RDataFrame reading Garbage Data

Newbie
1

I’m reading Hadron Data into an RDataFrame. I left the office last week for the holidays and came back 2 days ago. Neither my Code nor the Data nor the Root version has changed but I’m seeing unphysical results which my code did not produce before.

Our experiment measures the LorentzVector of Photons scattered from a target. I’m combining pairs of photons to reconstruct the mother particles mass. As a minimal example:

using namespace ROOT;

void check_photon_data() {
    RDataFrame df("t", "data/kaons.root");

    auto calculate_photon_pair_mass = [](const ROOT::RVec<TVector3>& Ps, const ROOT::RVec<double> Es) -> ROOT::RVec<double> {
        //Calculates the invariant mass of each photon pair in hit
        //Later the hits with only etas can be counted.

        ROOT::RVec<double> masses;
        for (size_t i = 0; i < Es.size(); ++i) {
                for (size_t j = i + 1; j < Es.size(); ++j) {
                    TLorentzVector p4_1, p4_2;
                    p4_1.SetVect(Ps[i]);
                    p4_1.SetE(Es[i]);
                    p4_2.SetVect(Ps[j]);
                    p4_2.SetE(Es[j]);
                    masses.push_back((p4_1 + p4_2).M());
                }
        }
        return masses;
    };

    auto df_out = df.Define("mass", calculate_photon_pair_mass, {"lP4BGONeutral.fP", "lP4BGONeutral.fE"})
                    .Define("p2",
                        [](const RVec<TVector3>& Ps){
                            RVec<double> p2;
                            for (TVector3 p:Ps) {
                                p2.push_back(p*p);
                            }
                            return p2;
                        },
                        {"lP4BGONeutral.fP"})
                    .Define("E2",
                        [](const RVec<double>& Es) {
                            RVec<double> E2;
                            for (double E:Es) {
                                E2.push_back(E*E);
                            }
                            return E2;
                        },
                        {"lP4BGONeutral.fE"})
                    .Define("nPhotonsP", [](const RVec<TVector3>& Ps){return Ps.size();}, {"lP4BGONeutral.fP"})
                    .Define("nPhotonsE", [](const RVec<double>& Es){return Es.size();}, {"lP4BGONeutral.fE"})
                    ;

    df_out.Display({"mass", "E2", "p2", "nPhotonsP", "nPhotonsE"}) -> Print();

}

The print statement shows the following:

+-----+-------------+---------------+---------------+-----------+-----------+
| Row | mass        | E2            | p2            | nPhotonsP | nPhotonsE | 
+-----+-------------+---------------+---------------+-----------+-----------+
| 0   | 0.000001    | 14082.835480  | 14082.835480  | 3         | 3         | 
|     | -150.167792 | 0.000000      | 0.000000      |           |           | 
|     | -143.386273 | 0.000000      | 20559.623230  |           |           | 
+-----+-------------+---------------+---------------+-----------+-----------+
| 1   | 0.000000    | 570013.964222 | 570013.964222 | 3         | 3         | 
|     | -443.282662 | 0.000000      | 0.000000      |           |           | 
|     | -170.116999 | 0.000000      | 28939.793313  |           |           | 
+-----+-------------+---------------+---------------+-----------+-----------+
| 2   | -0.000008   | 264146.546406 | 264146.546406 | 2         | 2         | 
|     |             | 0.000000      | 0.000000      |           |           | 
+-----+-------------+---------------+---------------+-----------+-----------+
| 3   | 0.000000    | 13026.406976  | 13026.406976  | 2         | 2         | 
|     |             | 0.000000      | 0.000000      |           |           | 
+-----+-------------+---------------+---------------+-----------+-----------+
| 4   | 0.000004    | 112994.245538 | 112994.245538 | 4         | 4         | 
|     | -389.224240 | 0.000000      | 0.000000      |           |           | 
|     | -198.731312 | 0.000000      | 55772.203213  |           |           | 
|     | -236.161392 | 0.000000      | 11281.660409  |           |           | 
|     | -106.215161 |               |               |           |           | 
|     | -206.536273 |               |               |           |           | 
+-----+-------------+---------------+---------------+-----------+-----------+

The first photon is about what I would expect, but each following photon is completely unphysical.

