto
    4. Concidence and accidental energy of charged and neutral events. Tagged neutral energy after charged tagged energy has been scaled with factors that depend on the neutral coin-acc difference (channel 10).
    5. Tagged neutral energy by channels ch 01 ch 10 ch 18
    6. Tagged energy with charged tagged spectra subtracted, full 3γ statistics.
    7. Tagged mass with true neutral tagged spectra end with pi0 selection.
    8. Tagged mass with no π°, up-tagged , and down-tagged spectra. correspondinfg bands in m2 (0.47-0.63) up-tagged , and down-tagged spectra. The same ones with η pair requirement up-tagged , and down-tagged spectra.
    9. full sample tagged phi , fitted up-tagged phi ,
    10. Tagged : up pTy and down pTy , up Δφ and down Δφ.
    11. Side band subtraction for uptaged pTy (2 Gaussinas fit with 32% contribution from the second one) and fit without sbs pTy . Subtraction is performed by fitting uptagged mass distribution (dashed line on plot) and taking the ratio r of backrgound within (0.75-0.95) and (0.65-1.05). The scaling factor for subtracting distribution (pTy or Δφ) obtained for mass range (0.65-1.05), H2, from the one obtained for mass within (0,75-0.95), H1, is calculated by S = (H1-rH2)/(1-r). The 2 Gaussian + p0 fit for Δφ sbs and no sbs Δφ.
      pTy (data) σ1 [GeV]R1 [%] σ2 [GeV]R2 [%]
      tagged 0.11868.7 0.29931.3
      Δφ (data) σ1 [°]R1 [%] σ2 [°]R2P0 [%]
      tagged 13.957 43.8349
      T-slopeσ1 [GeV]R1 [%] σ2 [GeV] pTy (MC) σ1 [GeV]R1 [%] σ2 [GeV]R2 [%]
      4 0.090400.290 Eg>Emc0.11257.2 0.26042.6
      4 0.090500.400 Eg>Emc0.10872.2 0.30027.5
      6 0.100500.400 Eg>Emc0.11571.8 0.26928.0
      8 0.110400.360 Eg>Emc0.11760.7 0.22738.4
      Δφ (MC) σ1 [°]R1 [%] σ2 [°]R2P0 [%]
      Eg>Emc 13.257.5 41.134.45
      Eg>Emc 12.468.5 41.823.76.4
      Eg>Emc 14.664.1 42.624.710
      Eg>Emc 17.351.5 43.730.511.8

[RTJ] March 1, 2005 MC acceptance
    ω(π°γ)
    CutYieldAcceptance
    3γ743840.248±0.007
    Nrec=1;647380.216±0.004
    CP veto511070.170±0.003
    BG veto510200.170±0.003
    low E-θ veto488050.163±0.002
    π°465610.155±0.002
    φ(ηγ)
    CutYieldAcceptance
    3γ440000.147±0.007
    Nrec=1;396360.132±0.003
    CP veto310300.103±0.002
    BG veto308300.103±0.002
    low E-θ veto297800.099±0.002
    η270930.090±0.002

    Additional ω channels low E-θ cut
    DecayYieldAcceptance
    γn -> ω n 18920.0063±0.0001
    γn -> ωΔ, Δ° -> π°n 65170.022±0.004
    γn -> ωΔ, Δ° -> π- p 338400.119±0.004
    γp -> ωΔ , Δ+ -> π+ n 480560.160±0.004
    γp -> ωΔ, Δ+ -> π° p 158790.053±0.002

    Recoil - Forward φ difference for ω production:

    • MC γp -> ωΔ: Δ plus(π+ n), Δ°(π- p).
    • MC γp -> ωp: diffractive, old Fermi Generator(FG)
    • Fitting real data with 3 functions obtained from MC histograms. Fitting parameter P1 gives contribution from difractive omega production, while P2 and P3 represent contribution when Δ+ and Δ° respectively (together shown as dashed line). The peak of the Δφ is not fitted well. This points to relatively wide distribution of MC difractive omegas, due to the Fermi smearing. The magnitude of Fermi motion was extracted from data without Δ contribution been taken into account. The next step is to estimate the influence of Δ to pTy distribution and re-do Fermi motion in MC.
    • Background suppresed Δφ fitted with new FG (18% Δ contribution) and old FG (58% Δ's) and

    pTy distributions

    Both pTy and Δφ are fitted with 2 parameters, one corresponding to difrctive ω distribution from MC and the other one correspondign to Δ distributions. Δ°(π- p) and Δ+(π+ n) are included in the fit by fixing their contributions according to their relative acceptances estimated in MC.

[RTJ] March 1, 2005 t-distribution

Useful links


[1] R.T. Jones, "Tagging photons with the Radphi detector" (March 2004).
This page is maintained by kornicer@phys.uconn.edu