I’m also seeing the following error, which was not thrown before:

Warning in <RTreeColumnReader::Get>: Branch lP4BGONeutral.fP hangs from a non-split branch. A copy is being performed in order to properly read the content.

The invariant mass should never return a negative number, regardless of the particle inputs.

I have tried:

  • Reverting to an older code version
  • Checking the difference in the bytes between a backup of the data
  • Reinstalling Root
  • Checking myself into a psych ward to increase my medications

According to git, neither the data nor the code has changed. Reinstalling root did actually help with some errors reading the trees when messing around in the console (something about non matching templates, unfortunately I cannot find the actual error message in the log), but did not help with this problem. The conclusion I have from my tests is, that all of my data corrupted in exactly the same way on all backups. This seems unlikely to me.

I also checked to match my event to our incoming photon beam. Each hit has at least one incoming photon, but where there is more than one photon noted the second one also always has an energy of 0MeV:

+-----+-------------+---------------+---------------+--------------+
| Row | mass        | E2            | p2            | lP4Tagger.fE | 
+-----+-------------+---------------+---------------+--------------+
| 14  | 0.000003    | 41852.464343  | 41852.464343  | 1088.988867  | 
|     |             | 0.000000      | 0.000000      | 0.000000     | 
+-----+-------------+---------------+---------------+--------------+
| 24  | 0.000000    | 16769.912434  | 16769.912434  | 616.491890   | 
|     | -211.097166 | 0.000000      | 0.000000      | 0.000000     | 
|     | 81.903904   | 0.000000      | 20215.899362  |              | 
|     | -142.182627 | 0.000000      | 3593.200360   |              | 
|     | -59.943310  |               |               |              | 
|     | -82.606515  |               |               |              | 
+-----+-------------+---------------+---------------+--------------+
| 39  | 0.000000    | 59959.183065  | 59959.183065  | 1447.773865  | 
|     | 123.132588  | 0.000000      | 0.000000      | 0.000000     | 
|     | -128.081809 | 0.000000      | 18806.866288  |              | 
|     | -137.138128 | 0.000000      | 7728.967910   |              | 
|     | -87.914549  |               |               |              | 
|     | -184.485314 |               |               |              | 
+-----+-------------+---------------+---------------+--------------+
| 47  | -0.000004   | 70022.036036  | 70022.036036  | 2441.479398  | 
|     |             | 0.000000      | 0.000000      | 0.000000     | 
+-----+-------------+---------------+---------------+--------------+

From our beam we expect about every 50th to 100th event to contain more than 1 photon in the tagger. I believe that my code fails to properly read the event arrays, but I have no idea how to diagnose this.

This is the relevant tree structure:

******************************************************************************
*Tree    :t         : t                                                      *
*Entries :     7853 : Total =         4376375 bytes  File  Size =    1826662 *
*        :          : Tree compression factor =   2.39                       *
******************************************************************************
*Br    0 :fs_p      : fs_p/D                                                 *
*Entries :     7853 : Total  Size=      63449 bytes  File Size  =      59302 *
*Baskets :        2 : Basket Size=      32000 bytes  Compression=   1.06     *
*............................................................................*
*Br    1 :fs_beta   : fs_beta/D                                              *
*Entries :     7853 : Total  Size=      63467 bytes  File Size  =      58612 *
*Baskets :        2 : Basket Size=      32000 bytes  Compression=   1.07     *
*............................................................................*
*Br    2 :lP4Tagger : Int_t lP4Tagger_                                       *
*Entries :     7853 : Total  Size=      66528 bytes  File Size  =      12080 *
*Baskets :        3 : Basket Size=      32000 bytes  Compression=   5.22     *
*............................................................................*
*Br    3 :lP4Tagger.fUniqueID : UInt_t fUniqueID[lP4Tagger_]                 *
*Entries :     7853 : Total  Size=      66085 bytes  File Size  =      10289 *
*Baskets :        4 : Basket Size=      32000 bytes  Compression=   6.36     *
*............................................................................*
*Br    4 :lP4Tagger.fBits : UInt_t fBits[lP4Tagger_]                         *
*Entries :     7853 : Total  Size=      66053 bytes  File Size  =      13920 *
*Baskets :        4 : Basket Size=      32000 bytes  Compression=   4.70     *
*............................................................................*
*Br    5 :lP4Tagger.fP : TVector3 fP[lP4Tagger_]                             *
*Entries :     7853 : Total  Size=     369985 bytes  File Size  =      61959 *
*Baskets :       13 : Basket Size=      32000 bytes  Compression=   5.96     *
*............................................................................*
*Br    6 :lP4Tagger.fE : Double_t fE[lP4Tagger_]                             *
*Entries :     7853 : Total  Size=      99793 bytes  File Size  =      38813 *
*Baskets :        5 : Basket Size=      32000 bytes  Compression=   2.56     *
*............................................................................*
*Br    7 :lP4BGONeutral : Int_t lP4BGONeutral_                               *
*Entries :     7853 : Total  Size=      66928 bytes  File Size  =      15620 *
*Baskets :        3 : Basket Size=      32000 bytes  Compression=   4.04     *
*............................................................................*
*Br    8 :lP4BGONeutral.fUniqueID : UInt_t fUniqueID[lP4BGONeutral_]         *
*Entries :     7853 : Total  Size=     112560 bytes  File Size  =      13859 *
*Baskets :        5 : Basket Size=      32000 bytes  Compression=   8.07     *
*............................................................................*
*Br    9 :lP4BGONeutral.fBits : UInt_t fBits[lP4BGONeutral_]                 *
*Entries :     7853 : Total  Size=     112524 bytes  File Size  =      19713 *
*Baskets :        5 : Basket Size=      32000 bytes  Compression=   5.68     *
*............................................................................*
*Br   10 :lP4BGONeutral.fP : TVector3 fP[lP4BGONeutral_]                     *
*Entries :     7853 : Total  Size=     835081 bytes  File Size  =     515802 *
*Baskets :       28 : Basket Size=      32000 bytes  Compression=   1.62     *
*............................................................................*
*Br   11 :lP4BGONeutral.fE : Double_t fE[lP4BGONeutral_]                     *
*Entries :     7853 : Total  Size=     192693 bytes  File Size  =     167687 *
*Baskets :        7 : Basket Size=      32000 bytes  Compression=   1.15     *
*............................................................................*
*Br   12 :lP4BGOProton : Int_t lP4BGOProton_                                 *
*Entries :     7853 : Total  Size=      66523 bytes  File Size  =      15420 *
*Baskets :        3 : Basket Size=      32000 bytes  Compression=   4.09     *
*............................................................................*
*Br   13 :lP4BGOProton.fUniqueID : UInt_t fUniqueID[lP4BGOProton_]           *
*Entries :     7853 : Total  Size=      46269 bytes  File Size  =       6438 *
*Baskets :        3 : Basket Size=      32000 bytes  Compression=   7.09     *
*............................................................................*
*Br   14 :lP4BGOProton.fBits : UInt_t fBits[lP4BGOProton_]                   *
*Entries :     7853 : Total  Size=      46241 bytes  File Size  =       7597 *
*Baskets :        3 : Basket Size=      32000 bytes  Compression=   6.00     *
*............................................................................*
*Br   15 :lP4BGOProton.fP : TVector3 fP[lP4BGOProton_]                       *
*Entries :     7853 : Total  Size=     171920 bytes  File Size  =      96094 *
*Baskets :        7 : Basket Size=      32000 bytes  Compression=   1.78     *
*............................................................................*
*Br   16 :lP4BGOProton.fE : Double_t fE[lP4BGOProton_]                       *
*Entries :     7853 : Total  Size=      60148 bytes  File Size  =      33948 *
*Baskets :        3 : Basket Size=      32000 bytes  Compression=   1.75     *
*............................................................................*
*Br   17 :lP4BGOPion : Int_t lP4BGOPion_                                     *
*Entries :     7853 : Total  Size=      66473 bytes  File Size  =      15434 *
*Baskets :        3 : Basket Size=      32000 bytes  Compression=   4.09     *
*............................................................................*
*Br   18 :lP4BGOPion.fUniqueID : UInt_t fUniqueID[lP4BGOPion_]               *
*Entries :     7853 : Total  Size=      46251 bytes  File Size  =       6406 *
*Baskets :        3 : Basket Size=      32000 bytes  Compression=   7.12     *
*............................................................................*
*Br   19 :lP4BGOPion.fBits : UInt_t fBits[lP4BGOPion_]                       *
*Entries :     7853 : Total  Size=      46223 bytes  File Size  =       7564 *
*Baskets :        3 : Basket Size=      32000 bytes  Compression=   6.03     *
*............................................................................*
*Br   20 :lP4BGOPion.fP : TVector3 fP[lP4BGOPion_]                           *
*Entries :     7853 : Total  Size=     171894 bytes  File Size  =      96129 *
*Baskets :        7 : Basket Size=      32000 bytes  Compression=   1.78     *
*............................................................................*
*Br   21 :lP4BGOPion.fE : Double_t fE[lP4BGOPion_]                           *
*Entries :     7853 : Total  Size=      60130 bytes  File Size  =      34336 *
*Baskets :        3 : Basket Size=      32000 bytes  Compression=   1.73     *
*............................................................................*

Edit: The problem persists with new data

Please read tips for efficient and successful posting and posting code

ROOT Version: ROOT 6.36.000
Platform: Arch Linux
Compiler: GCC

2

Hi David,

Thanks for reaching out.
From the description of the problem, I don’t know exactly how to comment. If I understand correctly, without changing the input data nor the sw (your code and the ROOT installation it relies on) the results changed.

It seems some debugging is needed. Did you take a single file, decide one quantity to double check (e.g. mass), take the first event in the ttree, calculate the invariant mass of the di-photon system and compare it with what you get with your RDF setup?

Cheers,
D

3

Hey Danilo,
The result is calculated as described above. The data cooking process outputs about 3000 files which are added into a single file with hadd.

hadd merged_20250619.root data/Export*

The di-photon mass is calculated by choosing two photons from each hit and adding their lorentz vectors.

I took a look at the raw data in the TBrowser:
px
fE

Which fits my expectations, however looking at the squared value of each photon energy, as calculated above, I do not see the expected output:

c1
c1872×919 6.52 KB

With the peak of the Energy being at 100MeV the peak of the squared values should be at approximately 10000MeV, but almost all photons are calculated to have an energy squared near 0.
This breaks all of my analysis. I get completely nonsense results for everything and my cuts filter all events beacause of this. I performed the test described above as a first debugging step but at this point a already have seriously considered that I am hallucinating this.

I didn’t quite understand what you mean - gramatically - by the last paragraph. What next steps would you recommend?

PS: My lab mates’ only idea was, that my laptop might be having a heat stroke.

Edit: This is the raw data as processed by the dataframe. This is already incorrect, therefore the squaring function is not the problem.

c1
c1698×476 4.37 KB

4

I generated the following subset of my data:

void get_subset() {

    TFile *input_file = TFile::Open("data/merged_20250610.root");
    TTree *tree = (TTree*)input_file->Get("t");
    
    TFile *output_file = TFile::Open("output_first1000.root", "RECREATE");
    TTree *new_tree = tree->CopyTree("", "", 1000);
    
    new_tree->Write();
    output_file->Close();
    input_file->Close();
   
}

output_first1000.root (233.7 KB)

5

Running this same code on root 6.24/06 does not yield the same problem. I must have upgraded root without knowing by

pacman -Syu

The problem was resolved by downgrading to root to Version 6.34.08. The bug will be reported to GitHub · Where software is built